bug#65632: 30.0.50; Proposal to improve `faces--attribute-at-point'.

[Eli Zaretskii]

> Date: Wed, 30 Aug 2023 20:04:49 +0200
> From: David Ponce <da_vid@orange.fr>
> 
> I noticed that the functions `foreground-color-at-point' and
> `background-color-at-point' don't return expected values when the face
> at point includes anonymous face or is a nested list of face, for
> example.
> 
> Here is a simple recipe that demonstrates the issue (emacs -Q):
> 
> In scratch buffer eval:
> -----------------------
> 
> ;; Display "TEST" in red, bold, italic on yellow background.
> (insert
>   (propertize
>    "TEST" 'font-lock-face
>    '(bold ((:background "yellow") "italic"
>            ((foreground-color . "red") underline)))))

This is not a valid face, AFAIU.  That it works is sheer luck (because
Emacs is very lenient with this stuff).  The correct face definition
for what you want is this (see 'set-face-attribute's doc string):

  (insert
    (propertize
     "TEST" 'font-lock-face
     '(:weight bold :background "yellow" :slant italic
             :foreground "red" :underline t)))

If you use the above, foreground-color-at-point etc. will work as
expected.

I'm not sure we want to go out of our way to support the kind of face
specifications that you used.