Merge {With,Graph}{Successors,Predecessors} into {Successors,Predecessors}

Now with GAT!

compiler/rustc_data_structures/src/graph/iterate/mod.rs

@@ -1,4 +1,4 @@
-use super::{DirectedGraph, WithStartNode, WithSuccessors};
+use super::{DirectedGraph, Successors, WithStartNode};
 use rustc_index::bit_set::BitSet;
 use rustc_index::{IndexSlice, IndexVec};
 use std::ops::ControlFlow;
@@ -6,14 +6,14 @@ use std::ops::ControlFlow;
 #[cfg(test)]
 mod tests;
 
-pub fn post_order_from<G: DirectedGraph + WithSuccessors>(
+pub fn post_order_from<G: DirectedGraph + Successors>(
     graph: &G,
     start_node: G::Node,
 ) -> Vec<G::Node> {
     post_order_from_to(graph, start_node, None)
 }
 
-pub fn post_order_from_to<G: DirectedGraph + WithSuccessors>(
+pub fn post_order_from_to<G: DirectedGraph + Successors>(
     graph: &G,
     start_node: G::Node,
     end_node: Option<G::Node>,
@@ -27,7 +27,7 @@ pub fn post_order_from_to<G: DirectedGraph + WithSuccessors>(
     result
 }
 
-fn post_order_walk<G: DirectedGraph + WithSuccessors>(
+fn post_order_walk<G: DirectedGraph + Successors>(
     graph: &G,
     node: G::Node,
     result: &mut Vec<G::Node>,
@@ -60,7 +60,7 @@ fn post_order_walk<G: DirectedGraph + WithSuccessors>(
     }
 }
 
-pub fn reverse_post_order<G: DirectedGraph + WithSuccessors>(
+pub fn reverse_post_order<G: DirectedGraph + Successors>(
     graph: &G,
     start_node: G::Node,
 ) -> Vec<G::Node> {
@@ -72,7 +72,7 @@ pub fn reverse_post_order<G: DirectedGraph + WithSuccessors>(
 /// A "depth-first search" iterator for a directed graph.
 pub struct DepthFirstSearch<'graph, G>
 where
-    G: ?Sized + DirectedGraph + WithSuccessors,
+    G: ?Sized + DirectedGraph + Successors,
 {
     graph: &'graph G,
     stack: Vec<G::Node>,
@@ -81,7 +81,7 @@ where
 
 impl<'graph, G> DepthFirstSearch<'graph, G>
 where
-    G: ?Sized + DirectedGraph + WithSuccessors,
+    G: ?Sized + DirectedGraph + Successors,
 {
     pub fn new(graph: &'graph G) -> Self {
         Self { graph, stack: vec![], visited: BitSet::new_empty(graph.num_nodes()) }
@@ -127,7 +127,7 @@ where
 
 impl<G> std::fmt::Debug for DepthFirstSearch<'_, G>
 where
-    G: ?Sized + DirectedGraph + WithSuccessors,
+    G: ?Sized + DirectedGraph + Successors,
 {
     fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         let mut f = fmt.debug_set();
@@ -140,7 +140,7 @@ where
 
 impl<G> Iterator for DepthFirstSearch<'_, G>
 where
-    G: ?Sized + DirectedGraph + WithSuccessors,
+    G: ?Sized + DirectedGraph + Successors,
 {
     type Item = G::Node;
 
@@ -201,7 +201,7 @@ struct Event<N> {
 /// [CLR]: https://en.wikipedia.org/wiki/Introduction_to_Algorithms
 pub struct TriColorDepthFirstSearch<'graph, G>
 where
-    G: ?Sized + DirectedGraph + WithSuccessors,
+    G: ?Sized + DirectedGraph + Successors,
 {
     graph: &'graph G,
     stack: Vec<Event<G::Node>>,
@@ -211,7 +211,7 @@ where
 
 impl<'graph, G> TriColorDepthFirstSearch<'graph, G>
 where
-    G: ?Sized + DirectedGraph + WithSuccessors,
+    G: ?Sized + DirectedGraph + Successors,
 {
     pub fn new(graph: &'graph G) -> Self {
         TriColorDepthFirstSearch {
@@ -278,7 +278,7 @@ where
 
 impl<G> TriColorDepthFirstSearch<'_, G>
 where
-    G: ?Sized + DirectedGraph + WithSuccessors + WithStartNode,
+    G: ?Sized + DirectedGraph + Successors + WithStartNode,
 {
     /// Performs a depth-first search, starting from `G::start_node()`.
     ///

compiler/rustc_data_structures/src/graph/mod.rs

@@ -20,55 +20,40 @@ pub trait WithNumEdges: DirectedGraph {
     fn num_edges(&self) -> usize;
 }
 
-pub trait WithSuccessors: DirectedGraph
-where
-    Self: for<'graph> GraphSuccessors<'graph, Item = <Self as DirectedGraph>::Node>,
-{
-    fn successors(&self, node: Self::Node) -> <Self as GraphSuccessors<'_>>::Iter;
+pub trait Successors: DirectedGraph {
+    type Successors<'g>: Iterator<Item = Self::Node>
+    where
+        Self: 'g;
+
+    fn successors(&self, node: Self::Node) -> Self::Successors<'_>;
 
     fn depth_first_search(&self, from: Self::Node) -> iterate::DepthFirstSearch<'_, Self> {
         iterate::DepthFirstSearch::new(self).with_start_node(from)
     }
 }
 
-#[allow(unused_lifetimes)]
-pub trait GraphSuccessors<'graph> {
-    type Item;
-    type Iter: Iterator<Item = Self::Item>;
-}
+pub trait Predecessors: DirectedGraph {
+    type Predecessors<'g>: Iterator<Item = Self::Node>
+    where
+        Self: 'g;
 
-pub trait WithPredecessors: DirectedGraph
-where
-    Self: for<'graph> GraphPredecessors<'graph, Item = <Self as DirectedGraph>::Node>,
-{
-    fn predecessors(&self, node: Self::Node) -> <Self as GraphPredecessors<'_>>::Iter;
-}
-
-#[allow(unused_lifetimes)]
-pub trait GraphPredecessors<'graph> {
-    type Item;
-    type Iter: Iterator<Item = Self::Item>;
+    fn predecessors(&self, node: Self::Node) -> Self::Predecessors<'_>;
 }
 
 pub trait WithStartNode: DirectedGraph {
     fn start_node(&self) -> Self::Node;
 }
 
-pub trait ControlFlowGraph:
-    DirectedGraph + WithStartNode + WithPredecessors + WithSuccessors
-{
+pub trait ControlFlowGraph: DirectedGraph + WithStartNode + Predecessors + Successors {
     // convenient trait
 }
 
-impl<T> ControlFlowGraph for T where
-    T: DirectedGraph + WithStartNode + WithPredecessors + WithSuccessors
-{
-}
+impl<T> ControlFlowGraph for T where T: DirectedGraph + WithStartNode + Predecessors + Successors {}
 
 /// Returns `true` if the graph has a cycle that is reachable from the start node.
 pub fn is_cyclic<G>(graph: &G) -> bool
 where
-    G: ?Sized + DirectedGraph + WithStartNode + WithSuccessors,
+    G: ?Sized + DirectedGraph + WithStartNode + Successors,
 {
     iterate::TriColorDepthFirstSearch::new(graph)
         .run_from_start(&mut iterate::CycleDetector)

compiler/rustc_data_structures/src/graph/reference.rs

@@ -14,24 +14,18 @@ impl<'graph, G: WithStartNode> WithStartNode for &'graph G {
     }
 }
 
-impl<'graph, G: WithSuccessors> WithSuccessors for &'graph G {
-    fn successors(&self, node: Self::Node) -> <Self as GraphSuccessors<'_>>::Iter {
+impl<'graph, G: Successors> Successors for &'graph G {
+    type Successors<'g> = G::Successors<'g> where 'graph: 'g;
+
+    fn successors(&self, node: Self::Node) -> Self::Successors<'_> {
         (**self).successors(node)
     }
 }
 
-impl<'graph, G: WithPredecessors> WithPredecessors for &'graph G {
-    fn predecessors(&self, node: Self::Node) -> <Self as GraphPredecessors<'_>>::Iter {
+impl<'graph, G: Predecessors> Predecessors for &'graph G {
+    type Predecessors<'g> = G::Predecessors<'g> where 'graph: 'g;
+
+    fn predecessors(&self, node: Self::Node) -> Self::Predecessors<'_> {
         (**self).predecessors(node)
     }
 }
-
-impl<'iter, 'graph, G: WithPredecessors> GraphPredecessors<'iter> for &'graph G {
-    type Item = G::Node;
-    type Iter = <G as GraphPredecessors<'iter>>::Iter;
-}
-
-impl<'iter, 'graph, G: WithSuccessors> GraphSuccessors<'iter> for &'graph G {
-    type Item = G::Node;
-    type Iter = <G as GraphSuccessors<'iter>>::Iter;
-}

compiler/rustc_data_structures/src/graph/scc/mod.rs

@@ -7,7 +7,7 @@
 
 use crate::fx::FxHashSet;
 use crate::graph::vec_graph::VecGraph;
-use crate::graph::{DirectedGraph, GraphSuccessors, WithNumEdges, WithSuccessors};
+use crate::graph::{DirectedGraph, Successors, WithNumEdges};
 use rustc_index::{Idx, IndexSlice, IndexVec};
 use std::ops::Range;
 
@@ -39,7 +39,7 @@ pub struct SccData<S: Idx> {
 }
 
 impl<N: Idx, S: Idx + Ord> Sccs<N, S> {
-    pub fn new(graph: &(impl DirectedGraph<Node = N> + WithSuccessors)) -> Self {
+    pub fn new(graph: &(impl DirectedGraph<Node = N> + Successors)) -> Self {
         SccsConstruction::construct(graph)
     }
 
@@ -103,14 +103,10 @@ impl<N: Idx, S: Idx + Ord> WithNumEdges for Sccs<N, S> {
     }
 }
 
-impl<'graph, N: Idx, S: Idx> GraphSuccessors<'graph> for Sccs<N, S> {
-    type Item = S;
+impl<N: Idx, S: Idx + Ord> Successors for Sccs<N, S> {
+    type Successors<'g> = std::iter::Cloned<std::slice::Iter<'g, S>>;
 
-    type Iter = std::iter::Cloned<std::slice::Iter<'graph, S>>;
-}
-
-impl<N: Idx, S: Idx + Ord> WithSuccessors for Sccs<N, S> {
-    fn successors(&self, node: S) -> <Self as GraphSuccessors<'_>>::Iter {
+    fn successors(&self, node: S) -> Self::Successors<'_> {
         self.successors(node).iter().cloned()
     }
 }
@@ -156,7 +152,7 @@ impl<S: Idx> SccData<S> {
     }
 }
 
-struct SccsConstruction<'c, G: DirectedGraph + WithSuccessors, S: Idx> {
+struct SccsConstruction<'c, G: DirectedGraph + Successors, S: Idx> {
     graph: &'c G,
 
     /// The state of each node; used during walk to record the stack
@@ -216,7 +212,7 @@ enum WalkReturn<S> {
 
 impl<'c, G, S> SccsConstruction<'c, G, S>
 where
-    G: DirectedGraph + WithSuccessors,
+    G: DirectedGraph + Successors,
     S: Idx,
 {
     /// Identifies SCCs in the graph `G` and computes the resulting

compiler/rustc_data_structures/src/graph/tests.rs

@@ -48,24 +48,18 @@ impl WithStartNode for TestGraph {
     }
 }
 
-impl WithPredecessors for TestGraph {
-    fn predecessors(&self, node: usize) -> <Self as GraphPredecessors<'_>>::Iter {
+impl Predecessors for TestGraph {
+    type Predecessors<'g> = iter::Cloned<slice::Iter<'g, usize>>;
+
+    fn predecessors(&self, node: usize) -> Self::Predecessors<'_> {
         self.predecessors[&node].iter().cloned()
     }
 }
 
-impl WithSuccessors for TestGraph {
-    fn successors(&self, node: usize) -> <Self as GraphSuccessors<'_>>::Iter {
+impl Successors for TestGraph {
+    type Successors<'g> = iter::Cloned<slice::Iter<'g, usize>>;
+
+    fn successors(&self, node: usize) -> Self::Successors<'_> {
         self.successors[&node].iter().cloned()
     }
 }
-
-impl<'graph> GraphPredecessors<'graph> for TestGraph {
-    type Item = usize;
-    type Iter = iter::Cloned<slice::Iter<'graph, usize>>;
-}
-
-impl<'graph> GraphSuccessors<'graph> for TestGraph {
-    type Item = usize;
-    type Iter = iter::Cloned<slice::Iter<'graph, usize>>;
-}

compiler/rustc_data_structures/src/graph/vec_graph/mod.rs

@@ -1,4 +1,4 @@
-use crate::graph::{DirectedGraph, GraphSuccessors, WithNumEdges, WithSuccessors};
+use crate::graph::{DirectedGraph, Successors, WithNumEdges};
 use rustc_index::{Idx, IndexVec};
 
 #[cfg(test)]
@@ -92,14 +92,10 @@ impl<N: Idx> WithNumEdges for VecGraph<N> {
     }
 }
 
-impl<'graph, N: Idx> GraphSuccessors<'graph> for VecGraph<N> {
-    type Item = N;
+impl<N: Idx + Ord> Successors for VecGraph<N> {
+    type Successors<'g> = std::iter::Cloned<std::slice::Iter<'g, N>>;
 
-    type Iter = std::iter::Cloned<std::slice::Iter<'graph, N>>;
-}
-
-impl<N: Idx + Ord> WithSuccessors for VecGraph<N> {
-    fn successors(&self, node: N) -> <Self as GraphSuccessors<'_>>::Iter {
+    fn successors(&self, node: N) -> Self::Successors<'_> {
         self.successors(node).iter().cloned()
     }
 }