bug#73911: Issue with `widget-specify-button'

[David Ponce via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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On 2024-12-31 12:34, Mauro Aranda wrote:
[...]
>  >> > > > Mauro, any comments?
>  >> > > >
>  >> > > >
>  >> > > >
> 
> I don't really know the effects that this change could have (whether
> good or bad).  The added invisible space comes from Bug#51550, which
> involved some discussions about the display engine itself.
> 
> I had trouble reproducing the bug itself, since I don't understand what
> the unexpected result is.
> 
> David, I'm sorry it took me so long to reply, but can you explain a bit
> more what's the unexpected result? Thank you.
> 

Hi Mauro,

I attached a screenshot of the result:

1. with the current version of `widget-specify-button' which clearly shows
    the unexpected appearance of the "OK" button when the button face has a
    :box attribute and the button prefix use a display space property.

2. with the patched version of `widget-specify-button' which shows the
    expected appearance of the same "OK" button.

It seems the problem is due to the invisible space inserted in front of the
button without specifying the face property, which causes a discontinuous
display of the button prefix when it uses a display space property.

I don't really know how to explain this better, sorry.

My proposed change just set the face of the invisible space to the button
face, which seems to fix the appearance of the button when the button
prefix has a display space text property.

I hope you will enjoy the new year.

Thank you for your help.

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