Sometimes scripts want (or need) the annotated tag name that exactly
matches a specific commit, or no tag at all. In such cases it can be
difficult to determine if the output of `git describe $commit` is a
real tag name or a tag+abbreviated commit. A common idiom is to run
git-describe twice:
if test $(git describe $commit) = $(git describe --abbrev=0 $commit)
...
but this is a huge waste of time if the caller is just going to pick a
different method to describe $commit or abort because it is not exactly
an annotated tag.
Setting the maximum number of candidates to 0 allows the caller to ask
for only a tag that directly points at the supplied commit, or to have
git-describe abort if no such item exists.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>