Remove `ToRegionVid`.

It is only implemented for `Region`, where it is equivalent to the
inherent `as_var` method.

11 files changed, 32 insertions, 55 deletions

diff --git a/compiler/rustc_borrowck/src/borrow_set.rs b/compiler/rustc_borrowck/src/borrow_set.rs
index fa0552e012d..4824f6346d4 100644
--- a/compiler/rustc_borrowck/src/borrow_set.rs
+++ b/compiler/rustc_borrowck/src/borrow_set.rs
@@ -1,6 +1,5 @@
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]
-use crate::nll::ToRegionVid;
 use crate::path_utils::allow_two_phase_borrow;
 use crate::place_ext::PlaceExt;
 use crate::BorrowIndex;
@@ -204,7 +203,7 @@ impl<'a, 'tcx> Visitor<'tcx> for GatherBorrows<'a, 'tcx> {
                 return;
             }
 
-            let region = region.to_region_vid();
+            let region = region.as_var();
 
             let borrow = BorrowData {
                 kind,
@@ -279,7 +278,7 @@ impl<'a, 'tcx> Visitor<'tcx> for GatherBorrows<'a, 'tcx> {
             let borrow_data = &self.location_map[&location];
             assert_eq!(borrow_data.reserve_location, location);
             assert_eq!(borrow_data.kind, kind);
-            assert_eq!(borrow_data.region, region.to_region_vid());
+            assert_eq!(borrow_data.region, region.as_var());
             assert_eq!(borrow_data.borrowed_place, place);
         }
 
diff --git a/compiler/rustc_borrowck/src/constraint_generation.rs b/compiler/rustc_borrowck/src/constraint_generation.rs
index 1427f5cb31d..2aa09a3f26c 100644
--- a/compiler/rustc_borrowck/src/constraint_generation.rs
+++ b/compiler/rustc_borrowck/src/constraint_generation.rs
@@ -12,8 +12,8 @@ use rustc_middle::ty::visit::TypeVisitable;
 use rustc_middle::ty::{self, RegionVid, Ty, TyCtxt};
 
 use crate::{
-    borrow_set::BorrowSet, facts::AllFacts, location::LocationTable, nll::ToRegionVid,
-    places_conflict, region_infer::values::LivenessValues,
+    borrow_set::BorrowSet, facts::AllFacts, location::LocationTable, places_conflict,
+    region_infer::values::LivenessValues,
 };
 
 pub(super) fn generate_constraints<'tcx>(
@@ -170,7 +170,7 @@ impl<'cx, 'tcx> ConstraintGeneration<'cx, 'tcx> {
         debug!("add_regular_live_constraint(live_ty={:?}, location={:?})", live_ty, location);
 
         self.infcx.tcx.for_each_free_region(&live_ty, |live_region| {
-            let vid = live_region.to_region_vid();
+            let vid = live_region.as_var();
             self.liveness_constraints.add_element(vid, location);
         });
     }
diff --git a/compiler/rustc_borrowck/src/diagnostics/find_use.rs b/compiler/rustc_borrowck/src/diagnostics/find_use.rs
index e2d04324f3b..2495613fea1 100644
--- a/compiler/rustc_borrowck/src/diagnostics/find_use.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/find_use.rs
@@ -6,7 +6,6 @@ use std::rc::Rc;
 
 use crate::{
     def_use::{self, DefUse},
-    nll::ToRegionVid,
     region_infer::{Cause, RegionInferenceContext},
 };
 use rustc_data_structures::fx::FxIndexSet;
@@ -117,7 +116,7 @@ impl<'cx, 'tcx> Visitor<'tcx> for DefUseVisitor<'cx, 'tcx> {
 
         let mut found_it = false;
         self.tcx.for_each_free_region(&local_ty, |r| {
-            if r.to_region_vid() == self.region_vid {
+            if r.as_var() == self.region_vid {
                 found_it = true;
             }
         });
diff --git a/compiler/rustc_borrowck/src/diagnostics/region_name.rs b/compiler/rustc_borrowck/src/diagnostics/region_name.rs
index cc5a1f5ab12..f69c4829ae2 100644
--- a/compiler/rustc_borrowck/src/diagnostics/region_name.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/region_name.rs
@@ -10,7 +10,7 @@ use rustc_middle::ty::{self, RegionVid, Ty};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 
-use crate::{nll::ToRegionVid, universal_regions::DefiningTy, MirBorrowckCtxt};
+use crate::{universal_regions::DefiningTy, MirBorrowckCtxt};
 
 /// A name for a particular region used in emitting diagnostics. This name could be a generated
 /// name like `'1`, a name used by the user like `'a`, or a name like `'static`.
@@ -497,7 +497,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
                 //     &
                 //     - let's call the lifetime of this reference `'1`
                 (ty::Ref(region, referent_ty, _), hir::TyKind::Ref(_lifetime, referent_hir_ty)) => {
-                    if region.to_region_vid() == needle_fr {
+                    if region.as_var() == needle_fr {
                         // Just grab the first character, the `&`.
                         let source_map = self.infcx.tcx.sess.source_map();
                         let ampersand_span = source_map.start_point(hir_ty.span);
@@ -598,7 +598,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
         for (kind, hir_arg) in iter::zip(substs, args.args) {
             match (kind.unpack(), hir_arg) {
                 (GenericArgKind::Lifetime(r), hir::GenericArg::Lifetime(lt)) => {
-                    if r.to_region_vid() == needle_fr {
+                    if r.as_var() == needle_fr {
                         return Some(lt);
                     }
                 }
@@ -666,7 +666,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
 
         let return_ty = self.regioncx.universal_regions().unnormalized_output_ty;
         debug!("give_name_if_anonymous_region_appears_in_output: return_ty = {:?}", return_ty);
-        if !tcx.any_free_region_meets(&return_ty, |r| r.to_region_vid() == fr) {
+        if !tcx.any_free_region_meets(&return_ty, |r| r.as_var() == fr) {
             return None;
         }
 
@@ -803,7 +803,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
 
         let tcx = self.infcx.tcx;
 
-        if !tcx.any_free_region_meets(&yield_ty, |r| r.to_region_vid() == fr) {
+        if !tcx.any_free_region_meets(&yield_ty, |r| r.as_var() == fr) {
             return None;
         }
 
diff --git a/compiler/rustc_borrowck/src/diagnostics/var_name.rs b/compiler/rustc_borrowck/src/diagnostics/var_name.rs
index 80b2787ce0c..376415e3d32 100644
--- a/compiler/rustc_borrowck/src/diagnostics/var_name.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/var_name.rs
@@ -1,8 +1,8 @@
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]
 
+use crate::region_infer::RegionInferenceContext;
 use crate::Upvar;
-use crate::{nll::ToRegionVid, region_infer::RegionInferenceContext};
 use rustc_index::vec::{Idx, IndexSlice};
 use rustc_middle::mir::{Body, Local};
 use rustc_middle::ty::{RegionVid, TyCtxt};
@@ -46,7 +46,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             self.universal_regions().defining_ty.upvar_tys().position(|upvar_ty| {
                 debug!("get_upvar_index_for_region: upvar_ty={upvar_ty:?}");
                 tcx.any_free_region_meets(&upvar_ty, |r| {
-                    let r = r.to_region_vid();
+                    let r = r.as_var();
                     debug!("get_upvar_index_for_region: r={r:?} fr={fr:?}");
                     r == fr
                 })
@@ -96,7 +96,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             self.universal_regions().unnormalized_input_tys.iter().skip(implicit_inputs).position(
                 |arg_ty| {
                     debug!("get_argument_index_for_region: arg_ty = {arg_ty:?}");
-                    tcx.any_free_region_meets(arg_ty, |r| r.to_region_vid() == fr)
+                    tcx.any_free_region_meets(arg_ty, |r| r.as_var() == fr)
                 },
             )?;
 
diff --git a/compiler/rustc_borrowck/src/nll.rs b/compiler/rustc_borrowck/src/nll.rs
index 8b5ff999e9b..59a3ab3189d 100644
--- a/compiler/rustc_borrowck/src/nll.rs
+++ b/compiler/rustc_borrowck/src/nll.rs
@@ -10,7 +10,7 @@ use rustc_middle::mir::{
     BasicBlock, Body, ClosureOutlivesSubject, ClosureRegionRequirements, LocalKind, Location,
     Promoted,
 };
-use rustc_middle::ty::{self, OpaqueHiddenType, Region, RegionVid, TyCtxt};
+use rustc_middle::ty::{self, OpaqueHiddenType, TyCtxt};
 use rustc_span::symbol::sym;
 use std::env;
 use std::io;
@@ -444,21 +444,6 @@ fn for_each_region_constraint<'tcx>(
     Ok(())
 }
 
-/// Right now, we piggy back on the `ReVar` to store our NLL inference
-/// regions. These are indexed with `RegionVid`. This method will
-/// assert that the region is a `ReVar` and extract its internal index.
-/// This is reasonable because in our MIR we replace all universal regions
-/// with inference variables.
-pub trait ToRegionVid {
-    fn to_region_vid(self) -> RegionVid;
-}
-
-impl<'tcx> ToRegionVid for Region<'tcx> {
-    fn to_region_vid(self) -> RegionVid {
-        if let ty::ReVar(vid) = *self { vid } else { bug!("region is not an ReVar: {:?}", self) }
-    }
-}
-
 pub(crate) trait ConstraintDescription {
     fn description(&self) -> &'static str;
 }
diff --git a/compiler/rustc_borrowck/src/region_infer/mod.rs b/compiler/rustc_borrowck/src/region_infer/mod.rs
index ce6f3690e19..729f3dbff3b 100644
--- a/compiler/rustc_borrowck/src/region_infer/mod.rs
+++ b/compiler/rustc_borrowck/src/region_infer/mod.rs
@@ -1130,7 +1130,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             let r_vid = self.to_region_vid(r);
             let r_scc = self.constraint_sccs.scc(r_vid);
 
-            // The challenge if this. We have some region variable `r`
+            // The challenge is this. We have some region variable `r`
             // whose value is a set of CFG points and universal
             // regions. We want to find if that set is *equivalent* to
             // any of the named regions found in the closure.
diff --git a/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs b/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs
index a9356135006..71eae7b27d1 100644
--- a/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs
+++ b/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs
@@ -12,7 +12,6 @@ use rustc_span::{Span, DUMMY_SP};
 
 use crate::{
     constraints::OutlivesConstraint,
-    nll::ToRegionVid,
     region_infer::TypeTest,
     type_check::{Locations, MirTypeckRegionConstraints},
     universal_regions::UniversalRegions,
@@ -198,7 +197,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
 
     fn to_region_vid(&mut self, r: ty::Region<'tcx>) -> ty::RegionVid {
         if let ty::RePlaceholder(placeholder) = *r {
-            self.constraints.placeholder_region(self.infcx, placeholder).to_region_vid()
+            self.constraints.placeholder_region(self.infcx, placeholder).as_var()
         } else {
             self.universal_regions.to_region_vid(r)
         }
diff --git a/compiler/rustc_borrowck/src/type_check/liveness/mod.rs b/compiler/rustc_borrowck/src/type_check/liveness/mod.rs
index a411aec518e..f1ad0ca55cc 100644
--- a/compiler/rustc_borrowck/src/type_check/liveness/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/liveness/mod.rs
@@ -11,7 +11,6 @@ use crate::{
     constraints::OutlivesConstraintSet,
     facts::{AllFacts, AllFactsExt},
     location::LocationTable,
-    nll::ToRegionVid,
     region_infer::values::RegionValueElements,
     universal_regions::UniversalRegions,
 };
@@ -80,9 +79,7 @@ fn compute_relevant_live_locals<'tcx>(
 ) -> (Vec<Local>, Vec<Local>) {
     let (boring_locals, relevant_live_locals): (Vec<_>, Vec<_>) =
         body.local_decls.iter_enumerated().partition_map(|(local, local_decl)| {
-            if tcx.all_free_regions_meet(&local_decl.ty, |r| {
-                free_regions.contains(&r.to_region_vid())
-            }) {
+            if tcx.all_free_regions_meet(&local_decl.ty, |r| free_regions.contains(&r.as_var())) {
                 Either::Left(local)
             } else {
                 Either::Right(local)
diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index 6d8305b7d47..375eca1b29d 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -56,7 +56,6 @@ use crate::{
     facts::AllFacts,
     location::LocationTable,
     member_constraints::MemberConstraintSet,
-    nll::ToRegionVid,
     path_utils,
     region_infer::values::{
         LivenessValues, PlaceholderIndex, PlaceholderIndices, RegionValueElements,
@@ -2419,7 +2418,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         if let Some(all_facts) = all_facts {
             let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");
             if let Some(borrow_index) = borrow_set.get_index_of(&location) {
-                let region_vid = borrow_region.to_region_vid();
+                let region_vid = borrow_region.as_var();
                 all_facts.loan_issued_at.push((
                     region_vid,
                     borrow_index,
@@ -2465,8 +2464,8 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                     match base_ty.kind() {
                         ty::Ref(ref_region, _, mutbl) => {
                             constraints.outlives_constraints.push(OutlivesConstraint {
-                                sup: ref_region.to_region_vid(),
-                                sub: borrow_region.to_region_vid(),
+                                sup: ref_region.as_var(),
+                                sub: borrow_region.as_var(),
                                 locations: location.to_locations(),
                                 span: location.to_locations().span(body),
                                 category,
diff --git a/compiler/rustc_borrowck/src/universal_regions.rs b/compiler/rustc_borrowck/src/universal_regions.rs
index 35dfc1f7d12..70fddb1057c 100644
--- a/compiler/rustc_borrowck/src/universal_regions.rs
+++ b/compiler/rustc_borrowck/src/universal_regions.rs
@@ -28,7 +28,6 @@ use rustc_span::symbol::{kw, sym};
 use rustc_span::Symbol;
 use std::iter;
 
-use crate::nll::ToRegionVid;
 use crate::renumber::{BoundRegionInfo, RegionCtxt};
 use crate::BorrowckInferCtxt;
 
@@ -406,7 +405,7 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
 
         // Create the "global" region that is always free in all contexts: 'static.
         let fr_static =
-            self.infcx.next_nll_region_var(FR, || RegionCtxt::Free(kw::Static)).to_region_vid();
+            self.infcx.next_nll_region_var(FR, || RegionCtxt::Free(kw::Static)).as_var();
 
         // We've now added all the global regions. The next ones we
         // add will be external.
@@ -446,7 +445,7 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
                         };
 
                         debug!(?region_vid);
-                        indices.insert_late_bound_region(r, region_vid.to_region_vid());
+                        indices.insert_late_bound_region(r, region_vid.as_var());
                     }
                 },
             );
@@ -480,7 +479,7 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
                 };
 
                 debug!(?region_vid);
-                indices.insert_late_bound_region(r, region_vid.to_region_vid());
+                indices.insert_late_bound_region(r, region_vid.as_var());
             }
         });
 
@@ -499,7 +498,7 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
                 let reg_vid = self
                     .infcx
                     .next_nll_region_var(FR, || RegionCtxt::Free(Symbol::intern("c-variadic")))
-                    .to_region_vid();
+                    .as_var();
 
                 let region = self.infcx.tcx.mk_re_var(reg_vid);
                 let va_list_ty =
@@ -514,7 +513,7 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
         let fr_fn_body = self
             .infcx
             .next_nll_region_var(FR, || RegionCtxt::Free(Symbol::intern("fn_body")))
-            .to_region_vid();
+            .as_var();
 
         let num_universals = self.infcx.num_region_vars();
 
@@ -635,7 +634,7 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
 
         let global_mapping = iter::once((tcx.lifetimes.re_static, fr_static));
         let subst_mapping =
-            iter::zip(identity_substs.regions(), fr_substs.regions().map(|r| r.to_region_vid()));
+            iter::zip(identity_substs.regions(), fr_substs.regions().map(|r| r.as_var()));
 
         UniversalRegionIndices { indices: global_mapping.chain(subst_mapping).collect(), fr_static }
     }
@@ -789,7 +788,7 @@ impl<'cx, 'tcx> InferCtxtExt<'tcx> for BorrowckInferCtxt<'cx, 'tcx> {
                 self.next_nll_region_var(origin, || RegionCtxt::Bound(BoundRegionInfo::Name(name)))
             };
 
-            indices.insert_late_bound_region(liberated_region, region_vid.to_region_vid());
+            indices.insert_late_bound_region(liberated_region, region_vid.as_var());
             debug!(?liberated_region, ?region_vid);
             region_vid
         });
@@ -822,7 +821,7 @@ impl<'cx, 'tcx> InferCtxtExt<'tcx> for BorrowckInferCtxt<'cx, 'tcx> {
                 };
 
                 debug!(?region_vid);
-                indices.insert_late_bound_region(r, region_vid.to_region_vid());
+                indices.insert_late_bound_region(r, region_vid.as_var());
             }
         });
     }
@@ -843,7 +842,7 @@ impl<'cx, 'tcx> InferCtxtExt<'tcx> for BorrowckInferCtxt<'cx, 'tcx> {
                     })
                 };
 
-                indices.insert_late_bound_region(r, region_vid.to_region_vid());
+                indices.insert_late_bound_region(r, region_vid.as_var());
             }
         });
     }
@@ -861,7 +860,7 @@ impl<'tcx> UniversalRegionIndices<'tcx> {
     }
 
     /// Converts `r` into a local inference variable: `r` can either
-    /// by a `ReVar` (i.e., already a reference to an inference
+    /// be a `ReVar` (i.e., already a reference to an inference
     /// variable) or it can be `'static` or some early-bound
     /// region. This is useful when taking the results from
     /// type-checking and trait-matching, which may sometimes
@@ -870,7 +869,7 @@ impl<'tcx> UniversalRegionIndices<'tcx> {
     /// fully initialized.
     pub fn to_region_vid(&self, r: ty::Region<'tcx>) -> RegionVid {
         if let ty::ReVar(..) = *r {
-            r.to_region_vid()
+            r.as_var()
         } else if r.is_error() {
             // We use the `'static` `RegionVid` because `ReError` doesn't actually exist in the
             // `UniversalRegionIndices`. This is fine because 1) it is a fallback only used if