bug#52349: 29.0.50; vc-git and diff-mode: stage hunks

[Juri Linkov <juri@linkov.net>]

close 52349 29.0.50
thanks

>> The problem is that currently using 'C-c C-d' (log-edit-show-diff)
>> in the *vc-log* buffer doesn't show the same diff that will be really
>> committed when different files were marked in *vc-dir* parent buffer
>> before typing 'C-c C-c' in *vc-log*.
>> This is because currently log-edit-diff-function is set to vc-diff
>> that is not suitable here since it tries to deduce fileset again
>> from *vc-dir*, but files to commit are set in the buffer-local
>> 'vc-log-fileset' in *vc-log*.  So I added a new function
>> 'log-edit-diff-fileset' that shows the diff from 'vc-log-fileset'.
>> Using the same naming scheme, I renamed 'vc-diff-patch' to
>> 'log-edit-diff-patch'.
>> This shows the difference from the previous patch,
>> but later these changes could be committed separately:
>
> Makes perfect sense, thanks.

So now pushed and closed.  If more changes are needed,
this could be reopened or a new bug report opened.

> Honestly, I think it's a long-requested advanced feature which we'd be
> happy to have even if there were rough edges remaining (as long as it
> doesn't corrupt users' files or otherwise loses changes, of course). But
> this seems to be coming along nicely.

'vc-finish-logentry' has such FIXME:

  (let ((logbuf (current-buffer))
	(log-operation vc-log-operation)
        ;; FIXME: When coming from VC-Dir, we should check that the
        ;; set of selected files is still equal to vc-log-fileset,
        ;; to avoid surprises.
	(log-fileset vc-log-fileset)
    (pop-to-buffer vc-parent-buffer)

I tried to fix this, but it requires duplicating too much code
from vc-next-action, including code that prepares 'ready-for-commit'
list of files.  I'm afraid that such check often will raise 
a false alarm.

OTOH, maybe this check is not needed since I fixed 'C-c C-d' above
to show the same diff that will be committed using vc-log-fileset,
and 'C-c C-c' uses the same vc-log-fileset as well.