bug#68174: 30.0.50; Project and VC disagree about what repository we're in

[Dmitry Gutov]

Version: 30.1

On 02/01/2024 15:28, Eli Zaretskii wrote:
> > Date: Tue, 2 Jan 2024 15:10:53 +0200
> > Cc: 68174@debbugs.gnu.org, juri@linkov.net
> > From: Dmitry Gutov <dmitry@gutov.dev>
> >
> > On 02/01/2024 10:55, Sean Whitton wrote:
> > > > This particular case though seems fixed with this patch, please test:
> > > >
> > > > diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
> > > > index 3cd835a9d6b..82051740b8f 100644
> > > > --- a/lisp/vc/vc.el
> > > > +++ b/lisp/vc/vc.el
> > > > @@ -1074,6 +1074,7 @@ vc-expand-dirs
> > > >
> > > >    (defvar vc-dir-backend)
> > > >    (defvar log-view-vc-backend)
> > > > +(defvar log-view-vc-fileset)
> > > >    (defvar log-edit-vc-backend)
> > > >    (defvar diff-vc-backend)
> > > >    (defvar diff-vc-revisions)
> > > > @@ -1155,6 +1156,8 @@ vc-deduce-fileset
> > > >               (vc-state buffer-file-name)
> > > >               (vc-checkout-model backend buffer-file-name))
> > > >         (list backend (list buffer-file-name))))
> > > > +     ((derived-mode-p 'log-view-mode)
> > > > +      (list log-view-vc-backend log-view-vc-fileset))
> > > >         ((and (buffer-live-p vc-parent-buffer)
> > > >               ;; FIXME: Why this test?  --Stef
> > > >               (or (buffer-file-name vc-parent-buffer)
> > > Yup, that works, thanks!
> >
> > Very good.
> >
> > Eli, do you think we could add this to emacs-29 as well?
> >
> > It would help the users of 29.2 avoid the described bug when/if they
> > upgrade to the latest project.el. Probably not very urgent, but OTOH the
> > change looks pretty safe.
>
> If it's safe, you'd need to convince me.  Because just by looking at
> it, I don't have a clear idea what else it could affect.

It's not a trivial transformation, but it's semantically sound: 
log-view-mode saves -- or one might say caches -- the backend and the 
fileset in its own variables locally (referenced in the diff above). The 
commands in log-view.el (of which there are several) use those vars 
rather than look up vc-parent-buffer, so the values should be correct.

> And the use
> case is pretty rare, AFAICT.  So I tend to be happier with this on
> master.

Ok, I'll push it to master for now.