func (g *Graph) FindPath(f func(module.Version) bool) []module.Version {
	// firstRequires[a] = b means that in a breadth-first traversal of the
	// requirement graph, the module version a was first required by b.
	firstRequires := make(map[module.Version]module.Version)

	queue := g.roots
	for _, m := range g.roots {
		firstRequires[m] = module.Version{}
	}

	for len(queue) > 0 {
		m := queue[0]