nodejs: Add a test for callback garbage collection

Replaces #3772
Closes #3706

api/node/__test__/api.spec.mts

@@ -4,6 +4,11 @@
 import test from 'ava'
 import * as path from 'node:path';
 import { fileURLToPath } from 'url';
+import { setFlagsFromString } from 'v8';
+import { runInNewContext } from 'vm';
+
+setFlagsFromString('--expose_gc');
+const gc = runInNewContext('gc');
 
 import { loadFile, loadSource, CompileError } from '../index.js'
 
@@ -159,3 +164,48 @@ test('loadSource component instances and modules are sealed', (t) => {
  test.no_such_callback = () => { };
  }, { instanceOf: TypeError });
 })
+
+test('callback closure cyclic references do not prevent GC', async (t) => {
+
+ // Setup:
+ // A component instance with a callback installed from JS:
+ // * The callback captures the surrounding environment, which
+ // includes an extra reference to the component instance itself
+ // --> a cyclic reference
+ // * Invoking the callback clears the reference in the outer captured
+ // environment.
+ //
+ // Note: WeakRef's deref is used to observe the GC. This means that we must
+ // separate the test into different jobs with await, to permit for collection.
+ // (See https://tc39.es/ecma262/multipage/managing-memory.html#sec-weak-ref.prototype.deref)
+
+ let demo = loadFile(path.join(__dirname, "resources/test-constructor.slint")) as any;
+ let callback_invoked = false;
+ let demo_weak = new WeakRef(demo);
+
+ demo.my_callback = () => {
+ demo = null;
+ callback_invoked = true;
+ };
+
+ t.true(demo_weak.deref() !== undefined);
+
+ // After the first GC, the instance should not have been collected because the
+ // current environment's demo variable is a strong reference.
+ await new Promise(resolve => setTimeout(resolve, 0));
+ gc();
+
+ t.true(demo_weak.deref() !== undefined);
+
+ // Invoke the callback, to clear "demo"
+ demo.my_callback();
+ t.true(callback_invoked);
+ t.true(demo === null);
+
+ // After the this GC call, the instance should have been collected. Strong references
+ // in Rust should not keep it alive.
+ await new Promise(resolve => setTimeout(resolve, 0));
+ gc();
+
+ t.is(demo_weak.deref(), undefined, "The demo instance should have been collected and the weak ref should deref to undefined");
+})