Fix edge case in tagName handling of unions

Closes #4226

1 files changed, 9 insertions, 0 deletions

diff --git a/src/ir.cpp b/src/ir.cpp
index ae02ac9cae..ff4b552a9b 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -22354,6 +22354,15 @@ static IrInstruction *ir_analyze_instruction_enum_tag_name(IrAnalyze *ira, IrIns
 
     assert(target->value->type->id == ZigTypeIdEnum);
 
+    if (target->value->type->data.enumeration.src_field_count == 1 &&
+        !target->value->type->data.enumeration.non_exhaustive) {
+        TypeEnumField *only_field = &target->value->type->data.enumeration.fields[0];
+        ZigValue *array_val = create_const_str_lit(ira->codegen, only_field->name)->data.x_ptr.data.ref.pointee;
+        IrInstruction *result = ir_const(ira, &instruction->base, nullptr);
+        init_const_slice(ira->codegen, result->value, array_val, 0, buf_len(only_field->name), true);
+        return result;
+    }
+
     if (instr_is_comptime(target)) {
         if ((err = type_resolve(ira->codegen, target->value->type, ResolveStatusZeroBitsKnown)))
             return ira->codegen->invalid_instruction;