test(runtime): cover for-in visited levels across GC

test-files/test_issue_9869_for_in_visited_levels_gc.ts

@@ -0,0 +1,22 @@
+// parity-env: PERRY_GC_SCHEDULE_SEED=9869 PERRY_GC_SCHEDULE_RATE=1 PERRY_GC_SCHEDULE_ALLOC_KB=0 PERRY_GC_FORCE_EVACUATE=1 PERRY_GC_VERIFY_EVACUATION=1 PERRY_GC_PROTECT_FROMSPACE=1
+
+// #9869: `for-in` defers building its shadow set until a prototype level has
+// an enumerable key to filter. The retained earlier levels must remain rooted
+// while key-array construction allocates and triggers a moving collection.
+const ancestor = {
+  own: "shadowed",
+  ancestor: "visible",
+};
+const emptyMiddle = Object.create(ancestor);
+const receiver = Object.create(emptyMiddle);
+receiver.own = "receiver";
+
+// Level zero records `receiver`; the empty middle level allocates a key array
+// but keeps the shadow set deferred; the ancestor's keys then trigger a rebuild
+// that reads both retained heap objects after evacuation.
+const keys: string[] = [];
+for (const key in receiver) {
+  keys.push(key);
+}
+
+console.log(keys.join(","));