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

[Dmitry Gutov]

On 24.09.2020 10:15, Andrii Kolomoiets wrote:

> > On 18.09.2020 18:45, Andrii Kolomoiets wrote:
> > > BTW vc-revert is also works fine in Git repo when point is on
> > > subdirectory.  So for the vc-git only reverting repo root is not
> > > working.
> >
> > That's an interesting observation.
>
> And the most interest part of that observation is that I can't reproduce
> it :)

Oh well. :-)

> > > Please see attached patch which make it possible for vc-hg to revert
> > > directory.
> >
> > Could you explain both changes in that patch?
>
> The idea is to make the 'vc-backend' function to return backend for
> directory.  'vc-backend' function uses the 'vc-registered' function.
> The change for vc-hg.el makes 'vc-hg-registered' return t for directory.
> The change to vc.el makes the 'vc-register' function called on directory
> to not error with "already registered" message.

Thanks.

Where is that vc-backend called from, in our scenario?

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'm not 100% sure about the original design, but vc-responsible-backend 
*does* work on directories.

Its downside is it doesn't cache the result to VC properties (hence it 
would be unwise to use it everywhere). But it's also an upside, because 
said properties are invalidated in a few strategic places like 
find-file-hook, and that never happens for directories (hence that cache 
will tend to get out of date, sooner or later).

> > And also: how does it change, or not change, the behavior of vc-revert
> > in backends that are not Git or Hg?
>
> Looks like everybody is ready for reverting dirs.
>
> bzr, mtn, svn - Should be fine reverting directory
> dav - do nothing on vc-revert
> rcs - reverting directory is added in c22b0a7da32360e34f6f0ff86a886c9028b3d863
> sccs - reverting directory is added in e7290559824406d111d306069b36dde8ced847f9
> src - reverting directory is supported initially 
> 1e81f6769013e1a0df9e10d7c5d0a3e3ca131143
> cvs - passing directory to 'unedit' command should be fine

Very good.