Re: Moving etc/NEWS around causing release branch merge to fail again

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Kangas <stefankangas@gmail.com>
> Date: Tue, 13 Dec 2022 21:32:41 -0800
> Cc: emacs-devel@gnu.org
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > What happened, exactly?  Please tell more about what you saw.
> 
> I saw the automatic merge fail with this error message:
> 
>     etc/NEWS has been modified

I looked at what gitmerge.el does for NEWS, and I admit that I'm
confused.  AFAIU, it does this:

  . use "git diff" to write the diffs for branch/NEWS to a patchfile
  . use "patch" to patch master/NEWS.29 using patchfile
  . delete patchfile
  . "git add master/NEWS.29"

So far so good, but then it also does this:

  . "git reset -- NEWS"
  . "git checkout NEWS"

Why does it do that?  AFAIU, these two commands _can_ produce changes
in master/NEWS.

> After a merge from the release branch (emacs-NN) to master, the etc/NEWS
> file should never be modified.  Only the etc/NEWS.NN file should have
> been modified.  Otherwise, it needs to be fixed manually.
> 
> See also these lines in admin/automerge:
> 
>     ## FIXME it would be better to trap this in gitmerge.
>     ## NEWS should never be modified, only eg NEWS.26.
>     git diff --stat --cached origin/master | grep -q "etc/NEWS " && \
>         die "etc/NEWS has been modified"

Right.