bug#43086: [PATCH] Allow tags backend to not query for TAGS file

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 10 Sep 2024 02:32:46 +0300
> Cc: philipk@posteo.net, 43086@debbugs.gnu.org
> From: Dmitry Gutov <dgutov@yandex.ru>
> 
> >>> I don't understand why the obvious way of asking the user whether they
> >>> would like to generate the tags table is not the solution here.  What
> >>> did I miss?
> >>
> >> I don't know if it's obvious, given that the optimal scenario at the
> >> beginning of the report describes
> >>
> >>     ... allow the backend to never query a TAGS file
> > 
> > But what do you expect from a backend that depends on TAGS to do when
> > TAGS is not there?  You yourself just noticed the regression.  Why
> > would we want that?
> 
> I'm thinking of the xref-find-references case - where the scanner 
> doesn't depend on the tags table being available. Just the identifier 
> completion step.

Completion is also important, IMO.

> > AFAIU, the problem here is that the backend can avoid querying when
> > the TAGS file exists.  But what do you expect it to do when it does
> > _not_ exist? > We have the regeneration feature now, so I suggested to
> > ask the user whether to regenerate the file, after which it could be
> > read without any further prompts.
> 
> We have an existing way to enable etags-regen-mode. And it's a global 
> mode, so it's not just an issue of using it that one time - the naive 
> solution will make stay on until the end of the session.

We could in this particular case enable it once, then disable it after
regenerating TAGS.

> Also, if the tags file is not loaded, we're not quite sure whether the 
> user wants an auto-generated file, or an existing one.

The query should allow the user to tell us his/her preference, no?

> >> As it is, we already have a hint of the user preference from the fact
> >> that they have visited a TAGS file already (or not), or enabled
> >> etags-regen-mode (or not). It's not ironclad, but we could rely on these
> >> indicators to decide.
> > 
> > Then regenerate TAGS without asking, if you think it's reasonable.
> > But letting the backend continue without TAGS is not a reasonable
> > solution, IMO.
> 
> How do you feel about etags-regen-mode being on by default in some next 
> Emacs release? It shouldn't conflict with the manual invocations of 'M-x 
> visit-tags-file' - and of course if any cases come up we'll work on 
> fixing those.

As long as there's a way of turning it off, I don't think I will mind
too much.