RecentTag(ctx context.Context, rev, prefix string, allowed func(tag string) bool) (tag string, err error)

	// DescendsFrom reports whether rev or any of its ancestors has the given tag.
	//
	// DescendsFrom must return true for any tag returned by RecentTag for the
	// same revision.
	DescendsFrom(ctx context.Context, rev, tag string) (bool, error)
}

// An Origin describes the provenance of a given repo method result.

	return "", vcsErrorf("vcs %s: RecentTag: %w", r.cmd.vcs, errors.ErrUnsupported)
}

func (r *vcsRepo) DescendsFrom(ctx context.Context, rev, tag string) (bool, error) {
	unlock, err := r.mu.Lock()
	if err != nil {
		return false, err
	}
	defer unlock()

	return false, vcsErrorf("vcs %s: DescendsFrom: %w", r.cmd.vcs, errors.ErrUnsupported)
}

// r.modPath and encodes a base version and commit metadata that agrees with
// info.
//
// Note that verifying a nontrivial base version in particular may be somewhat
// expensive: in order to do so, r.code.DescendsFrom will need to fetch at least
// enough of the commit history to find a path between version and its base.
// Fortunately, many pseudo-versions — such as those for untagged repositories —
// have trivial bases!

	// unreachable for a reason).
	//
	// Try one last time in case some other goroutine fetched rev while we were
	// waiting on the lock.
	describe()
	return tag, err
}

func (r *gitRepo) DescendsFrom(ctx context.Context, rev, tag string) (bool, error) {
	// The "--is-ancestor" flag was added to "git merge-base" in version 1.8.0, so
	// this won't work with Git 1.7.1. According to golang.org/issue/28550, cmd/go