compiler,std: implement ZON support

This commit allows using ZON (Zig Object Notation) in a few ways.

* `@import` can be used to load ZON at comptime and convert it to a
  normal Zig value. In this case, `@import` must have a result type.
* `std.zon.parse` can be used to parse ZON at runtime, akin to the
  parsing logic in `std.json`.
* `std.zon.stringify` can be used to convert arbitrary data structures
  to ZON at runtime, again akin to `std.json`.

build.zig

@@ -406,7 +406,7 @@ pub fn build(b: *std.Build) !void {
     const optimization_modes = chosen_opt_modes_buf[0..chosen_mode_index];
 
     const fmt_include_paths = &.{ "lib", "src", "test", "tools", "build.zig", "build.zig.zon" };
-    const fmt_exclude_paths = &.{"test/cases"};
+    const fmt_exclude_paths = &.{ "test/cases", "test/behavior/zon" };
     const do_fmt = b.addFmt(.{
         .paths = fmt_include_paths,
         .exclude_paths = fmt_exclude_paths,

lib/compiler/aro/aro/Value.zig

@@ -473,7 +473,7 @@ pub fn toInt(v: Value, comptime T: type, comp: *const Compilation) ?T {
     if (comp.interner.get(v.ref()) != .int) return null;
     var space: BigIntSpace = undefined;
     const big_int = v.toBigInt(&space, comp);
-    return big_int.to(T) catch null;
+    return big_int.toInt(T) catch null;
 }
 
 const ComplexOp = enum {

lib/compiler/aro/backend/Interner.zig

@@ -628,13 +628,13 @@ pub fn put(i: *Interner, gpa: Allocator, key: Key) !Ref {
                     if (data.fitsInTwosComp(.unsigned, 32)) {
                         i.items.appendAssumeCapacity(.{
                             .tag = .u32,
-                            .data = data.to(u32) catch unreachable,
+                            .data = data.toInt(u32) catch unreachable,
                         });
                         break :int;
                     } else if (data.fitsInTwosComp(.signed, 32)) {
                         i.items.appendAssumeCapacity(.{
                             .tag = .i32,
-                            .data = @bitCast(data.to(i32) catch unreachable),
+                            .data = @bitCast(data.toInt(i32) catch unreachable),
                         });
                         break :int;
                     }

lib/std/math/big/int.zig

@@ -2175,10 +2175,13 @@ pub const Const = struct {
         TargetTooSmall,
     };
 
-    /// Convert self to type T.
+    /// Deprecated; use `toInt`.
+    pub const to = toInt;
+
+    /// Convert self to integer type T.
     ///
     /// Returns an error if self cannot be narrowed into the requested type without truncation.
-    pub fn to(self: Const, comptime T: type) ConvertError!T {
+    pub fn toInt(self: Const, comptime T: type) ConvertError!T {
         switch (@typeInfo(T)) {
             .int => |info| {
                 // Make sure -0 is handled correctly.
@@ -2216,7 +2219,26 @@ pub const Const = struct {
                     }
                 }
             },
-            else => @compileError("cannot convert Const to type " ++ @typeName(T)),
+            else => @compileError("expected int type, found '" ++ @typeName(T) ++ "'"),
+        }
+    }
+
+    /// Convert self to float type T.
+    pub fn toFloat(self: Const, comptime T: type) T {
+        if (self.limbs.len == 0) return 0;
+
+        const base = std.math.maxInt(std.math.big.Limb) + 1;
+        var result: f128 = 0;
+        var i: usize = self.limbs.len;
+        while (i != 0) {
+            i -= 1;
+            const limb: f128 = @floatFromInt(self.limbs[i]);
+            result = @mulAdd(f128, base, result, limb);
+        }
+        if (self.positive) {
+            return @floatCast(result);
+        } else {
+            return @floatCast(-result);
         }
     }
 
@@ -2775,11 +2797,19 @@ pub const Managed = struct {
 
     pub const ConvertError = Const.ConvertError;
 
-    /// Convert self to type T.
+    /// Deprecated; use `toInt`.
+    pub const to = toInt;
+
+    /// Convert self to integer type T.
     ///
     /// Returns an error if self cannot be narrowed into the requested type without truncation.
-    pub fn to(self: Managed, comptime T: type) ConvertError!T {
+    pub fn toInt(self: Managed, comptime T: type) ConvertError!T {
-        return self.toConst().to(T);
+        return self.toConst().toInt(T);
+    }
+
+    /// Convert self to float type T.
+    pub fn toFloat(self: Managed, comptime T: type) T {
+        return self.toConst().toFloat(T);
     }
 
     /// Set self from the string representation `value`.

lib/std/math/big/rational.zig

@@ -518,28 +518,28 @@ test "set" {
     defer a.deinit();
 
     try a.setInt(5);
-    try testing.expect((try a.p.to(u32)) == 5);
+    try testing.expect((try a.p.toInt(u32)) == 5);
-    try testing.expect((try a.q.to(u32)) == 1);
+    try testing.expect((try a.q.toInt(u32)) == 1);
 
     try a.setRatio(7, 3);
-    try testing.expect((try a.p.to(u32)) == 7);
+    try testing.expect((try a.p.toInt(u32)) == 7);
-    try testing.expect((try a.q.to(u32)) == 3);
+    try testing.expect((try a.q.toInt(u32)) == 3);
 
     try a.setRatio(9, 3);
-    try testing.expect((try a.p.to(i32)) == 3);
+    try testing.expect((try a.p.toInt(i32)) == 3);
-    try testing.expect((try a.q.to(i32)) == 1);
+    try testing.expect((try a.q.toInt(i32)) == 1);
 
     try a.setRatio(-9, 3);
-    try testing.expect((try a.p.to(i32)) == -3);
+    try testing.expect((try a.p.toInt(i32)) == -3);
-    try testing.expect((try a.q.to(i32)) == 1);
+    try testing.expect((try a.q.toInt(i32)) == 1);
 
     try a.setRatio(9, -3);
-    try testing.expect((try a.p.to(i32)) == -3);
+    try testing.expect((try a.p.toInt(i32)) == -3);
-    try testing.expect((try a.q.to(i32)) == 1);
+    try testing.expect((try a.q.toInt(i32)) == 1);
 
     try a.setRatio(-9, -3);
-    try testing.expect((try a.p.to(i32)) == 3);
+    try testing.expect((try a.p.toInt(i32)) == 3);
-    try testing.expect((try a.q.to(i32)) == 1);
+    try testing.expect((try a.q.toInt(i32)) == 1);
 }
 
 test "setFloat" {
@@ -547,24 +547,24 @@ test "setFloat" {
     defer a.deinit();
 
     try a.setFloat(f64, 2.5);
-    try testing.expect((try a.p.to(i32)) == 5);
+    try testing.expect((try a.p.toInt(i32)) == 5);
-    try testing.expect((try a.q.to(i32)) == 2);
+    try testing.expect((try a.q.toInt(i32)) == 2);
 
     try a.setFloat(f32, -2.5);
-    try testing.expect((try a.p.to(i32)) == -5);
+    try testing.expect((try a.p.toInt(i32)) == -5);
-    try testing.expect((try a.q.to(i32)) == 2);
+    try testing.expect((try a.q.toInt(i32)) == 2);
 
     try a.setFloat(f32, 3.141593);
 
     //                = 3.14159297943115234375
-    try testing.expect((try a.p.to(u32)) == 3294199);
+    try testing.expect((try a.p.toInt(u32)) == 3294199);
-    try testing.expect((try a.q.to(u32)) == 1048576);
+    try testing.expect((try a.q.toInt(u32)) == 1048576);
 
     try a.setFloat(f64, 72.141593120712409172417410926841290461290467124);
 
     //                = 72.1415931207124145885245525278151035308837890625
-    try testing.expect((try a.p.to(u128)) == 5076513310880537);
+    try testing.expect((try a.p.toInt(u128)) == 5076513310880537);
-    try testing.expect((try a.q.to(u128)) == 70368744177664);
+    try testing.expect((try a.q.toInt(u128)) == 70368744177664);
 }
 
 test "setFloatString" {
@@ -574,8 +574,8 @@ test "setFloatString" {
     try a.setFloatString("72.14159312071241458852455252781510353");
 
     //                  = 72.1415931207124145885245525278151035308837890625
-    try testing.expect((try a.p.to(u128)) == 7214159312071241458852455252781510353);
+    try testing.expect((try a.p.toInt(u128)) == 7214159312071241458852455252781510353);
-    try testing.expect((try a.q.to(u128)) == 100000000000000000000000000000000000);
+    try testing.expect((try a.q.toInt(u128)) == 100000000000000000000000000000000000);
 }
 
 test "toFloat" {
@@ -612,8 +612,8 @@ test "copy" {
     defer b.deinit();
 
     try a.copyInt(b);
-    try testing.expect((try a.p.to(u32)) == 5);
+    try testing.expect((try a.p.toInt(u32)) == 5);
-    try testing.expect((try a.q.to(u32)) == 1);
+    try testing.expect((try a.q.toInt(u32)) == 1);
 
     var c = try Int.initSet(testing.allocator, 7);
     defer c.deinit();
@@ -621,8 +621,8 @@ test "copy" {
     defer d.deinit();
 
     try a.copyRatio(c, d);
-    try testing.expect((try a.p.to(u32)) == 7);
+    try testing.expect((try a.p.toInt(u32)) == 7);
-    try testing.expect((try a.q.to(u32)) == 3);
+    try testing.expect((try a.q.toInt(u32)) == 3);
 
     var e = try Int.initSet(testing.allocator, 9);
     defer e.deinit();
@@ -630,8 +630,8 @@ test "copy" {
     defer f.deinit();
 
     try a.copyRatio(e, f);
-    try testing.expect((try a.p.to(u32)) == 3);
+    try testing.expect((try a.p.toInt(u32)) == 3);
-    try testing.expect((try a.q.to(u32)) == 1);
+    try testing.expect((try a.q.toInt(u32)) == 1);
 }
 
 test "negate" {
@@ -639,16 +639,16 @@ test "negate" {
     defer a.deinit();
 
     try a.setInt(-50);
-    try testing.expect((try a.p.to(i32)) == -50);
+    try testing.expect((try a.p.toInt(i32)) == -50);
-    try testing.expect((try a.q.to(i32)) == 1);
+    try testing.expect((try a.q.toInt(i32)) == 1);
 
     a.negate();
-    try testing.expect((try a.p.to(i32)) == 50);
+    try testing.expect((try a.p.toInt(i32)) == 50);
-    try testing.expect((try a.q.to(i32)) == 1);
+    try testing.expect((try a.q.toInt(i32)) == 1);
 
     a.negate();
-    try testing.expect((try a.p.to(i32)) == -50);
+    try testing.expect((try a.p.toInt(i32)) == -50);
-    try testing.expect((try a.q.to(i32)) == 1);
+    try testing.expect((try a.q.toInt(i32)) == 1);
 }
 
 test "abs" {
@@ -656,16 +656,16 @@ test "abs" {
     defer a.deinit();
 
     try a.setInt(-50);
-    try testing.expect((try a.p.to(i32)) == -50);
+    try testing.expect((try a.p.toInt(i32)) == -50);
-    try testing.expect((try a.q.to(i32)) == 1);
+    try testing.expect((try a.q.toInt(i32)) == 1);
 
     a.abs();
-    try testing.expect((try a.p.to(i32)) == 50);
+    try testing.expect((try a.p.toInt(i32)) == 50);
-    try testing.expect((try a.q.to(i32)) == 1);
+    try testing.expect((try a.q.toInt(i32)) == 1);
 
     a.abs();
-    try testing.expect((try a.p.to(i32)) == 50);
+    try testing.expect((try a.p.toInt(i32)) == 50);
-    try testing.expect((try a.q.to(i32)) == 1);
+    try testing.expect((try a.q.toInt(i32)) == 1);
 }
 
 test "swap" {
@@ -677,19 +677,19 @@ test "swap" {
     try a.setRatio(50, 23);
     try b.setRatio(17, 3);
 
-    try testing.expect((try a.p.to(u32)) == 50);
+    try testing.expect((try a.p.toInt(u32)) == 50);
-    try testing.expect((try a.q.to(u32)) == 23);
+    try testing.expect((try a.q.toInt(u32)) == 23);
 
-    try testing.expect((try b.p.to(u32)) == 17);
+    try testing.expect((try b.p.toInt(u32)) == 17);
-    try testing.expect((try b.q.to(u32)) == 3);
+    try testing.expect((try b.q.toInt(u32)) == 3);
 
     a.swap(&b);
 
-    try testing.expect((try a.p.to(u32)) == 17);
+    try testing.expect((try a.p.toInt(u32)) == 17);
-    try testing.expect((try a.q.to(u32)) == 3);
+    try testing.expect((try a.q.toInt(u32)) == 3);
 
-    try testing.expect((try b.p.to(u32)) == 50);
+    try testing.expect((try b.p.toInt(u32)) == 50);
-    try testing.expect((try b.q.to(u32)) == 23);
+    try testing.expect((try b.q.toInt(u32)) == 23);
 }
 
 test "order" {

lib/std/std.zig

@@ -93,6 +93,7 @@ pub const valgrind = @import("valgrind.zig");
 pub const wasm = @import("wasm.zig");
 pub const zig = @import("zig.zig");
 pub const zip = @import("zip.zig");
+pub const zon = @import("zon.zig");
 pub const start = @import("start.zig");
 
 const root = @import("root");

lib/std/zig/AstGen.zig

@@ -9448,7 +9448,18 @@ fn builtinCall(
             } else if (str.len == 0) {
                 return astgen.failTok(str_lit_token, "import path cannot be empty", .{});
             }
-            const result = try gz.addStrTok(.import, str.index, str_lit_token);
+            const res_ty = try ri.rl.resultType(gz, node) orelse .none;
+            const payload_index = try addExtra(gz.astgen, Zir.Inst.Import{
+                .res_ty = res_ty,
+                .path = str.index,
+            });
+            const result = try gz.add(.{
+                .tag = .import,
+                .data = .{ .pl_tok = .{
+                    .src_tok = gz.tokenIndexToRelative(str_lit_token),
+                    .payload_index = payload_index,
+                } },
+            });
             const gop = try astgen.imports.getOrPut(astgen.gpa, str.index);
             if (!gop.found_existing) {
                 gop.value_ptr.* = str_lit_token;
@@ -11551,9 +11562,21 @@ fn parseStrLit(
     }
 }
 
-fn failWithStrLitError(astgen: *AstGen, err: std.zig.string_literal.Error, token: Ast.TokenIndex, bytes: []const u8, offset: u32) InnerError {
+fn failWithStrLitError(
+    astgen: *AstGen,
+    err: std.zig.string_literal.Error,
+    token: Ast.TokenIndex,
+    bytes: []const u8,
+    offset: u32,
+) InnerError {
     const raw_string = bytes[offset..];
-    return err.lower(raw_string, offset, AstGen.failOff, .{ astgen, token });
+    return failOff(
+        astgen,
+        token,
+        @intCast(offset + err.offset()),
+        "{}",
+        .{err.fmt(raw_string)},
+    );
 }
 
 fn failNode(

lib/std/zig/Zir.zig

@@ -483,7 +483,7 @@ pub const Inst = struct {
         /// Uses the `pl_node` union field. `payload_index` points to a `FuncFancy`.
         func_fancy,
         /// Implements the `@import` builtin.
-        /// Uses the `str_tok` field.
+        /// Uses the `pl_tok` field.
         import,
         /// Integer literal that fits in a u64. Uses the `int` union field.
         int,
@@ -1673,7 +1673,7 @@ pub const Inst = struct {
                 .func = .pl_node,
                 .func_inferred = .pl_node,
                 .func_fancy = .pl_node,
-                .import = .str_tok,
+                .import = .pl_tok,
                 .int = .int,
                 .int_big = .str,
                 .float = .float,
@@ -3841,6 +3841,13 @@ pub const Inst = struct {
         /// If `.none`, restore unconditionally.
         operand: Ref,
     };
+
+    pub const Import = struct {
+        /// The result type of the import, or `.none` if none was available.
+        res_ty: Ref,
+        /// The import path.
+        path: NullTerminatedString,
+    };
 };
 
 pub const SpecialProng = enum { none, @"else", under };

lib/std/zig/Zoir.zig

@@ -54,7 +54,7 @@ pub const Node = union(enum) {
     /// A floating-point literal.
     float_literal: f128,
     /// A Unicode codepoint literal.
-    char_literal: u32,
+    char_literal: u21,
     /// An enum literal. The string is the literal, i.e. `foo` for `.foo`.
     enum_literal: NullTerminatedString,
     /// A string literal.
@@ -96,7 +96,7 @@ pub const Node = union(enum) {
                 } } },
                 .float_literal_small => .{ .float_literal = @as(f32, @bitCast(repr.data)) },
                 .float_literal => .{ .float_literal = @bitCast(zoir.extra[repr.data..][0..4].*) },
-                .char_literal => .{ .char_literal = repr.data },
+                .char_literal => .{ .char_literal = @intCast(repr.data) },
                 .enum_literal => .{ .enum_literal = @enumFromInt(repr.data) },
                 .string_literal => .{ .string_literal = s: {
                     const start, const len = zoir.extra[repr.data..][0..2].*;

lib/std/zig/ZonGen.zig

@@ -3,6 +3,8 @@
 gpa: Allocator,
 tree: Ast,
 
+options: Options,
+
 nodes: std.MultiArrayList(Zoir.Node.Repr),
 extra: std.ArrayListUnmanaged(u32),
 limbs: std.ArrayListUnmanaged(std.math.big.Limb),
@@ -12,12 +14,21 @@ string_table: std.HashMapUnmanaged(u32, void, StringIndexContext, std.hash_map.d
 compile_errors: std.ArrayListUnmanaged(Zoir.CompileError),
 error_notes: std.ArrayListUnmanaged(Zoir.CompileError.Note),
 
-pub fn generate(gpa: Allocator, tree: Ast) Allocator.Error!Zoir {
+pub const Options = struct {
+    /// When false, string literals are not parsed. `string_literal` nodes will contain empty
+    /// strings, and errors that normally occur during string parsing will not be raised.
+    ///
+    /// `parseStrLit` and `strLitSizeHint` may be used to parse string literals after the fact.
+    parse_str_lits: bool = true,
+};
+
+pub fn generate(gpa: Allocator, tree: Ast, options: Options) Allocator.Error!Zoir {
     assert(tree.mode == .zon);
 
     var zg: ZonGen = .{
         .gpa = gpa,
         .tree = tree,
+        .options = options,
         .nodes = .empty,
         .extra = .empty,
         .limbs = .empty,
@@ -250,7 +261,20 @@ fn expr(zg: *ZonGen, node: Ast.Node.Index, dest_node: Zoir.Node.Index) Allocator
         .block_two_semicolon,
         .block,
         .block_semicolon,
-        => try zg.addErrorNode(node, "blocks are not allowed in ZON", .{}),
+        => {
+            const size = switch (node_tags[node]) {
+                .block_two, .block_two_semicolon => @intFromBool(node_datas[node].lhs != 0) + @intFromBool(node_datas[node].rhs != 0),
+                .block, .block_semicolon => node_datas[node].rhs - node_datas[node].lhs,
+                else => unreachable,
+            };
+            if (size == 0) {
+                try zg.addErrorNodeNotes(node, "void literals are not available in ZON", .{}, &.{
+                    try zg.errNoteNode(node, "void union payloads can be represented by enum literals", .{}),
+                });
+            } else {
+                try zg.addErrorNode(node, "blocks are not allowed in ZON", .{});
+            }
+        },
 
         .array_init_one,
         .array_init_one_comma,
@@ -403,58 +427,37 @@ fn expr(zg: *ZonGen, node: Ast.Node.Index, dest_node: Zoir.Node.Index) Allocator
                 .ast_node = node,
             });
 
+            // For short initializers, track the names on the stack rather than going through gpa.
+            var sfba_state = std.heap.stackFallback(256, gpa);
+            const sfba = sfba_state.get();
+            var field_names: std.AutoHashMapUnmanaged(Zoir.NullTerminatedString, Ast.TokenIndex) = .empty;
+            defer field_names.deinit(sfba);
+
+            var reported_any_duplicate = false;
+
             for (full.ast.fields, names_start.., first_elem..) |elem_node, extra_name_idx, elem_dest_node| {
                 const name_token = tree.firstToken(elem_node) - 2;
-                zg.extra.items[extra_name_idx] = @intFromEnum(zg.identAsString(name_token) catch |err| switch (err) {
+                if (zg.identAsString(name_token)) |name_str| {
-                    error.BadString => undefined, // doesn't matter, there's an error
+                    zg.extra.items[extra_name_idx] = @intFromEnum(name_str);
-                    error.OutOfMemory => |e| return e,
+                    const gop = try field_names.getOrPut(sfba, name_str);
+                    if (gop.found_existing and !reported_any_duplicate) {
+                        reported_any_duplicate = true;
+                        const earlier_token = gop.value_ptr.*;
+                        try zg.addErrorTokNotes(earlier_token, "duplicate struct field name", .{}, &.{
+                            try zg.errNoteTok(name_token, "duplicate name here", .{}),
                         });
+                    }
+                    gop.value_ptr.* = name_token;
+                } else |err| switch (err) {
+                    error.BadString => {}, // there's an error, so it's fine to not populate `zg.extra`
+                    error.OutOfMemory => |e| return e,
+                }
                 try zg.expr(elem_node, @enumFromInt(elem_dest_node));
             }
         },
     }
 }
 
-fn parseStrLit(zg: *ZonGen, token: Ast.TokenIndex, offset: u32) !u32 {
-    const raw_string = zg.tree.tokenSlice(token)[offset..];
-    const start = zg.string_bytes.items.len;
-    switch (try std.zig.string_literal.parseWrite(zg.string_bytes.writer(zg.gpa), raw_string)) {
-        .success => return @intCast(start),
-        .failure => |err| {
-            try zg.lowerStrLitError(err, token, raw_string, offset);
-            return error.BadString;
-        },
-    }
-}
-
-fn parseMultilineStrLit(zg: *ZonGen, node: Ast.Node.Index) !u32 {
-    const gpa = zg.gpa;
-    const tree = zg.tree;
-    const string_bytes = &zg.string_bytes;
-
-    const first_tok, const last_tok = bounds: {
-        const node_data = tree.nodes.items(.data)[node];
-        break :bounds .{ node_data.lhs, node_data.rhs };
-    };
-
-    const str_index: u32 = @intCast(string_bytes.items.len);
-
-    // First line: do not append a newline.
-    {
-        const line_bytes = tree.tokenSlice(first_tok)[2..];
-        try string_bytes.appendSlice(gpa, line_bytes);
-    }
-    // Following lines: each line prepends a newline.
-    for (first_tok + 1..last_tok + 1) |tok_idx| {
-        const line_bytes = tree.tokenSlice(@intCast(tok_idx))[2..];
-        try string_bytes.ensureUnusedCapacity(gpa, line_bytes.len + 1);
-        string_bytes.appendAssumeCapacity('\n');
-        string_bytes.appendSliceAssumeCapacity(line_bytes);
-    }
-
-    return @intCast(str_index);
-}
-
 fn appendIdentStr(zg: *ZonGen, ident_token: Ast.TokenIndex) !u32 {
     const tree = zg.tree;
     assert(tree.tokens.items(.tag)[ident_token] == .identifier);
@@ -464,7 +467,18 @@ fn appendIdentStr(zg: *ZonGen, ident_token: Ast.TokenIndex) !u32 {
         try zg.string_bytes.appendSlice(zg.gpa, ident_name);
         return @intCast(start);
     } else {
-        const start = try zg.parseStrLit(ident_token, 1);
+        const offset = 1;
+        const start: u32 = @intCast(zg.string_bytes.items.len);
+        const raw_string = zg.tree.tokenSlice(ident_token)[offset..];
+        try zg.string_bytes.ensureUnusedCapacity(zg.gpa, raw_string.len);
+        switch (try std.zig.string_literal.parseWrite(zg.string_bytes.writer(zg.gpa), raw_string)) {
+            .success => {},
+            .failure => |err| {
+                try zg.lowerStrLitError(err, ident_token, raw_string, offset);
+                return error.BadString;
+            },
+        }
+
         const slice = zg.string_bytes.items[start..];
         if (mem.indexOfScalar(u8, slice, 0) != null) {
             try zg.addErrorTok(ident_token, "identifier cannot contain null bytes", .{});
@@ -477,19 +491,93 @@ fn appendIdentStr(zg: *ZonGen, ident_token: Ast.TokenIndex) !u32 {
     }
 }
 
+/// Estimates the size of a string node without parsing it.
+pub fn strLitSizeHint(tree: Ast, node: Ast.Node.Index) usize {
+    switch (tree.nodes.items(.tag)[node]) {
+        // Parsed string literals are typically around the size of the raw strings.
+        .string_literal => {
+            const token = tree.nodes.items(.main_token)[node];
+            const raw_string = tree.tokenSlice(token);
+            return raw_string.len;
+        },
+        // Multiline string literal lengths can be computed exactly.
+        .multiline_string_literal => {
+            const first_tok, const last_tok = bounds: {
+                const node_data = tree.nodes.items(.data)[node];
+                break :bounds .{ node_data.lhs, node_data.rhs };
+            };
+
+            var size = tree.tokenSlice(first_tok)[2..].len;
+            for (first_tok + 1..last_tok + 1) |tok_idx| {
+                size += 1; // Newline
+                size += tree.tokenSlice(@intCast(tok_idx))[2..].len;
+            }
+            return size;
+        },
+        else => unreachable,
+    }
+}
+
+/// Parses the given node as a string literal.
+pub fn parseStrLit(
+    tree: Ast,
+    node: Ast.Node.Index,
+    writer: anytype,
+) error{OutOfMemory}!std.zig.string_literal.Result {
+    switch (tree.nodes.items(.tag)[node]) {
+        .string_literal => {
+            const token = tree.nodes.items(.main_token)[node];
+            const raw_string = tree.tokenSlice(token);
+            return std.zig.string_literal.parseWrite(writer, raw_string);
+        },
+        .multiline_string_literal => {
+            const first_tok, const last_tok = bounds: {
+                const node_data = tree.nodes.items(.data)[node];
+                break :bounds .{ node_data.lhs, node_data.rhs };
+            };
+
+            // First line: do not append a newline.
+            {
+                const line_bytes = tree.tokenSlice(first_tok)[2..];
+                try writer.writeAll(line_bytes);
+            }
+
+            // Following lines: each line prepends a newline.
+            for (first_tok + 1..last_tok + 1) |tok_idx| {
+                const line_bytes = tree.tokenSlice(@intCast(tok_idx))[2..];
+                try writer.writeByte('\n');
+                try writer.writeAll(line_bytes);
+            }
+
+            return .success;
+        },
+        // Node must represent a string
+        else => unreachable,
+    }
+}
+
 const StringLiteralResult = union(enum) {
     nts: Zoir.NullTerminatedString,
     slice: struct { start: u32, len: u32 },
 };
 
 fn strLitAsString(zg: *ZonGen, str_node: Ast.Node.Index) !StringLiteralResult {
+    if (!zg.options.parse_str_lits) return .{ .slice = .{ .start = 0, .len = 0 } };
+
     const gpa = zg.gpa;
     const string_bytes = &zg.string_bytes;
-    const str_index = switch (zg.tree.nodes.items(.tag)[str_node]) {
+    const str_index: u32 = @intCast(zg.string_bytes.items.len);
-        .string_literal => try zg.parseStrLit(zg.tree.nodes.items(.main_token)[str_node], 0),
+    const size_hint = strLitSizeHint(zg.tree, str_node);
-        .multiline_string_literal => try zg.parseMultilineStrLit(str_node),
+    try string_bytes.ensureUnusedCapacity(zg.gpa, size_hint);
-        else => unreachable,
+    switch (try parseStrLit(zg.tree, str_node, zg.string_bytes.writer(zg.gpa))) {
-    };
+        .success => {},
+        .failure => |err| {
+            const token = zg.tree.nodes.items(.main_token)[str_node];
+            const raw_string = zg.tree.tokenSlice(token);
+            try zg.lowerStrLitError(err, token, raw_string, 0);
+            return error.BadString;
+        },
+    }
     const key: []const u8 = string_bytes.items[str_index..];
     if (std.mem.indexOfScalar(u8, key, 0) != null) return .{ .slice = .{
         .start = str_index,
@@ -540,7 +628,7 @@ fn numberLiteral(zg: *ZonGen, num_node: Ast.Node.Index, src_node: Ast.Node.Index
             if (unsigned_num == 0 and sign == .negative) {
                 try zg.addErrorTokNotes(num_token, "integer literal '-0' is ambiguous", .{}, &.{
                     try zg.errNoteTok(num_token, "use '0' for an integer zero", .{}),
-                    try zg.errNoteTok(num_token, "use '-0.0' for a flaoting-point signed zero", .{}),
+                    try zg.errNoteTok(num_token, "use '-0.0' for a floating-point signed zero", .{}),
                 });
                 return;
             }
@@ -679,8 +767,20 @@ fn setNode(zg: *ZonGen, dest: Zoir.Node.Index, repr: Zoir.Node.Repr) void {
     zg.nodes.set(@intFromEnum(dest), repr);
 }
 
-fn lowerStrLitError(zg: *ZonGen, err: std.zig.string_literal.Error, token: Ast.TokenIndex, raw_string: []const u8, offset: u32) Allocator.Error!void {
+fn lowerStrLitError(
-    return err.lower(raw_string, offset, ZonGen.addErrorTokOff, .{ zg, token });
+    zg: *ZonGen,
+    err: std.zig.string_literal.Error,
+    token: Ast.TokenIndex,
+    raw_string: []const u8,
+    offset: u32,
+) Allocator.Error!void {
+    return ZonGen.addErrorTokOff(
+        zg,
+        token,
+        @intCast(offset + err.offset()),
+        "{}",
+        .{err.fmt(raw_string)},
+    );
 }
 
 fn lowerNumberError(zg: *ZonGen, err: std.zig.number_literal.Error, token: Ast.TokenIndex, bytes: []const u8) Allocator.Error!void {

lib/std/zig/string_literal.zig

@@ -39,40 +39,82 @@ pub const Error = union(enum) {
     /// `''`. Not returned for string literals.
     empty_char_literal,
 
-    /// Returns `func(first_args[0], ..., first_args[n], offset + bad_idx, format, args)`.
+    const FormatMessage = struct {
-    pub fn lower(
         err: Error,
         raw_string: []const u8,
-        offset: u32,
-        comptime func: anytype,
-        first_args: anytype,
-    ) @typeInfo(@TypeOf(func)).@"fn".return_type.? {
-        switch (err) {
-            inline else => |bad_index_or_void, tag| {
-                const bad_index: u32 = switch (@TypeOf(bad_index_or_void)) {
-                    void => 0,
-                    else => @intCast(bad_index_or_void),
     };
-                const fmt_str: []const u8, const args = switch (tag) {
+
-                    .invalid_escape_character => .{ "invalid escape character: '{c}'", .{raw_string[bad_index]} },
+    fn formatMessage(
-                    .expected_hex_digit => .{ "expected hex digit, found '{c}'", .{raw_string[bad_index]} },
+        self: FormatMessage,
-                    .empty_unicode_escape_sequence => .{ "empty unicode escape sequence", .{} },
+        comptime f: []const u8,
-                    .expected_hex_digit_or_rbrace => .{ "expected hex digit or '}}', found '{c}'", .{raw_string[bad_index]} },
+        options: std.fmt.FormatOptions,
-                    .invalid_unicode_codepoint => .{ "unicode escape does not correspond to a valid unicode scalar value", .{} },
+        writer: anytype,
-                    .expected_lbrace => .{ "expected '{{', found '{c}'", .{raw_string[bad_index]} },
+    ) !void {
-                    .expected_rbrace => .{ "expected '}}', found '{c}'", .{raw_string[bad_index]} },
+        _ = f;
-                    .expected_single_quote => .{ "expected singel quote ('), found '{c}'", .{raw_string[bad_index]} },
+        _ = options;
-                    .invalid_character => .{ "invalid byte in string or character literal: '{c}'", .{raw_string[bad_index]} },
+        switch (self.err) {
-                    .empty_char_literal => .{ "empty character literal", .{} },
+            .invalid_escape_character => |bad_index| try writer.print(
-                };
+                "invalid escape character: '{c}'",
-                return @call(.auto, func, first_args ++ .{
+                .{self.raw_string[bad_index]},
-                    offset + bad_index,
+            ),
-                    fmt_str,
+            .expected_hex_digit => |bad_index| try writer.print(
-                    args,
+                "expected hex digit, found '{c}'",
-                });
+                .{self.raw_string[bad_index]},
-            },
+            ),
+            .empty_unicode_escape_sequence => try writer.writeAll(
+                "empty unicode escape sequence",
+            ),
+            .expected_hex_digit_or_rbrace => |bad_index| try writer.print(
+                "expected hex digit or '}}', found '{c}'",
+                .{self.raw_string[bad_index]},
+            ),
+            .invalid_unicode_codepoint => try writer.writeAll(
+                "unicode escape does not correspond to a valid unicode scalar value",
+            ),
+            .expected_lbrace => |bad_index| try writer.print(
+                "expected '{{', found '{c}'",
+                .{self.raw_string[bad_index]},
+            ),
+            .expected_rbrace => |bad_index| try writer.print(
+                "expected '}}', found '{c}'",
+                .{self.raw_string[bad_index]},
+            ),
+            .expected_single_quote => |bad_index| try writer.print(
+                "expected single quote ('), found '{c}'",
+                .{self.raw_string[bad_index]},
+            ),
+            .invalid_character => |bad_index| try writer.print(
+                "invalid byte in string or character literal: '{c}'",
+                .{self.raw_string[bad_index]},
+            ),
+            .empty_char_literal => try writer.writeAll(
+                "empty character literal",
+            ),
         }
     }
+
+    pub fn fmt(self: @This(), raw_string: []const u8) std.fmt.Formatter(formatMessage) {
+        return .{ .data = .{
+            .err = self,
+            .raw_string = raw_string,
+        } };
+    }
+
+    pub fn offset(err: Error) usize {
+        return switch (err) {
+            inline .invalid_escape_character,
+            .expected_hex_digit,
+            .empty_unicode_escape_sequence,
+            .expected_hex_digit_or_rbrace,
+            .invalid_unicode_codepoint,
+            .expected_lbrace,
+            .expected_rbrace,
+            .expected_single_quote,
+            .invalid_character,
+            => |n| n,
+            .empty_char_literal => 0,
+        };
+    }
 };
 
 /// Asserts the slice starts and ends with single-quotes.

lib/std/zon.zig

@@ -0,0 +1,45 @@
+//! ZON parsing and stringification.
+//!
+//! ZON ("Zig Object Notation") is a textual file format. Outside of `nan` and `inf` literals, ZON's
+//! grammar is a subset of Zig's.
+//!
+//! Supported Zig primitives:
+//! * boolean literals
+//! * number literals (including `nan` and `inf`)
+//! * character literals
+//! * enum literals
+//! * `null` literals
+//! * string literals
+//! * multiline string literals
+//!
+//! Supported Zig container types:
+//! * anonymous struct literals
+//! * anonymous tuple literals
+//!
+//! Here is an example ZON object:
+//! ```
+//! .{
+//!     .a = 1.5,
+//!     .b = "hello, world!",
+//!     .c = .{ true, false },
+//!     .d = .{ 1, 2, 3 },
+//! }
+//! ```
+//!
+//! Individual primitives are also valid ZON, for example:
+//! ```
+//! "This string is a valid ZON object."
+//! ```
+//!
+//! ZON may not contain type names.
+//!
+//! ZON does not have syntax for pointers, but the parsers will allocate as needed to match the
+//! given Zig types. Similarly, the serializer will traverse pointers.
+
+pub const parse = @import("zon/parse.zig");
+pub const stringify = @import("zon/stringify.zig");
+
+test {
+    _ = parse;
+    _ = stringify;
+}

src/Compilation.zig

@@ -2220,8 +2220,11 @@ pub fn update(comp: *Compilation, main_progress_node: std.Progress.Node) !void {
         try comp.astgen_work_queue.ensureUnusedCapacity(zcu.import_table.count());
         for (zcu.import_table.values()) |file_index| {
             if (zcu.fileByIndex(file_index).mod.isBuiltin()) continue;
+            const file = zcu.fileByIndex(file_index);
+            if (file.getMode() == .zig) {
                 comp.astgen_work_queue.writeItemAssumeCapacity(file_index);
             }
+        }
         if (comp.file_system_inputs) |fsi| {
             for (zcu.import_table.values()) |file_index| {
                 const file = zcu.fileByIndex(file_index);
@@ -3206,10 +3209,16 @@ pub fn getAllErrorsAlloc(comp: *Compilation) !ErrorBundle {
             if (error_msg) |msg| {
                 try addModuleErrorMsg(zcu, &bundle, msg.*);
             } else {
-                // Must be ZIR errors. Note that this may include AST errors.
+                // Must be ZIR or Zoir errors. Note that this may include AST errors.
-                // addZirErrorMessages asserts that the tree is loaded.
+                _ = try file.getTree(gpa); // Tree must be loaded.
-                _ = try file.getTree(gpa);
+                if (file.zir_loaded) {
                     try addZirErrorMessages(&bundle, file);
+                } else if (file.zoir != null) {
+                    try addZoirErrorMessages(&bundle, file);
+                } else {
+                    // Either Zir or Zoir must have been loaded.
+                    unreachable;
+                }
             }
         }
         var sorted_failed_analysis: std.AutoArrayHashMapUnmanaged(InternPool.AnalUnit, *Zcu.ErrorMsg).DataList.Slice = s: {
@@ -3623,6 +3632,15 @@ pub fn addZirErrorMessages(eb: *ErrorBundle.Wip, file: *Zcu.File) !void {
     return eb.addZirErrorMessages(file.zir, file.tree, file.source, src_path);
 }
 
+pub fn addZoirErrorMessages(eb: *ErrorBundle.Wip, file: *Zcu.File) !void {
+    assert(file.source_loaded);
+    assert(file.tree_loaded);
+    const gpa = eb.gpa;
+    const src_path = try file.fullPath(gpa);
+    defer gpa.free(src_path);
+    return eb.addZoirErrorMessages(file.zoir.?, file.tree, file.source, src_path);
+}
+
 pub fn performAllTheWork(
     comp: *Compilation,
     main_progress_node: std.Progress.Node,
@@ -4272,6 +4290,7 @@ fn workerAstGenFile(
     wg: *WaitGroup,
     src: Zcu.AstGenSrc,
 ) void {
+    assert(file.getMode() == .zig);
     const child_prog_node = prog_node.start(file.sub_file_path, 0);
     defer child_prog_node.end();
 
@@ -4325,7 +4344,7 @@ fn workerAstGenFile(
                 const imported_path_digest = pt.zcu.filePathDigest(res.file_index);
                 break :blk .{ res, imported_path_digest };
             };
-            if (import_result.is_new) {
+            if (import_result.is_new and import_result.file.getMode() == .zig) {
                 log.debug("AstGen of {s} has import '{s}'; queuing AstGen of {s}", .{
                     file.sub_file_path, import_path, import_result.file.sub_file_path,
                 });

src/InternPool.zig

@@ -4389,7 +4389,7 @@ pub const LoadedEnumType = struct {
         // Auto-numbered enum. Convert `int_tag_val` to field index.
         const field_index = switch (ip.indexToKey(int_tag_val).int.storage) {
             inline .u64, .i64 => |x| std.math.cast(u32, x) orelse return null,
-            .big_int => |x| x.to(u32) catch return null,
+            .big_int => |x| x.toInt(u32) catch return null,
             .lazy_align, .lazy_size => unreachable,
         };
         return if (field_index < self.names.len) field_index else null;
@@ -7957,7 +7957,7 @@ pub fn get(ip: *InternPool, gpa: Allocator, tid: Zcu.PerThread.Id, key: Key) All
                     .big_int => |big_int| {
                         items.appendAssumeCapacity(.{
                             .tag = .int_u8,
-                            .data = big_int.to(u8) catch unreachable,
+                            .data = big_int.toInt(u8) catch unreachable,
                         });
                         break :b;
                     },
@@ -7974,7 +7974,7 @@ pub fn get(ip: *InternPool, gpa: Allocator, tid: Zcu.PerThread.Id, key: Key) All
                     .big_int => |big_int| {
                         items.appendAssumeCapacity(.{
                             .tag = .int_u16,
-                            .data = big_int.to(u16) catch unreachable,
+                            .data = big_int.toInt(u16) catch unreachable,
                         });
                         break :b;
                     },
@@ -7991,7 +7991,7 @@ pub fn get(ip: *InternPool, gpa: Allocator, tid: Zcu.PerThread.Id, key: Key) All
                     .big_int => |big_int| {
                         items.appendAssumeCapacity(.{
                             .tag = .int_u32,
-                            .data = big_int.to(u32) catch unreachable,
+                            .data = big_int.toInt(u32) catch unreachable,
                         });
                         break :b;
                     },
@@ -8006,7 +8006,7 @@ pub fn get(ip: *InternPool, gpa: Allocator, tid: Zcu.PerThread.Id, key: Key) All
                 },
                 .i32_type => switch (int.storage) {
                     .big_int => |big_int| {
-                        const casted = big_int.to(i32) catch unreachable;
+                        const casted = big_int.toInt(i32) catch unreachable;
                         items.appendAssumeCapacity(.{
                             .tag = .int_i32,
                             .data = @as(u32, @bitCast(casted)),
@@ -8024,7 +8024,7 @@ pub fn get(ip: *InternPool, gpa: Allocator, tid: Zcu.PerThread.Id, key: Key) All
                 },
                 .usize_type => switch (int.storage) {
                     .big_int => |big_int| {
-                        if (big_int.to(u32)) |casted| {
+                        if (big_int.toInt(u32)) |casted| {
                             items.appendAssumeCapacity(.{
                                 .tag = .int_usize,
                                 .data = casted,
@@ -8045,14 +8045,14 @@ pub fn get(ip: *InternPool, gpa: Allocator, tid: Zcu.PerThread.Id, key: Key) All
                 },
                 .comptime_int_type => switch (int.storage) {
                     .big_int => |big_int| {
-                        if (big_int.to(u32)) |casted| {
+                        if (big_int.toInt(u32)) |casted| {
                             items.appendAssumeCapacity(.{
                                 .tag = .int_comptime_int_u32,
                                 .data = casted,
                             });
                             break :b;
                         } else |_| {}
-                        if (big_int.to(i32)) |casted| {
+                        if (big_int.toInt(i32)) |casted| {
                             items.appendAssumeCapacity(.{
                                 .tag = .int_comptime_int_i32,
                                 .data = @as(u32, @bitCast(casted)),
@@ -8082,7 +8082,7 @@ pub fn get(ip: *InternPool, gpa: Allocator, tid: Zcu.PerThread.Id, key: Key) All
             }
             switch (int.storage) {
                 .big_int => |big_int| {
-                    if (big_int.to(u32)) |casted| {
+                    if (big_int.toInt(u32)) |casted| {
                         items.appendAssumeCapacity(.{
                             .tag = .int_small,
                             .data = try addExtra(extra, IntSmall{

src/Sema.zig

@@ -187,6 +187,7 @@ const Alignment = InternPool.Alignment;
 const AnalUnit = InternPool.AnalUnit;
 const ComptimeAllocIndex = InternPool.ComptimeAllocIndex;
 const Cache = std.Build.Cache;
+const LowerZon = @import("Sema/LowerZon.zig");
 
 pub const default_branch_quota = 1000;
 pub const default_reference_trace_len = 2;
@@ -5790,7 +5791,7 @@ fn addNullTerminatedStrLit(sema: *Sema, string: InternPool.NullTerminatedString)
     return sema.addStrLit(string.toString(), string.length(&sema.pt.zcu.intern_pool));
 }
 
-fn addStrLit(sema: *Sema, string: InternPool.String, len: u64) CompileError!Air.Inst.Ref {
+pub fn addStrLit(sema: *Sema, string: InternPool.String, len: u64) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const array_ty = try pt.arrayType(.{
         .len = len,
@@ -13964,9 +13965,10 @@ fn zirImport(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.
 
     const pt = sema.pt;
     const zcu = pt.zcu;
-    const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].str_tok;
+    const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_tok;
+    const extra = sema.code.extraData(Zir.Inst.Import, inst_data.payload_index).data;
     const operand_src = block.tokenOffset(inst_data.src_tok);
-    const operand = inst_data.get(sema.code);
+    const operand = sema.code.nullTerminatedString(extra.path);
 
     const result = pt.importFile(block.getFileScope(zcu), operand) catch |err| switch (err) {
         error.ImportOutsideModulePath => {
@@ -13983,12 +13985,42 @@ fn zirImport(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.
             return sema.fail(block, operand_src, "unable to open '{s}': {s}", .{ operand, @errorName(err) });
         },
     };
+    switch (result.file.getMode()) {
+        .zig => {
             try sema.declareDependency(.{ .file = result.file_index });
             try pt.ensureFileAnalyzed(result.file_index);
             const ty = zcu.fileRootType(result.file_index);
             try sema.declareDependency(.{ .interned = ty });
             try sema.addTypeReferenceEntry(operand_src, ty);
             return Air.internedToRef(ty);
+        },
+        .zon => {
+            _ = result.file.getTree(zcu.gpa) catch |err| {
+                // TODO: these errors are file system errors; make sure an update() will
+                // retry this and not cache the file system error, which may be transient.
+                return sema.fail(block, operand_src, "unable to open '{s}': {s}", .{ result.file.sub_file_path, @errorName(err) });
+            };
+
+            if (extra.res_ty == .none) {
+                return sema.fail(block, operand_src, "'@import' of ZON must have a known result type", .{});
+            }
+            const res_ty_inst = try sema.resolveInst(extra.res_ty);
+            const res_ty = try sema.analyzeAsType(block, operand_src, res_ty_inst);
+            if (res_ty.isGenericPoison()) {
+                return sema.fail(block, operand_src, "'@import' of ZON must have a known result type", .{});
+            }
+
+            const interned = try LowerZon.run(
+                sema,
+                result.file,
+                result.file_index,
+                res_ty,
+                operand_src,
+                block,
+            );
+            return Air.internedToRef(interned);
+        },
+    }
 }
 
 fn zirEmbedFile(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {

src/Sema/LowerZon.zig

@@ -0,0 +1,858 @@
+const std = @import("std");
+const Zcu = @import("../Zcu.zig");
+const Sema = @import("../Sema.zig");
+const Air = @import("../Air.zig");
+const InternPool = @import("../InternPool.zig");
+const Type = @import("../Type.zig");
+const Value = @import("../Value.zig");
+const Zir = std.zig.Zir;
+const AstGen = std.zig.AstGen;
+const CompileError = Zcu.CompileError;
+const Ast = std.zig.Ast;
+const Allocator = std.mem.Allocator;
+const assert = std.debug.assert;
+const File = Zcu.File;
+const LazySrcLoc = Zcu.LazySrcLoc;
+const Ref = std.zig.Zir.Inst.Ref;
+const NullTerminatedString = InternPool.NullTerminatedString;
+const NumberLiteralError = std.zig.number_literal.Error;
+const NodeIndex = std.zig.Ast.Node.Index;
+const Zoir = std.zig.Zoir;
+
+const LowerZon = @This();
+
+sema: *Sema,
+file: *File,
+file_index: Zcu.File.Index,
+import_loc: LazySrcLoc,
+block: *Sema.Block,
+base_node_inst: InternPool.TrackedInst.Index,
+
+/// Lowers the given file as ZON.
+pub fn run(
+    sema: *Sema,
+    file: *File,
+    file_index: Zcu.File.Index,
+    res_ty: Type,
+    import_loc: LazySrcLoc,
+    block: *Sema.Block,
+) CompileError!InternPool.Index {
+    const pt = sema.pt;
+
+    _ = try file.getZoir(pt.zcu);
+
+    const tracked_inst = try pt.zcu.intern_pool.trackZir(pt.zcu.gpa, pt.tid, .{
+        .file = file_index,
+        .inst = .main_struct_inst, // this is the only trackable instruction in a ZON file
+    });
+
+    var lower_zon: LowerZon = .{
+        .sema = sema,
+        .file = file,
+        .file_index = file_index,
+        .import_loc = import_loc,
+        .block = block,
+        .base_node_inst = tracked_inst,
+    };
+
+    try lower_zon.checkType(res_ty);
+
+    return lower_zon.lowerExpr(.root, res_ty);
+}
+
+/// Validate that `ty` is a valid ZON type. If not, emit a compile error.
+/// i.e. no nested optionals, no error sets, etc.
+fn checkType(self: *LowerZon, ty: Type) !void {
+    var visited: std.AutoHashMapUnmanaged(InternPool.Index, void) = .empty;
+    try self.checkTypeInner(ty, null, &visited);
+}
+
+fn checkTypeInner(
+    self: *LowerZon,
+    ty: Type,
+    parent_opt_ty: ?Type,
+    /// Visited structs and unions (not tuples). These are tracked because they are the only way in
+    /// which a type can be self-referential, so must be tracked to avoid loops. Tracking more types
+    /// consumes memory unnecessarily, and would be complicated by optionals.
+    /// Allocated into `self.sema.arena`.
+    visited: *std.AutoHashMapUnmanaged(InternPool.Index, void),
+) !void {
+    const sema = self.sema;
+    const pt = sema.pt;
+    const zcu = pt.zcu;
+    const ip = &zcu.intern_pool;
+
+    switch (ty.zigTypeTag(zcu)) {
+        .bool,
+        .int,
+        .float,
+        .null,
+        .@"enum",
+        .comptime_float,
+        .comptime_int,
+        .enum_literal,
+        => {},
+
+        .noreturn,
+        .void,
+        .type,
+        .undefined,
+        .error_union,
+        .error_set,
+        .@"fn",
+        .frame,
+        .@"anyframe",
+        .@"opaque",
+        => return self.failUnsupportedResultType(ty, null),
+
+        .pointer => {
+            const ptr_info = ty.ptrInfo(zcu);
+            if (!ptr_info.flags.is_const) {
+                return self.failUnsupportedResultType(
+                    ty,
+                    "ZON does not allow mutable pointers",
+                );
+            }
+            switch (ptr_info.flags.size) {
+                .one => try self.checkTypeInner(
+                    .fromInterned(ptr_info.child),
+                    parent_opt_ty, // preserved
+                    visited,
+                ),
+                .slice => try self.checkTypeInner(
+                    .fromInterned(ptr_info.child),
+                    null,
+                    visited,
+                ),
+                .many => return self.failUnsupportedResultType(ty, "ZON does not allow many-pointers"),
+                .c => return self.failUnsupportedResultType(ty, "ZON does not allow C pointers"),
+            }
+        },
+        .optional => if (parent_opt_ty) |p| {
+            return self.failUnsupportedResultType(p, "ZON does not allow nested optionals");
+        } else try self.checkTypeInner(
+            ty.optionalChild(zcu),
+            ty,
+            visited,
+        ),
+        .array, .vector => {
+            try self.checkTypeInner(ty.childType(zcu), null, visited);
+        },
+        .@"struct" => if (ty.isTuple(zcu)) {
+            const tuple_info = ip.indexToKey(ty.toIntern()).tuple_type;
+            const field_types = tuple_info.types.get(ip);
+            for (field_types) |field_type| {
+                try self.checkTypeInner(.fromInterned(field_type), null, visited);
+            }
+        } else {
+            const gop = try visited.getOrPut(sema.arena, ty.toIntern());
+            if (gop.found_existing) return;
+            try ty.resolveFields(pt);
+            const struct_info = zcu.typeToStruct(ty).?;
+            for (struct_info.field_types.get(ip)) |field_type| {
+                try self.checkTypeInner(.fromInterned(field_type), null, visited);
+            }
+        },
+        .@"union" => {
+            const gop = try visited.getOrPut(sema.arena, ty.toIntern());
+            if (gop.found_existing) return;
+            try ty.resolveFields(pt);
+            const union_info = zcu.typeToUnion(ty).?;
+            for (union_info.field_types.get(ip)) |field_type| {
+                if (field_type != .void_type) {
+                    try self.checkTypeInner(.fromInterned(field_type), null, visited);
+                }
+            }
+        },
+    }
+}
+
+fn nodeSrc(self: *LowerZon, node: Zoir.Node.Index) LazySrcLoc {
+    return .{
+        .base_node_inst = self.base_node_inst,
+        .offset = .{ .node_abs = node.getAstNode(self.file.zoir.?) },
+    };
+}
+
+fn failUnsupportedResultType(
+    self: *LowerZon,
+    ty: Type,
+    opt_note: ?[]const u8,
+) error{ AnalysisFail, OutOfMemory } {
+    @branchHint(.cold);
+    const sema = self.sema;
+    const gpa = sema.gpa;
+    const pt = sema.pt;
+    return sema.failWithOwnedErrorMsg(self.block, msg: {
+        const msg = try sema.errMsg(self.import_loc, "type '{}' is not available in ZON", .{ty.fmt(pt)});
+        errdefer msg.destroy(gpa);
+        if (opt_note) |n| try sema.errNote(self.import_loc, msg, "{s}", .{n});
+        break :msg msg;
+    });
+}
+
+fn fail(
+    self: *LowerZon,
+    node: Zoir.Node.Index,
+    comptime format: []const u8,
+    args: anytype,
+) error{ AnalysisFail, OutOfMemory } {
+    @branchHint(.cold);
+    const err_msg = try Zcu.ErrorMsg.create(self.sema.pt.zcu.gpa, self.nodeSrc(node), format, args);
+    try self.sema.pt.zcu.errNote(self.import_loc, err_msg, "imported here", .{});
+    return self.sema.failWithOwnedErrorMsg(self.block, err_msg);
+}
+
+fn lowerExpr(self: *LowerZon, node: Zoir.Node.Index, res_ty: Type) CompileError!InternPool.Index {
+    const pt = self.sema.pt;
+    return self.lowerExprInner(node, res_ty) catch |err| switch (err) {
+        error.WrongType => return self.fail(
+            node,
+            "expected type '{}'",
+            .{res_ty.fmt(pt)},
+        ),
+        else => |e| return e,
+    };
+}
+
+fn lowerExprInner(
+    self: *LowerZon,
+    node: Zoir.Node.Index,
+    res_ty: Type,
+) (CompileError || error{WrongType})!InternPool.Index {
+    const pt = self.sema.pt;
+    switch (res_ty.zigTypeTag(pt.zcu)) {
+        .optional => return pt.intern(.{
+            .opt = .{
+                .ty = res_ty.toIntern(),
+                .val = if (node.get(self.file.zoir.?) == .null) b: {
+                    break :b .none;
+                } else b: {
+                    const child_type = res_ty.optionalChild(pt.zcu);
+                    break :b try self.lowerExprInner(node, child_type);
+                },
+            },
+        }),
+        .pointer => {
+            const ptr_info = res_ty.ptrInfo(pt.zcu);
+            switch (ptr_info.flags.size) {
+                .one => return pt.intern(.{ .ptr = .{
+                    .ty = res_ty.toIntern(),
+                    .base_addr = .{
+                        .uav = .{
+                            .orig_ty = res_ty.toIntern(),
+                            .val = try self.lowerExprInner(node, .fromInterned(ptr_info.child)),
+                        },
+                    },
+                    .byte_offset = 0,
+                } }),
+                .slice => return self.lowerSlice(node, res_ty),
+                else => {
+                    // Unsupported pointer type, checked in `lower`
+                    unreachable;
+                },
+            }
+        },
+        .bool => return self.lowerBool(node),
+        .int, .comptime_int => return self.lowerInt(node, res_ty),
+        .float, .comptime_float => return self.lowerFloat(node, res_ty),
+        .null => return self.lowerNull(node),
+        .@"enum" => return self.lowerEnum(node, res_ty),
+        .enum_literal => return self.lowerEnumLiteral(node),
+        .array => return self.lowerArray(node, res_ty),
+        .@"struct" => return self.lowerStructOrTuple(node, res_ty),
+        .@"union" => return self.lowerUnion(node, res_ty),
+        .vector => return self.lowerVector(node, res_ty),
+
+        .type,
+        .noreturn,
+        .undefined,
+        .error_union,
+        .error_set,
+        .@"fn",
+        .@"opaque",
+        .frame,
+        .@"anyframe",
+        .void,
+        => return self.fail(node, "type '{}' not available in ZON", .{res_ty.fmt(pt)}),
+    }
+}
+
+fn lowerBool(self: *LowerZon, node: Zoir.Node.Index) !InternPool.Index {
+    return switch (node.get(self.file.zoir.?)) {
+        .true => .bool_true,
+        .false => .bool_false,
+        else => return error.WrongType,
+    };
+}
+
+fn lowerInt(
+    self: *LowerZon,
+    node: Zoir.Node.Index,
+    res_ty: Type,
+) !InternPool.Index {
+    @setFloatMode(.strict);
+    return switch (node.get(self.file.zoir.?)) {
+        .int_literal => |int| switch (int) {
+            .small => |val| {
+                const rhs: i32 = val;
+
+                // If our result is a fixed size integer, check that our value is not out of bounds
+                if (res_ty.zigTypeTag(self.sema.pt.zcu) == .int) {
+                    const lhs_info = res_ty.intInfo(self.sema.pt.zcu);
+
+                    // If lhs is unsigned and rhs is less than 0, we're out of bounds
+                    if (lhs_info.signedness == .unsigned and rhs < 0) return self.fail(
+                        node,
+                        "type '{}' cannot represent integer value '{}'",
+                        .{ res_ty.fmt(self.sema.pt), rhs },
+                    );
+
+                    // If lhs has less than the 32 bits rhs can hold, we need to check the max and
+                    // min values
+                    if (std.math.cast(u5, lhs_info.bits)) |bits| {
+                        const min_int: i32 = if (lhs_info.signedness == .unsigned or bits == 0) b: {
+                            break :b 0;
+                        } else b: {
+                            break :b -(@as(i32, 1) << (bits - 1));
+                        };
+                        const max_int: i32 = if (bits == 0) b: {
+                            break :b 0;
+                        } else b: {
+                            break :b (@as(i32, 1) << (bits - @intFromBool(lhs_info.signedness == .signed))) - 1;
+                        };
+                        if (rhs < min_int or rhs > max_int) {
+                            return self.fail(
+                                node,
+                                "type '{}' cannot represent integer value '{}'",
+                                .{ res_ty.fmt(self.sema.pt), rhs },
+                            );
+                        }
+                    }
+                }
+
+                return self.sema.pt.intern(.{ .int = .{
+                    .ty = res_ty.toIntern(),
+                    .storage = .{ .i64 = rhs },
+                } });
+            },
+            .big => |val| {
+                if (res_ty.zigTypeTag(self.sema.pt.zcu) == .int) {
+                    const int_info = res_ty.intInfo(self.sema.pt.zcu);
+                    if (!val.fitsInTwosComp(int_info.signedness, int_info.bits)) {
+                        return self.fail(
+                            node,
+                            "type '{}' cannot represent integer value '{}'",
+                            .{ res_ty.fmt(self.sema.pt), val },
+                        );
+                    }
+                }
+
+                return self.sema.pt.intern(.{ .int = .{
+                    .ty = res_ty.toIntern(),
+                    .storage = .{ .big_int = val },
+                } });
+            },
+        },
+        .float_literal => |val| {
+            // Check for fractional components
+            if (@rem(val, 1) != 0) {
+                return self.fail(
+                    node,
+                    "fractional component prevents float value '{}' from coercion to type '{}'",
+                    .{ val, res_ty.fmt(self.sema.pt) },
+                );
+            }
+
+            // Create a rational representation of the float
+            var rational = try std.math.big.Rational.init(self.sema.arena);
+            rational.setFloat(f128, val) catch |err| switch (err) {
+                error.NonFiniteFloat => unreachable,
+                error.OutOfMemory => return error.OutOfMemory,
+            };
+
+            // The float is reduced in rational.setFloat, so we assert that denominator is equal to
+            // one
+            const big_one = std.math.big.int.Const{ .limbs = &.{1}, .positive = true };
+            assert(rational.q.toConst().eqlAbs(big_one));
+
+            // Check that the result is in range of the result type
+            const int_info = res_ty.intInfo(self.sema.pt.zcu);
+            if (!rational.p.fitsInTwosComp(int_info.signedness, int_info.bits)) {
+                return self.fail(
+                    node,
+                    "type '{}' cannot represent integer value '{}'",
+                    .{ val, res_ty.fmt(self.sema.pt) },
+                );
+            }
+
+            return self.sema.pt.intern(.{
+                .int = .{
+                    .ty = res_ty.toIntern(),
+                    .storage = .{ .big_int = rational.p.toConst() },
+                },
+            });
+        },
+        .char_literal => |val| {
+            // If our result is a fixed size integer, check that our value is not out of bounds
+            if (res_ty.zigTypeTag(self.sema.pt.zcu) == .int) {
+                const dest_info = res_ty.intInfo(self.sema.pt.zcu);
+                const unsigned_bits = dest_info.bits - @intFromBool(dest_info.signedness == .signed);
+                if (unsigned_bits < 21) {
+                    const out_of_range: u21 = @as(u21, 1) << @intCast(unsigned_bits);
+                    if (val >= out_of_range) {
+                        return self.fail(
+                            node,
+                            "type '{}' cannot represent integer value '{}'",
+                            .{ res_ty.fmt(self.sema.pt), val },
+                        );
+                    }
+                }
+            }
+            return self.sema.pt.intern(.{
+                .int = .{
+                    .ty = res_ty.toIntern(),
+                    .storage = .{ .i64 = val },
+                },
+            });
+        },
+
+        else => return error.WrongType,
+    };
+}
+
+fn lowerFloat(
+    self: *LowerZon,
+    node: Zoir.Node.Index,
+    res_ty: Type,
+) !InternPool.Index {
+    @setFloatMode(.strict);
+    const value = switch (node.get(self.file.zoir.?)) {
+        .int_literal => |int| switch (int) {
+            .small => |val| try self.sema.pt.floatValue(res_ty, @as(f128, @floatFromInt(val))),
+            .big => |val| try self.sema.pt.floatValue(res_ty, val.toFloat(f128)),
+        },
+        .float_literal => |val| try self.sema.pt.floatValue(res_ty, val),
+        .char_literal => |val| try self.sema.pt.floatValue(res_ty, @as(f128, @floatFromInt(val))),
+        .pos_inf => b: {
+            if (res_ty.toIntern() == .comptime_float_type) return self.fail(
+                node,
+                "expected type '{}'",
+                .{res_ty.fmt(self.sema.pt)},
+            );
+            break :b try self.sema.pt.floatValue(res_ty, std.math.inf(f128));
+        },
+        .neg_inf => b: {
+            if (res_ty.toIntern() == .comptime_float_type) return self.fail(
+                node,
+                "expected type '{}'",
+                .{res_ty.fmt(self.sema.pt)},
+            );
+            break :b try self.sema.pt.floatValue(res_ty, -std.math.inf(f128));
+        },
+        .nan => b: {
+            if (res_ty.toIntern() == .comptime_float_type) return self.fail(
+                node,
+                "expected type '{}'",
+                .{res_ty.fmt(self.sema.pt)},
+            );
+            break :b try self.sema.pt.floatValue(res_ty, std.math.nan(f128));
+        },
+        else => return error.WrongType,
+    };
+    return value.toIntern();
+}
+
+fn lowerNull(self: *LowerZon, node: Zoir.Node.Index) !InternPool.Index {
+    switch (node.get(self.file.zoir.?)) {
+        .null => return .null_value,
+        else => return error.WrongType,
+    }
+}
+
+fn lowerArray(self: *LowerZon, node: Zoir.Node.Index, res_ty: Type) !InternPool.Index {
+    const array_info = res_ty.arrayInfo(self.sema.pt.zcu);
+    const nodes: Zoir.Node.Index.Range = switch (node.get(self.file.zoir.?)) {
+        .array_literal => |nodes| nodes,
+        .empty_literal => .{ .start = node, .len = 0 },
+        else => return error.WrongType,
+    };
+
+    if (nodes.len != array_info.len) {
+        return error.WrongType;
+    }
+
+    const elems = try self.sema.arena.alloc(
+        InternPool.Index,
+        nodes.len + @intFromBool(array_info.sentinel != null),
+    );
+
+    for (0..nodes.len) |i| {
+        elems[i] = try self.lowerExpr(nodes.at(@intCast(i)), array_info.elem_type);
+    }
+
+    if (array_info.sentinel) |sentinel| {
+        elems[elems.len - 1] = sentinel.toIntern();
+    }
+
+    return self.sema.pt.intern(.{ .aggregate = .{
+        .ty = res_ty.toIntern(),
+        .storage = .{ .elems = elems },
+    } });
+}
+
+fn lowerEnum(self: *LowerZon, node: Zoir.Node.Index, res_ty: Type) !InternPool.Index {
+    const ip = &self.sema.pt.zcu.intern_pool;
+    switch (node.get(self.file.zoir.?)) {
+        .enum_literal => |field_name| {
+            const field_name_interned = try ip.getOrPutString(
+                self.sema.gpa,
+                self.sema.pt.tid,
+                field_name.get(self.file.zoir.?),
+                .no_embedded_nulls,
+            );
+            const field_index = res_ty.enumFieldIndex(field_name_interned, self.sema.pt.zcu) orelse {
+                return self.fail(
+                    node,
+                    "enum {} has no member named '{}'",
+                    .{
+                        res_ty.fmt(self.sema.pt),
+                        std.zig.fmtId(field_name.get(self.file.zoir.?)),
+                    },
+                );
+            };
+
+            const value = try self.sema.pt.enumValueFieldIndex(res_ty, field_index);
+
+            return value.toIntern();
+        },
+        else => return error.WrongType,
+    }
+}
+
+fn lowerEnumLiteral(self: *LowerZon, node: Zoir.Node.Index) !InternPool.Index {
+    const ip = &self.sema.pt.zcu.intern_pool;
+    switch (node.get(self.file.zoir.?)) {
+        .enum_literal => |field_name| {
+            const field_name_interned = try ip.getOrPutString(
+                self.sema.gpa,
+                self.sema.pt.tid,
+                field_name.get(self.file.zoir.?),
+                .no_embedded_nulls,
+            );
+            return self.sema.pt.intern(.{ .enum_literal = field_name_interned });
+        },
+        else => return error.WrongType,
+    }
+}
+
+fn lowerStructOrTuple(self: *LowerZon, node: Zoir.Node.Index, res_ty: Type) !InternPool.Index {
+    const ip = &self.sema.pt.zcu.intern_pool;
+    return switch (ip.indexToKey(res_ty.toIntern())) {
+        .tuple_type => self.lowerTuple(node, res_ty),
+        .struct_type => self.lowerStruct(node, res_ty),
+        else => unreachable,
+    };
+}
+
+fn lowerTuple(self: *LowerZon, node: Zoir.Node.Index, res_ty: Type) !InternPool.Index {
+    const ip = &self.sema.pt.zcu.intern_pool;
+
+    const tuple_info = ip.indexToKey(res_ty.toIntern()).tuple_type;
+
+    const elem_nodes: Zoir.Node.Index.Range = switch (node.get(self.file.zoir.?)) {
+        .array_literal => |nodes| nodes,
+        .empty_literal => .{ .start = node, .len = 0 },
+        else => return error.WrongType,
+    };
+
+    const field_types = tuple_info.types.get(ip);
+    const elems = try self.sema.arena.alloc(InternPool.Index, field_types.len);
+
+    const field_comptime_vals = tuple_info.values.get(ip);
+    if (field_comptime_vals.len > 0) {
+        @memcpy(elems, field_comptime_vals);
+    } else {
+        @memset(elems, .none);
+    }
+
+    for (0..elem_nodes.len) |i| {
+        if (i >= elems.len) {
+            const elem_node = elem_nodes.at(@intCast(i));
+            return self.fail(
+                elem_node,
+                "index {} outside tuple of length {}",
+                .{
+                    elems.len,
+                    elem_nodes.at(@intCast(i)).getAstNode(self.file.zoir.?),
+                },
+            );
+        }
+
+        const val = try self.lowerExpr(elem_nodes.at(@intCast(i)), .fromInterned(field_types[i]));
+
+        if (elems[i] != .none and val != elems[i]) {
+            const elem_node = elem_nodes.at(@intCast(i));
+            return self.fail(
+                elem_node,
+                "value stored in comptime field does not match the default value of the field",
+                .{},
+            );
+        }
+
+        elems[i] = val;
+    }
+
+    for (elems, 0..) |val, i| {
+        if (val == .none) {
+            return self.fail(node, "missing tuple field with index {}", .{i});
+        }
+    }
+
+    return self.sema.pt.intern(.{ .aggregate = .{
+        .ty = res_ty.toIntern(),
+        .storage = .{ .elems = elems },
+    } });
+}
+
+fn lowerStruct(self: *LowerZon, node: Zoir.Node.Index, res_ty: Type) !InternPool.Index {
+    const ip = &self.sema.pt.zcu.intern_pool;
+    const gpa = self.sema.gpa;
+
+    try res_ty.resolveFields(self.sema.pt);
+    try res_ty.resolveStructFieldInits(self.sema.pt);
+    const struct_info = self.sema.pt.zcu.typeToStruct(res_ty).?;
+
+    const fields: @FieldType(Zoir.Node, "struct_literal") = switch (node.get(self.file.zoir.?)) {
+        .struct_literal => |fields| fields,
+        .empty_literal => .{ .names = &.{}, .vals = .{ .start = node, .len = 0 } },
+        else => return error.WrongType,
+    };
+
+    const field_values = try self.sema.arena.alloc(InternPool.Index, struct_info.field_names.len);
+
+    const field_defaults = struct_info.field_inits.get(ip);
+    if (field_defaults.len > 0) {
+        @memcpy(field_values, field_defaults);
+    } else {
+        @memset(field_values, .none);
+    }
+
+    for (0..fields.names.len) |i| {
+        const field_name = try ip.getOrPutString(
+            gpa,
+            self.sema.pt.tid,
+            fields.names[i].get(self.file.zoir.?),
+            .no_embedded_nulls,
+        );
+        const field_node = fields.vals.at(@intCast(i));
+
+        const name_index = struct_info.nameIndex(ip, field_name) orelse {
+            return self.fail(field_node, "unexpected field '{}'", .{field_name.fmt(ip)});
+        };
+
+        const field_type: Type = .fromInterned(struct_info.field_types.get(ip)[name_index]);
+        field_values[name_index] = try self.lowerExpr(field_node, field_type);
+
+        if (struct_info.comptime_bits.getBit(ip, name_index)) {
+            const val = ip.indexToKey(field_values[name_index]);
+            const default = ip.indexToKey(field_defaults[name_index]);
+            if (!val.eql(default, ip)) {
+                return self.fail(
+                    field_node,
+                    "value stored in comptime field does not match the default value of the field",
+                    .{},
+                );
+            }
+        }
+    }
+
+    const field_names = struct_info.field_names.get(ip);
+    for (field_values, field_names) |*value, name| {
+        if (value.* == .none) return self.fail(node, "missing field '{}'", .{name.fmt(ip)});
+    }
+
+    return self.sema.pt.intern(.{ .aggregate = .{
+        .ty = res_ty.toIntern(),
+        .storage = .{
+            .elems = field_values,
+        },
+    } });
+}
+
+fn lowerSlice(self: *LowerZon, node: Zoir.Node.Index, res_ty: Type) !InternPool.Index {
+    const ip = &self.sema.pt.zcu.intern_pool;
+    const gpa = self.sema.gpa;
+
+    const ptr_info = res_ty.ptrInfo(self.sema.pt.zcu);
+
+    assert(ptr_info.flags.size == .slice);
+
+    // String literals
+    const string_alignment = ptr_info.flags.alignment == .none or ptr_info.flags.alignment == .@"1";
+    const string_sentinel = ptr_info.sentinel == .none or ptr_info.sentinel == .zero_u8;
+    if (string_alignment and ptr_info.child == .u8_type and string_sentinel) {
+        switch (node.get(self.file.zoir.?)) {
+            .string_literal => |val| {
+                const ip_str = try ip.getOrPutString(gpa, self.sema.pt.tid, val, .maybe_embedded_nulls);
+                const str_ref = try self.sema.addStrLit(ip_str, val.len);
+                return (try self.sema.coerce(
+                    self.block,
+                    res_ty,
+                    str_ref,
+                    self.nodeSrc(node),
+                )).toInterned().?;
+            },
+            else => {},
+        }
+    }
+
+    // Slice literals
+    const elem_nodes: Zoir.Node.Index.Range = switch (node.get(self.file.zoir.?)) {
+        .array_literal => |nodes| nodes,
+        .empty_literal => .{ .start = node, .len = 0 },
+        else => return error.WrongType,
+    };
+
+    const elems = try self.sema.arena.alloc(InternPool.Index, elem_nodes.len + @intFromBool(ptr_info.sentinel != .none));
+
+    for (elems, 0..) |*elem, i| {
+        elem.* = try self.lowerExpr(elem_nodes.at(@intCast(i)), .fromInterned(ptr_info.child));
+    }
+
+    if (ptr_info.sentinel != .none) {
+        elems[elems.len - 1] = ptr_info.sentinel;
+    }
+
+    const array_ty = try self.sema.pt.intern(.{ .array_type = .{
+        .len = elems.len,
+        .sentinel = ptr_info.sentinel,
+        .child = ptr_info.child,
+    } });
+
+    const array = try self.sema.pt.intern(.{ .aggregate = .{
+        .ty = array_ty,
+        .storage = .{ .elems = elems },
+    } });
+
+    const many_item_ptr_type = try self.sema.pt.intern(.{ .ptr_type = .{
+        .child = ptr_info.child,
+        .sentinel = ptr_info.sentinel,
+        .flags = b: {
+            var flags = ptr_info.flags;
+            flags.size = .many;
+            break :b flags;
+        },
+        .packed_offset = ptr_info.packed_offset,
+    } });
+
+    const many_item_ptr = try self.sema.pt.intern(.{
+        .ptr = .{
+            .ty = many_item_ptr_type,
+            .base_addr = .{
+                .uav = .{
+                    .orig_ty = (try self.sema.pt.singleConstPtrType(.fromInterned(array_ty))).toIntern(),
+                    .val = array,
+                },
+            },
+            .byte_offset = 0,
+        },
+    });
+
+    const len = (try self.sema.pt.intValue(.usize, elems.len)).toIntern();
+
+    return self.sema.pt.intern(.{ .slice = .{
+        .ty = res_ty.toIntern(),
+        .ptr = many_item_ptr,
+        .len = len,
+    } });
+}
+
+fn lowerUnion(self: *LowerZon, node: Zoir.Node.Index, res_ty: Type) !InternPool.Index {
+    const ip = &self.sema.pt.zcu.intern_pool;
+    try res_ty.resolveFields(self.sema.pt);
+    const union_info = self.sema.pt.zcu.typeToUnion(res_ty).?;
+    const enum_tag_info = union_info.loadTagType(ip);
+
+    const field_name, const maybe_field_node = switch (node.get(self.file.zoir.?)) {
+        .enum_literal => |name| b: {
+            const field_name = try ip.getOrPutString(
+                self.sema.gpa,
+                self.sema.pt.tid,
+                name.get(self.file.zoir.?),
+                .no_embedded_nulls,
+            );
+            break :b .{ field_name, null };
+        },
+        .struct_literal => b: {
+            const fields: @FieldType(Zoir.Node, "struct_literal") = switch (node.get(self.file.zoir.?)) {
+                .struct_literal => |fields| fields,
+                else => return self.fail(node, "expected type '{}'", .{res_ty.fmt(self.sema.pt)}),
+            };
+            if (fields.names.len != 1) {
+                return error.WrongType;
+            }
+            const field_name = try ip.getOrPutString(
+                self.sema.gpa,
+                self.sema.pt.tid,
+                fields.names[0].get(self.file.zoir.?),
+                .no_embedded_nulls,
+            );
+            break :b .{ field_name, fields.vals.at(0) };
+        },
+        else => return error.WrongType,
+    };
+
+    const name_index = enum_tag_info.nameIndex(ip, field_name) orelse {
+        return error.WrongType;
+    };
+    const tag = try self.sema.pt.enumValueFieldIndex(.fromInterned(union_info.enum_tag_ty), name_index);
+    const field_type: Type = .fromInterned(union_info.field_types.get(ip)[name_index]);
+    const val = if (maybe_field_node) |field_node| b: {
+        if (field_type.toIntern() == .void_type) {
+            return self.fail(field_node, "expected type 'void'", .{});
+        }
+        break :b try self.lowerExpr(field_node, field_type);
+    } else b: {
+        if (field_type.toIntern() != .void_type) {
+            return error.WrongType;
+        }
+        break :b .void_value;
+    };
+    return ip.getUnion(self.sema.pt.zcu.gpa, self.sema.pt.tid, .{
+        .ty = res_ty.toIntern(),
+        .tag = tag.toIntern(),
+        .val = val,
+    });
+}
+
+fn lowerVector(self: *LowerZon, node: Zoir.Node.Index, res_ty: Type) !InternPool.Index {
+    const ip = &self.sema.pt.zcu.intern_pool;
+
+    const vector_info = ip.indexToKey(res_ty.toIntern()).vector_type;
+
+    const elem_nodes: Zoir.Node.Index.Range = switch (node.get(self.file.zoir.?)) {
+        .array_literal => |nodes| nodes,
+        .empty_literal => .{ .start = node, .len = 0 },
+        else => return error.WrongType,
+    };
+
+    const elems = try self.sema.arena.alloc(InternPool.Index, vector_info.len);
+
+    if (elem_nodes.len != vector_info.len) {
+        return self.fail(
+            node,
+            "expected {} vector elements; found {}",
+            .{ vector_info.len, elem_nodes.len },
+        );
+    }
+
+    for (elems, 0..) |*elem, i| {
+        elem.* = try self.lowerExpr(elem_nodes.at(@intCast(i)), .fromInterned(vector_info.child));
+    }
+
+    return self.sema.pt.intern(.{ .aggregate = .{
+        .ty = res_ty.toIntern(),
+        .storage = .{ .elems = elems },
+    } });
+}

src/Value.zig

@@ -270,7 +270,7 @@ pub fn getUnsignedIntInner(
         else => switch (zcu.intern_pool.indexToKey(val.toIntern())) {
             .undef => unreachable,
             .int => |int| switch (int.storage) {
-                .big_int => |big_int| big_int.to(u64) catch null,
+                .big_int => |big_int| big_int.toInt(u64) catch null,
                 .u64 => |x| x,
                 .i64 => |x| std.math.cast(u64, x),
                 .lazy_align => |ty| (try Type.fromInterned(ty).abiAlignmentInner(strat.toLazy(), zcu, tid)).scalar.toByteUnits() orelse 0,
@@ -311,7 +311,7 @@ pub fn toSignedInt(val: Value, zcu: *const Zcu) i64 {
         .bool_true => 1,
         else => switch (zcu.intern_pool.indexToKey(val.toIntern())) {
             .int => |int| switch (int.storage) {
-                .big_int => |big_int| big_int.to(i64) catch unreachable,
+                .big_int => |big_int| big_int.toInt(i64) catch unreachable,
                 .i64 => |x| x,
                 .u64 => |x| @intCast(x),
                 .lazy_align => |ty| @intCast(Type.fromInterned(ty).abiAlignment(zcu).toByteUnits() orelse 0),
@@ -898,7 +898,7 @@ pub fn readFromPackedMemory(
 pub fn toFloat(val: Value, comptime T: type, zcu: *Zcu) T {
     return switch (zcu.intern_pool.indexToKey(val.toIntern())) {
         .int => |int| switch (int.storage) {
-            .big_int => |big_int| @floatCast(bigIntToFloat(big_int.limbs, big_int.positive)),
+            .big_int => |big_int| big_int.toFloat(T),
             inline .u64, .i64 => |x| {
                 if (T == f80) {
                     @panic("TODO we can't lower this properly on non-x86 llvm backend yet");
@@ -915,25 +915,6 @@ pub fn toFloat(val: Value, comptime T: type, zcu: *Zcu) T {
     };
 }
 
-/// TODO move this to std lib big int code
-fn bigIntToFloat(limbs: []const std.math.big.Limb, positive: bool) f128 {
-    if (limbs.len == 0) return 0;
-
-    const base = std.math.maxInt(std.math.big.Limb) + 1;
-    var result: f128 = 0;
-    var i: usize = limbs.len;
-    while (i != 0) {
-        i -= 1;
-        const limb: f128 = @floatFromInt(limbs[i]);
-        result = @mulAdd(f128, base, result, limb);
-    }
-    if (positive) {
-        return result;
-    } else {
-        return -result;
-    }
-}
-
 pub fn clz(val: Value, ty: Type, zcu: *Zcu) u64 {
     var bigint_buf: BigIntSpace = undefined;
     const bigint = val.toBigInt(&bigint_buf, zcu);
@@ -1548,7 +1529,7 @@ pub fn floatFromIntScalar(val: Value, float_ty: Type, pt: Zcu.PerThread, comptim
         .undef => try pt.undefValue(float_ty),
         .int => |int| switch (int.storage) {
             .big_int => |big_int| {
-                const float = bigIntToFloat(big_int.limbs, big_int.positive);
+                const float = big_int.toFloat(f128);
                 return pt.floatValue(float_ty, float);
             },
             inline .u64, .i64 => |x| floatFromIntInner(x, float_ty, pt),
@@ -4583,7 +4564,7 @@ pub fn interpret(val: Value, comptime T: type, pt: Zcu.PerThread) error{ OutOfMe
         .int => switch (ip.indexToKey(val.toIntern()).int.storage) {
             .lazy_align, .lazy_size => unreachable, // `val` is fully resolved
             inline .u64, .i64 => |x| std.math.cast(T, x) orelse return error.TypeMismatch,
-            .big_int => |big| big.to(T) catch return error.TypeMismatch,
+            .big_int => |big| big.toInt(T) catch return error.TypeMismatch,
         },
 
         .float => val.toFloat(T, zcu),

src/Zcu.zig

@@ -39,6 +39,8 @@ const AnalUnit = InternPool.AnalUnit;
 const BuiltinFn = std.zig.BuiltinFn;
 const LlvmObject = @import("codegen/llvm.zig").Object;
 const dev = @import("dev.zig");
+const Zoir = std.zig.Zoir;
+const ZonGen = std.zig.ZonGen;
 
 comptime {
     @setEvalBranchQuota(4000);
@@ -672,6 +674,8 @@ pub const File = struct {
     tree: Ast,
     /// Whether this is populated or not depends on `zir_loaded`.
     zir: Zir,
+    /// Cached Zoir, generated lazily.
+    zoir: ?Zoir = null,
     /// Module that this file is a part of, managed externally.
     mod: *Package.Module,
     /// Whether this file is a part of multiple packages. This is an error condition which will be reported after AstGen.
@@ -704,7 +708,19 @@ pub const File = struct {
         root: *Package.Module,
     };
 
+    pub fn getMode(self: File) Ast.Mode {
+        if (std.mem.endsWith(u8, self.sub_file_path, ".zon")) {
+            return .zon;
+        } else if (std.mem.endsWith(u8, self.sub_file_path, ".zig")) {
+            return .zig;
+        } else {
+            // `Module.importFile` rejects all other extensions
+            unreachable;
+        }
+    }
+
     pub fn unload(file: *File, gpa: Allocator) void {
+        if (file.zoir) |zoir| zoir.deinit(gpa);
         file.unloadTree(gpa);
         file.unloadSource(gpa);
         file.unloadZir(gpa);
@@ -778,11 +794,24 @@ pub const File = struct {
         if (file.tree_loaded) return &file.tree;
 
         const source = try file.getSource(gpa);
-        file.tree = try Ast.parse(gpa, source.bytes, .zig);
+        file.tree = try Ast.parse(gpa, source.bytes, file.getMode());
         file.tree_loaded = true;
         return &file.tree;
     }
 
+    pub fn getZoir(file: *File, zcu: *Zcu) !*const Zoir {
+        if (file.zoir) |*zoir| return zoir;
+
+        assert(file.tree_loaded);
+        assert(file.tree.mode == .zon);
+        file.zoir = try ZonGen.generate(zcu.gpa, file.tree, .{});
+        if (file.zoir.?.hasCompileErrors()) {
+            try zcu.failed_files.putNoClobber(zcu.gpa, file, null);
+            return error.AnalysisFail;
+        }
+        return &file.zoir.?;
+    }
+
     pub fn fullyQualifiedNameLen(file: File) usize {
         const ext = std.fs.path.extension(file.sub_file_path);
         return file.sub_file_path.len - ext.len;
@@ -895,6 +924,7 @@ pub const File = struct {
     pub const Index = InternPool.FileIndex;
 };
 
+/// Represents the contents of a file loaded with `@embedFile`.
 pub const EmbedFile = struct {
     /// Module that this file is a part of, managed externally.
     owner: *Package.Module,
@@ -2372,6 +2402,12 @@ pub const LazySrcLoc = struct {
             break :inst .{ info.file, info.inst };
         };
         const file = zcu.fileByIndex(file_index);
+
+        // If we're relative to .main_struct_inst, we know the ast node is the root and don't need to resolve the ZIR,
+        // which may not exist e.g. in the case of errors in ZON files.
+        if (zir_inst == .main_struct_inst) return .{ file, 0 };
+
+        // Otherwise, make sure ZIR is loaded.
         assert(file.zir_loaded);
 
         const zir = file.zir;
@@ -3461,8 +3497,6 @@ pub fn atomicPtrAlignment(
 }
 
 /// Returns null in the following cases:
-/// * `@TypeOf(.{})`
-/// * A struct which has no fields (`struct {}`).
 /// * Not a struct.
 pub fn typeToStruct(zcu: *const Zcu, ty: Type) ?InternPool.LoadedStructType {
     if (ty.ip_index == .none) return null;

src/Zcu/PerThread.zig

@@ -1867,6 +1867,7 @@ fn semaFile(pt: Zcu.PerThread, file_index: Zcu.File.Index) Zcu.SemaError!void {
     const zcu = pt.zcu;
     const gpa = zcu.gpa;
     const file = zcu.fileByIndex(file_index);
+    assert(file.getMode() == .zig);
     assert(zcu.fileRootType(file_index) == .none);
 
     if (file.status != .success_zir) {
@@ -2022,7 +2023,9 @@ pub fn importFile(
     if (mod.deps.get(import_string)) |pkg| {
         return pt.importPkg(pkg);
     }
-    if (!std.mem.endsWith(u8, import_string, ".zig")) {
+    if (!std.mem.endsWith(u8, import_string, ".zig") and
+        !std.mem.endsWith(u8, import_string, ".zon"))
+    {
         return error.ModuleNotFound;
     }
     const gpa = zcu.gpa;

src/codegen/llvm/Builder.zig

@@ -13776,8 +13776,8 @@ pub fn toBitcode(self: *Builder, allocator: Allocator) bitcode_writer.Error![]co
                         };
                         const bit_count = extra.type.scalarBits(self);
                         const val: i64 = if (bit_count <= 64)
-                            bigint.to(i64) catch unreachable
+                            bigint.toInt(i64) catch unreachable
-                        else if (bigint.to(u64)) |val|
+                        else if (bigint.toInt(u64)) |val|
                             @bitCast(val)
                         else |_| {
                             const limbs = try record.addManyAsSlice(
@@ -14276,9 +14276,9 @@ pub fn toBitcode(self: *Builder, allocator: Allocator) bitcode_writer.Error![]co
                                 else => unreachable,
                             },
                         };
-                        const val: i64 = if (bigint.to(i64)) |val|
+                        const val: i64 = if (bigint.toInt(i64)) |val|
                             val
-                        else |_| if (bigint.to(u64)) |val|
+                        else |_| if (bigint.toInt(u64)) |val|
                             @bitCast(val)
                         else |_| {
                             const limbs_len = std.math.divCeil(u32, extra.bit_width, 64) catch unreachable;

src/fmt.zig

@@ -120,7 +120,7 @@ pub fn run(
                     process.exit(2);
                 }
             } else {
-                const zoir = try std.zig.ZonGen.generate(gpa, tree);
+                const zoir = try std.zig.ZonGen.generate(gpa, tree, .{});
                 defer zoir.deinit(gpa);
 
                 if (zoir.hasCompileErrors()) {
@@ -335,7 +335,7 @@ fn fmtPathFile(
                 }
             },
             .zon => {
-                var zoir = try std.zig.ZonGen.generate(gpa, tree);
+                var zoir = try std.zig.ZonGen.generate(gpa, tree, .{});
                 defer zoir.deinit(gpa);
 
                 if (zoir.hasCompileErrors()) {

src/main.zig

@@ -6278,7 +6278,7 @@ fn cmdAstCheck(
             }
         },
         .zon => {
-            const zoir = try ZonGen.generate(gpa, file.tree);
+            const zoir = try ZonGen.generate(gpa, file.tree, .{});
             defer zoir.deinit(gpa);
 
             if (zoir.hasCompileErrors()) {

src/print_zir.zig

@@ -488,7 +488,6 @@ const Writer = struct {
             .enum_literal,
             .decl_ref,
             .decl_val,
-            .import,
             .ret_err_value,
             .ret_err_value_code,
             .param_anytype,
@@ -515,6 +514,8 @@ const Writer = struct {
             .declaration => try self.writeDeclaration(stream, inst),
 
             .extended => try self.writeExtended(stream, inst),
+
+            .import => try self.writeImport(stream, inst),
         }
     }
 
@@ -2842,4 +2843,13 @@ const Writer = struct {
             try stream.writeByte('\n');
         }
     }
+
+    fn writeImport(self: *Writer, stream: anytype, inst: Zir.Inst.Index) !void {
+        const inst_data = self.code.instructions.items(.data)[@intFromEnum(inst)].pl_tok;
+        const extra = self.code.extraData(Zir.Inst.Import, inst_data.payload_index).data;
+        try self.writeInstRef(stream, extra.res_ty);
+        const import_path = self.code.nullTerminatedString(extra.path);
+        try stream.print(", \"{}\") ", .{std.zig.fmtEscapes(import_path)});
+        try self.writeSrcTok(stream, inst_data.src_tok);
+    }
 };

test/behavior/zon.zig

@@ -0,0 +1,519 @@
+const std = @import("std");
+
+const expect = std.testing.expect;
+const expectEqual = std.testing.expectEqual;
+const expectEqualDeep = std.testing.expectEqualDeep;
+const expectEqualSlices = std.testing.expectEqualSlices;
+const expectEqualStrings = std.testing.expectEqualStrings;
+
+test "bool" {
+    try expectEqual(true, @as(bool, @import("zon/true.zon")));
+    try expectEqual(false, @as(bool, @import("zon/false.zon")));
+}
+
+test "optional" {
+    const some: ?u32 = @import("zon/some.zon");
+    const none: ?u32 = @import("zon/none.zon");
+    const @"null": @TypeOf(null) = @import("zon/none.zon");
+    try expectEqual(@as(u32, 10), some);
+    try expectEqual(@as(?u32, null), none);
+    try expectEqual(null, @"null");
+}
+
+test "union" {
+    // No tag
+    {
+        const Union = union {
+            x: f32,
+            y: bool,
+            z: void,
+        };
+
+        const union1: Union = @import("zon/union1.zon");
+        const union2: Union = @import("zon/union2.zon");
+        const union3: Union = @import("zon/union3.zon");
+
+        try expectEqual(1.5, union1.x);
+        try expectEqual(true, union2.y);
+        try expectEqual({}, union3.z);
+    }
+
+    // Inferred tag
+    {
+        const Union = union(enum) {
+            x: f32,
+            y: bool,
+            z: void,
+        };
+
+        const union1: Union = comptime @import("zon/union1.zon");
+        const union2: Union = @import("zon/union2.zon");
+        const union3: Union = @import("zon/union3.zon");
+
+        try expectEqual(1.5, union1.x);
+        try expectEqual(true, union2.y);
+        try expectEqual({}, union3.z);
+    }
+
+    // Explicit tag
+    {
+        const Tag = enum(i128) {
+            x = -1,
+            y = 2,
+            z = 1,
+        };
+        const Union = union(Tag) {
+            x: f32,
+            y: bool,
+            z: void,
+        };
+
+        const union1: Union = @import("zon/union1.zon");
+        const union2: Union = @import("zon/union2.zon");
+        const union3: Union = @import("zon/union3.zon");
+
+        try expectEqual(1.5, union1.x);
+        try expectEqual(true, union2.y);
+        try expectEqual({}, union3.z);
+    }
+}
+
+test "struct" {
+    const Vec0 = struct {};
+    const Vec1 = struct { x: f32 };
+    const Vec2 = struct { x: f32, y: f32 };
+    const Escaped = struct { @"0": f32, foo: f32 };
+    try expectEqual(Vec0{}, @as(Vec0, @import("zon/vec0.zon")));
+    try expectEqual(Vec1{ .x = 1.5 }, @as(Vec1, @import("zon/vec1.zon")));
+    try expectEqual(Vec2{ .x = 1.5, .y = 2 }, @as(Vec2, @import("zon/vec2.zon")));
+    try expectEqual(Escaped{ .@"0" = 1.5, .foo = 2 }, @as(Escaped, @import("zon/escaped_struct.zon")));
+}
+
+test "struct default fields" {
+    const Vec3 = struct {
+        x: f32,
+        y: f32,
+        z: f32 = 123.4,
+    };
+    try expectEqual(Vec3{ .x = 1.5, .y = 2.0, .z = 123.4 }, @as(Vec3, @import("zon/vec2.zon")));
+    const ascribed: Vec3 = @import("zon/vec2.zon");
+    try expectEqual(Vec3{ .x = 1.5, .y = 2.0, .z = 123.4 }, ascribed);
+
+    const Vec2 = struct {
+        x: f32 = 20.0,
+        y: f32 = 10.0,
+    };
+    try expectEqual(Vec2{ .x = 1.5, .y = 2.0 }, @as(Vec2, @import("zon/vec2.zon")));
+}
+
+test "struct enum field" {
+    const Struct = struct {
+        x: enum { x, y, z },
+    };
+    try expectEqual(Struct{ .x = .z }, @as(Struct, @import("zon/enum_field.zon")));
+}
+
+test "tuple" {
+    const Tuple = struct { f32, bool, []const u8, u16 };
+    try expectEqualDeep(Tuple{ 1.2, true, "hello", 3 }, @as(Tuple, @import("zon/tuple.zon")));
+}
+
+test "comptime fields" {
+    // Test setting comptime tuple fields to the correct value
+    {
+        const Tuple = struct {
+            comptime f32 = 1.2,
+            comptime bool = true,
+            comptime []const u8 = "hello",
+            comptime u16 = 3,
+        };
+        try expectEqualDeep(Tuple{ 1.2, true, "hello", 3 }, @as(Tuple, @import("zon/tuple.zon")));
+    }
+
+    // Test setting comptime struct fields to the correct value
+    {
+        const Vec2 = struct {
+            comptime x: f32 = 1.5,
+            comptime y: f32 = 2.0,
+        };
+        try expectEqualDeep(Vec2{}, @as(Vec2, @import("zon/vec2.zon")));
+    }
+
+    // Test allowing comptime tuple fields to be set to their defaults
+    {
+        const Tuple = struct {
+            f32,
+            bool,
+            []const u8,
+            u16,
+            comptime u8 = 255,
+        };
+        try expectEqualDeep(Tuple{ 1.2, true, "hello", 3 }, @as(Tuple, @import("zon/tuple.zon")));
+    }
+
+    // Test allowing comptime struct fields to be set to their defaults
+    {
+        const Vec2 = struct {
+            comptime x: f32 = 1.5,
+            comptime y: f32 = 2.0,
+        };
+        try expectEqualDeep(Vec2{}, @as(Vec2, @import("zon/slice-empty.zon")));
+    }
+}
+
+test "char" {
+    try expectEqual(@as(u8, 'a'), @as(u8, @import("zon/a.zon")));
+    try expectEqual(@as(u8, 'z'), @as(u8, @import("zon/z.zon")));
+}
+
+test "arrays" {
+    try expectEqual([0]u8{}, @as([0]u8, @import("zon/vec0.zon")));
+    try expectEqual([0:1]u8{}, @as([0:1]u8, @import("zon/vec0.zon")));
+    try expectEqual(1, @as([0:1]u8, @import("zon/vec0.zon"))[0]);
+    try expectEqual([4]u8{ 'a', 'b', 'c', 'd' }, @as([4]u8, @import("zon/array.zon")));
+    try expectEqual([4:2]u8{ 'a', 'b', 'c', 'd' }, @as([4:2]u8, @import("zon/array.zon")));
+    try expectEqual(2, @as([4:2]u8, @import("zon/array.zon"))[4]);
+}
+
+test "slices, arrays, tuples" {
+    {
+        const expected_slice: []const u8 = &.{};
+        const found_slice: []const u8 = @import("zon/slice-empty.zon");
+        try expectEqualSlices(u8, expected_slice, found_slice);
+
+        const expected_array: [0]u8 = .{};
+        const found_array: [0]u8 = @import("zon/slice-empty.zon");
+        try expectEqual(expected_array, found_array);
+
+        const T = struct {};
+        const expected_tuple: T = .{};
+        const found_tuple: T = @import("zon/slice-empty.zon");
+        try expectEqual(expected_tuple, found_tuple);
+    }
+
+    {
+        const expected_slice: []const u8 = &.{1};
+        const found_slice: []const u8 = @import("zon/slice1_no_newline.zon");
+        try expectEqualSlices(u8, expected_slice, found_slice);
+
+        const expected_array: [1]u8 = .{1};
+        const found_array: [1]u8 = @import("zon/slice1_no_newline.zon");
+        try expectEqual(expected_array, found_array);
+
+        const T = struct { u8 };
+        const expected_tuple: T = .{1};
+        const found_tuple: T = @import("zon/slice1_no_newline.zon");
+        try expectEqual(expected_tuple, found_tuple);
+    }
+
+    {
+        const expected_slice: []const u8 = &.{ 'a', 'b', 'c' };
+        const found_slice: []const u8 = @import("zon/slice-abc.zon");
+        try expectEqualSlices(u8, expected_slice, found_slice);
+
+        const expected_array: [3]u8 = .{ 'a', 'b', 'c' };
+        const found_array: [3]u8 = @import("zon/slice-abc.zon");
+        try expectEqual(expected_array, found_array);
+
+        const T = struct { u8, u8, u8 };
+        const expected_tuple: T = .{ 'a', 'b', 'c' };
+        const found_tuple: T = @import("zon/slice-abc.zon");
+        try expectEqual(expected_tuple, found_tuple);
+    }
+}
+
+test "string literals" {
+    try expectEqualSlices(u8, "abc", @import("zon/abc.zon"));
+    try expectEqualSlices(u8, "ab\\c", @import("zon/abc-escaped.zon"));
+    const zero_terminated: [:0]const u8 = @import("zon/abc.zon");
+    try expectEqualDeep(zero_terminated, "abc");
+    try expectEqual(0, zero_terminated[zero_terminated.len]);
+    try expectEqualStrings(
+        \\Hello, world!
+        \\This is a multiline string!
+        \\ There are no escapes, we can, for example, include \n in the string
+    , @import("zon/multiline_string.zon"));
+    try expectEqualStrings("a\nb\x00c", @import("zon/string_embedded_null.zon"));
+}
+
+test "enum literals" {
+    const Enum = enum {
+        foo,
+        bar,
+        baz,
+        @"0\na",
+    };
+    try expectEqual(Enum.foo, @as(Enum, @import("zon/foo.zon")));
+    try expectEqual(.foo, @as(@TypeOf(.foo), @import("zon/foo.zon")));
+    try expectEqual(Enum.@"0\na", @as(Enum, @import("zon/escaped_enum.zon")));
+}
+
+test "int" {
+    const T = struct {
+        u8,
+        i16,
+        i14,
+        i32,
+        i8,
+        i8,
+        u8,
+        u8,
+        u65,
+        u65,
+        i128,
+        i128,
+        i66,
+        i66,
+        i8,
+        i8,
+        i16,
+        i16,
+        i16,
+        i16,
+        i16,
+        i16,
+        u65,
+        i66,
+        i66,
+        u65,
+        i66,
+        i66,
+        u65,
+        i66,
+        i66,
+    };
+    const expected: T = .{
+        // Test various numbers and types
+        10,
+        24,
+        -4,
+        -123,
+
+        // Test limits
+        127,
+        -128,
+
+        // Test characters
+        'a',
+        'z',
+
+        // Test big integers
+        36893488147419103231,
+        36893488147419103231,
+        -18446744073709551615, // Only a big int due to negation
+        -9223372036854775809, // Only a big int due to negation
+
+        // Test big integer limits
+        36893488147419103231,
+        -36893488147419103232,
+
+        // Test parsing whole number floats as integers
+        -1,
+        123,
+
+        // Test non-decimal integers
+        0xff,
+        -0xff,
+        0o77,
+        -0o77,
+        0b11,
+        -0b11,
+
+        // Test non-decimal big integers
+        0x1ffffffffffffffff,
+        0x1ffffffffffffffff,
+        -0x1ffffffffffffffff,
+        0x1ffffffffffffffff,
+        0x1ffffffffffffffff,
+        -0x1ffffffffffffffff,
+        0x1ffffffffffffffff,
+        0x1ffffffffffffffff,
+        -0x1ffffffffffffffff,
+    };
+    const actual: T = @import("zon/ints.zon");
+    try expectEqual(expected, actual);
+}
+
+test "floats" {
+    const T = struct {
+        f16,
+        f32,
+        f64,
+        f128,
+        f16,
+        f16,
+        f32,
+        f32,
+        f32,
+        f32,
+        f32,
+        f32,
+        f128,
+        f32,
+        f32,
+        f32,
+        f32,
+        f32,
+    };
+    const expected: T = .{
+        // Test decimals
+        0.5,
+        123.456,
+        -123.456,
+        42.5,
+
+        // Test whole numbers with and without decimals
+        5.0,
+        5.0,
+        -102,
+        -102,
+
+        // Test characters and negated characters
+        'a',
+        'z',
+
+        // Test big integers
+        36893488147419103231,
+        -36893488147419103231,
+        0x1ffffffffffffffff,
+        0x1ffffffffffffffff,
+
+        // Exponents, underscores
+        123.0E+77,
+
+        // Hexadecimal
+        0x103.70p-5,
+        -0x103.70,
+        0x1234_5678.9ABC_CDEFp-10,
+    };
+    const actual: T = @import("zon/floats.zon");
+    try expectEqual(expected, actual);
+}
+
+test "inf and nan" {
+    // f32
+    {
+        const actual: struct { f32, f32, f32 } = @import("zon/inf_and_nan.zon");
+        try expect(std.math.isNan(actual[0]));
+        try expect(std.math.isPositiveInf(actual[1]));
+        try expect(std.math.isNegativeInf(actual[2]));
+    }
+
+    // f128
+    {
+        const actual: struct { f128, f128, f128 } = @import("zon/inf_and_nan.zon");
+        try expect(std.math.isNan(actual[0]));
+        try expect(std.math.isPositiveInf(actual[1]));
+        try expect(std.math.isNegativeInf(actual[2]));
+    }
+}
+
+test "vector" {
+    {
+        const actual: @Vector(0, bool) = @import("zon/vec0.zon");
+        const expected: @Vector(0, bool) = .{};
+        try expectEqual(expected, actual);
+    }
+    {
+        const actual: @Vector(3, bool) = @import("zon/vec3_bool.zon");
+        const expected: @Vector(3, bool) = .{ false, false, true };
+        try expectEqual(expected, actual);
+    }
+
+    {
+        const actual: @Vector(0, f32) = @import("zon/vec0.zon");
+        const expected: @Vector(0, f32) = .{};
+        try expectEqual(expected, actual);
+    }
+    {
+        const actual: @Vector(3, f32) = @import("zon/vec3_float.zon");
+        const expected: @Vector(3, f32) = .{ 1.5, 2.5, 3.5 };
+        try expectEqual(expected, actual);
+    }
+
+    {
+        const actual: @Vector(0, u8) = @import("zon/vec0.zon");
+        const expected: @Vector(0, u8) = .{};
+        try expectEqual(expected, actual);
+    }
+    {
+        const actual: @Vector(3, u8) = @import("zon/vec3_int.zon");
+        const expected: @Vector(3, u8) = .{ 2, 4, 6 };
+        try expectEqual(expected, actual);
+    }
+
+    {
+        const actual: @Vector(0, *const u8) = @import("zon/vec0.zon");
+        const expected: @Vector(0, *const u8) = .{};
+        try expectEqual(expected, actual);
+    }
+    {
+        const actual: @Vector(3, *const u8) = @import("zon/vec3_int.zon");
+        const expected: @Vector(3, *const u8) = .{ &2, &4, &6 };
+        try expectEqual(expected, actual);
+    }
+
+    {
+        const actual: @Vector(0, ?*const u8) = @import("zon/vec0.zon");
+        const expected: @Vector(0, ?*const u8) = .{};
+        try expectEqual(expected, actual);
+    }
+    {
+        const actual: @Vector(3, ?*const u8) = @import("zon/vec3_int_opt.zon");
+        const expected: @Vector(3, ?*const u8) = .{ &2, null, &6 };
+        try expectEqual(expected, actual);
+    }
+}
+
+test "pointers" {
+    // Primitive with varying levels of pointers
+    try expectEqual(@as(u8, 'a'), @as(*const u8, @import("zon/a.zon")).*);
+    try expectEqual(@as(u8, 'a'), @as(*const *const u8, @import("zon/a.zon")).*.*);
+    try expectEqual(@as(u8, 'a'), @as(*const *const *const u8, @import("zon/a.zon")).*.*.*);
+
+    // Primitive optional with varying levels of pointers
+    try expectEqual(@as(u8, 'a'), @as(?*const u8, @import("zon/a.zon")).?.*);
+    try expectEqual(null, @as(?*const u8, @import("zon/none.zon")));
+
+    try expectEqual(@as(u8, 'a'), @as(*const ?u8, @import("zon/a.zon")).*.?);
+    try expectEqual(null, @as(*const ?u8, @import("zon/none.zon")).*);
+
+    try expectEqual(@as(u8, 'a'), @as(?*const *const u8, @import("zon/a.zon")).?.*.*);
+    try expectEqual(null, @as(?*const *const u8, @import("zon/none.zon")));
+
+    try expectEqual(@as(u8, 'a'), @as(*const ?*const u8, @import("zon/a.zon")).*.?.*);
+    try expectEqual(null, @as(*const ?*const u8, @import("zon/none.zon")).*);
+
+    try expectEqual(@as(u8, 'a'), @as(*const *const ?u8, @import("zon/a.zon")).*.*.?);
+    try expectEqual(null, @as(*const *const ?u8, @import("zon/none.zon")).*.*);
+
+    try expectEqual([3]u8{ 2, 4, 6 }, @as(*const [3]u8, @import("zon/vec3_int.zon")).*);
+
+    // A complicated type with nested internal pointers and string allocations
+    {
+        const Inner = struct {
+            f1: *const ?*const []const u8,
+            f2: *const ?*const []const u8,
+        };
+        const Outer = struct {
+            f1: *const ?*const Inner,
+            f2: *const ?*const Inner,
+        };
+        const expected: Outer = .{
+            .f1 = &&.{
+                .f1 = &null,
+                .f2 = &&"foo",
+            },
+            .f2 = &null,
+        };
+
+        const found: ?*const Outer = @import("zon/complex.zon");
+        try std.testing.expectEqualDeep(expected, found.?.*);
+    }
+}
+
+test "recursive" {
+    const Recursive = struct { foo: ?*const @This() };
+    const expected: Recursive = .{ .foo = &.{ .foo = null } };
+    try expectEqualDeep(expected, @as(Recursive, @import("zon/recursive.zon")));
+}

test/behavior/zon/a.zon

@@ -0,0 +1 @@
+'a'

test/behavior/zon/abc-escaped.zon

@@ -0,0 +1 @@
+"ab\\c"

test/behavior/zon/abc.zon

@@ -0,0 +1 @@
+"abc"

test/behavior/zon/array.zon

@@ -0,0 +1 @@
+.{ 'a', 'b', 'c', 'd' }

test/behavior/zon/complex.zon

@@ -0,0 +1,7 @@
+.{
+    .f1 = .{
+        .f1 = null,
+        .f2 = "foo",
+    },
+    .f2 = null,
+}

test/behavior/zon/enum_field.zon

@@ -0,0 +1 @@
+.{ .x = .z }

test/behavior/zon/escaped_enum.zon

@@ -0,0 +1 @@
+.@"0\na"

test/behavior/zon/escaped_struct.zon

@@ -0,0 +1,2 @@
+
+.{ .@"0" = 1.5, .@"foo" = 2 }

test/behavior/zon/false.zon

@@ -0,0 +1,4 @@
+// Comment
+false // Another comment
+// Yet another comment
+

test/behavior/zon/floats.zon

@@ -0,0 +1,25 @@
+.{
+    0.5,
+    123.456,
+    -123.456,
+    42.5,
+
+    5.0,
+    5,
+    -102.0,
+    -102,
+
+    'a',
+    'z',
+
+    36893488147419103231,
+    -36893488147419103231,
+    0x1ffffffffffffffff,
+    0x1ffffffffffffffff,
+
+    12_3.0E+77,
+
+    0x103.70p-5,
+    -0x103.70,
+    0x1234_5678.9ABC_CDEFp-10,
+}

test/behavior/zon/foo.zon

@@ -0,0 +1 @@
+.foo

test/behavior/zon/inf_and_nan.zon

@@ -0,0 +1,5 @@
+.{
+    nan,
+    inf,
+    -inf,
+}

test/behavior/zon/ints.zon

@@ -0,0 +1,40 @@
+.{
+    10,
+    24,
+    -4,
+    -123,
+
+    127,
+    -128,
+
+    'a',
+    'z',
+
+    36893488147419103231,
+    368934_881_474191032_31,
+    -18446744073709551615,
+    -9223372036854775809,
+
+    36893488147419103231,
+    -36893488147419103232,
+
+    -1.0,
+    123.0,
+
+    0xff,
+    -0xff,
+    0o77,
+    -0o77,
+    0b11,
+    -0b11,
+
+    0x1ffffffffffffffff,
+    0x1ffffffffffffffff,
+    -0x1ffffffffffffffff,
+    0o3777777777777777777777,
+    0o3777777777777777777777,
+    -0o3777777777777777777777,
+    0b11111111111111111111111111111111111111111111111111111111111111111,
+    0b11111111111111111111111111111111111111111111111111111111111111111,
+    -0b11111111111111111111111111111111111111111111111111111111111111111,
+}

test/behavior/zon/multiline_string.zon

@@ -0,0 +1,4 @@
+// zig fmt: off
+    \\Hello, world!
+\\This is a multiline string!
+  \\ There are no escapes, we can, for example, include \n in the string

test/behavior/zon/none.zon

@@ -0,0 +1 @@
+null

test/behavior/zon/recursive.zon

@@ -0,0 +1 @@
+.{ .foo = .{ .foo = null } }

test/behavior/zon/slice-abc.zon

@@ -0,0 +1 @@
+.{'a', 'b', 'c'}

test/behavior/zon/slice-empty.zon

@@ -0,0 +1 @@
+.{}

test/behavior/zon/slice1_no_newline.zon

@@ -0,0 +1 @@
+.{ 1 }

test/behavior/zon/some.zon

@@ -0,0 +1 @@
+10

test/behavior/zon/string_embedded_null.zon

@@ -0,0 +1 @@
+"a\nb\x00c"

test/behavior/zon/true.zon

@@ -0,0 +1 @@
+true

test/behavior/zon/tuple.zon

@@ -0,0 +1 @@
+.{ 1.2, true, "hello", 3 }

test/behavior/zon/union1.zon

@@ -0,0 +1 @@
+.{ .x = 1.5 }

test/behavior/zon/union2.zon

@@ -0,0 +1 @@
+.{ .y = true }

test/behavior/zon/union3.zon

@@ -0,0 +1 @@
+.z

test/behavior/zon/vec0.zon

@@ -0,0 +1 @@
+.{}

test/behavior/zon/vec1.zon

@@ -0,0 +1 @@
+.{ .x = 1.5 }

test/behavior/zon/vec2.zon

@@ -0,0 +1 @@
+.{ .x = 1.5, .y = 2 }

test/behavior/zon/vec3_bool.zon

@@ -0,0 +1 @@
+.{ false, false, true }

test/behavior/zon/vec3_float.zon

@@ -0,0 +1 @@
+.{ 1.5, 2.5, 3.5 }

test/behavior/zon/vec3_int.zon

@@ -0,0 +1 @@
+.{ 2, 4, 6 }

test/behavior/zon/vec3_int_opt.zon

@@ -0,0 +1 @@
+.{ 2, null, 6 }

test/behavior/zon/z.zon

@@ -0,0 +1 @@
+'z'

test/cases/compile_errors/@import_zon_addr_slice.zig

@@ -0,0 +1,9 @@
+pub fn main() void {
+    const f: struct { value: []const i32 } = @import("zon/addr_slice.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/addr_slice.zon
+//
+// addr_slice.zon:2:14: error: pointers are not available in ZON

test/cases/compile_errors/@import_zon_array_len.zig

@@ -0,0 +1,10 @@
+export fn entry() void {
+    const f: [4]u8 = @import("zon/array.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/array.zon
+//
+// array.zon:1:2: error: expected type '[4]u8'
+// tmp.zig:2:30: note: imported here

test/cases/compile_errors/@import_zon_bad_import.zig

@@ -0,0 +1,9 @@
+export fn entry() void {
+    _ = @import(
+        "bogus-does-not-exist.zon",
+    );
+}
+
+// error
+//
+// :3:9: error: unable to open 'bogus-does-not-exist.zon': FileNotFound

test/cases/compile_errors/@import_zon_bad_type.zig

@@ -0,0 +1,125 @@
+export fn testVoid() void {
+    const f: void = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+export fn testInStruct() void {
+    const f: struct { f: [*]const u8 } = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+export fn testError() void {
+    const f: struct { error{foo} } = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+export fn testInUnion() void {
+    const f: union(enum) { a: void, b: [*c]const u8 } = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+export fn testInVector() void {
+    const f: @Vector(0, [*c]const u8) = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+export fn testInOpt() void {
+    const f: *const ?[*c]const u8 = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+export fn testComptimeField() void {
+    const f: struct { comptime foo: ??u8 = null } = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+export fn testEnumLiteral() void {
+    const f: @TypeOf(.foo) = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+export fn testNestedOpt1() void {
+    const f: ??u8 = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+export fn testNestedOpt2() void {
+    const f: ?*const ?u8 = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+export fn testNestedOpt3() void {
+    const f: *const ?*const ?*const u8 = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+export fn testOpt() void {
+    const f: ?u8 = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+export fn testNonExhaustiveEnum() void {
+    const f: enum(u8) { _ } = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+export fn testUntaggedUnion() void {
+    const f: union { foo: void } = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+export fn testTaggedUnionVoid() void {
+    const f: union(enum) { foo: void } = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+export fn testVisited() void {
+    const V = struct {
+        ?f32, // Adds `?f32` to the visited list
+        ??f32, // `?f32` is already visited, we need to detect the nested opt anyway
+        f32,
+    };
+    const f: V = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+export fn testMutablePointer() void {
+    const f: *i32 = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/neg_inf.zon
+//
+// tmp.zig:2:29: error: type 'void' is not available in ZON
+// tmp.zig:7:50: error: type '[*]const u8' is not available in ZON
+// tmp.zig:7:50: note: ZON does not allow many-pointers
+// tmp.zig:12:46: error: type 'error{foo}' is not available in ZON
+// tmp.zig:17:65: error: type '[*c]const u8' is not available in ZON
+// tmp.zig:17:65: note: ZON does not allow C pointers
+// tmp.zig:22:49: error: type '[*c]const u8' is not available in ZON
+// tmp.zig:22:49: note: ZON does not allow C pointers
+// tmp.zig:27:45: error: type '[*c]const u8' is not available in ZON
+// tmp.zig:27:45: note: ZON does not allow C pointers
+// tmp.zig:32:61: error: type '??u8' is not available in ZON
+// tmp.zig:32:61: note: ZON does not allow nested optionals
+// tmp.zig:42:29: error: type '??u8' is not available in ZON
+// tmp.zig:42:29: note: ZON does not allow nested optionals
+// tmp.zig:47:36: error: type '?*const ?u8' is not available in ZON
+// tmp.zig:47:36: note: ZON does not allow nested optionals
+// tmp.zig:52:50: error: type '?*const ?*const u8' is not available in ZON
+// tmp.zig:52:50: note: ZON does not allow nested optionals
+// tmp.zig:82:26: error: type '??f32' is not available in ZON
+// tmp.zig:82:26: note: ZON does not allow nested optionals
+// tmp.zig:87:29: error: type '*i32' is not available in ZON
+// tmp.zig:87:29: note: ZON does not allow mutable pointers
+// neg_inf.zon:1:1: error: expected type '@Type(.enum_literal)'
+// tmp.zig:37:38: note: imported here
+// neg_inf.zon:1:1: error: expected type '?u8'
+// tmp.zig:57:28: note: imported here
+// neg_inf.zon:1:1: error: expected type 'tmp.testNonExhaustiveEnum__enum_490'
+// tmp.zig:62:39: note: imported here
+// neg_inf.zon:1:1: error: expected type 'tmp.testUntaggedUnion__union_492'
+// tmp.zig:67:44: note: imported here
+// neg_inf.zon:1:1: error: expected type 'tmp.testTaggedUnionVoid__union_495'
+// tmp.zig:72:50: note: imported here

test/cases/compile_errors/@import_zon_comptime_inf.zig

@@ -0,0 +1,10 @@
+export fn entry() void {
+    const f: comptime_float = @import("zon/inf.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/inf.zon
+//
+// inf.zon:1:1: error: expected type 'comptime_float'
+// tmp.zig:2:39: note: imported here

test/cases/compile_errors/@import_zon_comptime_nan.zig

@@ -0,0 +1,10 @@
+export fn entry() void {
+    const f: comptime_float = @import("zon/nan.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/nan.zon
+//
+// nan.zon:1:1: error: expected type 'comptime_float'
+// tmp.zig:2:39: note: imported here

test/cases/compile_errors/@import_zon_comptime_neg_inf.zig

@@ -0,0 +1,10 @@
+export fn entry() void {
+    const f: comptime_float = @import("zon/neg_inf.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/neg_inf.zon
+//
+// neg_inf.zon:1:1: error: expected type 'comptime_float'
+// tmp.zig:2:39: note: imported here

test/cases/compile_errors/@import_zon_doc_comment.zig

@@ -0,0 +1,9 @@
+export fn entry() void {
+    const f: struct { foo: type } = @import("zon/doc_comment.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/doc_comment.zon
+//
+// doc_comment.zon:1:1: error: expected expression, found 'a document comment'

test/cases/compile_errors/@import_zon_double_negation_float.zig

@@ -0,0 +1,9 @@
+export fn entry() void {
+    const f: f32 = @import("zon/double_negation_float.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/double_negation_float.zon
+//
+// double_negation_float.zon:1:1: error: expected number or 'inf' after '-'

test/cases/compile_errors/@import_zon_double_negation_int.zig

@@ -0,0 +1,9 @@
+export fn entry() void {
+    const f: i32 = @import("zon/double_negation_int.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/double_negation_int.zon
+//
+// double_negation_int.zon:1:1: error: expected number or 'inf' after '-'

test/cases/compile_errors/@import_zon_enum_embedded_null.zig

@@ -0,0 +1,11 @@
+const std = @import("std");
+export fn entry() void {
+    const E = enum { foo };
+    const f: struct { E, E } = @import("zon/enum_embedded_null.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/enum_embedded_null.zon
+//
+// enum_embedded_null.zon:2:6: error: identifier cannot contain null bytes

test/cases/compile_errors/@import_zon_expected_void.zig

@@ -0,0 +1,11 @@
+export fn entry() void {
+    const U = union(enum) { a: void };
+    const f: U = @import("zon/simple_union.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/simple_union.zon
+//
+// simple_union.zon:1:9: error: expected type 'void'
+// tmp.zig:3:26: note: imported here

test/cases/compile_errors/@import_zon_invalid_character.zig

@@ -0,0 +1,9 @@
+export fn entry() void {
+    const f: u8 = @import("zon/invalid_character.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/invalid_character.zon
+//
+// invalid_character.zon:1:3: error: invalid escape character: 'a'

test/cases/compile_errors/@import_zon_invalid_number.zig

@@ -0,0 +1,9 @@
+export fn entry() void {
+    const f: u128 = @import("zon/invalid_number.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/invalid_number.zon
+//
+// invalid_number.zon:1:19: error: invalid digit 'a' for decimal base

test/cases/compile_errors/@import_zon_invalid_string.zig

@@ -0,0 +1,9 @@
+export fn entry() void {
+    const f: []const u8 = @import("zon/invalid_string.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/invalid_string.zon
+//
+// invalid_string.zon:1:5: error: invalid escape character: 'a'

test/cases/compile_errors/@import_zon_leading_zero_in_integer.zig

@@ -0,0 +1,10 @@
+export fn entry() void {
+    const f: u128 = @import("zon/leading_zero_in_integer.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/leading_zero_in_integer.zon
+//
+// leading_zero_in_integer.zon:1:1: error: number '0012' has leading zero
+// leading_zero_in_integer.zon:1:1: note: use '0o' prefix for octal literals

test/cases/compile_errors/@import_zon_neg_char.zig

@@ -0,0 +1,9 @@
+export fn entry() void {
+    const f: u8 = @import("zon/neg_char.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/neg_char.zon
+//
+// neg_char.zon:1:1: error: expected number or 'inf' after '-'

test/cases/compile_errors/@import_zon_neg_nan.zig

@@ -0,0 +1,9 @@
+export fn entry() void {
+    const f: u8 = @import("zon/neg_nan.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/neg_nan.zon
+//
+// neg_nan.zon:1:1: error: expected number or 'inf' after '-'

test/cases/compile_errors/@import_zon_negative_zero.zig

@@ -0,0 +1,11 @@
+export fn entry() void {
+    const f: i8 = @import("zon/negative_zero.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/negative_zero.zon
+//
+// negative_zero.zon:1:2: error: integer literal '-0' is ambiguous
+// negative_zero.zon:1:2: note: use '0' for an integer zero
+// negative_zero.zon:1:2: note: use '-0.0' for a floating-point signed zero

test/cases/compile_errors/@import_zon_no_rt.zig

@@ -0,0 +1,9 @@
+export fn entry() void {
+    const f = @import("zon/simple_union.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/simple_union.zon
+//
+// tmp.zig:2:23: error: '@import' of ZON must have a known result type

test/cases/compile_errors/@import_zon_number_fail_limits.zig

@@ -0,0 +1,10 @@
+export fn entry() void {
+    const f: i66 = @import("zon/large_number.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/large_number.zon
+//
+// large_number.zon:1:1: error: type 'i66' cannot represent integer value '36893488147419103232'
+// tmp.zig:2:28: note: imported here

test/cases/compile_errors/@import_zon_oob_char_0.zig

@@ -0,0 +1,16 @@
+export fn entry() void {
+    {
+        const f: u6 = @import("zon/char_32.zon");
+        _ = f;
+    }
+    {
+        const f: u5 = @import("zon/char_32.zon");
+        _ = f;
+    }
+}
+
+// error
+// imports=zon/char_32.zon
+//
+// char_32.zon:1:1: error: type 'u5' cannot represent integer value '32'
+// tmp.zig:7:31: note: imported here

test/cases/compile_errors/@import_zon_oob_char_1.zig

@@ -0,0 +1,16 @@
+export fn entry() void {
+    {
+        const f: i7 = @import("zon/char_32.zon");
+        _ = f;
+    }
+    {
+        const f: i6 = @import("zon/char_32.zon");
+        _ = f;
+    }
+}
+
+// error
+// imports=zon/char_32.zon
+//
+// char_32.zon:1:1: error: type 'i6' cannot represent integer value '32'
+// tmp.zig:7:31: note: imported here

test/cases/compile_errors/@import_zon_oob_int_0.zig

@@ -0,0 +1,16 @@
+export fn entry() void {
+    {
+        const f: u6 = @import("zon/int_32.zon");
+        _ = f;
+    }
+    {
+        const f: u5 = @import("zon/int_32.zon");
+        _ = f;
+    }
+}
+
+// error
+// imports=zon/int_32.zon
+//
+// int_32.zon:1:1: error: type 'u5' cannot represent integer value '32'
+// tmp.zig:7:31: note: imported here

test/cases/compile_errors/@import_zon_oob_int_1.zig

@@ -0,0 +1,16 @@
+export fn entry() void {
+    {
+        const f: i7 = @import("zon/int_32.zon");
+        _ = f;
+    }
+    {
+        const f: i6 = @import("zon/int_32.zon");
+        _ = f;
+    }
+}
+
+// error
+// imports=zon/int_32.zon
+//
+// int_32.zon:1:1: error: type 'i6' cannot represent integer value '32'
+// tmp.zig:7:31: note: imported here

test/cases/compile_errors/@import_zon_oob_int_2.zig

@@ -0,0 +1,16 @@
+export fn entry() void {
+    {
+        const f: i7 = @import("zon/int_neg_33.zon");
+        _ = f;
+    }
+    {
+        const f: i6 = @import("zon/int_neg_33.zon");
+        _ = f;
+    }
+}
+
+// error
+// imports=zon/int_neg_33.zon
+//
+// int_neg_33.zon:1:1: error: type 'i6' cannot represent integer value '-33'
+// tmp.zig:7:31: note: imported here

test/cases/compile_errors/@import_zon_oob_int_3.zig

@@ -0,0 +1,10 @@
+export fn entry() void {
+    const f: u64 = @import("zon/int_neg_33.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/int_neg_33.zon
+//
+// int_neg_33.zon:1:1: error: type 'u64' cannot represent integer value '-33'
+// tmp.zig:2:28: note: imported here

test/cases/compile_errors/@import_zon_opt_in_err.zig

@@ -0,0 +1,82 @@
+export fn testFloatA() void {
+    const f: ?f32 = @import("zon/vec2.zon");
+    _ = f;
+}
+
+export fn testFloatB() void {
+    const f: *const ?f32 = @import("zon/vec2.zon");
+    _ = f;
+}
+
+export fn testFloatC() void {
+    const f: ?*const f32 = @import("zon/vec2.zon");
+    _ = f;
+}
+
+export fn testBool() void {
+    const f: ?bool = @import("zon/vec2.zon");
+    _ = f;
+}
+
+export fn testInt() void {
+    const f: ?i32 = @import("zon/vec2.zon");
+    _ = f;
+}
+
+const Enum = enum { foo };
+export fn testEnum() void {
+    const f: ?Enum = @import("zon/vec2.zon");
+    _ = f;
+}
+
+export fn testEnumLit() void {
+    const f: ?@TypeOf(.foo) = @import("zon/vec2.zon");
+    _ = f;
+}
+
+export fn testArray() void {
+    const f: ?[1]u8 = @import("zon/vec2.zon");
+    _ = f;
+}
+
+const Union = union {};
+export fn testUnion() void {
+    const f: ?Union = @import("zon/vec2.zon");
+    _ = f;
+}
+
+export fn testSlice() void {
+    const f: ?[]const u8 = @import("zon/vec2.zon");
+    _ = f;
+}
+
+export fn testVector() void {
+    const f: ?@Vector(3, f32) = @import("zon/vec2.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/vec2.zon
+//
+// vec2.zon:1:2: error: expected type '?f32'
+// tmp.zig:2:29: note: imported here
+// vec2.zon:1:2: error: expected type '*const ?f32'
+// tmp.zig:7:36: note: imported here
+// vec2.zon:1:2: error: expected type '?*const f32'
+// tmp.zig:12:36: note: imported here
+// vec2.zon:1:2: error: expected type '?bool'
+// tmp.zig:17:30: note: imported here
+// vec2.zon:1:2: error: expected type '?i32'
+// tmp.zig:22:29: note: imported here
+// vec2.zon:1:2: error: expected type '?tmp.Enum'
+// tmp.zig:28:30: note: imported here
+// vec2.zon:1:2: error: expected type '?@Type(.enum_literal)'
+// tmp.zig:33:39: note: imported here
+// vec2.zon:1:2: error: expected type '?[1]u8'
+// tmp.zig:38:31: note: imported here
+// vec2.zon:1:2: error: expected type '?tmp.Union'
+// tmp.zig:44:31: note: imported here
+// vec2.zon:1:2: error: expected type '?[]const u8'
+// tmp.zig:49:36: note: imported here
+// vec2.zon:1:2: error: expected type '?@Vector(3, f32)'
+// tmp.zig:54:41: note: imported here

test/cases/compile_errors/@import_zon_opt_in_err_struct.zig

@@ -0,0 +1,19 @@
+const Struct = struct { f: bool };
+export fn testStruct() void {
+    const f: ?Struct = @import("zon/nan.zon");
+    _ = f;
+}
+
+const Tuple = struct { bool };
+export fn testTuple() void {
+    const f: ?Tuple = @import("zon/nan.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/nan.zon
+//
+//nan.zon:1:1: error: expected type '?tmp.Struct'
+//tmp.zig:3:32: note: imported here
+//nan.zon:1:1: error: expected type '?struct { bool }'
+//tmp.zig:9:31: note: imported here

test/cases/compile_errors/@import_zon_string_as_array.zig

@@ -0,0 +1,10 @@
+export fn entry() void {
+    const f: [5]u8 = @import("zon/hello.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/hello.zon
+//
+// hello.zon:1:1: error: expected type '[5]u8'
+// tmp.zig:2:30: note: imported here

test/cases/compile_errors/@import_zon_struct_dup_field.zig

@@ -0,0 +1,11 @@
+const std = @import("std");
+export fn entry() void {
+    const f: struct { name: u8 } = @import("zon/struct_dup_field.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/struct_dup_field.zon
+//
+// struct_dup_field.zon:2:6: error: duplicate struct field name
+// struct_dup_field.zon:3:6: note: duplicate name here

test/cases/compile_errors/@import_zon_struct_wrong_comptime_field.zig

@@ -0,0 +1,14 @@
+export fn entry() void {
+    const Vec2 = struct {
+        comptime x: f32 = 1.5,
+        comptime y: f32 = 2.5,
+    };
+    const f: Vec2 = @import("zon/vec2.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/vec2.zon
+//
+// vec2.zon:1:19: error: value stored in comptime field does not match the default value of the field
+// tmp.zig:6:29: note: imported here

test/cases/compile_errors/@import_zon_syntax_error.zig

@@ -0,0 +1,9 @@
+export fn entry() void {
+    const f: bool = @import("zon/syntax_error.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/syntax_error.zon
+//
+// syntax_error.zon:3:13: error: expected ',' after initializer

test/cases/compile_errors/@import_zon_tuple_wrong_comptime_field.zig

@@ -0,0 +1,14 @@
+export fn entry() void {
+    const T = struct {
+        comptime f32 = 1.5,
+        comptime f32 = 2.5,
+    };
+    const f: T = @import("zon/tuple.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/tuple.zon
+//
+// tuple.zon:1:9: error: value stored in comptime field does not match the default value of the field
+// tmp.zig:6:26: note: imported here

test/cases/compile_errors/@import_zon_type_decl.zig

@@ -0,0 +1,9 @@
+export fn entry() void {
+    const f: struct { foo: type } = @import("zon/type_decl.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/type_decl.zon
+//
+// type_decl.zon:2:12: error: types are not available in ZON

test/cases/compile_errors/@import_zon_type_expr_array.zig

@@ -0,0 +1,10 @@
+export fn entry() void {
+    const f: [3]i32 = @import("zon/type_expr_array.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/type_expr_array.zon
+//
+// type_expr_array.zon:1:1: error: types are not available in ZON
+// type_expr_array.zon:1:1: note: replace the type with '.'

test/cases/compile_errors/@import_zon_type_expr_fn.zig

@@ -0,0 +1,10 @@
+export fn entry() void {
+    const f: i32 = @import("zon/type_expr_fn.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/type_expr_fn.zon
+//
+// type_expr_fn.zon:1:1: error: types are not available in ZON
+// type_expr_fn.zon:1:1: note: replace the type with '.'

test/cases/compile_errors/@import_zon_type_expr_struct.zig

@@ -0,0 +1,10 @@
+export fn entry() void {
+    const f: struct { x: f32, y: f32 } = @import("zon/type_expr_struct.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/type_expr_struct.zon
+//
+// type_expr_struct.zon:1:1: error: types are not available in ZON
+// type_expr_struct.zon:1:1: note: replace the type with '.'

test/cases/compile_errors/@import_zon_type_expr_tuple.zig

@@ -0,0 +1,10 @@
+export fn entry() void {
+    const f: struct { f32, f32 } = @import("zon/type_expr_tuple.zon");
+    _ = f;
+}
+
+// error
+// imports=zon/type_expr_tuple.zon
+//
+// type_expr_tuple.zon:1:1: error: types are not available in ZON
+// type_expr_tuple.zon:1:1: note: replace the type with '.'