bug#72733: 29.4; Warning message while attempting to view customization buffer

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Kangas <stefankangas@gmail.com>
> Date: Mon, 30 Sep 2024 00:12:12 -0700
> Cc: 72733@debbugs.gnu.org
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> From: tpeplt <tpeplt@gmail.com>
> >> Date: Tue, 20 Aug 2024 10:19:05 -0400
> >>
> >> Emacs Maintainers,
> >>
> >>    Emacs 29.4 appears to be running some (uninitialized?) code when a
> >> sequence of sub-menus is selected.  This results in a warning message
> >> about something that an Emacs user has not selected.  Here is a recipe
> >> for reproducing the problem.  I have run this several times and gotten
> >> the same result each time.
> >>
> >> 1. $ emacs -Q
> >>
> >> 2. M-x customize RET
> >>
> >> 3. The *Customize Group: Emacs* buffer is displayed.  In this buffer,
> >>    select "Programming" from the menu of the Emacs group.
> >>
> >> 4. The *Customize Group: Programming* buffer is displayed.  In this
> >>    buffer, select "Languages" from the menu.
> >>
> >> 5. A *Warnings* buffer is displayed in a new window.  The following
> >>    warning message is displayed in that buffer:
> >>
> >> ⛔ Warning (treesit): Cannot activate tree-sitter, because language grammar for ruby is unavailable (not-found): (libtree-sitter-ruby libtree-sitter-ruby.0 libtree-sitter-ruby.0.0 libtree-sitter-ruby.so libtree-sitter-ruby.so.0 libtree-sitter-ruby.so.0.0) No such file or directory
> >
> > It's a known issue for which there's no simple solution.  We want
> > users who load ruby-ts-mode to know that they lack the Ruby grammar
> > library, which is what this warning is about.  And Customize loads
> > ruby-ts-mode to allow its customization when you select Languages.
> >
> > We could perhaps shut up these specific warnings in that specific
> > situation, but that doesn't seem clean.  And the warning is just a
> > warning, and harmless.
> 
> Showing the warning doesn't seem very clean either.

Indeed.  But all the other solutions were either much more complex or
concealed the warning in important cases.