From 6f0f77494ab9f21002f76a7748b386fbb2ea1c44 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ralph=20K=C3=BCpper?= <ralph@skelpo.com>
Date: Sun, 6 Sep 2026 18:35:27 +0200
Subject: [PATCH] test(runtime): cover for-in visited levels across GC

---
 ...est_issue_9869_for_in_visited_levels_gc.ts | 22 +++++++++++++++++++
 1 file changed, 22 insertions(+)
 create mode 100644 test-files/test_issue_9869_for_in_visited_levels_gc.ts

diff --git a/test-files/test_issue_9869_for_in_visited_levels_gc.ts b/test-files/test_issue_9869_for_in_visited_levels_gc.ts
new file mode 100644
index 0000000000..0fcb5aa57a
--- /dev/null
+++ b/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(","));