Import dock randomly causes sidebar size jumps

[KoBeWi]

Godot version

e9e9e92

System information

Windows 10 x64

Issue description

Seems like minimum size of the import dock varies greatly and it can abruptly change sidebar's width. It always happens when switching to Import tab, but also randomly on it's own.

Might be caused #59303
But the random jumps and minsize weirdness looks similar to #43749

Steps to reproduce

1. Select different files in the filesystem dock (scene, texture, sample etc)
2. The left dock will randomly change size
3. If not, switch to Import tab and observe size jump

EDIT:
Better reproduction steps:

1. Select any texture in filesystem dock
2. Create a new folder -> the dock expands
3. Select a scene file
4. Rename the folder -> the dock shrinks again

Minimal reproduction project

No response

[KoBeWi]

Ok I found a way to trigger this reliably. The random jump seems to happen on filesystem update.

So it's indeed the same as #43749 + some random size refresh from filesystem + #59303 making the import dock wider.

[Rindbee]

It feels like the TabContainer here has use_hidden_tabs_for_min_size enabled.

And the split_offset of SplitContainer is not relative to the begin of the container, but the end (according to the minimum size) of the first child control.

When it is negative, it resets to 0 on dragging again, then the jump happens.

Changes in the minimum size of the first child control will not cause split_offset to change, but the absolute offset (relative to the begin of the container) does change.

[Rindbee]

Take back the previous conclusions. drag_ofs uses the split_offset at the start of dragging in the following code, which will cause the split_offset calculated by the change of the minimum size of the child control to be overwritten.

godot/scene/gui/split_container.cpp

Lines 267 to 273 in 4808d01

	if (!vertical && is_layout_rtl()) {
	split_offset = drag_ofs + (drag_from - (vertical ? mm->get_position().y : mm->get_position().x));
	} else {
	split_offset = drag_ofs + ((vertical ? mm->get_position().y : mm->get_position().x) - drag_from);
	}
	should_clamp_split_offset = true;
	queue_sort();

[KoBeWi]

This is the culprit for wide import dock:

It either should be shorter or the OptionButton should have trimming enabled