Propagating exceptions from JS through Python to JS has a memory leak

[mmomtchev]

The following test leaks memory:

it('catching JS exceptions propagated through Python', () => {
  const fn = PyObject.fromJS(() => {
    throw new Error('JS exception');
  });

  assert.isTrue(fn.callable);
  assert.equal(fn.type, 'pymport.js_function');

  const py_catch = pymport('python_helpers').get('dont_catch_exception');

  assert.throws(() => {
    py_catch.call(fn);
  }, /Python exception: JS exception/);
});

[mmomtchev]

Happens only with the fastcall protocol on Python > 3.9 V8 does not garbage collect fn

[mmomtchev]

This test does not have the leak:

it'catching JS exceptions propagated through Python', () => {
  const fn = PyObject.fromJS(() => {
    throw new Error('JS exception');
  });

  assert.isTrue(fn.callable);
  assert.equal(fn.type, 'pymport.js_function');

  const py_dont_catch = pymport('python_helpers').get('dont_catch_exception');

  try {
    py_dont_catch.call(fn);
  } catch { }
});

[mmomtchev]

However this one does:

it('catching JS exceptions propagated through Python', () => {
  const fn = PyObject.fromJS(() => {
    throw new Error('JS exception');
  });

  assert.isTrue(fn.callable);
  assert.equal(fn.type, 'pymport.js_function');

  const py_dont_catch = pymport('python_helpers').get('dont_catch_exception');

  try {
    (() => {
      py_dont_catch.call(fn);
    })();
  } catch (e: any) {
    assert.match(e.toString(), /Python exception: JS exception/);
  }
});