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

[David Ponce]

On 31/08/2023 10:18, David Ponce wrote:
> On 31/08/2023 00:30, David Ponce wrote:
> > 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
>
> Please find attached a revised patch.  I used the name
> `faces-attribute' instead of `face-attribute-lookup' for consistency
> with `faces--attribute-at-point'.  I simplified this new function
> because `face-attributes-as-vector' always returns the symbol
> `unspecified' when an attribute is not specified (according to what I
> understand of the implementation in xfaces.c).  I also improved the
> doc string to include a link to the Elisp manual regarding the meaning
> of face specification.
>
> Here is an updated changelog:
>
>      * faces.el: Improve attribute lookup of face at point.
>      (face--attribute-index): New constant.
>      (faces-attribute): New function.
>      (faces--attribute-at-point): Use it.  Remove unused argument.
>      (foreground-color-at-point)
>      (background-color-at-point): Call accordingly.
>
>
>
> Regards

Sorry, my previous patch was buggy.  Here is the correct one.

faces-attribute-lookup-V3.patch
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