Fix edge case in tagName handling of unions

Closes #4226

1 files changed, 9 insertions, 0 deletions

diff --git a/test/stage1/behavior/union.zig b/test/stage1/behavior/union.zig
index a24bee03e6..4625b7573a 100644
--- a/test/stage1/behavior/union.zig
+++ b/test/stage1/behavior/union.zig
@@ -629,3 +629,12 @@ test "union initializer generates padding only if needed" {
     var v = U{ .A = 532 };
     expect(v.A == 532);
 }
+
+test "runtime tag name with single field" {
+    const U = union(enum) {
+        A: i32,
+    };
+
+    var v = U{ .A = 42 };
+    expect(std.mem.eql(u8, @tagName(v), "A"));
+}