MenuButton ignores custom styles because it's flat by default

[Shadowblitz16]

the menubutton's normal style don't seem to be rendering even though it's set to a the same texturestyle as the button below it

[Gramps]

This still doesn't work. Am messing with it right now and none of the theme stuff functions.

[dominiks]

By default the MenuButton is set to be flat. In this state it ignores the backgrounds of its styleboxes. If you set flat to false it shows the styles as expected.

I think the MenuButton should not be flat by default as it leads to confusion. Or rename it to FlatMenuButton.

[Calinou]

If MenuButton wasn't flat by default, then we'd have to override the style in the editor. It can certainly be done, but it will break the appearance in existing projects.

[dominiks]

I see. It should be handled similar to the FlatButton then, with the editor using a FlatMenuButton. Until then the documentation should mention that this button is flat by default, contrary to its name.

[Calinou]

@dominiks We don't need to add a FlatMenuButton node for this. We just need to modify the editor theme so the normal style is invisible in MenuButton.

Speaking of which, we should also remove ToolButton in the long run as it's identical to a Button set to to be flat. (We'll have to add some code to import existing projects without breaking.)
Edit: Done in #39690.

Also, the flat override is already documented in the MenuButton class reference: https://docs.godotengine.org/en/latest/classes/class_menubutton.html
See the O: true part in the list of properties. The O stands for "override"; this means it overrides the base class' default value.

[dominiks]

Oh right it's the ToolButton I meant and mistakenly called FlatButton. I agree with the idea that the ToolButton should be replaced in favor of setting the appearance via the editor theme.

Yes, you can find the information that the button is flat by default in the documentation but the behaviour of the MenuButton is very unexpected in comparison to the other buttons and the override mention might to be not enough - as this issue shows.

[TheSecondReal0]

I've tentatively opened PR #72418 to fix it, not sure if it's too late in the beta process for a change like this to make it in.

I'm not sure how to keep the current behavior of MenuButtons in the editor, editing the theme alone doesn't look like it'll work that well. Maybe the best way is by manually setting the correct MenuButtons to flat when they're instanced? If anyone can offer advice it'd be much appreciated!