Re: VC mode and git

[Eli Zaretskii <eliz@gnu.org>]

> From: "Stephen J. Turnbull" <stephen@xemacs.org>
> Cc: sorganov@gmail.com,
>     emacs-devel@gnu.org
> Date: Sun, 05 Apr 2015 17:31:53 +0900
> 
>  >     I committed some changes using C-x v v in vc-dir.
>  >     Something went wrong with lisp/ChangeLog.
>  > 
>  >     It appears that my change log entries went into an old version of that
>  >     file; I don't know why this happened, since I wrote them today after
>  >     doing 'git pull'.
> 
> OK, so I interpreted this as
> 
> 1. Hack the "some changes" mentioned above.
> 2. Git pull successfully, implying the files changed in Richard's
>    workspace but (I assume) not committed did not conflict.
> 3. Edit ChangeLog and C-x v v to commit, successfully.
> 
>    But some log messages were missing.

Which ones?  I'm afraid I'm not following you in this part.

>  >     After this, I did 'git pull' again, and it said there was a merge
>  >     conflict in lisp/ChangeLpg.  A lot of text appears to be missing from
>  >     the file.  It said, "fix conflicts and then commit the result."
> 
> If the previous pull succeeded, does this mean that he lost a race in
> a handful of minutes?  And lost "a lot" of text?  Weird.

One possibility is a merge from emacs-24, which can potentially bring
quite a few commits from the release branch, and is done by a program,
so it can be very fast.  Look at the long list of the modified files
that are staged, which the pull succeeded to merge -- they do suggest
a lot of changes were fetched.

>  > The second error message, viz.:
>  > 
>  >   fatal: cannot do a partial commit during a merge.
>  > 
>  > is because "C-x v v" invokes "git commit --only lisp/ChangeLog", which
>  > AFAIR always fails in this situation, for the reason hinted by the
>  > error message.
> 
> Aha!  But "git commit --include lisp/ChangeLog" DTRTs in this case,
> committing the staged changes from the files successfully merged as
> well as the new changes from the files where conflicts were resolved.
> (Tested in a toy repo.)
> 
> In other words, *Emacs* screwed Richard, not git.

Yes, basically.  More accurately, too rudimentary support in VC for
Git and the "popular" problems that need to be resolved with it.

>  > Yes, something like that.  In fact, I think the root cause of the
>  > original problem was that "C-x v v", which tried to commit a single
>  > file in the middle of a merge.  Instead, the correct action is either
>  > 'v' from vc-dir or "git commit" from the shell prompt.
> 
> I don't think "git commit" will actually work.  "git commit" alone
> will either commit only the unconflicted staged files (I think this
> unlikely) or will refuse to commit because it remembers that ChangeLog
> was conflicted (more likely).  You need to "git add lisp/ChangeLog",

Saving a file after resolving all of its conflicts automatically runs
"git add" for that file in Emacs's VC, so it is already staged.

So yes, "git commit" should have worked.