Remove impl ToRegionVid for RegionVid.

It's weird and unnecessary.

compiler/rustc_borrowck/src/dataflow.rs

@@ -11,9 +11,7 @@ use rustc_mir_dataflow::{self, fmt::DebugWithContext, CallReturnPlaces, GenKill}
 use rustc_mir_dataflow::{Analysis, Direction, Results};
 use std::fmt;
 
-use crate::{
-    places_conflict, BorrowSet, PlaceConflictBias, PlaceExt, RegionInferenceContext, ToRegionVid,
-};
+use crate::{places_conflict, BorrowSet, PlaceConflictBias, PlaceExt, RegionInferenceContext};
 
 /// A tuple with named fields that can hold either the results or the transient state of the
 /// dataflow analyses used by the borrow checker.
@@ -242,7 +240,7 @@ impl<'a, 'tcx> Borrows<'a, 'tcx> {
     ) -> Self {
         let mut prec = OutOfScopePrecomputer::new(body, nonlexical_regioncx);
         for (borrow_index, borrow_data) in borrow_set.iter_enumerated() {
-            let borrow_region = borrow_data.region.to_region_vid();
+            let borrow_region = borrow_data.region;
             let location = borrow_data.reserve_location;
 
             prec.precompute_borrows_out_of_scope(borrow_index, borrow_region, location);

compiler/rustc_borrowck/src/lib.rs

@@ -94,7 +94,7 @@ pub mod consumers;
 
 use borrow_set::{BorrowData, BorrowSet};
 use dataflow::{BorrowIndex, BorrowckFlowState as Flows, BorrowckResults, Borrows};
-use nll::{PoloniusOutput, ToRegionVid};
+use nll::PoloniusOutput;
 use place_ext::PlaceExt;
 use places_conflict::{places_conflict, PlaceConflictBias};
 use region_infer::RegionInferenceContext;

compiler/rustc_borrowck/src/nll.rs

@@ -459,12 +459,6 @@ impl<'tcx> ToRegionVid for Region<'tcx> {
     }
 }
 
-impl ToRegionVid for RegionVid {
-    fn to_region_vid(self) -> RegionVid {
-        self
-    }
-}
-
 pub(crate) trait ConstraintDescription {
     fn description(&self) -> &'static str;
 }

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -27,7 +27,7 @@ use crate::{
     },
     diagnostics::{RegionErrorKind, RegionErrors, UniverseInfo},
     member_constraints::{MemberConstraintSet, NllMemberConstraintIndex},
-    nll::{PoloniusOutput, ToRegionVid},
+    nll::PoloniusOutput,
     region_infer::reverse_sccs::ReverseSccGraph,
     region_infer::values::{
         LivenessValues, PlaceholderIndices, RegionElement, RegionValueElements, RegionValues,
@@ -593,14 +593,14 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// Returns `true` if the region `r` contains the point `p`.
     ///
     /// Panics if called before `solve()` executes,
-    pub(crate) fn region_contains(&self, r: impl ToRegionVid, p: impl ToElementIndex) -> bool {
-        let scc = self.constraint_sccs.scc(r.to_region_vid());
+    pub(crate) fn region_contains(&self, r: RegionVid, p: impl ToElementIndex) -> bool {
+        let scc = self.constraint_sccs.scc(r);
         self.scc_values.contains(scc, p)
     }
 
     /// Returns access to the value of `r` for debugging purposes.
     pub(crate) fn region_value_str(&self, r: RegionVid) -> String {
-        let scc = self.constraint_sccs.scc(r.to_region_vid());
+        let scc = self.constraint_sccs.scc(r);
         self.scc_values.region_value_str(scc)
     }
 
@@ -608,24 +608,21 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         &'a self,
         r: RegionVid,
     ) -> impl Iterator<Item = ty::PlaceholderRegion> + 'a {
-        let scc = self.constraint_sccs.scc(r.to_region_vid());
+        let scc = self.constraint_sccs.scc(r);
         self.scc_values.placeholders_contained_in(scc)
     }
 
     /// Returns access to the value of `r` for debugging purposes.
     pub(crate) fn region_universe(&self, r: RegionVid) -> ty::UniverseIndex {
-        let scc = self.constraint_sccs.scc(r.to_region_vid());
+        let scc = self.constraint_sccs.scc(r);
         self.scc_universes[scc]
     }
 
     /// Once region solving has completed, this function will return
     /// the member constraints that were applied to the value of a given
     /// region `r`. See `AppliedMemberConstraint`.
-    pub(crate) fn applied_member_constraints(
-        &self,
-        r: impl ToRegionVid,
-    ) -> &[AppliedMemberConstraint] {
-        let scc = self.constraint_sccs.scc(r.to_region_vid());
+    pub(crate) fn applied_member_constraints(&self, r: RegionVid) -> &[AppliedMemberConstraint] {
+        let scc = self.constraint_sccs.scc(r);
         binary_search_util::binary_search_slice(
             &self.member_constraints_applied,
             |applied| applied.member_region_scc,
@@ -2234,7 +2231,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         r: RegionVid,
         body: &Body<'_>,
     ) -> Option<Location> {
-        let scc = self.constraint_sccs.scc(r.to_region_vid());
+        let scc = self.constraint_sccs.scc(r);
         let locations = self.scc_values.locations_outlived_by(scc);
         for location in locations {
             let bb = &body[location.block];