bug#51715: defface forms not having dynamic value

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 09 Nov 2021 14:17:03 +0000
> From: irenezerafa <irenezerafa@protonmail.com>
> Cc: 51715@debbugs.gnu.org
> >
> > Please tell more. Which face attributes did you want to make dynamic,
> > and how?
> 
> I take rainbow-delimiters as example.  Specifically, the
> 
> (eval-when-compile
>   (defmacro rainbow-delimiters--define-depth-faces ()
>     (let ( (faces '())
>            (dark-colors  [ "#ff62d4"  "#3fdfd0"  "#fba849"  "#9f80ff"
>             "#4fe42f"  "#fe6060"  "#4fafff"  "#f0dd60" "#ffffff" ])
> 	   (light-colors [ "#a8007f"  "#005f88"  "#904200"  "#7f10d0"
>             "#006800"  "#b60000"  "#1f1fce"  "#605b00" "#000000"]) )
>       (dotimes (i 9)
>         (push `( defface ,(intern (format "rainbow-delimiters-depth-%d-face" (1+ i)))
> 		 '( (default (:inherit rainbow-delimiters-base-face))
>                     ( ((class color) (background dark))
> 		      :foreground ,(aref dark-colors  i))
> 		    ( ((class color) (background light))
> 		      :foreground ,(aref light-colors i)) )
>                  ,(format "Nested delimiter face, depth %d." (1+ i))
>                  :group 'rainbow-delimiters-faces )
> 	      faces))
>       `(progn ,@faces)) ))
> 
> (rainbow-delimiters--define-depth-faces)
> 
> Now, suppose I want to use a colour scheme from modus-themes.
> 
> (require 'modus-themes)
> 
> (eval-when-compile
>   (defmacro rainbow-delimiters--define-depth-faces ()
>     (let ( (faces '())
>            (dark-colors (rainbow-delimiters-modus-vivendi-intense-colours
> 			 (list magenta-intense cyan-intense orange-intense
> 			       purple-intense green-intense red-intense
> 			       blue-intense yellow-intense fg-main)))
>            (light-colors (rainbow-delimiters-modus-operandi-intense-colours
>                           (list magenta-intense cyan-intense orange-intense
> 				purple-intense green-intense red-intense
> 				blue-intense yellow-intense fg-main))) )
>       (dotimes (i 9)
> 	(push `(defface ,(intern (format "rainbow-delimiters-depth-%d-face" (1+ i)))
> 		 '( (default (:inherit rainbow-delimiters-base-face))
>                     ( ((class color) (background light))
> 		      :foreground ,(nth i light-colors))
>                     ( ((class color) (background dark))
> 		      :foreground ,(nth i dark-colors)) )
> 		 ,(format "Nested delimiter face, depth %d." (1+ i))
> 		 :group 'rainbow-delimiters-faces)
>               faces))
>       `(progn ,@faces)) ))
> 
> This would not be workable in practice.  Because the dependency only
> matters when your macro is being evaluated and the faces are reified.
> Since you have a package, that will be the moment the package gets
> required. So you are making it a dependency for everyone.

I'm still not sure I get this.  You want to be able to control the
colors of a face indirectly, by changing some variable which the face
references?  If not, what do you mean by "the dependency"?

IOW, what is it that you want to be able to do that isn't possible by
calling set-face-attribute?