bug#67687: Feature request: automatic tags management

[Dmitry Gutov]

On 01/01/2024 19:39, Eli Zaretskii wrote:
> > Date: Mon, 1 Jan 2024 19:23:28 +0200
> > Cc: stefankangas@gmail.com, eskinjp@gmail.com, 67687@debbugs.gnu.org,
> >   michael.albinus@gmx.de
> > From: Dmitry Gutov <dmitry@gutov.dev>
> >
> > On 01/01/2024 18:50, Eli Zaretskii wrote:
> > > > +The exception is made when the user has already selected a tags
> > > > +table manually (for example, using \\[visit-tags-table]).  Then
> > > > +this mode doesn't do anything.  Reset the visited tags tables
> > > > +using \\[tags-reset-tags-tables]."
> > >
> > > The above is only true for the project whose TAGS was manually
> > > visited, right?  IOW, it's not that once the use invokes
> > > visit-tags-table once, this mode will be effectively disabled for the
> > > entire session, right?
> >
> > No, it's the latter. It's off for the whole session, just like a visited
> > TAGS file is active for the whole session (not limited to any specific
> > project).
>
> OK, then please tweak my suggested text to explain the situation
> correctly instead.

How about this?

If you select a tags table manually (for example, using
\\[visit-tags-table]), then this mode will be effectively
disabled for the entire session.  Use \\[tags-reset-tags-tables]
to countermand the effect of a previous \\[visit-tags-table].

> > a tags file, in general, can't always be attributed to a specific
> > project.
>
> That's too bad, IMO, but it's a separate issue.  One of the annoyances
> I had with tags was that it was difficult to have several independent
> tags tables loaded, each one for a different set of sources.  I hoped
> that project.el has solved this already, but I guess we are not there
> yet.

etags-regen-mode kind of solves that, by checking and resynchronizing 
tags tables when you switch between projects. That works when a tags 
file already exists with the recognized name in that other project (e.g. 
because you worked on it just recently).

Projectile has a different solution using local tags tables, which is 
easy to adapt to project.el:

(defun project-visit-tags ()
  (let* ((pr (project-current))
         (tags-file (and pr
                         (expand-file-name "TAGS" (project-root pr)))))
    (and tags-file
         (file-exists-p tags-file)
         (visit-tags-table tags-file t))))

(add-hook 'find-file-hook #'project-visit-tags)

And if you limit the above to only certain projects (by e.g. checking 
for some additional file in the directory), then etags-regen-mode should 
stay active in the other projects, because it won't see the buffer-local 
bindings for tags-file-name and tags-table-list (the above snippet keeps 
the global value nil).

The buffer-local tag tables are not that well-tested overall (e.g. even 
tags-reset-tags-tables resets the local binding, if available, rather 
than the global one), but this combination should work in a personal config.