bug#45920: 28.0.50; set-face-attribute cannot read :family when different :weight exist

[Protesilaos Stavrou <info@protesilaos.com>]

On 2021-01-16, 22:25 +0200, Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Protesilaos Stavrou <info@protesilaos.com>
>> Date: Sat, 16 Jan 2021 22:09:54 +0200
>> 
>>    ;; Sample 1
>>    (set-face-attribute 'default nil
>>                        :family "Source Code Pro"
>>                        :weight 'light)
>> 
>>    ;; Sample 2
>>    (set-face-attribute 'default nil
>>                        :family "Hack"
>>                        :weight 'normal)
>> 
>> If you evaluate sample 1, you will get the desired behaviour.  Namely,
>> the font family for the default face is the one specified, as is the
>> typographic weight.
>> 
>> Now if you proceed to evaluate sample 2, you will notice that only the
>> weight gets updated.  The family continues to be that of sample 1.
>> 
>> At this point, to get the family of sample 2, you need to evaluate
>> sample 2 one more time.
>> 
>> I tried various combinations and my impression is that the problem
>> occurs when the :weight properties are different.  Other properties,
>> such as :height, do not exhibit this behaviour.
>
> I didn't try to reproduce, because I don't have one of these fonts.
> However, it might be relevant that when you call set-face-attribute
> with several attributes related to the face's font, the underlying
> primitive, internal-set-lisp-face-attribute, is called multiple time,
> one time for every attribute.  So the order of those calls might
> matter, especially if one of the fonts doesn't support some of the
> values of all the attributes (e.g., the 'normal' weight in this case).

Thank you Eli for the prompt reply!

Following your input, I tried alternating between those two and they
both give me the right results:

   (progn
     (internal-set-lisp-face-attribute 'default :family "Source Code Pro" 0)
     (internal-set-lisp-face-attribute 'default :weight 'light 0))
   
   (progn
     (internal-set-lisp-face-attribute 'default :weight 'normal 0)
     (internal-set-lisp-face-attribute 'default :family "Hack" 0))

Please feel free to close this.

-- 
Protesilaos Stavrou
protesilaos.com