Add regression test

Author: ahejlsberg

tests/cases/compiler/discriminantPropertyCheck.ts

@@ -121,3 +121,29 @@ const u: U = {} as any;
 u.a && u.b && f(u.a, u.b);
 
 u.b && u.a && f(u.a, u.b);
+
+// Repro from #29496
+
+declare function never(value: never): never;
+
+const enum BarEnum {
+    bar1 = 1,
+    bar2 = 2,
+}
+
+type UnionOfBar = TypeBar1 | TypeBar2;
+type TypeBar1 = { type: BarEnum.bar1 };
+type TypeBar2 = { type: BarEnum.bar2 };
+
+function func3(value: Partial<UnionOfBar>) {
+    if (value.type !== undefined) {
+        switch (value.type) {
+            case BarEnum.bar1:
+                break;
+            case BarEnum.bar2:
+                break;
+            default:
+                never(value.type);
+        }
+    }
+}