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

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From: David Ponce <da_vid <at> orange.fr>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 65632 <at> debbugs.gnu.org
Subject: bug#65632: 30.0.50; Proposal to improve `faces--attribute-at-point'.
Date: Thu, 31 Aug 2023 14:08:04 +0200

[Message part 1 (text/plain, inline)]

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 <at> debbugs.gnu.org
>>>> Date: Wed, 30 Aug 2023 21:35:11 +0300
>>>> From: Eli Zaretskii <eliz <at> 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 (text/x-patch, attachment)]

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