bug#60841: 30.0.50; kill-ring-save pauses despite region being highlighted

[Eli Zaretskii <eliz@gnu.org>]

> Cc: gregory@heytings.org, 60841@debbugs.gnu.org, kevin.legouguec@gmail.com
> Date: Sun, 29 Jan 2023 21:09:18 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> 
> > > 2. (face-differs-from-default-p list-matching-lines-prefix-face)
> > >    ↦ :stipple
> > 
> > I still don't understand why (face-differs-from-default-p 'default)
> > should return :stipple even in a clean state after emacs -Q.
> > This means that the default face always differs from itself?
> 
> Because face-differs-from-default-p thinks attributes are unset only
> if their value is 'unspecified'.  We should fix that so the function
> knows about nil as well.

I think face-differs-from-default-p should look like this:

(defun face-differs-from-default-p (face &optional frame)
  "Return non-nil if FACE displays differently from the default face.
If the optional argument FRAME is given, report on face FACE in that frame.
If FRAME is t, report on the defaults for face FACE (for new frames).
If FRAME is omitted or nil, use the selected frame."
  (let ((attrs
	 (delq :inherit (delq :extend (mapcar 'car face-attribute-name-alist))))
	(differs nil))
    (while (and attrs (not differs))
      (let* ((attr (pop attrs))
	     (attr-val (face-attribute face attr frame t)))
	(when (and
	       (not (eq attr-val 'unspecified))
	       (not (equal attr-val (face-attribute 'default attr frame)))
	       (display-supports-face-attributes-p (list attr attr-val)
						   frame))
	  (setq differs attr))))
    differs))