Merge pull request #21189 from emberjs/copilot/fix-stale-references-metadata

[BUGFIX] clear stale metadata references after destruction to allow GC

Author: NullVoxPopuli

packages/@glimmer/destroyable/index.ts

@@ -189,7 +189,7 @@ export function destroy(destroyable: Destroyable) {
 function removeChildFromParent(child: Destroyable, parent: Destroyable) {
   let parentMeta = getDestroyableMeta(parent);
 
-  if (parentMeta.state === LIVE_STATE) {
+  if (parentMeta.state !== DESTROYED_STATE) {
     parentMeta.children = remove(
       parentMeta.children,
       child,

packages/@glimmer/destroyable/test/destroyables-test.ts

@@ -2,6 +2,7 @@ import { DEBUG } from '@glimmer/env';
 import type { GlobalContext } from '@glimmer/global-context';
 import { unwrap } from '@glimmer/debug-util';
 import {
+  _hasDestroyableChildren,
   assertDestroyablesDestroyed,
   associateDestroyableChild,
   destroy,
@@ -384,6 +385,23 @@ module('Destroyables', (hooks) => {
     assert.verifySteps(['child destructor', 'parent destructor'], 'destructors run bottom up');
   });
 
+  test('parent no longer references child after cascaded destruction', (assert) => {
+    const parent = {};
+    const child = {};
+
+    associateDestroyableChild(parent, child);
+
+    assert.true(_hasDestroyableChildren(parent), 'parent has children before destruction');
+
+    destroy(parent);
+    flush();
+
+    assert.false(
+      _hasDestroyableChildren(parent),
+      'parent metadata releases child reference during cascaded destruction, allowing GC to reclaim the tree'
+    );
+  });
+
   if (DEBUG) {
     test('attempting to unregister a destructor that was not registered throws an error', (assert) => {
       assert.throws(() => {