From c8cd8dd2db9a895091f5151d0831c46407025369 Mon Sep 17 00:00:00 2001
From: Leandro Libanio <leandro.libanio@libaniol.com>
Date: Wed, 1 Apr 2026 12:39:48 -0300
Subject: [PATCH] allow in-progress union variants when validating union
 members

Fixes: #5961
---
 src/check_type.cpp | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/check_type.cpp b/src/check_type.cpp
index 18cbb4900..b7ff56536 100644
--- a/src/check_type.cpp
+++ b/src/check_type.cpp
@@ -796,11 +796,19 @@ gb_internal void check_union_type(CheckerContext *ctx, Type *union_type, Ast *no
 		if (t != nullptr && t != t_invalid) {
 			bool ok = true;
 			t = default_type(t);
-			if (is_type_untyped(t) || is_type_empty_union(t)) {
+			if (is_type_untyped(t)) {
 				ok = false;
 				gbString str = type_to_string(t);
 				error(node, "Invalid variant type in union '%s'", str);
 				gb_string_free(str);
+			} else if (is_type_empty_union(t)) {
+				Type *base = base_type(t);
+				if (base == nullptr || base->kind != Type_Union || base->Union.node == nullptr) {
+					ok = false;
+					gbString str = type_to_string(t);
+					error(node, "Invalid variant type in union '%s'", str);
+					gb_string_free(str);
+				}
 			} else {
 				for_array(j, variants) {
 					if (union_variant_index_types_equal(t, variants[j])) {