Rollup merge of #123934 - WaffleLapkin:graph-mini-refactor, r=fmease

`rustc_data_structures::graph` mini refactor

Who doesn't love to breathe dust from the ancient times?

compiler/rustc_borrowck/src/constraints/graph.rs

@@ -216,23 +216,14 @@ impl<'s, 'tcx, D: ConstraintGraphDirection> Iterator for Successors<'s, 'tcx, D>
 
 impl<'s, 'tcx, D: ConstraintGraphDirection> graph::DirectedGraph for RegionGraph<'s, 'tcx, D> {
     type Node = RegionVid;
-}
 
-impl<'s, 'tcx, D: ConstraintGraphDirection> graph::WithNumNodes for RegionGraph<'s, 'tcx, D> {
     fn num_nodes(&self) -> usize {
         self.constraint_graph.first_constraints.len()
     }
 }
 
-impl<'s, 'tcx, D: ConstraintGraphDirection> graph::WithSuccessors for RegionGraph<'s, 'tcx, D> {
-    fn successors(&self, node: Self::Node) -> <Self as graph::GraphSuccessors<'_>>::Iter {
+impl<'s, 'tcx, D: ConstraintGraphDirection> graph::Successors for RegionGraph<'s, 'tcx, D> {
+    fn successors(&self, node: Self::Node) -> impl Iterator<Item = Self::Node> {
         self.outgoing_regions(node)
     }
 }
-
-impl<'s, 'tcx, D: ConstraintGraphDirection> graph::GraphSuccessors<'_>
-    for RegionGraph<'s, 'tcx, D>
-{
-    type Item = RegionVid;
-    type Iter = Successors<'s, 'tcx, D>;
-}

compiler/rustc_borrowck/src/dataflow.rs

@@ -1,5 +1,5 @@
 use rustc_data_structures::fx::FxIndexMap;
-use rustc_data_structures::graph::WithSuccessors;
+use rustc_data_structures::graph;
 use rustc_index::bit_set::BitSet;
 use rustc_middle::mir::{
     self, BasicBlock, Body, CallReturnPlaces, Location, Place, TerminatorEdges,
@@ -262,7 +262,7 @@ impl<'tcx> PoloniusOutOfScopePrecomputer<'_, 'tcx> {
 
         // We first handle the cases where the loan doesn't go out of scope, depending on the issuing
         // region's successors.
-        for successor in self.regioncx.region_graph().depth_first_search(issuing_region) {
+        for successor in graph::depth_first_search(&self.regioncx.region_graph(), issuing_region) {
             // 1. Via applied member constraints
             //
             // The issuing region can flow into the choice regions, and they are either:

compiler/rustc_borrowck/src/region_infer/reverse_sccs.rs

@@ -1,8 +1,8 @@
 use crate::constraints::ConstraintSccIndex;
 use crate::RegionInferenceContext;
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
+use rustc_data_structures::graph;
 use rustc_data_structures::graph::vec_graph::VecGraph;
-use rustc_data_structures::graph::WithSuccessors;
 use rustc_middle::ty::RegionVid;
 use std::ops::Range;
 
@@ -23,8 +23,7 @@ impl ReverseSccGraph {
         scc0: ConstraintSccIndex,
     ) -> impl Iterator<Item = RegionVid> + 'a {
         let mut duplicates = FxIndexSet::default();
-        self.graph
-            .depth_first_search(scc0)
+        graph::depth_first_search(&self.graph, scc0)
             .flat_map(move |scc1| {
                 self.scc_regions
                     .get(&scc1)

compiler/rustc_borrowck/src/type_check/liveness/trace.rs

@@ -1,5 +1,4 @@
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
-use rustc_data_structures::graph::WithSuccessors;
 use rustc_index::bit_set::BitSet;
 use rustc_index::interval::IntervalSet;
 use rustc_infer::infer::canonical::QueryRegionConstraints;
@@ -64,7 +63,10 @@ pub(super) fn trace<'mir, 'tcx>(
         // Traverse each issuing region's constraints, and record the loan as flowing into the
         // outlived region.
         for (loan, issuing_region_data) in borrow_set.iter_enumerated() {
-            for succ in region_graph.depth_first_search(issuing_region_data.region) {
+            for succ in rustc_data_structures::graph::depth_first_search(
+                &region_graph,
+                issuing_region_data.region,
+            ) {
                 // We don't need to mention that a loan flows into its issuing region.
                 if succ == issuing_region_data.region {
                     continue;

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

@@ -1,4 +1,4 @@
-use super::{DirectedGraph, WithNumNodes, WithStartNode, WithSuccessors};
+use super::{DirectedGraph, StartNode, Successors};
 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 + WithNumNodes>(
+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 + WithNumNodes>(
+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 + WithNumNodes>(
     result
 }
 
-fn post_order_walk<G: DirectedGraph + WithSuccessors + WithNumNodes>(
+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 + WithNumNodes>(
     }
 }
 
-pub fn reverse_post_order<G: DirectedGraph + WithSuccessors + WithNumNodes>(
+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 + WithNumNodes>(
 /// A "depth-first search" iterator for a directed graph.
 pub struct DepthFirstSearch<'graph, G>
 where
-    G: ?Sized + DirectedGraph + WithNumNodes + 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 + WithNumNodes + 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 + WithNumNodes + 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 + WithNumNodes + 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 + WithNumNodes + 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 + WithNumNodes + 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 + WithNumNodes + WithSuccessors + WithStartNode,
+    G: ?Sized + DirectedGraph + Successors + StartNode,
 {
     /// Performs a depth-first search, starting from `G::start_node()`.
     ///

compiler/rustc_data_structures/src/graph/mod.rs

@@ -12,70 +12,43 @@ mod tests;
 
 pub trait DirectedGraph {
     type Node: Idx;
-}
 
-pub trait WithNumNodes: DirectedGraph {
     fn num_nodes(&self) -> usize;
 }
 
-pub trait WithNumEdges: DirectedGraph {
+pub trait NumEdges: 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;
-
-    fn depth_first_search(&self, from: Self::Node) -> iterate::DepthFirstSearch<'_, Self>
-    where
-        Self: WithNumNodes,
-    {
-        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 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>;
-}
-
-pub trait WithStartNode: DirectedGraph {
+pub trait StartNode: DirectedGraph {
     fn start_node(&self) -> Self::Node;
 }
 
-pub trait ControlFlowGraph:
-    DirectedGraph + WithStartNode + WithPredecessors + WithSuccessors + WithNumNodes
-{
-    // convenient trait
+pub trait Successors: DirectedGraph {
+    fn successors(&self, node: Self::Node) -> impl Iterator<Item = Self::Node>;
 }
 
-impl<T> ControlFlowGraph for T where
-    T: DirectedGraph + WithStartNode + WithPredecessors + WithSuccessors + WithNumNodes
-{
+pub trait Predecessors: DirectedGraph {
+    fn predecessors(&self, node: Self::Node) -> impl Iterator<Item = Self::Node>;
 }
 
+/// Alias for [`DirectedGraph`] + [`StartNode`] + [`Predecessors`] + [`Successors`].
+pub trait ControlFlowGraph: DirectedGraph + StartNode + Predecessors + Successors {}
+impl<T> ControlFlowGraph for T where T: DirectedGraph + StartNode + 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 + WithNumNodes,
+    G: ?Sized + DirectedGraph + StartNode + Successors,
 {
     iterate::TriColorDepthFirstSearch::new(graph)
         .run_from_start(&mut iterate::CycleDetector)
         .is_some()
 }
+
+pub fn depth_first_search<G>(graph: &G, from: G::Node) -> iterate::DepthFirstSearch<'_, G>
+where
+    G: ?Sized + Successors,
+{
+    iterate::DepthFirstSearch::new(graph).with_start_node(from)
+}

compiler/rustc_data_structures/src/graph/reference.rs

@@ -2,38 +2,26 @@ use super::*;
 
 impl<'graph, G: DirectedGraph> DirectedGraph for &'graph G {
     type Node = G::Node;
-}
 
-impl<'graph, G: WithNumNodes> WithNumNodes for &'graph G {
     fn num_nodes(&self) -> usize {
         (**self).num_nodes()
     }
 }
 
-impl<'graph, G: WithStartNode> WithStartNode for &'graph G {
+impl<'graph, G: StartNode> StartNode for &'graph G {
     fn start_node(&self) -> Self::Node {
         (**self).start_node()
     }
 }
 
-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 {
+    fn successors(&self, node: Self::Node) -> impl Iterator<Item = Self::Node> {
         (**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 {
+    fn predecessors(&self, node: Self::Node) -> impl Iterator<Item = Self::Node> {
         (**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, WithNumNodes, WithSuccessors};
+use crate::graph::{DirectedGraph, NumEdges, Successors};
 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> + WithNumNodes + WithSuccessors)) -> Self {
+    pub fn new(graph: &(impl DirectedGraph<Node = N> + Successors)) -> Self {
         SccsConstruction::construct(graph)
     }
 
@@ -89,30 +89,22 @@ impl<N: Idx, S: Idx + Ord> Sccs<N, S> {
     }
 }
 
-impl<N: Idx, S: Idx> DirectedGraph for Sccs<N, S> {
+impl<N: Idx, S: Idx + Ord> DirectedGraph for Sccs<N, S> {
     type Node = S;
-}
 
-impl<N: Idx, S: Idx + Ord> WithNumNodes for Sccs<N, S> {
     fn num_nodes(&self) -> usize {
         self.num_sccs()
     }
 }
 
-impl<N: Idx, S: Idx> WithNumEdges for Sccs<N, S> {
+impl<N: Idx, S: Idx + Ord> NumEdges for Sccs<N, S> {
     fn num_edges(&self) -> usize {
         self.scc_data.all_successors.len()
     }
 }
 
-impl<'graph, 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 + Ord> WithSuccessors for Sccs<N, S> {
-    fn successors(&self, node: S) -> <Self as GraphSuccessors<'_>>::Iter {
+impl<N: Idx, S: Idx + Ord> Successors for Sccs<N, S> {
+    fn successors(&self, node: S) -> impl Iterator<Item = Self::Node> {
         self.successors(node).iter().cloned()
     }
 }
@@ -158,7 +150,7 @@ impl<S: Idx> SccData<S> {
     }
 }
 
-struct SccsConstruction<'c, G: DirectedGraph + WithNumNodes + 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
@@ -218,7 +210,7 @@ enum WalkReturn<S> {
 
 impl<'c, G, S> SccsConstruction<'c, G, S>
 where
-    G: DirectedGraph + WithNumNodes + WithSuccessors,
+    G: DirectedGraph + Successors,
     S: Idx,
 {
     /// Identifies SCCs in the graph `G` and computes the resulting

compiler/rustc_data_structures/src/graph/tests.rs

@@ -1,7 +1,5 @@
 use crate::fx::FxHashMap;
 use std::cmp::max;
-use std::iter;
-use std::slice;
 
 use super::*;
 
@@ -36,38 +34,26 @@ impl TestGraph {
 
 impl DirectedGraph for TestGraph {
     type Node = usize;
-}
 
-impl WithStartNode for TestGraph {
-    fn start_node(&self) -> usize {
-        self.start_node
-    }
-}
-
-impl WithNumNodes for TestGraph {
     fn num_nodes(&self) -> usize {
         self.num_nodes
     }
 }
 
-impl WithPredecessors for TestGraph {
-    fn predecessors(&self, node: usize) -> <Self as GraphPredecessors<'_>>::Iter {
+impl StartNode for TestGraph {
+    fn start_node(&self) -> usize {
+        self.start_node
+    }
+}
+
+impl Predecessors for TestGraph {
+    fn predecessors(&self, node: usize) -> impl Iterator<Item = Self::Node> {
         self.predecessors[&node].iter().cloned()
     }
 }
 
-impl WithSuccessors for TestGraph {
-    fn successors(&self, node: usize) -> <Self as GraphSuccessors<'_>>::Iter {
+impl Successors for TestGraph {
+    fn successors(&self, node: usize) -> impl Iterator<Item = Self::Node> {
         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, WithNumNodes, WithSuccessors};
+use crate::graph::{DirectedGraph, NumEdges, Successors};
 use rustc_index::{Idx, IndexVec};
 
 #[cfg(test)]
@@ -80,28 +80,20 @@ impl<N: Idx + Ord> VecGraph<N> {
 
 impl<N: Idx> DirectedGraph for VecGraph<N> {
     type Node = N;
-}
 
-impl<N: Idx> WithNumNodes for VecGraph<N> {
     fn num_nodes(&self) -> usize {
         self.node_starts.len() - 1
     }
 }
 
-impl<N: Idx> WithNumEdges for VecGraph<N> {
+impl<N: Idx> NumEdges for VecGraph<N> {
     fn num_edges(&self) -> usize {
         self.edge_targets.len()
     }
 }
 
-impl<'graph, N: Idx> GraphSuccessors<'graph> for VecGraph<N> {
-    type Item = 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 {
+impl<N: Idx + Ord> Successors for VecGraph<N> {
+    fn successors(&self, node: N) -> impl Iterator<Item = Self::Node> {
         self.successors(node).iter().cloned()
     }
 }

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

@@ -1,3 +1,5 @@
+use crate::graph;
+
 use super::*;
 
 fn create_graph() -> VecGraph<usize> {
@@ -37,6 +39,6 @@ fn successors() {
 #[test]
 fn dfs() {
     let graph = create_graph();
-    let dfs: Vec<_> = graph.depth_first_search(0).collect();
+    let dfs: Vec<_> = graph::depth_first_search(&graph, 0).collect();
     assert_eq!(dfs, vec![0, 1, 3, 4, 2]);
 }

compiler/rustc_hir_typeck/src/fallback.rs

@@ -1,7 +1,6 @@
 use crate::FnCtxt;
 use rustc_data_structures::{
-    graph::WithSuccessors,
-    graph::{iterate::DepthFirstSearch, vec_graph::VecGraph},
+    graph::{self, iterate::DepthFirstSearch, vec_graph::VecGraph},
     unord::{UnordBag, UnordMap, UnordSet},
 };
 use rustc_infer::infer::{DefineOpaqueTypes, InferOk};
@@ -300,7 +299,7 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
                 debug!(
                     "calculate_diverging_fallback: root_vid={:?} reaches {:?}",
                     root_vid,
-                    coercion_graph.depth_first_search(root_vid).collect::<Vec<_>>()
+                    graph::depth_first_search(&coercion_graph, root_vid).collect::<Vec<_>>()
                 );
 
                 // drain the iterator to visit all nodes reachable from this node
@@ -342,8 +341,7 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
         for &diverging_vid in &diverging_vids {
             let diverging_ty = Ty::new_var(self.tcx, diverging_vid);
             let root_vid = self.root_var(diverging_vid);
-            let can_reach_non_diverging = coercion_graph
-                .depth_first_search(root_vid)
+            let can_reach_non_diverging = graph::depth_first_search(&coercion_graph, root_vid)
                 .any(|n| roots_reachable_from_non_diverging.visited(n));
 
             let infer_var_infos: UnordBag<_> = self

compiler/rustc_middle/src/mir/basic_blocks.rs

@@ -1,5 +1,5 @@
 use crate::mir::traversal::Postorder;
-use crate::mir::{BasicBlock, BasicBlockData, Successors, Terminator, TerminatorKind, START_BLOCK};
+use crate::mir::{BasicBlock, BasicBlockData, Terminator, TerminatorKind, START_BLOCK};
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::graph;
@@ -141,42 +141,30 @@ impl<'tcx> std::ops::Deref for BasicBlocks<'tcx> {
 
 impl<'tcx> graph::DirectedGraph for BasicBlocks<'tcx> {
     type Node = BasicBlock;
-}
 
-impl<'tcx> graph::WithNumNodes for BasicBlocks<'tcx> {
     #[inline]
     fn num_nodes(&self) -> usize {
         self.basic_blocks.len()
     }
 }
 
-impl<'tcx> graph::WithStartNode for BasicBlocks<'tcx> {
+impl<'tcx> graph::StartNode for BasicBlocks<'tcx> {
     #[inline]
     fn start_node(&self) -> Self::Node {
         START_BLOCK
     }
 }
 
-impl<'tcx> graph::WithSuccessors for BasicBlocks<'tcx> {
+impl<'tcx> graph::Successors for BasicBlocks<'tcx> {
     #[inline]
-    fn successors(&self, node: Self::Node) -> <Self as graph::GraphSuccessors<'_>>::Iter {
+    fn successors(&self, node: Self::Node) -> impl Iterator<Item = Self::Node> {
         self.basic_blocks[node].terminator().successors()
     }
 }
 
-impl<'a, 'b> graph::GraphSuccessors<'b> for BasicBlocks<'a> {
-    type Item = BasicBlock;
-    type Iter = Successors<'b>;
-}
-
-impl<'tcx, 'graph> graph::GraphPredecessors<'graph> for BasicBlocks<'tcx> {
-    type Item = BasicBlock;
-    type Iter = std::iter::Copied<std::slice::Iter<'graph, BasicBlock>>;
-}
-
-impl<'tcx> graph::WithPredecessors for BasicBlocks<'tcx> {
+impl<'tcx> graph::Predecessors for BasicBlocks<'tcx> {
     #[inline]
-    fn predecessors(&self, node: Self::Node) -> <Self as graph::GraphPredecessors<'_>>::Iter {
+    fn predecessors(&self, node: Self::Node) -> impl Iterator<Item = Self::Node> {
         self.predecessors()[node].iter().copied()
     }
 }

compiler/rustc_middle/src/mir/generic_graphviz.rs

@@ -5,7 +5,7 @@ use std::io::{self, Write};
 
 pub struct GraphvizWriter<
     'a,
-    G: graph::DirectedGraph + graph::WithSuccessors + graph::WithStartNode + graph::WithNumNodes,
+    G: graph::DirectedGraph + graph::Successors + graph::StartNode,
     NodeContentFn: Fn(<G as graph::DirectedGraph>::Node) -> Vec<String>,
     EdgeLabelsFn: Fn(<G as graph::DirectedGraph>::Node) -> Vec<String>,
 > {
@@ -19,7 +19,7 @@ pub struct GraphvizWriter<
 
 impl<
     'a,
-    G: graph::DirectedGraph + graph::WithSuccessors + graph::WithStartNode + graph::WithNumNodes,
+    G: graph::DirectedGraph + graph::Successors + graph::StartNode,
     NodeContentFn: Fn(<G as graph::DirectedGraph>::Node) -> Vec<String>,
     EdgeLabelsFn: Fn(<G as graph::DirectedGraph>::Node) -> Vec<String>,
 > GraphvizWriter<'a, G, NodeContentFn, EdgeLabelsFn>

compiler/rustc_mir_transform/src/coverage/counters.rs

@@ -2,7 +2,7 @@ use std::fmt::{self, Debug};
 
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::FxHashMap;
-use rustc_data_structures::graph::WithNumNodes;
+use rustc_data_structures::graph::DirectedGraph;
 use rustc_index::IndexVec;
 use rustc_middle::mir::coverage::{CounterId, CovTerm, Expression, ExpressionId, Op};
 

compiler/rustc_mir_transform/src/coverage/graph.rs

@@ -1,7 +1,7 @@
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::graph::dominators::{self, Dominators};
-use rustc_data_structures::graph::{self, GraphSuccessors, WithNumNodes, WithStartNode};
+use rustc_data_structures::graph::{self, DirectedGraph, StartNode};
 use rustc_index::bit_set::BitSet;
 use rustc_index::IndexVec;
 use rustc_middle::mir::{self, BasicBlock, Terminator, TerminatorKind};
@@ -193,16 +193,14 @@ impl IndexMut<BasicCoverageBlock> for CoverageGraph {
 
 impl graph::DirectedGraph for CoverageGraph {
     type Node = BasicCoverageBlock;
-}
 
-impl graph::WithNumNodes for CoverageGraph {
     #[inline]
     fn num_nodes(&self) -> usize {
         self.bcbs.len()
     }
 }
 
-impl graph::WithStartNode for CoverageGraph {
+impl graph::StartNode for CoverageGraph {
     #[inline]
     fn start_node(&self) -> Self::Node {
         self.bcb_from_bb(mir::START_BLOCK)
@@ -210,28 +208,16 @@ impl graph::WithStartNode for CoverageGraph {
     }
 }
 
-type BcbSuccessors<'graph> = std::slice::Iter<'graph, BasicCoverageBlock>;
-
-impl<'graph> graph::GraphSuccessors<'graph> for CoverageGraph {
-    type Item = BasicCoverageBlock;
-    type Iter = std::iter::Cloned<BcbSuccessors<'graph>>;
-}
-
-impl graph::WithSuccessors for CoverageGraph {
+impl graph::Successors for CoverageGraph {
     #[inline]
-    fn successors(&self, node: Self::Node) -> <Self as GraphSuccessors<'_>>::Iter {
+    fn successors(&self, node: Self::Node) -> impl Iterator<Item = Self::Node> {
         self.successors[node].iter().cloned()
     }
 }
 
-impl<'graph> graph::GraphPredecessors<'graph> for CoverageGraph {
-    type Item = BasicCoverageBlock;
-    type Iter = std::iter::Copied<std::slice::Iter<'graph, BasicCoverageBlock>>;
-}
-
-impl graph::WithPredecessors for CoverageGraph {
+impl graph::Predecessors for CoverageGraph {
     #[inline]
-    fn predecessors(&self, node: Self::Node) -> <Self as graph::GraphPredecessors<'_>>::Iter {
+    fn predecessors(&self, node: Self::Node) -> impl Iterator<Item = Self::Node> {
         self.predecessors[node].iter().copied()
     }
 }

compiler/rustc_mir_transform/src/coverage/spans.rs

@@ -1,4 +1,4 @@
-use rustc_data_structures::graph::WithNumNodes;
+use rustc_data_structures::graph::DirectedGraph;
 use rustc_index::bit_set::BitSet;
 use rustc_middle::mir;
 use rustc_span::{BytePos, Span};

compiler/rustc_mir_transform/src/coverage/tests.rs

@@ -28,8 +28,7 @@ use super::counters;
 use super::graph::{self, BasicCoverageBlock};
 
 use itertools::Itertools;
-use rustc_data_structures::graph::WithNumNodes;
-use rustc_data_structures::graph::WithSuccessors;
+use rustc_data_structures::graph::{DirectedGraph, Successors};
 use rustc_index::{Idx, IndexVec};
 use rustc_middle::mir::*;
 use rustc_middle::ty;