def resolve_revision(cls, dest, url, rev_options):
        # type: (str, HiddenText, RevOptions) -> RevOptions
        """
        Resolve a revision to a new RevOptions object with the SHA1 of the
        branch, tag, or ref if found.

        Args:
          rev_options: a RevOptions object.
        """
        rev = rev_options.arg_rev
        # The arg_rev property's implementation for Git ensures that the
        # rev return value is always non-None.
        assert rev is not None

        sha, is_branch = cls.get_revision_sha(dest, rev)

        if sha is not None:
            rev_options = rev_options.make_new(sha)
            rev_options.branch_name = rev if is_branch else None

            return rev_options

        # Do not show a warning for the common case of something that has
        # the form of a Git commit hash.
        if not looks_like_hash(rev):
            logger.warning(
                "Did not find branch or tag '%s', assuming revision or ref.",
                rev,
            )

        if not cls._should_fetch(dest, rev):
            return rev_options

        # fetch the requested revision
        cls.run_command(
            make_command('fetch', '-q', url, rev_options.to_args()),
            cwd=dest,
        )
        # Change the revision to the SHA of the ref we fetched
        sha = cls.get_revision(dest, rev='FETCH_HEAD')
        rev_options = rev_options.make_new(sha)

        return rev_options