bug#50798: 28.0.50; Tab line close button is off-center until it is highlighted with the mouse

[Juri Linkov]

>> It's possible to put properties on the close button only, but wouldn't this 
>> be
>> too ugly?  This means that hovering the mouse over the tab name will 
>> highlight only
>> the tab name without highlighting the close button.  And hovering the mouse
>> over the close button will highlight only the close button without 
>> highlighting
>> the tab name.
>
> How did you intend this to look?  You said previously:
>
>> 'tab-line-close-highlight' was supposed to be applied to the close button
>> to emulate how the close button behaves on the tab bar where hovering mouse
>> over the button displays it with the face style 'released-button'.
>> 
>> But mouse-face of the face 'tab-line-highlight' overrides the mouse-face
>> 'tab-line-close-highlight' in 'tab-line-tab-name-format-default'
>> that applies 'propertize' with 'mouse-face tab-line-highlight'.
>
> If what you intended was not to highlight the close button
> differently, then what was the intent?

The intent for the close button was to look exactly like
the close button on the tab-bar.  Well, almost.  Because
while the close button hovering looks nice on the tab-bar,
it has another problem that hovering its tab doesn't highlight it
like mouse-face highlights the tab on the tab-line.

So both the tab-bar and the tab-line are still not perfect.

>> So highlighting will be separate for the close button and
>> the rest of the tab with such patch:
>
> Does this solve the problem with vertical movement of the button?

It solves the problem because tab-line-close-highlight doesn't inherit
from other faces.  It's face inheritance that caused the problem
with vertical movement of the button.