implement the graph traits for SCC

src/librustc_data_structures/graph/scc/mod.rs

@@ -4,7 +4,7 @@
 //! O(n) time.
 
 use crate::fx::FxHashSet;
-use crate::graph::{DirectedGraph, WithNumNodes, WithSuccessors};
+use crate::graph::{DirectedGraph, WithNumNodes, WithSuccessors, GraphSuccessors};
 use crate::indexed_vec::{Idx, IndexVec};
 use std::ops::Range;
 
@@ -60,6 +60,31 @@ impl<N: Idx, S: Idx> Sccs<N, S> {
     }
 }
 
+impl<N: Idx, S: Idx> DirectedGraph for Sccs<N, S> {
+    type Node = S;
+}
+
+impl<N: Idx, S: Idx> WithNumNodes for Sccs<N, S> {
+    fn num_nodes(&self) -> usize {
+        self.num_sccs()
+    }
+}
+
+impl<N: Idx, S: Idx> GraphSuccessors<'graph> for Sccs<N, S> {
+    type Item = S;
+
+    type Iter = std::iter::Cloned<std::slice::Iter<'graph, S>>;
+}
+
+impl<N: Idx, S: Idx> WithSuccessors for Sccs<N, S> {
+    fn successors<'graph>(
+        &'graph self,
+        node: S
+    ) -> <Self as GraphSuccessors<'graph>>::Iter {
+        self.successors(node).iter().cloned()
+    }
+}
+
 impl<S: Idx> SccData<S> {
     /// Number of SCCs,
     fn len(&self) -> usize {