bug#43464: 28.0.50; vc: Error calling vc-revert for repo root

[Dmitry Gutov]

On 07.10.2020 16:16, Andrii Kolomoiets wrote:
> Dmitry Gutov <dgutov@yandex.ru> writes:
>
> > On 05.10.2020 09:02, Andrii Kolomoiets wrote:
> > > Dmitry Gutov <dgutov@yandex.ru> writes:
> > >
> > > > Where is that vc-backend called from, in our scenario?
> > > It's called from 'vc-call'.  The 'vc-revert-file' used it twice
> > > to call the 'make-version-backups-p' and the 'revert' backend functions.
> >
> > Then a change in vc-revert-file could be sufficient.
>
> Can you please advice me what this change should look like?  Get rid of
> calling 'vc-call'?

Yes. How about the attached patch?

> In this case the function 'vc-version-backup-file'
> must be changed as well.

Does it actually make sense to use it on a directory?

> > > > Could we make do with changing that code to use vc-responsible-backend
> > > > instead of vc-backend instead? If it's not a function called
> > > > frequently.
> > > I went a little different way and made the 'vc-backend' return
> > > correct
> > > backend for directories.  In case you missed it somehow here is the link
> > > to the message:
> > > https://lists.gnu.org/archive/html/bug-gnu-emacs/2020-09/msg02508.html
> >
> > Like I explained, it will create a cache entry that is never invalidated.
>
> In what way VC backend for directory could be changed? Like 'rm -rf .hg
> && git init'?  We can make the 'vc-backend' function to ignore cached
> backend for directories.  Though I think it's not efficient.

Something like that. Or 'git init' inside a subdirectory. Not a frequent 
occurrence, but if we start using directories and files interchangeably 
in more places, we are likely to start caching other properties on them, 
too. So it's better to use a different function to detect which backend 
a directory belongs to.

Also, your patch makes vc-registered work on directories. What does it 
mean to have a directory "registered"? It's not a well-defined notion, 
given that most of contemporary VC systems don't track directories, only 
the files inside them.

vc-revert-dirs.diff
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