bug#53900: 29.0.50; pgtk: Gtk-CRITICAL warning with customized default face

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

Stephen Berman <stephen.berman@gmx.net> writes:

> 0. emacs -Q
> 1. Sanity check: evaluating the following sexp displays a non-GTK
>    tooltip and the shell emits no warning:
>    (let (use-system-tooltips)
>     (tooltip-show "Test"))
> 2. Evaluate this sexp:
>    (custom-set-faces '(default ((t (:background "lightblue")))))
> 3. Evaluate the sexp in step 1 again:
> => A non-GTK tooltip is displayed and the shell emit a warning:
>
> emacs-pgtk:12321): Gtk-CRITICAL **: 17:05:36.422: gtk_css_provider_load_from_data: assertion 'GTK_IS_CSS_PROVIDER (css_provider)' failed
>
> In my tests this happens only when customizing the `default' face
> (though admittedly I haven't tested all faces nor all face attributes).
> It also happens when step 2 is replaced by loading any built-in theme
> (all of which customize the `default' face).  (As a test I created a
> theme that does not customize the `default' face and with that theme did
> not get the warning.)
>
> My first pgtk-build that shows this warning is from commit
> dc5930ba973c9d921e9124b7afa1a65bba568b45.  My previous pgtk-build at
> commit 988d3d79bac0343dd2b1b89d1b15470edbb5e6ac does not show the
> warning with the above recipe.  Unfortunately, I don't have time now to
> do a git bisect to pinpoint the commit that causes the warning to be
> emitted.
>
> There is no warning if use-system-tooltips is non-nil.  And there is no
> warning with the above recipe in a non-PGTK GTK3 build.

Should be fixed now on master.  Thanks.