queue = append(queue, r)
				enqueued[r] = true
			}
		}
	}
}

// FindPath reports a shortest requirement path starting at one of the roots of
// the graph and ending at a module version m for which f(m) returns true, or
// nil if no such path exists.
func (g *Graph) FindPath(f func(module.Version) bool) []module.Version {
	// firstRequires[a] = b means that in a breadth-first traversal of the