Make `depth_first_search` into a standalone function

Does not necessarily change much, but we never overwrite it, so I see no reason
for it to be in the `Successors` trait. (+we already have a similar `is_cyclic`)

3 files changed, 8 insertions, 7 deletions

diff --git a/compiler/rustc_borrowck/src/dataflow.rs b/compiler/rustc_borrowck/src/dataflow.rs
index c185986a7d8..ec7d4582a60 100644
--- a/compiler/rustc_borrowck/src/dataflow.rs
+++ b/compiler/rustc_borrowck/src/dataflow.rs
@@ -1,5 +1,5 @@
 use rustc_data_structures::fx::FxIndexMap;
-use rustc_data_structures::graph::Successors;
+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:
diff --git a/compiler/rustc_borrowck/src/region_infer/reverse_sccs.rs b/compiler/rustc_borrowck/src/region_infer/reverse_sccs.rs
index 7d7a3c09370..97ddc45ee47 100644
--- a/compiler/rustc_borrowck/src/region_infer/reverse_sccs.rs
+++ b/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::Successors;
 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)
diff --git a/compiler/rustc_borrowck/src/type_check/liveness/trace.rs b/compiler/rustc_borrowck/src/type_check/liveness/trace.rs
index 5b92dca430f..6cc0e67c0f8 100644
--- a/compiler/rustc_borrowck/src/type_check/liveness/trace.rs
+++ b/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::Successors;
 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;