Reset Memory::popup to None if a popup was abandoned

[juancampa]

• Closes any_popup_open() remains true even when there are no popups #3657

BEFORE

Screenshot.2024-06-23.at.18.41.41.mp4

AFTER

Screenshot.2024-06-23.at.18.56.01.mp4

Notice that WRONG flashes for one frame. That's expected because on the frame the combo box disappears, any_popup_open still returns true, since we don't know it has disappeared until the end of the frame.

[juancampa]

I'm using an AtomicBool here because I didn't want to change is_popup_open to take &mut self.

An alternative is to add another function, something like retain_popup(&mut self) that explicitly sets a retained bool to true. But would will be a breaking change and existing apps will need to call it or popups will only last for one frame.

I'm open to suggestions.

[emilk]

it's not at all obvious from reading this what the bool is for though., or why it is behind an Arc.

It seems to answer the question "Was is_popup_open called for this this frame?", i.e. "Does anyone care that this is open?".

I suggest making a struct with a name field so the motivation behind this can be documented.

We should also document that if is_popup_open is not called during a frame, the popup auto-closes.
Since this in fact makes it change state, I think making it take a &mut makes sense.

So I suggest

struct OpenPopup {
    id: Id,
    shown_this_frame: bool,
}

…

popup: Option<OpenPopup>,