Re: buffer-face-set changes the fringe, is it a bug?

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 7 Jul 2020 17:47:55 +0200 (CEST)
> From: Gregory Heytings via "Emacs development discussions." <emacs-devel@gnu.org>
> 
> >  (set-face-attribute 'fringe nil :background "red")
> >  (let ((o (make-overlay 0 1)) (s "_"))
> >    (put-text-property 0 1 'display '(left-fringe question-mark) s)
> >    (overlay-put o 'after-string s)
> >    (set-face-foreground 'default "green"))
> >
> 
> Why did you change my code, which demonstrated the problem, into another 
> one which indeed does not show the problem?

Because I tried to explain something, in the text that you removed.

> Try this:
> 
> (set-face-attribute 'fringe nil :background "red" :foreground "blue")
> (let ((o (make-overlay 0 1)) (s "_"))
>    (put-text-property 0 1 'display '(left-fringe question-mark) s)
>    (overlay-put o 'after-string s))
> (progn (set-face-background 'default "yellow") (set-face-foreground 'default "red")) [1]
> (face-remap-add-relative 'default '(:background "yellow" :foreground "red")) [2]
> 
> After [1] the behavior is what I expect: red on yellow in the buffer, blue 
> on red in the fringe.

Certainly: since in this example the 'fringe' face defines both the
foreground and the background colors, none of the colors of the
'default' face show.

> After [2] the behavior is *not* what I expect anymore: red on yellow in 
> the buffer, red on yellow for the question mark in the fringe (the other 
> parts of the fringe remain red, and other bitmaps in the fringe, e.g. 
> curly arrows, remain blue on a red background).

Because now what you call 'default' is not the original 'default'
face, it's a new face created by face-remapping machinery.