Some questions about git-name-rev

Hi, I am working on git support in Emacs.  This involves putting
version labels into the mode line and using them for specifying
revisions to diff.

40 digit commit numbers are not really fun for that.

So I need to use git-name-rev.  If I call it with the option --tags,
it might return an empty string.

If I don't call it with --tags, _and_ the commit number I feed into it
is the output of some git-rev-list, am I _guaranteed_ to become some
output?

Now is there a way to _abbreviate_ the output to the shortest _valid_
form, namely not have something like ref/remote/heads/branchname (or
similar) when branchname is sufficient?

-- 
David Kastrup