Auto merge of #117876 - lcnr:region-kind-rename, r=BoxyUwU

`ReLateBound` -> `ReBound`

first step of rust-lang/types-team#95

already fairly large xx

there's some future work here I intentionally did not contribute as part of this PR, from my notes:
- `DescriptionCtx` to `DescriptionCtxt`
- what is `CheckRegions::Bound`?
- `collect_late_bound_regions` et al
- `erase_late_bound_regions` -> `instantiate_bound_regions_with_erased`?
- `EraseEarlyRegions` should be removed, feels duplicate

r? `@BoxyUwU`

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -10,7 +10,7 @@ use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, Namespace};
 use rustc_hir::CoroutineKind;
 use rustc_index::IndexSlice;
-use rustc_infer::infer::LateBoundRegionConversionTime;
+use rustc_infer::infer::BoundRegionConversionTime;
 use rustc_middle::mir::tcx::PlaceTy;
 use rustc_middle::mir::{
     AggregateKind, CallSource, ConstOperand, FakeReadCause, Local, LocalInfo, LocalKind, Location,
@@ -462,7 +462,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         // lifetimes without names with the value `'0`.
         if let ty::Ref(region, ..) = ty.kind() {
             match **region {
-                ty::ReLateBound(_, ty::BoundRegion { kind: br, .. })
+                ty::ReBound(_, ty::BoundRegion { kind: br, .. })
                 | ty::RePlaceholder(ty::PlaceholderRegion {
                     bound: ty::BoundRegion { kind: br, .. },
                     ..
@@ -482,7 +482,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 
         let region = if let ty::Ref(region, ..) = ty.kind() {
             match **region {
-                ty::ReLateBound(_, ty::BoundRegion { kind: br, .. })
+                ty::ReBound(_, ty::BoundRegion { kind: br, .. })
                 | ty::RePlaceholder(ty::PlaceholderRegion {
                     bound: ty::BoundRegion { kind: br, .. },
                     ..
@@ -1113,7 +1113,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                             && let ty::Ref(_, _, hir::Mutability::Mut) = args.type_at(0).kind()
                             && let self_ty = self.infcx.instantiate_binder_with_fresh_vars(
                                 fn_call_span,
-                                LateBoundRegionConversionTime::FnCall,
+                                BoundRegionConversionTime::FnCall,
                                 tcx.fn_sig(method_did).instantiate(tcx, method_args).input(0),
                             )
                             && self.infcx.can_eq(self.param_env, ty, self_ty)

compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -357,7 +357,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
                 ty::BoundRegionKind::BrAnon => None,
             },
 
-            ty::ReLateBound(..)
+            ty::ReBound(..)
             | ty::ReVar(..)
             | ty::RePlaceholder(..)
             | ty::ReErased

compiler/rustc_borrowck/src/renumber.rs

@@ -28,6 +28,9 @@ pub fn renumber_mir<'tcx>(
     renumberer.visit_body(body);
 }
 
+// FIXME(@lcnr): A lot of these variants overlap and it seems like
+// this type is only used to decide which region should be used
+// as representative. This should be cleaned up.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
 pub(crate) enum RegionCtxt {
     Location(Location),

compiler/rustc_borrowck/src/type_check/input_output.rs

@@ -7,7 +7,7 @@
 //! `RETURN_PLACE` the MIR arguments) are always fully normalized (and
 //! contain revealed `impl Trait` values).
 
-use rustc_infer::infer::LateBoundRegionConversionTime;
+use rustc_infer::infer::BoundRegionConversionTime;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, Ty};
 use rustc_span::Span;
@@ -35,7 +35,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             .instantiate_canonical_with_fresh_inference_vars(body.span, &user_provided_poly_sig);
         let user_provided_sig = self.infcx.instantiate_binder_with_fresh_vars(
             body.span,
-            LateBoundRegionConversionTime::FnCall,
+            BoundRegionConversionTime::FnCall,
             user_provided_sig,
         );
 

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -21,7 +21,7 @@ use rustc_infer::infer::outlives::env::RegionBoundPairs;
 use rustc_infer::infer::region_constraints::RegionConstraintData;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_infer::infer::{
-    InferCtxt, LateBoundRegion, LateBoundRegionConversionTime, NllRegionVariableOrigin,
+    BoundRegion, BoundRegionConversionTime, InferCtxt, NllRegionVariableOrigin,
 };
 use rustc_middle::mir::tcx::PlaceTy;
 use rustc_middle::mir::visit::{NonMutatingUseContext, PlaceContext, Visitor};
@@ -1401,10 +1401,10 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                     };
 
                     self.infcx.next_region_var(
-                        LateBoundRegion(
+                        BoundRegion(
                             term.source_info.span,
                             br.kind,
-                            LateBoundRegionConversionTime::FnCall,
+                            BoundRegionConversionTime::FnCall,
                         ),
                         region_ctxt_fn,
                     )

compiler/rustc_borrowck/src/type_check/relate_tys.rs

@@ -107,12 +107,12 @@ impl<'tcx> TypeRelatingDelegate<'tcx> for NllTypeRelatingDelegate<'_, '_, 'tcx>
     fn next_existential_region_var(
         &mut self,
         from_forall: bool,
-        _name: Option<Symbol>,
+        name: Option<Symbol>,
     ) -> ty::Region<'tcx> {
         let origin = NllRegionVariableOrigin::Existential { from_forall };
 
         let reg_var =
-            self.type_checker.infcx.next_nll_region_var(origin, || RegionCtxt::Existential(_name));
+            self.type_checker.infcx.next_nll_region_var(origin, || RegionCtxt::Existential(name));
 
         reg_var
     }

compiler/rustc_borrowck/src/universal_regions.rs

@@ -665,7 +665,7 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
                     var: ty::BoundVar::from_usize(bound_vars.len() - 1),
                     kind: ty::BrEnv,
                 };
-                let env_region = ty::Region::new_late_bound(tcx, ty::INNERMOST, br);
+                let env_region = ty::Region::new_bound(tcx, ty::INNERMOST, br);
                 let closure_ty = tcx.closure_env_ty(def_id, args, env_region).unwrap();
 
                 // The "inputs" of the closure in the

compiler/rustc_hir_analysis/src/astconv/bounds.rs

@@ -350,7 +350,7 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
             let args =
                 candidate.skip_binder().args.extend_to(tcx, assoc_item.def_id, |param, _| {
                     let subst = match param.kind {
-                        ty::GenericParamDefKind::Lifetime => ty::Region::new_late_bound(
+                        ty::GenericParamDefKind::Lifetime => ty::Region::new_bound(
                             tcx,
                             ty::INNERMOST,
                             ty::BoundRegion {

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -250,7 +250,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     var: ty::BoundVar::from_u32(index),
                     kind: ty::BrNamed(def_id, name),
                 };
-                ty::Region::new_late_bound(tcx, debruijn, br)
+                ty::Region::new_bound(tcx, debruijn, br)
             }
 
             Some(rbv::ResolvedArg::EarlyBound(def_id)) => {
@@ -1622,7 +1622,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 }
 
                 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-                    if r.is_late_bound() { self.tcx.lifetimes.re_erased } else { r }
+                    // FIXME(@lcnr): This is broken, erasing bound regions
+                    // impacts selection as it results in different types.
+                    if r.is_bound() { self.tcx.lifetimes.re_erased } else { r }
                 }
 
                 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -2345,7 +2345,7 @@ fn param_env_with_gat_bounds<'tcx>(
                     let kind = ty::BoundRegionKind::BrNamed(param.def_id, param.name);
                     let bound_var = ty::BoundVariableKind::Region(kind);
                     bound_vars.push(bound_var);
-                    ty::Region::new_late_bound(
+                    ty::Region::new_bound(
                         tcx,
                         ty::INNERMOST,
                         ty::BoundRegion {

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -143,12 +143,12 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
     ]);
     let mk_va_list_ty = |mutbl| {
         tcx.lang_items().va_list().map(|did| {
-            let region = ty::Region::new_late_bound(
+            let region = ty::Region::new_bound(
                 tcx,
                 ty::INNERMOST,
                 ty::BoundRegion { var: ty::BoundVar::from_u32(0), kind: ty::BrAnon },
             );
-            let env_region = ty::Region::new_late_bound(
+            let env_region = ty::Region::new_bound(
                 tcx,
                 ty::INNERMOST,
                 ty::BoundRegion { var: ty::BoundVar::from_u32(1), kind: ty::BrEnv },
@@ -411,7 +411,7 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
                     1,
                     vec![Ty::new_imm_ref(
                         tcx,
-                        ty::Region::new_late_bound(tcx, ty::INNERMOST, br),
+                        ty::Region::new_bound(tcx, ty::INNERMOST, br),
                         param(0),
                     )],
                     Ty::new_projection(tcx, discriminant_def_id, tcx.mk_args(&[param(0).into()])),
@@ -465,11 +465,8 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
 
             sym::raw_eq => {
                 let br = ty::BoundRegion { var: ty::BoundVar::from_u32(0), kind: ty::BrAnon };
-                let param_ty = Ty::new_imm_ref(
-                    tcx,
-                    ty::Region::new_late_bound(tcx, ty::INNERMOST, br),
-                    param(0),
-                );
+                let param_ty =
+                    Ty::new_imm_ref(tcx, ty::Region::new_bound(tcx, ty::INNERMOST, br), param(0));
                 (1, vec![param_ty; 2], tcx.types.bool)
             }
 

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -763,7 +763,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for GATSubstCollector<'tcx> {
             ty::Alias(ty::Projection, p) if p.def_id == self.gat => {
                 for (idx, subst) in p.args.iter().enumerate() {
                     match subst.unpack() {
-                        GenericArgKind::Lifetime(lt) if !lt.is_late_bound() => {
+                        GenericArgKind::Lifetime(lt) if !lt.is_bound() => {
                             self.regions.insert((lt, idx));
                         }
                         GenericArgKind::Type(t) => {

compiler/rustc_hir_analysis/src/hir_wf_check.rs

@@ -196,6 +196,7 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for EraseAllBoundRegions<'tcx> {
         self.tcx
     }
     fn fold_region(&mut self, r: Region<'tcx>) -> Region<'tcx> {
-        if r.is_late_bound() { self.tcx.lifetimes.re_erased } else { r }
+        // FIXME(@lcnr): only erase escaping bound regions!
+        if r.is_bound() { self.tcx.lifetimes.re_erased } else { r }
     }
 }

compiler/rustc_hir_analysis/src/outlives/utils.rs

@@ -167,8 +167,8 @@ fn is_free_region(region: Region<'_>) -> bool {
         //     }
         //
         // The type above might generate a `T: 'b` bound, but we can
-        // ignore it. We can't put it on the struct header anyway.
-        ty::ReLateBound(..) => false,
+        // ignore it. We can't name this lifetime pn the struct header anyway.
+        ty::ReBound(..) => false,
 
         ty::ReError(_) => false,
 

compiler/rustc_hir_analysis/src/variance/constraints.rs

@@ -419,9 +419,11 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
 
             ty::ReStatic => {}
 
-            ty::ReLateBound(..) => {
-                // Late-bound regions do not get substituted the same
-                // way early-bound regions do, so we skip them here.
+            ty::ReBound(..) => {
+                // Either a higher-ranked region inside of a type or a
+                // late-bound function parameter.
+                //
+                // We do not compute constraints for either of these.
             }
 
             ty::ReError(_) => {}

compiler/rustc_hir_typeck/src/check.rs

@@ -214,15 +214,15 @@ fn check_panic_info_fn(tcx: TyCtxt<'_>, fn_id: LocalDefId, fn_sig: ty::FnSig<'_>
     // build type `for<'a, 'b> fn(&'a PanicInfo<'b>) -> !`
     let panic_info_ty = tcx.type_of(panic_info_did).instantiate(
         tcx,
-        &[ty::GenericArg::from(ty::Region::new_late_bound(
+        &[ty::GenericArg::from(ty::Region::new_bound(
             tcx,
             ty::INNERMOST,
             ty::BoundRegion { var: ty::BoundVar::from_u32(1), kind: ty::BrAnon },
         ))],
     );
     let panic_info_ref_ty = Ty::new_imm_ref(
         tcx,
-        ty::Region::new_late_bound(
+        ty::Region::new_bound(
             tcx,
             ty::INNERMOST,
             ty::BoundRegion { var: ty::BoundVar::from_u32(0), kind: ty::BrAnon },

compiler/rustc_hir_typeck/src/closure.rs

@@ -7,7 +7,7 @@ use rustc_hir as hir;
 use rustc_hir::lang_items::LangItem;
 use rustc_hir_analysis::astconv::AstConv;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
-use rustc_infer::infer::{DefineOpaqueTypes, LateBoundRegionConversionTime};
+use rustc_infer::infer::{BoundRegionConversionTime, DefineOpaqueTypes};
 use rustc_infer::infer::{InferOk, InferResult};
 use rustc_macros::{TypeFoldable, TypeVisitable};
 use rustc_middle::ty::visit::{TypeVisitable, TypeVisitableExt};
@@ -558,7 +558,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // Instantiate (this part of..) S to S', i.e., with fresh variables.
                 self.instantiate_binder_with_fresh_vars(
                     hir_ty.span,
-                    LateBoundRegionConversionTime::FnCall,
+                    BoundRegionConversionTime::FnCall,
                     // (*) binder moved to here
                     supplied_sig.inputs().rebind(supplied_ty),
                 )
@@ -583,7 +583,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
             let supplied_output_ty = self.instantiate_binder_with_fresh_vars(
                 decl.output.span(),
-                LateBoundRegionConversionTime::FnCall,
+                BoundRegionConversionTime::FnCall,
                 supplied_sig.output(),
             );
             let cause = &self.misc(decl.output.span());

compiler/rustc_hir_typeck/src/expr.rs

@@ -564,7 +564,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     let span = args.get(i).map(|a| a.span).unwrap_or(expr.span);
                     let input = self.instantiate_binder_with_fresh_vars(
                         span,
-                        infer::LateBoundRegionConversionTime::FnCall,
+                        infer::BoundRegionConversionTime::FnCall,
                         fn_sig.input(i),
                     );
                     self.require_type_is_sized_deferred(
@@ -582,7 +582,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // with fresh vars.
             let output = self.instantiate_binder_with_fresh_vars(
                 expr.span,
-                infer::LateBoundRegionConversionTime::FnCall,
+                infer::BoundRegionConversionTime::FnCall,
                 fn_sig.output(),
             );
             self.require_type_is_sized_deferred(output, expr.span, traits::SizedReturnType);

compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs

@@ -289,7 +289,7 @@ impl<'a, 'tcx> AstConv<'tcx> for FnCtxt<'a, 'tcx> {
     ) -> Ty<'tcx> {
         let trait_ref = self.instantiate_binder_with_fresh_vars(
             span,
-            infer::LateBoundRegionConversionTime::AssocTypeProjection(item_def_id),
+            infer::BoundRegionConversionTime::AssocTypeProjection(item_def_id),
             poly_trait_ref,
         );
 

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -801,7 +801,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         // a `&self` method will wind up with an argument type like `&dyn Trait`.
         let trait_ref = principal.with_self_ty(self.tcx, self_ty);
         self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
-            if new_trait_ref.has_non_region_late_bound() {
+            if new_trait_ref.has_non_region_bound_vars() {
                 this.tcx.sess.delay_span_bug(
                     this.span,
                     "tried to select method from HRTB with non-lifetime bound vars",
@@ -853,7 +853,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
             let trait_ref = this.instantiate_binder_with_fresh_vars(
                 this.span,
-                infer::LateBoundRegionConversionTime::FnCall,
+                infer::BoundRegionConversionTime::FnCall,
                 poly_trait_ref,
             );
 
@@ -971,7 +971,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                     } else {
                         let new_trait_ref = self.instantiate_binder_with_fresh_vars(
                             self.span,
-                            infer::LateBoundRegionConversionTime::FnCall,
+                            infer::BoundRegionConversionTime::FnCall,
                             bound_trait_ref,
                         );
 

compiler/rustc_hir_typeck/src/writeback.rs

@@ -784,7 +784,7 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for EraseEarlyRegions<'tcx> {
         }
     }
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        if r.is_late_bound() { r } else { self.tcx.lifetimes.re_erased }
+        if r.is_bound() { r } else { self.tcx.lifetimes.re_erased }
     }
 }
 
@@ -822,7 +822,7 @@ impl<'cx, 'tcx> TypeFolder<TyCtxt<'tcx>> for Resolver<'cx, 'tcx> {
     }
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        debug_assert!(!r.is_late_bound(), "Should not be resolving bound region.");
+        debug_assert!(!r.is_bound(), "Should not be resolving bound region.");
         self.fcx.tcx.lifetimes.re_erased
     }
 

compiler/rustc_infer/src/errors/note_and_explain.rs

@@ -73,8 +73,11 @@ impl<'a> DescriptionCtx<'a> {
             // ReFree rather than dumping Debug output on the user.
             //
             // We shouldn't really be having unification failures with ReVar
-            // and ReLateBound though.
-            ty::ReVar(_) | ty::ReLateBound(..) | ty::ReErased => {
+            // and ReBound though.
+            //
+            // FIXME(@lcnr): figure out why we `ReBound` have to handle `ReBound`
+            // here, this feels somewhat off.
+            ty::ReVar(_) | ty::ReBound(..) | ty::ReErased => {
                 (alt_span, "revar", format!("{region:?}"))
             }
         };

compiler/rustc_infer/src/infer/canonical/canonicalizer.rs

@@ -232,7 +232,7 @@ impl CanonicalizeMode for CanonicalizeUserTypeAnnotation {
         match *r {
             ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReErased | ty::ReStatic | ty::ReError(_) => r,
             ty::ReVar(_) => canonicalizer.canonical_var_for_region_in_root_universe(r),
-            ty::RePlaceholder(..) | ty::ReLateBound(..) => {
+            ty::RePlaceholder(..) | ty::ReBound(..) => {
                 // We only expect region names that the user can type.
                 bug!("unexpected region in query response: `{:?}`", r)
             }
@@ -343,7 +343,7 @@ impl<'cx, 'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'cx, 'tcx> {
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
         match *r {
-            ty::ReLateBound(index, ..) => {
+            ty::ReBound(index, ..) => {
                 if index >= self.binder_index {
                     bug!("escaping late-bound region during canonicalization");
                 } else {
@@ -776,7 +776,7 @@ impl<'cx, 'tcx> Canonicalizer<'cx, 'tcx> {
     ) -> ty::Region<'tcx> {
         let var = self.canonical_var(info, r.into());
         let br = ty::BoundRegion { var, kind: ty::BrAnon };
-        ty::Region::new_late_bound(self.interner(), self.binder_index, br)
+        ty::Region::new_bound(self.interner(), self.binder_index, br)
     }
 
     /// Given a type variable `ty_var` of the given kind, first check