bug#58912: 29.0.50; set-face-attribute call in init.el has no lasting effect

[Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Matt Armstrong <matt@rfc20.org> writes:

> I see the same symptoms as Dmitry.  I'm running a current Debian Testing
> system, Gnome, Wayland.
>
> Namely:
>
> 1) emacs -Q --> the 'default font family is the Gnome system monospace font.
>
> 2) emacs -Q -l test.el --> still uses the Gnome system mono font despite
>    setting the 'default face otherwise early in init.
>
> I changed the .el file to this:
>
>     (set-face-attribute
>      'default nil :height 110 :weight 'semi-light :family
>      "Cascadia Mono")
>     (debug-on-entry #'set-face-attribute)
>
> And the origin of the font change back to the system defaults is this:
>
>     Debugger entered--entering a function:
>     * set-face-attribute(default #<frame *scratch* - GNU Emacs at naz 0x55ad505df290> :width normal :weight normal :slant normal :font "Go Mono 11")
>       font-setting-change-default-font(":0" nil)
>       dynamic-setting-handle-config-changed-event((config-changed-event font-render ":0"))
>       funcall-interactively(dynamic-setting-handle-config-changed-event (config-changed-event font-render ":0"))
>       call-interactively(dynamic-setting-handle-config-changed-event nil [(config-changed-event font-render ":0")])
>       command-execute(dynamic-setting-handle-config-changed-event nil [(config-changed-event font-render ":0")] t)
>
> It looks like `font-setting-change-default-font' is pulling the system
> font (in my case "Go Mono") from the frame, which probably wasn't
> modified by the earlier `set-face-attribute` call.  To confirm I changed
> test.el to this:
>
>     (set-face-attribute
>      'default nil :height 110 :weight 'semi-light :family
>      "Cascadia Mono")
>     (dolist (frame (frame-list))
>       (let ((frame-font
>              (or (font-get (face-attribute 'default :font frame 'default)
>                            :user-spec)
>                  (frame-parameter frame 'font-parameter))))
>         (message "frame %S frame-font %S" frame frame-font)))
>
> And re-run "emacs -Q -l test.el" and get this in *Messages*:
>
>     frame #<frame *scratch* - GNU Emacs at naz 0x55d8362ca7f0> frame-font "Go Mono 11"
>
> So I change test.el yet again to have only this:
>
>     (set-frame-font "Cascadia Mono")
>
> ...and that font change sticks.  `set-frame-font` is what is called by
> the Options -> Set Default Font menu item and has logic to walk through
> frames and set their parameters accordingly.
>
> And again to have only this:
>
>     (set-frame-font (font-spec :height 110
>                                :weight 'semi-light
>                                :family "Cascadia Mono"))
>
>
> ...I wonder if setting the 'default face attribute in 'early-init.el'
> would be enough, too.

Doesn't it only do that if font-use-system-font is t?  Here is the
relevant part of dynamic-setting.el:

	;; Just redraw the existing fonts on all frames:
	(dolist (f frame-list)
	  (let ((frame-font
		 (or (font-get (face-attribute 'default :font f 'default)
			       :user-spec) <=====

this should return "Cascadia Mono"... what does it return for you?