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

[Yuan Fu]

> On Apr 21, 2024, at 10:47 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> 
>> 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?

Right, it can use Ftreesit_available_p (we can define a C equivalent if pdumper 
can’t call lisp), and decide whether to compile the query or just keep the 
query as a string, or signal an error?

Yuan