bug#2982: 23.0.92; `vc-diff' behaves inconsistently with git

[Stefan Monnier]

>> So when you open the file, Emacs asks `git' the status of the file and
>> so knows that this modtime corresponds to "up-to-date".  After `touch',
>> OTOH, Emacs isn't so sure any more, so it runs `git diff'
> OK, external modtime changes may be harder to handle than an Emacs use
> case: Say you resume working on a file with uncommitted changes, and you
> first do vc-diff and decide to throw them away. Then in the *vc-diff*
> buffer, you do C-u C-c C-a until all chunks are reverted, then save the
> file and see if really all changes are gone with C-x v =. At this point
> the *vc-diff* buffer is shown unexpectedly without remaining changes.

Yup: Emacs has no idea that the buffer-modifications you've performed
ended up undoing all the changes.  Figuring this out would be
a major challenge.  In the case of git, it would be easier to ask git
the status of the file.


        Stefan