Auto merge of rust-lang#117944 - lcnr:region-refactor-uwu, r=BoxyUwU

some additional region refactorings

the commits are selfcontained ✨

r? `@BoxyUwU`

Author: bors

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;
                 };