bug#69952: [PATCH] Support pdumping compiled queries by dumping their source

[Eli Zaretskii <eliz@gnu.org>]

> From: Yuan Fu <casouri@gmail.com>
> Date: Sun, 21 Apr 2024 16:41:54 -0700
> Cc: Daniel Colascione <dancol@dancol.org>,
>  serg.foo@gmail.com,
>  69952@debbugs.gnu.org
> 
> 
> 
> > On Apr 20, 2024, at 9:53 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> > 
> >> From: Yuan Fu <casouri@gmail.com>
> >> Date: Sat, 20 Apr 2024 15:50:36 -0700
> >> Cc: Daniel Colascione <dancol@dancol.org>,
> >> serg.foo@gmail.com,
> >> 69952@debbugs.gnu.org
> >> 
> >>>>> On Apr 13, 2024, at 12:41 AM, Eli Zaretskii <eliz@gnu.org> wrote:
> >>>>>> 
> >>>>>> And I have a question: what happens if the pdumper file dumped with
> >>>>>> tree-sitter available is loaded by an Emacs session in which
> >>>>>> tree-sitter is not available?  That can happen on Windows, for
> >>>>>> example, if the tree-sitter library or the grammar library required
> >>>>>> for recomputing the query is not available.  I think we need some code
> >>>>>> to prevent Emacs from crashing on startup in that case.
> >>>> 
> >>>> Yeah, being able to dump queries is certainly nice. There will be problems if the Emacs session that later loads the query either have a different grammar version loaded, or a difference grammar library for the same language, or outright doesn’t have tree-sitter like Eli mentioned. I don’t know if they are big enough problems to give up dumping queries, though.
> >>> 
> >>> Giving up: no.  But I think the code which loads the queries from the
> >>> pdumper file should be protected from crashing in those cases.  Can
> >>> you suggest how to do that?
> >> 
> >> Would Emacs crash? If the dump file just contains the query (which is a string), then Emacs would just compile the query with treesit-query-compile, it could fail (due to the reasons I mentioned), but shouldn’t crash Emacs.
> > 
> > Can Emacs compile a query if the tree-sitter shared library and/or the
> > grammar library is not available?
> 
> No. You need both tree-sitter library and the grammar library.

That's what I thought.  So starting Emacs in that case will attempt to
call a function from the tree-sitter library, and will segfault,
right?  If so, we should have some protection in the code in
pdumper.c that loads queries, which tests that tree-sitter is
availabale, and if not does something to prevent the segfault, like
not loading the query, perhaps?