diff --git a/build.zig b/build.zig
index 707094d36b..0788e2e762 100644
--- a/build.zig
+++ b/build.zig
@@ -154,7 +154,7 @@ fn dependOnLib(b: *Builder, lib_exe_obj: var, dep: LibraryDep) void {
         const static_bare_name = if (mem.eql(u8, lib, "curses"))
             @as([]const u8, "libncurses.a")
         else
-            b.fmt("lib{}.a", lib);
+            b.fmt("lib{}.a", .{lib});
         const static_lib_name = fs.path.join(
             b.allocator,
             &[_][]const u8{ lib_dir, static_bare_name },
@@ -186,7 +186,7 @@ fn addCppLib(b: *Builder, lib_exe_obj: var, cmake_binary_dir: []const u8, lib_na
     lib_exe_obj.addObjectFile(fs.path.join(b.allocator, &[_][]const u8{
         cmake_binary_dir,
         "zig_cpp",
-        b.fmt("{}{}{}", lib_exe_obj.target.libPrefix(), lib_name, lib_exe_obj.target.staticLibSuffix()),
+        b.fmt("{}{}{}", .{ lib_exe_obj.target.libPrefix(), lib_name, lib_exe_obj.target.staticLibSuffix() }),
     }) catch unreachable);
 }
 
@@ -343,14 +343,14 @@ fn addCxxKnownPath(
 ) !void {
     const path_padded = try b.exec(&[_][]const u8{
         ctx.cxx_compiler,
-        b.fmt("-print-file-name={}", objname),
+        b.fmt("-print-file-name={}", .{objname}),
     });
     const path_unpadded = mem.tokenize(path_padded, "\r\n").next().?;
     if (mem.eql(u8, path_unpadded, objname)) {
         if (errtxt) |msg| {
-            warn("{}", msg);
+            warn("{}", .{msg});
         } else {
-            warn("Unable to determine path to {}\n", objname);
+            warn("Unable to determine path to {}\n", .{objname});
         }
         return error.RequiredLibraryNotFound;
     }
diff --git a/doc/docgen.zig b/doc/docgen.zig
index 430d6eb1e2..6fb9b93e1d 100644
--- a/doc/docgen.zig
+++ b/doc/docgen.zig
@@ -215,32 +215,33 @@ const Tokenizer = struct {
     }
 };
 
-fn parseError(tokenizer: *Tokenizer, token: Token, comptime fmt: []const u8, args: ...) anyerror {
+fn parseError(tokenizer: *Tokenizer, token: Token, comptime fmt: []const u8, args: var) anyerror {
     const loc = tokenizer.getTokenLocation(token);
-    warn("{}:{}:{}: error: " ++ fmt ++ "\n", tokenizer.source_file_name, loc.line + 1, loc.column + 1, args);
+    const args_prefix = .{ tokenizer.source_file_name, loc.line + 1, loc.column + 1 };
+    warn("{}:{}:{}: error: " ++ fmt ++ "\n", args_prefix ++ args);
     if (loc.line_start <= loc.line_end) {
-        warn("{}\n", tokenizer.buffer[loc.line_start..loc.line_end]);
+        warn("{}\n", .{tokenizer.buffer[loc.line_start..loc.line_end]});
         {
             var i: usize = 0;
             while (i < loc.column) : (i += 1) {
-                warn(" ");
+                warn(" ", .{});
             }
         }
         {
             const caret_count = token.end - token.start;
             var i: usize = 0;
             while (i < caret_count) : (i += 1) {
-                warn("~");
+                warn("~", .{});
             }
         }
-        warn("\n");
+        warn("\n", .{});
     }
     return error.ParseError;
 }
 
 fn assertToken(tokenizer: *Tokenizer, token: Token, id: Token.Id) !void {
     if (token.id != id) {
-        return parseError(tokenizer, token, "expected {}, found {}", @tagName(id), @tagName(token.id));
+        return parseError(tokenizer, token, "expected {}, found {}", .{ @tagName(id), @tagName(token.id) });
     }
 }
 
@@ -339,7 +340,7 @@ fn genToc(allocator: *mem.Allocator, tokenizer: *Tokenizer) !Toc {
         switch (token.id) {
             Token.Id.Eof => {
                 if (header_stack_size != 0) {
-                    return parseError(tokenizer, token, "unbalanced headers");
+                    return parseError(tokenizer, token, "unbalanced headers", .{});
                 }
                 try toc.write("    </ul>\n");
                 break;
@@ -373,10 +374,15 @@ fn genToc(allocator: *mem.Allocator, tokenizer: *Tokenizer) !Toc {
                                 if (mem.eql(u8, param, "3col")) {
                                     columns = 3;
                                 } else {
-                                    return parseError(tokenizer, bracket_tok, "unrecognized header_open param: {}", param);
+                                    return parseError(
+                                        tokenizer,
+                                        bracket_tok,
+                                        "unrecognized header_open param: {}",
+                                        .{param},
+                                    );
                                 }
                             },
-                            else => return parseError(tokenizer, bracket_tok, "invalid header_open token"),
+                            else => return parseError(tokenizer, bracket_tok, "invalid header_open token", .{}),
                         }
                     }
 
@@ -391,15 +397,15 @@ fn genToc(allocator: *mem.Allocator, tokenizer: *Tokenizer) !Toc {
                         },
                     });
                     if (try urls.put(urlized, tag_token)) |entry| {
-                        parseError(tokenizer, tag_token, "duplicate header url: #{}", urlized) catch {};
-                        parseError(tokenizer, entry.value, "other tag here") catch {};
+                        parseError(tokenizer, tag_token, "duplicate header url: #{}", .{urlized}) catch {};
+                        parseError(tokenizer, entry.value, "other tag here", .{}) catch {};
                         return error.ParseError;
                     }
                     if (last_action == Action.Open) {
                         try toc.writeByte('\n');
                         try toc.writeByteNTimes(' ', header_stack_size * 4);
                         if (last_columns) |n| {
-                            try toc.print("<ul style=\"columns: {}\">\n", n);
+                            try toc.print("<ul style=\"columns: {}\">\n", .{n});
                         } else {
                             try toc.write("<ul>\n");
                         }
@@ -408,10 +414,10 @@ fn genToc(allocator: *mem.Allocator, tokenizer: *Tokenizer) !Toc {
                     }
                     last_columns = columns;
                     try toc.writeByteNTimes(' ', 4 + header_stack_size * 4);
-                    try toc.print("<li><a id=\"toc-{}\" href=\"#{}\">{}</a>", urlized, urlized, content);
+                    try toc.print("<li><a id=\"toc-{}\" href=\"#{}\">{}</a>", .{ urlized, urlized, content });
                 } else if (mem.eql(u8, tag_name, "header_close")) {
                     if (header_stack_size == 0) {
-                        return parseError(tokenizer, tag_token, "unbalanced close header");
+                        return parseError(tokenizer, tag_token, "unbalanced close header", .{});
                     }
                     header_stack_size -= 1;
                     _ = try eatToken(tokenizer, Token.Id.BracketClose);
@@ -442,7 +448,7 @@ fn genToc(allocator: *mem.Allocator, tokenizer: *Tokenizer) !Toc {
                                 try nodes.append(Node{ .SeeAlso = list.toOwnedSlice() });
                                 break;
                             },
-                            else => return parseError(tokenizer, see_also_tok, "invalid see_also token"),
+                            else => return parseError(tokenizer, see_also_tok, "invalid see_also token", .{}),
                         }
                     }
                 } else if (mem.eql(u8, tag_name, "link")) {
@@ -459,7 +465,7 @@ fn genToc(allocator: *mem.Allocator, tokenizer: *Tokenizer) !Toc {
                                 _ = try eatToken(tokenizer, Token.Id.BracketClose);
                                 break :blk tokenizer.buffer[explicit_text.start..explicit_text.end];
                             },
-                            else => return parseError(tokenizer, tok, "invalid link token"),
+                            else => return parseError(tokenizer, tok, "invalid link token", .{}),
                         }
                     };
 
@@ -482,7 +488,7 @@ fn genToc(allocator: *mem.Allocator, tokenizer: *Tokenizer) !Toc {
                             _ = try eatToken(tokenizer, Token.Id.BracketClose);
                         },
                         Token.Id.BracketClose => {},
-                        else => return parseError(tokenizer, token, "invalid token"),
+                        else => return parseError(tokenizer, token, "invalid token", .{}),
                     }
                     const code_kind_str = tokenizer.buffer[code_kind_tok.start..code_kind_tok.end];
                     var code_kind_id: Code.Id = undefined;
@@ -512,7 +518,7 @@ fn genToc(allocator: *mem.Allocator, tokenizer: *Tokenizer) !Toc {
                         code_kind_id = Code.Id{ .Obj = null };
                         is_inline = true;
                     } else {
-                        return parseError(tokenizer, code_kind_tok, "unrecognized code kind: {}", code_kind_str);
+                        return parseError(tokenizer, code_kind_tok, "unrecognized code kind: {}", .{code_kind_str});
                     }
 
                     var mode = builtin.Mode.Debug;
@@ -550,7 +556,12 @@ fn genToc(allocator: *mem.Allocator, tokenizer: *Tokenizer) !Toc {
                             _ = try eatToken(tokenizer, Token.Id.BracketClose);
                             break content_tok;
                         } else {
-                            return parseError(tokenizer, end_code_tag, "invalid token inside code_begin: {}", end_tag_name);
+                            return parseError(
+                                tokenizer,
+                                end_code_tag,
+                                "invalid token inside code_begin: {}",
+                                .{end_tag_name},
+                            );
                         }
                         _ = try eatToken(tokenizer, Token.Id.BracketClose);
                     } else
@@ -575,15 +586,20 @@ fn genToc(allocator: *mem.Allocator, tokenizer: *Tokenizer) !Toc {
                     const end_syntax_tag = try eatToken(tokenizer, Token.Id.TagContent);
                     const end_tag_name = tokenizer.buffer[end_syntax_tag.start..end_syntax_tag.end];
                     if (!mem.eql(u8, end_tag_name, "endsyntax")) {
-                        return parseError(tokenizer, end_syntax_tag, "invalid token inside syntax: {}", end_tag_name);
+                        return parseError(
+                            tokenizer,
+                            end_syntax_tag,
+                            "invalid token inside syntax: {}",
+                            .{end_tag_name},
+                        );
                     }
                     _ = try eatToken(tokenizer, Token.Id.BracketClose);
                     try nodes.append(Node{ .Syntax = content_tok });
                 } else {
-                    return parseError(tokenizer, tag_token, "unrecognized tag name: {}", tag_name);
+                    return parseError(tokenizer, tag_token, "unrecognized tag name: {}", .{tag_name});
                 }
             },
-            else => return parseError(tokenizer, token, "invalid token"),
+            else => return parseError(tokenizer, token, "invalid token", .{}),
         }
     }
 
@@ -729,7 +745,7 @@ fn termColor(allocator: *mem.Allocator, input: []const u8) ![]u8 {
                         try out.write("</span>");
                     }
                     if (first_number != 0 or second_number != 0) {
-                        try out.print("<span class=\"t{}_{}\">", first_number, second_number);
+                        try out.print("<span class=\"t{}_{}\">", .{ first_number, second_number });
                         open_span_count += 1;
                     }
                 },
@@ -960,6 +976,7 @@ fn tokenizeAndPrintRaw(docgen_tokenizer: *Tokenizer, out: var, source_token: Tok
                 docgen_tokenizer,
                 source_token,
                 "syntax error",
+                .{},
             ),
         }
         index = token.end;
@@ -987,9 +1004,9 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
             },
             Node.Link => |info| {
                 if (!toc.urls.contains(info.url)) {
-                    return parseError(tokenizer, info.token, "url not found: {}", info.url);
+                    return parseError(tokenizer, info.token, "url not found: {}", .{info.url});
                 }
-                try out.print("<a href=\"#{}\">{}</a>", info.url, info.name);
+                try out.print("<a href=\"#{}\">{}</a>", .{ info.url, info.name });
             },
             Node.Nav => {
                 try out.write(toc.toc);
@@ -1002,12 +1019,7 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
             Node.HeaderOpen => |info| {
                 try out.print(
                     "<h{} id=\"{}\"><a href=\"#toc-{}\">{}</a> <a class=\"hdr\" href=\"#{}\">§</a></h{}>\n",
-                    info.n,
-                    info.url,
-                    info.url,
-                    info.name,
-                    info.url,
-                    info.n,
+                    .{ info.n, info.url, info.url, info.name, info.url, info.n },
                 );
             },
             Node.SeeAlso => |items| {
@@ -1015,9 +1027,9 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
                 for (items) |item| {
                     const url = try urlize(allocator, item.name);
                     if (!toc.urls.contains(url)) {
-                        return parseError(tokenizer, item.token, "url not found: {}", url);
+                        return parseError(tokenizer, item.token, "url not found: {}", .{url});
                     }
-                    try out.print("<li><a href=\"#{}\">{}</a></li>\n", url, item.name);
+                    try out.print("<li><a href=\"#{}\">{}</a></li>\n", .{ url, item.name });
                 }
                 try out.write("</ul>\n");
             },
@@ -1026,17 +1038,17 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
             },
             Node.Code => |code| {
                 code_progress_index += 1;
-                warn("docgen example code {}/{}...", code_progress_index, tokenizer.code_node_count);
+                warn("docgen example code {}/{}...", .{ code_progress_index, tokenizer.code_node_count });
 
                 const raw_source = tokenizer.buffer[code.source_token.start..code.source_token.end];
                 const trimmed_raw_source = mem.trim(u8, raw_source, " \n");
                 if (!code.is_inline) {
-                    try out.print("<p class=\"file\">{}.zig</p>", code.name);
+                    try out.print("<p class=\"file\">{}.zig</p>", .{code.name});
                 }
                 try out.write("<pre>");
                 try tokenizeAndPrint(tokenizer, out, code.source_token);
                 try out.write("</pre>");
-                const name_plus_ext = try std.fmt.allocPrint(allocator, "{}.zig", code.name);
+                const name_plus_ext = try std.fmt.allocPrint(allocator, "{}.zig", .{code.name});
                 const tmp_source_file_name = try fs.path.join(
                     allocator,
                     &[_][]const u8{ tmp_dir_name, name_plus_ext },
@@ -1045,7 +1057,7 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
 
                 switch (code.id) {
                     Code.Id.Exe => |expected_outcome| code_block: {
-                        const name_plus_bin_ext = try std.fmt.allocPrint(allocator, "{}{}", code.name, exe_ext);
+                        const name_plus_bin_ext = try std.fmt.allocPrint(allocator, "{}{}", .{ code.name, exe_ext });
                         var build_args = std.ArrayList([]const u8).init(allocator);
                         defer build_args.deinit();
                         try build_args.appendSlice(&[_][]const u8{
@@ -1059,40 +1071,40 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
                             "--cache",
                             "on",
                         });
-                        try out.print("<pre><code class=\"shell\">$ zig build-exe {}.zig", code.name);
+                        try out.print("<pre><code class=\"shell\">$ zig build-exe {}.zig", .{code.name});
                         switch (code.mode) {
                             builtin.Mode.Debug => {},
                             builtin.Mode.ReleaseSafe => {
                                 try build_args.append("--release-safe");
-                                try out.print(" --release-safe");
+                                try out.print(" --release-safe", .{});
                             },
                             builtin.Mode.ReleaseFast => {
                                 try build_args.append("--release-fast");
-                                try out.print(" --release-fast");
+                                try out.print(" --release-fast", .{});
                             },
                             builtin.Mode.ReleaseSmall => {
                                 try build_args.append("--release-small");
-                                try out.print(" --release-small");
+                                try out.print(" --release-small", .{});
                             },
                         }
                         for (code.link_objects) |link_object| {
-                            const name_with_ext = try std.fmt.allocPrint(allocator, "{}{}", link_object, obj_ext);
+                            const name_with_ext = try std.fmt.allocPrint(allocator, "{}{}", .{ link_object, obj_ext });
                             const full_path_object = try fs.path.join(
                                 allocator,
                                 &[_][]const u8{ tmp_dir_name, name_with_ext },
                             );
                             try build_args.append("--object");
                             try build_args.append(full_path_object);
-                            try out.print(" --object {}", name_with_ext);
+                            try out.print(" --object {}", .{name_with_ext});
                         }
                         if (code.link_libc) {
                             try build_args.append("-lc");
-                            try out.print(" -lc");
+                            try out.print(" -lc", .{});
                         }
                         if (code.target_str) |triple| {
                             try build_args.appendSlice(&[_][]const u8{ "-target", triple });
                             if (!code.is_inline) {
-                                try out.print(" -target {}", triple);
+                                try out.print(" -target {}", .{triple});
                             }
                         }
                         if (expected_outcome == .BuildFail) {
@@ -1106,29 +1118,29 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
                             switch (result.term) {
                                 .Exited => |exit_code| {
                                     if (exit_code == 0) {
-                                        warn("{}\nThe following command incorrectly succeeded:\n", result.stderr);
+                                        warn("{}\nThe following command incorrectly succeeded:\n", .{result.stderr});
                                         for (build_args.toSliceConst()) |arg|
-                                            warn("{} ", arg)
+                                            warn("{} ", .{arg})
                                         else
-                                            warn("\n");
-                                        return parseError(tokenizer, code.source_token, "example incorrectly compiled");
+                                            warn("\n", .{});
+                                        return parseError(tokenizer, code.source_token, "example incorrectly compiled", .{});
                                     }
                                 },
                                 else => {
-                                    warn("{}\nThe following command crashed:\n", result.stderr);
+                                    warn("{}\nThe following command crashed:\n", .{result.stderr});
                                     for (build_args.toSliceConst()) |arg|
-                                        warn("{} ", arg)
+                                        warn("{} ", .{arg})
                                     else
-                                        warn("\n");
-                                    return parseError(tokenizer, code.source_token, "example compile crashed");
+                                        warn("\n", .{});
+                                    return parseError(tokenizer, code.source_token, "example compile crashed", .{});
                                 },
                             }
                             const escaped_stderr = try escapeHtml(allocator, result.stderr);
                             const colored_stderr = try termColor(allocator, escaped_stderr);
-                            try out.print("\n{}</code></pre>\n", colored_stderr);
+                            try out.print("\n{}</code></pre>\n", .{colored_stderr});
                             break :code_block;
                         }
-                        const exec_result = exec(allocator, &env_map, build_args.toSliceConst()) catch return parseError(tokenizer, code.source_token, "example failed to compile");
+                        const exec_result = exec(allocator, &env_map, build_args.toSliceConst()) catch return parseError(tokenizer, code.source_token, "example failed to compile", .{});
 
                         if (code.target_str) |triple| {
                             if (mem.startsWith(u8, triple, "wasm32") or
@@ -1137,7 +1149,7 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
                                 (builtin.os != .linux or builtin.arch != .x86_64))
                             {
                                 // skip execution
-                                try out.print("</code></pre>\n");
+                                try out.print("</code></pre>\n", .{});
                                 break :code_block;
                             }
                         }
@@ -1152,12 +1164,12 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
                             switch (result.term) {
                                 .Exited => |exit_code| {
                                     if (exit_code == 0) {
-                                        warn("{}\nThe following command incorrectly succeeded:\n", result.stderr);
+                                        warn("{}\nThe following command incorrectly succeeded:\n", .{result.stderr});
                                         for (run_args) |arg|
-                                            warn("{} ", arg)
+                                            warn("{} ", .{arg})
                                         else
-                                            warn("\n");
-                                        return parseError(tokenizer, code.source_token, "example incorrectly compiled");
+                                            warn("\n", .{});
+                                        return parseError(tokenizer, code.source_token, "example incorrectly compiled", .{});
                                     }
                                 },
                                 .Signal => exited_with_signal = true,
@@ -1165,7 +1177,7 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
                             }
                             break :blk result;
                         } else blk: {
-                            break :blk exec(allocator, &env_map, run_args) catch return parseError(tokenizer, code.source_token, "example crashed");
+                            break :blk exec(allocator, &env_map, run_args) catch return parseError(tokenizer, code.source_token, "example crashed", .{});
                         };
 
                         const escaped_stderr = try escapeHtml(allocator, result.stderr);
@@ -1174,11 +1186,11 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
                         const colored_stderr = try termColor(allocator, escaped_stderr);
                         const colored_stdout = try termColor(allocator, escaped_stdout);
 
-                        try out.print("\n$ ./{}\n{}{}", code.name, colored_stdout, colored_stderr);
+                        try out.print("\n$ ./{}\n{}{}", .{ code.name, colored_stdout, colored_stderr });
                         if (exited_with_signal) {
-                            try out.print("(process terminated by signal)");
+                            try out.print("(process terminated by signal)", .{});
                         }
-                        try out.print("</code></pre>\n");
+                        try out.print("</code></pre>\n", .{});
                     },
                     Code.Id.Test => {
                         var test_args = std.ArrayList([]const u8).init(allocator);
@@ -1191,34 +1203,34 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
                             "--cache",
                             "on",
                         });
-                        try out.print("<pre><code class=\"shell\">$ zig test {}.zig", code.name);
+                        try out.print("<pre><code class=\"shell\">$ zig test {}.zig", .{code.name});
                         switch (code.mode) {
                             builtin.Mode.Debug => {},
                             builtin.Mode.ReleaseSafe => {
                                 try test_args.append("--release-safe");
-                                try out.print(" --release-safe");
+                                try out.print(" --release-safe", .{});
                             },
                             builtin.Mode.ReleaseFast => {
                                 try test_args.append("--release-fast");
-                                try out.print(" --release-fast");
+                                try out.print(" --release-fast", .{});
                             },
                             builtin.Mode.ReleaseSmall => {
                                 try test_args.append("--release-small");
-                                try out.print(" --release-small");
+                                try out.print(" --release-small", .{});
                             },
                         }
                         if (code.link_libc) {
                             try test_args.append("-lc");
-                            try out.print(" -lc");
+                            try out.print(" -lc", .{});
                         }
                         if (code.target_str) |triple| {
                             try test_args.appendSlice(&[_][]const u8{ "-target", triple });
-                            try out.print(" -target {}", triple);
+                            try out.print(" -target {}", .{triple});
                         }
-                        const result = exec(allocator, &env_map, test_args.toSliceConst()) catch return parseError(tokenizer, code.source_token, "test failed");
+                        const result = exec(allocator, &env_map, test_args.toSliceConst()) catch return parseError(tokenizer, code.source_token, "test failed", .{});
                         const escaped_stderr = try escapeHtml(allocator, result.stderr);
                         const escaped_stdout = try escapeHtml(allocator, result.stdout);
-                        try out.print("\n{}{}</code></pre>\n", escaped_stderr, escaped_stdout);
+                        try out.print("\n{}{}</code></pre>\n", .{ escaped_stderr, escaped_stdout });
                     },
                     Code.Id.TestError => |error_match| {
                         var test_args = std.ArrayList([]const u8).init(allocator);
@@ -1233,50 +1245,50 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
                             "--output-dir",
                             tmp_dir_name,
                         });
-                        try out.print("<pre><code class=\"shell\">$ zig test {}.zig", code.name);
+                        try out.print("<pre><code class=\"shell\">$ zig test {}.zig", .{code.name});
                         switch (code.mode) {
                             builtin.Mode.Debug => {},
                             builtin.Mode.ReleaseSafe => {
                                 try test_args.append("--release-safe");
-                                try out.print(" --release-safe");
+                                try out.print(" --release-safe", .{});
                             },
                             builtin.Mode.ReleaseFast => {
                                 try test_args.append("--release-fast");
-                                try out.print(" --release-fast");
+                                try out.print(" --release-fast", .{});
                             },
                             builtin.Mode.ReleaseSmall => {
                                 try test_args.append("--release-small");
-                                try out.print(" --release-small");
+                                try out.print(" --release-small", .{});
                             },
                         }
                         const result = try ChildProcess.exec(allocator, test_args.toSliceConst(), null, &env_map, max_doc_file_size);
                         switch (result.term) {
                             .Exited => |exit_code| {
                                 if (exit_code == 0) {
-                                    warn("{}\nThe following command incorrectly succeeded:\n", result.stderr);
+                                    warn("{}\nThe following command incorrectly succeeded:\n", .{result.stderr});
                                     for (test_args.toSliceConst()) |arg|
-                                        warn("{} ", arg)
+                                        warn("{} ", .{arg})
                                     else
-                                        warn("\n");
-                                    return parseError(tokenizer, code.source_token, "example incorrectly compiled");
+                                        warn("\n", .{});
+                                    return parseError(tokenizer, code.source_token, "example incorrectly compiled", .{});
                                 }
                             },
                             else => {
-                                warn("{}\nThe following command crashed:\n", result.stderr);
+                                warn("{}\nThe following command crashed:\n", .{result.stderr});
                                 for (test_args.toSliceConst()) |arg|
-                                    warn("{} ", arg)
+                                    warn("{} ", .{arg})
                                 else
-                                    warn("\n");
-                                return parseError(tokenizer, code.source_token, "example compile crashed");
+                                    warn("\n", .{});
+                                return parseError(tokenizer, code.source_token, "example compile crashed", .{});
                             },
                         }
                         if (mem.indexOf(u8, result.stderr, error_match) == null) {
-                            warn("{}\nExpected to find '{}' in stderr", result.stderr, error_match);
-                            return parseError(tokenizer, code.source_token, "example did not have expected compile error");
+                            warn("{}\nExpected to find '{}' in stderr", .{ result.stderr, error_match });
+                            return parseError(tokenizer, code.source_token, "example did not have expected compile error", .{});
                         }
                         const escaped_stderr = try escapeHtml(allocator, result.stderr);
                         const colored_stderr = try termColor(allocator, escaped_stderr);
-                        try out.print("\n{}</code></pre>\n", colored_stderr);
+                        try out.print("\n{}</code></pre>\n", .{colored_stderr});
                     },
 
                     Code.Id.TestSafety => |error_match| {
@@ -1311,38 +1323,37 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
                         switch (result.term) {
                             .Exited => |exit_code| {
                                 if (exit_code == 0) {
-                                    warn("{}\nThe following command incorrectly succeeded:\n", result.stderr);
+                                    warn("{}\nThe following command incorrectly succeeded:\n", .{result.stderr});
                                     for (test_args.toSliceConst()) |arg|
-                                        warn("{} ", arg)
+                                        warn("{} ", .{arg})
                                     else
-                                        warn("\n");
-                                    return parseError(tokenizer, code.source_token, "example test incorrectly succeeded");
+                                        warn("\n", .{});
+                                    return parseError(tokenizer, code.source_token, "example test incorrectly succeeded", .{});
                                 }
                             },
                             else => {
-                                warn("{}\nThe following command crashed:\n", result.stderr);
+                                warn("{}\nThe following command crashed:\n", .{result.stderr});
                                 for (test_args.toSliceConst()) |arg|
-                                    warn("{} ", arg)
+                                    warn("{} ", .{arg})
                                 else
-                                    warn("\n");
-                                return parseError(tokenizer, code.source_token, "example compile crashed");
+                                    warn("\n", .{});
+                                return parseError(tokenizer, code.source_token, "example compile crashed", .{});
                             },
                         }
                         if (mem.indexOf(u8, result.stderr, error_match) == null) {
-                            warn("{}\nExpected to find '{}' in stderr", result.stderr, error_match);
-                            return parseError(tokenizer, code.source_token, "example did not have expected runtime safety error message");
+                            warn("{}\nExpected to find '{}' in stderr", .{ result.stderr, error_match });
+                            return parseError(tokenizer, code.source_token, "example did not have expected runtime safety error message", .{});
                         }
                         const escaped_stderr = try escapeHtml(allocator, result.stderr);
                         const colored_stderr = try termColor(allocator, escaped_stderr);
-                        try out.print(
-                            "<pre><code class=\"shell\">$ zig test {}.zig{}\n{}</code></pre>\n",
+                        try out.print("<pre><code class=\"shell\">$ zig test {}.zig{}\n{}</code></pre>\n", .{
                             code.name,
                             mode_arg,
                             colored_stderr,
-                        );
+                        });
                     },
                     Code.Id.Obj => |maybe_error_match| {
-                        const name_plus_obj_ext = try std.fmt.allocPrint(allocator, "{}{}", code.name, obj_ext);
+                        const name_plus_obj_ext = try std.fmt.allocPrint(allocator, "{}{}", .{ code.name, obj_ext });
                         const tmp_obj_file_name = try fs.path.join(
                             allocator,
                             &[_][]const u8{ tmp_dir_name, name_plus_obj_ext },
@@ -1350,7 +1361,7 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
                         var build_args = std.ArrayList([]const u8).init(allocator);
                         defer build_args.deinit();
 
-                        const name_plus_h_ext = try std.fmt.allocPrint(allocator, "{}.h", code.name);
+                        const name_plus_h_ext = try std.fmt.allocPrint(allocator, "{}.h", .{code.name});
                         const output_h_file_name = try fs.path.join(
                             allocator,
                             &[_][]const u8{ tmp_dir_name, name_plus_h_ext },
@@ -1369,7 +1380,7 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
                         });
 
                         if (!code.is_inline) {
-                            try out.print("<pre><code class=\"shell\">$ zig build-obj {}.zig", code.name);
+                            try out.print("<pre><code class=\"shell\">$ zig build-obj {}.zig", .{code.name});
                         }
 
                         switch (code.mode) {
@@ -1377,26 +1388,26 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
                             builtin.Mode.ReleaseSafe => {
                                 try build_args.append("--release-safe");
                                 if (!code.is_inline) {
-                                    try out.print(" --release-safe");
+                                    try out.print(" --release-safe", .{});
                                 }
                             },
                             builtin.Mode.ReleaseFast => {
                                 try build_args.append("--release-fast");
                                 if (!code.is_inline) {
-                                    try out.print(" --release-fast");
+                                    try out.print(" --release-fast", .{});
                                 }
                             },
                             builtin.Mode.ReleaseSmall => {
                                 try build_args.append("--release-small");
                                 if (!code.is_inline) {
-                                    try out.print(" --release-small");
+                                    try out.print(" --release-small", .{});
                                 }
                             },
                         }
 
                         if (code.target_str) |triple| {
                             try build_args.appendSlice(&[_][]const u8{ "-target", triple });
-                            try out.print(" -target {}", triple);
+                            try out.print(" -target {}", .{triple});
                         }
 
                         if (maybe_error_match) |error_match| {
@@ -1404,35 +1415,35 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
                             switch (result.term) {
                                 .Exited => |exit_code| {
                                     if (exit_code == 0) {
-                                        warn("{}\nThe following command incorrectly succeeded:\n", result.stderr);
+                                        warn("{}\nThe following command incorrectly succeeded:\n", .{result.stderr});
                                         for (build_args.toSliceConst()) |arg|
-                                            warn("{} ", arg)
+                                            warn("{} ", .{arg})
                                         else
-                                            warn("\n");
-                                        return parseError(tokenizer, code.source_token, "example build incorrectly succeeded");
+                                            warn("\n", .{});
+                                        return parseError(tokenizer, code.source_token, "example build incorrectly succeeded", .{});
                                     }
                                 },
                                 else => {
-                                    warn("{}\nThe following command crashed:\n", result.stderr);
+                                    warn("{}\nThe following command crashed:\n", .{result.stderr});
                                     for (build_args.toSliceConst()) |arg|
-                                        warn("{} ", arg)
+                                        warn("{} ", .{arg})
                                     else
-                                        warn("\n");
-                                    return parseError(tokenizer, code.source_token, "example compile crashed");
+                                        warn("\n", .{});
+                                    return parseError(tokenizer, code.source_token, "example compile crashed", .{});
                                 },
                             }
                             if (mem.indexOf(u8, result.stderr, error_match) == null) {
-                                warn("{}\nExpected to find '{}' in stderr", result.stderr, error_match);
-                                return parseError(tokenizer, code.source_token, "example did not have expected compile error message");
+                                warn("{}\nExpected to find '{}' in stderr", .{ result.stderr, error_match });
+                                return parseError(tokenizer, code.source_token, "example did not have expected compile error message", .{});
                             }
                             const escaped_stderr = try escapeHtml(allocator, result.stderr);
                             const colored_stderr = try termColor(allocator, escaped_stderr);
-                            try out.print("\n{}", colored_stderr);
+                            try out.print("\n{}", .{colored_stderr});
                         } else {
-                            _ = exec(allocator, &env_map, build_args.toSliceConst()) catch return parseError(tokenizer, code.source_token, "example failed to compile");
+                            _ = exec(allocator, &env_map, build_args.toSliceConst()) catch return parseError(tokenizer, code.source_token, "example failed to compile", .{});
                         }
                         if (!code.is_inline) {
-                            try out.print("</code></pre>\n");
+                            try out.print("</code></pre>\n", .{});
                         }
                     },
                     Code.Id.Lib => {
@@ -1446,33 +1457,33 @@ fn genHtml(allocator: *mem.Allocator, tokenizer: *Tokenizer, toc: *Toc, out: var
                             "--output-dir",
                             tmp_dir_name,
                         });
-                        try out.print("<pre><code class=\"shell\">$ zig build-lib {}.zig", code.name);
+                        try out.print("<pre><code class=\"shell\">$ zig build-lib {}.zig", .{code.name});
                         switch (code.mode) {
                             builtin.Mode.Debug => {},
                             builtin.Mode.ReleaseSafe => {
                                 try test_args.append("--release-safe");
-                                try out.print(" --release-safe");
+                                try out.print(" --release-safe", .{});
                             },
                             builtin.Mode.ReleaseFast => {
                                 try test_args.append("--release-fast");
-                                try out.print(" --release-fast");
+                                try out.print(" --release-fast", .{});
                             },
                             builtin.Mode.ReleaseSmall => {
                                 try test_args.append("--release-small");
-                                try out.print(" --release-small");
+                                try out.print(" --release-small", .{});
                             },
                         }
                         if (code.target_str) |triple| {
                             try test_args.appendSlice(&[_][]const u8{ "-target", triple });
-                            try out.print(" -target {}", triple);
+                            try out.print(" -target {}", .{triple});
                         }
-                        const result = exec(allocator, &env_map, test_args.toSliceConst()) catch return parseError(tokenizer, code.source_token, "test failed");
+                        const result = exec(allocator, &env_map, test_args.toSliceConst()) catch return parseError(tokenizer, code.source_token, "test failed", .{});
                         const escaped_stderr = try escapeHtml(allocator, result.stderr);
                         const escaped_stdout = try escapeHtml(allocator, result.stdout);
-                        try out.print("\n{}{}</code></pre>\n", escaped_stderr, escaped_stdout);
+                        try out.print("\n{}{}</code></pre>\n", .{ escaped_stderr, escaped_stdout });
                     },
                 }
-                warn("OK\n");
+                warn("OK\n", .{});
             },
         }
     }
@@ -1483,20 +1494,20 @@ fn exec(allocator: *mem.Allocator, env_map: *std.BufMap, args: []const []const u
     switch (result.term) {
         .Exited => |exit_code| {
             if (exit_code != 0) {
-                warn("{}\nThe following command exited with code {}:\n", result.stderr, exit_code);
+                warn("{}\nThe following command exited with code {}:\n", .{ result.stderr, exit_code });
                 for (args) |arg|
-                    warn("{} ", arg)
+                    warn("{} ", .{arg})
                 else
-                    warn("\n");
+                    warn("\n", .{});
                 return error.ChildExitError;
             }
         },
         else => {
-            warn("{}\nThe following command crashed:\n", result.stderr);
+            warn("{}\nThe following command crashed:\n", .{result.stderr});
             for (args) |arg|
-                warn("{} ", arg)
+                warn("{} ", .{arg})
             else
-                warn("\n");
+                warn("\n", .{});
             return error.ChildCrashed;
         },
     }
diff --git a/doc/langref.html.in b/doc/langref.html.in
index 64c039d533..48ec5e39fe 100644
--- a/doc/langref.html.in
+++ b/doc/langref.html.in
@@ -205,7 +205,7 @@ const std = @import("std");
 
 pub fn main() !void {
     const stdout = &std.io.getStdOut().outStream().stream;
-    try stdout.print("Hello, {}!\n", "world");
+    try stdout.print("Hello, {}!\n", .{"world"});
 }
       {#code_end#}
       <p>
@@ -217,7 +217,7 @@ pub fn main() !void {
 const warn = @import("std").debug.warn;
 
 pub fn main() void {
-    warn("Hello, world!\n");
+    warn("Hello, world!\n", .{});
 }
       {#code_end#}
       <p>
@@ -289,41 +289,50 @@ const assert = std.debug.assert;
 pub fn main() void {
     // integers
     const one_plus_one: i32 = 1 + 1;
-    warn("1 + 1 = {}\n", one_plus_one);
+    warn("1 + 1 = {}\n", .{one_plus_one});
 
     // floats
     const seven_div_three: f32 = 7.0 / 3.0;
-    warn("7.0 / 3.0 = {}\n", seven_div_three);
+    warn("7.0 / 3.0 = {}\n", .{seven_div_three});
 
     // boolean
-    warn("{}\n{}\n{}\n",
+    warn("{}\n{}\n{}\n", .{
         true and false,
         true or false,
-        !true);
+        !true,
+    });
 
     // optional
     var optional_value: ?[]const u8 = null;
     assert(optional_value == null);
 
-    warn("\noptional 1\ntype: {}\nvalue: {}\n",
-        @typeName(@typeOf(optional_value)), optional_value);
+    warn("\noptional 1\ntype: {}\nvalue: {}\n", .{
+        @typeName(@typeOf(optional_value)),
+        optional_value,
+    });
 
     optional_value = "hi";
     assert(optional_value != null);
 
-    warn("\noptional 2\ntype: {}\nvalue: {}\n",
-        @typeName(@typeOf(optional_value)), optional_value);
+    warn("\noptional 2\ntype: {}\nvalue: {}\n", .{
+        @typeName(@typeOf(optional_value)),
+        optional_value,
+    });
 
     // error union
     var number_or_error: anyerror!i32 = error.ArgNotFound;
 
-    warn("\nerror union 1\ntype: {}\nvalue: {}\n",
-        @typeName(@typeOf(number_or_error)), number_or_error);
+    warn("\nerror union 1\ntype: {}\nvalue: {}\n", .{
+        @typeName(@typeOf(number_or_error)),
+        number_or_error,
+    });
 
     number_or_error = 1234;
 
-    warn("\nerror union 2\ntype: {}\nvalue: {}\n",
-        @typeName(@typeOf(number_or_error)), number_or_error);
+    warn("\nerror union 2\ntype: {}\nvalue: {}\n", .{
+        @typeName(@typeOf(number_or_error)),
+        number_or_error,
+    });
 }
       {#code_end#}
       {#header_open|Primitive Types#}
@@ -954,8 +963,8 @@ extern fn foo_optimized(x: f64) f64;
 
 pub fn main() void {
     const x = 0.001;
-    warn("optimized = {}\n", foo_optimized(x));
-    warn("strict = {}\n", foo_strict(x));
+    warn("optimized = {}\n", .{foo_optimized(x)});
+    warn("strict = {}\n", .{foo_strict(x)});
 }
       {#code_end#}
       {#see_also|@setFloatMode|Division by Zero#}
@@ -2182,7 +2191,7 @@ test "using slices for strings" {
     // You can use slice syntax on an array to convert an array into a slice.
     const all_together_slice = all_together[0..];
     // String concatenation example.
-    const hello_world = try fmt.bufPrint(all_together_slice, "{} {}", hello, world);
+    const hello_world = try fmt.bufPrint(all_together_slice, "{} {}", .{hello, world});
 
     // Generally, you can use UTF-8 and not worry about whether something is a
     // string. If you don't need to deal with individual characters, no need
@@ -2623,9 +2632,9 @@ const std = @import("std");
 
 pub fn main() void {
     const Foo = struct {};
-    std.debug.warn("variable: {}\n", @typeName(Foo));
-    std.debug.warn("anonymous: {}\n", @typeName(struct {}));
-    std.debug.warn("function: {}\n", @typeName(List(i32)));
+    std.debug.warn("variable: {}\n", .{@typeName(Foo)});
+    std.debug.warn("anonymous: {}\n", .{@typeName(struct {})});
+    std.debug.warn("function: {}\n", .{@typeName(List(i32))});
 }
 
 fn List(comptime T: type) type {
@@ -3806,18 +3815,18 @@ test "defer basics" {
 // If multiple defer statements are specified, they will be executed in
 // the reverse order they were run.
 fn deferUnwindExample() void {
-    warn("\n");
+    warn("\n", .{});
 
     defer {
-        warn("1 ");
+        warn("1 ", .{});
     }
     defer {
-        warn("2 ");
+        warn("2 ", .{});
     }
     if (false) {
         // defers are not run if they are never executed.
         defer {
-            warn("3 ");
+            warn("3 ", .{});
         }
     }
 }
@@ -3832,15 +3841,15 @@ test "defer unwinding" {
 // This is especially useful in allowing a function to clean up properly
 // on error, and replaces goto error handling tactics as seen in c.
 fn deferErrorExample(is_error: bool) !void {
-    warn("\nstart of function\n");
+    warn("\nstart of function\n", .{});
 
     // This will always be executed on exit
     defer {
-        warn("end of function\n");
+        warn("end of function\n", .{});
     }
 
     errdefer {
-        warn("encountered an error!\n");
+        warn("encountered an error!\n", .{});
     }
 
     if (is_error) {
@@ -5843,7 +5852,7 @@ const a_number: i32 = 1234;
 const a_string = "foobar";
 
 pub fn main() void {
-    warn("here is a string: '{}' here is a number: {}\n", a_string, a_number);
+    warn("here is a string: '{}' here is a number: {}\n", .{a_string, a_number});
 }
       {#code_end#}
 
@@ -5960,8 +5969,11 @@ const a_number: i32 = 1234;
 const a_string = "foobar";
 
 test "printf too many arguments" {
-    warn("here is a string: '{}' here is a number: {}\n",
-        a_string, a_number, a_number);
+    warn("here is a string: '{}' here is a number: {}\n", .{
+        a_string,
+        a_number,
+        a_number,
+    });
 }
       {#code_end#}
       <p>
@@ -5979,7 +5991,7 @@ const a_string = "foobar";
 const fmt = "here is a string: '{}' here is a number: {}\n";
 
 pub fn main() void {
-    warn(fmt, a_string, a_number);
+    warn(fmt, .{a_string, a_number});
 }
       {#code_end#}
       <p>
@@ -6417,7 +6429,7 @@ pub fn main() void {
 
 fn amainWrap() void {
     amain() catch |e| {
-        std.debug.warn("{}\n", e);
+        std.debug.warn("{}\n", .{e});
         if (@errorReturnTrace()) |trace| {
             std.debug.dumpStackTrace(trace.*);
         }
@@ -6447,8 +6459,8 @@ fn amain() !void {
     const download_text = try await download_frame;
     defer allocator.free(download_text);
 
-    std.debug.warn("download_text: {}\n", download_text);
-    std.debug.warn("file_text: {}\n", file_text);
+    std.debug.warn("download_text: {}\n", .{download_text});
+    std.debug.warn("file_text: {}\n", .{file_text});
 }
 
 var global_download_frame: anyframe = undefined;
@@ -6458,7 +6470,7 @@ fn fetchUrl(allocator: *Allocator, url: []const u8) ![]u8 {
     suspend {
         global_download_frame = @frame();
     }
-    std.debug.warn("fetchUrl returning\n");
+    std.debug.warn("fetchUrl returning\n", .{});
     return result;
 }
 
@@ -6469,7 +6481,7 @@ fn readFile(allocator: *Allocator, filename: []const u8) ![]u8 {
     suspend {
         global_file_frame = @frame();
     }
-    std.debug.warn("readFile returning\n");
+    std.debug.warn("readFile returning\n", .{});
     return result;
 }
       {#code_end#}
@@ -6487,7 +6499,7 @@ pub fn main() void {
 
 fn amainWrap() void {
     amain() catch |e| {
-        std.debug.warn("{}\n", e);
+        std.debug.warn("{}\n", .{e});
         if (@errorReturnTrace()) |trace| {
             std.debug.dumpStackTrace(trace.*);
         }
@@ -6517,21 +6529,21 @@ fn amain() !void {
     const download_text = try await download_frame;
     defer allocator.free(download_text);
 
-    std.debug.warn("download_text: {}\n", download_text);
-    std.debug.warn("file_text: {}\n", file_text);
+    std.debug.warn("download_text: {}\n", .{download_text});
+    std.debug.warn("file_text: {}\n", .{file_text});
 }
 
 fn fetchUrl(allocator: *Allocator, url: []const u8) ![]u8 {
     const result = try std.mem.dupe(allocator, u8, "this is the downloaded url contents");
     errdefer allocator.free(result);
-    std.debug.warn("fetchUrl returning\n");
+    std.debug.warn("fetchUrl returning\n", .{});
     return result;
 }
 
 fn readFile(allocator: *Allocator, filename: []const u8) ![]u8 {
     const result = try std.mem.dupe(allocator, u8, "this is the file contents");
     errdefer allocator.free(result);
-    std.debug.warn("readFile returning\n");
+    std.debug.warn("readFile returning\n", .{});
     return result;
 }
       {#code_end#}
@@ -7103,7 +7115,7 @@ const num1 = blk: {
 test "main" {
     @compileLog("comptime in main");
 
-    warn("Runtime in main, num1 = {}.\n", num1);
+    warn("Runtime in main, num1 = {}.\n", .{num1});
 }
       {#code_end#}
       <p>
@@ -7124,7 +7136,7 @@ const num1 = blk: {
 };
 
 test "main" {
-    warn("Runtime in main, num1 = {}.\n", num1);
+    warn("Runtime in main, num1 = {}.\n", .{num1});
 }
       {#code_end#}
       {#header_close#}
@@ -8706,7 +8718,7 @@ const std = @import("std");
 pub fn main() void {
     var value: i32 = -1;
     var unsigned = @intCast(u32, value);
-    std.debug.warn("value: {}\n", unsigned);
+    std.debug.warn("value: {}\n", .{unsigned});
 }
       {#code_end#}
       <p>
@@ -8728,7 +8740,7 @@ const std = @import("std");
 pub fn main() void {
     var spartan_count: u16 = 300;
     const byte = @intCast(u8, spartan_count);
-    std.debug.warn("value: {}\n", byte);
+    std.debug.warn("value: {}\n", .{byte});
 }
       {#code_end#}
       <p>
@@ -8762,7 +8774,7 @@ const std = @import("std");
 pub fn main() void {
     var byte: u8 = 255;
     byte += 1;
-    std.debug.warn("value: {}\n", byte);
+    std.debug.warn("value: {}\n", .{byte});
 }
       {#code_end#}
       {#header_close#}
@@ -8785,11 +8797,11 @@ pub fn main() !void {
     var byte: u8 = 255;
 
     byte = if (math.add(u8, byte, 1)) |result| result else |err| {
-        warn("unable to add one: {}\n", @errorName(err));
+        warn("unable to add one: {}\n", .{@errorName(err)});
         return err;
     };
 
-    warn("result: {}\n", byte);
+    warn("result: {}\n", .{byte});
 }
       {#code_end#}
       {#header_close#}
@@ -8814,9 +8826,9 @@ pub fn main() void {
 
     var result: u8 = undefined;
     if (@addWithOverflow(u8, byte, 10, &result)) {
-        warn("overflowed result: {}\n", result);
+        warn("overflowed result: {}\n", .{result});
     } else {
-        warn("result: {}\n", result);
+        warn("result: {}\n", .{result});
     }
 }
       {#code_end#}
@@ -8861,7 +8873,7 @@ const std = @import("std");
 pub fn main() void {
     var x: u8 = 0b01010101;
     var y = @shlExact(x, 2);
-    std.debug.warn("value: {}\n", y);
+    std.debug.warn("value: {}\n", .{y});
 }
       {#code_end#}
       {#header_close#}
@@ -8879,7 +8891,7 @@ const std = @import("std");
 pub fn main() void {
     var x: u8 = 0b10101010;
     var y = @shrExact(x, 2);
-    std.debug.warn("value: {}\n", y);
+    std.debug.warn("value: {}\n", .{y});
 }
       {#code_end#}
       {#header_close#}
@@ -8900,7 +8912,7 @@ pub fn main() void {
     var a: u32 = 1;
     var b: u32 = 0;
     var c = a / b;
-    std.debug.warn("value: {}\n", c);
+    std.debug.warn("value: {}\n", .{c});
 }
       {#code_end#}
       {#header_close#}
@@ -8921,7 +8933,7 @@ pub fn main() void {
     var a: u32 = 10;
     var b: u32 = 0;
     var c = a % b;
-    std.debug.warn("value: {}\n", c);
+    std.debug.warn("value: {}\n", .{c});
 }
       {#code_end#}
       {#header_close#}
@@ -8942,7 +8954,7 @@ pub fn main() void {
     var a: u32 = 10;
     var b: u32 = 3;
     var c = @divExact(a, b);
-    std.debug.warn("value: {}\n", c);
+    std.debug.warn("value: {}\n", .{c});
 }
       {#code_end#}
       {#header_close#}
@@ -8961,7 +8973,7 @@ const std = @import("std");
 pub fn main() void {
     var bytes = [5]u8{ 1, 2, 3, 4, 5 };
     var slice = @bytesToSlice(u32, bytes[0..]);
-    std.debug.warn("value: {}\n", slice[0]);
+    std.debug.warn("value: {}\n", .{slice[0]});
 }
       {#code_end#}
       {#header_close#}
@@ -8980,7 +8992,7 @@ const std = @import("std");
 pub fn main() void {
     var optional_number: ?i32 = null;
     var number = optional_number.?;
-    std.debug.warn("value: {}\n", number);
+    std.debug.warn("value: {}\n", .{number});
 }
       {#code_end#}
       <p>One way to avoid this crash is to test for null instead of assuming non-null, with
@@ -8991,9 +9003,9 @@ pub fn main() void {
     const optional_number: ?i32 = null;
 
     if (optional_number) |number| {
-        warn("got number: {}\n", number);
+        warn("got number: {}\n", .{number});
     } else {
-        warn("it's null\n");
+        warn("it's null\n", .{});
     }
 }
       {#code_end#}
@@ -9016,7 +9028,7 @@ const std = @import("std");
 
 pub fn main() void {
     const number = getNumberOrFail() catch unreachable;
-    std.debug.warn("value: {}\n", number);
+    std.debug.warn("value: {}\n", .{number});
 }
 
 fn getNumberOrFail() !i32 {
@@ -9032,9 +9044,9 @@ pub fn main() void {
     const result = getNumberOrFail();
 
     if (result) |number| {
-        warn("got number: {}\n", number);
+        warn("got number: {}\n", .{number});
     } else |err| {
-        warn("got error: {}\n", @errorName(err));
+        warn("got error: {}\n", .{@errorName(err)});
     }
 }
 
@@ -9061,7 +9073,7 @@ pub fn main() void {
     var err = error.AnError;
     var number = @errorToInt(err) + 500;
     var invalid_err = @intToError(number);
-    std.debug.warn("value: {}\n", number);
+    std.debug.warn("value: {}\n", .{number});
 }
       {#code_end#}
       {#header_close#}
@@ -9091,7 +9103,7 @@ const Foo = enum {
 pub fn main() void {
     var a: u2 = 3;
     var b = @intToEnum(Foo, a);
-    std.debug.warn("value: {}\n", @tagName(b));
+    std.debug.warn("value: {}\n", .{@tagName(b)});
 }
       {#code_end#}
       {#header_close#}
@@ -9128,7 +9140,7 @@ pub fn main() void {
 }
 fn foo(set1: Set1) void {
     const x = @errSetCast(Set2, set1);
-    std.debug.warn("value: {}\n", x);
+    std.debug.warn("value: {}\n", .{x});
 }
       {#code_end#}
       {#header_close#}
@@ -9184,7 +9196,7 @@ pub fn main() void {
 
 fn bar(f: *Foo) void {
     f.float = 12.34;
-    std.debug.warn("value: {}\n", f.float);
+    std.debug.warn("value: {}\n", .{f.float});
 }
       {#code_end#}
       <p>
@@ -9208,7 +9220,7 @@ pub fn main() void {
 
 fn bar(f: *Foo) void {
     f.* = Foo{ .float = 12.34 };
-    std.debug.warn("value: {}\n", f.float);
+    std.debug.warn("value: {}\n", .{f.float});
 }
       {#code_end#}
       <p>
@@ -9227,7 +9239,7 @@ pub fn main() void {
     var f = Foo{ .int = 42 };
     f = Foo{ .float = undefined };
     bar(&f);
-    std.debug.warn("value: {}\n", f.float);
+    std.debug.warn("value: {}\n", .{f.float});
 }
 
 fn bar(f: *Foo) void {
@@ -9348,7 +9360,7 @@ pub fn main() !void {
     const allocator = &arena.allocator;
 
     const ptr = try allocator.create(i32);
-    std.debug.warn("ptr={*}\n", ptr);
+    std.debug.warn("ptr={*}\n", .{ptr});
 }
               {#code_end#}
               When using this kind of allocator, there is no need to free anything manually. Everything
@@ -9881,7 +9893,7 @@ pub fn main() !void {
     defer std.process.argsFree(std.heap.page_allocator, args);
 
     for (args) |arg, i| {
-        std.debug.warn("{}: {}\n", i, arg);
+        std.debug.warn("{}: {}\n", .{i, arg});
     }
 }
       {#code_end#}
diff --git a/lib/std/atomic/queue.zig b/lib/std/atomic/queue.zig
index 53f1d99f13..63bacb4fb5 100644
--- a/lib/std/atomic/queue.zig
+++ b/lib/std/atomic/queue.zig
@@ -116,19 +116,19 @@ pub fn Queue(comptime T: type) type {
                 fn dumpRecursive(s: *std.io.OutStream(Error), optional_node: ?*Node, indent: usize) Error!void {
                     try s.writeByteNTimes(' ', indent);
                     if (optional_node) |node| {
-                        try s.print("0x{x}={}\n", @ptrToInt(node), node.data);
+                        try s.print("0x{x}={}\n", .{ @ptrToInt(node), node.data });
                         try dumpRecursive(s, node.next, indent + 1);
                     } else {
-                        try s.print("(null)\n");
+                        try s.print("(null)\n", .{});
                     }
                 }
             };
             const held = self.mutex.acquire();
             defer held.release();
 
-            try stream.print("head: ");
+            try stream.print("head: ", .{});
             try S.dumpRecursive(stream, self.head, 0);
-            try stream.print("tail: ");
+            try stream.print("tail: ", .{});
             try S.dumpRecursive(stream, self.tail, 0);
         }
     };
@@ -207,16 +207,15 @@ test "std.atomic.Queue" {
     }
 
     if (context.put_sum != context.get_sum) {
-        std.debug.panic("failure\nput_sum:{} != get_sum:{}", context.put_sum, context.get_sum);
+        std.debug.panic("failure\nput_sum:{} != get_sum:{}", .{ context.put_sum, context.get_sum });
     }
 
     if (context.get_count != puts_per_thread * put_thread_count) {
-        std.debug.panic(
-            "failure\nget_count:{} != puts_per_thread:{} * put_thread_count:{}",
+        std.debug.panic("failure\nget_count:{} != puts_per_thread:{} * put_thread_count:{}", .{
             context.get_count,
             @as(u32, puts_per_thread),
             @as(u32, put_thread_count),
-        );
+        });
     }
 }
 
@@ -351,7 +350,7 @@ test "std.atomic.Queue dump" {
         \\tail: 0x{x}=1
         \\ (null)
         \\
-    , @ptrToInt(queue.head), @ptrToInt(queue.tail));
+    , .{ @ptrToInt(queue.head), @ptrToInt(queue.tail) });
     expect(mem.eql(u8, buffer[0..sos.pos], expected));
 
     // Test a stream with two elements
@@ -372,6 +371,6 @@ test "std.atomic.Queue dump" {
         \\tail: 0x{x}=2
         \\ (null)
         \\
-    , @ptrToInt(queue.head), @ptrToInt(queue.head.?.next), @ptrToInt(queue.tail));
+    , .{ @ptrToInt(queue.head), @ptrToInt(queue.head.?.next), @ptrToInt(queue.tail) });
     expect(mem.eql(u8, buffer[0..sos.pos], expected));
 }
diff --git a/lib/std/atomic/stack.zig b/lib/std/atomic/stack.zig
index 2636b20528..9de8e36f87 100644
--- a/lib/std/atomic/stack.zig
+++ b/lib/std/atomic/stack.zig
@@ -134,16 +134,15 @@ test "std.atomic.stack" {
     }
 
     if (context.put_sum != context.get_sum) {
-        std.debug.panic("failure\nput_sum:{} != get_sum:{}", context.put_sum, context.get_sum);
+        std.debug.panic("failure\nput_sum:{} != get_sum:{}", .{ context.put_sum, context.get_sum });
     }
 
     if (context.get_count != puts_per_thread * put_thread_count) {
-        std.debug.panic(
-            "failure\nget_count:{} != puts_per_thread:{} * put_thread_count:{}",
+        std.debug.panic("failure\nget_count:{} != puts_per_thread:{} * put_thread_count:{}", .{
             context.get_count,
             @as(u32, puts_per_thread),
             @as(u32, put_thread_count),
-        );
+        });
     }
 }
 
diff --git a/lib/std/buffer.zig b/lib/std/buffer.zig
index 46c55a32b8..55a5a890d6 100644
--- a/lib/std/buffer.zig
+++ b/lib/std/buffer.zig
@@ -16,7 +16,7 @@ pub const Buffer = struct {
         mem.copy(u8, self.list.items, m);
         return self;
     }
-    
+
     /// Initialize memory to size bytes of undefined values.
     /// Must deinitialize with deinit.
     pub fn initSize(allocator: *Allocator, size: usize) !Buffer {
@@ -24,7 +24,7 @@ pub const Buffer = struct {
         try self.resize(size);
         return self;
     }
-    
+
     /// Initialize with capacity to hold at least num bytes.
     /// Must deinitialize with deinit.
     pub fn initCapacity(allocator: *Allocator, num: usize) !Buffer {
@@ -64,7 +64,7 @@ pub const Buffer = struct {
         return result;
     }
 
-    pub fn allocPrint(allocator: *Allocator, comptime format: []const u8, args: ...) !Buffer {
+    pub fn allocPrint(allocator: *Allocator, comptime format: []const u8, args: var) !Buffer {
         const countSize = struct {
             fn countSize(size: *usize, bytes: []const u8) (error{}!void) {
                 size.* += bytes.len;
@@ -107,7 +107,7 @@ pub const Buffer = struct {
     pub fn len(self: Buffer) usize {
         return self.list.len - 1;
     }
-    
+
     pub fn capacity(self: Buffer) usize {
         return if (self.list.items.len > 0)
             self.list.items.len - 1
diff --git a/lib/std/build.zig b/lib/std/build.zig
index bfde2f52d7..82681e3069 100644
--- a/lib/std/build.zig
+++ b/lib/std/build.zig
@@ -232,7 +232,7 @@ pub const Builder = struct {
     /// To run an executable built with zig build, see `LibExeObjStep.run`.
     pub fn addSystemCommand(self: *Builder, argv: []const []const u8) *RunStep {
         assert(argv.len >= 1);
-        const run_step = RunStep.create(self, self.fmt("run {}", argv[0]));
+        const run_step = RunStep.create(self, self.fmt("run {}", .{argv[0]}));
         run_step.addArgs(argv);
         return run_step;
     }
@@ -258,7 +258,7 @@ pub const Builder = struct {
         return write_file_step;
     }
 
-    pub fn addLog(self: *Builder, comptime format: []const u8, args: ...) *LogStep {
+    pub fn addLog(self: *Builder, comptime format: []const u8, args: var) *LogStep {
         const data = self.fmt(format, args);
         const log_step = self.allocator.create(LogStep) catch unreachable;
         log_step.* = LogStep.init(self, data);
@@ -330,7 +330,7 @@ pub const Builder = struct {
         for (self.installed_files.toSliceConst()) |installed_file| {
             const full_path = self.getInstallPath(installed_file.dir, installed_file.path);
             if (self.verbose) {
-                warn("rm {}\n", full_path);
+                warn("rm {}\n", .{full_path});
             }
             fs.deleteTree(full_path) catch {};
         }
@@ -340,7 +340,7 @@ pub const Builder = struct {
 
     fn makeOneStep(self: *Builder, s: *Step) anyerror!void {
         if (s.loop_flag) {
-            warn("Dependency loop detected:\n  {}\n", s.name);
+            warn("Dependency loop detected:\n  {}\n", .{s.name});
             return error.DependencyLoopDetected;
         }
         s.loop_flag = true;
@@ -348,7 +348,7 @@ pub const Builder = struct {
         for (s.dependencies.toSlice()) |dep| {
             self.makeOneStep(dep) catch |err| {
                 if (err == error.DependencyLoopDetected) {
-                    warn("  {}\n", s.name);
+                    warn("  {}\n", .{s.name});
                 }
                 return err;
             };
@@ -365,7 +365,7 @@ pub const Builder = struct {
                 return &top_level_step.step;
             }
         }
-        warn("Cannot run step '{}' because it does not exist\n", name);
+        warn("Cannot run step '{}' because it does not exist\n", .{name});
         return error.InvalidStepName;
     }
 
@@ -378,12 +378,12 @@ pub const Builder = struct {
                 const word = it.next() orelse break;
                 if (mem.eql(u8, word, "-isystem")) {
                     const include_path = it.next() orelse {
-                        warn("Expected argument after -isystem in NIX_CFLAGS_COMPILE\n");
+                        warn("Expected argument after -isystem in NIX_CFLAGS_COMPILE\n", .{});
                         break;
                     };
                     self.addNativeSystemIncludeDir(include_path);
                 } else {
-                    warn("Unrecognized C flag from NIX_CFLAGS_COMPILE: {}\n", word);
+                    warn("Unrecognized C flag from NIX_CFLAGS_COMPILE: {}\n", .{word});
                     break;
                 }
             }
@@ -397,7 +397,7 @@ pub const Builder = struct {
                 const word = it.next() orelse break;
                 if (mem.eql(u8, word, "-rpath")) {
                     const rpath = it.next() orelse {
-                        warn("Expected argument after -rpath in NIX_LDFLAGS\n");
+                        warn("Expected argument after -rpath in NIX_LDFLAGS\n", .{});
                         break;
                     };
                     self.addNativeSystemRPath(rpath);
@@ -405,7 +405,7 @@ pub const Builder = struct {
                     const lib_path = word[2..];
                     self.addNativeSystemLibPath(lib_path);
                 } else {
-                    warn("Unrecognized C flag from NIX_LDFLAGS: {}\n", word);
+                    warn("Unrecognized C flag from NIX_LDFLAGS: {}\n", .{word});
                     break;
                 }
             }
@@ -431,8 +431,8 @@ pub const Builder = struct {
                 self.addNativeSystemIncludeDir("/usr/local/include");
                 self.addNativeSystemLibPath("/usr/local/lib");
 
-                self.addNativeSystemIncludeDir(self.fmt("/usr/include/{}", triple));
-                self.addNativeSystemLibPath(self.fmt("/usr/lib/{}", triple));
+                self.addNativeSystemIncludeDir(self.fmt("/usr/include/{}", .{triple}));
+                self.addNativeSystemLibPath(self.fmt("/usr/lib/{}", .{triple}));
 
                 self.addNativeSystemIncludeDir("/usr/include");
                 self.addNativeSystemLibPath("/usr/lib");
@@ -440,7 +440,7 @@ pub const Builder = struct {
                 // example: on a 64-bit debian-based linux distro, with zlib installed from apt:
                 // zlib.h is in /usr/include (added above)
                 // libz.so.1 is in /lib/x86_64-linux-gnu (added here)
-                self.addNativeSystemLibPath(self.fmt("/lib/{}", triple));
+                self.addNativeSystemLibPath(self.fmt("/lib/{}", .{triple}));
             },
         }
     }
@@ -453,7 +453,7 @@ pub const Builder = struct {
             .description = description,
         };
         if ((self.available_options_map.put(name, available_option) catch unreachable) != null) {
-            panic("Option '{}' declared twice", name);
+            panic("Option '{}' declared twice", .{name});
         }
         self.available_options_list.append(available_option) catch unreachable;
 
@@ -468,33 +468,33 @@ pub const Builder = struct {
                     } else if (mem.eql(u8, s, "false")) {
                         return false;
                     } else {
-                        warn("Expected -D{} to be a boolean, but received '{}'\n", name, s);
+                        warn("Expected -D{} to be a boolean, but received '{}'\n", .{ name, s });
                         self.markInvalidUserInput();
                         return null;
                     }
                 },
                 UserValue.List => {
-                    warn("Expected -D{} to be a boolean, but received a list.\n", name);
+                    warn("Expected -D{} to be a boolean, but received a list.\n", .{name});
                     self.markInvalidUserInput();
                     return null;
                 },
             },
-            TypeId.Int => panic("TODO integer options to build script"),
-            TypeId.Float => panic("TODO float options to build script"),
+            TypeId.Int => panic("TODO integer options to build script", .{}),
+            TypeId.Float => panic("TODO float options to build script", .{}),
             TypeId.String => switch (entry.value.value) {
                 UserValue.Flag => {
-                    warn("Expected -D{} to be a string, but received a boolean.\n", name);
+                    warn("Expected -D{} to be a string, but received a boolean.\n", .{name});
                     self.markInvalidUserInput();
                     return null;
                 },
                 UserValue.List => {
-                    warn("Expected -D{} to be a string, but received a list.\n", name);
+                    warn("Expected -D{} to be a string, but received a list.\n", .{name});
                     self.markInvalidUserInput();
                     return null;
                 },
                 UserValue.Scalar => |s| return s,
             },
-            TypeId.List => panic("TODO list options to build script"),
+            TypeId.List => panic("TODO list options to build script", .{}),
         }
     }
 
@@ -513,7 +513,7 @@ pub const Builder = struct {
         if (self.release_mode != null) {
             @panic("setPreferredReleaseMode must be called before standardReleaseOptions and may not be called twice");
         }
-        const description = self.fmt("create a release build ({})", @tagName(mode));
+        const description = self.fmt("create a release build ({})", .{@tagName(mode)});
         self.is_release = self.option(bool, "release", description) orelse false;
         self.release_mode = if (self.is_release) mode else builtin.Mode.Debug;
     }
@@ -536,7 +536,7 @@ pub const Builder = struct {
         else if (!release_fast and !release_safe and !release_small)
             builtin.Mode.Debug
         else x: {
-            warn("Multiple release modes (of -Drelease-safe, -Drelease-fast and -Drelease-small)");
+            warn("Multiple release modes (of -Drelease-safe, -Drelease-fast and -Drelease-small)", .{});
             self.markInvalidUserInput();
             break :x builtin.Mode.Debug;
         };
@@ -599,7 +599,7 @@ pub const Builder = struct {
                 }) catch unreachable;
             },
             UserValue.Flag => {
-                warn("Option '-D{}={}' conflicts with flag '-D{}'.\n", name, value, name);
+                warn("Option '-D{}={}' conflicts with flag '-D{}'.\n", .{ name, value, name });
                 return true;
             },
         }
@@ -620,11 +620,11 @@ pub const Builder = struct {
         // option already exists
         switch (gop.kv.value.value) {
             UserValue.Scalar => |s| {
-                warn("Flag '-D{}' conflicts with option '-D{}={}'.\n", name, name, s);
+                warn("Flag '-D{}' conflicts with option '-D{}={}'.\n", .{ name, name, s });
                 return true;
             },
             UserValue.List => {
-                warn("Flag '-D{}' conflicts with multiple options of the same name.\n", name);
+                warn("Flag '-D{}' conflicts with multiple options of the same name.\n", .{name});
                 return true;
             },
             UserValue.Flag => {},
@@ -665,7 +665,7 @@ pub const Builder = struct {
         while (true) {
             const entry = it.next() orelse break;
             if (!entry.value.used) {
-                warn("Invalid option: -D{}\n\n", entry.key);
+                warn("Invalid option: -D{}\n\n", .{entry.key});
                 self.markInvalidUserInput();
             }
         }
@@ -678,11 +678,11 @@ pub const Builder = struct {
     }
 
     fn printCmd(cwd: ?[]const u8, argv: []const []const u8) void {
-        if (cwd) |yes_cwd| warn("cd {} && ", yes_cwd);
+        if (cwd) |yes_cwd| warn("cd {} && ", .{yes_cwd});
         for (argv) |arg| {
-            warn("{} ", arg);
+            warn("{} ", .{arg});
         }
-        warn("\n");
+        warn("\n", .{});
     }
 
     fn spawnChildEnvMap(self: *Builder, cwd: ?[]const u8, env_map: *const BufMap, argv: []const []const u8) !void {
@@ -697,20 +697,20 @@ pub const Builder = struct {
         child.env_map = env_map;
 
         const term = child.spawnAndWait() catch |err| {
-            warn("Unable to spawn {}: {}\n", argv[0], @errorName(err));
+            warn("Unable to spawn {}: {}\n", .{ argv[0], @errorName(err) });
             return err;
         };
 
         switch (term) {
             .Exited => |code| {
                 if (code != 0) {
-                    warn("The following command exited with error code {}:\n", code);
+                    warn("The following command exited with error code {}:\n", .{code});
                     printCmd(cwd, argv);
                     return error.UncleanExit;
                 }
             },
             else => {
-                warn("The following command terminated unexpectedly:\n");
+                warn("The following command terminated unexpectedly:\n", .{});
                 printCmd(cwd, argv);
 
                 return error.UncleanExit;
@@ -720,7 +720,7 @@ pub const Builder = struct {
 
     pub fn makePath(self: *Builder, path: []const u8) !void {
         fs.makePath(self.allocator, self.pathFromRoot(path)) catch |err| {
-            warn("Unable to create path {}: {}\n", path, @errorName(err));
+            warn("Unable to create path {}: {}\n", .{ path, @errorName(err) });
             return err;
         };
     }
@@ -793,12 +793,12 @@ pub const Builder = struct {
 
     fn updateFile(self: *Builder, source_path: []const u8, dest_path: []const u8) !void {
         if (self.verbose) {
-            warn("cp {} {} ", source_path, dest_path);
+            warn("cp {} {} ", .{ source_path, dest_path });
         }
         const prev_status = try fs.updateFile(source_path, dest_path);
         if (self.verbose) switch (prev_status) {
-            .stale => warn("# installed\n"),
-            .fresh => warn("# up-to-date\n"),
+            .stale => warn("# installed\n", .{}),
+            .fresh => warn("# up-to-date\n", .{}),
         };
     }
 
@@ -806,7 +806,7 @@ pub const Builder = struct {
         return fs.path.resolve(self.allocator, &[_][]const u8{ self.build_root, rel_path }) catch unreachable;
     }
 
-    pub fn fmt(self: *Builder, comptime format: []const u8, args: ...) []u8 {
+    pub fn fmt(self: *Builder, comptime format: []const u8, args: var) []u8 {
         return fmt_lib.allocPrint(self.allocator, format, args) catch unreachable;
     }
 
@@ -818,7 +818,11 @@ pub const Builder = struct {
                 if (fs.path.isAbsolute(name)) {
                     return name;
                 }
-                const full_path = try fs.path.join(self.allocator, &[_][]const u8{ search_prefix, "bin", self.fmt("{}{}", name, exe_extension) });
+                const full_path = try fs.path.join(self.allocator, &[_][]const u8{
+                    search_prefix,
+                    "bin",
+                    self.fmt("{}{}", .{ name, exe_extension }),
+                });
                 return fs.realpathAlloc(self.allocator, full_path) catch continue;
             }
         }
@@ -829,7 +833,10 @@ pub const Builder = struct {
                 }
                 var it = mem.tokenize(PATH, &[_]u8{fs.path.delimiter});
                 while (it.next()) |path| {
-                    const full_path = try fs.path.join(self.allocator, &[_][]const u8{ path, self.fmt("{}{}", name, exe_extension) });
+                    const full_path = try fs.path.join(self.allocator, &[_][]const u8{
+                        path,
+                        self.fmt("{}{}", .{ name, exe_extension }),
+                    });
                     return fs.realpathAlloc(self.allocator, full_path) catch continue;
                 }
             }
@@ -839,7 +846,10 @@ pub const Builder = struct {
                 return name;
             }
             for (paths) |path| {
-                const full_path = try fs.path.join(self.allocator, &[_][]const u8{ path, self.fmt("{}{}", name, exe_extension) });
+                const full_path = try fs.path.join(self.allocator, &[_][]const u8{
+                    path,
+                    self.fmt("{}{}", .{ name, exe_extension }),
+                });
                 return fs.realpathAlloc(self.allocator, full_path) catch continue;
             }
         }
@@ -896,17 +906,17 @@ pub const Builder = struct {
         var code: u8 = undefined;
         return self.execAllowFail(argv, &code, .Inherit) catch |err| switch (err) {
             error.FileNotFound => {
-                warn("Unable to spawn the following command: file not found\n");
+                warn("Unable to spawn the following command: file not found\n", .{});
                 printCmd(null, argv);
                 std.os.exit(@truncate(u8, code));
             },
             error.ExitCodeFailure => {
-                warn("The following command exited with error code {}:\n", code);
+                warn("The following command exited with error code {}:\n", .{code});
                 printCmd(null, argv);
                 std.os.exit(@truncate(u8, code));
             },
             error.ProcessTerminated => {
-                warn("The following command terminated unexpectedly:\n");
+                warn("The following command terminated unexpectedly:\n", .{});
                 printCmd(null, argv);
                 std.os.exit(@truncate(u8, code));
             },
@@ -1133,7 +1143,7 @@ pub const LibExeObjStep = struct {
 
     fn initExtraArgs(builder: *Builder, name: []const u8, root_src: ?[]const u8, kind: Kind, is_dynamic: bool, ver: Version) LibExeObjStep {
         if (mem.indexOf(u8, name, "/") != null or mem.indexOf(u8, name, "\\") != null) {
-            panic("invalid name: '{}'. It looks like a file path, but it is supposed to be the library or application name.", name);
+            panic("invalid name: '{}'. It looks like a file path, but it is supposed to be the library or application name.", .{name});
         }
         var self = LibExeObjStep{
             .strip = false,
@@ -1150,9 +1160,9 @@ pub const LibExeObjStep = struct {
             .step = Step.init(name, builder.allocator, make),
             .version = ver,
             .out_filename = undefined,
-            .out_h_filename = builder.fmt("{}.h", name),
+            .out_h_filename = builder.fmt("{}.h", .{name}),
             .out_lib_filename = undefined,
-            .out_pdb_filename = builder.fmt("{}.pdb", name),
+            .out_pdb_filename = builder.fmt("{}.pdb", .{name}),
             .major_only_filename = undefined,
             .name_only_filename = undefined,
             .packages = ArrayList(Pkg).init(builder.allocator),
@@ -1186,36 +1196,48 @@ pub const LibExeObjStep = struct {
     fn computeOutFileNames(self: *LibExeObjStep) void {
         switch (self.kind) {
             .Obj => {
-                self.out_filename = self.builder.fmt("{}{}", self.name, self.target.oFileExt());
+                self.out_filename = self.builder.fmt("{}{}", .{ self.name, self.target.oFileExt() });
             },
             .Exe => {
-                self.out_filename = self.builder.fmt("{}{}", self.name, self.target.exeFileExt());
+                self.out_filename = self.builder.fmt("{}{}", .{ self.name, self.target.exeFileExt() });
             },
             .Test => {
-                self.out_filename = self.builder.fmt("test{}", self.target.exeFileExt());
+                self.out_filename = self.builder.fmt("test{}", .{self.target.exeFileExt()});
             },
             .Lib => {
                 if (!self.is_dynamic) {
-                    self.out_filename = self.builder.fmt(
-                        "{}{}{}",
+                    self.out_filename = self.builder.fmt("{}{}{}", .{
                         self.target.libPrefix(),
                         self.name,
                         self.target.staticLibSuffix(),
-                    );
+                    });
                     self.out_lib_filename = self.out_filename;
                 } else {
                     if (self.target.isDarwin()) {
-                        self.out_filename = self.builder.fmt("lib{}.{d}.{d}.{d}.dylib", self.name, self.version.major, self.version.minor, self.version.patch);
-                        self.major_only_filename = self.builder.fmt("lib{}.{d}.dylib", self.name, self.version.major);
-                        self.name_only_filename = self.builder.fmt("lib{}.dylib", self.name);
+                        self.out_filename = self.builder.fmt("lib{}.{d}.{d}.{d}.dylib", .{
+                            self.name,
+                            self.version.major,
+                            self.version.minor,
+                            self.version.patch,
+                        });
+                        self.major_only_filename = self.builder.fmt("lib{}.{d}.dylib", .{
+                            self.name,
+                            self.version.major,
+                        });
+                        self.name_only_filename = self.builder.fmt("lib{}.dylib", .{self.name});
                         self.out_lib_filename = self.out_filename;
                     } else if (self.target.isWindows()) {
-                        self.out_filename = self.builder.fmt("{}.dll", self.name);
-                        self.out_lib_filename = self.builder.fmt("{}.lib", self.name);
+                        self.out_filename = self.builder.fmt("{}.dll", .{self.name});
+                        self.out_lib_filename = self.builder.fmt("{}.lib", .{self.name});
                     } else {
-                        self.out_filename = self.builder.fmt("lib{}.so.{d}.{d}.{d}", self.name, self.version.major, self.version.minor, self.version.patch);
-                        self.major_only_filename = self.builder.fmt("lib{}.so.{d}", self.name, self.version.major);
-                        self.name_only_filename = self.builder.fmt("lib{}.so", self.name);
+                        self.out_filename = self.builder.fmt("lib{}.so.{d}.{d}.{d}", .{
+                            self.name,
+                            self.version.major,
+                            self.version.minor,
+                            self.version.patch,
+                        });
+                        self.major_only_filename = self.builder.fmt("lib{}.so.{d}", .{ self.name, self.version.major });
+                        self.name_only_filename = self.builder.fmt("lib{}.so", .{self.name});
                         self.out_lib_filename = self.out_filename;
                     }
                 }
@@ -1268,7 +1290,7 @@ pub const LibExeObjStep = struct {
         // It doesn't have to be native. We catch that if you actually try to run it.
         // Consider that this is declarative; the run step may not be run unless a user
         // option is supplied.
-        const run_step = RunStep.create(exe.builder, exe.builder.fmt("run {}", exe.step.name));
+        const run_step = RunStep.create(exe.builder, exe.builder.fmt("run {}", .{exe.step.name}));
         run_step.addArtifactArg(exe);
 
         if (exe.vcpkg_bin_path) |path| {
@@ -1420,7 +1442,7 @@ pub const LibExeObjStep = struct {
             } else if (mem.eql(u8, tok, "-pthread")) {
                 self.linkLibC();
             } else if (self.builder.verbose) {
-                warn("Ignoring pkg-config flag '{}'\n", tok);
+                warn("Ignoring pkg-config flag '{}'\n", .{tok});
             }
         }
     }
@@ -1653,7 +1675,7 @@ pub const LibExeObjStep = struct {
         const builder = self.builder;
 
         if (self.root_src == null and self.link_objects.len == 0) {
-            warn("{}: linker needs 1 or more objects to link\n", self.step.name);
+            warn("{}: linker needs 1 or more objects to link\n", .{self.step.name});
             return error.NeedAnObject;
         }
 
@@ -1725,7 +1747,7 @@ pub const LibExeObjStep = struct {
         if (self.build_options_contents.len() > 0) {
             const build_options_file = try fs.path.join(
                 builder.allocator,
-                &[_][]const u8{ builder.cache_root, builder.fmt("{}_build_options.zig", self.name) },
+                &[_][]const u8{ builder.cache_root, builder.fmt("{}_build_options.zig", .{self.name}) },
             );
             try std.io.writeFile(build_options_file, self.build_options_contents.toSliceConst());
             try zig_args.append("--pkg-begin");
@@ -1780,13 +1802,13 @@ pub const LibExeObjStep = struct {
 
         if (self.kind == Kind.Lib and self.is_dynamic) {
             zig_args.append("--ver-major") catch unreachable;
-            zig_args.append(builder.fmt("{}", self.version.major)) catch unreachable;
+            zig_args.append(builder.fmt("{}", .{self.version.major})) catch unreachable;
 
             zig_args.append("--ver-minor") catch unreachable;
-            zig_args.append(builder.fmt("{}", self.version.minor)) catch unreachable;
+            zig_args.append(builder.fmt("{}", .{self.version.minor})) catch unreachable;
 
             zig_args.append("--ver-patch") catch unreachable;
-            zig_args.append(builder.fmt("{}", self.version.patch)) catch unreachable;
+            zig_args.append(builder.fmt("{}", .{self.version.patch})) catch unreachable;
         }
         if (self.is_dynamic) {
             try zig_args.append("-dynamic");
@@ -1811,7 +1833,7 @@ pub const LibExeObjStep = struct {
 
         if (self.target_glibc) |ver| {
             try zig_args.append("-target-glibc");
-            try zig_args.append(builder.fmt("{}.{}.{}", ver.major, ver.minor, ver.patch));
+            try zig_args.append(builder.fmt("{}.{}.{}", .{ ver.major, ver.minor, ver.patch }));
         }
 
         if (self.linker_script) |linker_script| {
@@ -2079,7 +2101,7 @@ pub const RunStep = struct {
         }
 
         if (prev_path) |pp| {
-            const new_path = self.builder.fmt("{}" ++ [1]u8{fs.path.delimiter} ++ "{}", pp, search_path);
+            const new_path = self.builder.fmt("{}" ++ [1]u8{fs.path.delimiter} ++ "{}", .{ pp, search_path });
             env_map.set(key, new_path) catch unreachable;
         } else {
             env_map.set(key, search_path) catch unreachable;
@@ -2153,7 +2175,7 @@ const InstallArtifactStep = struct {
         const self = builder.allocator.create(Self) catch unreachable;
         self.* = Self{
             .builder = builder,
-            .step = Step.init(builder.fmt("install {}", artifact.step.name), builder.allocator, make),
+            .step = Step.init(builder.fmt("install {}", .{artifact.step.name}), builder.allocator, make),
             .artifact = artifact,
             .dest_dir = switch (artifact.kind) {
                 .Obj => unreachable,
@@ -2219,7 +2241,7 @@ pub const InstallFileStep = struct {
         builder.pushInstalledFile(dir, dest_rel_path);
         return InstallFileStep{
             .builder = builder,
-            .step = Step.init(builder.fmt("install {}", src_path), builder.allocator, make),
+            .step = Step.init(builder.fmt("install {}", .{src_path}), builder.allocator, make),
             .src_path = src_path,
             .dir = dir,
             .dest_rel_path = dest_rel_path,
@@ -2253,7 +2275,7 @@ pub const InstallDirStep = struct {
         builder.pushInstalledFile(options.install_dir, options.install_subdir);
         return InstallDirStep{
             .builder = builder,
-            .step = Step.init(builder.fmt("install {}/", options.source_dir), builder.allocator, make),
+            .step = Step.init(builder.fmt("install {}/", .{options.source_dir}), builder.allocator, make),
             .options = options,
         };
     }
@@ -2290,7 +2312,7 @@ pub const WriteFileStep = struct {
     pub fn init(builder: *Builder, file_path: []const u8, data: []const u8) WriteFileStep {
         return WriteFileStep{
             .builder = builder,
-            .step = Step.init(builder.fmt("writefile {}", file_path), builder.allocator, make),
+            .step = Step.init(builder.fmt("writefile {}", .{file_path}), builder.allocator, make),
             .file_path = file_path,
             .data = data,
         };
@@ -2301,11 +2323,11 @@ pub const WriteFileStep = struct {
         const full_path = self.builder.pathFromRoot(self.file_path);
         const full_path_dir = fs.path.dirname(full_path) orelse ".";
         fs.makePath(self.builder.allocator, full_path_dir) catch |err| {
-            warn("unable to make path {}: {}\n", full_path_dir, @errorName(err));
+            warn("unable to make path {}: {}\n", .{ full_path_dir, @errorName(err) });
             return err;
         };
         io.writeFile(full_path, self.data) catch |err| {
-            warn("unable to write {}: {}\n", full_path, @errorName(err));
+            warn("unable to write {}: {}\n", .{ full_path, @errorName(err) });
             return err;
         };
     }
@@ -2319,14 +2341,14 @@ pub const LogStep = struct {
     pub fn init(builder: *Builder, data: []const u8) LogStep {
         return LogStep{
             .builder = builder,
-            .step = Step.init(builder.fmt("log {}", data), builder.allocator, make),
+            .step = Step.init(builder.fmt("log {}", .{data}), builder.allocator, make),
             .data = data,
         };
     }
 
     fn make(step: *Step) anyerror!void {
         const self = @fieldParentPtr(LogStep, "step", step);
-        warn("{}", self.data);
+        warn("{}", .{self.data});
     }
 };
 
@@ -2338,7 +2360,7 @@ pub const RemoveDirStep = struct {
     pub fn init(builder: *Builder, dir_path: []const u8) RemoveDirStep {
         return RemoveDirStep{
             .builder = builder,
-            .step = Step.init(builder.fmt("RemoveDir {}", dir_path), builder.allocator, make),
+            .step = Step.init(builder.fmt("RemoveDir {}", .{dir_path}), builder.allocator, make),
             .dir_path = dir_path,
         };
     }
@@ -2348,7 +2370,7 @@ pub const RemoveDirStep = struct {
 
         const full_path = self.builder.pathFromRoot(self.dir_path);
         fs.deleteTree(full_path) catch |err| {
-            warn("Unable to remove {}: {}\n", full_path, @errorName(err));
+            warn("Unable to remove {}: {}\n", .{ full_path, @errorName(err) });
             return err;
         };
     }
@@ -2397,7 +2419,7 @@ fn doAtomicSymLinks(allocator: *Allocator, output_path: []const u8, filename_maj
         &[_][]const u8{ out_dir, filename_major_only },
     ) catch unreachable;
     fs.atomicSymLink(allocator, out_basename, major_only_path) catch |err| {
-        warn("Unable to symlink {} -> {}\n", major_only_path, out_basename);
+        warn("Unable to symlink {} -> {}\n", .{ major_only_path, out_basename });
         return err;
     };
     // sym link for libfoo.so to libfoo.so.1
@@ -2406,7 +2428,7 @@ fn doAtomicSymLinks(allocator: *Allocator, output_path: []const u8, filename_maj
         &[_][]const u8{ out_dir, filename_name_only },
     ) catch unreachable;
     fs.atomicSymLink(allocator, filename_major_only, name_only_path) catch |err| {
-        warn("Unable to symlink {} -> {}\n", name_only_path, filename_major_only);
+        warn("Unable to symlink {} -> {}\n", .{ name_only_path, filename_major_only });
         return err;
     };
 }
diff --git a/lib/std/builtin.zig b/lib/std/builtin.zig
index 35188b61e3..b3a80dc317 100644
--- a/lib/std/builtin.zig
+++ b/lib/std/builtin.zig
@@ -429,7 +429,7 @@ pub fn default_panic(msg: []const u8, error_return_trace: ?*StackTrace) noreturn
             }
         },
         .wasi => {
-            std.debug.warn("{}", msg);
+            std.debug.warn("{}", .{msg});
             _ = std.os.wasi.proc_raise(std.os.wasi.SIGABRT);
             unreachable;
         },
@@ -439,7 +439,7 @@ pub fn default_panic(msg: []const u8, error_return_trace: ?*StackTrace) noreturn
         },
         else => {
             const first_trace_addr = @returnAddress();
-            std.debug.panicExtra(error_return_trace, first_trace_addr, "{}", msg);
+            std.debug.panicExtra(error_return_trace, first_trace_addr, "{}", .{msg});
         },
     }
 }
diff --git a/lib/std/crypto/benchmark.zig b/lib/std/crypto/benchmark.zig
index 80615fd5c5..95761b7ba6 100644
--- a/lib/std/crypto/benchmark.zig
+++ b/lib/std/crypto/benchmark.zig
@@ -114,7 +114,7 @@ fn usage() void {
         \\  --seed   [int]
         \\  --help
         \\
-    );
+    , .{});
 }
 
 fn mode(comptime x: comptime_int) comptime_int {
diff --git a/lib/std/debug.zig b/lib/std/debug.zig
index e31f847d79..04a83c39f3 100644
--- a/lib/std/debug.zig
+++ b/lib/std/debug.zig
@@ -46,7 +46,7 @@ var stderr_file_out_stream: File.OutStream = undefined;
 var stderr_stream: ?*io.OutStream(File.WriteError) = null;
 var stderr_mutex = std.Mutex.init();
 
-pub fn warn(comptime fmt: []const u8, args: ...) void {
+pub fn warn(comptime fmt: []const u8, args: var) void {
     const held = stderr_mutex.acquire();
     defer held.release();
     const stderr = getStderrStream();
@@ -92,15 +92,15 @@ fn wantTtyColor() bool {
 pub fn dumpCurrentStackTrace(start_addr: ?usize) void {
     const stderr = getStderrStream();
     if (builtin.strip_debug_info) {
-        stderr.print("Unable to dump stack trace: debug info stripped\n") catch return;
+        stderr.print("Unable to dump stack trace: debug info stripped\n", .{}) catch return;
         return;
     }
     const debug_info = getSelfDebugInfo() catch |err| {
-        stderr.print("Unable to dump stack trace: Unable to open debug info: {}\n", @errorName(err)) catch return;
+        stderr.print("Unable to dump stack trace: Unable to open debug info: {}\n", .{@errorName(err)}) catch return;
         return;
     };
     writeCurrentStackTrace(stderr, debug_info, wantTtyColor(), start_addr) catch |err| {
-        stderr.print("Unable to dump stack trace: {}\n", @errorName(err)) catch return;
+        stderr.print("Unable to dump stack trace: {}\n", .{@errorName(err)}) catch return;
         return;
     };
 }
@@ -111,11 +111,11 @@ pub fn dumpCurrentStackTrace(start_addr: ?usize) void {
 pub fn dumpStackTraceFromBase(bp: usize, ip: usize) void {
     const stderr = getStderrStream();
     if (builtin.strip_debug_info) {
-        stderr.print("Unable to dump stack trace: debug info stripped\n") catch return;
+        stderr.print("Unable to dump stack trace: debug info stripped\n", .{}) catch return;
         return;
     }
     const debug_info = getSelfDebugInfo() catch |err| {
-        stderr.print("Unable to dump stack trace: Unable to open debug info: {}\n", @errorName(err)) catch return;
+        stderr.print("Unable to dump stack trace: Unable to open debug info: {}\n", .{@errorName(err)}) catch return;
         return;
     };
     const tty_color = wantTtyColor();
@@ -184,15 +184,15 @@ pub fn captureStackTrace(first_address: ?usize, stack_trace: *builtin.StackTrace
 pub fn dumpStackTrace(stack_trace: builtin.StackTrace) void {
     const stderr = getStderrStream();
     if (builtin.strip_debug_info) {
-        stderr.print("Unable to dump stack trace: debug info stripped\n") catch return;
+        stderr.print("Unable to dump stack trace: debug info stripped\n", .{}) catch return;
         return;
     }
     const debug_info = getSelfDebugInfo() catch |err| {
-        stderr.print("Unable to dump stack trace: Unable to open debug info: {}\n", @errorName(err)) catch return;
+        stderr.print("Unable to dump stack trace: Unable to open debug info: {}\n", .{@errorName(err)}) catch return;
         return;
     };
     writeStackTrace(stack_trace, stderr, getDebugInfoAllocator(), debug_info, wantTtyColor()) catch |err| {
-        stderr.print("Unable to dump stack trace: {}\n", @errorName(err)) catch return;
+        stderr.print("Unable to dump stack trace: {}\n", .{@errorName(err)}) catch return;
         return;
     };
 }
@@ -211,7 +211,7 @@ pub fn assert(ok: bool) void {
     if (!ok) unreachable; // assertion failure
 }
 
-pub fn panic(comptime format: []const u8, args: ...) noreturn {
+pub fn panic(comptime format: []const u8, args: var) noreturn {
     @setCold(true);
     // TODO: remove conditional once wasi / LLVM defines __builtin_return_address
     const first_trace_addr = if (builtin.os == .wasi) null else @returnAddress();
@@ -221,7 +221,7 @@ pub fn panic(comptime format: []const u8, args: ...) noreturn {
 /// TODO multithreaded awareness
 var panicking: u8 = 0; // TODO make this a bool
 
-pub fn panicExtra(trace: ?*const builtin.StackTrace, first_trace_addr: ?usize, comptime format: []const u8, args: ...) noreturn {
+pub fn panicExtra(trace: ?*const builtin.StackTrace, first_trace_addr: ?usize, comptime format: []const u8, args: var) noreturn {
     @setCold(true);
 
     if (enable_segfault_handler) {
@@ -376,13 +376,13 @@ fn printSourceAtAddressWindows(di: *DebugInfo, out_stream: var, relocated_addres
     } else {
         // we have no information to add to the address
         if (tty_color) {
-            try out_stream.print("???:?:?: ");
+            try out_stream.print("???:?:?: ", .{});
             setTtyColor(TtyColor.Dim);
-            try out_stream.print("0x{x} in ??? (???)", relocated_address);
+            try out_stream.print("0x{x} in ??? (???)", .{relocated_address});
             setTtyColor(TtyColor.Reset);
-            try out_stream.print("\n\n\n");
+            try out_stream.print("\n\n\n", .{});
         } else {
-            try out_stream.print("???:?:?: 0x{x} in ??? (???)\n\n\n", relocated_address);
+            try out_stream.print("???:?:?: 0x{x} in ??? (???)\n\n\n", .{relocated_address});
         }
         return;
     };
@@ -509,18 +509,18 @@ fn printSourceAtAddressWindows(di: *DebugInfo, out_stream: var, relocated_addres
     if (tty_color) {
         setTtyColor(TtyColor.White);
         if (opt_line_info) |li| {
-            try out_stream.print("{}:{}:{}", li.file_name, li.line, li.column);
+            try out_stream.print("{}:{}:{}", .{ li.file_name, li.line, li.column });
         } else {
-            try out_stream.print("???:?:?");
+            try out_stream.print("???:?:?", .{});
         }
         setTtyColor(TtyColor.Reset);
-        try out_stream.print(": ");
+        try out_stream.print(": ", .{});
         setTtyColor(TtyColor.Dim);
-        try out_stream.print("0x{x} in {} ({})", relocated_address, symbol_name, obj_basename);
+        try out_stream.print("0x{x} in {} ({})", .{ relocated_address, symbol_name, obj_basename });
         setTtyColor(TtyColor.Reset);
 
         if (opt_line_info) |line_info| {
-            try out_stream.print("\n");
+            try out_stream.print("\n", .{});
             if (printLineFromFileAnyOs(out_stream, line_info)) {
                 if (line_info.column == 0) {
                     try out_stream.write("\n");
@@ -546,13 +546,24 @@ fn printSourceAtAddressWindows(di: *DebugInfo, out_stream: var, relocated_addres
                 else => return err,
             }
         } else {
-            try out_stream.print("\n\n\n");
+            try out_stream.print("\n\n\n", .{});
         }
     } else {
         if (opt_line_info) |li| {
-            try out_stream.print("{}:{}:{}: 0x{x} in {} ({})\n\n\n", li.file_name, li.line, li.column, relocated_address, symbol_name, obj_basename);
+            try out_stream.print("{}:{}:{}: 0x{x} in {} ({})\n\n\n", .{
+                li.file_name,
+                li.line,
+                li.column,
+                relocated_address,
+                symbol_name,
+                obj_basename,
+            });
         } else {
-            try out_stream.print("???:?:?: 0x{x} in {} ({})\n\n\n", relocated_address, symbol_name, obj_basename);
+            try out_stream.print("???:?:?: 0x{x} in {} ({})\n\n\n", .{
+                relocated_address,
+                symbol_name,
+                obj_basename,
+            });
         }
     }
 }
@@ -697,9 +708,9 @@ fn printSourceAtAddressMacOs(di: *DebugInfo, out_stream: var, address: usize, tt
 
     const symbol = machoSearchSymbols(di.symbols, adjusted_addr) orelse {
         if (tty_color) {
-            try out_stream.print("???:?:?: " ++ DIM ++ "0x{x} in ??? (???)" ++ RESET ++ "\n\n\n", address);
+            try out_stream.print("???:?:?: " ++ DIM ++ "0x{x} in ??? (???)" ++ RESET ++ "\n\n\n", .{address});
         } else {
-            try out_stream.print("???:?:?: 0x{x} in ??? (???)\n\n\n", address);
+            try out_stream.print("???:?:?: 0x{x} in ??? (???)\n\n\n", .{address});
         }
         return;
     };
@@ -723,9 +734,11 @@ fn printSourceAtAddressMacOs(di: *DebugInfo, out_stream: var, address: usize, tt
     } else |err| switch (err) {
         error.MissingDebugInfo, error.InvalidDebugInfo => {
             if (tty_color) {
-                try out_stream.print("???:?:?: " ++ DIM ++ "0x{x} in {} ({})" ++ RESET ++ "\n\n\n", address, symbol_name, compile_unit_name);
+                try out_stream.print("???:?:?: " ++ DIM ++ "0x{x} in {} ({})" ++ RESET ++ "\n\n\n", .{
+                    address, symbol_name, compile_unit_name,
+                });
             } else {
-                try out_stream.print("???:?:?: 0x{x} in {} ({})\n\n\n", address, symbol_name, compile_unit_name);
+                try out_stream.print("???:?:?: 0x{x} in {} ({})\n\n\n", .{ address, symbol_name, compile_unit_name });
             }
         },
         else => return err,
@@ -746,15 +759,14 @@ fn printLineInfo(
     comptime printLineFromFile: var,
 ) !void {
     if (tty_color) {
-        try out_stream.print(
-            WHITE ++ "{}:{}:{}" ++ RESET ++ ": " ++ DIM ++ "0x{x} in {} ({})" ++ RESET ++ "\n",
+        try out_stream.print(WHITE ++ "{}:{}:{}" ++ RESET ++ ": " ++ DIM ++ "0x{x} in {} ({})" ++ RESET ++ "\n", .{
             line_info.file_name,
             line_info.line,
             line_info.column,
             address,
             symbol_name,
             compile_unit_name,
-        );
+        });
         if (printLineFromFile(out_stream, line_info)) {
             if (line_info.column == 0) {
                 try out_stream.write("\n");
@@ -772,15 +784,14 @@ fn printLineInfo(
             else => return err,
         }
     } else {
-        try out_stream.print(
-            "{}:{}:{}: 0x{x} in {} ({})\n",
+        try out_stream.print("{}:{}:{}: 0x{x} in {} ({})\n", .{
             line_info.file_name,
             line_info.line,
             line_info.column,
             address,
             symbol_name,
             compile_unit_name,
-        );
+        });
     }
 }
 
@@ -1226,9 +1237,9 @@ pub const DwarfInfo = struct {
     ) !void {
         const compile_unit = self.findCompileUnit(address) catch {
             if (tty_color) {
-                try out_stream.print("???:?:?: " ++ DIM ++ "0x{x} in ??? (???)" ++ RESET ++ "\n\n\n", address);
+                try out_stream.print("???:?:?: " ++ DIM ++ "0x{x} in ??? (???)" ++ RESET ++ "\n\n\n", .{address});
             } else {
-                try out_stream.print("???:?:?: 0x{x} in ??? (???)\n\n\n", address);
+                try out_stream.print("???:?:?: 0x{x} in ??? (???)\n\n\n", .{address});
             }
             return;
         };
@@ -1248,9 +1259,11 @@ pub const DwarfInfo = struct {
         } else |err| switch (err) {
             error.MissingDebugInfo, error.InvalidDebugInfo => {
                 if (tty_color) {
-                    try out_stream.print("???:?:?: " ++ DIM ++ "0x{x} in ??? ({})" ++ RESET ++ "\n\n\n", address, compile_unit_name);
+                    try out_stream.print("???:?:?: " ++ DIM ++ "0x{x} in ??? ({})" ++ RESET ++ "\n\n\n", .{
+                        address, compile_unit_name,
+                    });
                 } else {
-                    try out_stream.print("???:?:?: 0x{x} in ??? ({})\n\n\n", address, compile_unit_name);
+                    try out_stream.print("???:?:?: 0x{x} in ??? ({})\n\n\n", .{ address, compile_unit_name });
                 }
             },
             else => return err,
@@ -2416,7 +2429,7 @@ extern fn handleSegfaultLinux(sig: i32, info: *const os.siginfo_t, ctx_ptr: *con
     resetSegfaultHandler();
 
     const addr = @ptrToInt(info.fields.sigfault.addr);
-    std.debug.warn("Segmentation fault at address 0x{x}\n", addr);
+    std.debug.warn("Segmentation fault at address 0x{x}\n", .{addr});
 
     switch (builtin.arch) {
         .i386 => {
@@ -2456,10 +2469,10 @@ extern fn handleSegfaultLinux(sig: i32, info: *const os.siginfo_t, ctx_ptr: *con
 stdcallcc fn handleSegfaultWindows(info: *windows.EXCEPTION_POINTERS) c_long {
     const exception_address = @ptrToInt(info.ExceptionRecord.ExceptionAddress);
     switch (info.ExceptionRecord.ExceptionCode) {
-        windows.EXCEPTION_DATATYPE_MISALIGNMENT => panicExtra(null, exception_address, "Unaligned Memory Access"),
-        windows.EXCEPTION_ACCESS_VIOLATION => panicExtra(null, exception_address, "Segmentation fault at address 0x{x}", info.ExceptionRecord.ExceptionInformation[1]),
-        windows.EXCEPTION_ILLEGAL_INSTRUCTION => panicExtra(null, exception_address, "Illegal Instruction"),
-        windows.EXCEPTION_STACK_OVERFLOW => panicExtra(null, exception_address, "Stack Overflow"),
+        windows.EXCEPTION_DATATYPE_MISALIGNMENT => panicExtra(null, exception_address, "Unaligned Memory Access", .{}),
+        windows.EXCEPTION_ACCESS_VIOLATION => panicExtra(null, exception_address, "Segmentation fault at address 0x{x}", .{info.ExceptionRecord.ExceptionInformation[1]}),
+        windows.EXCEPTION_ILLEGAL_INSTRUCTION => panicExtra(null, exception_address, "Illegal Instruction", .{}),
+        windows.EXCEPTION_STACK_OVERFLOW => panicExtra(null, exception_address, "Stack Overflow", .{}),
         else => return windows.EXCEPTION_CONTINUE_SEARCH,
     }
 }
@@ -2468,7 +2481,7 @@ pub fn dumpStackPointerAddr(prefix: []const u8) void {
     const sp = asm (""
         : [argc] "={rsp}" (-> usize)
     );
-    std.debug.warn("{} sp = 0x{x}\n", prefix, sp);
+    std.debug.warn("{} sp = 0x{x}\n", .{ prefix, sp });
 }
 
 // Reference everything so it gets tested.
diff --git a/lib/std/event/channel.zig b/lib/std/event/channel.zig
index 96cfd706be..2bcf6a4c50 100644
--- a/lib/std/event/channel.zig
+++ b/lib/std/event/channel.zig
@@ -294,14 +294,14 @@ test "std.event.Channel wraparound" {
 
     const channel_size = 2;
 
-    var buf : [channel_size]i32 = undefined;
+    var buf: [channel_size]i32 = undefined;
     var channel: Channel(i32) = undefined;
     channel.init(&buf);
     defer channel.deinit();
 
     // add items to channel and pull them out until
     // the buffer wraps around, make sure it doesn't crash.
-    var result : i32 = undefined;
+    var result: i32 = undefined;
     channel.put(5);
     testing.expectEqual(@as(i32, 5), channel.get());
     channel.put(6);
diff --git a/lib/std/fifo.zig b/lib/std/fifo.zig
index fdd746dfcc..7870979abb 100644
--- a/lib/std/fifo.zig
+++ b/lib/std/fifo.zig
@@ -293,7 +293,7 @@ pub fn LinearFifo(
 
         pub usingnamespace if (T == u8)
             struct {
-                pub fn print(self: *Self, comptime format: []const u8, args: ...) !void {
+                pub fn print(self: *Self, comptime format: []const u8, args: var) !void {
                     return std.fmt.format(self, error{OutOfMemory}, Self.write, format, args);
                 }
             }
@@ -407,7 +407,7 @@ test "LinearFifo(u8, .Dynamic)" {
     fifo.shrink(0);
 
     {
-        try fifo.print("{}, {}!", "Hello", "World");
+        try fifo.print("{}, {}!", .{ "Hello", "World" });
         var result: [30]u8 = undefined;
         testing.expectEqualSlices(u8, "Hello, World!", result[0..fifo.read(&result)]);
         testing.expectEqual(@as(usize, 0), fifo.readableLength());
diff --git a/lib/std/fmt.zig b/lib/std/fmt.zig
index da0cfd4318..a0871d52a6 100644
--- a/lib/std/fmt.zig
+++ b/lib/std/fmt.zig
@@ -91,10 +91,12 @@ pub fn format(
     comptime Errors: type,
     output: fn (@typeOf(context), []const u8) Errors!void,
     comptime fmt: []const u8,
-    args: ...,
+    args: var,
 ) Errors!void {
     const ArgSetType = @IntType(false, 32);
-    if (args.len > ArgSetType.bit_count) {
+    const args_fields = std.meta.fields(@typeOf(args));
+    const args_len = args_fields.len;
+    if (args_len > ArgSetType.bit_count) {
         @compileError("32 arguments max are supported per format call");
     }
 
@@ -158,14 +160,14 @@ pub fn format(
                     maybe_pos_arg.? += c - '0';
                     specifier_start = i + 1;
 
-                    if (maybe_pos_arg.? >= args.len) {
+                    if (maybe_pos_arg.? >= args_len) {
                         @compileError("Positional value refers to non-existent argument");
                     }
                 },
                 '}' => {
                     const arg_to_print = comptime nextArg(&used_pos_args, maybe_pos_arg, &next_arg);
 
-                    if (arg_to_print >= args.len) {
+                    if (arg_to_print >= args_len) {
                         @compileError("Too few arguments");
                     }
 
@@ -302,7 +304,7 @@ pub fn format(
             used_pos_args |= 1 << i;
         }
 
-        if (@popCount(ArgSetType, used_pos_args) != args.len) {
+        if (@popCount(ArgSetType, used_pos_args) != args_len) {
             @compileError("Unused arguments");
         }
         if (state != State.Start) {
@@ -389,7 +391,7 @@ pub fn formatType(
                 }
                 try output(context, " }");
             } else {
-                try format(context, Errors, output, "@{x}", @ptrToInt(&value));
+                try format(context, Errors, output, "@{x}", .{@ptrToInt(&value)});
             }
         },
         .Struct => {
@@ -421,12 +423,12 @@ pub fn formatType(
                     if (info.child == u8) {
                         return formatText(value, fmt, options, context, Errors, output);
                     }
-                    return format(context, Errors, output, "{}@{x}", @typeName(T.Child), @ptrToInt(value));
+                    return format(context, Errors, output, "{}@{x}", .{ @typeName(T.Child), @ptrToInt(value) });
                 },
                 builtin.TypeId.Enum, builtin.TypeId.Union, builtin.TypeId.Struct => {
                     return formatType(value.*, fmt, options, context, Errors, output, max_depth);
                 },
-                else => return format(context, Errors, output, "{}@{x}", @typeName(T.Child), @ptrToInt(value)),
+                else => return format(context, Errors, output, "{}@{x}", .{ @typeName(T.Child), @ptrToInt(value) }),
             },
             .Many => {
                 if (ptr_info.child == u8) {
@@ -435,7 +437,7 @@ pub fn formatType(
                         return formatText(value[0..len], fmt, options, context, Errors, output);
                     }
                 }
-                return format(context, Errors, output, "{}@{x}", @typeName(T.Child), @ptrToInt(value));
+                return format(context, Errors, output, "{}@{x}", .{ @typeName(T.Child), @ptrToInt(value) });
             },
             .Slice => {
                 if (fmt.len > 0 and ((fmt[0] == 'x') or (fmt[0] == 'X'))) {
@@ -444,10 +446,10 @@ pub fn formatType(
                 if (ptr_info.child == u8) {
                     return formatText(value, fmt, options, context, Errors, output);
                 }
-                return format(context, Errors, output, "{}@{x}", @typeName(ptr_info.child), @ptrToInt(value.ptr));
+                return format(context, Errors, output, "{}@{x}", .{ @typeName(ptr_info.child), @ptrToInt(value.ptr) });
             },
             .C => {
-                return format(context, Errors, output, "{}@{x}", @typeName(T.Child), @ptrToInt(value));
+                return format(context, Errors, output, "{}@{x}", .{ @typeName(T.Child), @ptrToInt(value) });
             },
         },
         .Array => |info| {
@@ -465,7 +467,7 @@ pub fn formatType(
             return formatType(@as(Slice, &value), fmt, options, context, Errors, output, max_depth);
         },
         .Fn => {
-            return format(context, Errors, output, "{}@{x}", @typeName(T), @ptrToInt(value));
+            return format(context, Errors, output, "{}@{x}", .{ @typeName(T), @ptrToInt(value) });
         },
         else => @compileError("Unable to format type '" ++ @typeName(T) ++ "'"),
     }
@@ -1113,7 +1115,7 @@ pub const BufPrintError = error{
     /// As much as possible was written to the buffer, but it was too small to fit all the printed bytes.
     BufferTooSmall,
 };
-pub fn bufPrint(buf: []u8, comptime fmt: []const u8, args: ...) BufPrintError![]u8 {
+pub fn bufPrint(buf: []u8, comptime fmt: []const u8, args: var) BufPrintError![]u8 {
     var context = BufPrintContext{ .remaining = buf };
     try format(&context, BufPrintError, bufPrintWrite, fmt, args);
     return buf[0 .. buf.len - context.remaining.len];
@@ -1121,7 +1123,7 @@ pub fn bufPrint(buf: []u8, comptime fmt: []const u8, args: ...) BufPrintError![]
 
 pub const AllocPrintError = error{OutOfMemory};
 
-pub fn allocPrint(allocator: *mem.Allocator, comptime fmt: []const u8, args: ...) AllocPrintError![]u8 {
+pub fn allocPrint(allocator: *mem.Allocator, comptime fmt: []const u8, args: var) AllocPrintError![]u8 {
     var size: usize = 0;
     format(&size, error{}, countSize, fmt, args) catch |err| switch (err) {};
     const buf = try allocator.alloc(u8, size);
@@ -1173,46 +1175,46 @@ test "parse unsigned comptime" {
 test "optional" {
     {
         const value: ?i32 = 1234;
-        try testFmt("optional: 1234\n", "optional: {}\n", value);
+        try testFmt("optional: 1234\n", "optional: {}\n", .{value});
     }
     {
         const value: ?i32 = null;
-        try testFmt("optional: null\n", "optional: {}\n", value);
+        try testFmt("optional: null\n", "optional: {}\n", .{value});
     }
 }
 
 test "error" {
     {
         const value: anyerror!i32 = 1234;
-        try testFmt("error union: 1234\n", "error union: {}\n", value);
+        try testFmt("error union: 1234\n", "error union: {}\n", .{value});
     }
     {
         const value: anyerror!i32 = error.InvalidChar;
-        try testFmt("error union: error.InvalidChar\n", "error union: {}\n", value);
+        try testFmt("error union: error.InvalidChar\n", "error union: {}\n", .{value});
     }
 }
 
 test "int.small" {
     {
         const value: u3 = 0b101;
-        try testFmt("u3: 5\n", "u3: {}\n", value);
+        try testFmt("u3: 5\n", "u3: {}\n", .{value});
     }
 }
 
 test "int.specifier" {
     {
         const value: u8 = 'a';
-        try testFmt("u8: a\n", "u8: {c}\n", value);
+        try testFmt("u8: a\n", "u8: {c}\n", .{value});
     }
     {
         const value: u8 = 0b1100;
-        try testFmt("u8: 0b1100\n", "u8: 0b{b}\n", value);
+        try testFmt("u8: 0b1100\n", "u8: 0b{b}\n", .{value});
     }
 }
 
 test "int.padded" {
-    try testFmt("u8: '   1'", "u8: '{:4}'", @as(u8, 1));
-    try testFmt("u8: 'xxx1'", "u8: '{:x<4}'", @as(u8, 1));
+    try testFmt("u8: '   1'", "u8: '{:4}'", .{@as(u8, 1)});
+    try testFmt("u8: 'xxx1'", "u8: '{:x<4}'", .{@as(u8, 1)});
 }
 
 test "buffer" {
@@ -1238,14 +1240,14 @@ test "buffer" {
 test "array" {
     {
         const value: [3]u8 = "abc".*;
-        try testFmt("array: abc\n", "array: {}\n", value);
-        try testFmt("array: abc\n", "array: {}\n", &value);
+        try testFmt("array: abc\n", "array: {}\n", .{value});
+        try testFmt("array: abc\n", "array: {}\n", .{&value});
 
         var buf: [100]u8 = undefined;
         try testFmt(
-            try bufPrint(buf[0..], "array: [3]u8@{x}\n", @ptrToInt(&value)),
+            try bufPrint(buf[0..], "array: [3]u8@{x}\n", .{@ptrToInt(&value)}),
             "array: {*}\n",
-            &value,
+            .{&value},
         );
     }
 }
@@ -1253,36 +1255,36 @@ test "array" {
 test "slice" {
     {
         const value: []const u8 = "abc";
-        try testFmt("slice: abc\n", "slice: {}\n", value);
+        try testFmt("slice: abc\n", "slice: {}\n", .{value});
     }
     {
         const value = @intToPtr([*]const []const u8, 0xdeadbeef)[0..0];
-        try testFmt("slice: []const u8@deadbeef\n", "slice: {}\n", value);
+        try testFmt("slice: []const u8@deadbeef\n", "slice: {}\n", .{value});
     }
 
-    try testFmt("buf: Test \n", "buf: {s:5}\n", "Test");
-    try testFmt("buf: Test\n Other text", "buf: {s}\n Other text", "Test");
+    try testFmt("buf: Test \n", "buf: {s:5}\n", .{"Test"});
+    try testFmt("buf: Test\n Other text", "buf: {s}\n Other text", .{"Test"});
 }
 
 test "pointer" {
     {
         const value = @intToPtr(*i32, 0xdeadbeef);
-        try testFmt("pointer: i32@deadbeef\n", "pointer: {}\n", value);
-        try testFmt("pointer: i32@deadbeef\n", "pointer: {*}\n", value);
+        try testFmt("pointer: i32@deadbeef\n", "pointer: {}\n", .{value});
+        try testFmt("pointer: i32@deadbeef\n", "pointer: {*}\n", .{value});
     }
     {
         const value = @intToPtr(fn () void, 0xdeadbeef);
-        try testFmt("pointer: fn() void@deadbeef\n", "pointer: {}\n", value);
+        try testFmt("pointer: fn() void@deadbeef\n", "pointer: {}\n", .{value});
     }
     {
         const value = @intToPtr(fn () void, 0xdeadbeef);
-        try testFmt("pointer: fn() void@deadbeef\n", "pointer: {}\n", value);
+        try testFmt("pointer: fn() void@deadbeef\n", "pointer: {}\n", .{value});
     }
 }
 
 test "cstr" {
-    try testFmt("cstr: Test C\n", "cstr: {s}\n", "Test C");
-    try testFmt("cstr: Test C    \n", "cstr: {s:10}\n", "Test C");
+    try testFmt("cstr: Test C\n", "cstr: {s}\n", .{"Test C"});
+    try testFmt("cstr: Test C    \n", "cstr: {s:10}\n", .{"Test C"});
 }
 
 test "filesize" {
@@ -1290,8 +1292,8 @@ test "filesize" {
         // TODO https://github.com/ziglang/zig/issues/3289
         return error.SkipZigTest;
     }
-    try testFmt("file size: 63MiB\n", "file size: {Bi}\n", @as(usize, 63 * 1024 * 1024));
-    try testFmt("file size: 66.06MB\n", "file size: {B:.2}\n", @as(usize, 63 * 1024 * 1024));
+    try testFmt("file size: 63MiB\n", "file size: {Bi}\n", .{@as(usize, 63 * 1024 * 1024)});
+    try testFmt("file size: 66.06MB\n", "file size: {B:.2}\n", .{@as(usize, 63 * 1024 * 1024)});
 }
 
 test "struct" {
@@ -1300,8 +1302,8 @@ test "struct" {
             field: u8,
         };
         const value = Struct{ .field = 42 };
-        try testFmt("struct: Struct{ .field = 42 }\n", "struct: {}\n", value);
-        try testFmt("struct: Struct{ .field = 42 }\n", "struct: {}\n", &value);
+        try testFmt("struct: Struct{ .field = 42 }\n", "struct: {}\n", .{value});
+        try testFmt("struct: Struct{ .field = 42 }\n", "struct: {}\n", .{&value});
     }
     {
         const Struct = struct {
@@ -1309,7 +1311,7 @@ test "struct" {
             b: u1,
         };
         const value = Struct{ .a = 0, .b = 1 };
-        try testFmt("struct: Struct{ .a = 0, .b = 1 }\n", "struct: {}\n", value);
+        try testFmt("struct: Struct{ .a = 0, .b = 1 }\n", "struct: {}\n", .{value});
     }
 }
 
@@ -1319,8 +1321,8 @@ test "enum" {
         Two,
     };
     const value = Enum.Two;
-    try testFmt("enum: Enum.Two\n", "enum: {}\n", value);
-    try testFmt("enum: Enum.Two\n", "enum: {}\n", &value);
+    try testFmt("enum: Enum.Two\n", "enum: {}\n", .{value});
+    try testFmt("enum: Enum.Two\n", "enum: {}\n", .{&value});
 }
 
 test "float.scientific" {
@@ -1328,10 +1330,10 @@ test "float.scientific" {
         // TODO https://github.com/ziglang/zig/issues/3289
         return error.SkipZigTest;
     }
-    try testFmt("f32: 1.34000003e+00", "f32: {e}", @as(f32, 1.34));
-    try testFmt("f32: 1.23400001e+01", "f32: {e}", @as(f32, 12.34));
-    try testFmt("f64: -1.234e+11", "f64: {e}", @as(f64, -12.34e10));
-    try testFmt("f64: 9.99996e-40", "f64: {e}", @as(f64, 9.999960e-40));
+    try testFmt("f32: 1.34000003e+00", "f32: {e}", .{@as(f32, 1.34)});
+    try testFmt("f32: 1.23400001e+01", "f32: {e}", .{@as(f32, 12.34)});
+    try testFmt("f64: -1.234e+11", "f64: {e}", .{@as(f64, -12.34e10)});
+    try testFmt("f64: 9.99996e-40", "f64: {e}", .{@as(f64, 9.999960e-40)});
 }
 
 test "float.scientific.precision" {
@@ -1339,12 +1341,12 @@ test "float.scientific.precision" {
         // TODO https://github.com/ziglang/zig/issues/3289
         return error.SkipZigTest;
     }
-    try testFmt("f64: 1.40971e-42", "f64: {e:.5}", @as(f64, 1.409706e-42));
-    try testFmt("f64: 1.00000e-09", "f64: {e:.5}", @as(f64, @bitCast(f32, @as(u32, 814313563))));
-    try testFmt("f64: 7.81250e-03", "f64: {e:.5}", @as(f64, @bitCast(f32, @as(u32, 1006632960))));
+    try testFmt("f64: 1.40971e-42", "f64: {e:.5}", .{@as(f64, 1.409706e-42)});
+    try testFmt("f64: 1.00000e-09", "f64: {e:.5}", .{@as(f64, @bitCast(f32, @as(u32, 814313563)))});
+    try testFmt("f64: 7.81250e-03", "f64: {e:.5}", .{@as(f64, @bitCast(f32, @as(u32, 1006632960)))});
     // libc rounds 1.000005e+05 to 1.00000e+05 but zig does 1.00001e+05.
     // In fact, libc doesn't round a lot of 5 cases up when one past the precision point.
-    try testFmt("f64: 1.00001e+05", "f64: {e:.5}", @as(f64, @bitCast(f32, @as(u32, 1203982400))));
+    try testFmt("f64: 1.00001e+05", "f64: {e:.5}", .{@as(f64, @bitCast(f32, @as(u32, 1203982400)))});
 }
 
 test "float.special" {
@@ -1352,14 +1354,14 @@ test "float.special" {
         // TODO https://github.com/ziglang/zig/issues/3289
         return error.SkipZigTest;
     }
-    try testFmt("f64: nan", "f64: {}", math.nan_f64);
+    try testFmt("f64: nan", "f64: {}", .{math.nan_f64});
     // negative nan is not defined by IEE 754,
     // and ARM thus normalizes it to positive nan
     if (builtin.arch != builtin.Arch.arm) {
-        try testFmt("f64: -nan", "f64: {}", -math.nan_f64);
+        try testFmt("f64: -nan", "f64: {}", .{-math.nan_f64});
     }
-    try testFmt("f64: inf", "f64: {}", math.inf_f64);
-    try testFmt("f64: -inf", "f64: {}", -math.inf_f64);
+    try testFmt("f64: inf", "f64: {}", .{math.inf_f64});
+    try testFmt("f64: -inf", "f64: {}", .{-math.inf_f64});
 }
 
 test "float.decimal" {
@@ -1367,21 +1369,21 @@ test "float.decimal" {
         // TODO https://github.com/ziglang/zig/issues/3289
         return error.SkipZigTest;
     }
-    try testFmt("f64: 152314000000000000000000000000", "f64: {d}", @as(f64, 1.52314e+29));
-    try testFmt("f32: 1.1", "f32: {d:.1}", @as(f32, 1.1234));
-    try testFmt("f32: 1234.57", "f32: {d:.2}", @as(f32, 1234.567));
+    try testFmt("f64: 152314000000000000000000000000", "f64: {d}", .{@as(f64, 1.52314e+29)});
+    try testFmt("f32: 1.1", "f32: {d:.1}", .{@as(f32, 1.1234)});
+    try testFmt("f32: 1234.57", "f32: {d:.2}", .{@as(f32, 1234.567)});
     // -11.1234 is converted to f64 -11.12339... internally (errol3() function takes f64).
     // -11.12339... is rounded back up to -11.1234
-    try testFmt("f32: -11.1234", "f32: {d:.4}", @as(f32, -11.1234));
-    try testFmt("f32: 91.12345", "f32: {d:.5}", @as(f32, 91.12345));
-    try testFmt("f64: 91.1234567890", "f64: {d:.10}", @as(f64, 91.12345678901235));
-    try testFmt("f64: 0.00000", "f64: {d:.5}", @as(f64, 0.0));
-    try testFmt("f64: 6", "f64: {d:.0}", @as(f64, 5.700));
-    try testFmt("f64: 10.0", "f64: {d:.1}", @as(f64, 9.999));
-    try testFmt("f64: 1.000", "f64: {d:.3}", @as(f64, 1.0));
-    try testFmt("f64: 0.00030000", "f64: {d:.8}", @as(f64, 0.0003));
-    try testFmt("f64: 0.00000", "f64: {d:.5}", @as(f64, 1.40130e-45));
-    try testFmt("f64: 0.00000", "f64: {d:.5}", @as(f64, 9.999960e-40));
+    try testFmt("f32: -11.1234", "f32: {d:.4}", .{@as(f32, -11.1234)});
+    try testFmt("f32: 91.12345", "f32: {d:.5}", .{@as(f32, 91.12345)});
+    try testFmt("f64: 91.1234567890", "f64: {d:.10}", .{@as(f64, 91.12345678901235)});
+    try testFmt("f64: 0.00000", "f64: {d:.5}", .{@as(f64, 0.0)});
+    try testFmt("f64: 6", "f64: {d:.0}", .{@as(f64, 5.700)});
+    try testFmt("f64: 10.0", "f64: {d:.1}", .{@as(f64, 9.999)});
+    try testFmt("f64: 1.000", "f64: {d:.3}", .{@as(f64, 1.0)});
+    try testFmt("f64: 0.00030000", "f64: {d:.8}", .{@as(f64, 0.0003)});
+    try testFmt("f64: 0.00000", "f64: {d:.5}", .{@as(f64, 1.40130e-45)});
+    try testFmt("f64: 0.00000", "f64: {d:.5}", .{@as(f64, 9.999960e-40)});
 }
 
 test "float.libc.sanity" {
@@ -1389,22 +1391,22 @@ test "float.libc.sanity" {
         // TODO https://github.com/ziglang/zig/issues/3289
         return error.SkipZigTest;
     }
-    try testFmt("f64: 0.00001", "f64: {d:.5}", @as(f64, @bitCast(f32, @as(u32, 916964781))));
-    try testFmt("f64: 0.00001", "f64: {d:.5}", @as(f64, @bitCast(f32, @as(u32, 925353389))));
-    try testFmt("f64: 0.10000", "f64: {d:.5}", @as(f64, @bitCast(f32, @as(u32, 1036831278))));
-    try testFmt("f64: 1.00000", "f64: {d:.5}", @as(f64, @bitCast(f32, @as(u32, 1065353133))));
-    try testFmt("f64: 10.00000", "f64: {d:.5}", @as(f64, @bitCast(f32, @as(u32, 1092616192))));
+    try testFmt("f64: 0.00001", "f64: {d:.5}", .{@as(f64, @bitCast(f32, @as(u32, 916964781)))});
+    try testFmt("f64: 0.00001", "f64: {d:.5}", .{@as(f64, @bitCast(f32, @as(u32, 925353389)))});
+    try testFmt("f64: 0.10000", "f64: {d:.5}", .{@as(f64, @bitCast(f32, @as(u32, 1036831278)))});
+    try testFmt("f64: 1.00000", "f64: {d:.5}", .{@as(f64, @bitCast(f32, @as(u32, 1065353133)))});
+    try testFmt("f64: 10.00000", "f64: {d:.5}", .{@as(f64, @bitCast(f32, @as(u32, 1092616192)))});
 
     // libc differences
     //
     // This is 0.015625 exactly according to gdb. We thus round down,
     // however glibc rounds up for some reason. This occurs for all
     // floats of the form x.yyyy25 on a precision point.
-    try testFmt("f64: 0.01563", "f64: {d:.5}", @as(f64, @bitCast(f32, @as(u32, 1015021568))));
+    try testFmt("f64: 0.01563", "f64: {d:.5}", .{@as(f64, @bitCast(f32, @as(u32, 1015021568)))});
     // errol3 rounds to ... 630 but libc rounds to ...632. Grisu3
     // also rounds to 630 so I'm inclined to believe libc is not
     // optimal here.
-    try testFmt("f64: 18014400656965630.00000", "f64: {d:.5}", @as(f64, @bitCast(f32, @as(u32, 1518338049))));
+    try testFmt("f64: 18014400656965630.00000", "f64: {d:.5}", .{@as(f64, @bitCast(f32, @as(u32, 1518338049)))});
 }
 
 test "custom" {
@@ -1422,9 +1424,9 @@ test "custom" {
             output: fn (@typeOf(context), []const u8) Errors!void,
         ) Errors!void {
             if (fmt.len == 0 or comptime std.mem.eql(u8, fmt, "p")) {
-                return std.fmt.format(context, Errors, output, "({d:.3},{d:.3})", self.x, self.y);
+                return std.fmt.format(context, Errors, output, "({d:.3},{d:.3})", .{ self.x, self.y });
             } else if (comptime std.mem.eql(u8, fmt, "d")) {
-                return std.fmt.format(context, Errors, output, "{d:.3}x{d:.3}", self.x, self.y);
+                return std.fmt.format(context, Errors, output, "{d:.3}x{d:.3}", .{ self.x, self.y });
             } else {
                 @compileError("Unknown format character: '" ++ fmt ++ "'");
             }
@@ -1436,12 +1438,12 @@ test "custom" {
         .x = 10.2,
         .y = 2.22,
     };
-    try testFmt("point: (10.200,2.220)\n", "point: {}\n", &value);
-    try testFmt("dim: 10.200x2.220\n", "dim: {d}\n", &value);
+    try testFmt("point: (10.200,2.220)\n", "point: {}\n", .{&value});
+    try testFmt("dim: 10.200x2.220\n", "dim: {d}\n", .{&value});
 
     // same thing but not passing a pointer
-    try testFmt("point: (10.200,2.220)\n", "point: {}\n", value);
-    try testFmt("dim: 10.200x2.220\n", "dim: {d}\n", value);
+    try testFmt("point: (10.200,2.220)\n", "point: {}\n", .{value});
+    try testFmt("dim: 10.200x2.220\n", "dim: {d}\n", .{value});
 }
 
 test "struct" {
@@ -1455,7 +1457,7 @@ test "struct" {
         .b = error.Unused,
     };
 
-    try testFmt("S{ .a = 456, .b = error.Unused }", "{}", inst);
+    try testFmt("S{ .a = 456, .b = error.Unused }", "{}", .{inst});
 }
 
 test "union" {
@@ -1478,13 +1480,13 @@ test "union" {
     const uu_inst = UU{ .int = 456 };
     const eu_inst = EU{ .float = 321.123 };
 
-    try testFmt("TU{ .int = 123 }", "{}", tu_inst);
+    try testFmt("TU{ .int = 123 }", "{}", .{tu_inst});
 
     var buf: [100]u8 = undefined;
-    const uu_result = try bufPrint(buf[0..], "{}", uu_inst);
+    const uu_result = try bufPrint(buf[0..], "{}", .{uu_inst});
     std.testing.expect(mem.eql(u8, uu_result[0..3], "UU@"));
 
-    const eu_result = try bufPrint(buf[0..], "{}", eu_inst);
+    const eu_result = try bufPrint(buf[0..], "{}", .{eu_inst});
     std.testing.expect(mem.eql(u8, uu_result[0..3], "EU@"));
 }
 
@@ -1497,7 +1499,7 @@ test "enum" {
 
     const inst = E.Two;
 
-    try testFmt("E.Two", "{}", inst);
+    try testFmt("E.Two", "{}", .{inst});
 }
 
 test "struct.self-referential" {
@@ -1511,7 +1513,7 @@ test "struct.self-referential" {
     };
     inst.a = &inst;
 
-    try testFmt("S{ .a = S{ .a = S{ .a = S{ ... } } } }", "{}", inst);
+    try testFmt("S{ .a = S{ .a = S{ .a = S{ ... } } } }", "{}", .{inst});
 }
 
 test "struct.zero-size" {
@@ -1526,30 +1528,30 @@ test "struct.zero-size" {
     const a = A{};
     const b = B{ .a = a, .c = 0 };
 
-    try testFmt("B{ .a = A{ }, .c = 0 }", "{}", b);
+    try testFmt("B{ .a = A{ }, .c = 0 }", "{}", .{b});
 }
 
 test "bytes.hex" {
     const some_bytes = "\xCA\xFE\xBA\xBE";
-    try testFmt("lowercase: cafebabe\n", "lowercase: {x}\n", some_bytes);
-    try testFmt("uppercase: CAFEBABE\n", "uppercase: {X}\n", some_bytes);
+    try testFmt("lowercase: cafebabe\n", "lowercase: {x}\n", .{some_bytes});
+    try testFmt("uppercase: CAFEBABE\n", "uppercase: {X}\n", .{some_bytes});
     //Test Slices
-    try testFmt("uppercase: CAFE\n", "uppercase: {X}\n", some_bytes[0..2]);
-    try testFmt("lowercase: babe\n", "lowercase: {x}\n", some_bytes[2..]);
+    try testFmt("uppercase: CAFE\n", "uppercase: {X}\n", .{some_bytes[0..2]});
+    try testFmt("lowercase: babe\n", "lowercase: {x}\n", .{some_bytes[2..]});
     const bytes_with_zeros = "\x00\x0E\xBA\xBE";
-    try testFmt("lowercase: 000ebabe\n", "lowercase: {x}\n", bytes_with_zeros);
+    try testFmt("lowercase: 000ebabe\n", "lowercase: {x}\n", .{bytes_with_zeros});
 }
 
-fn testFmt(expected: []const u8, comptime template: []const u8, args: ...) !void {
+fn testFmt(expected: []const u8, comptime template: []const u8, args: var) !void {
     var buf: [100]u8 = undefined;
     const result = try bufPrint(buf[0..], template, args);
     if (mem.eql(u8, result, expected)) return;
 
-    std.debug.warn("\n====== expected this output: =========\n");
-    std.debug.warn("{}", expected);
-    std.debug.warn("\n======== instead found this: =========\n");
-    std.debug.warn("{}", result);
-    std.debug.warn("\n======================================\n");
+    std.debug.warn("\n====== expected this output: =========\n", .{});
+    std.debug.warn("{}", .{expected});
+    std.debug.warn("\n======== instead found this: =========\n", .{});
+    std.debug.warn("{}", .{result});
+    std.debug.warn("\n======================================\n", .{});
     return error.TestFailed;
 }
 
@@ -1602,7 +1604,7 @@ test "hexToBytes" {
     const test_hex_str = "909A312BB12ED1F819B3521AC4C1E896F2160507FFC1C8381E3B07BB16BD1706";
     var pb: [32]u8 = undefined;
     try hexToBytes(pb[0..], test_hex_str);
-    try testFmt(test_hex_str, "{X}", pb);
+    try testFmt(test_hex_str, "{X}", .{pb});
 }
 
 test "formatIntValue with comptime_int" {
@@ -1628,7 +1630,7 @@ test "formatType max_depth" {
             output: fn (@typeOf(context), []const u8) Errors!void,
         ) Errors!void {
             if (fmt.len == 0) {
-                return std.fmt.format(context, Errors, output, "({d:.3},{d:.3})", self.x, self.y);
+                return std.fmt.format(context, Errors, output, "({d:.3},{d:.3})", .{ self.x, self.y });
             } else {
                 @compileError("Unknown format string: '" ++ fmt ++ "'");
             }
@@ -1680,17 +1682,17 @@ test "formatType max_depth" {
 }
 
 test "positional" {
-    try testFmt("2 1 0", "{2} {1} {0}", @as(usize, 0), @as(usize, 1), @as(usize, 2));
-    try testFmt("2 1 0", "{2} {1} {}", @as(usize, 0), @as(usize, 1), @as(usize, 2));
-    try testFmt("0 0", "{0} {0}", @as(usize, 0));
-    try testFmt("0 1", "{} {1}", @as(usize, 0), @as(usize, 1));
-    try testFmt("1 0 0 1", "{1} {} {0} {}", @as(usize, 0), @as(usize, 1));
+    try testFmt("2 1 0", "{2} {1} {0}", .{ @as(usize, 0), @as(usize, 1), @as(usize, 2) });
+    try testFmt("2 1 0", "{2} {1} {}", .{ @as(usize, 0), @as(usize, 1), @as(usize, 2) });
+    try testFmt("0 0", "{0} {0}", .{@as(usize, 0)});
+    try testFmt("0 1", "{} {1}", .{ @as(usize, 0), @as(usize, 1) });
+    try testFmt("1 0 0 1", "{1} {} {0} {}", .{ @as(usize, 0), @as(usize, 1) });
 }
 
 test "positional with specifier" {
-    try testFmt("10.0", "{0d:.1}", @as(f64, 9.999));
+    try testFmt("10.0", "{0d:.1}", .{@as(f64, 9.999)});
 }
 
 test "positional/alignment/width/precision" {
-    try testFmt("10.0", "{0d: >3.1}", @as(f64, 9.999));
+    try testFmt("10.0", "{0d: >3.1}", .{@as(f64, 9.999)});
 }
diff --git a/lib/std/hash/benchmark.zig b/lib/std/hash/benchmark.zig
index 4553d928ec..f1b39bff64 100644
--- a/lib/std/hash/benchmark.zig
+++ b/lib/std/hash/benchmark.zig
@@ -164,7 +164,7 @@ fn usage() void {
         \\  --iterative-only
         \\  --help
         \\
-    );
+    , .{});
 }
 
 fn mode(comptime x: comptime_int) comptime_int {
diff --git a/lib/std/http/headers.zig b/lib/std/http/headers.zig
index 1d573aebc0..7cac6648de 100644
--- a/lib/std/http/headers.zig
+++ b/lib/std/http/headers.zig
@@ -610,5 +610,5 @@ test "Headers.format" {
         \\foo: bar
         \\cookie: somevalue
         \\
-    , try std.fmt.bufPrint(buf[0..], "{}", h));
+    , try std.fmt.bufPrint(buf[0..], "{}", .{h}));
 }
diff --git a/lib/std/io.zig b/lib/std/io.zig
index 238f7eb0f0..68c147a33c 100644
--- a/lib/std/io.zig
+++ b/lib/std/io.zig
@@ -492,7 +492,7 @@ test "io.SliceOutStream" {
     var slice_stream = SliceOutStream.init(buf[0..]);
     const stream = &slice_stream.stream;
 
-    try stream.print("{}{}!", "Hello", "World");
+    try stream.print("{}{}!", .{ "Hello", "World" });
     testing.expectEqualSlices(u8, "HelloWorld!", slice_stream.getWritten());
 }
 
diff --git a/lib/std/io/out_stream.zig b/lib/std/io/out_stream.zig
index 77698b333c..b8f5db6fff 100644
--- a/lib/std/io/out_stream.zig
+++ b/lib/std/io/out_stream.zig
@@ -35,7 +35,7 @@ pub fn OutStream(comptime WriteError: type) type {
             }
         }
 
-        pub fn print(self: *Self, comptime format: []const u8, args: ...) Error!void {
+        pub fn print(self: *Self, comptime format: []const u8, args: var) Error!void {
             return std.fmt.format(self, Error, self.writeFn, format, args);
         }
 
diff --git a/lib/std/io/test.zig b/lib/std/io/test.zig
index 5b189cbe5a..92259fd6e9 100644
--- a/lib/std/io/test.zig
+++ b/lib/std/io/test.zig
@@ -27,9 +27,9 @@ test "write a file, read it, then delete it" {
         var file_out_stream = file.outStream();
         var buf_stream = io.BufferedOutStream(File.WriteError).init(&file_out_stream.stream);
         const st = &buf_stream.stream;
-        try st.print("begin");
+        try st.print("begin", .{});
         try st.write(data[0..]);
-        try st.print("end");
+        try st.print("end", .{});
         try buf_stream.flush();
     }
 
@@ -72,7 +72,7 @@ test "BufferOutStream" {
 
     const x: i32 = 42;
     const y: i32 = 1234;
-    try buf_stream.print("x: {}\ny: {}\n", x, y);
+    try buf_stream.print("x: {}\ny: {}\n", .{ x, y });
 
     expect(mem.eql(u8, buffer.toSlice(), "x: 42\ny: 1234\n"));
 }
@@ -605,7 +605,7 @@ test "c out stream" {
     }
 
     const out_stream = &io.COutStream.init(out_file).stream;
-    try out_stream.print("hi: {}\n", @as(i32, 123));
+    try out_stream.print("hi: {}\n", .{@as(i32, 123)});
 }
 
 test "File seek ops" {
diff --git a/lib/std/json/write_stream.zig b/lib/std/json/write_stream.zig
index fbf860965f..7cff613dad 100644
--- a/lib/std/json/write_stream.zig
+++ b/lib/std/json/write_stream.zig
@@ -158,24 +158,24 @@ pub fn WriteStream(comptime OutStream: type, comptime max_depth: usize) type {
             switch (@typeInfo(@typeOf(value))) {
                 .Int => |info| {
                     if (info.bits < 53) {
-                        try self.stream.print("{}", value);
+                        try self.stream.print("{}", .{value});
                         self.popState();
                         return;
                     }
                     if (value < 4503599627370496 and (!info.is_signed or value > -4503599627370496)) {
-                        try self.stream.print("{}", value);
+                        try self.stream.print("{}", .{value});
                         self.popState();
                         return;
                     }
                 },
                 .Float => if (@floatCast(f64, value) == value) {
-                    try self.stream.print("{}", value);
+                    try self.stream.print("{}", .{value});
                     self.popState();
                     return;
                 },
                 else => {},
             }
-            try self.stream.print("\"{}\"", value);
+            try self.stream.print("\"{}\"", .{value});
             self.popState();
         }
 
diff --git a/lib/std/math/big/int.zig b/lib/std/math/big/int.zig
index 5c84dc462b..0d0b186332 100644
--- a/lib/std/math/big/int.zig
+++ b/lib/std/math/big/int.zig
@@ -180,9 +180,9 @@ pub const Int = struct {
 
     pub fn dump(self: Int) void {
         for (self.limbs) |limb| {
-            debug.warn("{x} ", limb);
+            debug.warn("{x} ", .{limb});
         }
-        debug.warn("\n");
+        debug.warn("\n", .{});
     }
 
     /// Negate the sign of an Int.
diff --git a/lib/std/net.zig b/lib/std/net.zig
index 6091564a93..a3f9c1c6d1 100644
--- a/lib/std/net.zig
+++ b/lib/std/net.zig
@@ -277,32 +277,24 @@ pub const Address = extern union {
             os.AF_INET => {
                 const port = mem.bigToNative(u16, self.in.port);
                 const bytes = @ptrCast(*const [4]u8, &self.in.addr);
-                try std.fmt.format(
-                    context,
-                    Errors,
-                    output,
-                    "{}.{}.{}.{}:{}",
+                try std.fmt.format(context, Errors, output, "{}.{}.{}.{}:{}", .{
                     bytes[0],
                     bytes[1],
                     bytes[2],
                     bytes[3],
                     port,
-                );
+                });
             },
             os.AF_INET6 => {
                 const port = mem.bigToNative(u16, self.in6.port);
                 if (mem.eql(u8, self.in6.addr[0..12], &[_]u8{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff })) {
-                    try std.fmt.format(
-                        context,
-                        Errors,
-                        output,
-                        "[::ffff:{}.{}.{}.{}]:{}",
+                    try std.fmt.format(context, Errors, output, "[::ffff:{}.{}.{}.{}]:{}", .{
                         self.in6.addr[12],
                         self.in6.addr[13],
                         self.in6.addr[14],
                         self.in6.addr[15],
                         port,
-                    );
+                    });
                     return;
                 }
                 const big_endian_parts = @ptrCast(*align(1) const [8]u16, &self.in6.addr);
@@ -327,19 +319,19 @@ pub const Address = extern union {
                         }
                         continue;
                     }
-                    try std.fmt.format(context, Errors, output, "{x}", native_endian_parts[i]);
+                    try std.fmt.format(context, Errors, output, "{x}", .{native_endian_parts[i]});
                     if (i != native_endian_parts.len - 1) {
                         try output(context, ":");
                     }
                 }
-                try std.fmt.format(context, Errors, output, "]:{}", port);
+                try std.fmt.format(context, Errors, output, "]:{}", .{port});
             },
             os.AF_UNIX => {
                 if (!has_unix_sockets) {
                     unreachable;
                 }
 
-                try std.fmt.format(context, Errors, output, "{}", &self.un.path);
+                try std.fmt.format(context, Errors, output, "{}", .{&self.un.path});
             },
             else => unreachable,
         }
@@ -445,7 +437,7 @@ pub fn getAddressList(allocator: *mem.Allocator, name: []const u8, port: u16) !*
         const name_c = try std.cstr.addNullByte(allocator, name);
         defer allocator.free(name_c);
 
-        const port_c = try std.fmt.allocPrint(allocator, "{}\x00", port);
+        const port_c = try std.fmt.allocPrint(allocator, "{}\x00", .{port});
         defer allocator.free(port_c);
 
         const hints = os.addrinfo{
diff --git a/lib/std/net/test.zig b/lib/std/net/test.zig
index 6400b022c6..2dd11b391e 100644
--- a/lib/std/net/test.zig
+++ b/lib/std/net/test.zig
@@ -29,7 +29,7 @@ test "parse and render IPv6 addresses" {
     };
     for (ips) |ip, i| {
         var addr = net.Address.parseIp6(ip, 0) catch unreachable;
-        var newIp = std.fmt.bufPrint(buffer[0..], "{}", addr) catch unreachable;
+        var newIp = std.fmt.bufPrint(buffer[0..], "{}", .{addr}) catch unreachable;
         std.testing.expect(std.mem.eql(u8, printed[i], newIp[1 .. newIp.len - 3]));
     }
 
@@ -51,7 +51,7 @@ test "parse and render IPv4 addresses" {
         "127.0.0.1",
     }) |ip| {
         var addr = net.Address.parseIp4(ip, 0) catch unreachable;
-        var newIp = std.fmt.bufPrint(buffer[0..], "{}", addr) catch unreachable;
+        var newIp = std.fmt.bufPrint(buffer[0..], "{}", .{addr}) catch unreachable;
         std.testing.expect(std.mem.eql(u8, ip, newIp[0 .. newIp.len - 2]));
     }
 
@@ -118,5 +118,5 @@ fn testServer(server: *net.StreamServer) anyerror!void {
     var client = try server.accept();
 
     const stream = &client.file.outStream().stream;
-    try stream.print("hello from server\n");
+    try stream.print("hello from server\n", .{});
 }
diff --git a/lib/std/os.zig b/lib/std/os.zig
index 5d3bb705a9..8d6c7dd05e 100644
--- a/lib/std/os.zig
+++ b/lib/std/os.zig
@@ -2603,7 +2603,7 @@ pub fn realpathC(pathname: [*:0]const u8, out_buffer: *[MAX_PATH_BYTES]u8) RealP
         defer close(fd);
 
         var procfs_buf: ["/proc/self/fd/-2147483648".len:0]u8 = undefined;
-        const proc_path = std.fmt.bufPrint(procfs_buf[0..], "/proc/self/fd/{}\x00", fd) catch unreachable;
+        const proc_path = std.fmt.bufPrint(procfs_buf[0..], "/proc/self/fd/{}\x00", .{fd}) catch unreachable;
 
         return readlinkC(@ptrCast([*:0]const u8, proc_path.ptr), out_buffer);
     }
@@ -2832,7 +2832,7 @@ pub const UnexpectedError = error{
 /// and you get an unexpected error.
 pub fn unexpectedErrno(err: usize) UnexpectedError {
     if (unexpected_error_tracing) {
-        std.debug.warn("unexpected errno: {}\n", err);
+        std.debug.warn("unexpected errno: {}\n", .{err});
         std.debug.dumpCurrentStackTrace(null);
     }
     return error.Unexpected;
diff --git a/lib/std/os/windows.zig b/lib/std/os/windows.zig
index e832f66254..b7b1edeb89 100644
--- a/lib/std/os/windows.zig
+++ b/lib/std/os/windows.zig
@@ -323,7 +323,7 @@ pub fn GetQueuedCompletionStatus(
             ERROR.HANDLE_EOF => return GetQueuedCompletionStatusResult.EOF,
             else => |err| {
                 if (std.debug.runtime_safety) {
-                    std.debug.panic("unexpected error: {}\n", err);
+                    std.debug.panic("unexpected error: {}\n", .{err});
                 }
             },
         }
@@ -1039,7 +1039,7 @@ pub fn unexpectedError(err: DWORD) std.os.UnexpectedError {
         var buf_u8: [614]u8 = undefined;
         var len = kernel32.FormatMessageW(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, null, err, MAKELANGID(LANG.NEUTRAL, SUBLANG.DEFAULT), buf_u16[0..].ptr, buf_u16.len / @sizeOf(TCHAR), null);
         _ = std.unicode.utf16leToUtf8(&buf_u8, buf_u16[0..len]) catch unreachable;
-        std.debug.warn("error.Unexpected: GetLastError({}): {}\n", err, buf_u8[0..len]);
+        std.debug.warn("error.Unexpected: GetLastError({}): {}\n", .{ err, buf_u8[0..len] });
         std.debug.dumpCurrentStackTrace(null);
     }
     return error.Unexpected;
@@ -1053,7 +1053,7 @@ pub fn unexpectedWSAError(err: c_int) std.os.UnexpectedError {
 /// and you get an unexpected status.
 pub fn unexpectedStatus(status: NTSTATUS) std.os.UnexpectedError {
     if (std.os.unexpected_error_tracing) {
-        std.debug.warn("error.Unexpected NTSTATUS=0x{x}\n", status);
+        std.debug.warn("error.Unexpected NTSTATUS=0x{x}\n", .{status});
         std.debug.dumpCurrentStackTrace(null);
     }
     return error.Unexpected;
diff --git a/lib/std/os/zen.zig b/lib/std/os/zen.zig
deleted file mode 100644
index 190b7ffe08..0000000000
--- a/lib/std/os/zen.zig
+++ /dev/null
@@ -1,260 +0,0 @@
-const std = @import("../std.zig");
-const assert = std.debug.assert;
-
-//////////////////////////
-////  IPC structures  ////
-//////////////////////////
-
-pub const Message = struct {
-    sender: MailboxId,
-    receiver: MailboxId,
-    code: usize,
-    args: [5]usize,
-    payload: ?[]const u8,
-
-    pub fn from(mailbox_id: MailboxId) Message {
-        return Message{
-            .sender = MailboxId.Undefined,
-            .receiver = mailbox_id,
-            .code = undefined,
-            .args = undefined,
-            .payload = null,
-        };
-    }
-
-    pub fn to(mailbox_id: MailboxId, msg_code: usize, args: ...) Message {
-        var message = Message{
-            .sender = MailboxId.This,
-            .receiver = mailbox_id,
-            .code = msg_code,
-            .args = undefined,
-            .payload = null,
-        };
-
-        assert(args.len <= message.args.len);
-        comptime var i = 0;
-        inline while (i < args.len) : (i += 1) {
-            message.args[i] = args[i];
-        }
-
-        return message;
-    }
-
-    pub fn as(self: Message, sender: MailboxId) Message {
-        var message = self;
-        message.sender = sender;
-        return message;
-    }
-
-    pub fn withPayload(self: Message, payload: []const u8) Message {
-        var message = self;
-        message.payload = payload;
-        return message;
-    }
-};
-
-pub const MailboxId = union(enum) {
-    Undefined,
-    This,
-    Kernel,
-    Port: u16,
-    Thread: u16,
-};
-
-//////////////////////////////////////
-////  Ports reserved for servers  ////
-//////////////////////////////////////
-
-pub const Server = struct {
-    pub const Keyboard = MailboxId{ .Port = 0 };
-    pub const Terminal = MailboxId{ .Port = 1 };
-};
-
-////////////////////////
-////  POSIX things  ////
-////////////////////////
-
-// Standard streams.
-pub const STDIN_FILENO = 0;
-pub const STDOUT_FILENO = 1;
-pub const STDERR_FILENO = 2;
-
-// FIXME: let's borrow Linux's error numbers for now.
-usingnamespace @import("bits/linux/errno-generic.zig");
-// Get the errno from a syscall return value, or 0 for no error.
-pub fn getErrno(r: usize) usize {
-    const signed_r = @bitCast(isize, r);
-    return if (signed_r > -4096 and signed_r < 0) @intCast(usize, -signed_r) else 0;
-}
-
-// TODO: implement this correctly.
-pub fn read(fd: i32, buf: [*]u8, count: usize) usize {
-    switch (fd) {
-        STDIN_FILENO => {
-            var i: usize = 0;
-            while (i < count) : (i += 1) {
-                send(&Message.to(Server.Keyboard, 0));
-
-                // FIXME: we should be certain that we are receiving from Keyboard.
-                var message = Message.from(MailboxId.This);
-                receive(&message);
-
-                buf[i] = @intCast(u8, message.args[0]);
-            }
-        },
-        else => unreachable,
-    }
-    return count;
-}
-
-// TODO: implement this correctly.
-pub fn write(fd: i32, buf: [*]const u8, count: usize) usize {
-    switch (fd) {
-        STDOUT_FILENO, STDERR_FILENO => {
-            send(&Message.to(Server.Terminal, 1).withPayload(buf[0..count]));
-        },
-        else => unreachable,
-    }
-    return count;
-}
-
-///////////////////////////
-////  Syscall numbers  ////
-///////////////////////////
-
-pub const Syscall = enum(usize) {
-    exit = 0,
-    send = 1,
-    receive = 2,
-    subscribeIRQ = 3,
-    inb = 4,
-    outb = 5,
-    map = 6,
-    createThread = 7,
-};
-
-////////////////////
-////  Syscalls  ////
-////////////////////
-
-pub fn exit(status: i32) noreturn {
-    _ = syscall1(Syscall.exit, @bitCast(usize, @as(isize, status)));
-    unreachable;
-}
-
-pub fn send(message: *const Message) void {
-    _ = syscall1(Syscall.send, @ptrToInt(message));
-}
-
-pub fn receive(destination: *Message) void {
-    _ = syscall1(Syscall.receive, @ptrToInt(destination));
-}
-
-pub fn subscribeIRQ(irq: u8, mailbox_id: *const MailboxId) void {
-    _ = syscall2(Syscall.subscribeIRQ, irq, @ptrToInt(mailbox_id));
-}
-
-pub fn inb(port: u16) u8 {
-    return @intCast(u8, syscall1(Syscall.inb, port));
-}
-
-pub fn outb(port: u16, value: u8) void {
-    _ = syscall2(Syscall.outb, port, value);
-}
-
-pub fn map(v_addr: usize, p_addr: usize, size: usize, writable: bool) bool {
-    return syscall4(Syscall.map, v_addr, p_addr, size, @boolToInt(writable)) != 0;
-}
-
-pub fn createThread(function: fn () void) u16 {
-    return @as(u16, syscall1(Syscall.createThread, @ptrToInt(function)));
-}
-
-/////////////////////////
-////  Syscall stubs  ////
-/////////////////////////
-
-inline fn syscall0(number: Syscall) usize {
-    return asm volatile ("int $0x80"
-        : [ret] "={eax}" (-> usize)
-        : [number] "{eax}" (number)
-    );
-}
-
-inline fn syscall1(number: Syscall, arg1: usize) usize {
-    return asm volatile ("int $0x80"
-        : [ret] "={eax}" (-> usize)
-        : [number] "{eax}" (number),
-          [arg1] "{ecx}" (arg1)
-    );
-}
-
-inline fn syscall2(number: Syscall, arg1: usize, arg2: usize) usize {
-    return asm volatile ("int $0x80"
-        : [ret] "={eax}" (-> usize)
-        : [number] "{eax}" (number),
-          [arg1] "{ecx}" (arg1),
-          [arg2] "{edx}" (arg2)
-    );
-}
-
-inline fn syscall3(number: Syscall, arg1: usize, arg2: usize, arg3: usize) usize {
-    return asm volatile ("int $0x80"
-        : [ret] "={eax}" (-> usize)
-        : [number] "{eax}" (number),
-          [arg1] "{ecx}" (arg1),
-          [arg2] "{edx}" (arg2),
-          [arg3] "{ebx}" (arg3)
-    );
-}
-
-inline fn syscall4(number: Syscall, arg1: usize, arg2: usize, arg3: usize, arg4: usize) usize {
-    return asm volatile ("int $0x80"
-        : [ret] "={eax}" (-> usize)
-        : [number] "{eax}" (number),
-          [arg1] "{ecx}" (arg1),
-          [arg2] "{edx}" (arg2),
-          [arg3] "{ebx}" (arg3),
-          [arg4] "{esi}" (arg4)
-    );
-}
-
-inline fn syscall5(
-    number: Syscall,
-    arg1: usize,
-    arg2: usize,
-    arg3: usize,
-    arg4: usize,
-    arg5: usize,
-) usize {
-    return asm volatile ("int $0x80"
-        : [ret] "={eax}" (-> usize)
-        : [number] "{eax}" (number),
-          [arg1] "{ecx}" (arg1),
-          [arg2] "{edx}" (arg2),
-          [arg3] "{ebx}" (arg3),
-          [arg4] "{esi}" (arg4),
-          [arg5] "{edi}" (arg5)
-    );
-}
-
-inline fn syscall6(
-    number: Syscall,
-    arg1: usize,
-    arg2: usize,
-    arg3: usize,
-    arg4: usize,
-    arg5: usize,
-    arg6: usize,
-) usize {
-    return asm volatile ("int $0x80"
-        : [ret] "={eax}" (-> usize)
-        : [number] "{eax}" (number),
-          [arg1] "{ecx}" (arg1),
-          [arg2] "{edx}" (arg2),
-          [arg3] "{ebx}" (arg3),
-          [arg4] "{esi}" (arg4),
-          [arg5] "{edi}" (arg5),
-          [arg6] "{ebp}" (arg6)
-    );
-}
diff --git a/lib/std/priority_queue.zig b/lib/std/priority_queue.zig
index 3351ac994b..77c76e4a70 100644
--- a/lib/std/priority_queue.zig
+++ b/lib/std/priority_queue.zig
@@ -199,19 +199,19 @@ pub fn PriorityQueue(comptime T: type) type {
         }
 
         fn dump(self: *Self) void {
-            warn("{{ ");
-            warn("items: ");
+            warn("{{ ", .{});
+            warn("items: ", .{});
             for (self.items) |e, i| {
                 if (i >= self.len) break;
-                warn("{}, ", e);
+                warn("{}, ", .{e});
             }
-            warn("array: ");
+            warn("array: ", .{});
             for (self.items) |e, i| {
-                warn("{}, ", e);
+                warn("{}, ", .{e});
             }
-            warn("len: {} ", self.len);
-            warn("capacity: {}", self.capacity());
-            warn(" }}\n");
+            warn("len: {} ", .{self.len});
+            warn("capacity: {}", .{self.capacity()});
+            warn(" }}\n", .{});
         }
     };
 }
diff --git a/lib/std/progress.zig b/lib/std/progress.zig
index 034d7ade26..1c5ecd261a 100644
--- a/lib/std/progress.zig
+++ b/lib/std/progress.zig
@@ -130,11 +130,11 @@ pub const Progress = struct {
         var end: usize = 0;
         if (self.columns_written > 0) {
             // restore cursor position
-            end += (std.fmt.bufPrint(self.output_buffer[end..], "\x1b[{}D", self.columns_written) catch unreachable).len;
+            end += (std.fmt.bufPrint(self.output_buffer[end..], "\x1b[{}D", .{self.columns_written}) catch unreachable).len;
             self.columns_written = 0;
 
             // clear rest of line
-            end += (std.fmt.bufPrint(self.output_buffer[end..], "\x1b[0K") catch unreachable).len;
+            end += (std.fmt.bufPrint(self.output_buffer[end..], "\x1b[0K", .{}) catch unreachable).len;
         }
 
         if (!self.done) {
@@ -142,28 +142,28 @@ pub const Progress = struct {
             var maybe_node: ?*Node = &self.root;
             while (maybe_node) |node| {
                 if (need_ellipse) {
-                    self.bufWrite(&end, "...");
+                    self.bufWrite(&end, "...", .{});
                 }
                 need_ellipse = false;
                 if (node.name.len != 0 or node.estimated_total_items != null) {
                     if (node.name.len != 0) {
-                        self.bufWrite(&end, "{}", node.name);
+                        self.bufWrite(&end, "{}", .{node.name});
                         need_ellipse = true;
                     }
                     if (node.estimated_total_items) |total| {
-                        if (need_ellipse) self.bufWrite(&end, " ");
-                        self.bufWrite(&end, "[{}/{}] ", node.completed_items + 1, total);
+                        if (need_ellipse) self.bufWrite(&end, " ", .{});
+                        self.bufWrite(&end, "[{}/{}] ", .{ node.completed_items + 1, total });
                         need_ellipse = false;
                     } else if (node.completed_items != 0) {
-                        if (need_ellipse) self.bufWrite(&end, " ");
-                        self.bufWrite(&end, "[{}] ", node.completed_items + 1);
+                        if (need_ellipse) self.bufWrite(&end, " ", .{});
+                        self.bufWrite(&end, "[{}] ", .{node.completed_items + 1});
                         need_ellipse = false;
                     }
                 }
                 maybe_node = node.recently_updated_child;
             }
             if (need_ellipse) {
-                self.bufWrite(&end, "...");
+                self.bufWrite(&end, "...", .{});
             }
         }
 
@@ -174,7 +174,7 @@ pub const Progress = struct {
         self.prev_refresh_timestamp = self.timer.read();
     }
 
-    pub fn log(self: *Progress, comptime format: []const u8, args: ...) void {
+    pub fn log(self: *Progress, comptime format: []const u8, args: var) void {
         const file = self.terminal orelse return;
         self.refresh();
         file.outStream().stream.print(format, args) catch {
@@ -184,7 +184,7 @@ pub const Progress = struct {
         self.columns_written = 0;
     }
 
-    fn bufWrite(self: *Progress, end: *usize, comptime format: []const u8, args: ...) void {
+    fn bufWrite(self: *Progress, end: *usize, comptime format: []const u8, args: var) void {
         if (std.fmt.bufPrint(self.output_buffer[end.*..], format, args)) |written| {
             const amt = written.len;
             end.* += amt;
diff --git a/lib/std/special/build_runner.zig b/lib/std/special/build_runner.zig
index 27d3283a3c..03d1e8fe1d 100644
--- a/lib/std/special/build_runner.zig
+++ b/lib/std/special/build_runner.zig
@@ -26,15 +26,15 @@ pub fn main() !void {
     _ = arg_it.skip();
 
     const zig_exe = try unwrapArg(arg_it.next(allocator) orelse {
-        warn("Expected first argument to be path to zig compiler\n");
+        warn("Expected first argument to be path to zig compiler\n", .{});
         return error.InvalidArgs;
     });
     const build_root = try unwrapArg(arg_it.next(allocator) orelse {
-        warn("Expected second argument to be build root directory path\n");
+        warn("Expected second argument to be build root directory path\n", .{});
         return error.InvalidArgs;
     });
     const cache_root = try unwrapArg(arg_it.next(allocator) orelse {
-        warn("Expected third argument to be cache root directory path\n");
+        warn("Expected third argument to be cache root directory path\n", .{});
         return error.InvalidArgs;
     });
 
@@ -51,7 +51,7 @@ pub fn main() !void {
         if (mem.startsWith(u8, arg, "-D")) {
             const option_contents = arg[2..];
             if (option_contents.len == 0) {
-                warn("Expected option name after '-D'\n\n");
+                warn("Expected option name after '-D'\n\n", .{});
                 return usageAndErr(builder, false, stderr_stream);
             }
             if (mem.indexOfScalar(u8, option_contents, '=')) |name_end| {
@@ -70,18 +70,18 @@ pub fn main() !void {
                 return usage(builder, false, stdout_stream);
             } else if (mem.eql(u8, arg, "--prefix")) {
                 builder.install_prefix = try unwrapArg(arg_it.next(allocator) orelse {
-                    warn("Expected argument after --prefix\n\n");
+                    warn("Expected argument after --prefix\n\n", .{});
                     return usageAndErr(builder, false, stderr_stream);
                 });
             } else if (mem.eql(u8, arg, "--search-prefix")) {
                 const search_prefix = try unwrapArg(arg_it.next(allocator) orelse {
-                    warn("Expected argument after --search-prefix\n\n");
+                    warn("Expected argument after --search-prefix\n\n", .{});
                     return usageAndErr(builder, false, stderr_stream);
                 });
                 builder.addSearchPrefix(search_prefix);
             } else if (mem.eql(u8, arg, "--override-lib-dir")) {
                 builder.override_lib_dir = try unwrapArg(arg_it.next(allocator) orelse {
-                    warn("Expected argument after --override-lib-dir\n\n");
+                    warn("Expected argument after --override-lib-dir\n\n", .{});
                     return usageAndErr(builder, false, stderr_stream);
                 });
             } else if (mem.eql(u8, arg, "--verbose-tokenize")) {
@@ -99,7 +99,7 @@ pub fn main() !void {
             } else if (mem.eql(u8, arg, "--verbose-cc")) {
                 builder.verbose_cc = true;
             } else {
-                warn("Unrecognized argument: {}\n\n", arg);
+                warn("Unrecognized argument: {}\n\n", .{arg});
                 return usageAndErr(builder, false, stderr_stream);
             }
         } else {
@@ -145,15 +145,15 @@ fn usage(builder: *Builder, already_ran_build: bool, out_stream: var) !void {
         \\
         \\Steps:
         \\
-    , builder.zig_exe);
+    , .{builder.zig_exe});
 
     const allocator = builder.allocator;
     for (builder.top_level_steps.toSliceConst()) |top_level_step| {
         const name = if (&top_level_step.step == builder.default_step)
-            try fmt.allocPrint(allocator, "{} (default)", top_level_step.step.name)
+            try fmt.allocPrint(allocator, "{} (default)", .{top_level_step.step.name})
         else
             top_level_step.step.name;
-        try out_stream.print("  {s:22} {}\n", name, top_level_step.description);
+        try out_stream.print("  {s:22} {}\n", .{ name, top_level_step.description });
     }
 
     try out_stream.write(
@@ -169,12 +169,15 @@ fn usage(builder: *Builder, already_ran_build: bool, out_stream: var) !void {
     );
 
     if (builder.available_options_list.len == 0) {
-        try out_stream.print("  (none)\n");
+        try out_stream.print("  (none)\n", .{});
     } else {
         for (builder.available_options_list.toSliceConst()) |option| {
-            const name = try fmt.allocPrint(allocator, "  -D{}=[{}]", option.name, Builder.typeIdName(option.type_id));
+            const name = try fmt.allocPrint(allocator, "  -D{}=[{}]", .{
+                option.name,
+                Builder.typeIdName(option.type_id),
+            });
             defer allocator.free(name);
-            try out_stream.print("{s:24} {}\n", name, option.description);
+            try out_stream.print("{s:24} {}\n", .{ name, option.description });
         }
     }
 
@@ -204,7 +207,7 @@ const UnwrapArgError = error{OutOfMemory};
 
 fn unwrapArg(arg: UnwrapArgError![]u8) UnwrapArgError![]u8 {
     return arg catch |err| {
-        warn("Unable to parse command line: {}\n", err);
+        warn("Unable to parse command line: {}\n", .{err});
         return err;
     };
 }
diff --git a/lib/std/special/compiler_rt/truncXfYf2_test.zig b/lib/std/special/compiler_rt/truncXfYf2_test.zig
index d1dd837ddc..baec2a4450 100644
--- a/lib/std/special/compiler_rt/truncXfYf2_test.zig
+++ b/lib/std/special/compiler_rt/truncXfYf2_test.zig
@@ -217,7 +217,7 @@ fn test__truncdfsf2(a: f64, expected: u32) void {
         }
     }
 
-    @import("std").debug.warn("got 0x{x} wanted 0x{x}\n", rep, expected);
+    @import("std").debug.warn("got 0x{x} wanted 0x{x}\n", .{ rep, expected });
 
     @panic("__trunctfsf2 test failure");
 }
diff --git a/lib/std/special/init-exe/src/main.zig b/lib/std/special/init-exe/src/main.zig
index 128820d3ee..5f35540dc0 100644
--- a/lib/std/special/init-exe/src/main.zig
+++ b/lib/std/special/init-exe/src/main.zig
@@ -1,5 +1,5 @@
 const std = @import("std");
 
 pub fn main() anyerror!void {
-    std.debug.warn("All your base are belong to us.\n");
+    std.debug.warn("All your base are belong to us.\n", .{});
 }
diff --git a/lib/std/special/start.zig b/lib/std/special/start.zig
index d6c6350ff4..b5e4e2edab 100644
--- a/lib/std/special/start.zig
+++ b/lib/std/special/start.zig
@@ -217,7 +217,7 @@ inline fn initEventLoopAndCallMain() u8 {
     if (std.event.Loop.instance) |loop| {
         if (!@hasDecl(root, "event_loop")) {
             loop.init() catch |err| {
-                std.debug.warn("error: {}\n", @errorName(err));
+                std.debug.warn("error: {}\n", .{@errorName(err)});
                 if (@errorReturnTrace()) |trace| {
                     std.debug.dumpStackTrace(trace.*);
                 }
@@ -264,7 +264,7 @@ fn callMain() u8 {
         },
         .ErrorUnion => {
             const result = root.main() catch |err| {
-                std.debug.warn("error: {}\n", @errorName(err));
+                std.debug.warn("error: {}\n", .{@errorName(err)});
                 if (@errorReturnTrace()) |trace| {
                     std.debug.dumpStackTrace(trace.*);
                 }
diff --git a/lib/std/special/test_runner.zig b/lib/std/special/test_runner.zig
index 4dc8be0fec..7bb53774d3 100644
--- a/lib/std/special/test_runner.zig
+++ b/lib/std/special/test_runner.zig
@@ -16,28 +16,28 @@ pub fn main() anyerror!void {
         var test_node = root_node.start(test_fn.name, null);
         test_node.activate();
         progress.refresh();
-        if (progress.terminal == null) std.debug.warn("{}/{} {}...", i + 1, test_fn_list.len, test_fn.name);
+        if (progress.terminal == null) std.debug.warn("{}/{} {}...", .{ i + 1, test_fn_list.len, test_fn.name });
         if (test_fn.func()) |_| {
             ok_count += 1;
             test_node.end();
-            if (progress.terminal == null) std.debug.warn("OK\n");
+            if (progress.terminal == null) std.debug.warn("OK\n", .{});
         } else |err| switch (err) {
             error.SkipZigTest => {
                 skip_count += 1;
                 test_node.end();
-                progress.log("{}...SKIP\n", test_fn.name);
-                if (progress.terminal == null) std.debug.warn("SKIP\n");
+                progress.log("{}...SKIP\n", .{test_fn.name});
+                if (progress.terminal == null) std.debug.warn("SKIP\n", .{});
             },
             else => {
-                progress.log("");
+                progress.log("", .{});
                 return err;
             },
         }
     }
     root_node.end();
     if (ok_count == test_fn_list.len) {
-        std.debug.warn("All {} tests passed.\n", ok_count);
+        std.debug.warn("All {} tests passed.\n", .{ok_count});
     } else {
-        std.debug.warn("{} passed; {} skipped.\n", ok_count, skip_count);
+        std.debug.warn("{} passed; {} skipped.\n", .{ ok_count, skip_count });
     }
 }
diff --git a/lib/std/target.zig b/lib/std/target.zig
index e4beea4552..aaa19ad609 100644
--- a/lib/std/target.zig
+++ b/lib/std/target.zig
@@ -321,14 +321,12 @@ pub const Target = union(enum) {
     pub const stack_align = 16;
 
     pub fn zigTriple(self: Target, allocator: *mem.Allocator) ![]u8 {
-        return std.fmt.allocPrint(
-            allocator,
-            "{}{}-{}-{}",
+        return std.fmt.allocPrint(allocator, "{}{}-{}-{}", .{
             @tagName(self.getArch()),
             Target.archSubArchName(self.getArch()),
             @tagName(self.getOs()),
             @tagName(self.getAbi()),
-        );
+        });
     }
 
     /// Returned slice must be freed by the caller.
@@ -372,23 +370,19 @@ pub const Target = union(enum) {
     }
 
     pub fn zigTripleNoSubArch(self: Target, allocator: *mem.Allocator) ![]u8 {
-        return std.fmt.allocPrint(
-            allocator,
-            "{}-{}-{}",
+        return std.fmt.allocPrint(allocator, "{}-{}-{}", .{
             @tagName(self.getArch()),
             @tagName(self.getOs()),
             @tagName(self.getAbi()),
-        );
+        });
     }
 
     pub fn linuxTriple(self: Target, allocator: *mem.Allocator) ![]u8 {
-        return std.fmt.allocPrint(
-            allocator,
-            "{}-{}-{}",
+        return std.fmt.allocPrint(allocator, "{}-{}-{}", .{
             @tagName(self.getArch()),
             @tagName(self.getOs()),
             @tagName(self.getAbi()),
-        );
+        });
     }
 
     pub fn parse(text: []const u8) !Target {
diff --git a/lib/std/testing.zig b/lib/std/testing.zig
index 2ed6c66fe6..e808930b60 100644
--- a/lib/std/testing.zig
+++ b/lib/std/testing.zig
@@ -8,13 +8,19 @@ pub fn expectError(expected_error: anyerror, actual_error_union: var) void {
     if (actual_error_union) |actual_payload| {
         // TODO remove workaround here for https://github.com/ziglang/zig/issues/557
         if (@sizeOf(@typeOf(actual_payload)) == 0) {
-            std.debug.panic("expected error.{}, found {} value", @errorName(expected_error), @typeName(@typeOf(actual_payload)));
+            std.debug.panic("expected error.{}, found {} value", .{
+                @errorName(expected_error),
+                @typeName(@typeOf(actual_payload)),
+            });
         } else {
-            std.debug.panic("expected error.{}, found {}", @errorName(expected_error), actual_payload);
+            std.debug.panic("expected error.{}, found {}", .{ @errorName(expected_error), actual_payload });
         }
     } else |actual_error| {
         if (expected_error != actual_error) {
-            std.debug.panic("expected error.{}, found error.{}", @errorName(expected_error), @errorName(actual_error));
+            std.debug.panic("expected error.{}, found error.{}", .{
+                @errorName(expected_error),
+                @errorName(actual_error),
+            });
         }
     }
 }
@@ -51,7 +57,7 @@ pub fn expectEqual(expected: var, actual: @typeOf(expected)) void {
         .ErrorSet,
         => {
             if (actual != expected) {
-                std.debug.panic("expected {}, found {}", expected, actual);
+                std.debug.panic("expected {}, found {}", .{ expected, actual });
             }
         },
 
@@ -62,16 +68,16 @@ pub fn expectEqual(expected: var, actual: @typeOf(expected)) void {
                 builtin.TypeInfo.Pointer.Size.C,
                 => {
                     if (actual != expected) {
-                        std.debug.panic("expected {*}, found {*}", expected, actual);
+                        std.debug.panic("expected {*}, found {*}", .{ expected, actual });
                     }
                 },
 
                 builtin.TypeInfo.Pointer.Size.Slice => {
                     if (actual.ptr != expected.ptr) {
-                        std.debug.panic("expected slice ptr {}, found {}", expected.ptr, actual.ptr);
+                        std.debug.panic("expected slice ptr {}, found {}", .{ expected.ptr, actual.ptr });
                     }
                     if (actual.len != expected.len) {
-                        std.debug.panic("expected slice len {}, found {}", expected.len, actual.len);
+                        std.debug.panic("expected slice len {}, found {}", .{ expected.len, actual.len });
                     }
                 },
             }
@@ -106,7 +112,7 @@ pub fn expectEqual(expected: var, actual: @typeOf(expected)) void {
             }
 
             // we iterate over *all* union fields
-            // => we should never get here as the loop above is 
+            // => we should never get here as the loop above is
             //    including all possible values.
             unreachable;
         },
@@ -116,11 +122,11 @@ pub fn expectEqual(expected: var, actual: @typeOf(expected)) void {
                 if (actual) |actual_payload| {
                     expectEqual(expected_payload, actual_payload);
                 } else {
-                    std.debug.panic("expected {}, found null", expected_payload);
+                    std.debug.panic("expected {}, found null", .{expected_payload});
                 }
             } else {
                 if (actual) |actual_payload| {
-                    std.debug.panic("expected null, found {}", actual_payload);
+                    std.debug.panic("expected null, found {}", .{actual_payload});
                 }
             }
         },
@@ -130,11 +136,11 @@ pub fn expectEqual(expected: var, actual: @typeOf(expected)) void {
                 if (actual) |actual_payload| {
                     expectEqual(expected_payload, actual_payload);
                 } else |actual_err| {
-                    std.debug.panic("expected {}, found {}", expected_payload, actual_err);
+                    std.debug.panic("expected {}, found {}", .{ expected_payload, actual_err });
                 }
             } else |expected_err| {
                 if (actual) |actual_payload| {
-                    std.debug.panic("expected {}, found {}", expected_err, actual_payload);
+                    std.debug.panic("expected {}, found {}", .{ expected_err, actual_payload });
                 } else |actual_err| {
                     expectEqual(expected_err, actual_err);
                 }
@@ -143,15 +149,14 @@ pub fn expectEqual(expected: var, actual: @typeOf(expected)) void {
     }
 }
 
-test "expectEqual.union(enum)"
-{
+test "expectEqual.union(enum)" {
     const T = union(enum) {
         a: i32,
         b: f32,
     };
 
-    const a10 = T { .a = 10 };
-    const a20 = T { .a = 20 };
+    const a10 = T{ .a = 10 };
+    const a20 = T{ .a = 20 };
 
     expectEqual(a10, a10);
 }
@@ -165,12 +170,12 @@ pub fn expectEqualSlices(comptime T: type, expected: []const T, actual: []const
     // If the child type is u8 and no weird bytes, we could print it as strings
     // Even for the length difference, it would be useful to see the values of the slices probably.
     if (expected.len != actual.len) {
-        std.debug.panic("slice lengths differ. expected {}, found {}", expected.len, actual.len);
+        std.debug.panic("slice lengths differ. expected {}, found {}", .{ expected.len, actual.len });
     }
     var i: usize = 0;
     while (i < expected.len) : (i += 1) {
         if (expected[i] != actual[i]) {
-            std.debug.panic("index {} incorrect. expected {}, found {}", i, expected[i], actual[i]);
+            std.debug.panic("index {} incorrect. expected {}, found {}", .{ i, expected[i], actual[i] });
         }
     }
 }
diff --git a/lib/std/unicode.zig b/lib/std/unicode.zig
index 4af1b63a69..0352c91f60 100644
--- a/lib/std/unicode.zig
+++ b/lib/std/unicode.zig
@@ -170,7 +170,7 @@ pub fn utf8ValidateSlice(s: []const u8) bool {
 /// ```
 /// var utf8 = (try std.unicode.Utf8View.init("hi there")).iterator();
 /// while (utf8.nextCodepointSlice()) |codepoint| {
-///   std.debug.warn("got codepoint {}\n", codepoint);
+///   std.debug.warn("got codepoint {}\n", .{codepoint});
 /// }
 /// ```
 pub const Utf8View = struct {
diff --git a/lib/std/unicode/throughput_test.zig b/lib/std/unicode/throughput_test.zig
index f76f14b3ac..a9a211d24a 100644
--- a/lib/std/unicode/throughput_test.zig
+++ b/lib/std/unicode/throughput_test.zig
@@ -24,8 +24,12 @@ pub fn main() !void {
     const elapsed_ns_better = timer.lap();
     @fence(.SeqCst);
 
-    std.debug.warn("original utf8ToUtf16Le: elapsed: {} ns ({} ms)\n", elapsed_ns_orig, elapsed_ns_orig / 1000000);
-    std.debug.warn("new utf8ToUtf16Le: elapsed: {} ns ({} ms)\n", elapsed_ns_better, elapsed_ns_better / 1000000);
+    std.debug.warn("original utf8ToUtf16Le: elapsed: {} ns ({} ms)\n", .{
+        elapsed_ns_orig, elapsed_ns_orig / 1000000,
+    });
+    std.debug.warn("new utf8ToUtf16Le: elapsed: {} ns ({} ms)\n", .{
+        elapsed_ns_better, elapsed_ns_better / 1000000,
+    });
     asm volatile ("nop"
         :
         : [a] "r" (&buffer1),
diff --git a/lib/std/valgrind.zig b/lib/std/valgrind.zig
index ffdce1b729..fe1eb65b7a 100644
--- a/lib/std/valgrind.zig
+++ b/lib/std/valgrind.zig
@@ -114,20 +114,6 @@ pub fn innerThreads(qzz: [*]u8) void {
     doClientRequestStmt(.InnerThreads, qzz, 0, 0, 0, 0);
 }
 
-//pub fn printf(format: [*]const u8, args: ...) usize {
-//    return doClientRequestExpr(0,
-//        .PrintfValistByRef,
-//        @ptrToInt(format), @ptrToInt(args),
-//        0, 0, 0);
-//}
-
-//pub fn printfBacktrace(format: [*]const u8, args: ...) usize {
-//    return doClientRequestExpr(0,
-//        .PrintfBacktraceValistByRef,
-//        @ptrToInt(format), @ptrToInt(args),
-//        0, 0, 0);
-//}
-
 pub fn nonSIMDCall0(func: fn (usize) usize) usize {
     return doClientRequestExpr(0, .ClientCall0, @ptrToInt(func), 0, 0, 0, 0);
 }
diff --git a/lib/std/zig/ast.zig b/lib/std/zig/ast.zig
index bedb980463..5fa519aa90 100644
--- a/lib/std/zig/ast.zig
+++ b/lib/std/zig/ast.zig
@@ -301,7 +301,9 @@ pub const Error = union(enum) {
         node: *Node,
 
         pub fn render(self: *const ExpectedCall, tokens: *Tree.TokenList, stream: var) !void {
-            return stream.print("expected " ++ @tagName(@TagType(Node.SuffixOp.Op).Call) ++ ", found {}", @tagName(self.node.id));
+            return stream.print("expected " ++ @tagName(@TagType(Node.SuffixOp.Op).Call) ++ ", found {}", .{
+                @tagName(self.node.id),
+            });
         }
     };
 
@@ -309,7 +311,8 @@ pub const Error = union(enum) {
         node: *Node,
 
         pub fn render(self: *const ExpectedCallOrFnProto, tokens: *Tree.TokenList, stream: var) !void {
-            return stream.print("expected " ++ @tagName(@TagType(Node.SuffixOp.Op).Call) ++ " or " ++ @tagName(Node.Id.FnProto) ++ ", found {}", @tagName(self.node.id));
+            return stream.print("expected " ++ @tagName(@TagType(Node.SuffixOp.Op).Call) ++ " or " ++
+                @tagName(Node.Id.FnProto) ++ ", found {}", .{@tagName(self.node.id)});
         }
     };
 
@@ -321,14 +324,14 @@ pub const Error = union(enum) {
             const found_token = tokens.at(self.token);
             switch (found_token.id) {
                 .Invalid_ampersands => {
-                    return stream.print("`&&` is invalid. Note that `and` is boolean AND.");
+                    return stream.print("`&&` is invalid. Note that `and` is boolean AND.", .{});
                 },
                 .Invalid => {
-                    return stream.print("expected '{}', found invalid bytes", self.expected_id.symbol());
+                    return stream.print("expected '{}', found invalid bytes", .{self.expected_id.symbol()});
                 },
                 else => {
                     const token_name = found_token.id.symbol();
-                    return stream.print("expected '{}', found '{}'", self.expected_id.symbol(), token_name);
+                    return stream.print("expected '{}', found '{}'", .{ self.expected_id.symbol(), token_name });
                 },
             }
         }
@@ -340,7 +343,10 @@ pub const Error = union(enum) {
 
         pub fn render(self: *const ExpectedCommaOrEnd, tokens: *Tree.TokenList, stream: var) !void {
             const actual_token = tokens.at(self.token);
-            return stream.print("expected ',' or '{}', found '{}'", self.end_id.symbol(), actual_token.id.symbol());
+            return stream.print("expected ',' or '{}', found '{}'", .{
+                self.end_id.symbol(),
+                actual_token.id.symbol(),
+            });
         }
     };
 
@@ -352,7 +358,7 @@ pub const Error = union(enum) {
 
             pub fn render(self: *const ThisError, tokens: *Tree.TokenList, stream: var) !void {
                 const actual_token = tokens.at(self.token);
-                return stream.print(msg, actual_token.id.symbol());
+                return stream.print(msg, .{actual_token.id.symbol()});
             }
         };
     }
@@ -563,10 +569,10 @@ pub const Node = struct {
         {
             var i: usize = 0;
             while (i < indent) : (i += 1) {
-                std.debug.warn(" ");
+                std.debug.warn(" ", .{});
             }
         }
-        std.debug.warn("{}\n", @tagName(self.id));
+        std.debug.warn("{}\n", .{@tagName(self.id)});
 
         var child_i: usize = 0;
         while (self.iterate(child_i)) |child| : (child_i += 1) {
diff --git a/lib/std/zig/parser_test.zig b/lib/std/zig/parser_test.zig
index 7f3cc3694a..a47e2bdc7e 100644
--- a/lib/std/zig/parser_test.zig
+++ b/lib/std/zig/parser_test.zig
@@ -642,15 +642,6 @@ test "zig fmt: fn decl with trailing comma" {
     );
 }
 
-test "zig fmt: var_args with trailing comma" {
-    try testCanonical(
-        \\pub fn add(
-        \\    a: ...,
-        \\) void {}
-        \\
-    );
-}
-
 test "zig fmt: enum decl with no trailing comma" {
     try testTransform(
         \\const StrLitKind = enum {Normal, C};
@@ -1750,13 +1741,6 @@ test "zig fmt: call expression" {
     );
 }
 
-test "zig fmt: var args" {
-    try testCanonical(
-        \\fn print(args: ...) void {}
-        \\
-    );
-}
-
 test "zig fmt: var type" {
     try testCanonical(
         \\fn print(args: var) var {}
@@ -2705,9 +2689,9 @@ fn testParse(source: []const u8, allocator: *mem.Allocator, anything_changed: *b
     while (error_it.next()) |parse_error| {
         const token = tree.tokens.at(parse_error.loc());
         const loc = tree.tokenLocation(0, parse_error.loc());
-        try stderr.print("(memory buffer):{}:{}: error: ", loc.line + 1, loc.column + 1);
+        try stderr.print("(memory buffer):{}:{}: error: ", .{ loc.line + 1, loc.column + 1 });
         try tree.renderError(parse_error, stderr);
-        try stderr.print("\n{}\n", source[loc.line_start..loc.line_end]);
+        try stderr.print("\n{}\n", .{source[loc.line_start..loc.line_end]});
         {
             var i: usize = 0;
             while (i < loc.column) : (i += 1) {
@@ -2743,16 +2727,16 @@ fn testTransform(source: []const u8, expected_source: []const u8) !void {
         var anything_changed: bool = undefined;
         const result_source = try testParse(source, &failing_allocator.allocator, &anything_changed);
         if (!mem.eql(u8, result_source, expected_source)) {
-            warn("\n====== expected this output: =========\n");
-            warn("{}", expected_source);
-            warn("\n======== instead found this: =========\n");
-            warn("{}", result_source);
-            warn("\n======================================\n");
+            warn("\n====== expected this output: =========\n", .{});
+            warn("{}", .{expected_source});
+            warn("\n======== instead found this: =========\n", .{});
+            warn("{}", .{result_source});
+            warn("\n======================================\n", .{});
             return error.TestFailed;
         }
         const changes_expected = source.ptr != expected_source.ptr;
         if (anything_changed != changes_expected) {
-            warn("std.zig.render returned {} instead of {}\n", anything_changed, changes_expected);
+            warn("std.zig.render returned {} instead of {}\n", .{ anything_changed, changes_expected });
             return error.TestFailed;
         }
         std.testing.expect(anything_changed == changes_expected);
@@ -2772,12 +2756,14 @@ fn testTransform(source: []const u8, expected_source: []const u8) !void {
                 if (failing_allocator.allocated_bytes != failing_allocator.freed_bytes) {
                     warn(
                         "\nfail_index: {}/{}\nallocated bytes: {}\nfreed bytes: {}\nallocations: {}\ndeallocations: {}\n",
-                        fail_index,
-                        needed_alloc_count,
-                        failing_allocator.allocated_bytes,
-                        failing_allocator.freed_bytes,
-                        failing_allocator.allocations,
-                        failing_allocator.deallocations,
+                        .{
+                            fail_index,
+                            needed_alloc_count,
+                            failing_allocator.allocated_bytes,
+                            failing_allocator.freed_bytes,
+                            failing_allocator.allocations,
+                            failing_allocator.deallocations,
+                        },
                     );
                     return error.MemoryLeakDetected;
                 }
diff --git a/lib/std/zig/render.zig b/lib/std/zig/render.zig
index 8b0ce7ee1a..09482b5109 100644
--- a/lib/std/zig/render.zig
+++ b/lib/std/zig/render.zig
@@ -76,7 +76,7 @@ fn renderRoot(
     // render all the line comments at the beginning of the file
     while (tok_it.next()) |token| {
         if (token.id != .LineComment) break;
-        try stream.print("{}\n", mem.trimRight(u8, tree.tokenSlicePtr(token), " "));
+        try stream.print("{}\n", .{mem.trimRight(u8, tree.tokenSlicePtr(token), " ")});
         if (tok_it.peek()) |next_token| {
             const loc = tree.tokenLocationPtr(token.end, next_token);
             if (loc.line >= 2) {
@@ -1226,7 +1226,7 @@ fn renderExpression(
 
             var skip_first_indent = true;
             if (tree.tokens.at(multiline_str_literal.firstToken() - 1).id != .LineComment) {
-                try stream.print("\n");
+                try stream.print("\n", .{});
                 skip_first_indent = false;
             }
 
@@ -2129,7 +2129,7 @@ fn renderTokenOffset(
 
     var loc = tree.tokenLocationPtr(token.end, next_token);
     if (loc.line == 0) {
-        try stream.print(" {}", mem.trimRight(u8, tree.tokenSlicePtr(next_token), " "));
+        try stream.print(" {}", .{mem.trimRight(u8, tree.tokenSlicePtr(next_token), " ")});
         offset = 2;
         token = next_token;
         next_token = tree.tokens.at(token_index + offset);
diff --git a/lib/std/zig/tokenizer.zig b/lib/std/zig/tokenizer.zig
index e7d2b41784..93fbfa18a7 100644
--- a/lib/std/zig/tokenizer.zig
+++ b/lib/std/zig/tokenizer.zig
@@ -330,7 +330,7 @@ pub const Tokenizer = struct {
 
     /// For debugging purposes
     pub fn dump(self: *Tokenizer, token: *const Token) void {
-        std.debug.warn("{} \"{}\"\n", @tagName(token.id), self.buffer[token.start..token.end]);
+        std.debug.warn("{} \"{}\"\n", .{ @tagName(token.id), self.buffer[token.start..token.end] });
     }
 
     pub fn init(buffer: []const u8) Tokenizer {
@@ -1576,7 +1576,7 @@ fn testTokenize(source: []const u8, expected_tokens: []const Token.Id) void {
     for (expected_tokens) |expected_token_id| {
         const token = tokenizer.next();
         if (token.id != expected_token_id) {
-            std.debug.panic("expected {}, found {}\n", @tagName(expected_token_id), @tagName(token.id));
+            std.debug.panic("expected {}, found {}\n", .{ @tagName(expected_token_id), @tagName(token.id) });
         }
     }
     const last_token = tokenizer.next();
diff --git a/src-self-hosted/arg.zig b/src-self-hosted/arg.zig
index 3d12bb3e83..066080f9ef 100644
--- a/src-self-hosted/arg.zig
+++ b/src-self-hosted/arg.zig
@@ -98,15 +98,15 @@ pub const Args = struct {
                         const flag_args = readFlagArguments(allocator, args, flag.required, flag.allowed_set, &i) catch |err| {
                             switch (err) {
                                 error.ArgumentNotInAllowedSet => {
-                                    std.debug.warn("argument '{}' is invalid for flag '{}'\n", args[i], arg);
-                                    std.debug.warn("allowed options are ");
+                                    std.debug.warn("argument '{}' is invalid for flag '{}'\n", .{ args[i], arg });
+                                    std.debug.warn("allowed options are ", .{});
                                     for (flag.allowed_set.?) |possible| {
-                                        std.debug.warn("'{}' ", possible);
+                                        std.debug.warn("'{}' ", .{possible});
                                     }
-                                    std.debug.warn("\n");
+                                    std.debug.warn("\n", .{});
                                 },
                                 error.MissingFlagArguments => {
-                                    std.debug.warn("missing argument for flag: {}\n", arg);
+                                    std.debug.warn("missing argument for flag: {}\n", .{arg});
                                 },
                                 else => {},
                             }
@@ -134,7 +134,7 @@ pub const Args = struct {
                 }
 
                 // TODO: Better errors with context, global error state and return is sufficient.
-                std.debug.warn("could not match flag: {}\n", arg);
+                std.debug.warn("could not match flag: {}\n", .{arg});
                 return error.UnknownFlag;
             } else {
                 try parsed.positionals.append(arg);
diff --git a/src-self-hosted/codegen.zig b/src-self-hosted/codegen.zig
index 030112985a..702f2c2883 100644
--- a/src-self-hosted/codegen.zig
+++ b/src-self-hosted/codegen.zig
@@ -45,13 +45,11 @@ pub async fn renderToLlvm(comp: *Compilation, fn_val: *Value.Fn, code: *ir.Code)
 
     // Don't use ZIG_VERSION_STRING here. LLVM misparses it when it includes
     // the git revision.
-    const producer = try std.Buffer.allocPrint(
-        &code.arena.allocator,
-        "zig {}.{}.{}",
+    const producer = try std.Buffer.allocPrint(&code.arena.allocator, "zig {}.{}.{}", .{
         @as(u32, c.ZIG_VERSION_MAJOR),
         @as(u32, c.ZIG_VERSION_MINOR),
         @as(u32, c.ZIG_VERSION_PATCH),
-    );
+    });
     const flags = "";
     const runtime_version = 0;
     const compile_unit_file = llvm.CreateFile(
@@ -93,7 +91,7 @@ pub async fn renderToLlvm(comp: *Compilation, fn_val: *Value.Fn, code: *ir.Code)
     llvm.DIBuilderFinalize(dibuilder);
 
     if (comp.verbose_llvm_ir) {
-        std.debug.warn("raw module:\n");
+        std.debug.warn("raw module:\n", .{});
         llvm.DumpModule(ofile.module);
     }
 
@@ -120,18 +118,18 @@ pub async fn renderToLlvm(comp: *Compilation, fn_val: *Value.Fn, code: *ir.Code)
         is_small,
     )) {
         if (std.debug.runtime_safety) {
-            std.debug.panic("unable to write object file {}: {s}\n", output_path.toSliceConst(), err_msg);
+            std.debug.panic("unable to write object file {}: {s}\n", .{ output_path.toSliceConst(), err_msg });
         }
         return error.WritingObjectFileFailed;
     }
     //validate_inline_fns(g); TODO
     fn_val.containing_object = output_path;
     if (comp.verbose_llvm_ir) {
-        std.debug.warn("optimized module:\n");
+        std.debug.warn("optimized module:\n", .{});
         llvm.DumpModule(ofile.module);
     }
     if (comp.verbose_link) {
-        std.debug.warn("created {}\n", output_path.toSliceConst());
+        std.debug.warn("created {}\n", .{output_path.toSliceConst()});
     }
 }
 
diff --git a/src-self-hosted/compilation.zig b/src-self-hosted/compilation.zig
index a825ba3903..47ea595cad 100644
--- a/src-self-hosted/compilation.zig
+++ b/src-self-hosted/compilation.zig
@@ -807,7 +807,7 @@ pub const Compilation = struct {
                 root_scope.realpath,
                 max_src_size,
             ) catch |err| {
-                try self.addCompileErrorCli(root_scope.realpath, "unable to open: {}", @errorName(err));
+                try self.addCompileErrorCli(root_scope.realpath, "unable to open: {}", .{@errorName(err)});
                 return;
             };
             errdefer self.gpa().free(source_code);
@@ -878,7 +878,7 @@ pub const Compilation = struct {
                         try self.addCompileError(tree_scope, Span{
                             .first = fn_proto.fn_token,
                             .last = fn_proto.fn_token + 1,
-                        }, "missing function name");
+                        }, "missing function name", .{});
                         continue;
                     };
 
@@ -942,7 +942,7 @@ pub const Compilation = struct {
             const root_scope = blk: {
                 // TODO async/await std.fs.realpath
                 const root_src_real_path = std.fs.realpathAlloc(self.gpa(), root_src_path) catch |err| {
-                    try self.addCompileErrorCli(root_src_path, "unable to open: {}", @errorName(err));
+                    try self.addCompileErrorCli(root_src_path, "unable to open: {}", .{@errorName(err)});
                     return;
                 };
                 errdefer self.gpa().free(root_src_real_path);
@@ -991,7 +991,7 @@ pub const Compilation = struct {
         defer unanalyzed_code.destroy(comp.gpa());
 
         if (comp.verbose_ir) {
-            std.debug.warn("unanalyzed:\n");
+            std.debug.warn("unanalyzed:\n", .{});
             unanalyzed_code.dump();
         }
 
@@ -1003,7 +1003,7 @@ pub const Compilation = struct {
         errdefer analyzed_code.destroy(comp.gpa());
 
         if (comp.verbose_ir) {
-            std.debug.warn("analyzed:\n");
+            std.debug.warn("analyzed:\n", .{});
             analyzed_code.dump();
         }
 
@@ -1048,14 +1048,14 @@ pub const Compilation = struct {
 
         const gop = try locked_table.getOrPut(decl.name);
         if (gop.found_existing) {
-            try self.addCompileError(decl.tree_scope, decl.getSpan(), "redefinition of '{}'", decl.name);
+            try self.addCompileError(decl.tree_scope, decl.getSpan(), "redefinition of '{}'", .{decl.name});
             // TODO note: other definition here
         } else {
             gop.kv.value = decl;
         }
     }
 
-    fn addCompileError(self: *Compilation, tree_scope: *Scope.AstTree, span: Span, comptime fmt: []const u8, args: ...) !void {
+    fn addCompileError(self: *Compilation, tree_scope: *Scope.AstTree, span: Span, comptime fmt: []const u8, args: var) !void {
         const text = try std.fmt.allocPrint(self.gpa(), fmt, args);
         errdefer self.gpa().free(text);
 
@@ -1065,7 +1065,7 @@ pub const Compilation = struct {
         try self.prelink_group.call(addCompileErrorAsync, self, msg);
     }
 
-    fn addCompileErrorCli(self: *Compilation, realpath: []const u8, comptime fmt: []const u8, args: ...) !void {
+    fn addCompileErrorCli(self: *Compilation, realpath: []const u8, comptime fmt: []const u8, args: var) !void {
         const text = try std.fmt.allocPrint(self.gpa(), fmt, args);
         errdefer self.gpa().free(text);
 
@@ -1092,12 +1092,9 @@ pub const Compilation = struct {
         defer exported_symbol_names.release();
 
         if (try exported_symbol_names.value.put(decl.name, decl)) |other_decl| {
-            try self.addCompileError(
-                decl.tree_scope,
-                decl.getSpan(),
-                "exported symbol collision: '{}'",
+            try self.addCompileError(decl.tree_scope, decl.getSpan(), "exported symbol collision: '{}'", .{
                 decl.name,
-            );
+            });
             // TODO add error note showing location of other symbol
         }
     }
@@ -1162,7 +1159,7 @@ pub const Compilation = struct {
         const tmp_dir = try self.getTmpDir();
         const file_prefix = self.getRandomFileName();
 
-        const file_name = try std.fmt.allocPrint(self.gpa(), "{}{}", file_prefix[0..], suffix);
+        const file_name = try std.fmt.allocPrint(self.gpa(), "{}{}", .{ file_prefix[0..], suffix });
         defer self.gpa().free(file_name);
 
         const full_path = try std.fs.path.join(self.gpa(), &[_][]const u8{ tmp_dir, file_name[0..] });
@@ -1303,7 +1300,7 @@ fn generateDeclFn(comp: *Compilation, fn_decl: *Decl.Fn) !void {
             try comp.addCompileError(tree_scope, Span{
                 .first = param_decl.firstToken(),
                 .last = param_decl.type_node.firstToken(),
-            }, "missing parameter name");
+            }, "missing parameter name", .{});
             return error.SemanticAnalysisFailed;
         };
         const param_name = tree_scope.tree.tokenSlice(name_token);
diff --git a/src-self-hosted/dep_tokenizer.zig b/src-self-hosted/dep_tokenizer.zig
index 9509aab702..b4e46bc1ad 100644
--- a/src-self-hosted/dep_tokenizer.zig
+++ b/src-self-hosted/dep_tokenizer.zig
@@ -38,7 +38,7 @@ pub const Tokenizer = struct {
                     },
                     .target => |*target| switch (char) {
                         '\t', '\n', '\r', ' ' => {
-                            return self.errorIllegalChar(self.index, char, "invalid target");
+                            return self.errorIllegalChar(self.index, char, "invalid target", .{});
                         },
                         '$' => {
                             self.state = State{ .target_dollar_sign = target.* };
@@ -59,7 +59,7 @@ pub const Tokenizer = struct {
                     },
                     .target_reverse_solidus => |*target| switch (char) {
                         '\t', '\n', '\r' => {
-                            return self.errorIllegalChar(self.index, char, "bad target escape");
+                            return self.errorIllegalChar(self.index, char, "bad target escape", .{});
                         },
                         ' ', '#', '\\' => {
                             try target.appendByte(char);
@@ -84,7 +84,7 @@ pub const Tokenizer = struct {
                             break; // advance
                         },
                         else => {
-                            return self.errorIllegalChar(self.index, char, "expecting '$'");
+                            return self.errorIllegalChar(self.index, char, "expecting '$'", .{});
                         },
                     },
                     .target_colon => |*target| switch (char) {
@@ -161,7 +161,7 @@ pub const Tokenizer = struct {
                             break; // advance
                         },
                         else => {
-                            return self.errorIllegalChar(self.index, char, "continuation expecting end-of-line");
+                            return self.errorIllegalChar(self.index, char, "continuation expecting end-of-line", .{});
                         },
                     },
                     .rhs_continuation_linefeed => switch (char) {
@@ -170,7 +170,7 @@ pub const Tokenizer = struct {
                             break; // advance
                         },
                         else => {
-                            return self.errorIllegalChar(self.index, char, "continuation expecting end-of-line");
+                            return self.errorIllegalChar(self.index, char, "continuation expecting end-of-line", .{});
                         },
                     },
                     .prereq_quote => |*prereq| switch (char) {
@@ -231,7 +231,7 @@ pub const Tokenizer = struct {
                             return Token{ .id = .prereq, .bytes = bytes };
                         },
                         else => {
-                            return self.errorIllegalChar(self.index, char, "continuation expecting end-of-line");
+                            return self.errorIllegalChar(self.index, char, "continuation expecting end-of-line", .{});
                         },
                     },
                 }
@@ -249,13 +249,13 @@ pub const Tokenizer = struct {
             .rhs_continuation_linefeed,
             => {},
             .target => |target| {
-                return self.errorPosition(idx, target.toSlice(), "incomplete target");
+                return self.errorPosition(idx, target.toSlice(), "incomplete target", .{});
             },
             .target_reverse_solidus,
             .target_dollar_sign,
             => {
                 const index = self.index - 1;
-                return self.errorIllegalChar(idx, self.bytes[idx], "incomplete escape");
+                return self.errorIllegalChar(idx, self.bytes[idx], "incomplete escape", .{});
             },
             .target_colon => |target| {
                 const bytes = target.toSlice();
@@ -278,7 +278,7 @@ pub const Tokenizer = struct {
                 self.state = State{ .lhs = {} };
             },
             .prereq_quote => |prereq| {
-                return self.errorPosition(idx, prereq.toSlice(), "incomplete quoted prerequisite");
+                return self.errorPosition(idx, prereq.toSlice(), "incomplete quoted prerequisite", .{});
             },
             .prereq => |prereq| {
                 const bytes = prereq.toSlice();
@@ -299,29 +299,29 @@ pub const Tokenizer = struct {
         return null;
     }
 
-    fn errorf(self: *Tokenizer, comptime fmt: []const u8, args: ...) Error {
+    fn errorf(self: *Tokenizer, comptime fmt: []const u8, args: var) Error {
         self.error_text = (try std.Buffer.allocPrint(&self.arena.allocator, fmt, args)).toSlice();
         return Error.InvalidInput;
     }
 
-    fn errorPosition(self: *Tokenizer, position: usize, bytes: []const u8, comptime fmt: []const u8, args: ...) Error {
+    fn errorPosition(self: *Tokenizer, position: usize, bytes: []const u8, comptime fmt: []const u8, args: var) Error {
         var buffer = try std.Buffer.initSize(&self.arena.allocator, 0);
         std.fmt.format(&buffer, anyerror, std.Buffer.append, fmt, args) catch {};
         try buffer.append(" '");
         var out = makeOutput(std.Buffer.append, &buffer);
         try printCharValues(&out, bytes);
         try buffer.append("'");
-        std.fmt.format(&buffer, anyerror, std.Buffer.append, " at position {}", position - (bytes.len - 1)) catch {};
+        std.fmt.format(&buffer, anyerror, std.Buffer.append, " at position {}", .{position - (bytes.len - 1)}) catch {};
         self.error_text = buffer.toSlice();
         return Error.InvalidInput;
     }
 
-    fn errorIllegalChar(self: *Tokenizer, position: usize, char: u8, comptime fmt: []const u8, args: ...) Error {
+    fn errorIllegalChar(self: *Tokenizer, position: usize, char: u8, comptime fmt: []const u8, args: var) Error {
         var buffer = try std.Buffer.initSize(&self.arena.allocator, 0);
         try buffer.append("illegal char ");
         var out = makeOutput(std.Buffer.append, &buffer);
         try printUnderstandableChar(&out, char);
-        std.fmt.format(&buffer, anyerror, std.Buffer.append, " at position {}", position) catch {};
+        std.fmt.format(&buffer, anyerror, std.Buffer.append, " at position {}", .{position}) catch {};
         if (fmt.len != 0) std.fmt.format(&buffer, anyerror, std.Buffer.append, ": " ++ fmt, args) catch {};
         self.error_text = buffer.toSlice();
         return Error.InvalidInput;
@@ -998,7 +998,7 @@ fn printCharValues(out: var, bytes: []const u8) !void {
 
 fn printUnderstandableChar(out: var, char: u8) !void {
     if (!std.ascii.isPrint(char) or char == ' ') {
-        std.fmt.format(out.context, anyerror, out.output, "\\x{X:2}", char) catch {};
+        std.fmt.format(out.context, anyerror, out.output, "\\x{X:2}", .{char}) catch {};
     } else {
         try out.write("'");
         try out.write(&[_]u8{printable_char_tab[char]});
diff --git a/src-self-hosted/errmsg.zig b/src-self-hosted/errmsg.zig
index 9782fdda1c..c1ebf0058e 100644
--- a/src-self-hosted/errmsg.zig
+++ b/src-self-hosted/errmsg.zig
@@ -231,7 +231,7 @@ pub const Msg = struct {
     pub fn printToStream(msg: *const Msg, stream: var, color_on: bool) !void {
         switch (msg.data) {
             .Cli => {
-                try stream.print("{}:-:-: error: {}\n", msg.realpath, msg.text);
+                try stream.print("{}:-:-: error: {}\n", .{ msg.realpath, msg.text });
                 return;
             },
             else => {},
@@ -254,24 +254,22 @@ pub const Msg = struct {
         const start_loc = tree.tokenLocationPtr(0, first_token);
         const end_loc = tree.tokenLocationPtr(first_token.end, last_token);
         if (!color_on) {
-            try stream.print(
-                "{}:{}:{}: error: {}\n",
+            try stream.print("{}:{}:{}: error: {}\n", .{
                 path,
                 start_loc.line + 1,
                 start_loc.column + 1,
                 msg.text,
-            );
+            });
             return;
         }
 
-        try stream.print(
-            "{}:{}:{}: error: {}\n{}\n",
+        try stream.print("{}:{}:{}: error: {}\n{}\n", .{
             path,
             start_loc.line + 1,
             start_loc.column + 1,
             msg.text,
             tree.source[start_loc.line_start..start_loc.line_end],
-        );
+        });
         try stream.writeByteNTimes(' ', start_loc.column);
         try stream.writeByteNTimes('~', last_token.end - first_token.start);
         try stream.write("\n");
diff --git a/src-self-hosted/introspect.zig b/src-self-hosted/introspect.zig
index 8f822c79df..67181b40a8 100644
--- a/src-self-hosted/introspect.zig
+++ b/src-self-hosted/introspect.zig
@@ -48,7 +48,7 @@ pub fn resolveZigLibDir(allocator: *mem.Allocator) ![]u8 {
             \\Unable to find zig lib directory: {}.
             \\Reinstall Zig or use --zig-install-prefix.
             \\
-        , @errorName(err));
+        , .{@errorName(err)});
 
         return error.ZigLibDirNotFound;
     };
diff --git a/src-self-hosted/ir.zig b/src-self-hosted/ir.zig
index 1d11d7969d..741dbb6e3d 100644
--- a/src-self-hosted/ir.zig
+++ b/src-self-hosted/ir.zig
@@ -32,16 +32,16 @@ pub const IrVal = union(enum) {
 
     pub fn dump(self: IrVal) void {
         switch (self) {
-            .Unknown => std.debug.warn("Unknown"),
+            .Unknown => std.debug.warn("Unknown", .{}),
             .KnownType => |typ| {
-                std.debug.warn("KnownType(");
+                std.debug.warn("KnownType(", .{});
                 typ.dump();
-                std.debug.warn(")");
+                std.debug.warn(")", .{});
             },
             .KnownValue => |value| {
-                std.debug.warn("KnownValue(");
+                std.debug.warn("KnownValue(", .{});
                 value.dump();
-                std.debug.warn(")");
+                std.debug.warn(")", .{});
             },
         }
     }
@@ -90,9 +90,9 @@ pub const Inst = struct {
         inline while (i < @memberCount(Id)) : (i += 1) {
             if (base.id == @field(Id, @memberName(Id, i))) {
                 const T = @field(Inst, @memberName(Id, i));
-                std.debug.warn("#{} = {}(", base.debug_id, @tagName(base.id));
+                std.debug.warn("#{} = {}(", .{ base.debug_id, @tagName(base.id) });
                 @fieldParentPtr(T, "base", base).dump();
-                std.debug.warn(")");
+                std.debug.warn(")", .{});
                 return;
             }
         }
@@ -173,7 +173,7 @@ pub const Inst = struct {
         if (self.isCompTime()) {
             return self.val.KnownValue;
         } else {
-            try ira.addCompileError(self.span, "unable to evaluate constant expression");
+            try ira.addCompileError(self.span, "unable to evaluate constant expression", .{});
             return error.SemanticAnalysisFailed;
         }
     }
@@ -269,11 +269,11 @@ pub const Inst = struct {
         const ir_val_init = IrVal.Init.Unknown;
 
         pub fn dump(self: *const Call) void {
-            std.debug.warn("#{}(", self.params.fn_ref.debug_id);
+            std.debug.warn("#{}(", .{self.params.fn_ref.debug_id});
             for (self.params.args) |arg| {
-                std.debug.warn("#{},", arg.debug_id);
+                std.debug.warn("#{},", .{arg.debug_id});
             }
-            std.debug.warn(")");
+            std.debug.warn(")", .{});
         }
 
         pub fn hasSideEffects(self: *const Call) bool {
@@ -284,19 +284,17 @@ pub const Inst = struct {
             const fn_ref = try self.params.fn_ref.getAsParam();
             const fn_ref_type = fn_ref.getKnownType();
             const fn_type = fn_ref_type.cast(Type.Fn) orelse {
-                try ira.addCompileError(fn_ref.span, "type '{}' not a function", fn_ref_type.name);
+                try ira.addCompileError(fn_ref.span, "type '{}' not a function", .{fn_ref_type.name});
                 return error.SemanticAnalysisFailed;
             };
 
             const fn_type_param_count = fn_type.paramCount();
 
             if (fn_type_param_count != self.params.args.len) {
-                try ira.addCompileError(
-                    self.base.span,
-                    "expected {} arguments, found {}",
+                try ira.addCompileError(self.base.span, "expected {} arguments, found {}", .{
                     fn_type_param_count,
                     self.params.args.len,
-                );
+                });
                 return error.SemanticAnalysisFailed;
             }
 
@@ -375,7 +373,7 @@ pub const Inst = struct {
         const ir_val_init = IrVal.Init.NoReturn;
 
         pub fn dump(self: *const Return) void {
-            std.debug.warn("#{}", self.params.return_value.debug_id);
+            std.debug.warn("#{}", .{self.params.return_value.debug_id});
         }
 
         pub fn hasSideEffects(self: *const Return) bool {
@@ -509,7 +507,7 @@ pub const Inst = struct {
         const ir_val_init = IrVal.Init.Unknown;
 
         pub fn dump(inst: *const VarPtr) void {
-            std.debug.warn("{}", inst.params.var_scope.name);
+            std.debug.warn("{}", .{inst.params.var_scope.name});
         }
 
         pub fn hasSideEffects(inst: *const VarPtr) bool {
@@ -567,7 +565,7 @@ pub const Inst = struct {
             const target = try self.params.target.getAsParam();
             const target_type = target.getKnownType();
             if (target_type.id != .Pointer) {
-                try ira.addCompileError(self.base.span, "dereference of non pointer type '{}'", target_type.name);
+                try ira.addCompileError(self.base.span, "dereference of non pointer type '{}'", .{target_type.name});
                 return error.SemanticAnalysisFailed;
             }
             const ptr_type = @fieldParentPtr(Type.Pointer, "base", target_type);
@@ -705,7 +703,7 @@ pub const Inst = struct {
         const ir_val_init = IrVal.Init.Unknown;
 
         pub fn dump(self: *const CheckVoidStmt) void {
-            std.debug.warn("#{}", self.params.target.debug_id);
+            std.debug.warn("#{}", .{self.params.target.debug_id});
         }
 
         pub fn hasSideEffects(inst: *const CheckVoidStmt) bool {
@@ -715,7 +713,7 @@ pub const Inst = struct {
         pub fn analyze(self: *const CheckVoidStmt, ira: *Analyze) !*Inst {
             const target = try self.params.target.getAsParam();
             if (target.getKnownType().id != .Void) {
-                try ira.addCompileError(self.base.span, "expression value is ignored");
+                try ira.addCompileError(self.base.span, "expression value is ignored", .{});
                 return error.SemanticAnalysisFailed;
             }
             return ira.irb.buildConstVoid(self.base.scope, self.base.span, true);
@@ -801,7 +799,7 @@ pub const Inst = struct {
         const ir_val_init = IrVal.Init.Unknown;
 
         pub fn dump(inst: *const AddImplicitReturnType) void {
-            std.debug.warn("#{}", inst.params.target.debug_id);
+            std.debug.warn("#{}", .{inst.params.target.debug_id});
         }
 
         pub fn hasSideEffects(inst: *const AddImplicitReturnType) bool {
@@ -826,7 +824,7 @@ pub const Inst = struct {
         const ir_val_init = IrVal.Init.Unknown;
 
         pub fn dump(inst: *const TestErr) void {
-            std.debug.warn("#{}", inst.params.target.debug_id);
+            std.debug.warn("#{}", .{inst.params.target.debug_id});
         }
 
         pub fn hasSideEffects(inst: *const TestErr) bool {
@@ -888,7 +886,7 @@ pub const Inst = struct {
         const ir_val_init = IrVal.Init.Unknown;
 
         pub fn dump(inst: *const TestCompTime) void {
-            std.debug.warn("#{}", inst.params.target.debug_id);
+            std.debug.warn("#{}", .{inst.params.target.debug_id});
         }
 
         pub fn hasSideEffects(inst: *const TestCompTime) bool {
@@ -971,11 +969,11 @@ pub const Code = struct {
     pub fn dump(self: *Code) void {
         var bb_i: usize = 0;
         for (self.basic_block_list.toSliceConst()) |bb| {
-            std.debug.warn("{s}_{}:\n", bb.name_hint, bb.debug_id);
+            std.debug.warn("{s}_{}:\n", .{ bb.name_hint, bb.debug_id });
             for (bb.instruction_list.toSliceConst()) |instr| {
-                std.debug.warn("  ");
+                std.debug.warn("  ", .{});
                 instr.dump();
-                std.debug.warn("\n");
+                std.debug.warn("\n", .{});
             }
         }
     }
@@ -993,6 +991,7 @@ pub const Code = struct {
                     self.tree_scope,
                     ret_value.span,
                     "unable to evaluate constant expression",
+                    .{},
                 );
                 return error.SemanticAnalysisFailed;
             } else if (inst.hasSideEffects()) {
@@ -1000,6 +999,7 @@ pub const Code = struct {
                     self.tree_scope,
                     inst.span,
                     "unable to evaluate constant expression",
+                    .{},
                 );
                 return error.SemanticAnalysisFailed;
             }
@@ -1359,7 +1359,7 @@ pub const Builder = struct {
                     irb.code.tree_scope,
                     src_span,
                     "invalid character in string literal: '{c}'",
-                    str_token[bad_index],
+                    .{str_token[bad_index]},
                 );
                 return error.SemanticAnalysisFailed;
             },
@@ -1523,6 +1523,7 @@ pub const Builder = struct {
                         irb.code.tree_scope,
                         src_span,
                         "return expression outside function definition",
+                        .{},
                     );
                     return error.SemanticAnalysisFailed;
                 }
@@ -1533,6 +1534,7 @@ pub const Builder = struct {
                             irb.code.tree_scope,
                             src_span,
                             "cannot return from defer expression",
+                            .{},
                         );
                         scope_defer_expr.reported_err = true;
                     }
@@ -1629,7 +1631,7 @@ pub const Builder = struct {
             }
         } else |err| switch (err) {
             error.Overflow => {
-                try irb.comp.addCompileError(irb.code.tree_scope, src_span, "integer too large");
+                try irb.comp.addCompileError(irb.code.tree_scope, src_span, "integer too large", .{});
                 return error.SemanticAnalysisFailed;
             },
             error.OutOfMemory => return error.OutOfMemory,
@@ -1663,7 +1665,7 @@ pub const Builder = struct {
         // TODO put a variable of same name with invalid type in global scope
         // so that future references to this same name will find a variable with an invalid type
 
-        try irb.comp.addCompileError(irb.code.tree_scope, src_span, "unknown identifier '{}'", name);
+        try irb.comp.addCompileError(irb.code.tree_scope, src_span, "unknown identifier '{}'", .{name});
         return error.SemanticAnalysisFailed;
     }
 
@@ -2008,7 +2010,7 @@ const Analyze = struct {
             const next_instruction = ira.parent_basic_block.instruction_list.at(ira.instruction_index);
 
             if (!next_instruction.is_generated) {
-                try ira.addCompileError(next_instruction.span, "unreachable code");
+                try ira.addCompileError(next_instruction.span, "unreachable code", .{});
                 break;
             }
             ira.instruction_index += 1;
@@ -2041,7 +2043,7 @@ const Analyze = struct {
         }
     }
 
-    fn addCompileError(self: *Analyze, span: Span, comptime fmt: []const u8, args: ...) !void {
+    fn addCompileError(self: *Analyze, span: Span, comptime fmt: []const u8, args: var) !void {
         return self.irb.comp.addCompileError(self.irb.code.tree_scope, span, fmt, args);
     }
 
@@ -2330,12 +2332,10 @@ const Analyze = struct {
                 break :cast;
             };
             if (!fits) {
-                try ira.addCompileError(
-                    source_instr.span,
-                    "integer value '{}' cannot be stored in type '{}'",
+                try ira.addCompileError(source_instr.span, "integer value '{}' cannot be stored in type '{}'", .{
                     from_int,
                     dest_type.name,
-                );
+                });
                 return error.SemanticAnalysisFailed;
             }
 
@@ -2498,12 +2498,10 @@ const Analyze = struct {
         //    }
         //}
 
-        try ira.addCompileError(
-            source_instr.span,
-            "expected type '{}', found '{}'",
+        try ira.addCompileError(source_instr.span, "expected type '{}', found '{}'", .{
             dest_type.name,
             from_type.name,
-        );
+        });
         //ErrorMsg *parent_msg = ir_add_error_node(ira, source_instr->source_node,
         //    buf_sprintf("expected type '%s', found '%s'",
         //        buf_ptr(&wanted_type->name),
diff --git a/src-self-hosted/libc_installation.zig b/src-self-hosted/libc_installation.zig
index b339a07c90..970fc97823 100644
--- a/src-self-hosted/libc_installation.zig
+++ b/src-self-hosted/libc_installation.zig
@@ -65,7 +65,7 @@ pub const LibCInstallation = struct {
             if (line.len == 0 or line[0] == '#') continue;
             var line_it = std.mem.separate(line, "=");
             const name = line_it.next() orelse {
-                try stderr.print("missing equal sign after field name\n");
+                try stderr.print("missing equal sign after field name\n", .{});
                 return error.ParseError;
             };
             const value = line_it.rest();
@@ -83,7 +83,7 @@ pub const LibCInstallation = struct {
                         },
                         else => {
                             if (value.len == 0) {
-                                try stderr.print("field cannot be empty: {}\n", key);
+                                try stderr.print("field cannot be empty: {}\n", .{key});
                                 return error.ParseError;
                             }
                             const dupe = try std.mem.dupe(allocator, u8, value);
@@ -97,7 +97,7 @@ pub const LibCInstallation = struct {
         }
         for (found_keys) |found_key, i| {
             if (!found_key.found) {
-                try stderr.print("missing field: {}\n", keys[i]);
+                try stderr.print("missing field: {}\n", .{keys[i]});
                 return error.ParseError;
             }
         }
@@ -105,6 +105,11 @@ pub const LibCInstallation = struct {
 
     pub fn render(self: *const LibCInstallation, out: *std.io.OutStream(fs.File.WriteError)) !void {
         @setEvalBranchQuota(4000);
+        const lib_dir = self.lib_dir orelse "";
+        const static_lib_dir = self.static_lib_dir orelse "";
+        const msvc_lib_dir = self.msvc_lib_dir orelse "";
+        const kernel32_lib_dir = self.kernel32_lib_dir orelse "";
+        const dynamic_linker_path = self.dynamic_linker_path orelse util.getDynamicLinkerPath(Target{ .Native = {} });
         try out.print(
             \\# The directory that contains `stdlib.h`.
             \\# On Linux, can be found with: `cc -E -Wp,-v -xc /dev/null`
@@ -132,14 +137,7 @@ pub const LibCInstallation = struct {
             \\# Only needed when targeting Linux.
             \\dynamic_linker_path={}
             \\
-        ,
-            self.include_dir,
-            self.lib_dir orelse "",
-            self.static_lib_dir orelse "",
-            self.msvc_lib_dir orelse "",
-            self.kernel32_lib_dir orelse "",
-            self.dynamic_linker_path orelse util.getDynamicLinkerPath(Target{ .Native = {} }),
-        );
+        , .{ self.include_dir, lib_dir, static_lib_dir, msvc_lib_dir, kernel32_lib_dir, dynamic_linker_path });
     }
 
     /// Finds the default, native libc.
@@ -255,7 +253,7 @@ pub const LibCInstallation = struct {
         for (searches) |search| {
             result_buf.shrink(0);
             const stream = &std.io.BufferOutStream.init(&result_buf).stream;
-            try stream.print("{}\\Include\\{}\\ucrt", search.path, search.version);
+            try stream.print("{}\\Include\\{}\\ucrt", .{ search.path, search.version });
 
             const stdlib_path = try fs.path.join(
                 allocator,
@@ -282,7 +280,7 @@ pub const LibCInstallation = struct {
         for (searches) |search| {
             result_buf.shrink(0);
             const stream = &std.io.BufferOutStream.init(&result_buf).stream;
-            try stream.print("{}\\Lib\\{}\\ucrt\\", search.path, search.version);
+            try stream.print("{}\\Lib\\{}\\ucrt\\", .{ search.path, search.version });
             switch (builtin.arch) {
                 .i386 => try stream.write("x86"),
                 .x86_64 => try stream.write("x64"),
@@ -360,7 +358,7 @@ pub const LibCInstallation = struct {
         for (searches) |search| {
             result_buf.shrink(0);
             const stream = &std.io.BufferOutStream.init(&result_buf).stream;
-            try stream.print("{}\\Lib\\{}\\um\\", search.path, search.version);
+            try stream.print("{}\\Lib\\{}\\um\\", .{ search.path, search.version });
             switch (builtin.arch) {
                 .i386 => try stream.write("x86\\"),
                 .x86_64 => try stream.write("x64\\"),
@@ -395,7 +393,7 @@ pub const LibCInstallation = struct {
 /// caller owns returned memory
 fn ccPrintFileName(allocator: *Allocator, o_file: []const u8, want_dirname: bool) ![]u8 {
     const cc_exe = std.os.getenv("CC") orelse "cc";
-    const arg1 = try std.fmt.allocPrint(allocator, "-print-file-name={}", o_file);
+    const arg1 = try std.fmt.allocPrint(allocator, "-print-file-name={}", .{o_file});
     defer allocator.free(arg1);
     const argv = [_][]const u8{ cc_exe, arg1 };
 
diff --git a/src-self-hosted/link.zig b/src-self-hosted/link.zig
index 339acfd3ef..935b2f2937 100644
--- a/src-self-hosted/link.zig
+++ b/src-self-hosted/link.zig
@@ -75,9 +75,9 @@ pub fn link(comp: *Compilation) !void {
     if (comp.verbose_link) {
         for (ctx.args.toSliceConst()) |arg, i| {
             const space = if (i == 0) "" else " ";
-            std.debug.warn("{}{s}", space, arg);
+            std.debug.warn("{}{s}", .{ space, arg });
         }
-        std.debug.warn("\n");
+        std.debug.warn("\n", .{});
     }
 
     const extern_ofmt = toExternObjectFormatType(util.getObjectFormat(comp.target));
@@ -94,7 +94,7 @@ pub fn link(comp: *Compilation) !void {
                 // TODO capture these messages and pass them through the system, reporting them through the
                 // event system instead of printing them directly here.
                 // perhaps try to parse and understand them.
-                std.debug.warn("{}\n", ctx.link_msg.toSliceConst());
+                std.debug.warn("{}\n", .{ctx.link_msg.toSliceConst()});
             }
             return error.LinkFailed;
         }
@@ -334,13 +334,13 @@ fn constructLinkerArgsCoff(ctx: *Context) !void {
 
     const is_library = ctx.comp.kind == .Lib;
 
-    const out_arg = try std.fmt.allocPrint(&ctx.arena.allocator, "-OUT:{}\x00", ctx.out_file_path.toSliceConst());
+    const out_arg = try std.fmt.allocPrint(&ctx.arena.allocator, "-OUT:{}\x00", .{ctx.out_file_path.toSliceConst()});
     try ctx.args.append(@ptrCast([*:0]const u8, out_arg.ptr));
 
     if (ctx.comp.haveLibC()) {
-        try ctx.args.append(@ptrCast([*:0]const u8, (try std.fmt.allocPrint(&ctx.arena.allocator, "-LIBPATH:{}\x00", ctx.libc.msvc_lib_dir.?)).ptr));
-        try ctx.args.append(@ptrCast([*:0]const u8, (try std.fmt.allocPrint(&ctx.arena.allocator, "-LIBPATH:{}\x00", ctx.libc.kernel32_lib_dir.?)).ptr));
-        try ctx.args.append(@ptrCast([*:0]const u8, (try std.fmt.allocPrint(&ctx.arena.allocator, "-LIBPATH:{}\x00", ctx.libc.lib_dir.?)).ptr));
+        try ctx.args.append(@ptrCast([*:0]const u8, (try std.fmt.allocPrint(&ctx.arena.allocator, "-LIBPATH:{}\x00", .{ctx.libc.msvc_lib_dir.?})).ptr));
+        try ctx.args.append(@ptrCast([*:0]const u8, (try std.fmt.allocPrint(&ctx.arena.allocator, "-LIBPATH:{}\x00", .{ctx.libc.kernel32_lib_dir.?})).ptr));
+        try ctx.args.append(@ptrCast([*:0]const u8, (try std.fmt.allocPrint(&ctx.arena.allocator, "-LIBPATH:{}\x00", .{ctx.libc.lib_dir.?})).ptr));
     }
 
     if (ctx.link_in_crt) {
@@ -348,17 +348,20 @@ fn constructLinkerArgsCoff(ctx: *Context) !void {
         const d_str = if (ctx.comp.build_mode == .Debug) "d" else "";
 
         if (ctx.comp.is_static) {
-            const cmt_lib_name = try std.fmt.allocPrint(&ctx.arena.allocator, "libcmt{}.lib\x00", d_str);
+            const cmt_lib_name = try std.fmt.allocPrint(&ctx.arena.allocator, "libcmt{}.lib\x00", .{d_str});
             try ctx.args.append(@ptrCast([*:0]const u8, cmt_lib_name.ptr));
         } else {
-            const msvcrt_lib_name = try std.fmt.allocPrint(&ctx.arena.allocator, "msvcrt{}.lib\x00", d_str);
+            const msvcrt_lib_name = try std.fmt.allocPrint(&ctx.arena.allocator, "msvcrt{}.lib\x00", .{d_str});
             try ctx.args.append(@ptrCast([*:0]const u8, msvcrt_lib_name.ptr));
         }
 
-        const vcruntime_lib_name = try std.fmt.allocPrint(&ctx.arena.allocator, "{}vcruntime{}.lib\x00", lib_str, d_str);
+        const vcruntime_lib_name = try std.fmt.allocPrint(&ctx.arena.allocator, "{}vcruntime{}.lib\x00", .{
+            lib_str,
+            d_str,
+        });
         try ctx.args.append(@ptrCast([*:0]const u8, vcruntime_lib_name.ptr));
 
-        const crt_lib_name = try std.fmt.allocPrint(&ctx.arena.allocator, "{}ucrt{}.lib\x00", lib_str, d_str);
+        const crt_lib_name = try std.fmt.allocPrint(&ctx.arena.allocator, "{}ucrt{}.lib\x00", .{ lib_str, d_str });
         try ctx.args.append(@ptrCast([*:0]const u8, crt_lib_name.ptr));
 
         // Visual C++ 2015 Conformance Changes
@@ -508,7 +511,11 @@ fn constructLinkerArgsMachO(ctx: *Context) !void {
         .IPhoneOS => try ctx.args.append("-iphoneos_version_min"),
         .IPhoneOSSimulator => try ctx.args.append("-ios_simulator_version_min"),
     }
-    const ver_str = try std.fmt.allocPrint(&ctx.arena.allocator, "{}.{}.{}\x00", platform.major, platform.minor, platform.micro);
+    const ver_str = try std.fmt.allocPrint(&ctx.arena.allocator, "{}.{}.{}\x00", .{
+        platform.major,
+        platform.minor,
+        platform.micro,
+    });
     try ctx.args.append(@ptrCast([*:0]const u8, ver_str.ptr));
 
     if (ctx.comp.kind == .Exe) {
@@ -584,7 +591,7 @@ fn constructLinkerArgsMachO(ctx: *Context) !void {
                 try ctx.args.append("-lSystem");
             } else {
                 if (mem.indexOfScalar(u8, lib.name, '/') == null) {
-                    const arg = try std.fmt.allocPrint(&ctx.arena.allocator, "-l{}\x00", lib.name);
+                    const arg = try std.fmt.allocPrint(&ctx.arena.allocator, "-l{}\x00", .{lib.name});
                     try ctx.args.append(@ptrCast([*:0]const u8, arg.ptr));
                 } else {
                     const arg = try std.cstr.addNullByte(&ctx.arena.allocator, lib.name);
diff --git a/src-self-hosted/main.zig b/src-self-hosted/main.zig
index 01319e62ce..e5371ce25d 100644
--- a/src-self-hosted/main.zig
+++ b/src-self-hosted/main.zig
@@ -128,7 +128,7 @@ pub fn main() !void {
         }
     }
 
-    try stderr.print("unknown command: {}\n\n", args[1]);
+    try stderr.print("unknown command: {}\n\n", .{args[1]});
     try stderr.write(usage);
     process.argsFree(allocator, args);
     process.exit(1);
@@ -329,14 +329,14 @@ fn buildOutputType(allocator: *Allocator, args: []const []const u8, out_type: Co
             if (cur_pkg.parent) |parent| {
                 cur_pkg = parent;
             } else {
-                try stderr.print("encountered --pkg-end with no matching --pkg-begin\n");
+                try stderr.print("encountered --pkg-end with no matching --pkg-begin\n", .{});
                 process.exit(1);
             }
         }
     }
 
     if (cur_pkg.parent != null) {
-        try stderr.print("unmatched --pkg-begin\n");
+        try stderr.print("unmatched --pkg-begin\n", .{});
         process.exit(1);
     }
 
@@ -345,7 +345,7 @@ fn buildOutputType(allocator: *Allocator, args: []const []const u8, out_type: Co
         0 => null,
         1 => flags.positionals.at(0),
         else => {
-            try stderr.print("unexpected extra parameter: {}\n", flags.positionals.at(1));
+            try stderr.print("unexpected extra parameter: {}\n", .{flags.positionals.at(1)});
             process.exit(1);
         },
     };
@@ -477,13 +477,13 @@ fn processBuildEvents(comp: *Compilation, color: errmsg.Color) void {
 
         switch (build_event) {
             .Ok => {
-                stderr.print("Build {} succeeded\n", count) catch process.exit(1);
+                stderr.print("Build {} succeeded\n", .{count}) catch process.exit(1);
             },
             .Error => |err| {
-                stderr.print("Build {} failed: {}\n", count, @errorName(err)) catch process.exit(1);
+                stderr.print("Build {} failed: {}\n", .{ count, @errorName(err) }) catch process.exit(1);
             },
             .Fail => |msgs| {
-                stderr.print("Build {} compile errors:\n", count) catch process.exit(1);
+                stderr.print("Build {} compile errors:\n", .{count}) catch process.exit(1);
                 for (msgs) |msg| {
                     defer msg.destroy();
                     msg.printToFile(stderr_file, color) catch process.exit(1);
@@ -544,12 +544,11 @@ const Fmt = struct {
 
 fn parseLibcPaths(allocator: *Allocator, libc: *LibCInstallation, libc_paths_file: []const u8) void {
     libc.parse(allocator, libc_paths_file, stderr) catch |err| {
-        stderr.print(
-            "Unable to parse libc path file '{}': {}.\n" ++
-                "Try running `zig libc` to see an example for the native target.\n",
+        stderr.print("Unable to parse libc path file '{}': {}.\n" ++
+            "Try running `zig libc` to see an example for the native target.\n", .{
             libc_paths_file,
             @errorName(err),
-        ) catch {};
+        }) catch {};
         process.exit(1);
     };
 }
@@ -563,7 +562,7 @@ fn cmdLibC(allocator: *Allocator, args: []const []const u8) !void {
             return;
         },
         else => {
-            try stderr.print("unexpected extra parameter: {}\n", args[1]);
+            try stderr.print("unexpected extra parameter: {}\n", .{args[1]});
             process.exit(1);
         },
     }
@@ -572,7 +571,7 @@ fn cmdLibC(allocator: *Allocator, args: []const []const u8) !void {
     defer zig_compiler.deinit();
 
     const libc = zig_compiler.getNativeLibC() catch |err| {
-        stderr.print("unable to find libc: {}\n", @errorName(err)) catch {};
+        stderr.print("unable to find libc: {}\n", .{@errorName(err)}) catch {};
         process.exit(1);
     };
     libc.render(stdout) catch process.exit(1);
@@ -614,7 +613,7 @@ fn cmdFmt(allocator: *Allocator, args: []const []const u8) !void {
         defer allocator.free(source_code);
 
         const tree = std.zig.parse(allocator, source_code) catch |err| {
-            try stderr.print("error parsing stdin: {}\n", err);
+            try stderr.print("error parsing stdin: {}\n", .{err});
             process.exit(1);
         };
         defer tree.deinit();
@@ -718,7 +717,7 @@ async fn fmtPath(fmt: *Fmt, file_path_ref: []const u8, check_mode: bool) FmtErro
         },
         else => {
             // TODO lock stderr printing
-            try stderr.print("unable to open '{}': {}\n", file_path, err);
+            try stderr.print("unable to open '{}': {}\n", .{ file_path, err });
             fmt.any_error = true;
             return;
         },
@@ -726,7 +725,7 @@ async fn fmtPath(fmt: *Fmt, file_path_ref: []const u8, check_mode: bool) FmtErro
     defer fmt.allocator.free(source_code);
 
     const tree = std.zig.parse(fmt.allocator, source_code) catch |err| {
-        try stderr.print("error parsing file '{}': {}\n", file_path, err);
+        try stderr.print("error parsing file '{}': {}\n", .{ file_path, err });
         fmt.any_error = true;
         return;
     };
@@ -747,7 +746,7 @@ async fn fmtPath(fmt: *Fmt, file_path_ref: []const u8, check_mode: bool) FmtErro
     if (check_mode) {
         const anything_changed = try std.zig.render(fmt.allocator, io.null_out_stream, tree);
         if (anything_changed) {
-            try stderr.print("{}\n", file_path);
+            try stderr.print("{}\n", .{file_path});
             fmt.any_error = true;
         }
     } else {
@@ -757,7 +756,7 @@ async fn fmtPath(fmt: *Fmt, file_path_ref: []const u8, check_mode: bool) FmtErro
 
         const anything_changed = try std.zig.render(fmt.allocator, baf.stream(), tree);
         if (anything_changed) {
-            try stderr.print("{}\n", file_path);
+            try stderr.print("{}\n", .{file_path});
             try baf.finish();
         }
     }
@@ -774,7 +773,7 @@ fn cmdTargets(allocator: *Allocator, args: []const []const u8) !void {
             // NOTE: Cannot use empty string, see #918.
             comptime const native_str = if (comptime mem.eql(u8, arch_tag, @tagName(builtin.arch))) " (native)\n" else "\n";
 
-            try stdout.print("  {}{}", arch_tag, native_str);
+            try stdout.print("  {}{}", .{ arch_tag, native_str });
         }
     }
     try stdout.write("\n");
@@ -787,7 +786,7 @@ fn cmdTargets(allocator: *Allocator, args: []const []const u8) !void {
             // NOTE: Cannot use empty string, see #918.
             comptime const native_str = if (comptime mem.eql(u8, os_tag, @tagName(builtin.os))) " (native)\n" else "\n";
 
-            try stdout.print("  {}{}", os_tag, native_str);
+            try stdout.print("  {}{}", .{ os_tag, native_str });
         }
     }
     try stdout.write("\n");
@@ -800,13 +799,13 @@ fn cmdTargets(allocator: *Allocator, args: []const []const u8) !void {
             // NOTE: Cannot use empty string, see #918.
             comptime const native_str = if (comptime mem.eql(u8, abi_tag, @tagName(builtin.abi))) " (native)\n" else "\n";
 
-            try stdout.print("  {}{}", abi_tag, native_str);
+            try stdout.print("  {}{}", .{ abi_tag, native_str });
         }
     }
 }
 
 fn cmdVersion(allocator: *Allocator, args: []const []const u8) !void {
-    try stdout.print("{}\n", std.mem.toSliceConst(u8, c.ZIG_VERSION_STRING));
+    try stdout.print("{}\n", .{std.mem.toSliceConst(u8, c.ZIG_VERSION_STRING)});
 }
 
 const args_test_spec = [_]Flag{Flag.Bool("--help")};
@@ -865,7 +864,7 @@ fn cmdInternal(allocator: *Allocator, args: []const []const u8) !void {
         }
     }
 
-    try stderr.print("unknown sub command: {}\n\n", args[0]);
+    try stderr.print("unknown sub command: {}\n\n", .{args[0]});
     try stderr.write(usage_internal);
 }
 
@@ -878,14 +877,14 @@ fn cmdInternalBuildInfo(allocator: *Allocator, args: []const []const u8) !void {
         \\ZIG_LLVM_CONFIG_EXE  {}
         \\ZIG_DIA_GUIDS_LIB    {}
         \\
-    ,
+    , .{
         std.mem.toSliceConst(u8, c.ZIG_CMAKE_BINARY_DIR),
         std.mem.toSliceConst(u8, c.ZIG_CXX_COMPILER),
         std.mem.toSliceConst(u8, c.ZIG_LLD_INCLUDE_PATH),
         std.mem.toSliceConst(u8, c.ZIG_LLD_LIBRARIES),
         std.mem.toSliceConst(u8, c.ZIG_LLVM_CONFIG_EXE),
         std.mem.toSliceConst(u8, c.ZIG_DIA_GUIDS_LIB),
-    );
+    });
 }
 
 const CliPkg = struct {
diff --git a/src-self-hosted/stage1.zig b/src-self-hosted/stage1.zig
index a0fd689a36..909572bee0 100644
--- a/src-self-hosted/stage1.zig
+++ b/src-self-hosted/stage1.zig
@@ -149,7 +149,7 @@ export fn stage2_fmt(argc: c_int, argv: [*]const [*:0]const u8) c_int {
         fmtMain(argc, argv) catch unreachable;
     } else {
         fmtMain(argc, argv) catch |e| {
-            std.debug.warn("{}\n", @errorName(e));
+            std.debug.warn("{}\n", .{@errorName(e)});
             return -1;
         };
     }
@@ -205,7 +205,7 @@ fn fmtMain(argc: c_int, argv: [*]const [*:0]const u8) !void {
         defer allocator.free(source_code);
 
         const tree = std.zig.parse(allocator, source_code) catch |err| {
-            try stderr.print("error parsing stdin: {}\n", err);
+            try stderr.print("error parsing stdin: {}\n", .{err});
             process.exit(1);
         };
         defer tree.deinit();
@@ -294,7 +294,7 @@ fn fmtPath(fmt: *Fmt, file_path_ref: []const u8, check_mode: bool) FmtError!void
         },
         else => {
             // TODO lock stderr printing
-            try stderr.print("unable to open '{}': {}\n", file_path, err);
+            try stderr.print("unable to open '{}': {}\n", .{ file_path, err });
             fmt.any_error = true;
             return;
         },
@@ -302,7 +302,7 @@ fn fmtPath(fmt: *Fmt, file_path_ref: []const u8, check_mode: bool) FmtError!void
     defer fmt.allocator.free(source_code);
 
     const tree = std.zig.parse(fmt.allocator, source_code) catch |err| {
-        try stderr.print("error parsing file '{}': {}\n", file_path, err);
+        try stderr.print("error parsing file '{}': {}\n", .{ file_path, err });
         fmt.any_error = true;
         return;
     };
@@ -320,7 +320,7 @@ fn fmtPath(fmt: *Fmt, file_path_ref: []const u8, check_mode: bool) FmtError!void
     if (check_mode) {
         const anything_changed = try std.zig.render(fmt.allocator, io.null_out_stream, tree);
         if (anything_changed) {
-            try stderr.print("{}\n", file_path);
+            try stderr.print("{}\n", .{file_path});
             fmt.any_error = true;
         }
     } else {
@@ -329,7 +329,7 @@ fn fmtPath(fmt: *Fmt, file_path_ref: []const u8, check_mode: bool) FmtError!void
 
         const anything_changed = try std.zig.render(fmt.allocator, baf.stream(), tree);
         if (anything_changed) {
-            try stderr.print("{}\n", file_path);
+            try stderr.print("{}\n", .{file_path});
             try baf.finish();
         }
     }
@@ -374,7 +374,7 @@ fn printErrMsgToFile(
     const text = text_buf.toOwnedSlice();
 
     const stream = &file.outStream().stream;
-    try stream.print("{}:{}:{}: error: {}\n", path, start_loc.line + 1, start_loc.column + 1, text);
+    try stream.print("{}:{}:{}: error: {}\n", .{ path, start_loc.line + 1, start_loc.column + 1, text });
 
     if (!color_on) return;
 
diff --git a/src-self-hosted/translate_c.zig b/src-self-hosted/translate_c.zig
index 0470ab92dc..134e0b7672 100644
--- a/src-self-hosted/translate_c.zig
+++ b/src-self-hosted/translate_c.zig
@@ -125,7 +125,7 @@ const Context = struct {
 
         const line = ZigClangSourceManager_getSpellingLineNumber(c.source_manager, spelling_loc);
         const column = ZigClangSourceManager_getSpellingColumnNumber(c.source_manager, spelling_loc);
-        return std.fmt.allocPrint(c.a(), "{}:{}:{}", filename, line, column);
+        return std.fmt.allocPrint(c.a(), "{}:{}:{}", .{ filename, line, column });
     }
 };
 
@@ -228,20 +228,20 @@ fn declVisitor(c: *Context, decl: *const ZigClangDecl) Error!void {
             return visitFnDecl(c, @ptrCast(*const ZigClangFunctionDecl, decl));
         },
         .Typedef => {
-            try emitWarning(c, ZigClangDecl_getLocation(decl), "TODO implement translate-c for typedefs");
+            try emitWarning(c, ZigClangDecl_getLocation(decl), "TODO implement translate-c for typedefs", .{});
         },
         .Enum => {
-            try emitWarning(c, ZigClangDecl_getLocation(decl), "TODO implement translate-c for enums");
+            try emitWarning(c, ZigClangDecl_getLocation(decl), "TODO implement translate-c for enums", .{});
         },
         .Record => {
-            try emitWarning(c, ZigClangDecl_getLocation(decl), "TODO implement translate-c for structs");
+            try emitWarning(c, ZigClangDecl_getLocation(decl), "TODO implement translate-c for structs", .{});
         },
         .Var => {
-            try emitWarning(c, ZigClangDecl_getLocation(decl), "TODO implement translate-c for variables");
+            try emitWarning(c, ZigClangDecl_getLocation(decl), "TODO implement translate-c for variables", .{});
         },
         else => {
             const decl_name = try c.str(ZigClangDecl_getDeclKindName(decl));
-            try emitWarning(c, ZigClangDecl_getLocation(decl), "ignoring {} declaration", decl_name);
+            try emitWarning(c, ZigClangDecl_getLocation(decl), "ignoring {} declaration", .{decl_name});
         },
     }
 }
@@ -264,7 +264,7 @@ fn visitFnDecl(c: *Context, fn_decl: *const ZigClangFunctionDecl) Error!void {
         .is_export = switch (storage_class) {
             .None => has_body and c.mode != .import,
             .Extern, .Static => false,
-            .PrivateExtern => return failDecl(c, fn_decl_loc, fn_name, "unsupported storage class: private extern"),
+            .PrivateExtern => return failDecl(c, fn_decl_loc, fn_name, "unsupported storage class: private extern", .{}),
             .Auto => unreachable, // Not legal on functions
             .Register => unreachable, // Not legal on functions
         },
@@ -274,7 +274,7 @@ fn visitFnDecl(c: *Context, fn_decl: *const ZigClangFunctionDecl) Error!void {
             const fn_proto_type = @ptrCast(*const ZigClangFunctionProtoType, fn_type);
             break :blk transFnProto(rp, fn_proto_type, fn_decl_loc, decl_ctx, true) catch |err| switch (err) {
                 error.UnsupportedType => {
-                    return failDecl(c, fn_decl_loc, fn_name, "unable to resolve prototype of function");
+                    return failDecl(c, fn_decl_loc, fn_name, "unable to resolve prototype of function", .{});
                 },
                 error.OutOfMemory => |e| return e,
             };
@@ -283,7 +283,7 @@ fn visitFnDecl(c: *Context, fn_decl: *const ZigClangFunctionDecl) Error!void {
             const fn_no_proto_type = @ptrCast(*const ZigClangFunctionType, fn_type);
             break :blk transFnNoProto(rp, fn_no_proto_type, fn_decl_loc, decl_ctx, true) catch |err| switch (err) {
                 error.UnsupportedType => {
-                    return failDecl(c, fn_decl_loc, fn_name, "unable to resolve prototype of function");
+                    return failDecl(c, fn_decl_loc, fn_name, "unable to resolve prototype of function", .{});
                 },
                 error.OutOfMemory => |e| return e,
             };
@@ -302,7 +302,7 @@ fn visitFnDecl(c: *Context, fn_decl: *const ZigClangFunctionDecl) Error!void {
         error.OutOfMemory => |e| return e,
         error.UnsupportedTranslation,
         error.UnsupportedType,
-        => return failDecl(c, fn_decl_loc, fn_name, "unable to translate function"),
+        => return failDecl(c, fn_decl_loc, fn_name, "unable to translate function", .{}),
     };
     assert(result.node.id == ast.Node.Id.Block);
     proto_node.body_node = result.node;
@@ -344,7 +344,7 @@ fn transStmt(
                 error.UnsupportedTranslation,
                 ZigClangStmt_getBeginLoc(stmt),
                 "TODO implement translation of stmt class {}",
-                @tagName(sc),
+                .{@tagName(sc)},
             );
         },
     }
@@ -364,7 +364,7 @@ fn transBinaryOperator(
             error.UnsupportedTranslation,
             ZigClangBinaryOperator_getBeginLoc(stmt),
             "TODO: handle more C binary operators: {}",
-            op,
+            .{op},
         ),
         .Assign => return TransResult{
             .node = &(try transCreateNodeAssign(rp, scope, result_used, ZigClangBinaryOperator_getLHS(stmt), ZigClangBinaryOperator_getRHS(stmt))).base,
@@ -415,7 +415,7 @@ fn transBinaryOperator(
             error.UnsupportedTranslation,
             ZigClangBinaryOperator_getBeginLoc(stmt),
             "TODO: handle more C binary operators: {}",
-            op,
+            .{op},
         ),
         .MulAssign,
         .DivAssign,
@@ -567,7 +567,7 @@ fn transDeclStmt(rp: RestorePoint, parent_scope: *Scope, stmt: *const ZigClangDe
                 error.UnsupportedTranslation,
                 ZigClangStmt_getBeginLoc(@ptrCast(*const ZigClangStmt, stmt)),
                 "TODO implement translation of DeclStmt kind {}",
-                @tagName(kind),
+                .{@tagName(kind)},
             ),
         }
     }
@@ -636,7 +636,7 @@ fn transImplicitCastExpr(
             error.UnsupportedTranslation,
             ZigClangStmt_getBeginLoc(@ptrCast(*const ZigClangStmt, expr)),
             "TODO implement translation of CastKind {}",
-            @tagName(kind),
+            .{@tagName(kind)},
         ),
     }
 }
@@ -650,7 +650,7 @@ fn transIntegerLiteral(
     var eval_result: ZigClangExprEvalResult = undefined;
     if (!ZigClangIntegerLiteral_EvaluateAsInt(expr, &eval_result, rp.c.clang_context)) {
         const loc = ZigClangIntegerLiteral_getBeginLoc(expr);
-        return revertAndWarn(rp, error.UnsupportedTranslation, loc, "invalid integer literal");
+        return revertAndWarn(rp, error.UnsupportedTranslation, loc, "invalid integer literal", .{});
     }
     const node = try transCreateNodeAPInt(rp.c, ZigClangAPValue_getInt(&eval_result.Val));
     const res = TransResult{
@@ -719,7 +719,7 @@ fn transStringLiteral(
             error.UnsupportedTranslation,
             ZigClangStmt_getBeginLoc(@ptrCast(*const ZigClangStmt, stmt)),
             "TODO: support string literal kind {}",
-            kind,
+            .{kind},
         ),
     }
 }
@@ -751,7 +751,7 @@ fn escapeChar(c: u8, char_buf: *[4]u8) []const u8 {
         '\n' => return "\\n"[0..],
         '\r' => return "\\r"[0..],
         '\t' => return "\\t"[0..],
-        else => return std.fmt.bufPrint(char_buf[0..], "\\x{x:2}", c) catch unreachable,
+        else => return std.fmt.bufPrint(char_buf[0..], "\\x{x:2}", .{c}) catch unreachable,
     };
     std.mem.copy(u8, char_buf, escaped);
     return char_buf[0..escaped.len];
@@ -1016,7 +1016,13 @@ fn transCreateNodeAssign(
     // zig:     lhs = _tmp;
     // zig:     break :x _tmp
     // zig: })
-    return revertAndWarn(rp, error.UnsupportedTranslation, ZigClangExpr_getBeginLoc(lhs), "TODO: worst case assign op expr");
+    return revertAndWarn(
+        rp,
+        error.UnsupportedTranslation,
+        ZigClangExpr_getBeginLoc(lhs),
+        "TODO: worst case assign op expr",
+        .{},
+    );
 }
 
 fn transCreateNodeBuiltinFnCall(c: *Context, name: []const u8) !*ast.Node.BuiltinCall {
@@ -1211,7 +1217,7 @@ fn transType(rp: RestorePoint, ty: *const ZigClangType, source_loc: ZigClangSour
                 .Float128 => return appendIdentifier(rp.c, "f128"),
                 .Float16 => return appendIdentifier(rp.c, "f16"),
                 .LongDouble => return appendIdentifier(rp.c, "c_longdouble"),
-                else => return revertAndWarn(rp, error.UnsupportedType, source_loc, "unsupported builtin type"),
+                else => return revertAndWarn(rp, error.UnsupportedType, source_loc, "unsupported builtin type", .{}),
             }
         },
         .FunctionProto => {
@@ -1253,7 +1259,7 @@ fn transType(rp: RestorePoint, ty: *const ZigClangType, source_loc: ZigClangSour
         },
         else => {
             const type_name = rp.c.str(ZigClangType_getTypeClassName(ty));
-            return revertAndWarn(rp, error.UnsupportedType, source_loc, "unsupported type: '{}'", type_name);
+            return revertAndWarn(rp, error.UnsupportedType, source_loc, "unsupported type: '{}'", .{type_name});
         },
     }
 }
@@ -1275,7 +1281,13 @@ fn transCC(
     switch (clang_cc) {
         .C => return CallingConvention.C,
         .X86StdCall => return CallingConvention.Stdcall,
-        else => return revertAndWarn(rp, error.UnsupportedType, source_loc, "unsupported calling convention: {}", @tagName(clang_cc)),
+        else => return revertAndWarn(
+            rp,
+            error.UnsupportedType,
+            source_loc,
+            "unsupported calling convention: {}",
+            .{@tagName(clang_cc)},
+        ),
     }
 }
 
@@ -1292,7 +1304,13 @@ fn transFnProto(
     const param_count: usize = ZigClangFunctionProtoType_getNumParams(fn_proto_ty);
     var i: usize = 0;
     while (i < param_count) : (i += 1) {
-        return revertAndWarn(rp, error.UnsupportedType, source_loc, "TODO: implement parameters for FunctionProto in transType");
+        return revertAndWarn(
+            rp,
+            error.UnsupportedType,
+            source_loc,
+            "TODO: implement parameters for FunctionProto in transType",
+            .{},
+        );
     }
 
     return finishTransFnProto(rp, fn_ty, source_loc, fn_decl_context, is_var_args, cc, is_pub);
@@ -1350,7 +1368,7 @@ fn finishTransFnProto(
             } else {
                 break :blk transQualType(rp, return_qt, source_loc) catch |err| switch (err) {
                     error.UnsupportedType => {
-                        try emitWarning(rp.c, source_loc, "unsupported function proto return type");
+                        try emitWarning(rp.c, source_loc, "unsupported function proto return type", .{});
                         return err;
                     },
                     error.OutOfMemory => |e| return e,
@@ -1397,18 +1415,19 @@ fn revertAndWarn(
     err: var,
     source_loc: ZigClangSourceLocation,
     comptime format: []const u8,
-    args: ...,
+    args: var,
 ) (@typeOf(err) || error{OutOfMemory}) {
     rp.activate();
     try emitWarning(rp.c, source_loc, format, args);
     return err;
 }
 
-fn emitWarning(c: *Context, loc: ZigClangSourceLocation, comptime format: []const u8, args: ...) !void {
-    _ = try appendTokenFmt(c, .LineComment, "// {}: warning: " ++ format, c.locStr(loc), args);
+fn emitWarning(c: *Context, loc: ZigClangSourceLocation, comptime format: []const u8, args: var) !void {
+    const args_prefix = .{c.locStr(loc)};
+    _ = try appendTokenFmt(c, .LineComment, "// {}: warning: " ++ format, args_prefix ++ args);
 }
 
-fn failDecl(c: *Context, loc: ZigClangSourceLocation, name: []const u8, comptime format: []const u8, args: ...) !void {
+fn failDecl(c: *Context, loc: ZigClangSourceLocation, name: []const u8, comptime format: []const u8, args: var) !void {
     // const name = @compileError(msg);
     const const_tok = try appendToken(c, .Keyword_const, "const");
     const name_tok = try appendToken(c, .Identifier, name);
@@ -1456,10 +1475,10 @@ fn failDecl(c: *Context, loc: ZigClangSourceLocation, name: []const u8, comptime
 }
 
 fn appendToken(c: *Context, token_id: Token.Id, bytes: []const u8) !ast.TokenIndex {
-    return appendTokenFmt(c, token_id, "{}", bytes);
+    return appendTokenFmt(c, token_id, "{}", .{bytes});
 }
 
-fn appendTokenFmt(c: *Context, token_id: Token.Id, comptime format: []const u8, args: ...) !ast.TokenIndex {
+fn appendTokenFmt(c: *Context, token_id: Token.Id, comptime format: []const u8, args: var) !ast.TokenIndex {
     const S = struct {
         fn callback(context: *Context, bytes: []const u8) error{OutOfMemory}!void {
             return context.source_buffer.append(bytes);
diff --git a/src-self-hosted/type.zig b/src-self-hosted/type.zig
index 8b068150b6..fa8e133b69 100644
--- a/src-self-hosted/type.zig
+++ b/src-self-hosted/type.zig
@@ -399,7 +399,7 @@ pub const Type = struct {
                 .Generic => |generic| {
                     self.non_key = NonKey{ .Generic = {} };
                     const cc_str = ccFnTypeStr(generic.cc);
-                    try name_stream.print("{}fn(", cc_str);
+                    try name_stream.print("{}fn(", .{cc_str});
                     var param_i: usize = 0;
                     while (param_i < generic.param_count) : (param_i += 1) {
                         const arg = if (param_i == 0) "var" else ", var";
@@ -407,7 +407,7 @@ pub const Type = struct {
                     }
                     try name_stream.write(")");
                     if (key.alignment) |alignment| {
-                        try name_stream.print(" align({})", alignment);
+                        try name_stream.print(" align({})", .{alignment});
                     }
                     try name_stream.write(" var");
                 },
@@ -416,7 +416,7 @@ pub const Type = struct {
                         .Normal = NonKey.Normal{ .variable_list = std.ArrayList(*Scope.Var).init(comp.gpa()) },
                     };
                     const cc_str = ccFnTypeStr(normal.cc);
-                    try name_stream.print("{}fn(", cc_str);
+                    try name_stream.print("{}fn(", .{cc_str});
                     for (normal.params) |param, i| {
                         if (i != 0) try name_stream.write(", ");
                         if (param.is_noalias) try name_stream.write("noalias ");
@@ -428,9 +428,9 @@ pub const Type = struct {
                     }
                     try name_stream.write(")");
                     if (key.alignment) |alignment| {
-                        try name_stream.print(" align({})", alignment);
+                        try name_stream.print(" align({})", .{alignment});
                     }
-                    try name_stream.print(" {}", normal.return_type.name);
+                    try name_stream.print(" {}", .{normal.return_type.name});
                 },
             }
 
@@ -584,7 +584,7 @@ pub const Type = struct {
             errdefer comp.gpa().destroy(self);
 
             const u_or_i = "ui"[@boolToInt(key.is_signed)];
-            const name = try std.fmt.allocPrint(comp.gpa(), "{c}{}", u_or_i, key.bit_count);
+            const name = try std.fmt.allocPrint(comp.gpa(), "{c}{}", .{ u_or_i, key.bit_count });
             errdefer comp.gpa().free(name);
 
             self.base.init(comp, .Int, name);
@@ -767,23 +767,19 @@ pub const Type = struct {
                 .Non => "",
             };
             const name = switch (self.key.alignment) {
-                .Abi => try std.fmt.allocPrint(
-                    comp.gpa(),
-                    "{}{}{}{}",
+                .Abi => try std.fmt.allocPrint(comp.gpa(), "{}{}{}{}", .{
                     size_str,
                     mut_str,
                     vol_str,
                     self.key.child_type.name,
-                ),
-                .Override => |alignment| try std.fmt.allocPrint(
-                    comp.gpa(),
-                    "{}align<{}> {}{}{}",
+                }),
+                .Override => |alignment| try std.fmt.allocPrint(comp.gpa(), "{}align<{}> {}{}{}", .{
                     size_str,
                     alignment,
                     mut_str,
                     vol_str,
                     self.key.child_type.name,
-                ),
+                }),
             };
             errdefer comp.gpa().free(name);
 
@@ -852,7 +848,7 @@ pub const Type = struct {
             };
             errdefer comp.gpa().destroy(self);
 
-            const name = try std.fmt.allocPrint(comp.gpa(), "[{}]{}", key.len, key.elem_type.name);
+            const name = try std.fmt.allocPrint(comp.gpa(), "[{}]{}", .{ key.len, key.elem_type.name });
             errdefer comp.gpa().free(name);
 
             self.base.init(comp, .Array, name);
diff --git a/src-self-hosted/util.zig b/src-self-hosted/util.zig
index 070ba9ba87..85e2fc0e73 100644
--- a/src-self-hosted/util.zig
+++ b/src-self-hosted/util.zig
@@ -175,7 +175,7 @@ pub fn llvmTargetFromTriple(triple: std.Buffer) !*llvm.Target {
     var result: *llvm.Target = undefined;
     var err_msg: [*:0]u8 = undefined;
     if (llvm.GetTargetFromTriple(triple.toSlice(), &result, &err_msg) != 0) {
-        std.debug.warn("triple: {s} error: {s}\n", triple.toSlice(), err_msg);
+        std.debug.warn("triple: {s} error: {s}\n", .{ triple.toSlice(), err_msg });
         return error.UnsupportedTarget;
     }
     return result;
@@ -206,7 +206,7 @@ pub fn getTriple(allocator: *std.mem.Allocator, self: std.Target) !std.Buffer {
     const env_name = if (self.isWasm()) "wasm" else @tagName(self.getAbi());
 
     var out = &std.io.BufferOutStream.init(&result).stream;
-    try out.print("{}-unknown-{}-{}", @tagName(self.getArch()), @tagName(self.getOs()), env_name);
+    try out.print("{}-unknown-{}-{}", .{ @tagName(self.getArch()), @tagName(self.getOs()), env_name });
 
     return result;
 }
diff --git a/src-self-hosted/value.zig b/src-self-hosted/value.zig
index accd70d9cc..03c0db0c3c 100644
--- a/src-self-hosted/value.zig
+++ b/src-self-hosted/value.zig
@@ -53,7 +53,7 @@ pub const Value = struct {
     }
 
     pub fn dump(base: *const Value) void {
-        std.debug.warn("{}", @tagName(base.id));
+        std.debug.warn("{}", .{@tagName(base.id)});
     }
 
     pub fn getLlvmConst(base: *Value, ofile: *ObjectFile) (error{OutOfMemory}!?*llvm.Value) {
diff --git a/src/ir.cpp b/src/ir.cpp
index 09e0b70928..0f66965a80 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -17025,7 +17025,7 @@ static IrInstruction *ir_resolve_result(IrAnalyze *ira, IrInstruction *suspend_s
     {
         result_loc_pass1 = no_result_loc();
     }
-    bool was_written = result_loc_pass1->written;
+    bool was_already_resolved = result_loc_pass1->resolved_loc != nullptr;
     IrInstruction *result_loc = ir_resolve_result_raw(ira, suspend_source_instr, result_loc_pass1, value_type,
             value, force_runtime, non_null_comptime, allow_discard);
     if (result_loc == nullptr || (instr_is_unreachable(result_loc) || type_is_invalid(result_loc->value->type)))
@@ -17038,7 +17038,7 @@ static IrInstruction *ir_resolve_result(IrAnalyze *ira, IrInstruction *suspend_s
     }
 
     InferredStructField *isf = result_loc->value->type->data.pointer.inferred_struct_field;
-    if (!was_written && isf != nullptr) {
+    if (!was_already_resolved && isf != nullptr) {
         // Now it's time to add the field to the struct type.
         uint32_t old_field_count = isf->inferred_struct_type->data.structure.src_field_count;
         uint32_t new_field_count = old_field_count + 1;
@@ -18077,7 +18077,11 @@ static IrInstruction *ir_analyze_fn_call(IrAnalyze *ira, IrInstruction *source_i
                 if (type_is_invalid(result_loc->value->type) || instr_is_unreachable(result_loc)) {
                     return result_loc;
                 }
-                if (!handle_is_ptr(result_loc->value->type->data.pointer.child_type)) {
+                ZigType *res_child_type = result_loc->value->type->data.pointer.child_type;
+                if (res_child_type == ira->codegen->builtin_types.entry_var) {
+                    res_child_type = impl_fn_type_id->return_type;
+                }
+                if (!handle_is_ptr(res_child_type)) {
                     ir_reset_result(call_result_loc);
                     result_loc = nullptr;
                 }
@@ -18240,7 +18244,11 @@ static IrInstruction *ir_analyze_fn_call(IrAnalyze *ira, IrInstruction *source_i
             if (type_is_invalid(result_loc->value->type) || instr_is_unreachable(result_loc)) {
                 return result_loc;
             }
-            if (!handle_is_ptr(result_loc->value->type->data.pointer.child_type)) {
+            ZigType *res_child_type = result_loc->value->type->data.pointer.child_type;
+            if (res_child_type == ira->codegen->builtin_types.entry_var) {
+                res_child_type = return_type;
+            }
+            if (!handle_is_ptr(res_child_type)) {
                 ir_reset_result(call_result_loc);
                 result_loc = nullptr;
             }
diff --git a/test/cli.zig b/test/cli.zig
index b36742566a..0527b5c923 100644
--- a/test/cli.zig
+++ b/test/cli.zig
@@ -19,11 +19,11 @@ pub fn main() !void {
     a = &arena.allocator;
 
     const zig_exe_rel = try (arg_it.next(a) orelse {
-        std.debug.warn("Expected first argument to be path to zig compiler\n");
+        std.debug.warn("Expected first argument to be path to zig compiler\n", .{});
         return error.InvalidArgs;
     });
     const cache_root = try (arg_it.next(a) orelse {
-        std.debug.warn("Expected second argument to be cache root directory path\n");
+        std.debug.warn("Expected second argument to be cache root directory path\n", .{});
         return error.InvalidArgs;
     });
     const zig_exe = try fs.path.resolve(a, &[_][]const u8{zig_exe_rel});
@@ -45,39 +45,39 @@ pub fn main() !void {
 
 fn unwrapArg(arg: UnwrapArgError![]u8) UnwrapArgError![]u8 {
     return arg catch |err| {
-        warn("Unable to parse command line: {}\n", err);
+        warn("Unable to parse command line: {}\n", .{err});
         return err;
     };
 }
 
 fn printCmd(cwd: []const u8, argv: []const []const u8) void {
-    std.debug.warn("cd {} && ", cwd);
+    std.debug.warn("cd {} && ", .{cwd});
     for (argv) |arg| {
-        std.debug.warn("{} ", arg);
+        std.debug.warn("{} ", .{arg});
     }
-    std.debug.warn("\n");
+    std.debug.warn("\n", .{});
 }
 
 fn exec(cwd: []const u8, argv: []const []const u8) !ChildProcess.ExecResult {
     const max_output_size = 100 * 1024;
     const result = ChildProcess.exec(a, argv, cwd, null, max_output_size) catch |err| {
-        std.debug.warn("The following command failed:\n");
+        std.debug.warn("The following command failed:\n", .{});
         printCmd(cwd, argv);
         return err;
     };
     switch (result.term) {
         .Exited => |code| {
             if (code != 0) {
-                std.debug.warn("The following command exited with error code {}:\n", code);
+                std.debug.warn("The following command exited with error code {}:\n", .{code});
                 printCmd(cwd, argv);
-                std.debug.warn("stderr:\n{}\n", result.stderr);
+                std.debug.warn("stderr:\n{}\n", .{result.stderr});
                 return error.CommandFailed;
             }
         },
         else => {
-            std.debug.warn("The following command terminated unexpectedly:\n");
+            std.debug.warn("The following command terminated unexpectedly:\n", .{});
             printCmd(cwd, argv);
-            std.debug.warn("stderr:\n{}\n", result.stderr);
+            std.debug.warn("stderr:\n{}\n", .{result.stderr});
             return error.CommandFailed;
         },
     }
diff --git a/test/compare_output.zig b/test/compare_output.zig
index 35687b6a6c..80bac9b1f7 100644
--- a/test/compare_output.zig
+++ b/test/compare_output.zig
@@ -20,7 +20,7 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
             \\pub fn main() void {
             \\    privateFunction();
             \\    const stdout = &getStdOut().outStream().stream;
-            \\    stdout.print("OK 2\n") catch unreachable;
+            \\    stdout.print("OK 2\n", .{}) catch unreachable;
             \\}
             \\
             \\fn privateFunction() void {
@@ -35,7 +35,7 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
             \\// but it's private so it should be OK
             \\fn privateFunction() void {
             \\    const stdout = &getStdOut().outStream().stream;
-            \\    stdout.print("OK 1\n") catch unreachable;
+            \\    stdout.print("OK 1\n", .{}) catch unreachable;
             \\}
             \\
             \\pub fn printText() void {
@@ -61,7 +61,7 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
             \\usingnamespace @import("std").io;
             \\pub fn foo_function() void {
             \\    const stdout = &getStdOut().outStream().stream;
-            \\    stdout.print("OK\n") catch unreachable;
+            \\    stdout.print("OK\n", .{}) catch unreachable;
             \\}
         );
 
@@ -72,7 +72,7 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
             \\pub fn bar_function() void {
             \\    if (foo_function()) {
             \\        const stdout = &getStdOut().outStream().stream;
-            \\        stdout.print("OK\n") catch unreachable;
+            \\        stdout.print("OK\n", .{}) catch unreachable;
             \\    }
             \\}
         );
@@ -104,7 +104,7 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
             \\
             \\pub fn ok() void {
             \\    const stdout = &io.getStdOut().outStream().stream;
-            \\    stdout.print(b_text) catch unreachable;
+            \\    stdout.print(b_text, .{}) catch unreachable;
             \\}
         );
 
@@ -122,7 +122,7 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
         \\
         \\pub fn main() void {
         \\    const stdout = &io.getStdOut().outStream().stream;
-        \\    stdout.print("Hello, world!\n{d:4} {x:3} {c}\n", @as(u32, 12), @as(u16, 0x12), @as(u8, 'a')) catch unreachable;
+        \\    stdout.print("Hello, world!\n{d:4} {x:3} {c}\n", .{@as(u32, 12), @as(u16, 0x12), @as(u8, 'a')}) catch unreachable;
         \\}
     , "Hello, world!\n  12  12 a\n");
 
@@ -265,7 +265,7 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
         \\}
         \\fn print_ok(val: @typeOf(x)) @typeOf(foo) {
         \\    const stdout = &io.getStdOut().outStream().stream;
-        \\    stdout.print("OK\n") catch unreachable;
+        \\    stdout.print("OK\n", .{}) catch unreachable;
         \\    return 0;
         \\}
         \\const foo : i32 = 0;
@@ -348,12 +348,12 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
         \\    const foo = Foo {.field1 = bar,};
         \\    const stdout = &io.getStdOut().outStream().stream;
         \\    if (!foo.method()) {
-        \\        stdout.print("BAD\n") catch unreachable;
+        \\        stdout.print("BAD\n", .{}) catch unreachable;
         \\    }
         \\    if (!bar.method()) {
-        \\        stdout.print("BAD\n") catch unreachable;
+        \\        stdout.print("BAD\n", .{}) catch unreachable;
         \\    }
-        \\    stdout.print("OK\n") catch unreachable;
+        \\    stdout.print("OK\n", .{}) catch unreachable;
         \\}
     , "OK\n");
 
@@ -361,11 +361,11 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
         \\const io = @import("std").io;
         \\pub fn main() void {
         \\    const stdout = &io.getStdOut().outStream().stream;
-        \\    stdout.print("before\n") catch unreachable;
-        \\    defer stdout.print("defer1\n") catch unreachable;
-        \\    defer stdout.print("defer2\n") catch unreachable;
-        \\    defer stdout.print("defer3\n") catch unreachable;
-        \\    stdout.print("after\n") catch unreachable;
+        \\    stdout.print("before\n", .{}) catch unreachable;
+        \\    defer stdout.print("defer1\n", .{}) catch unreachable;
+        \\    defer stdout.print("defer2\n", .{}) catch unreachable;
+        \\    defer stdout.print("defer3\n", .{}) catch unreachable;
+        \\    stdout.print("after\n", .{}) catch unreachable;
         \\}
     , "before\nafter\ndefer3\ndefer2\ndefer1\n");
 
@@ -374,13 +374,13 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
         \\const os = @import("std").os;
         \\pub fn main() void {
         \\    const stdout = &io.getStdOut().outStream().stream;
-        \\    stdout.print("before\n") catch unreachable;
-        \\    defer stdout.print("defer1\n") catch unreachable;
-        \\    defer stdout.print("defer2\n") catch unreachable;
+        \\    stdout.print("before\n", .{}) catch unreachable;
+        \\    defer stdout.print("defer1\n", .{}) catch unreachable;
+        \\    defer stdout.print("defer2\n", .{}) catch unreachable;
         \\    var args_it = @import("std").process.args();
         \\    if (args_it.skip() and !args_it.skip()) return;
-        \\    defer stdout.print("defer3\n") catch unreachable;
-        \\    stdout.print("after\n") catch unreachable;
+        \\    defer stdout.print("defer3\n", .{}) catch unreachable;
+        \\    stdout.print("after\n", .{}) catch unreachable;
         \\}
     , "before\ndefer2\ndefer1\n");
 
@@ -391,12 +391,12 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
         \\}
         \\fn do_test() !void {
         \\    const stdout = &io.getStdOut().outStream().stream;
-        \\    stdout.print("before\n") catch unreachable;
-        \\    defer stdout.print("defer1\n") catch unreachable;
-        \\    errdefer stdout.print("deferErr\n") catch unreachable;
+        \\    stdout.print("before\n", .{}) catch unreachable;
+        \\    defer stdout.print("defer1\n", .{}) catch unreachable;
+        \\    errdefer stdout.print("deferErr\n", .{}) catch unreachable;
         \\    try its_gonna_fail();
-        \\    defer stdout.print("defer3\n") catch unreachable;
-        \\    stdout.print("after\n") catch unreachable;
+        \\    defer stdout.print("defer3\n", .{}) catch unreachable;
+        \\    stdout.print("after\n", .{}) catch unreachable;
         \\}
         \\fn its_gonna_fail() !void {
         \\    return error.IToldYouItWouldFail;
@@ -410,12 +410,12 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
         \\}
         \\fn do_test() !void {
         \\    const stdout = &io.getStdOut().outStream().stream;
-        \\    stdout.print("before\n") catch unreachable;
-        \\    defer stdout.print("defer1\n") catch unreachable;
-        \\    errdefer stdout.print("deferErr\n") catch unreachable;
+        \\    stdout.print("before\n", .{}) catch unreachable;
+        \\    defer stdout.print("defer1\n", .{}) catch unreachable;
+        \\    errdefer stdout.print("deferErr\n", .{}) catch unreachable;
         \\    try its_gonna_pass();
-        \\    defer stdout.print("defer3\n") catch unreachable;
-        \\    stdout.print("after\n") catch unreachable;
+        \\    defer stdout.print("defer3\n", .{}) catch unreachable;
+        \\    stdout.print("after\n", .{}) catch unreachable;
         \\}
         \\fn its_gonna_pass() anyerror!void { }
     , "before\nafter\ndefer3\ndefer1\n");
@@ -427,7 +427,7 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
             \\
             \\pub fn main() void {
             \\    const stdout = &io.getStdOut().outStream().stream;
-            \\    stdout.print(foo_txt) catch unreachable;
+            \\    stdout.print(foo_txt, .{}) catch unreachable;
             \\}
         , "1234\nabcd\n");
 
@@ -452,7 +452,7 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
             \\    _ = args_it.skip();
             \\    while (args_it.next(allocator)) |arg_or_err| : (index += 1) {
             \\        const arg = try arg_or_err;
-            \\        try stdout.print("{}: {}\n", index, arg);
+            \\        try stdout.print("{}: {}\n", .{index, arg});
             \\    }
             \\}
         ,
@@ -493,7 +493,7 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
             \\    _ = args_it.skip();
             \\    while (args_it.next(allocator)) |arg_or_err| : (index += 1) {
             \\        const arg = try arg_or_err;
-            \\        try stdout.print("{}: {}\n", index, arg);
+            \\        try stdout.print("{}: {}\n", .{index, arg});
             \\    }
             \\}
         ,
diff --git a/test/compile_errors.zig b/test/compile_errors.zig
index 3cdf8723ac..ebc57d264d 100644
--- a/test/compile_errors.zig
+++ b/test/compile_errors.zig
@@ -2598,14 +2598,12 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
         \\fn a(b: fn (*const u8) void) void {
         \\    b('a');
         \\}
-        \\fn c(d: u8) void {
-        \\    @import("std").debug.warn("{c}\n", d);
-        \\}
+        \\fn c(d: u8) void {}
         \\export fn entry() void {
         \\    a(c);
         \\}
     ,
-        "tmp.zig:8:7: error: expected type 'fn(*const u8) void', found 'fn(u8) void'",
+        "tmp.zig:6:7: error: expected type 'fn(*const u8) void', found 'fn(u8) void'",
     );
 
     cases.add(
diff --git a/test/standalone/cat/main.zig b/test/standalone/cat/main.zig
index f22329050c..f0cd9728ab 100644
--- a/test/standalone/cat/main.zig
+++ b/test/standalone/cat/main.zig
@@ -23,7 +23,7 @@ pub fn main() !void {
             return usage(exe);
         } else {
             const file = cwd.openFile(arg, .{}) catch |err| {
-                warn("Unable to open file: {}\n", @errorName(err));
+                warn("Unable to open file: {}\n", .{@errorName(err)});
                 return err;
             };
             defer file.close();
@@ -38,7 +38,7 @@ pub fn main() !void {
 }
 
 fn usage(exe: []const u8) !void {
-    warn("Usage: {} [FILE]...\n", exe);
+    warn("Usage: {} [FILE]...\n", .{exe});
     return error.Invalid;
 }
 
@@ -47,7 +47,7 @@ fn cat_file(stdout: fs.File, file: fs.File) !void {
 
     while (true) {
         const bytes_read = file.read(buf[0..]) catch |err| {
-            warn("Unable to read from stream: {}\n", @errorName(err));
+            warn("Unable to read from stream: {}\n", .{@errorName(err)});
             return err;
         };
 
@@ -56,7 +56,7 @@ fn cat_file(stdout: fs.File, file: fs.File) !void {
         }
 
         stdout.write(buf[0..bytes_read]) catch |err| {
-            warn("Unable to write to stdout: {}\n", @errorName(err));
+            warn("Unable to write to stdout: {}\n", .{@errorName(err)});
             return err;
         };
     }
@@ -64,7 +64,7 @@ fn cat_file(stdout: fs.File, file: fs.File) !void {
 
 fn unwrapArg(arg: anyerror![]u8) ![]u8 {
     return arg catch |err| {
-        warn("Unable to parse command line: {}\n", err);
+        warn("Unable to parse command line: {}\n", .{err});
         return err;
     };
 }
diff --git a/test/standalone/guess_number/main.zig b/test/standalone/guess_number/main.zig
index 8119b70d7e..ce7d58ac17 100644
--- a/test/standalone/guess_number/main.zig
+++ b/test/standalone/guess_number/main.zig
@@ -6,11 +6,11 @@ const fmt = std.fmt;
 pub fn main() !void {
     const stdout = &io.getStdOut().outStream().stream;
 
-    try stdout.print("Welcome to the Guess Number Game in Zig.\n");
+    try stdout.print("Welcome to the Guess Number Game in Zig.\n", .{});
 
     var seed_bytes: [@sizeOf(u64)]u8 = undefined;
     std.crypto.randomBytes(seed_bytes[0..]) catch |err| {
-        std.debug.warn("unable to seed random number generator: {}", err);
+        std.debug.warn("unable to seed random number generator: {}", .{err});
         return err;
     };
     const seed = std.mem.readIntNative(u64, &seed_bytes);
@@ -19,27 +19,27 @@ pub fn main() !void {
     const answer = prng.random.range(u8, 0, 100) + 1;
 
     while (true) {
-        try stdout.print("\nGuess a number between 1 and 100: ");
+        try stdout.print("\nGuess a number between 1 and 100: ", .{});
         var line_buf: [20]u8 = undefined;
 
         const line = io.readLineSlice(line_buf[0..]) catch |err| switch (err) {
             error.OutOfMemory => {
-                try stdout.print("Input too long.\n");
+                try stdout.print("Input too long.\n", .{});
                 continue;
             },
             else => return err,
         };
 
         const guess = fmt.parseUnsigned(u8, line, 10) catch {
-            try stdout.print("Invalid number.\n");
+            try stdout.print("Invalid number.\n", .{});
             continue;
         };
         if (guess > answer) {
-            try stdout.print("Guess lower.\n");
+            try stdout.print("Guess lower.\n", .{});
         } else if (guess < answer) {
-            try stdout.print("Guess higher.\n");
+            try stdout.print("Guess higher.\n", .{});
         } else {
-            try stdout.print("You win!\n");
+            try stdout.print("You win!\n", .{});
             return;
         }
     }
diff --git a/test/tests.zig b/test/tests.zig
index f908b889f2..7548be6c4b 100644
--- a/test/tests.zig
+++ b/test/tests.zig
@@ -411,7 +411,7 @@ pub fn addPkgTests(
     is_qemu_enabled: bool,
     glibc_dir: ?[]const u8,
 ) *build.Step {
-    const step = b.step(b.fmt("test-{}", name), desc);
+    const step = b.step(b.fmt("test-{}", .{name}), desc);
 
     for (test_targets) |test_target| {
         if (skip_non_native and test_target.target != .Native)
@@ -454,14 +454,14 @@ pub fn addPkgTests(
             test_target.target.zigTripleNoSubArch(b.allocator) catch unreachable;
 
         const these_tests = b.addTest(root_src);
-        these_tests.setNamePrefix(b.fmt(
-            "{}-{}-{}-{}-{} ",
+        const single_threaded_txt = if (test_target.single_threaded) "single" else "multi";
+        these_tests.setNamePrefix(b.fmt("{}-{}-{}-{}-{} ", .{
             name,
             triple_prefix,
             @tagName(test_target.mode),
             libc_prefix,
-            if (test_target.single_threaded) "single" else "multi",
-        ));
+            single_threaded_txt,
+        }));
         these_tests.single_threaded = test_target.single_threaded;
         these_tests.setFilter(test_filter);
         these_tests.setBuildMode(test_target.mode);
@@ -562,7 +562,7 @@ pub const CompareOutputContext = struct {
                 args.append(arg) catch unreachable;
             }
 
-            warn("Test {}/{} {}...", self.test_index + 1, self.context.test_index, self.name);
+            warn("Test {}/{} {}...", .{ self.test_index + 1, self.context.test_index, self.name });
 
             const child = std.ChildProcess.init(args.toSliceConst(), b.allocator) catch unreachable;
             defer child.deinit();
@@ -572,7 +572,7 @@ pub const CompareOutputContext = struct {
             child.stderr_behavior = .Pipe;
             child.env_map = b.env_map;
 
-            child.spawn() catch |err| debug.panic("Unable to spawn {}: {}\n", full_exe_path, @errorName(err));
+            child.spawn() catch |err| debug.panic("Unable to spawn {}: {}\n", .{ full_exe_path, @errorName(err) });
 
             var stdout = Buffer.initNull(b.allocator);
             var stderr = Buffer.initNull(b.allocator);
@@ -584,18 +584,18 @@ pub const CompareOutputContext = struct {
             stderr_file_in_stream.stream.readAllBuffer(&stderr, max_stdout_size) catch unreachable;
 
             const term = child.wait() catch |err| {
-                debug.panic("Unable to spawn {}: {}\n", full_exe_path, @errorName(err));
+                debug.panic("Unable to spawn {}: {}\n", .{ full_exe_path, @errorName(err) });
             };
             switch (term) {
                 .Exited => |code| {
                     if (code != 0) {
-                        warn("Process {} exited with error code {}\n", full_exe_path, code);
+                        warn("Process {} exited with error code {}\n", .{ full_exe_path, code });
                         printInvocation(args.toSliceConst());
                         return error.TestFailed;
                     }
                 },
                 else => {
-                    warn("Process {} terminated unexpectedly\n", full_exe_path);
+                    warn("Process {} terminated unexpectedly\n", .{full_exe_path});
                     printInvocation(args.toSliceConst());
                     return error.TestFailed;
                 },
@@ -609,10 +609,10 @@ pub const CompareOutputContext = struct {
                     \\========= But found: ====================
                     \\{}
                     \\
-                , self.expected_output, stdout.toSliceConst());
+                , .{ self.expected_output, stdout.toSliceConst() });
                 return error.TestFailed;
             }
-            warn("OK\n");
+            warn("OK\n", .{});
         }
     };
 
@@ -644,7 +644,7 @@ pub const CompareOutputContext = struct {
 
             const full_exe_path = self.exe.getOutputPath();
 
-            warn("Test {}/{} {}...", self.test_index + 1, self.context.test_index, self.name);
+            warn("Test {}/{} {}...", .{ self.test_index + 1, self.context.test_index, self.name });
 
             const child = std.ChildProcess.init(&[_][]const u8{full_exe_path}, b.allocator) catch unreachable;
             defer child.deinit();
@@ -655,28 +655,34 @@ pub const CompareOutputContext = struct {
             child.stderr_behavior = .Ignore;
 
             const term = child.spawnAndWait() catch |err| {
-                debug.panic("Unable to spawn {}: {}\n", full_exe_path, @errorName(err));
+                debug.panic("Unable to spawn {}: {}\n", .{ full_exe_path, @errorName(err) });
             };
 
             const expected_exit_code: u32 = 126;
             switch (term) {
                 .Exited => |code| {
                     if (code != expected_exit_code) {
-                        warn("\nProgram expected to exit with code {} " ++ "but exited with code {}\n", expected_exit_code, code);
+                        warn("\nProgram expected to exit with code {} but exited with code {}\n", .{
+                            expected_exit_code, code,
+                        });
                         return error.TestFailed;
                     }
                 },
                 .Signal => |sig| {
-                    warn("\nProgram expected to exit with code {} " ++ "but instead signaled {}\n", expected_exit_code, sig);
+                    warn("\nProgram expected to exit with code {} but instead signaled {}\n", .{
+                        expected_exit_code, sig,
+                    });
                     return error.TestFailed;
                 },
                 else => {
-                    warn("\nProgram expected to exit with code {}" ++ " but exited in an unexpected way\n", expected_exit_code);
+                    warn("\nProgram expected to exit with code {} but exited in an unexpected way\n", .{
+                        expected_exit_code,
+                    });
                     return error.TestFailed;
                 },
             }
 
-            warn("OK\n");
+            warn("OK\n", .{});
         }
     };
 
@@ -729,7 +735,9 @@ pub const CompareOutputContext = struct {
 
         switch (case.special) {
             Special.Asm => {
-                const annotated_case_name = fmt.allocPrint(self.b.allocator, "assemble-and-link {}", case.name) catch unreachable;
+                const annotated_case_name = fmt.allocPrint(self.b.allocator, "assemble-and-link {}", .{
+                    case.name,
+                }) catch unreachable;
                 if (self.test_filter) |filter| {
                     if (mem.indexOf(u8, annotated_case_name, filter) == null) return;
                 }
@@ -758,7 +766,11 @@ pub const CompareOutputContext = struct {
             },
             Special.None => {
                 for (self.modes) |mode| {
-                    const annotated_case_name = fmt.allocPrint(self.b.allocator, "{} {} ({})", "compare-output", case.name, @tagName(mode)) catch unreachable;
+                    const annotated_case_name = fmt.allocPrint(self.b.allocator, "{} {} ({})", .{
+                        "compare-output",
+                        case.name,
+                        @tagName(mode),
+                    }) catch unreachable;
                     if (self.test_filter) |filter| {
                         if (mem.indexOf(u8, annotated_case_name, filter) == null) continue;
                     }
@@ -790,7 +802,7 @@ pub const CompareOutputContext = struct {
                 }
             },
             Special.RuntimeSafety => {
-                const annotated_case_name = fmt.allocPrint(self.b.allocator, "safety {}", case.name) catch unreachable;
+                const annotated_case_name = fmt.allocPrint(self.b.allocator, "safety {}", .{case.name}) catch unreachable;
                 if (self.test_filter) |filter| {
                     if (mem.indexOf(u8, annotated_case_name, filter) == null) return;
                 }
@@ -843,7 +855,11 @@ pub const StackTracesContext = struct {
             const expect_for_mode = expect[@enumToInt(mode)];
             if (expect_for_mode.len == 0) continue;
 
-            const annotated_case_name = fmt.allocPrint(self.b.allocator, "{} {} ({})", "stack-trace", name, @tagName(mode)) catch unreachable;
+            const annotated_case_name = fmt.allocPrint(self.b.allocator, "{} {} ({})", .{
+                "stack-trace",
+                name,
+                @tagName(mode),
+            }) catch unreachable;
             if (self.test_filter) |filter| {
                 if (mem.indexOf(u8, annotated_case_name, filter) == null) continue;
             }
@@ -907,7 +923,7 @@ pub const StackTracesContext = struct {
             defer args.deinit();
             args.append(full_exe_path) catch unreachable;
 
-            warn("Test {}/{} {}...", self.test_index + 1, self.context.test_index, self.name);
+            warn("Test {}/{} {}...", .{ self.test_index + 1, self.context.test_index, self.name });
 
             const child = std.ChildProcess.init(args.toSliceConst(), b.allocator) catch unreachable;
             defer child.deinit();
@@ -917,7 +933,7 @@ pub const StackTracesContext = struct {
             child.stderr_behavior = .Pipe;
             child.env_map = b.env_map;
 
-            child.spawn() catch |err| debug.panic("Unable to spawn {}: {}\n", full_exe_path, @errorName(err));
+            child.spawn() catch |err| debug.panic("Unable to spawn {}: {}\n", .{ full_exe_path, @errorName(err) });
 
             var stdout = Buffer.initNull(b.allocator);
             var stderr = Buffer.initNull(b.allocator);
@@ -929,30 +945,34 @@ pub const StackTracesContext = struct {
             stderr_file_in_stream.stream.readAllBuffer(&stderr, max_stdout_size) catch unreachable;
 
             const term = child.wait() catch |err| {
-                debug.panic("Unable to spawn {}: {}\n", full_exe_path, @errorName(err));
+                debug.panic("Unable to spawn {}: {}\n", .{ full_exe_path, @errorName(err) });
             };
 
             switch (term) {
                 .Exited => |code| {
                     const expect_code: u32 = 1;
                     if (code != expect_code) {
-                        warn("Process {} exited with error code {} but expected code {}\n", full_exe_path, code, expect_code);
+                        warn("Process {} exited with error code {} but expected code {}\n", .{
+                            full_exe_path,
+                            code,
+                            expect_code,
+                        });
                         printInvocation(args.toSliceConst());
                         return error.TestFailed;
                     }
                 },
                 .Signal => |signum| {
-                    warn("Process {} terminated on signal {}\n", full_exe_path, signum);
+                    warn("Process {} terminated on signal {}\n", .{ full_exe_path, signum });
                     printInvocation(args.toSliceConst());
                     return error.TestFailed;
                 },
                 .Stopped => |signum| {
-                    warn("Process {} stopped on signal {}\n", full_exe_path, signum);
+                    warn("Process {} stopped on signal {}\n", .{ full_exe_path, signum });
                     printInvocation(args.toSliceConst());
                     return error.TestFailed;
                 },
                 .Unknown => |code| {
-                    warn("Process {} terminated unexpectedly with error code {}\n", full_exe_path, code);
+                    warn("Process {} terminated unexpectedly with error code {}\n", .{ full_exe_path, code });
                     printInvocation(args.toSliceConst());
                     return error.TestFailed;
                 },
@@ -1003,10 +1023,10 @@ pub const StackTracesContext = struct {
                     \\================================================
                     \\{}
                     \\
-                , self.expect_output, got);
+                , .{ self.expect_output, got });
                 return error.TestFailed;
             }
-            warn("OK\n");
+            warn("OK\n", .{});
         }
     };
 };
@@ -1129,7 +1149,7 @@ pub const CompileErrorContext = struct {
                 Mode.ReleaseSmall => zig_args.append("--release-small") catch unreachable,
             }
 
-            warn("Test {}/{} {}...", self.test_index + 1, self.context.test_index, self.name);
+            warn("Test {}/{} {}...", .{ self.test_index + 1, self.context.test_index, self.name });
 
             if (b.verbose) {
                 printInvocation(zig_args.toSliceConst());
@@ -1143,7 +1163,7 @@ pub const CompileErrorContext = struct {
             child.stdout_behavior = .Pipe;
             child.stderr_behavior = .Pipe;
 
-            child.spawn() catch |err| debug.panic("Unable to spawn {}: {}\n", zig_args.items[0], @errorName(err));
+            child.spawn() catch |err| debug.panic("Unable to spawn {}: {}\n", .{ zig_args.items[0], @errorName(err) });
 
             var stdout_buf = Buffer.initNull(b.allocator);
             var stderr_buf = Buffer.initNull(b.allocator);
@@ -1155,7 +1175,7 @@ pub const CompileErrorContext = struct {
             stderr_file_in_stream.stream.readAllBuffer(&stderr_buf, max_stdout_size) catch unreachable;
 
             const term = child.wait() catch |err| {
-                debug.panic("Unable to spawn {}: {}\n", zig_args.items[0], @errorName(err));
+                debug.panic("Unable to spawn {}: {}\n", .{ zig_args.items[0], @errorName(err) });
             };
             switch (term) {
                 .Exited => |code| {
@@ -1165,7 +1185,7 @@ pub const CompileErrorContext = struct {
                     }
                 },
                 else => {
-                    warn("Process {} terminated unexpectedly\n", b.zig_exe);
+                    warn("Process {} terminated unexpectedly\n", .{b.zig_exe});
                     printInvocation(zig_args.toSliceConst());
                     return error.TestFailed;
                 },
@@ -1182,7 +1202,7 @@ pub const CompileErrorContext = struct {
                     \\{}
                     \\================================================
                     \\
-                , stdout);
+                , .{stdout});
                 return error.TestFailed;
             }
 
@@ -1200,9 +1220,9 @@ pub const CompileErrorContext = struct {
                 ok = ok and i == self.case.expected_errors.len;
 
                 if (!ok) {
-                    warn("\n======== Expected these compile errors: ========\n");
+                    warn("\n======== Expected these compile errors: ========\n", .{});
                     for (self.case.expected_errors.toSliceConst()) |expected| {
-                        warn("{}\n", expected);
+                        warn("{}\n", .{expected});
                     }
                 }
             } else {
@@ -1213,7 +1233,7 @@ pub const CompileErrorContext = struct {
                             \\=========== Expected compile error: ============
                             \\{}
                             \\
-                        , expected);
+                        , .{expected});
                         ok = false;
                         break;
                     }
@@ -1225,11 +1245,11 @@ pub const CompileErrorContext = struct {
                     \\================= Full output: =================
                     \\{}
                     \\
-                , stderr);
+                , .{stderr});
                 return error.TestFailed;
             }
 
-            warn("OK\n");
+            warn("OK\n", .{});
         }
     };
 
@@ -1279,7 +1299,9 @@ pub const CompileErrorContext = struct {
     pub fn addCase(self: *CompileErrorContext, case: *const TestCase) void {
         const b = self.b;
 
-        const annotated_case_name = fmt.allocPrint(self.b.allocator, "compile-error {}", case.name) catch unreachable;
+        const annotated_case_name = fmt.allocPrint(self.b.allocator, "compile-error {}", .{
+            case.name,
+        }) catch unreachable;
         if (self.test_filter) |filter| {
             if (mem.indexOf(u8, annotated_case_name, filter) == null) return;
         }
@@ -1316,7 +1338,7 @@ pub const StandaloneContext = struct {
     pub fn addBuildFile(self: *StandaloneContext, build_file: []const u8) void {
         const b = self.b;
 
-        const annotated_case_name = b.fmt("build {} (Debug)", build_file);
+        const annotated_case_name = b.fmt("build {} (Debug)", .{build_file});
         if (self.test_filter) |filter| {
             if (mem.indexOf(u8, annotated_case_name, filter) == null) return;
         }
@@ -1337,7 +1359,7 @@ pub const StandaloneContext = struct {
 
         const run_cmd = b.addSystemCommand(zig_args.toSliceConst());
 
-        const log_step = b.addLog("PASS {}\n", annotated_case_name);
+        const log_step = b.addLog("PASS {}\n", .{annotated_case_name});
         log_step.step.dependOn(&run_cmd.step);
 
         self.step.dependOn(&log_step.step);
@@ -1347,7 +1369,10 @@ pub const StandaloneContext = struct {
         const b = self.b;
 
         for (self.modes) |mode| {
-            const annotated_case_name = fmt.allocPrint(self.b.allocator, "build {} ({})", root_src, @tagName(mode)) catch unreachable;
+            const annotated_case_name = fmt.allocPrint(self.b.allocator, "build {} ({})", .{
+                root_src,
+                @tagName(mode),
+            }) catch unreachable;
             if (self.test_filter) |filter| {
                 if (mem.indexOf(u8, annotated_case_name, filter) == null) continue;
             }
@@ -1358,7 +1383,7 @@ pub const StandaloneContext = struct {
                 exe.linkSystemLibrary("c");
             }
 
-            const log_step = b.addLog("PASS {}\n", annotated_case_name);
+            const log_step = b.addLog("PASS {}\n", .{annotated_case_name});
             log_step.step.dependOn(&exe.step);
 
             self.step.dependOn(&log_step.step);
@@ -1434,7 +1459,7 @@ pub const TranslateCContext = struct {
             zig_args.append(translate_c_cmd) catch unreachable;
             zig_args.append(b.pathFromRoot(root_src)) catch unreachable;
 
-            warn("Test {}/{} {}...", self.test_index + 1, self.context.test_index, self.name);
+            warn("Test {}/{} {}...", .{ self.test_index + 1, self.context.test_index, self.name });
 
             if (b.verbose) {
                 printInvocation(zig_args.toSliceConst());
@@ -1448,7 +1473,10 @@ pub const TranslateCContext = struct {
             child.stdout_behavior = .Pipe;
             child.stderr_behavior = .Pipe;
 
-            child.spawn() catch |err| debug.panic("Unable to spawn {}: {}\n", zig_args.toSliceConst()[0], @errorName(err));
+            child.spawn() catch |err| debug.panic("Unable to spawn {}: {}\n", .{
+                zig_args.toSliceConst()[0],
+                @errorName(err),
+            });
 
             var stdout_buf = Buffer.initNull(b.allocator);
             var stderr_buf = Buffer.initNull(b.allocator);
@@ -1460,23 +1488,23 @@ pub const TranslateCContext = struct {
             stderr_file_in_stream.stream.readAllBuffer(&stderr_buf, max_stdout_size) catch unreachable;
 
             const term = child.wait() catch |err| {
-                debug.panic("Unable to spawn {}: {}\n", zig_args.toSliceConst()[0], @errorName(err));
+                debug.panic("Unable to spawn {}: {}\n", .{ zig_args.toSliceConst()[0], @errorName(err) });
             };
             switch (term) {
                 .Exited => |code| {
                     if (code != 0) {
-                        warn("Compilation failed with exit code {}\n", code);
+                        warn("Compilation failed with exit code {}\n", .{code});
                         printInvocation(zig_args.toSliceConst());
                         return error.TestFailed;
                     }
                 },
                 .Signal => |code| {
-                    warn("Compilation failed with signal {}\n", code);
+                    warn("Compilation failed with signal {}\n", .{code});
                     printInvocation(zig_args.toSliceConst());
                     return error.TestFailed;
                 },
                 else => {
-                    warn("Compilation terminated unexpectedly\n");
+                    warn("Compilation terminated unexpectedly\n", .{});
                     printInvocation(zig_args.toSliceConst());
                     return error.TestFailed;
                 },
@@ -1491,7 +1519,7 @@ pub const TranslateCContext = struct {
                     \\{}
                     \\============================================
                     \\
-                , stderr);
+                , .{stderr});
                 printInvocation(zig_args.toSliceConst());
                 return error.TestFailed;
             }
@@ -1505,20 +1533,20 @@ pub const TranslateCContext = struct {
                         \\========= But found: ===========================
                         \\{}
                         \\
-                    , expected_line, stdout);
+                    , .{ expected_line, stdout });
                     printInvocation(zig_args.toSliceConst());
                     return error.TestFailed;
                 }
             }
-            warn("OK\n");
+            warn("OK\n", .{});
         }
     };
 
     fn printInvocation(args: []const []const u8) void {
         for (args) |arg| {
-            warn("{} ", arg);
+            warn("{} ", .{arg});
         }
-        warn("\n");
+        warn("\n", .{});
     }
 
     pub fn create(self: *TranslateCContext, allow_warnings: bool, filename: []const u8, name: []const u8, source: []const u8, expected_lines: ...) *TestCase {
@@ -1586,7 +1614,7 @@ pub const TranslateCContext = struct {
         const b = self.b;
 
         const translate_c_cmd = if (case.stage2) "translate-c-2" else "translate-c";
-        const annotated_case_name = fmt.allocPrint(self.b.allocator, "{} {}", translate_c_cmd, case.name) catch unreachable;
+        const annotated_case_name = fmt.allocPrint(self.b.allocator, "{} {}", .{ translate_c_cmd, case.name }) catch unreachable;
         if (self.test_filter) |filter| {
             if (mem.indexOf(u8, annotated_case_name, filter) == null) return;
         }
@@ -1666,7 +1694,7 @@ pub const GenHContext = struct {
             const self = @fieldParentPtr(GenHCmpOutputStep, "step", step);
             const b = self.context.b;
 
-            warn("Test {}/{} {}...", self.test_index + 1, self.context.test_index, self.name);
+            warn("Test {}/{} {}...", .{ self.test_index + 1, self.context.test_index, self.name });
 
             const full_h_path = self.obj.getOutputHPath();
             const actual_h = try io.readFileAlloc(b.allocator, full_h_path);
@@ -1680,19 +1708,19 @@ pub const GenHContext = struct {
                         \\========= But found: ===========================
                         \\{}
                         \\
-                    , expected_line, actual_h);
+                    , .{ expected_line, actual_h });
                     return error.TestFailed;
                 }
             }
-            warn("OK\n");
+            warn("OK\n", .{});
         }
     };
 
     fn printInvocation(args: []const []const u8) void {
         for (args) |arg| {
-            warn("{} ", arg);
+            warn("{} ", .{arg});
         }
-        warn("\n");
+        warn("\n", .{});
     }
 
     pub fn create(self: *GenHContext, filename: []const u8, name: []const u8, source: []const u8, expected_lines: ...) *TestCase {
@@ -1724,7 +1752,7 @@ pub const GenHContext = struct {
         ) catch unreachable;
 
         const mode = builtin.Mode.Debug;
-        const annotated_case_name = fmt.allocPrint(self.b.allocator, "gen-h {} ({})", case.name, @tagName(mode)) catch unreachable;
+        const annotated_case_name = fmt.allocPrint(self.b.allocator, "gen-h {} ({})", .{ case.name, @tagName(mode) }) catch unreachable;
         if (self.test_filter) |filter| {
             if (mem.indexOf(u8, annotated_case_name, filter) == null) return;
         }
@@ -1749,7 +1777,7 @@ pub const GenHContext = struct {
 
 fn printInvocation(args: []const []const u8) void {
     for (args) |arg| {
-        warn("{} ", arg);
+        warn("{} ", .{arg});
     }
-    warn("\n");
+    warn("\n", .{});
 }