stage2: implement referenced by trace for error messages

Closes #7668
Closes #12141

lib/build_runner.zig

@@ -185,6 +185,16 @@ pub fn main() !void {
                 builder.use_stage1 = true;
             } else if (mem.eql(u8, arg, "-fno-stage1")) {
                 builder.use_stage1 = false;
+            } else if (mem.eql(u8, arg, "-freference-trace")) {
+                builder.reference_trace = 256;
+            } else if (mem.startsWith(u8, arg, "-freference-trace=")) {
+                const num = arg["-freference-trace=".len..];
+                builder.reference_trace = std.fmt.parseUnsigned(u32, num, 10) catch |err| {
+                    std.debug.print("unable to parse reference_trace count '{s}': {s}", .{ num, @errorName(err) });
+                    process.exit(1);
+                };
+            } else if (mem.eql(u8, arg, "-fno-reference-trace")) {
+                builder.reference_trace = null;
             } else if (mem.eql(u8, arg, "--")) {
                 builder.args = argsRest(args, arg_idx);
                 break;
@@ -308,6 +318,8 @@ fn usage(builder: *Builder, already_ran_build: bool, out_stream: anytype) !void
         \\Advanced Options:
         \\  -fstage1                     Force using bootstrap compiler as the codegen backend
         \\  -fno-stage1                  Prevent using bootstrap compiler as the codegen backend
+        \\  -freference-trace[=num]      How many lines of reference trace should be shown per compile error
+        \\  -fno-reference-trace         Disable reference trace
         \\  --build-file [file]          Override path to build.zig
         \\  --cache-dir [path]           Override path to local Zig cache directory
         \\  --global-cache-dir [path]    Override path to global Zig cache directory

lib/std/build.zig

@@ -45,6 +45,7 @@ pub const Builder = struct {
     /// The purpose of executing the command is for a human to read compile errors from the terminal
     prominent_compile_errors: bool,
     color: enum { auto, on, off } = .auto,
+    reference_trace: ?u32 = null,
     use_stage1: ?bool = null,
     invalid_user_input: bool,
     zig_exe: []const u8,
@@ -2475,6 +2476,10 @@ pub const LibExeObjStep = struct {
             try zig_args.append(@tagName(builder.color));
         }
 
+        if (builder.reference_trace) |some| {
+            try zig_args.append(try std.fmt.allocPrint(builder.allocator, "-freference-trace={d}", .{some}));
+        }
+
         if (self.use_stage1) |stage1| {
             if (stage1) {
                 try zig_args.append("-fstage1");

src/Compilation.zig

@@ -154,6 +154,10 @@ owned_link_dir: ?std.fs.Dir,
 /// Don't use this for anything other than stage1 compatibility.
 color: Color = .auto,
 
+/// How many lines of reference trace should be included per compile error.
+/// Null means only show snippet on first error.
+reference_trace: ?u32 = null,
+
 libcxx_abi_version: libcxx.AbiVersion = libcxx.AbiVersion.default,
 
 /// This mutex guards all `Compilation` mutable state.
@@ -348,6 +352,7 @@ pub const AllErrors = struct {
             /// Does not include the trailing newline.
             source_line: ?[]const u8,
             notes: []Message = &.{},
+            reference_trace: []Message = &.{},
 
             /// Splits the error message up into lines to properly indent them
             /// to allow for long, good-looking error messages.
@@ -447,6 +452,34 @@ pub const AllErrors = struct {
                     for (src.notes) |note| {
                         try note.renderToWriter(ttyconf, stderr, "note", .Cyan, indent);
                     }
+                    if (src.reference_trace.len != 0) {
+                        ttyconf.setColor(stderr, .Reset);
+                        ttyconf.setColor(stderr, .Dim);
+                        try stderr.print("referenced by:\n", .{});
+                        for (src.reference_trace) |reference| {
+                            switch (reference) {
+                                .src => |ref_src| try stderr.print("    {s}: {s}:{d}:{d}\n", .{
+                                    ref_src.msg,
+                                    ref_src.src_path,
+                                    ref_src.line + 1,
+                                    ref_src.column + 1,
+                                }),
+                                .plain => |plain| if (plain.count != 0) {
+                                    try stderr.print(
+                                        "    {d} reference(s) hidden; use '-freference-trace={d}' to see all references\n",
+                                        .{ plain.count, plain.count + src.reference_trace.len - 1 },
+                                    );
+                                } else {
+                                    try stderr.print(
+                                        "    remaining reference traces hidden; use '-freference-trace' to see all reference traces\n",
+                                        .{},
+                                    );
+                                },
+                            }
+                        }
+                        try stderr.writeByte('\n');
+                        ttyconf.setColor(stderr, .Reset);
+                    }
                 },
                 .plain => |plain| {
                     ttyconf.setColor(stderr, color);
@@ -572,6 +605,32 @@ pub const AllErrors = struct {
             });
             return;
         }
+
+        const reference_trace = try allocator.alloc(Message, module_err_msg.reference_trace.len);
+        for (reference_trace) |*reference, i| {
+            const module_reference = module_err_msg.reference_trace[i];
+            if (module_reference.hidden != 0) {
+                reference.* = .{ .plain = .{ .msg = undefined, .count = module_reference.hidden } };
+                break;
+            } else if (module_reference.decl == null) {
+                reference.* = .{ .plain = .{ .msg = undefined, .count = 0 } };
+                break;
+            }
+            const source = try module_reference.src_loc.file_scope.getSource(module.gpa);
+            const span = try module_reference.src_loc.span(module.gpa);
+            const loc = std.zig.findLineColumn(source.bytes, span.main);
+            const file_path = try module_reference.src_loc.file_scope.fullPath(allocator);
+            reference.* = .{
+                .src = .{
+                    .src_path = file_path,
+                    .msg = try allocator.dupe(u8, std.mem.sliceTo(module_reference.decl.?, 0)),
+                    .span = span,
+                    .line = @intCast(u32, loc.line),
+                    .column = @intCast(u32, loc.column),
+                    .source_line = null,
+                },
+            };
+        }
         const file_path = try module_err_msg.src_loc.file_scope.fullPath(allocator);
         try errors.append(.{
             .src = .{
@@ -581,6 +640,7 @@ pub const AllErrors = struct {
                 .line = @intCast(u32, err_loc.line),
                 .column = @intCast(u32, err_loc.column),
                 .notes = notes_buf[0..note_i],
+                .reference_trace = reference_trace,
                 .source_line = try allocator.dupe(u8, err_loc.source_line),
             },
         });
@@ -929,6 +989,7 @@ pub const InitOptions = struct {
     clang_preprocessor_mode: ClangPreprocessorMode = .no,
     /// This is for stage1 and should be deleted upon completion of self-hosting.
     color: Color = .auto,
+    reference_trace: ?u32 = null,
     test_filter: ?[]const u8 = null,
     test_name_prefix: ?[]const u8 = null,
     subsystem: ?std.Target.SubSystem = null,
@@ -1838,6 +1899,7 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
             .disable_c_depfile = options.disable_c_depfile,
             .owned_link_dir = owned_link_dir,
             .color = options.color,
+            .reference_trace = options.reference_trace,
             .time_report = options.time_report,
             .stack_report = options.stack_report,
             .unwind_tables = unwind_tables,

src/Module.zig

@@ -166,6 +166,11 @@ decls_free_list: std.ArrayListUnmanaged(Decl.Index) = .{},
 
 global_assembly: std.AutoHashMapUnmanaged(Decl.Index, []u8) = .{},
 
+reference_table: std.AutoHashMapUnmanaged(Decl.Index, struct {
+    referencer: Decl.Index,
+    src: LazySrcLoc,
+}) = .{},
+
 pub const StringLiteralContext = struct {
     bytes: *std.ArrayListUnmanaged(u8),
 
@@ -2084,6 +2089,13 @@ pub const ErrorMsg = struct {
     src_loc: SrcLoc,
     msg: []const u8,
     notes: []ErrorMsg = &.{},
+    reference_trace: []Trace = &.{},
+
+    pub const Trace = struct {
+        decl: ?[*:0]const u8,
+        src_loc: SrcLoc,
+        hidden: u32 = 0,
+    };
 
     pub fn create(
         gpa: Allocator,
@@ -2122,8 +2134,15 @@ pub const ErrorMsg = struct {
         }
         gpa.free(err_msg.notes);
         gpa.free(err_msg.msg);
+        gpa.free(err_msg.reference_trace);
         err_msg.* = undefined;
     }
+
+    pub fn clearTrace(err_msg: *ErrorMsg, gpa: Allocator) void {
+        if (err_msg.reference_trace.len == 0) return;
+        gpa.free(err_msg.reference_trace);
+        err_msg.reference_trace = &.{};
+    }
 };
 
 /// Canonical reference to a position within a source file.
@@ -3411,6 +3430,7 @@ pub fn deinit(mod: *Module) void {
     mod.decls_free_list.deinit(gpa);
     mod.allocated_decls.deinit(gpa);
     mod.global_assembly.deinit(gpa);
+    mod.reference_table.deinit(gpa);
 
     mod.string_literal_table.deinit(gpa);
     mod.string_literal_bytes.deinit(gpa);

src/Sema.zig

@@ -111,6 +111,7 @@ const crash_report = @import("crash_report.zig");
 const build_options = @import("build_options");
 
 pub const default_branch_quota = 1000;
+pub const default_reference_trace_len = 2;
 
 pub const InstMap = std.AutoHashMapUnmanaged(Zir.Inst.Index, Air.Inst.Ref);
 
@@ -1958,13 +1959,53 @@ fn failWithOwnedErrorMsg(sema: *Sema, err_msg: *Module.ErrorMsg) CompileError {
     }
 
     const mod = sema.mod;
-    {
+    ref: {
         errdefer err_msg.destroy(mod.gpa);
         if (err_msg.src_loc.lazy == .unneeded) {
             return error.NeededSourceLocation;
         }
         try mod.failed_decls.ensureUnusedCapacity(mod.gpa, 1);
         try mod.failed_files.ensureUnusedCapacity(mod.gpa, 1);
+
+        const max_references = blk: {
+            if (sema.mod.comp.reference_trace) |num| break :blk num;
+            // Do not add multiple traces without explicit request.
+            if (sema.mod.failed_decls.count() != 0) break :ref;
+            break :blk default_reference_trace_len;
+        };
+
+        var referenced_by = if (sema.func) |some| some.owner_decl else sema.owner_decl_index;
+        var reference_stack = std.ArrayList(Module.ErrorMsg.Trace).init(sema.gpa);
+        defer reference_stack.deinit();
+
+        // Avoid infinite loops.
+        var seen = std.AutoHashMap(Module.Decl.Index, void).init(sema.gpa);
+        defer seen.deinit();
+
+        var cur_reference_trace: u32 = 0;
+        while (sema.mod.reference_table.get(referenced_by)) |ref| : (cur_reference_trace += 1) {
+            const gop = try seen.getOrPut(ref.referencer);
+            if (gop.found_existing) break;
+            if (cur_reference_trace < max_references) {
+                const decl = sema.mod.declPtr(ref.referencer);
+                try reference_stack.append(.{ .decl = decl.name, .src_loc = ref.src.toSrcLoc(decl) });
+            }
+            referenced_by = ref.referencer;
+        }
+        if (sema.mod.comp.reference_trace == null and cur_reference_trace > 0) {
+            try reference_stack.append(.{
+                .decl = null,
+                .src_loc = undefined,
+                .hidden = 0,
+            });
+        } else if (cur_reference_trace > max_references) {
+            try reference_stack.append(.{
+                .decl = undefined,
+                .src_loc = undefined,
+                .hidden = cur_reference_trace - max_references,
+            });
+        }
+        err_msg.reference_trace = reference_stack.toOwnedSlice();
     }
     if (sema.owner_func) |func| {
         func.state = .sema_failure;
@@ -5366,14 +5407,8 @@ fn zirDeclRef(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air
     const src = inst_data.src();
     const decl_name = inst_data.get(sema.code);
     const decl_index = try sema.lookupIdentifier(block, src, decl_name);
-    return sema.analyzeDeclRef(decl_index) catch |err| switch (err) {
+    try sema.addReferencedBy(block, src, decl_index);
-        error.AnalysisFail => {
+    return sema.analyzeDeclRef(decl_index);
-            const msg = sema.err orelse return err;
-            try sema.errNote(block, src, msg, "referenced here", .{});
-            return err;
-        },
-        else => return err,
-    };
 }
 
 fn zirDeclVal(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
@@ -6107,6 +6142,7 @@ fn analyzeCall(
                     error.AnalysisFail => {
                         const err_msg = sema.err orelse return err;
                         try sema.errNote(block, call_src, err_msg, "called from here", .{});
+                        err_msg.clearTrace(sema.gpa);
                         return err;
                     },
                     else => |e| return e,
@@ -21741,14 +21777,8 @@ fn namespaceLookupRef(
     decl_name: []const u8,
 ) CompileError!?Air.Inst.Ref {
     const decl = (try sema.namespaceLookup(block, src, namespace, decl_name)) orelse return null;
-    return sema.analyzeDeclRef(decl) catch |err| switch (err) {
+    try sema.addReferencedBy(block, src, decl);
-        error.AnalysisFail => {
+    return try sema.analyzeDeclRef(decl);
-            const msg = sema.err orelse return err;
-            try sema.errNote(block, src, msg, "referenced here", .{});
-            return err;
-        },
-        else => return err,
-    };
 }
 
 fn namespaceLookupVal(
@@ -26001,14 +26031,8 @@ fn analyzeDeclVal(
     if (sema.decl_val_table.get(decl_index)) |result| {
         return result;
     }
-    const decl_ref = sema.analyzeDeclRef(decl_index) catch |err| switch (err) {
+    try sema.addReferencedBy(block, src, decl_index);
-        error.AnalysisFail => {
+    const decl_ref = try sema.analyzeDeclRef(decl_index);
-            const msg = sema.err orelse return err;
-            try sema.errNote(block, src, msg, "referenced here", .{});
-            return err;
-        },
-        else => return err,
-    };
     const result = try sema.analyzeLoad(block, src, decl_ref, src);
     if (Air.refToIndex(result)) |index| {
         if (sema.air_instructions.items(.tag)[index] == .constant and !block.is_typeof) {
@@ -26018,6 +26042,19 @@ fn analyzeDeclVal(
     return result;
 }
 
+fn addReferencedBy(
+    sema: *Sema,
+    block: *Block,
+    src: LazySrcLoc,
+    decl_index: Decl.Index,
+) !void {
+    if (sema.mod.comp.reference_trace == @as(u32, 0)) return;
+    try sema.mod.reference_table.put(sema.gpa, decl_index, .{
+        .referencer = block.src_decl,
+        .src = src,
+    });
+}
+
 fn ensureDeclAnalyzed(sema: *Sema, decl_index: Decl.Index) CompileError!void {
     const decl = sema.mod.declPtr(decl_index);
     if (decl.analysis == .in_progress) {

src/main.zig

@@ -396,6 +396,8 @@ const usage_build_generic =
     \\  -fno-Clang                Prevent using Clang as the C/C++ compilation backend
     \\  -fstage1                  Force using bootstrap compiler as the codegen backend
     \\  -fno-stage1               Prevent using bootstrap compiler as the codegen backend
+    \\  -freference-trace[=num]   How many lines of reference trace should be shown per compile error
+    \\  -fno-reference-trace      Disable reference trace
     \\  -fsingle-threaded         Code assumes there is only one thread
     \\  -fno-single-threaded      Code may not assume there is only one thread
     \\  -fbuiltin                 Enable implicit builtin knowledge of functions
@@ -742,6 +744,7 @@ fn buildOutputType(
     var headerpad_size: ?u32 = null;
     var headerpad_max_install_names: bool = false;
     var dead_strip_dylibs: bool = false;
+    var reference_trace: ?u32 = null;
 
     // e.g. -m3dnow or -mno-outline-atomics. They correspond to std.Target llvm cpu feature names.
     // This array is populated by zig cc frontend and then has to be converted to zig-style
@@ -928,14 +931,14 @@ fn buildOutputType(
                             fatal("expected parameter after {s}", .{arg});
                         };
                         stack_size_override = std.fmt.parseUnsigned(u64, next_arg, 0) catch |err| {
-                            fatal("unable to parse '{s}': {s}", .{ arg, @errorName(err) });
+                            fatal("unable to parse stack size '{s}': {s}", .{ next_arg, @errorName(err) });
                         };
                     } else if (mem.eql(u8, arg, "--image-base")) {
                         const next_arg = args_iter.next() orelse {
                             fatal("expected parameter after {s}", .{arg});
                         };
                         image_base_override = std.fmt.parseUnsigned(u64, next_arg, 0) catch |err| {
-                            fatal("unable to parse '{s}': {s}", .{ arg, @errorName(err) });
+                            fatal("unable to parse image base override '{s}': {s}", .{ next_arg, @errorName(err) });
                         };
                     } else if (mem.eql(u8, arg, "--name")) {
                         provided_name = args_iter.next() orelse {
@@ -984,7 +987,7 @@ fn buildOutputType(
                             fatal("expected parameter after {s}", .{arg});
                         };
                         pagezero_size = std.fmt.parseUnsigned(u64, eatIntPrefix(next_arg, 16), 16) catch |err| {
-                            fatal("unable to parse '{s}': {s}", .{ arg, @errorName(err) });
+                            fatal("unable to parse pagezero size'{s}': {s}", .{ next_arg, @errorName(err) });
                         };
                     } else if (mem.eql(u8, arg, "-search_paths_first")) {
                         search_strategy = .paths_first;
@@ -995,7 +998,7 @@ fn buildOutputType(
                             fatal("expected parameter after {s}", .{arg});
                         };
                         headerpad_size = std.fmt.parseUnsigned(u32, eatIntPrefix(next_arg, 16), 16) catch |err| {
-                            fatal("unable to parser '{s}': {s}", .{ arg, @errorName(err) });
+                            fatal("unable to parse headerpat size '{s}': {s}", .{ next_arg, @errorName(err) });
                         };
                     } else if (mem.eql(u8, arg, "-headerpad_max_install_names")) {
                         headerpad_max_install_names = true;
@@ -1214,6 +1217,15 @@ fn buildOutputType(
                         use_stage1 = true;
                     } else if (mem.eql(u8, arg, "-fno-stage1")) {
                         use_stage1 = false;
+                    } else if (mem.eql(u8, arg, "-freference-trace")) {
+                        reference_trace = 256;
+                    } else if (mem.startsWith(u8, arg, "-freference-trace=")) {
+                        const num = arg["-freference-trace=".len..];
+                        reference_trace = std.fmt.parseUnsigned(u32, num, 10) catch |err| {
+                            fatal("unable to parse reference_trace count '{s}': {s}", .{ num, @errorName(err) });
+                        };
+                    } else if (mem.eql(u8, arg, "-fno-reference-trace")) {
+                        reference_trace = null;
                     } else if (mem.eql(u8, arg, "-rdynamic")) {
                         rdynamic = true;
                     } else if (mem.eql(u8, arg, "-fsoname")) {
@@ -1785,11 +1797,11 @@ fn buildOutputType(
                         fatal("expected linker arg after '{s}'", .{arg});
                     }
                     linker_optimization = std.fmt.parseUnsigned(u8, linker_args.items[i], 10) catch |err| {
-                        fatal("unable to parse '{s}': {s}", .{ arg, @errorName(err) });
+                        fatal("unable to parse optimization level '{s}': {s}", .{ linker_args.items[i], @errorName(err) });
                     };
                 } else if (mem.startsWith(u8, arg, "-O")) {
                     linker_optimization = std.fmt.parseUnsigned(u8, arg["-O".len..], 10) catch |err| {
-                        fatal("unable to parse '{s}': {s}", .{ arg, @errorName(err) });
+                        fatal("unable to parse optimization level '{s}': {s}", .{ arg, @errorName(err) });
                     };
                 } else if (mem.eql(u8, arg, "-pagezero_size")) {
                     i += 1;
@@ -1798,7 +1810,7 @@ fn buildOutputType(
                     }
                     const next_arg = linker_args.items[i];
                     pagezero_size = std.fmt.parseUnsigned(u64, eatIntPrefix(next_arg, 16), 16) catch |err| {
-                        fatal("unable to parse '{s}': {s}", .{ arg, @errorName(err) });
+                        fatal("unable to parse pagezero size '{s}': {s}", .{ next_arg, @errorName(err) });
                     };
                 } else if (mem.eql(u8, arg, "-headerpad")) {
                     i += 1;
@@ -1807,7 +1819,7 @@ fn buildOutputType(
                     }
                     const next_arg = linker_args.items[i];
                     headerpad_size = std.fmt.parseUnsigned(u32, eatIntPrefix(next_arg, 16), 16) catch |err| {
-                        fatal("unable to parse '{s}': {s}", .{ arg, @errorName(err) });
+                        fatal("unable to parse  headerpad size '{s}': {s}", .{ next_arg, @errorName(err) });
                     };
                 } else if (mem.eql(u8, arg, "-headerpad_max_install_names")) {
                     headerpad_max_install_names = true;
@@ -1899,7 +1911,7 @@ fn buildOutputType(
                         fatal("expected linker arg after '{s}'", .{arg});
                     }
                     version.major = std.fmt.parseUnsigned(u32, linker_args.items[i], 10) catch |err| {
-                        fatal("unable to parse '{s}': {s}", .{ arg, @errorName(err) });
+                        fatal("unable to parse major image version '{s}': {s}", .{ linker_args.items[i], @errorName(err) });
                     };
                     have_version = true;
                 } else if (mem.eql(u8, arg, "--minor-image-version")) {
@@ -1908,7 +1920,7 @@ fn buildOutputType(
                         fatal("expected linker arg after '{s}'", .{arg});
                     }
                     version.minor = std.fmt.parseUnsigned(u32, linker_args.items[i], 10) catch |err| {
-                        fatal("unable to parse '{s}': {s}", .{ arg, @errorName(err) });
+                        fatal("unable to parse minor image version '{s}': {s}", .{ linker_args.items[i], @errorName(err) });
                     };
                     have_version = true;
                 } else if (mem.eql(u8, arg, "-e") or mem.eql(u8, arg, "--entry")) {
@@ -1923,7 +1935,7 @@ fn buildOutputType(
                         fatal("expected linker arg after '{s}'", .{arg});
                     }
                     stack_size_override = std.fmt.parseUnsigned(u64, linker_args.items[i], 0) catch |err| {
-                        fatal("unable to parse '{s}': {s}", .{ arg, @errorName(err) });
+                        fatal("unable to parse stack size override '{s}': {s}", .{ linker_args.items[i], @errorName(err) });
                     };
                 } else if (mem.eql(u8, arg, "--image-base")) {
                     i += 1;
@@ -1931,7 +1943,7 @@ fn buildOutputType(
                         fatal("expected linker arg after '{s}'", .{arg});
                     }
                     image_base_override = std.fmt.parseUnsigned(u64, linker_args.items[i], 0) catch |err| {
-                        fatal("unable to parse '{s}': {s}", .{ arg, @errorName(err) });
+                        fatal("unable to parse image base override '{s}': {s}", .{ linker_args.items[i], @errorName(err) });
                     };
                 } else if (mem.eql(u8, arg, "-T") or mem.eql(u8, arg, "--script")) {
                     i += 1;
@@ -1984,7 +1996,7 @@ fn buildOutputType(
                         linker_args.items[i],
                         10,
                     ) catch |err| {
-                        fatal("unable to parse '{s}': {s}", .{ arg, @errorName(err) });
+                        fatal("unable to parse major subsystem version '{s}': {s}", .{ linker_args.items[i], @errorName(err) });
                     };
                 } else if (mem.eql(u8, arg, "--minor-subsystem-version")) {
                     i += 1;
@@ -1997,7 +2009,7 @@ fn buildOutputType(
                         linker_args.items[i],
                         10,
                     ) catch |err| {
-                        fatal("unable to parse '{s}': {s}", .{ arg, @errorName(err) });
+                        fatal("unable to parse minor subsystem version '{s}': {s}", .{ linker_args.items[i], @errorName(err) });
                     };
                 } else if (mem.eql(u8, arg, "-framework")) {
                     i += 1;
@@ -2981,6 +2993,7 @@ fn buildOutputType(
         .headerpad_size = headerpad_size,
         .headerpad_max_install_names = headerpad_max_install_names,
         .dead_strip_dylibs = dead_strip_dylibs,
+        .reference_trace = reference_trace,
     }) catch |err| switch (err) {
         error.LibCUnavailable => {
             const target = target_info.target;
@@ -3740,6 +3753,8 @@ pub const usage_build =
     \\Options:
     \\   -fstage1                      Force using bootstrap compiler as the codegen backend
     \\   -fno-stage1                   Prevent using bootstrap compiler as the codegen backend
+    \\   -freference-trace[=num]       How many lines of reference trace should be shown per compile error
+    \\   -fno-reference-trace          Disable reference trace
     \\   --build-file [file]           Override path to build.zig
     \\   --cache-dir [path]            Override path to local Zig cache directory
     \\   --global-cache-dir [path]     Override path to global Zig cache directory
@@ -3812,6 +3827,12 @@ pub fn cmdBuild(gpa: Allocator, arena: Allocator, args: []const []const u8) !voi
                     } else if (mem.eql(u8, arg, "-fno-stage1")) {
                         use_stage1 = false;
                         try child_argv.append(arg);
+                    } else if (mem.eql(u8, arg, "-freference-trace")) {
+                        try child_argv.append(arg);
+                    } else if (mem.startsWith(u8, arg, "-freference-trace=")) {
+                        try child_argv.append(arg);
+                    } else if (mem.eql(u8, arg, "-fno-reference-trace")) {
+                        try child_argv.append(arg);
                     }
                 }
                 try child_argv.append(arg);

src/test.zig

@@ -1548,6 +1548,7 @@ pub const TestContext = struct {
             .self_exe_path = std.testing.zig_exe_path,
             // TODO instead of turning off color, pass in a std.Progress.Node
             .color = .off,
+            .reference_trace = 0,
             // TODO: force self-hosted linkers with stage2 backend to avoid LLD creeping in
             //       until the auto-select mechanism deems them worthy
             .use_lld = switch (case.backend) {

test/cases/compile_errors/top_level_decl_dependency_loop.zig

@@ -10,4 +10,3 @@ export fn entry() void {
 // target=native
 //
 // :1:1: error: dependency loop detected
-// :2:19: note: referenced here