some additional region refactorings

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -1578,8 +1578,9 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             return;
         };
         let sig = args.as_closure().sig();
-        let tupled_params =
-            tcx.erase_late_bound_regions(sig.inputs().iter().next().unwrap().map_bound(|&b| b));
+        let tupled_params = tcx.instantiate_bound_regions_with_erased(
+            sig.inputs().iter().next().unwrap().map_bound(|&b| b),
+        );
         let ty::Tuple(params) = tupled_params.kind() else { return };
 
         // Find the first argument with a matching type, get its name

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1387,7 +1387,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                         return;
                     }
                 };
-                let (sig, map) = tcx.replace_late_bound_regions(sig, |br| {
+                let (sig, map) = tcx.instantiate_bound_regions(sig, |br| {
                     use crate::renumber::RegionCtxt;
 
                     let region_ctxt_fn = || {

compiler/rustc_borrowck/src/universal_regions.rs

@@ -738,13 +738,13 @@ trait InferCtxtExt<'tcx> {
     where
         T: TypeFoldable<TyCtxt<'tcx>>;
 
-    fn replace_late_bound_regions_with_nll_infer_vars_in_recursive_scope(
+    fn instantiate_bound_regions_with_nll_infer_vars_in_recursive_scope(
         &self,
         mir_def_id: LocalDefId,
         indices: &mut UniversalRegionIndices<'tcx>,
     );
 
-    fn replace_late_bound_regions_with_nll_infer_vars_in_item(
+    fn instantiate_bound_regions_with_nll_infer_vars_in_item(
         &self,
         mir_def_id: LocalDefId,
         indices: &mut UniversalRegionIndices<'tcx>,
@@ -780,7 +780,7 @@ impl<'cx, 'tcx> InferCtxtExt<'tcx> for BorrowckInferCtxt<'cx, 'tcx> {
     where
         T: TypeFoldable<TyCtxt<'tcx>>,
     {
-        let (value, _map) = self.tcx.replace_late_bound_regions(value, |br| {
+        let (value, _map) = self.tcx.instantiate_bound_regions(value, |br| {
             debug!(?br);
             let liberated_region =
                 ty::Region::new_late_param(self.tcx, all_outlive_scope.to_def_id(), br.kind);
@@ -810,7 +810,7 @@ impl<'cx, 'tcx> InferCtxtExt<'tcx> for BorrowckInferCtxt<'cx, 'tcx> {
     /// set of late-bound regions and checks for any that we have not yet seen, adding them to the
     /// inputs vector.
     #[instrument(skip(self, indices))]
-    fn replace_late_bound_regions_with_nll_infer_vars_in_recursive_scope(
+    fn instantiate_bound_regions_with_nll_infer_vars_in_recursive_scope(
         &self,
         mir_def_id: LocalDefId,
         indices: &mut UniversalRegionIndices<'tcx>,
@@ -830,7 +830,7 @@ impl<'cx, 'tcx> InferCtxtExt<'tcx> for BorrowckInferCtxt<'cx, 'tcx> {
     }
 
     #[instrument(skip(self, indices))]
-    fn replace_late_bound_regions_with_nll_infer_vars_in_item(
+    fn instantiate_bound_regions_with_nll_infer_vars_in_item(
         &self,
         mir_def_id: LocalDefId,
         indices: &mut UniversalRegionIndices<'tcx>,

compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs

@@ -249,7 +249,7 @@ fn push_debuginfo_type_name<'tcx>(
                     .projection_bounds()
                     .map(|bound| {
                         let ExistentialProjection { def_id: item_def_id, term, .. } =
-                            tcx.erase_late_bound_regions(bound);
+                            tcx.instantiate_bound_regions_with_erased(bound);
                         // FIXME(associated_const_equality): allow for consts here
                         (item_def_id, term.ty().unwrap())
                     })

compiler/rustc_const_eval/src/transform/promote_consts.rs

@@ -864,6 +864,7 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
             };
 
             // Use the underlying local for this (necessarily interior) borrow.
+            debug_assert!(region.is_erased());
             let ty = local_decls[place.local].ty;
             let span = statement.source_info.span;
 
@@ -873,8 +874,6 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
                 ty::TypeAndMut { ty, mutbl: borrow_kind.to_mutbl_lossy() },
             );
 
-            *region = tcx.lifetimes.re_erased;
-
             let mut projection = vec![PlaceElem::Deref];
             projection.extend(place.projection);
             place.projection = tcx.mk_place_elems(&projection);

compiler/rustc_hir_analysis/src/collect.rs

@@ -440,7 +440,7 @@ impl<'tcx> AstConv<'tcx> for ItemCtxt<'tcx> {
                                 second: format!(
                                     "{}::",
                                     // Replace the existing lifetimes with a new named lifetime.
-                                    self.tcx.replace_late_bound_regions_uncached(
+                                    self.tcx.instantiate_bound_regions_uncached(
                                         poly_trait_ref,
                                         |_| {
                                             ty::Region::new_early_param(self.tcx, ty::EarlyParamRegion {

compiler/rustc_hir_analysis/src/hir_wf_check.rs

@@ -5,7 +5,7 @@ use rustc_hir::{ForeignItem, ForeignItemKind};
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::traits::{ObligationCause, WellFormedLoc};
 use rustc_middle::query::Providers;
-use rustc_middle::ty::{self, Region, TyCtxt, TypeFoldable, TypeFolder};
+use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::def_id::LocalDefId;
 use rustc_trait_selection::traits::{self, ObligationCtxt};
 
@@ -68,7 +68,13 @@ fn diagnostic_hir_wf_check<'tcx>(
             let infcx = self.tcx.infer_ctxt().build();
             let ocx = ObligationCtxt::new(&infcx);
 
-            let tcx_ty = self.icx.to_ty(ty).fold_with(&mut EraseAllBoundRegions { tcx: self.tcx });
+            let tcx_ty = self.icx.to_ty(ty);
+            // This visitor can walk into binders, resulting in the `tcx_ty` to
+            // potentially reference escaping bound variables. We simply erase
+            // those here.
+            let tcx_ty = self.tcx.fold_regions(tcx_ty, |r, _| {
+                if r.is_bound() { self.tcx.lifetimes.re_erased } else { r }
+            });
             let cause = traits::ObligationCause::new(
                 ty.span,
                 self.def_id,
@@ -178,25 +184,3 @@ fn diagnostic_hir_wf_check<'tcx>(
     }
     visitor.cause
 }
-
-struct EraseAllBoundRegions<'tcx> {
-    tcx: TyCtxt<'tcx>,
-}
-
-// Higher ranked regions are complicated.
-// To make matters worse, the HIR WF check can instantiate them
-// outside of a `Binder`, due to the way we (ab)use
-// `ItemCtxt::to_ty`. To make things simpler, we just erase all
-// of them, regardless of depth. At worse, this will give
-// us an inaccurate span for an error message, but cannot
-// lead to unsoundness (we call `delay_span_bug` at the start
-// of `diagnostic_hir_wf_check`).
-impl<'tcx> TypeFolder<TyCtxt<'tcx>> for EraseAllBoundRegions<'tcx> {
-    fn interner(&self) -> TyCtxt<'tcx> {
-        self.tcx
-    }
-    fn fold_region(&mut self, r: Region<'tcx>) -> Region<'tcx> {
-        // FIXME(@lcnr): only erase escaping bound regions!
-        if r.is_bound() { self.tcx.lifetimes.re_erased } else { r }
-    }
-}

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -846,7 +846,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     let bound_vars = self.tcx.late_bound_vars(hir_ty.hir_id.owner.into());
                     let ty = Binder::bind_with_vars(ty, bound_vars);
                     let ty = self.normalize(hir_ty.span, ty);
-                    let ty = self.tcx.erase_late_bound_regions(ty);
+                    let ty = self.tcx.instantiate_bound_regions_with_erased(ty);
                     if self.can_coerce(expected, ty) {
                         err.subdiagnostic(errors::ExpectedReturnTypeLabel::Other {
                             span: hir_ty.span,
@@ -1023,7 +1023,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         if let hir::FnRetTy::Return(ty) = fn_decl.output {
             let ty = self.astconv().ast_ty_to_ty(ty);
             let bound_vars = self.tcx.late_bound_vars(fn_id);
-            let ty = self.tcx.erase_late_bound_regions(Binder::bind_with_vars(ty, bound_vars));
+            let ty = self
+                .tcx
+                .instantiate_bound_regions_with_erased(Binder::bind_with_vars(ty, bound_vars));
             let ty = match self.tcx.asyncness(fn_id.owner) {
                 ty::Asyncness::Yes => self.get_impl_future_output_ty(ty).unwrap_or_else(|| {
                     span_bug!(fn_decl.output.span(), "failed to get output type of async function")

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -809,7 +809,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 return;
             }
 
-            let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
+            let new_trait_ref = this.instantiate_bound_regions_with_erased(new_trait_ref);
 
             let (xform_self_ty, xform_ret_ty) =
                 this.xform_self_ty(item, new_trait_ref.self_ty(), new_trait_ref.args);
@@ -1885,7 +1885,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
             fn_sig.instantiate(self.tcx, args)
         };
 
-        self.erase_late_bound_regions(xform_fn_sig)
+        self.instantiate_bound_regions_with_erased(xform_fn_sig)
     }
 
     /// Gets the type of an impl and generate substitutions with inference vars.
@@ -1897,7 +1897,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
     }
 
     /// Replaces late-bound-regions bound by `value` with `'static` using
-    /// `ty::erase_late_bound_regions`.
+    /// `ty::instantiate_bound_regions_with_erased`.
     ///
     /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
     /// method matching. It is reasonable during the probe phase because we don't consider region
@@ -1914,11 +1914,11 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
     ///    region got replaced with the same variable, which requires a bit more coordination
     ///    and/or tracking the substitution and
     ///    so forth.
-    fn erase_late_bound_regions<T>(&self, value: ty::Binder<'tcx, T>) -> T
+    fn instantiate_bound_regions_with_erased<T>(&self, value: ty::Binder<'tcx, T>) -> T
     where
         T: TypeFoldable<TyCtxt<'tcx>>,
     {
-        self.tcx.erase_late_bound_regions(value)
+        self.tcx.instantiate_bound_regions_with_erased(value)
     }
 
     /// Determine if the given associated item type is relevant in the current context.

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -1454,7 +1454,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             .filter_map(|item| {
                 // Only assoc fns that return `Self`, `Option<Self>` or `Result<Self, _>`.
                 let ret_ty = self.tcx.fn_sig(item.def_id).skip_binder().output();
-                let ret_ty = self.tcx.erase_late_bound_regions(ret_ty);
+                let ret_ty = self.tcx.instantiate_bound_regions_with_erased(ret_ty);
                 let ty::Adt(def, args) = ret_ty.kind() else {
                     return None;
                 };

compiler/rustc_hir_typeck/src/writeback.rs

@@ -9,7 +9,7 @@ use rustc_hir as hir;
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_infer::infer::error_reporting::TypeAnnotationNeeded::E0282;
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, PointerCoercion};
-use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
+use rustc_middle::ty::fold::{TypeFoldable, TypeFolder};
 use rustc_middle::ty::visit::TypeVisitableExt;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::symbol::sym;
@@ -768,49 +768,30 @@ impl<'cx, 'tcx> Resolver<'cx, 'tcx> {
     }
 }
 
-struct EraseEarlyRegions<'tcx> {
-    tcx: TyCtxt<'tcx>,
-}
-
-impl<'tcx> TypeFolder<TyCtxt<'tcx>> for EraseEarlyRegions<'tcx> {
-    fn interner(&self) -> TyCtxt<'tcx> {
-        self.tcx
-    }
-    fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
-        if ty.has_type_flags(ty::TypeFlags::HAS_FREE_REGIONS) {
-            ty.super_fold_with(self)
-        } else {
-            ty
-        }
-    }
-    fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        if r.is_bound() { r } else { self.tcx.lifetimes.re_erased }
-    }
-}
-
 impl<'cx, 'tcx> TypeFolder<TyCtxt<'tcx>> for Resolver<'cx, 'tcx> {
     fn interner(&self) -> TyCtxt<'tcx> {
         self.fcx.tcx
     }
 
     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
+        let tcx = self.fcx.tcx;
         match self.fcx.fully_resolve(t) {
             Ok(t) if self.fcx.next_trait_solver() => {
                 // We must normalize erasing regions here, since later lints
                 // expect that types that show up in the typeck are fully
                 // normalized.
-                if let Ok(t) = self.fcx.tcx.try_normalize_erasing_regions(self.fcx.param_env, t) {
+                if let Ok(t) = tcx.try_normalize_erasing_regions(self.fcx.param_env, t) {
                     t
                 } else {
-                    EraseEarlyRegions { tcx: self.fcx.tcx }.fold_ty(t)
+                    tcx.fold_regions(t, |_, _| tcx.lifetimes.re_erased)
                 }
             }
             Ok(t) => {
                 // Do not anonymize late-bound regions
                 // (e.g. keep `for<'a>` named `for<'a>`).
                 // This allows NLL to generate error messages that
                 // refer to the higher-ranked lifetime names written by the user.
-                EraseEarlyRegions { tcx: self.fcx.tcx }.fold_ty(t)
+                tcx.fold_regions(t, |_, _| tcx.lifetimes.re_erased)
             }
             Err(_) => {
                 debug!("Resolver::fold_ty: input type `{:?}` not fully resolvable", t);

compiler/rustc_infer/src/errors/note_and_explain.rs

@@ -75,7 +75,7 @@ impl<'a> DescriptionCtx<'a> {
             // We shouldn't really be having unification failures with ReVar
             // and ReBound though.
             //
-            // FIXME(@lcnr): figure out why we `ReBound` have to handle `ReBound`
+            // FIXME(@lcnr): figure out why we have to handle `ReBound`
             // here, this feels somewhat off.
             ty::ReVar(_) | ty::ReBound(..) | ty::ReErased => {
                 (alt_span, "revar", format!("{region:?}"))

compiler/rustc_lint/src/foreign_modules.rs

@@ -341,8 +341,8 @@ fn structurally_same_type_impl<'tcx>(
 
                     // We don't compare regions, but leaving bound regions around ICEs, so
                     // we erase them.
-                    let a_sig = tcx.erase_late_bound_regions(a_poly_sig);
-                    let b_sig = tcx.erase_late_bound_regions(b_poly_sig);
+                    let a_sig = tcx.instantiate_bound_regions_with_erased(a_poly_sig);
+                    let b_sig = tcx.instantiate_bound_regions_with_erased(b_poly_sig);
 
                     (a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
                         == (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)

compiler/rustc_lint/src/types.rs

@@ -1234,7 +1234,7 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
                     };
                 }
 
-                let sig = tcx.erase_late_bound_regions(sig);
+                let sig = tcx.instantiate_bound_regions_with_erased(sig);
                 for arg in sig.inputs() {
                     match self.check_type_for_ffi(cache, *arg) {
                         FfiSafe => {}
@@ -1391,7 +1391,7 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
     /// types that have external ABIs, as these still need checked.
     fn check_fn(&mut self, def_id: LocalDefId, decl: &'tcx hir::FnDecl<'_>) {
         let sig = self.cx.tcx.fn_sig(def_id).instantiate_identity();
-        let sig = self.cx.tcx.erase_late_bound_regions(sig);
+        let sig = self.cx.tcx.instantiate_bound_regions_with_erased(sig);
 
         for (input_ty, input_hir) in iter::zip(sig.inputs(), decl.inputs) {
             for (fn_ptr_ty, span) in self.find_fn_ptr_ty_with_external_abi(input_hir, *input_ty) {
@@ -1409,7 +1409,7 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
     /// Check if a function's argument types and result type are "ffi-safe".
     fn check_foreign_fn(&mut self, def_id: LocalDefId, decl: &'tcx hir::FnDecl<'_>) {
         let sig = self.cx.tcx.fn_sig(def_id).instantiate_identity();
-        let sig = self.cx.tcx.erase_late_bound_regions(sig);
+        let sig = self.cx.tcx.instantiate_bound_regions_with_erased(sig);
 
         for (input_ty, input_hir) in iter::zip(sig.inputs(), decl.inputs) {
             self.check_type_for_ffi_and_report_errors(input_hir.span, *input_ty, false, false);

compiler/rustc_metadata/src/native_libs.rs

@@ -470,7 +470,7 @@ impl<'tcx> Collector<'tcx> {
     }
 
     fn i686_arg_list_size(&self, item: DefId) -> usize {
-        let argument_types: &List<Ty<'_>> = self.tcx.erase_late_bound_regions(
+        let argument_types: &List<Ty<'_>> = self.tcx.instantiate_bound_regions_with_erased(
             self.tcx
                 .type_of(item)
                 .instantiate_identity()

compiler/rustc_middle/src/ty/fold.rs

@@ -250,7 +250,7 @@ impl<'tcx> TyCtxt<'tcx> {
     ///
     /// This method only replaces late bound regions. Any types or
     /// constants bound by `value` will cause an ICE.
-    pub fn replace_late_bound_regions<T, F>(
+    pub fn instantiate_bound_regions<T, F>(
         self,
         value: Binder<'tcx, T>,
         mut fld_r: F,
@@ -261,11 +261,11 @@ impl<'tcx> TyCtxt<'tcx> {
     {
         let mut region_map = BTreeMap::new();
         let real_fld_r = |br: ty::BoundRegion| *region_map.entry(br).or_insert_with(|| fld_r(br));
-        let value = self.replace_late_bound_regions_uncached(value, real_fld_r);
+        let value = self.instantiate_bound_regions_uncached(value, real_fld_r);
         (value, region_map)
     }
 
-    pub fn replace_late_bound_regions_uncached<T, F>(
+    pub fn instantiate_bound_regions_uncached<T, F>(
         self,
         value: Binder<'tcx, T>,
         mut replace_regions: F,
@@ -325,7 +325,7 @@ impl<'tcx> TyCtxt<'tcx> {
     where
         T: TypeFoldable<TyCtxt<'tcx>>,
     {
-        self.replace_late_bound_regions_uncached(value, |br| {
+        self.instantiate_bound_regions_uncached(value, |br| {
             ty::Region::new_late_param(self, all_outlive_scope, br.kind)
         })
     }
@@ -361,11 +361,11 @@ impl<'tcx> TyCtxt<'tcx> {
 
     /// Replaces any late-bound regions bound in `value` with `'erased`. Useful in codegen but also
     /// method lookup and a few other places where precise region relationships are not required.
-    pub fn erase_late_bound_regions<T>(self, value: Binder<'tcx, T>) -> T
+    pub fn instantiate_bound_regions_with_erased<T>(self, value: Binder<'tcx, T>) -> T
     where
         T: TypeFoldable<TyCtxt<'tcx>>,
     {
-        self.replace_late_bound_regions(value, |_| self.lifetimes.re_erased).0
+        self.instantiate_bound_regions(value, |_| self.lifetimes.re_erased).0
     }
 
     /// Anonymize all bound variables in `value`, this is mostly used to improve caching.