gh-118331: Don't raise an error if tuple allocation fails when clearing weakrefs

[mpage]

It's not safe to raise an exception in PyObject_ClearWeakRefs() if one is not already set. PyObject_ClearWeakRefs() may be called (transitively) by _Py_Dealloc(), which contains

cpython/Objects/object.c

Lines 2843 to 2860 in 5a90de0

	// gh-89373: The tp_dealloc function must leave the current exception
	// unchanged.
	if (tstate != NULL && tstate->current_exception != old_exc) {
	const char *err;
	if (old_exc == NULL) {
	err = "Deallocator of type '%s' raised an exception";
	}
	else if (tstate->current_exception == NULL) {
	err = "Deallocator of type '%s' cleared the current exception";
	}
	else {
	// It can happen if dealloc() normalized the current exception.
	// A deallocator function must not change the current exception,
	// not even normalize it.
	err = "Deallocator of type '%s' overrode the current exception";
	}
	_Py_FatalErrorFormat(__func__, err, type->tp_name);
	}

Additionally, make sure we clear the weakrefs when tuple allocation fails.

This bug predates gh-111926. It exists in 3.12 and likely in earlier versions too. If it's getting tickled now, I suspect it's because we always allocate a tuple now when clearing weakrefs that have callbacks, whereas previously we only did so if there was more than one weakref with a callback, making it more likely that we fail to allocate a tuple when running test_repl.TestInteractiveInterpreter.test_no_memory.

• Issue: test_repl's test_no_memory: AssertionError: -6 not found in (1, 120) #118331

[hugovk]

Thanks, this fixes gh-118331 for me.

[colesbury]

Thanks!

[bedevere-app]

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[mpage]

I have made the requested changes; please review again.

[bedevere-app]

Thanks for making the requested changes!

@Fidget-Spinner, @colesbury: please review the changes made to this pull request.