Commit dc79f181a5

@@ -16286,6 +16286,15 @@ static IrInstGen *ir_analyze_bin_op_cmp(IrAnalyze *ira, IrInstSrcBinOp *bin_op_i
         IrInstGen *union_val = op1->value->type->id == ZigTypeIdUnion ? op1 : op2;
         IrInstGen *enum_val = op1->value->type->id == ZigTypeIdUnion ? op2 : op1;
 
+        if (!is_tagged_union(union_val->value->type)) {
+            ErrorMsg *msg = ir_add_error_node(ira, source_node,
+                buf_sprintf("comparison of union and enum literal is only valid for tagged union types"));
+            add_error_note(ira->codegen, msg, union_val->value->type->data.unionation.decl_node,
+                buf_sprintf("type %s is not a tagged union",
+                    buf_ptr(&union_val->value->type->name)));
+            return ira->codegen->invalid_inst_gen;
+        }
+
         ZigType *tag_type = union_val->value->type->data.unionation.tag_type;
         assert(tag_type != nullptr);
 

@@ -14,6 +14,17 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
         "tmp.zig:2:15: error: unused variable: 'a'",
     });
 
+    cases.addTest("comparison of non-tagged union and enum literal",
+        \\export fn entry() void {
+        \\    const U = union { A: u32, B: u64 };
+        \\    var u = U{ .A = 42 };
+        \\    var ok = u == .A;
+        \\}
+    , &[_][]const u8{
+        "tmp.zig:4:16: error: comparison of union and enum literal is only valid for tagged union types",
+        "tmp.zig:2:15: note: type U is not a tagged union",
+    });
+
     cases.addTest("shift on type with non-power-of-two size",
         \\export fn entry() void {
         \\    const S = struct {