introduce std.debug.Trace

And use it to debug a LazySrcLoc in stage2 that is set to a bogus value.

The actual fix in this commit is:

```diff
-        try sema.emitBackwardBranch(&child_block, call_src);
+        try sema.emitBackwardBranch(block, call_src);
```

9 files changed, 185 insertions, 95 deletions

diff --git a/lib/std/debug.zig b/lib/std/debug.zig
index 7fb632084b..f4ca0f0354 100644
--- a/lib/std/debug.zig
+++ b/lib/std/debug.zig
@@ -1943,3 +1943,60 @@ test "#4353: std.debug should manage resources correctly" {
 noinline fn showMyTrace() usize {
     return @returnAddress();
 }
+
+pub fn Trace(comptime size: usize, comptime stack_frame_count: usize) type {
+    return struct {
+        addrs: [size][stack_frame_count]usize = undefined,
+        notes: [size][]const u8 = undefined,
+        index: usize = 0,
+
+        const frames_init = [1]usize{0} ** stack_frame_count;
+
+        pub noinline fn add(t: *@This(), note: []const u8) void {
+            return addAddr(t, @returnAddress(), note);
+        }
+
+        pub fn addAddr(t: *@This(), addr: usize, note: []const u8) void {
+            if (t.index < size) {
+                t.notes[t.index] = note;
+                t.addrs[t.index] = [1]usize{0} ** stack_frame_count;
+                var stack_trace: std.builtin.StackTrace = .{
+                    .index = 0,
+                    .instruction_addresses = &t.addrs[t.index],
+                };
+                captureStackTrace(addr, &stack_trace);
+            }
+            // Keep counting even if the end is reached so that the
+            // user can find out how much more size they need.
+            t.index += 1;
+        }
+
+        pub fn dump(t: @This()) void {
+            const tty_config = detectTTYConfig();
+            const stderr = io.getStdErr().writer();
+            const end = @maximum(t.index, size);
+            const debug_info = getSelfDebugInfo() catch |err| {
+                stderr.print(
+                    "Unable to dump stack trace: Unable to open debug info: {s}\n",
+                    .{@errorName(err)},
+                ) catch return;
+                return;
+            };
+            for (t.addrs[0..end]) |frames_array, i| {
+                stderr.print("{s}:\n", .{t.notes[i]}) catch return;
+                var frames_array_mutable = frames_array;
+                const frames = mem.sliceTo(frames_array_mutable[0..], 0);
+                const stack_trace: std.builtin.StackTrace = .{
+                    .index = frames.len,
+                    .instruction_addresses = frames,
+                };
+                writeStackTrace(stack_trace, stderr, getDebugInfoAllocator(), debug_info, tty_config) catch continue;
+            }
+            if (t.index > end) {
+                stderr.print("{d} more traces not shown; consider increasing trace size\n", .{
+                    t.index - end,
+                }) catch return;
+            }
+        }
+    };
+}
diff --git a/src/Module.zig b/src/Module.zig
index 12d311046a..724fa2ebc4 100644
--- a/src/Module.zig
+++ b/src/Module.zig
@@ -659,7 +659,7 @@ pub const Decl = struct {
     }
 
     pub fn nodeSrcLoc(decl: Decl, node_index: Ast.Node.Index) LazySrcLoc {
-        return .{ .node_offset = decl.nodeIndexToRelative(node_index) };
+        return LazySrcLoc.nodeOffset(decl.nodeIndexToRelative(node_index));
     }
 
     pub fn srcLoc(decl: Decl) SrcLoc {
@@ -670,7 +670,7 @@ pub const Decl = struct {
         return .{
             .file_scope = decl.getFileScope(),
             .parent_decl_node = decl.src_node,
-            .lazy = .{ .node_offset = node_offset },
+            .lazy = LazySrcLoc.nodeOffset(node_offset),
         };
     }
 
@@ -861,7 +861,7 @@ pub const ErrorSet = struct {
         return .{
             .file_scope = owner_decl.getFileScope(),
             .parent_decl_node = owner_decl.src_node,
-            .lazy = .{ .node_offset = self.node_offset },
+            .lazy = LazySrcLoc.nodeOffset(self.node_offset),
         };
     }
 
@@ -947,7 +947,7 @@ pub const Struct = struct {
         return .{
             .file_scope = owner_decl.getFileScope(),
             .parent_decl_node = owner_decl.src_node,
-            .lazy = .{ .node_offset = s.node_offset },
+            .lazy = LazySrcLoc.nodeOffset(s.node_offset),
         };
     }
 
@@ -1066,7 +1066,7 @@ pub const EnumSimple = struct {
         return .{
             .file_scope = owner_decl.getFileScope(),
             .parent_decl_node = owner_decl.src_node,
-            .lazy = .{ .node_offset = self.node_offset },
+            .lazy = LazySrcLoc.nodeOffset(self.node_offset),
         };
     }
 };
@@ -1097,7 +1097,7 @@ pub const EnumNumbered = struct {
         return .{
             .file_scope = owner_decl.getFileScope(),
             .parent_decl_node = owner_decl.src_node,
-            .lazy = .{ .node_offset = self.node_offset },
+            .lazy = LazySrcLoc.nodeOffset(self.node_offset),
         };
     }
 };
@@ -1131,7 +1131,7 @@ pub const EnumFull = struct {
         return .{
             .file_scope = owner_decl.getFileScope(),
             .parent_decl_node = owner_decl.src_node,
-            .lazy = .{ .node_offset = self.node_offset },
+            .lazy = LazySrcLoc.nodeOffset(self.node_offset),
         };
     }
 };
@@ -1197,7 +1197,7 @@ pub const Union = struct {
         return .{
             .file_scope = owner_decl.getFileScope(),
             .parent_decl_node = owner_decl.src_node,
-            .lazy = .{ .node_offset = self.node_offset },
+            .lazy = LazySrcLoc.nodeOffset(self.node_offset),
         };
     }
 
@@ -1404,7 +1404,7 @@ pub const Opaque = struct {
         return .{
             .file_scope = owner_decl.getFileScope(),
             .parent_decl_node = owner_decl.src_node,
-            .lazy = .{ .node_offset = self.node_offset },
+            .lazy = LazySrcLoc.nodeOffset(self.node_offset),
         };
     }
 
@@ -2105,7 +2105,17 @@ pub const SrcLoc = struct {
                 const token_starts = tree.tokens.items(.start);
                 return token_starts[tok_index];
             },
-            .node_offset, .node_offset_bin_op => |node_off| {
+            .node_offset => |traced_off| {
+                const node_off = traced_off.x;
+                const tree = try src_loc.file_scope.getTree(gpa);
+                const node = src_loc.declRelativeToNodeIndex(node_off);
+                assert(src_loc.file_scope.tree_loaded);
+                const main_tokens = tree.nodes.items(.main_token);
+                const tok_index = main_tokens[node];
+                const token_starts = tree.tokens.items(.start);
+                return token_starts[tok_index];
+            },
+            .node_offset_bin_op => |node_off| {
                 const tree = try src_loc.file_scope.getTree(gpa);
                 const node = src_loc.declRelativeToNodeIndex(node_off);
                 assert(src_loc.file_scope.tree_loaded);
@@ -2515,6 +2525,17 @@ pub const SrcLoc = struct {
     }
 };
 
+/// This wraps a simple integer in debug builds so that later on we can find out
+/// where in semantic analysis the value got set.
+const TracedOffset = struct {
+    x: i32,
+    trace: Trace = trace_init,
+
+    const want_tracing = builtin.mode == .Debug;
+    const trace_init = if (want_tracing) std.debug.Trace(1, 3){} else {};
+    const Trace = @TypeOf(trace_init);
+};
+
 /// Resolving a source location into a byte offset may require doing work
 /// that we would rather not do unless the error actually occurs.
 /// Therefore we need a data structure that contains the information necessary
@@ -2555,7 +2576,7 @@ pub const LazySrcLoc = union(enum) {
     /// The source location points to an AST node, which is this value offset
     /// from its containing Decl node AST index.
     /// The Decl is determined contextually.
-    node_offset: i32,
+    node_offset: TracedOffset,
     /// The source location points to two tokens left of the first token of an AST node,
     /// which is this value offset from its containing Decl node AST index.
     /// The Decl is determined contextually.
@@ -2705,6 +2726,18 @@ pub const LazySrcLoc = union(enum) {
     /// The Decl is determined contextually.
     node_offset_array_type_elem: i32,
 
+    pub const nodeOffset = if (TracedOffset.want_tracing) nodeOffsetDebug else nodeOffsetRelease;
+
+    noinline fn nodeOffsetDebug(node_offset: i32) LazySrcLoc {
+        var result: LazySrcLoc = .{ .node_offset = .{ .x = node_offset } };
+        result.node_offset.trace.addAddr(@returnAddress(), "init");
+        return result;
+    }
+
+    fn nodeOffsetRelease(node_offset: i32) LazySrcLoc {
+        return .{ .node_offset = .{ .x = node_offset } };
+    }
+
     /// Upgrade to a `SrcLoc` based on the `Decl` provided.
     pub fn toSrcLoc(lazy: LazySrcLoc, decl: *Decl) SrcLoc {
         return switch (lazy) {
@@ -4014,7 +4047,7 @@ fn semaDecl(mod: *Module, decl_index: Decl.Index) !bool {
     const body = zir.extra[extra.end..][0..extra.data.body_len];
     const result_ref = (try sema.analyzeBodyBreak(&block_scope, body)).?.operand;
     try wip_captures.finalize();
-    const src: LazySrcLoc = .{ .node_offset = 0 };
+    const src = LazySrcLoc.nodeOffset(0);
     const decl_tv = try sema.resolveInstValue(&block_scope, src, result_ref);
     const decl_align: u32 = blk: {
         const align_ref = decl.zirAlignRef();
@@ -5044,7 +5077,7 @@ pub fn analyzeFnBody(mod: *Module, func: *Fn, arena: Allocator) SemaError!Air {
     // Crucially, this happens *after* we set the function state to success above,
     // so that dependencies on the function body will now be satisfied rather than
     // result in circular dependency errors.
-    const src: LazySrcLoc = .{ .node_offset = 0 };
+    const src = LazySrcLoc.nodeOffset(0);
     sema.resolveFnTypes(&inner_block, src, fn_ty_info) catch |err| switch (err) {
         error.NeededSourceLocation => unreachable,
         error.GenericPoison => unreachable,
@@ -5338,7 +5371,7 @@ pub const SwitchProngSrc = union(enum) {
             log.warn("unable to load {s}: {s}", .{
                 decl.getFileScope().sub_file_path, @errorName(err),
             });
-            return LazySrcLoc{ .node_offset = 0 };
+            return LazySrcLoc.nodeOffset(0);
         };
         const switch_node = decl.relativeToNodeIndex(switch_node_offset);
         const main_tokens = tree.nodes.items(.main_token);
@@ -5367,17 +5400,17 @@ pub const SwitchProngSrc = union(enum) {
                 node_tags[case.ast.values[0]] == .switch_range;
 
             switch (prong_src) {
-                .scalar => |i| if (!is_multi and i == scalar_i) return LazySrcLoc{
-                    .node_offset = decl.nodeIndexToRelative(case.ast.values[0]),
-                },
+                .scalar => |i| if (!is_multi and i == scalar_i) return LazySrcLoc.nodeOffset(
+                    decl.nodeIndexToRelative(case.ast.values[0]),
+                ),
                 .multi => |s| if (is_multi and s.prong == multi_i) {
                     var item_i: u32 = 0;
                     for (case.ast.values) |item_node| {
                         if (node_tags[item_node] == .switch_range) continue;
 
-                        if (item_i == s.item) return LazySrcLoc{
-                            .node_offset = decl.nodeIndexToRelative(item_node),
-                        };
+                        if (item_i == s.item) return LazySrcLoc.nodeOffset(
+                            decl.nodeIndexToRelative(item_node),
+                        );
                         item_i += 1;
                     } else unreachable;
                 },
@@ -5387,15 +5420,15 @@ pub const SwitchProngSrc = union(enum) {
                         if (node_tags[range] != .switch_range) continue;
 
                         if (range_i == s.item) switch (range_expand) {
-                            .none => return LazySrcLoc{
-                                .node_offset = decl.nodeIndexToRelative(range),
-                            },
-                            .first => return LazySrcLoc{
-                                .node_offset = decl.nodeIndexToRelative(node_datas[range].lhs),
-                            },
-                            .last => return LazySrcLoc{
-                                .node_offset = decl.nodeIndexToRelative(node_datas[range].rhs),
-                            },
+                            .none => return LazySrcLoc.nodeOffset(
+                                decl.nodeIndexToRelative(range),
+                            ),
+                            .first => return LazySrcLoc.nodeOffset(
+                                decl.nodeIndexToRelative(node_datas[range].lhs),
+                            ),
+                            .last => return LazySrcLoc.nodeOffset(
+                                decl.nodeIndexToRelative(node_datas[range].rhs),
+                            ),
                         };
                         range_i += 1;
                     } else unreachable;
@@ -5450,7 +5483,7 @@ pub const PeerTypeCandidateSrc = union(enum) {
                     log.warn("unable to load {s}: {s}", .{
                         decl.getFileScope().sub_file_path, @errorName(err),
                     });
-                    return LazySrcLoc{ .node_offset = 0 };
+                    return LazySrcLoc.nodeOffset(0);
                 };
                 const node = decl.relativeToNodeIndex(node_offset);
                 const node_datas = tree.nodes.items(.data);
diff --git a/src/Sema.zig b/src/Sema.zig
index 2d3c38faeb..882c18fe55 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -1154,7 +1154,7 @@ fn analyzeBodyInner(
             .repeat => {
                 if (block.is_comptime) {
                     // Send comptime control flow back to the beginning of this block.
-                    const src: LazySrcLoc = .{ .node_offset = datas[inst].node };
+                    const src = LazySrcLoc.nodeOffset(datas[inst].node);
                     try sema.emitBackwardBranch(block, src);
                     if (wip_captures.scope.captures.count() != orig_captures) {
                         try wip_captures.reset(parent_capture_scope);
@@ -1165,14 +1165,14 @@ fn analyzeBodyInner(
                     continue;
                 } else {
                     const src_node = sema.code.instructions.items(.data)[inst].node;
-                    const src: LazySrcLoc = .{ .node_offset = src_node };
+                    const src = LazySrcLoc.nodeOffset(src_node);
                     try sema.requireRuntimeBlock(block, src);
                     break always_noreturn;
                 }
             },
             .repeat_inline => {
                 // Send comptime control flow back to the beginning of this block.
-                const src: LazySrcLoc = .{ .node_offset = datas[inst].node };
+                const src = LazySrcLoc.nodeOffset(datas[inst].node);
                 try sema.emitBackwardBranch(block, src);
                 if (wip_captures.scope.captures.count() != orig_captures) {
                     try wip_captures.reset(parent_capture_scope);
@@ -2087,7 +2087,7 @@ fn zirStructDecl(
     const small = @bitCast(Zir.Inst.StructDecl.Small, extended.small);
     const src: LazySrcLoc = if (small.has_src_node) blk: {
         const node_offset = @bitCast(i32, sema.code.extra[extended.operand]);
-        break :blk .{ .node_offset = node_offset };
+        break :blk LazySrcLoc.nodeOffset(node_offset);
     } else sema.src;
 
     var new_decl_arena = std.heap.ArenaAllocator.init(sema.gpa);
@@ -2108,7 +2108,7 @@ fn zirStructDecl(
     struct_obj.* = .{
         .owner_decl = new_decl_index,
         .fields = .{},
-        .node_offset = src.node_offset,
+        .node_offset = src.node_offset.x,
         .zir_index = inst,
         .layout = small.layout,
         .status = .none,
@@ -2210,7 +2210,7 @@ fn zirEnumDecl(
     const src: LazySrcLoc = if (small.has_src_node) blk: {
         const node_offset = @bitCast(i32, sema.code.extra[extra_index]);
         extra_index += 1;
-        break :blk .{ .node_offset = node_offset };
+        break :blk LazySrcLoc.nodeOffset(node_offset);
     } else sema.src;
 
     const tag_type_ref = if (small.has_tag_type) blk: {
@@ -2263,7 +2263,7 @@ fn zirEnumDecl(
         .tag_ty_inferred = true,
         .fields = .{},
         .values = .{},
-        .node_offset = src.node_offset,
+        .node_offset = src.node_offset.x,
         .namespace = .{
             .parent = block.namespace,
             .ty = enum_ty,
@@ -2385,8 +2385,8 @@ fn zirEnumDecl(
         const gop = enum_obj.fields.getOrPutAssumeCapacity(field_name);
         if (gop.found_existing) {
             const tree = try sema.getAstTree(block);
-            const field_src = enumFieldSrcLoc(sema.mod.declPtr(block.src_decl), tree.*, src.node_offset, field_i);
-            const other_tag_src = enumFieldSrcLoc(sema.mod.declPtr(block.src_decl), tree.*, src.node_offset, gop.index);
+            const field_src = enumFieldSrcLoc(sema.mod.declPtr(block.src_decl), tree.*, src.node_offset.x, field_i);
+            const other_tag_src = enumFieldSrcLoc(sema.mod.declPtr(block.src_decl), tree.*, src.node_offset.x, gop.index);
             const msg = msg: {
                 const msg = try sema.errMsg(block, field_src, "duplicate enum tag", .{});
                 errdefer msg.destroy(gpa);
@@ -2442,7 +2442,7 @@ fn zirUnionDecl(
     const src: LazySrcLoc = if (small.has_src_node) blk: {
         const node_offset = @bitCast(i32, sema.code.extra[extra_index]);
         extra_index += 1;
-        break :blk .{ .node_offset = node_offset };
+        break :blk LazySrcLoc.nodeOffset(node_offset);
     } else sema.src;
 
     extra_index += @boolToInt(small.has_tag_type);
@@ -2480,7 +2480,7 @@ fn zirUnionDecl(
         .owner_decl = new_decl_index,
         .tag_ty = Type.initTag(.@"null"),
         .fields = .{},
-        .node_offset = src.node_offset,
+        .node_offset = src.node_offset.x,
         .zir_index = inst,
         .layout = small.layout,
         .status = .none,
@@ -2516,7 +2516,7 @@ fn zirOpaqueDecl(
     const src: LazySrcLoc = if (small.has_src_node) blk: {
         const node_offset = @bitCast(i32, sema.code.extra[extra_index]);
         extra_index += 1;
-        break :blk .{ .node_offset = node_offset };
+        break :blk LazySrcLoc.nodeOffset(node_offset);
     } else sema.src;
 
     const decls_len = if (small.has_decls_len) blk: {
@@ -2547,7 +2547,7 @@ fn zirOpaqueDecl(
 
     opaque_obj.* = .{
         .owner_decl = new_decl_index,
-        .node_offset = src.node_offset,
+        .node_offset = src.node_offset.x,
         .namespace = .{
             .parent = block.namespace,
             .ty = opaque_ty,
@@ -2623,7 +2623,7 @@ fn zirRetPtr(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[inst].node;
-    const src: LazySrcLoc = .{ .node_offset = inst_data };
+    const src = LazySrcLoc.nodeOffset(inst_data);
     try sema.requireFunctionBlock(block, src);
 
     if (block.is_comptime or try sema.typeRequiresComptime(block, src, sema.fn_ret_ty)) {
@@ -2661,7 +2661,7 @@ fn zirRetType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[inst].node;
-    const src: LazySrcLoc = .{ .node_offset = inst_data };
+    const src = LazySrcLoc.nodeOffset(inst_data);
     try sema.requireFunctionBlock(block, src);
     return sema.addType(sema.fn_ret_ty);
 }
@@ -2750,7 +2750,7 @@ fn zirAllocExtended(
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.AllocExtended, extended.operand);
-    const src: LazySrcLoc = .{ .node_offset = extra.data.src_node };
+    const src = LazySrcLoc.nodeOffset(extra.data.src_node);
     const ty_src = src; // TODO better source location
     const align_src = src; // TODO better source location
     const small = @bitCast(Zir.Inst.AllocExtended.Small, extended.small);
@@ -2903,7 +2903,7 @@ fn zirAllocInferredComptime(
     inferred_alloc_ty: Type,
 ) CompileError!Air.Inst.Ref {
     const src_node = sema.code.instructions.items(.data)[inst].node;
-    const src: LazySrcLoc = .{ .node_offset = src_node };
+    const src = LazySrcLoc.nodeOffset(src_node);
     sema.src = src;
     return sema.addConstant(
         inferred_alloc_ty,
@@ -2967,7 +2967,7 @@ fn zirAllocInferred(
     defer tracy.end();
 
     const src_node = sema.code.instructions.items(.data)[inst].node;
-    const src: LazySrcLoc = .{ .node_offset = src_node };
+    const src = LazySrcLoc.nodeOffset(src_node);
     sema.src = src;
 
     if (block.is_comptime) {
@@ -3718,7 +3718,7 @@ fn zirValidateArrayInit(
 
     outer: for (instrs) |elem_ptr, i| {
         const elem_ptr_data = sema.code.instructions.items(.data)[elem_ptr].pl_node;
-        const elem_src: LazySrcLoc = .{ .node_offset = elem_ptr_data.src_node };
+        const elem_src = LazySrcLoc.nodeOffset(elem_ptr_data.src_node);
 
         // Determine whether the value stored to this pointer is comptime-known.
 
@@ -4203,7 +4203,7 @@ fn zirCompileLog(
 
     const extra = sema.code.extraData(Zir.Inst.NodeMultiOp, extended.operand);
     const src_node = extra.data.src_node;
-    const src: LazySrcLoc = .{ .node_offset = src_node };
+    const src = LazySrcLoc.nodeOffset(src_node);
     const args = sema.code.refSlice(extra.end, extended.small);
 
     for (args) |arg_ref, i| {
@@ -4707,7 +4707,7 @@ pub fn analyzeExport(
 fn zirSetAlignStack(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!void {
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
-    const src: LazySrcLoc = .{ .node_offset = extra.node };
+    const src = LazySrcLoc.nodeOffset(extra.node);
     const alignment = try sema.resolveAlign(block, operand_src, extra.operand);
     if (alignment > 256) {
         return sema.fail(block, src, "attempt to @setAlignStack({d}); maximum is 256", .{
@@ -5312,7 +5312,7 @@ fn analyzeCall(
             delete_memoized_call_key = true;
         }
 
-        try sema.emitBackwardBranch(&child_block, call_src);
+        try sema.emitBackwardBranch(block, call_src);
 
         // Whether this call should be memoized, set to false if the call can mutate
         // comptime state.
@@ -6988,7 +6988,7 @@ fn funcCommon(
         const param_types = try sema.arena.alloc(Type, block.params.items.len);
         const comptime_params = try sema.arena.alloc(bool, block.params.items.len);
         for (block.params.items) |param, i| {
-            const param_src: LazySrcLoc = .{ .node_offset = src_node_offset }; // TODO better src
+            const param_src = LazySrcLoc.nodeOffset(src_node_offset); // TODO better src
             param_types[i] = param.ty;
             comptime_params[i] = param.is_comptime or
                 try sema.typeRequiresComptime(block, param_src, param.ty);
@@ -7378,7 +7378,7 @@ fn zirFieldCallBindNamed(sema: *Sema, block: *Block, extended: Zir.Inst.Extended
     defer tracy.end();
 
     const extra = sema.code.extraData(Zir.Inst.FieldNamedNode, extended.operand).data;
-    const src: LazySrcLoc = .{ .node_offset = extra.node };
+    const src = LazySrcLoc.nodeOffset(extra.node);
     const field_name_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = extra.node };
     const object_ptr = try sema.resolveInst(extra.lhs);
     const field_name = try sema.resolveConstString(block, field_name_src, extra.field_name);
@@ -10088,7 +10088,7 @@ fn zirOverflowArithmetic(
     defer tracy.end();
 
     const extra = sema.code.extraData(Zir.Inst.OverflowArithmetic, extended.operand).data;
-    const src: LazySrcLoc = .{ .node_offset = extra.node };
+    const src = LazySrcLoc.nodeOffset(extra.node);
 
     const lhs_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const rhs_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = extra.node };
@@ -11309,7 +11309,7 @@ fn zirAsm(
     defer tracy.end();
 
     const extra = sema.code.extraData(Zir.Inst.Asm, extended.operand);
-    const src: LazySrcLoc = .{ .node_offset = extra.data.src_node };
+    const src = LazySrcLoc.nodeOffset(extra.data.src_node);
     const ret_ty_src: LazySrcLoc = .{ .node_offset_asm_ret_ty = extra.data.src_node };
     const outputs_len = @truncate(u5, extended.small);
     const inputs_len = @truncate(u5, extended.small >> 5);
@@ -11761,7 +11761,7 @@ fn zirThis(
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const this_decl_index = block.namespace.getDeclIndex();
-    const src: LazySrcLoc = .{ .node_offset = @bitCast(i32, extended.operand) };
+    const src = LazySrcLoc.nodeOffset(@bitCast(i32, extended.operand));
     return sema.analyzeDeclVal(block, src, this_decl_index);
 }
 
@@ -11815,7 +11815,7 @@ fn zirRetAddr(
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
-    const src: LazySrcLoc = .{ .node_offset = @bitCast(i32, extended.operand) };
+    const src = LazySrcLoc.nodeOffset(@bitCast(i32, extended.operand));
     try sema.requireRuntimeBlock(block, src);
     return try block.addNoOp(.ret_addr);
 }
@@ -11825,7 +11825,7 @@ fn zirFrameAddress(
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
-    const src: LazySrcLoc = .{ .node_offset = @bitCast(i32, extended.operand) };
+    const src = LazySrcLoc.nodeOffset(@bitCast(i32, extended.operand));
     try sema.requireRuntimeBlock(block, src);
     return try block.addNoOp(.frame_addr);
 }
@@ -11838,7 +11838,7 @@ fn zirBuiltinSrc(
     const tracy = trace(@src());
     defer tracy.end();
 
-    const src: LazySrcLoc = .{ .node_offset = @bitCast(i32, extended.operand) };
+    const src = LazySrcLoc.nodeOffset(@bitCast(i32, extended.operand));
     const extra = sema.code.extraData(Zir.Inst.LineColumn, extended.operand).data;
     const func = sema.func orelse return sema.fail(block, src, "@src outside function", .{});
     const fn_owner_decl = sema.mod.declPtr(func.owner_decl);
@@ -12842,7 +12842,7 @@ fn zirTypeofPeer(
     defer tracy.end();
 
     const extra = sema.code.extraData(Zir.Inst.TypeOfPeer, extended.operand);
-    const src: LazySrcLoc = .{ .node_offset = extra.data.src_node };
+    const src = LazySrcLoc.nodeOffset(extra.data.src_node);
     const body = sema.code.extra[extra.data.body_index..][0..extra.data.body_len];
 
     var child_block: Block = .{
@@ -14157,7 +14157,7 @@ fn zirErrorReturnTrace(
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
-    const src: LazySrcLoc = .{ .node_offset = @bitCast(i32, extended.operand) };
+    const src = LazySrcLoc.nodeOffset(@bitCast(i32, extended.operand));
     return sema.getErrorReturnTrace(block, src);
 }
 
@@ -14185,7 +14185,7 @@ fn zirFrame(
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
-    const src: LazySrcLoc = .{ .node_offset = @bitCast(i32, extended.operand) };
+    const src = LazySrcLoc.nodeOffset(@bitCast(i32, extended.operand));
     return sema.fail(block, src, "TODO: Sema.zirFrame", .{});
 }
 
@@ -14629,7 +14629,7 @@ fn zirReify(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.I
                 .tag_ty_inferred = false,
                 .fields = .{},
                 .values = .{},
-                .node_offset = src.node_offset,
+                .node_offset = src.node_offset.x,
                 .namespace = .{
                     .parent = block.namespace,
                     .ty = enum_ty,
@@ -14711,7 +14711,7 @@ fn zirReify(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.I
 
             opaque_obj.* = .{
                 .owner_decl = new_decl_index,
-                .node_offset = src.node_offset,
+                .node_offset = src.node_offset.x,
                 .namespace = .{
                     .parent = block.namespace,
                     .ty = opaque_ty,
@@ -14763,7 +14763,7 @@ fn zirReify(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.I
                 .owner_decl = new_decl_index,
                 .tag_ty = Type.initTag(.@"null"),
                 .fields = .{},
-                .node_offset = src.node_offset,
+                .node_offset = src.node_offset.x,
                 .zir_index = inst,
                 .layout = layout_val.toEnum(std.builtin.Type.ContainerLayout),
                 .status = .have_field_types,
@@ -14930,7 +14930,7 @@ fn reifyStruct(
     struct_obj.* = .{
         .owner_decl = new_decl_index,
         .fields = .{},
-        .node_offset = src.node_offset,
+        .node_offset = src.node_offset.x,
         .zir_index = inst,
         .layout = layout_val.toEnum(std.builtin.Type.ContainerLayout),
         .status = .have_field_types,
@@ -15130,7 +15130,7 @@ fn zirIntToPtr(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Ai
 
 fn zirErrSetCast(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.BinNode, extended.operand).data;
-    const src: LazySrcLoc = .{ .node_offset = extra.node };
+    const src = LazySrcLoc.nodeOffset(extra.node);
     const dest_ty_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = extra.node };
     const dest_ty = try sema.resolveType(block, dest_ty_src, extra.lhs);
@@ -17114,7 +17114,7 @@ fn zirAwaitNosuspend(
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
-    const src: LazySrcLoc = .{ .node_offset = extra.node };
+    const src = LazySrcLoc.nodeOffset(extra.node);
 
     return sema.fail(block, src, "TODO: Sema.zirAwaitNosuspend", .{});
 }
@@ -17443,7 +17443,7 @@ fn zirWasmMemorySize(
 ) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const index_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
-    const builtin_src: LazySrcLoc = .{ .node_offset = extra.node };
+    const builtin_src = LazySrcLoc.nodeOffset(extra.node);
     const target = sema.mod.getTarget();
     if (!target.isWasm()) {
         return sema.fail(block, builtin_src, "builtin @wasmMemorySize is available when targeting WebAssembly; targeted CPU architecture is {s}", .{@tagName(target.cpu.arch)});
@@ -17466,7 +17466,7 @@ fn zirWasmMemoryGrow(
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.BinNode, extended.operand).data;
-    const builtin_src: LazySrcLoc = .{ .node_offset = extra.node };
+    const builtin_src = LazySrcLoc.nodeOffset(extra.node);
     const index_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const delta_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = extra.node };
     const target = sema.mod.getTarget();
@@ -17534,7 +17534,7 @@ fn zirBuiltinExtern(
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.BinNode, extended.operand).data;
-    const src: LazySrcLoc = .{ .node_offset = extra.node };
+    const src = LazySrcLoc.nodeOffset(extra.node);
     const ty_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const options_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = extra.node };
 
@@ -23586,7 +23586,7 @@ fn semaStructFields(
     const small = @bitCast(Zir.Inst.StructDecl.Small, extended.small);
     var extra_index: usize = extended.operand;
 
-    const src: LazySrcLoc = .{ .node_offset = struct_obj.node_offset };
+    const src = LazySrcLoc.nodeOffset(struct_obj.node_offset);
     extra_index += @boolToInt(small.has_src_node);
 
     const body_len = if (small.has_body_len) blk: {
@@ -23773,7 +23773,7 @@ fn semaUnionFields(block: *Block, mod: *Module, union_obj: *Module.Union) Compil
     const small = @bitCast(Zir.Inst.UnionDecl.Small, extended.small);
     var extra_index: usize = extended.operand;
 
-    const src: LazySrcLoc = .{ .node_offset = union_obj.node_offset };
+    const src = LazySrcLoc.nodeOffset(union_obj.node_offset);
     extra_index += @boolToInt(small.has_src_node);
 
     const tag_type_ref: Zir.Inst.Ref = if (small.has_tag_type) blk: {
@@ -24459,7 +24459,7 @@ fn enumFieldSrcLoc(
             .container_field,
             => {
                 if (it_index == field_index) {
-                    return .{ .node_offset = decl.nodeIndexToRelative(member_node) };
+                    return LazySrcLoc.nodeOffset(decl.nodeIndexToRelative(member_node));
                 }
                 it_index += 1;
             },
diff --git a/src/Zir.zig b/src/Zir.zig
index 370f996fd5..1ca31755f7 100644
--- a/src/Zir.zig
+++ b/src/Zir.zig
@@ -2427,7 +2427,7 @@ pub const Inst = struct {
             operand: Ref,
 
             pub fn src(self: @This()) LazySrcLoc {
-                return .{ .node_offset = self.src_node };
+                return LazySrcLoc.nodeOffset(self.src_node);
             }
         },
         /// Used for unary operators, with a token source location.
@@ -2450,7 +2450,7 @@ pub const Inst = struct {
             payload_index: u32,
 
             pub fn src(self: @This()) LazySrcLoc {
-                return .{ .node_offset = self.src_node };
+                return LazySrcLoc.nodeOffset(self.src_node);
             }
         },
         pl_tok: struct {
@@ -2526,7 +2526,7 @@ pub const Inst = struct {
             bit_count: u16,
 
             pub fn src(self: @This()) LazySrcLoc {
-                return .{ .node_offset = self.src_node };
+                return LazySrcLoc.nodeOffset(self.src_node);
             }
         },
         bool_br: struct {
@@ -2545,7 +2545,7 @@ pub const Inst = struct {
             force_comptime: bool,
 
             pub fn src(self: @This()) LazySrcLoc {
-                return .{ .node_offset = self.src_node };
+                return LazySrcLoc.nodeOffset(self.src_node);
             }
         },
         @"break": struct {
@@ -2566,7 +2566,7 @@ pub const Inst = struct {
             inst: Index,
 
             pub fn src(self: @This()) LazySrcLoc {
-                return .{ .node_offset = self.src_node };
+                return LazySrcLoc.nodeOffset(self.src_node);
             }
         },
         str_op: struct {
diff --git a/src/arch/wasm/CodeGen.zig b/src/arch/wasm/CodeGen.zig
index da4e84b587..33cf5422f2 100644
--- a/src/arch/wasm/CodeGen.zig
+++ b/src/arch/wasm/CodeGen.zig
@@ -622,7 +622,7 @@ pub fn deinit(self: *Self) void {
 
 /// Sets `err_msg` on `CodeGen` and returns `error.CodegenFail` which is caught in link/Wasm.zig
 fn fail(self: *Self, comptime fmt: []const u8, args: anytype) InnerError {
-    const src: LazySrcLoc = .{ .node_offset = 0 };
+    const src = LazySrcLoc.nodeOffset(0);
     const src_loc = src.toSrcLoc(self.decl);
     self.err_msg = try Module.ErrorMsg.create(self.gpa, src_loc, fmt, args);
     return error.CodegenFail;
diff --git a/src/codegen/c.zig b/src/codegen/c.zig
index 4c2239b306..45191f3107 100644
--- a/src/codegen/c.zig
+++ b/src/codegen/c.zig
@@ -363,7 +363,7 @@ pub const DeclGen = struct {
 
     fn fail(dg: *DeclGen, comptime format: []const u8, args: anytype) error{ AnalysisFail, OutOfMemory } {
         @setCold(true);
-        const src: LazySrcLoc = .{ .node_offset = 0 };
+        const src = LazySrcLoc.nodeOffset(0);
         const src_loc = src.toSrcLoc(dg.decl);
         dg.error_msg = try Module.ErrorMsg.create(dg.module.gpa, src_loc, format, args);
         return error.AnalysisFail;
diff --git a/src/codegen/llvm.zig b/src/codegen/llvm.zig
index 188c2f6f11..60803eff69 100644
--- a/src/codegen/llvm.zig
+++ b/src/codegen/llvm.zig
@@ -2163,7 +2163,7 @@ pub const DeclGen = struct {
     fn todo(self: *DeclGen, comptime format: []const u8, args: anytype) Error {
         @setCold(true);
         assert(self.err_msg == null);
-        const src_loc = @as(LazySrcLoc, .{ .node_offset = 0 }).toSrcLoc(self.decl);
+        const src_loc = LazySrcLoc.nodeOffset(0).toSrcLoc(self.decl);
         self.err_msg = try Module.ErrorMsg.create(self.gpa, src_loc, "TODO (LLVM): " ++ format, args);
         return error.CodegenFail;
     }
diff --git a/src/codegen/spirv.zig b/src/codegen/spirv.zig
index 0dc39db134..9879bc7f35 100644
--- a/src/codegen/spirv.zig
+++ b/src/codegen/spirv.zig
@@ -184,7 +184,7 @@ pub const DeclGen = struct {
 
     fn fail(self: *DeclGen, comptime format: []const u8, args: anytype) Error {
         @setCold(true);
-        const src: LazySrcLoc = .{ .node_offset = 0 };
+        const src = LazySrcLoc.nodeOffset(0);
         const src_loc = src.toSrcLoc(self.decl);
         assert(self.error_msg == null);
         self.error_msg = try Module.ErrorMsg.create(self.module.gpa, src_loc, format, args);
@@ -193,7 +193,7 @@ pub const DeclGen = struct {
 
     fn todo(self: *DeclGen, comptime format: []const u8, args: anytype) Error {
         @setCold(true);
-        const src: LazySrcLoc = .{ .node_offset = 0 };
+        const src = LazySrcLoc.nodeOffset(0);
         const src_loc = src.toSrcLoc(self.decl);
         assert(self.error_msg == null);
         self.error_msg = try Module.ErrorMsg.create(self.module.gpa, src_loc, "TODO (SPIR-V): " ++ format, args);
diff --git a/src/print_zir.zig b/src/print_zir.zig
index 3257a3cb58..1760c617ce 100644
--- a/src/print_zir.zig
+++ b/src/print_zir.zig
@@ -497,7 +497,7 @@ const Writer = struct {
             .wasm_memory_size,
             => {
                 const inst_data = self.code.extraData(Zir.Inst.UnNode, extended.operand).data;
-                const src: LazySrcLoc = .{ .node_offset = inst_data.node };
+                const src = LazySrcLoc.nodeOffset(inst_data.node);
                 try self.writeInstRef(stream, inst_data.operand);
                 try stream.writeAll(")) ");
                 try self.writeSrc(stream, src);
@@ -510,7 +510,7 @@ const Writer = struct {
             .prefetch,
             => {
                 const inst_data = self.code.extraData(Zir.Inst.BinNode, extended.operand).data;
-                const src: LazySrcLoc = .{ .node_offset = inst_data.node };
+                const src = LazySrcLoc.nodeOffset(inst_data.node);
                 try self.writeInstRef(stream, inst_data.lhs);
                 try stream.writeAll(", ");
                 try self.writeInstRef(stream, inst_data.rhs);
@@ -520,7 +520,7 @@ const Writer = struct {
 
             .field_call_bind_named => {
                 const extra = self.code.extraData(Zir.Inst.FieldNamedNode, extended.operand).data;
-                const src: LazySrcLoc = .{ .node_offset = extra.node };
+                const src = LazySrcLoc.nodeOffset(extra.node);
                 try self.writeInstRef(stream, extra.lhs);
                 try stream.writeAll(", ");
                 try self.writeInstRef(stream, extra.field_name);
@@ -531,7 +531,7 @@ const Writer = struct {
     }
 
     fn writeExtNode(self: *Writer, stream: anytype, extended: Zir.Inst.Extended.InstData) !void {
-        const src: LazySrcLoc = .{ .node_offset = @bitCast(i32, extended.operand) };
+        const src = LazySrcLoc.nodeOffset(@bitCast(i32, extended.operand));
         try stream.writeAll(")) ");
         try self.writeSrc(stream, src);
     }
@@ -1050,7 +1050,7 @@ const Writer = struct {
 
     fn writeNodeMultiOp(self: *Writer, stream: anytype, extended: Zir.Inst.Extended.InstData) !void {
         const extra = self.code.extraData(Zir.Inst.NodeMultiOp, extended.operand);
-        const src: LazySrcLoc = .{ .node_offset = extra.data.src_node };
+        const src = LazySrcLoc.nodeOffset(extra.data.src_node);
         const operands = self.code.refSlice(extra.end, extended.small);
 
         for (operands) |operand, i| {
@@ -1074,7 +1074,7 @@ const Writer = struct {
 
     fn writeAsm(self: *Writer, stream: anytype, extended: Zir.Inst.Extended.InstData) !void {
         const extra = self.code.extraData(Zir.Inst.Asm, extended.operand);
-        const src: LazySrcLoc = .{ .node_offset = extra.data.src_node };
+        const src = LazySrcLoc.nodeOffset(extra.data.src_node);
         const outputs_len = @truncate(u5, extended.small);
         const inputs_len = @truncate(u5, extended.small >> 5);
         const clobbers_len = @truncate(u5, extended.small >> 10);
@@ -1145,7 +1145,7 @@ const Writer = struct {
 
     fn writeOverflowArithmetic(self: *Writer, stream: anytype, extended: Zir.Inst.Extended.InstData) !void {
         const extra = self.code.extraData(Zir.Inst.OverflowArithmetic, extended.operand).data;
-        const src: LazySrcLoc = .{ .node_offset = extra.node };
+        const src = LazySrcLoc.nodeOffset(extra.node);
 
         try self.writeInstRef(stream, extra.lhs);
         try stream.writeAll(", ");
@@ -1898,7 +1898,7 @@ const Writer = struct {
         inst: Zir.Inst.Index,
     ) (@TypeOf(stream).Error || error{OutOfMemory})!void {
         const src_node = self.code.instructions.items(.data)[inst].node;
-        const src: LazySrcLoc = .{ .node_offset = src_node };
+        const src = LazySrcLoc.nodeOffset(src_node);
         try stream.writeAll(") ");
         try self.writeSrc(stream, src);
     }
@@ -2117,7 +2117,7 @@ const Writer = struct {
     fn writeAllocExtended(self: *Writer, stream: anytype, extended: Zir.Inst.Extended.InstData) !void {
         const extra = self.code.extraData(Zir.Inst.AllocExtended, extended.operand);
         const small = @bitCast(Zir.Inst.AllocExtended.Small, extended.small);
-        const src: LazySrcLoc = .{ .node_offset = extra.data.src_node };
+        const src = LazySrcLoc.nodeOffset(extra.data.src_node);
 
         var extra_index: usize = extra.end;
         const type_inst: Zir.Inst.Ref = if (!small.has_type) .none else blk: {
@@ -2351,7 +2351,7 @@ const Writer = struct {
 
     fn writeSrcNode(self: *Writer, stream: anytype, src_node: ?i32) !void {
         const node_offset = src_node orelse return;
-        const src: LazySrcLoc = .{ .node_offset = node_offset };
+        const src = LazySrcLoc.nodeOffset(node_offset);
         try stream.writeAll(" ");
         return self.writeSrc(stream, src);
     }