If your upstream is git, you don't have monotonically increasing
revision numbers, but (unordered) commit hashes. I usually use something
based on 'git describe' as that gives you a number of commits since a
reference tag in addition to a release.
E.g. git describe returns 0.56-24-gffe37cd which is
<tag>-<number_of_commits_since_tag>-g<shortened_hash_of_HEAD>
and I would version the snapshot as 0.56+git24-gffe37cd.