stage1: fix tagged union with no payloads

closes #1478

2 files changed, 14 insertions, 1 deletions

diff --git a/src/codegen.cpp b/src/codegen.cpp
index 2f7a25cf93..f5c1019892 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -5490,7 +5490,7 @@ static LLVMValueRef gen_const_val(CodeGen *g, ConstExprValue *const_val, const c
                 LLVMTypeRef union_type_ref = type_entry->data.unionation.union_type_ref;
 
                 if (type_entry->data.unionation.gen_field_count == 0) {
-                    if (type_entry->data.unionation.gen_tag_index == SIZE_MAX) {
+                    if (type_entry->data.unionation.tag_type == nullptr) {
                         return nullptr;
                     } else {
                         return bigint_to_llvm_const(type_entry->data.unionation.tag_type->type_ref,
diff --git a/test/cases/union.zig b/test/cases/union.zig
index 08969e64fe..0c55fb92e7 100644
--- a/test/cases/union.zig
+++ b/test/cases/union.zig
@@ -311,3 +311,16 @@ fn testTaggedUnionInit(x: var) bool {
     const y = TaggedUnionWithAVoid{ .A = x };
     return @TagType(TaggedUnionWithAVoid)(y) == TaggedUnionWithAVoid.A;
 }
+
+pub const UnionEnumNoPayloads = union(enum) {
+    A,
+    B,
+};
+
+test "tagged union with no payloads" {
+    const a = UnionEnumNoPayloads{ .B = {} };
+    switch (a) {
+        @TagType(UnionEnumNoPayloads).A => @panic("wrong"),
+        @TagType(UnionEnumNoPayloads).B => {},
+    }
+}