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

[Andrii Kolomoiets]

Dmitry Gutov <dgutov@yandex.ru> writes:

> On 17.09.2020 10:29, Andrii Kolomoiets wrote:
>> Debugger entered--Lisp error: (file-missing "Cannot open load file" "No such 
>> file or directory" "vc-nil")
>>    require(vc-nil)
>>    vc-find-backend-function(nil make-version-backups-p)
>>    vc-call-backend(nil make-version-backups-p "/private/tmp/gittest/")
>>    vc-version-backup-file("/private/tmp/gittest/")
>>    vc-revert-file("/private/tmp/gittest/")
>>    vc-revert()
>>    funcall-interactively(vc-revert)
>>    call-interactively(vc-revert nil nil)
>>    command-execute(vc-revert)
>> At least for `hg` and `git` backends.  Maybe because `vc-registered`
>> for
>> repo root is nil.
>
> I don't think we support vc-revrt on directories, repo root or not.

Calling `vc-git-revert` or `vc-hg-revert` directly with repo root or any
directory within repo works fine.