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

[Eli Zaretskii <eliz@gnu.org>]

> 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.