From 09eb81de8b000a760680f42c07ef50cd30f97d08 Mon Sep 17 00:00:00 2001
From: David Rubin <sinon@vortan.dev>
Date: Sat, 3 Oct 2026 18:54:25 -0500
Subject: [PATCH] AstGen: increment baseline when inside backing tag

---
 lib/std/zig/AstGen.zig                        |  6 ++++
 .../compile_error_in_backing_tag.zig          | 29 +++++++++++++++++++
 2 files changed, 35 insertions(+)
 create mode 100644 test/cases/compile_errors/compile_error_in_backing_tag.zig

diff --git a/lib/std/zig/AstGen.zig b/lib/std/zig/AstGen.zig
index 0b98fcf2b92d6b3f80e187f54f8060343fd8e24e..7e47a3e06d9d888b9680c3d2b3f6842543a114d0 100644
--- a/lib/std/zig/AstGen.zig
+++ b/lib/std/zig/AstGen.zig
@@ -4920,6 +4920,8 @@ fn structDeclInner(
 
     // Before any field bodies comes the backing int type, if specified.
     const backing_int_type_body_len: ?u32 = if (maybe_backing_int_node.unwrap()) |backing_int_node| len: {
+        block_scope.src_baseline = backing_int_node;
+        defer block_scope.src_baseline = node;
         if (layout != .@"packed") return astgen.failNode(
             backing_int_node,
             "non-packed struct does not support backing integer type",
@@ -5215,6 +5217,8 @@ fn unionDeclInner(
 
     // Before any field bodies comes the tag/backing type, if specified.
     const arg_type_body_len: ?u32 = if (opt_arg_node.unwrap()) |arg_node| len: {
+        block_scope.src_baseline = arg_node;
+        defer block_scope.src_baseline = node;
         astgen.src_hasher.update(astgen.tree.getNodeSource(arg_node));
         const type_ref = try typeExpr(&block_scope, &namespace.base, arg_node);
         if (!block_scope.endsWithNoReturn()) {
@@ -5435,6 +5439,8 @@ fn containerDecl(
 
             // Before any field bodies comes the tag type, if specified.
             const tag_type_body_len: ?u32 = if (container_decl.ast.arg.unwrap()) |tag_type_node| len: {
+                block_scope.src_baseline = tag_type_node;
+                defer block_scope.src_baseline = node;
                 astgen.src_hasher.update(astgen.tree.getNodeSource(tag_type_node));
                 const type_ref = try typeExpr(&block_scope, &namespace.base, tag_type_node);
                 if (!block_scope.endsWithNoReturn()) {
diff --git a/test/cases/compile_errors/compile_error_in_backing_tag.zig b/test/cases/compile_errors/compile_error_in_backing_tag.zig
new file mode 100644
index 0000000000000000000000000000000000000000..1ff9a2f0dbce5822382faa9b585dbdd444e83113
--- /dev/null
+++ b/test/cases/compile_errors/compile_error_in_backing_tag.zig
@@ -0,0 +1,29 @@
+const E = enum(@compileError("enum")) {
+    x = 0,
+};
+
+const U = union(enum(@compileError("union"))) {
+    x = 0,
+};
+
+const S = packed struct(@compileError("struct")) {
+    x: u8 = 0,
+};
+
+comptime {
+    _ = &E.x;
+}
+
+comptime {
+    _ = &U.x;
+}
+
+comptime {
+    _ = &S{};
+}
+
+// error
+//
+// :1:16: error: enum
+// :5:22: error: union
+// :9:25: error: struct
-- 
2.54.0