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

[David Ponce]

On 30/08/2023 21:22, Eli Zaretskii wrote:
> > Cc: 65632@debbugs.gnu.org
> > Date: Wed, 30 Aug 2023 21:35:11 +0300
> > From: Eli Zaretskii <eliz@gnu.org>
> >
> > > ;; 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.
>
> However, if we do want that, we already have the technology:
>
>    (face-attributes-as-vector (get-char-property (point) 'font-lock-face))
>
> This will return a vector of face attribute values, where you can find
> the value of any attribute you like.  For example, to get the
> foreground color, evaluate:
>
>    (aref 9
>      (face-attributes-as-vector (get-char-property (point) 'font-lock-face)))

Hi Eli,

Thank you very much for letting me know about `face-attributes-as-vector'
(maybe its doc string could be improved?).  It is exactly the function I need 
:-)

In case you are interested, I attached an updated patch to faces.el that use
this function to lookup face attribute, which improves and simplify  the
functions `faces--attribute-at-point', `foreground-color-at-point' and
`background-color-at-point'.

Regards

faces-attribute-lookup-V1.patch
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