Hanging await leaks memory, throws error (aka resume after free)

[vpellen]

Godot version

v4.0.beta17.official [c400205]

System information

Windows 10

Issue description

In spite of the fact that this issue is, I believe, one of the most infamous issues plaguing GDScript at the current time, I couldn't find an existing ticket that references the issue explicitly.

Here's the core of it: If you await a signal that has a longer lifetime than the object containing the coroutine itself, and then free the object before resuming the coroutine, you get a memory leak if the signal is never emitted, and an error if it is. There are a number of ways to interpret why this happens, but the core of it seems to be that freeing an object does not appear to disconnect any GDFunctionState instances that depend on the object itself. I experimented with a release build, and while it doesn't appear to cause a crash, I think it's fair to say that ignoring an error that arguably shouldn't exist is not a graceful solution. There may also be other side effects I'm not actually aware of.

There are ways of working around this, but they're all fickle, and the quintessential coroutine example of:

await get_tree().process_frame

is one of the fastest ways to trip over the problem.

Steps to reproduce

Stick the following in your node of choice:

func _ready():
	queue_free()
	await get_tree().process_frame

Minimal reproduction project

N/A

[vpellen]

Possibly fixed by #65910?

[KoBeWi]

And duplicate of #24311 ;)