bug#60841: 30.0.50; kill-ring-save pauses despite region being highlighted

[Gregory Heytings]

> > > But it would be better to have there a test which would tell us 
> > > whether the region face is "visually different" from the default face. 
> > > Can we do something like that?
> >
> > face-differs-from-default-p?
>
> Nice catch; IIUC display-supports-face-attributes-p is what is doing the 
> heavy work.
>
> Might need to be made smarter wrt :extend though?

Indeed...

> (set-face-background 'region (face-background 'default nil t))
> (face-differs-from-default-p 'region nil)
> ; ⇒ :extend

... although that's a really contrived example.

I'm not sure it's TRT to add too much complexity there, so I would suggest 
to add an additional optional argument to face-differs-from-default-p, to 
exclude one or more attributes from the comparison (in this case :extend, 
but someone else might be interested in excluding other attributes in the 
future).