Closes https://github.com/ppy/osu/issues/28938.
This is related to reloading the composer on timing point changes in
scrolling rulesets. The lack of unsubscription from this would cause
blueprints to be created for disposed composers via the
`hitObjectAdded()` flow.
The following line looks as if a sync load should be forced on a newly
created placement blueprint:
da4d37c4ad/osu.Game/Screens/Edit/Compose/Components/ComposeBlueprintContainer.cs (L364)
however, it is not the case if the parent
(`placementBlueprintContainer`) is disposed, which it would be in this
case. Therefore, the blueprint stays `NotLoaded` rather than `Ready`,
therefore it never receives its DI dependencies, therefore it dies on
an `EditorBeatmap` nullref.
This was reported in https://github.com/ppy/osu/pull/28474, albeit the
code changes proposed there did not fix the issue at all.
See 8b6385f7d0 for demonstration of the
crash scenario. Basically what is happening there is:
- The starting premise is that there is a spinner placement active.
- At this time, a drag selection is started via the timeline.
- Once the drag selection finds at least one suitable object to select,
it mutates `SelectedItems`.
- When selection changes for any reason, the `HitObjectComposer`
decides to switch to the "select" tool, regardless of why
the selection changed.
- Changing the active tool causes the current placement - if any -
to be committed, which mutates the beatmap.
- Back at the drag box selection code, this causes a "collection
modified when enumerating" exception.
The proposed fix here is to eagerly commit active placement - if any -
when drag selection is initiated via the timeline, which avoids this
issue. This also appears to vaguely match stable behaviour and is sort
of consistent with the logic of committing any outstanding changes upon
switching to the selection tool.
`SelectionHandler` is receiving input from anywhere out of necessity:
19f892687a/osu.Game/Screens/Edit/Compose/Components/SelectionHandler.cs (L119-L125)
Also important is that `BlueprintContainer` will selectively not block
right clicks to make sure they fall through to the
`ContextMenuContainer`:
19f892687a/osu.Game/Screens/Edit/Compose/Components/BlueprintContainer.cs (L122-L126)
But because the whole editor is sharing a `ContextMenuContainer` and
it's at a higher level than both components, we observe here the
playfield's `SelectionHandler` intercepting the right click before it
can reach the `ContextMenuContainer`.
The fix here is similar to what we're already doing in
`TimelineBlueprintContaienr`.
Seems to have had no consequence due to the way
`AutomaticBankAssignment` works (that flag is checked in
`PlacementBlueprint.UpdateTimeAndPosition()`, which runs essentially
every frame), but let's avoid putting it there at all ever.
`AllowDeselectionDuringDrag` is remove.
Instead, selected hit objects are not automatically deselected
when clock is seeked to a later time (the hit object is dead).
Update drag box selection even if mouse is not moved
(in case clock is running or scroll wheel is used).
