diff --git a/compiler/rustc_borrowck/src/region_infer/mod.rs b/compiler/rustc_borrowck/src/region_infer/mod.rs index d0e0203bf8c44..ea3602e8a056a 100644 --- a/compiler/rustc_borrowck/src/region_infer/mod.rs +++ b/compiler/rustc_borrowck/src/region_infer/mod.rs @@ -495,8 +495,7 @@ impl<'tcx> RegionInferenceContext<'tcx> { } } - NllRegionVariableOrigin::RootEmptyRegion - | NllRegionVariableOrigin::Existential { .. } => { + NllRegionVariableOrigin::Existential { .. } => { // For existential, regions, nothing to do. } } @@ -1410,8 +1409,7 @@ impl<'tcx> RegionInferenceContext<'tcx> { self.check_bound_universal_region(fr, placeholder, errors_buffer); } - NllRegionVariableOrigin::RootEmptyRegion - | NllRegionVariableOrigin::Existential { .. } => { + NllRegionVariableOrigin::Existential { .. } => { // nothing to check here } } @@ -1513,8 +1511,7 @@ impl<'tcx> RegionInferenceContext<'tcx> { self.check_bound_universal_region(fr, placeholder, errors_buffer); } - NllRegionVariableOrigin::RootEmptyRegion - | NllRegionVariableOrigin::Existential { .. } => { + NllRegionVariableOrigin::Existential { .. } => { // nothing to check here } } @@ -1788,9 +1785,9 @@ impl<'tcx> RegionInferenceContext<'tcx> { universe1.cannot_name(placeholder.universe) } - NllRegionVariableOrigin::RootEmptyRegion - | NllRegionVariableOrigin::FreeRegion - | NllRegionVariableOrigin::Existential { .. } => false, + NllRegionVariableOrigin::FreeRegion | NllRegionVariableOrigin::Existential { .. } => { + false + } } } @@ -2152,8 +2149,7 @@ impl<'tcx> RegionInferenceContext<'tcx> { let blame_source = match from_region_origin { NllRegionVariableOrigin::FreeRegion | NllRegionVariableOrigin::Existential { from_forall: false } => true, - NllRegionVariableOrigin::RootEmptyRegion - | NllRegionVariableOrigin::Placeholder(_) + NllRegionVariableOrigin::Placeholder(_) | NllRegionVariableOrigin::Existential { from_forall: true } => false, }; diff --git a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs index d129e8454265b..7c1fa28b8dfcc 100644 --- a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs +++ b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs @@ -1,11 +1,20 @@ +use rustc_data_structures::fx::FxHashMap; use rustc_data_structures::vec_map::VecMap; use rustc_hir::def_id::DefId; use rustc_hir::OpaqueTyOrigin; +use rustc_infer::infer::error_reporting::unexpected_hidden_region_diagnostic; use rustc_infer::infer::InferCtxt; +use rustc_infer::infer::TyCtxtInferExt as _; +use rustc_infer::traits::{Obligation, ObligationCause, TraitEngine}; +use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable}; +use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts}; +use rustc_middle::ty::visit::TypeVisitable; use rustc_middle::ty::{ - self, OpaqueHiddenType, OpaqueTypeKey, TyCtxt, TypeFoldable, TypeVisitable, + self, OpaqueHiddenType, OpaqueTypeKey, ToPredicate, Ty, TyCtxt, TypeFoldable, }; -use rustc_trait_selection::opaque_types::InferCtxtExt; +use rustc_span::Span; +use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _; +use rustc_trait_selection::traits::TraitEngineExt as _; use super::RegionInferenceContext; @@ -173,3 +182,474 @@ impl<'tcx> RegionInferenceContext<'tcx> { }) } } + +pub trait InferCtxtExt<'tcx> { + fn infer_opaque_definition_from_instantiation( + &self, + opaque_type_key: OpaqueTypeKey<'tcx>, + instantiated_ty: OpaqueHiddenType<'tcx>, + origin: OpaqueTyOrigin, + ) -> Ty<'tcx>; +} + +impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> { + /// Given the fully resolved, instantiated type for an opaque + /// type, i.e., the value of an inference variable like C1 or C2 + /// (*), computes the "definition type" for an opaque type + /// definition -- that is, the inferred value of `Foo1<'x>` or + /// `Foo2<'x>` that we would conceptually use in its definition: + /// ```ignore (illustrative) + /// type Foo1<'x> = impl Bar<'x> = AAA; // <-- this type AAA + /// type Foo2<'x> = impl Bar<'x> = BBB; // <-- or this type BBB + /// fn foo<'a, 'b>(..) -> (Foo1<'a>, Foo2<'b>) { .. } + /// ``` + /// Note that these values are defined in terms of a distinct set of + /// generic parameters (`'x` instead of `'a`) from C1 or C2. The main + /// purpose of this function is to do that translation. + /// + /// (*) C1 and C2 were introduced in the comments on + /// `register_member_constraints`. Read that comment for more context. + /// + /// # Parameters + /// + /// - `def_id`, the `impl Trait` type + /// - `substs`, the substs used to instantiate this opaque type + /// - `instantiated_ty`, the inferred type C1 -- fully resolved, lifted version of + /// `opaque_defn.concrete_ty` + #[instrument(level = "debug", skip(self))] + fn infer_opaque_definition_from_instantiation( + &self, + opaque_type_key: OpaqueTypeKey<'tcx>, + instantiated_ty: OpaqueHiddenType<'tcx>, + origin: OpaqueTyOrigin, + ) -> Ty<'tcx> { + if self.is_tainted_by_errors() { + return self.tcx.ty_error(); + } + + let OpaqueTypeKey { def_id, substs } = opaque_type_key; + + // Use substs to build up a reverse map from regions to their + // identity mappings. This is necessary because of `impl + // Trait` lifetimes are computed by replacing existing + // lifetimes with 'static and remapping only those used in the + // `impl Trait` return type, resulting in the parameters + // shifting. + let id_substs = InternalSubsts::identity_for_item(self.tcx, def_id); + debug!(?id_substs); + let map: FxHashMap, GenericArg<'tcx>> = + substs.iter().enumerate().map(|(index, subst)| (subst, id_substs[index])).collect(); + debug!("map = {:#?}", map); + + // Convert the type from the function into a type valid outside + // the function, by replacing invalid regions with 'static, + // after producing an error for each of them. + let definition_ty = instantiated_ty.ty.fold_with(&mut ReverseMapper::new( + self.tcx, + def_id, + map, + instantiated_ty.ty, + instantiated_ty.span, + )); + debug!(?definition_ty); + + if !check_opaque_type_parameter_valid( + self.tcx, + opaque_type_key, + origin, + instantiated_ty.span, + ) { + return self.tcx.ty_error(); + } + + // Only check this for TAIT. RPIT already supports `src/test/ui/impl-trait/nested-return-type2.rs` + // on stable and we'd break that. + if let OpaqueTyOrigin::TyAlias = origin { + // This logic duplicates most of `check_opaque_meets_bounds`. + // FIXME(oli-obk): Also do region checks here and then consider removing `check_opaque_meets_bounds` entirely. + let param_env = self.tcx.param_env(def_id); + let body_id = self.tcx.local_def_id_to_hir_id(def_id.as_local().unwrap()); + self.tcx.infer_ctxt().enter(move |infcx| { + // Require the hidden type to be well-formed with only the generics of the opaque type. + // Defining use functions may have more bounds than the opaque type, which is ok, as long as the + // hidden type is well formed even without those bounds. + let predicate = + ty::Binder::dummy(ty::PredicateKind::WellFormed(definition_ty.into())) + .to_predicate(infcx.tcx); + let mut fulfillment_cx = >::new(infcx.tcx); + + // Require that the hidden type actually fulfills all the bounds of the opaque type, even without + // the bounds that the function supplies. + match infcx.register_hidden_type( + OpaqueTypeKey { def_id, substs: id_substs }, + ObligationCause::misc(instantiated_ty.span, body_id), + param_env, + definition_ty, + origin, + ) { + Ok(infer_ok) => { + for obligation in infer_ok.obligations { + fulfillment_cx.register_predicate_obligation(&infcx, obligation); + } + } + Err(err) => { + infcx + .report_mismatched_types( + &ObligationCause::misc(instantiated_ty.span, body_id), + self.tcx.mk_opaque(def_id, id_substs), + definition_ty, + err, + ) + .emit(); + } + } + + fulfillment_cx.register_predicate_obligation( + &infcx, + Obligation::misc(instantiated_ty.span, body_id, param_env, predicate), + ); + + // Check that all obligations are satisfied by the implementation's + // version. + let errors = fulfillment_cx.select_all_or_error(&infcx); + + let _ = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types(); + + if errors.is_empty() { + definition_ty + } else { + infcx.report_fulfillment_errors(&errors, None, false); + self.tcx.ty_error() + } + }) + } else { + definition_ty + } + } +} + +fn check_opaque_type_parameter_valid( + tcx: TyCtxt<'_>, + opaque_type_key: OpaqueTypeKey<'_>, + origin: OpaqueTyOrigin, + span: Span, +) -> bool { + match origin { + // No need to check return position impl trait (RPIT) + // because for type and const parameters they are correct + // by construction: we convert + // + // fn foo() -> impl Trait + // + // into + // + // type Foo + // fn foo() -> Foo. + // + // For lifetime parameters we convert + // + // fn foo<'l0..'ln>() -> impl Trait<'l0..'lm> + // + // into + // + // type foo::<'p0..'pn>::Foo<'q0..'qm> + // fn foo() -> foo::<'static..'static>::Foo<'l0..'lm>. + // + // which would error here on all of the `'static` args. + OpaqueTyOrigin::FnReturn(..) | OpaqueTyOrigin::AsyncFn(..) => return true, + // Check these + OpaqueTyOrigin::TyAlias => {} + } + let opaque_generics = tcx.generics_of(opaque_type_key.def_id); + let mut seen_params: FxHashMap<_, Vec<_>> = FxHashMap::default(); + for (i, arg) in opaque_type_key.substs.iter().enumerate() { + let arg_is_param = match arg.unpack() { + GenericArgKind::Type(ty) => matches!(ty.kind(), ty::Param(_)), + GenericArgKind::Lifetime(lt) if lt.is_static() => { + tcx.sess + .struct_span_err(span, "non-defining opaque type use in defining scope") + .span_label( + tcx.def_span(opaque_generics.param_at(i, tcx).def_id), + "cannot use static lifetime; use a bound lifetime \ + instead or remove the lifetime parameter from the \ + opaque type", + ) + .emit(); + return false; + } + GenericArgKind::Lifetime(lt) => { + matches!(*lt, ty::ReEarlyBound(_) | ty::ReFree(_)) + } + GenericArgKind::Const(ct) => matches!(ct.kind(), ty::ConstKind::Param(_)), + }; + + if arg_is_param { + seen_params.entry(arg).or_default().push(i); + } else { + // Prevent `fn foo() -> Foo` from being defining. + let opaque_param = opaque_generics.param_at(i, tcx); + tcx.sess + .struct_span_err(span, "non-defining opaque type use in defining scope") + .span_note( + tcx.def_span(opaque_param.def_id), + &format!( + "used non-generic {} `{}` for generic parameter", + opaque_param.kind.descr(), + arg, + ), + ) + .emit(); + return false; + } + } + + for (_, indices) in seen_params { + if indices.len() > 1 { + let descr = opaque_generics.param_at(indices[0], tcx).kind.descr(); + let spans: Vec<_> = indices + .into_iter() + .map(|i| tcx.def_span(opaque_generics.param_at(i, tcx).def_id)) + .collect(); + tcx.sess + .struct_span_err(span, "non-defining opaque type use in defining scope") + .span_note(spans, &format!("{} used multiple times", descr)) + .emit(); + return false; + } + } + true +} + +struct ReverseMapper<'tcx> { + tcx: TyCtxt<'tcx>, + + opaque_type_def_id: DefId, + map: FxHashMap, GenericArg<'tcx>>, + map_missing_regions_to_empty: bool, + + /// initially `Some`, set to `None` once error has been reported + hidden_ty: Option>, + + /// Span of function being checked. + span: Span, +} + +impl<'tcx> ReverseMapper<'tcx> { + fn new( + tcx: TyCtxt<'tcx>, + opaque_type_def_id: DefId, + map: FxHashMap, GenericArg<'tcx>>, + hidden_ty: Ty<'tcx>, + span: Span, + ) -> Self { + Self { + tcx, + opaque_type_def_id, + map, + map_missing_regions_to_empty: false, + hidden_ty: Some(hidden_ty), + span, + } + } + + fn fold_kind_mapping_missing_regions_to_empty( + &mut self, + kind: GenericArg<'tcx>, + ) -> GenericArg<'tcx> { + assert!(!self.map_missing_regions_to_empty); + self.map_missing_regions_to_empty = true; + let kind = kind.fold_with(self); + self.map_missing_regions_to_empty = false; + kind + } + + fn fold_kind_normally(&mut self, kind: GenericArg<'tcx>) -> GenericArg<'tcx> { + assert!(!self.map_missing_regions_to_empty); + kind.fold_with(self) + } +} + +impl<'tcx> TypeFolder<'tcx> for ReverseMapper<'tcx> { + fn tcx(&self) -> TyCtxt<'tcx> { + self.tcx + } + + #[instrument(skip(self), level = "debug")] + fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> { + match *r { + // Ignore bound regions and `'static` regions that appear in the + // type, we only need to remap regions that reference lifetimes + // from the function declaration. + // This would ignore `'r` in a type like `for<'r> fn(&'r u32)`. + ty::ReLateBound(..) | ty::ReStatic => return r, + + // If regions have been erased (by writeback), don't try to unerase + // them. + ty::ReErased => return r, + + // The regions that we expect from borrow checking. + ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReEmpty(ty::UniverseIndex::ROOT) => {} + + ty::ReEmpty(_) | ty::RePlaceholder(_) | ty::ReVar(_) => { + // All of the regions in the type should either have been + // erased by writeback, or mapped back to named regions by + // borrow checking. + bug!("unexpected region kind in opaque type: {:?}", r); + } + } + + let generics = self.tcx().generics_of(self.opaque_type_def_id); + match self.map.get(&r.into()).map(|k| k.unpack()) { + Some(GenericArgKind::Lifetime(r1)) => r1, + Some(u) => panic!("region mapped to unexpected kind: {:?}", u), + None if self.map_missing_regions_to_empty => self.tcx.lifetimes.re_root_empty, + None if generics.parent.is_some() => { + if let Some(hidden_ty) = self.hidden_ty.take() { + unexpected_hidden_region_diagnostic( + self.tcx, + self.tcx.def_span(self.opaque_type_def_id), + hidden_ty, + r, + ) + .emit(); + } + self.tcx.lifetimes.re_root_empty + } + None => { + self.tcx + .sess + .struct_span_err(self.span, "non-defining opaque type use in defining scope") + .span_label( + self.span, + format!( + "lifetime `{}` is part of concrete type but not used in \ + parameter list of the `impl Trait` type alias", + r + ), + ) + .emit(); + + self.tcx().lifetimes.re_static + } + } + } + + fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> { + match *ty.kind() { + ty::Closure(def_id, substs) => { + // I am a horrible monster and I pray for death. When + // we encounter a closure here, it is always a closure + // from within the function that we are currently + // type-checking -- one that is now being encapsulated + // in an opaque type. Ideally, we would + // go through the types/lifetimes that it references + // and treat them just like we would any other type, + // which means we would error out if we find any + // reference to a type/region that is not in the + // "reverse map". + // + // **However,** in the case of closures, there is a + // somewhat subtle (read: hacky) consideration. The + // problem is that our closure types currently include + // all the lifetime parameters declared on the + // enclosing function, even if they are unused by the + // closure itself. We can't readily filter them out, + // so here we replace those values with `'empty`. This + // can't really make a difference to the rest of the + // compiler; those regions are ignored for the + // outlives relation, and hence don't affect trait + // selection or auto traits, and they are erased + // during codegen. + + let generics = self.tcx.generics_of(def_id); + let substs = self.tcx.mk_substs(substs.iter().enumerate().map(|(index, kind)| { + if index < generics.parent_count { + // Accommodate missing regions in the parent kinds... + self.fold_kind_mapping_missing_regions_to_empty(kind) + } else { + // ...but not elsewhere. + self.fold_kind_normally(kind) + } + })); + + self.tcx.mk_closure(def_id, substs) + } + + ty::Generator(def_id, substs, movability) => { + let generics = self.tcx.generics_of(def_id); + let substs = self.tcx.mk_substs(substs.iter().enumerate().map(|(index, kind)| { + if index < generics.parent_count { + // Accommodate missing regions in the parent kinds... + self.fold_kind_mapping_missing_regions_to_empty(kind) + } else { + // ...but not elsewhere. + self.fold_kind_normally(kind) + } + })); + + self.tcx.mk_generator(def_id, substs, movability) + } + + ty::Param(param) => { + // Look it up in the substitution list. + match self.map.get(&ty.into()).map(|k| k.unpack()) { + // Found it in the substitution list; replace with the parameter from the + // opaque type. + Some(GenericArgKind::Type(t1)) => t1, + Some(u) => panic!("type mapped to unexpected kind: {:?}", u), + None => { + debug!(?param, ?self.map); + self.tcx + .sess + .struct_span_err( + self.span, + &format!( + "type parameter `{}` is part of concrete type but not \ + used in parameter list for the `impl Trait` type alias", + ty + ), + ) + .emit(); + + self.tcx().ty_error() + } + } + } + + _ => ty.super_fold_with(self), + } + } + + fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> { + trace!("checking const {:?}", ct); + // Find a const parameter + match ct.kind() { + ty::ConstKind::Param(..) => { + // Look it up in the substitution list. + match self.map.get(&ct.into()).map(|k| k.unpack()) { + // Found it in the substitution list, replace with the parameter from the + // opaque type. + Some(GenericArgKind::Const(c1)) => c1, + Some(u) => panic!("const mapped to unexpected kind: {:?}", u), + None => { + self.tcx + .sess + .struct_span_err( + self.span, + &format!( + "const parameter `{}` is part of concrete type but not \ + used in parameter list for the `impl Trait` type alias", + ct + ), + ) + .emit(); + + self.tcx().const_error(ct.ty()) + } + } + } + + _ => ct, + } + } +} diff --git a/compiler/rustc_borrowck/src/universal_regions.rs b/compiler/rustc_borrowck/src/universal_regions.rs index 89d84fcf09cfe..2a7713bc4df3b 100644 --- a/compiler/rustc_borrowck/src/universal_regions.rs +++ b/compiler/rustc_borrowck/src/universal_regions.rs @@ -503,7 +503,7 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> { let root_empty = self .infcx - .next_nll_region_var(NllRegionVariableOrigin::RootEmptyRegion) + .next_nll_region_var(NllRegionVariableOrigin::Existential { from_forall: true }) .to_region_vid(); UniversalRegions { diff --git a/compiler/rustc_infer/src/infer/free_regions.rs b/compiler/rustc_infer/src/infer/free_regions.rs index fad949a3bc6a1..d566634a49203 100644 --- a/compiler/rustc_infer/src/infer/free_regions.rs +++ b/compiler/rustc_infer/src/infer/free_regions.rs @@ -4,7 +4,7 @@ //! and use that to decide when one free region outlives another, and so forth. use rustc_data_structures::transitive_relation::TransitiveRelation; -use rustc_middle::ty::{self, Lift, Region, TyCtxt}; +use rustc_middle::ty::{Lift, Region, TyCtxt}; /// Combines a `FreeRegionMap` and a `TyCtxt`. /// @@ -49,7 +49,7 @@ impl<'tcx> FreeRegionMap<'tcx> { // (with the exception that `'static: 'x` is not notable) pub fn relate_regions(&mut self, sub: Region<'tcx>, sup: Region<'tcx>) { debug!("relate_regions(sub={:?}, sup={:?})", sub, sup); - if self.is_free_or_static(sub) && self.is_free(sup) { + if sub.is_free_or_static() && sup.is_free() { self.relation.add(sub, sup) } } @@ -68,7 +68,7 @@ impl<'tcx> FreeRegionMap<'tcx> { r_a: Region<'tcx>, r_b: Region<'tcx>, ) -> bool { - assert!(self.is_free_or_static(r_a) && self.is_free_or_static(r_b)); + assert!(r_a.is_free_or_static() && r_b.is_free_or_static()); let re_static = tcx.lifetimes.re_static; if self.check_relation(re_static, r_b) { // `'a <= 'static` is always true, and not stored in the @@ -85,20 +85,6 @@ impl<'tcx> FreeRegionMap<'tcx> { r_a == r_b || self.relation.contains(r_a, r_b) } - /// True for free regions other than `'static`. - pub fn is_free(&self, r: Region<'_>) -> bool { - matches!(*r, ty::ReEarlyBound(_) | ty::ReFree(_)) - } - - /// True if `r` is a free region or static of the sort that this - /// free region map can be used with. - pub fn is_free_or_static(&self, r: Region<'_>) -> bool { - match *r { - ty::ReStatic => true, - _ => self.is_free(r), - } - } - /// Computes the least-upper-bound of two free regions. In some /// cases, this is more conservative than necessary, in order to /// avoid making arbitrary choices. See @@ -110,8 +96,8 @@ impl<'tcx> FreeRegionMap<'tcx> { r_b: Region<'tcx>, ) -> Region<'tcx> { debug!("lub_free_regions(r_a={:?}, r_b={:?})", r_a, r_b); - assert!(self.is_free(r_a)); - assert!(self.is_free(r_b)); + assert!(r_a.is_free()); + assert!(r_b.is_free()); let result = if r_a == r_b { r_a } else { diff --git a/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs b/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs index 87fa22b3835ef..3783cfb4cc5c8 100644 --- a/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs +++ b/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs @@ -47,7 +47,6 @@ pub(crate) fn resolve<'tcx>( #[derive(Clone)] pub struct LexicalRegionResolutions<'tcx> { pub(crate) values: IndexVec>, - pub(crate) error_region: ty::Region<'tcx>, } #[derive(Copy, Clone, Debug)] @@ -140,7 +139,6 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> { /// empty region. The `expansion` phase will grow this larger. fn construct_var_data(&self, tcx: TyCtxt<'tcx>) -> LexicalRegionResolutions<'tcx> { LexicalRegionResolutions { - error_region: tcx.lifetimes.re_static, values: IndexVec::from_fn_n( |vid| { let vid_universe = self.var_infos[vid].universe; @@ -310,7 +308,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> { // Check for the case where we know that `'b: 'static` -- in that case, // `a <= b` for all `a`. - let b_free_or_static = self.region_rels.free_regions.is_free_or_static(b); + let b_free_or_static = b.is_free_or_static(); if b_free_or_static && sub_free_regions(tcx.lifetimes.re_static, b) { return true; } @@ -320,7 +318,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> { // `lub` relationship defined below, since sometimes the "lub" // is actually the `postdom_upper_bound` (see // `TransitiveRelation` for more details). - let a_free_or_static = self.region_rels.free_regions.is_free_or_static(a); + let a_free_or_static = a.is_free_or_static(); if a_free_or_static && b_free_or_static { return sub_free_regions(a, b); } @@ -864,10 +862,7 @@ impl<'tcx> LexicalRegionResolutions<'tcx> { where T: TypeFoldable<'tcx>, { - tcx.fold_regions(value, |r, _db| match *r { - ty::ReVar(rid) => self.resolve_var(rid), - _ => r, - }) + tcx.fold_regions(value, |r, _db| self.resolve_region(tcx, r)) } fn value(&self, rid: RegionVid) -> &VarValue<'tcx> { @@ -878,12 +873,19 @@ impl<'tcx> LexicalRegionResolutions<'tcx> { &mut self.values[rid] } - pub fn resolve_var(&self, rid: RegionVid) -> ty::Region<'tcx> { - let result = match self.values[rid] { - VarValue::Value(r) => r, - VarValue::ErrorValue => self.error_region, + pub(crate) fn resolve_region( + &self, + tcx: TyCtxt<'tcx>, + r: ty::Region<'tcx>, + ) -> ty::Region<'tcx> { + let result = match *r { + ty::ReVar(rid) => match self.values[rid] { + VarValue::Value(r) => r, + VarValue::ErrorValue => tcx.lifetimes.re_static, + }, + _ => r, }; - debug!("resolve_var({:?}) = {:?}", rid, result); + debug!("resolve_region({:?}) = {:?}", r, result); result } } diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs index 991fd23ab4344..6e0f2d687437b 100644 --- a/compiler/rustc_infer/src/infer/mod.rs +++ b/compiler/rustc_infer/src/infer/mod.rs @@ -466,9 +466,6 @@ pub enum NllRegionVariableOrigin { /// from a `for<'a> T` binder). Meant to represent "any region". Placeholder(ty::PlaceholderRegion), - /// The variable we create to represent `'empty(U0)`. - RootEmptyRegion, - Existential { /// If this is true, then this variable was created to represent a lifetime /// bound in a `for` binder. For example, it might have been created to @@ -1250,7 +1247,6 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> { }; let lexical_region_resolutions = LexicalRegionResolutions { - error_region: self.tcx.lifetimes.re_static, values: rustc_index::vec::IndexVec::from_elem_n( crate::infer::lexical_region_resolve::VarValue::Value(self.tcx.lifetimes.re_erased), var_infos.len(), diff --git a/compiler/rustc_infer/src/infer/resolve.rs b/compiler/rustc_infer/src/infer/resolve.rs index a614568742920..3d99f0958f7f9 100644 --- a/compiler/rustc_infer/src/infer/resolve.rs +++ b/compiler/rustc_infer/src/infer/resolve.rs @@ -206,13 +206,13 @@ impl<'a, 'tcx> FallibleTypeFolder<'tcx> for FullTypeResolver<'a, 'tcx> { fn try_fold_region(&mut self, r: ty::Region<'tcx>) -> Result, Self::Error> { match *r { - ty::ReVar(rid) => Ok(self + ty::ReVar(_) => Ok(self .infcx .lexical_region_resolutions .borrow() .as_ref() .expect("region resolution not performed") - .resolve_var(rid)), + .resolve_region(self.infcx.tcx, r)), _ => Ok(r), } } diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs index 815e39aab5715..03e4319bbf1a8 100644 --- a/compiler/rustc_middle/src/ty/sty.rs +++ b/compiler/rustc_middle/src/ty/sty.rs @@ -1570,6 +1570,19 @@ impl<'tcx> Region<'tcx> { _ => bug!("free_region_binding_scope invoked on inappropriate region: {:?}", self), } } + + /// True for free regions other than `'static`. + pub fn is_free(self) -> bool { + matches!(*self, ty::ReEarlyBound(_) | ty::ReFree(_)) + } + + /// True if `self` is a free region or static. + pub fn is_free_or_static(self) -> bool { + match *self { + ty::ReStatic => true, + _ => self.is_free(), + } + } } /// Type utilities diff --git a/compiler/rustc_trait_selection/src/lib.rs b/compiler/rustc_trait_selection/src/lib.rs index 44ff3fd73061e..282ee632ce581 100644 --- a/compiler/rustc_trait_selection/src/lib.rs +++ b/compiler/rustc_trait_selection/src/lib.rs @@ -37,5 +37,4 @@ extern crate smallvec; pub mod autoderef; pub mod infer; -pub mod opaque_types; pub mod traits; diff --git a/compiler/rustc_trait_selection/src/opaque_types.rs b/compiler/rustc_trait_selection/src/opaque_types.rs deleted file mode 100644 index d290f7b074cb5..0000000000000 --- a/compiler/rustc_trait_selection/src/opaque_types.rs +++ /dev/null @@ -1,545 +0,0 @@ -use crate::traits; -use crate::traits::error_reporting::InferCtxtExt as _; -use crate::traits::TraitEngineExt as _; -use rustc_data_structures::fx::FxHashMap; -use rustc_hir::def_id::DefId; -use rustc_hir::OpaqueTyOrigin; -use rustc_infer::infer::error_reporting::unexpected_hidden_region_diagnostic; -use rustc_infer::infer::{InferCtxt, TyCtxtInferExt as _}; -use rustc_infer::traits::{Obligation, ObligationCause, TraitEngine}; -use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable}; -use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts}; -use rustc_middle::ty::visit::TypeVisitable; -use rustc_middle::ty::{self, OpaqueHiddenType, OpaqueTypeKey, ToPredicate, Ty, TyCtxt}; -use rustc_span::Span; - -pub trait InferCtxtExt<'tcx> { - fn infer_opaque_definition_from_instantiation( - &self, - opaque_type_key: OpaqueTypeKey<'tcx>, - instantiated_ty: OpaqueHiddenType<'tcx>, - origin: OpaqueTyOrigin, - ) -> Ty<'tcx>; -} - -impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> { - /// Given the fully resolved, instantiated type for an opaque - /// type, i.e., the value of an inference variable like C1 or C2 - /// (*), computes the "definition type" for an opaque type - /// definition -- that is, the inferred value of `Foo1<'x>` or - /// `Foo2<'x>` that we would conceptually use in its definition: - /// ```ignore (illustrative) - /// type Foo1<'x> = impl Bar<'x> = AAA; // <-- this type AAA - /// type Foo2<'x> = impl Bar<'x> = BBB; // <-- or this type BBB - /// fn foo<'a, 'b>(..) -> (Foo1<'a>, Foo2<'b>) { .. } - /// ``` - /// Note that these values are defined in terms of a distinct set of - /// generic parameters (`'x` instead of `'a`) from C1 or C2. The main - /// purpose of this function is to do that translation. - /// - /// (*) C1 and C2 were introduced in the comments on - /// `register_member_constraints`. Read that comment for more context. - /// - /// # Parameters - /// - /// - `def_id`, the `impl Trait` type - /// - `substs`, the substs used to instantiate this opaque type - /// - `instantiated_ty`, the inferred type C1 -- fully resolved, lifted version of - /// `opaque_defn.concrete_ty` - #[instrument(level = "debug", skip(self))] - fn infer_opaque_definition_from_instantiation( - &self, - opaque_type_key: OpaqueTypeKey<'tcx>, - instantiated_ty: OpaqueHiddenType<'tcx>, - origin: OpaqueTyOrigin, - ) -> Ty<'tcx> { - if self.is_tainted_by_errors() { - return self.tcx.ty_error(); - } - - let OpaqueTypeKey { def_id, substs } = opaque_type_key; - - // Use substs to build up a reverse map from regions to their - // identity mappings. This is necessary because of `impl - // Trait` lifetimes are computed by replacing existing - // lifetimes with 'static and remapping only those used in the - // `impl Trait` return type, resulting in the parameters - // shifting. - let id_substs = InternalSubsts::identity_for_item(self.tcx, def_id); - debug!(?id_substs); - let map: FxHashMap, GenericArg<'tcx>> = - substs.iter().enumerate().map(|(index, subst)| (subst, id_substs[index])).collect(); - debug!("map = {:#?}", map); - - // Convert the type from the function into a type valid outside - // the function, by replacing invalid regions with 'static, - // after producing an error for each of them. - let definition_ty = instantiated_ty.ty.fold_with(&mut ReverseMapper::new( - self.tcx, - def_id, - map, - instantiated_ty.ty, - instantiated_ty.span, - )); - debug!(?definition_ty); - - if !check_opaque_type_parameter_valid( - self.tcx, - opaque_type_key, - origin, - instantiated_ty.span, - ) { - return self.tcx.ty_error(); - } - - // Only check this for TAIT. RPIT already supports `src/test/ui/impl-trait/nested-return-type2.rs` - // on stable and we'd break that. - if let OpaqueTyOrigin::TyAlias = origin { - // This logic duplicates most of `check_opaque_meets_bounds`. - // FIXME(oli-obk): Also do region checks here and then consider removing `check_opaque_meets_bounds` entirely. - let param_env = self.tcx.param_env(def_id); - let body_id = self.tcx.local_def_id_to_hir_id(def_id.as_local().unwrap()); - self.tcx.infer_ctxt().enter(move |infcx| { - // Require the hidden type to be well-formed with only the generics of the opaque type. - // Defining use functions may have more bounds than the opaque type, which is ok, as long as the - // hidden type is well formed even without those bounds. - let predicate = - ty::Binder::dummy(ty::PredicateKind::WellFormed(definition_ty.into())) - .to_predicate(infcx.tcx); - let mut fulfillment_cx = >::new(infcx.tcx); - - // Require that the hidden type actually fulfills all the bounds of the opaque type, even without - // the bounds that the function supplies. - match infcx.register_hidden_type( - OpaqueTypeKey { def_id, substs: id_substs }, - ObligationCause::misc(instantiated_ty.span, body_id), - param_env, - definition_ty, - origin, - ) { - Ok(infer_ok) => { - for obligation in infer_ok.obligations { - fulfillment_cx.register_predicate_obligation(&infcx, obligation); - } - } - Err(err) => { - infcx - .report_mismatched_types( - &ObligationCause::misc(instantiated_ty.span, body_id), - self.tcx.mk_opaque(def_id, id_substs), - definition_ty, - err, - ) - .emit(); - } - } - - fulfillment_cx.register_predicate_obligation( - &infcx, - Obligation::misc(instantiated_ty.span, body_id, param_env, predicate), - ); - - // Check that all obligations are satisfied by the implementation's - // version. - let errors = fulfillment_cx.select_all_or_error(&infcx); - - let _ = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types(); - - if errors.is_empty() { - definition_ty - } else { - infcx.report_fulfillment_errors(&errors, None, false); - self.tcx.ty_error() - } - }) - } else { - definition_ty - } - } -} - -fn check_opaque_type_parameter_valid( - tcx: TyCtxt<'_>, - opaque_type_key: OpaqueTypeKey<'_>, - origin: OpaqueTyOrigin, - span: Span, -) -> bool { - match origin { - // No need to check return position impl trait (RPIT) - // because for type and const parameters they are correct - // by construction: we convert - // - // fn foo() -> impl Trait - // - // into - // - // type Foo - // fn foo() -> Foo. - // - // For lifetime parameters we convert - // - // fn foo<'l0..'ln>() -> impl Trait<'l0..'lm> - // - // into - // - // type foo::<'p0..'pn>::Foo<'q0..'qm> - // fn foo() -> foo::<'static..'static>::Foo<'l0..'lm>. - // - // which would error here on all of the `'static` args. - OpaqueTyOrigin::FnReturn(..) | OpaqueTyOrigin::AsyncFn(..) => return true, - // Check these - OpaqueTyOrigin::TyAlias => {} - } - let opaque_generics = tcx.generics_of(opaque_type_key.def_id); - let mut seen_params: FxHashMap<_, Vec<_>> = FxHashMap::default(); - for (i, arg) in opaque_type_key.substs.iter().enumerate() { - let arg_is_param = match arg.unpack() { - GenericArgKind::Type(ty) => matches!(ty.kind(), ty::Param(_)), - GenericArgKind::Lifetime(lt) if lt.is_static() => { - tcx.sess - .struct_span_err(span, "non-defining opaque type use in defining scope") - .span_label( - tcx.def_span(opaque_generics.param_at(i, tcx).def_id), - "cannot use static lifetime; use a bound lifetime \ - instead or remove the lifetime parameter from the \ - opaque type", - ) - .emit(); - return false; - } - GenericArgKind::Lifetime(lt) => { - matches!(*lt, ty::ReEarlyBound(_) | ty::ReFree(_)) - } - GenericArgKind::Const(ct) => matches!(ct.kind(), ty::ConstKind::Param(_)), - }; - - if arg_is_param { - seen_params.entry(arg).or_default().push(i); - } else { - // Prevent `fn foo() -> Foo` from being defining. - let opaque_param = opaque_generics.param_at(i, tcx); - tcx.sess - .struct_span_err(span, "non-defining opaque type use in defining scope") - .span_note( - tcx.def_span(opaque_param.def_id), - &format!( - "used non-generic {} `{}` for generic parameter", - opaque_param.kind.descr(), - arg, - ), - ) - .emit(); - return false; - } - } - - for (_, indices) in seen_params { - if indices.len() > 1 { - let descr = opaque_generics.param_at(indices[0], tcx).kind.descr(); - let spans: Vec<_> = indices - .into_iter() - .map(|i| tcx.def_span(opaque_generics.param_at(i, tcx).def_id)) - .collect(); - tcx.sess - .struct_span_err(span, "non-defining opaque type use in defining scope") - .span_note(spans, &format!("{} used multiple times", descr)) - .emit(); - return false; - } - } - true -} - -struct ReverseMapper<'tcx> { - tcx: TyCtxt<'tcx>, - - opaque_type_def_id: DefId, - map: FxHashMap, GenericArg<'tcx>>, - map_missing_regions_to_empty: bool, - - /// initially `Some`, set to `None` once error has been reported - hidden_ty: Option>, - - /// Span of function being checked. - span: Span, -} - -impl<'tcx> ReverseMapper<'tcx> { - fn new( - tcx: TyCtxt<'tcx>, - opaque_type_def_id: DefId, - map: FxHashMap, GenericArg<'tcx>>, - hidden_ty: Ty<'tcx>, - span: Span, - ) -> Self { - Self { - tcx, - opaque_type_def_id, - map, - map_missing_regions_to_empty: false, - hidden_ty: Some(hidden_ty), - span, - } - } - - fn fold_kind_mapping_missing_regions_to_empty( - &mut self, - kind: GenericArg<'tcx>, - ) -> GenericArg<'tcx> { - assert!(!self.map_missing_regions_to_empty); - self.map_missing_regions_to_empty = true; - let kind = kind.fold_with(self); - self.map_missing_regions_to_empty = false; - kind - } - - fn fold_kind_normally(&mut self, kind: GenericArg<'tcx>) -> GenericArg<'tcx> { - assert!(!self.map_missing_regions_to_empty); - kind.fold_with(self) - } -} - -impl<'tcx> TypeFolder<'tcx> for ReverseMapper<'tcx> { - fn tcx(&self) -> TyCtxt<'tcx> { - self.tcx - } - - #[instrument(skip(self), level = "debug")] - fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> { - match *r { - // Ignore bound regions and `'static` regions that appear in the - // type, we only need to remap regions that reference lifetimes - // from the function declaration. - // This would ignore `'r` in a type like `for<'r> fn(&'r u32)`. - ty::ReLateBound(..) | ty::ReStatic => return r, - - // If regions have been erased (by writeback), don't try to unerase - // them. - ty::ReErased => return r, - - // The regions that we expect from borrow checking. - ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReEmpty(ty::UniverseIndex::ROOT) => {} - - ty::ReEmpty(_) | ty::RePlaceholder(_) | ty::ReVar(_) => { - // All of the regions in the type should either have been - // erased by writeback, or mapped back to named regions by - // borrow checking. - bug!("unexpected region kind in opaque type: {:?}", r); - } - } - - let generics = self.tcx().generics_of(self.opaque_type_def_id); - match self.map.get(&r.into()).map(|k| k.unpack()) { - Some(GenericArgKind::Lifetime(r1)) => r1, - Some(u) => panic!("region mapped to unexpected kind: {:?}", u), - None if self.map_missing_regions_to_empty => self.tcx.lifetimes.re_root_empty, - None if generics.parent.is_some() => { - if let Some(hidden_ty) = self.hidden_ty.take() { - unexpected_hidden_region_diagnostic( - self.tcx, - self.tcx.def_span(self.opaque_type_def_id), - hidden_ty, - r, - ) - .emit(); - } - self.tcx.lifetimes.re_root_empty - } - None => { - self.tcx - .sess - .struct_span_err(self.span, "non-defining opaque type use in defining scope") - .span_label( - self.span, - format!( - "lifetime `{}` is part of concrete type but not used in \ - parameter list of the `impl Trait` type alias", - r - ), - ) - .emit(); - - self.tcx().lifetimes.re_static - } - } - } - - fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> { - match *ty.kind() { - ty::Closure(def_id, substs) => { - // I am a horrible monster and I pray for death. When - // we encounter a closure here, it is always a closure - // from within the function that we are currently - // type-checking -- one that is now being encapsulated - // in an opaque type. Ideally, we would - // go through the types/lifetimes that it references - // and treat them just like we would any other type, - // which means we would error out if we find any - // reference to a type/region that is not in the - // "reverse map". - // - // **However,** in the case of closures, there is a - // somewhat subtle (read: hacky) consideration. The - // problem is that our closure types currently include - // all the lifetime parameters declared on the - // enclosing function, even if they are unused by the - // closure itself. We can't readily filter them out, - // so here we replace those values with `'empty`. This - // can't really make a difference to the rest of the - // compiler; those regions are ignored for the - // outlives relation, and hence don't affect trait - // selection or auto traits, and they are erased - // during codegen. - - let generics = self.tcx.generics_of(def_id); - let substs = self.tcx.mk_substs(substs.iter().enumerate().map(|(index, kind)| { - if index < generics.parent_count { - // Accommodate missing regions in the parent kinds... - self.fold_kind_mapping_missing_regions_to_empty(kind) - } else { - // ...but not elsewhere. - self.fold_kind_normally(kind) - } - })); - - self.tcx.mk_closure(def_id, substs) - } - - ty::Generator(def_id, substs, movability) => { - let generics = self.tcx.generics_of(def_id); - let substs = self.tcx.mk_substs(substs.iter().enumerate().map(|(index, kind)| { - if index < generics.parent_count { - // Accommodate missing regions in the parent kinds... - self.fold_kind_mapping_missing_regions_to_empty(kind) - } else { - // ...but not elsewhere. - self.fold_kind_normally(kind) - } - })); - - self.tcx.mk_generator(def_id, substs, movability) - } - - ty::Param(param) => { - // Look it up in the substitution list. - match self.map.get(&ty.into()).map(|k| k.unpack()) { - // Found it in the substitution list; replace with the parameter from the - // opaque type. - Some(GenericArgKind::Type(t1)) => t1, - Some(u) => panic!("type mapped to unexpected kind: {:?}", u), - None => { - debug!(?param, ?self.map); - self.tcx - .sess - .struct_span_err( - self.span, - &format!( - "type parameter `{}` is part of concrete type but not \ - used in parameter list for the `impl Trait` type alias", - ty - ), - ) - .emit(); - - self.tcx().ty_error() - } - } - } - - _ => ty.super_fold_with(self), - } - } - - fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> { - trace!("checking const {:?}", ct); - // Find a const parameter - match ct.kind() { - ty::ConstKind::Param(..) => { - // Look it up in the substitution list. - match self.map.get(&ct.into()).map(|k| k.unpack()) { - // Found it in the substitution list, replace with the parameter from the - // opaque type. - Some(GenericArgKind::Const(c1)) => c1, - Some(u) => panic!("const mapped to unexpected kind: {:?}", u), - None => { - self.tcx - .sess - .struct_span_err( - self.span, - &format!( - "const parameter `{}` is part of concrete type but not \ - used in parameter list for the `impl Trait` type alias", - ct - ), - ) - .emit(); - - self.tcx().const_error(ct.ty()) - } - } - } - - _ => ct, - } - } -} - -/// Given a set of predicates that apply to an object type, returns -/// the region bounds that the (erased) `Self` type must -/// outlive. Precisely *because* the `Self` type is erased, the -/// parameter `erased_self_ty` must be supplied to indicate what type -/// has been used to represent `Self` in the predicates -/// themselves. This should really be a unique type; `FreshTy(0)` is a -/// popular choice. -/// -/// N.B., in some cases, particularly around higher-ranked bounds, -/// this function returns a kind of conservative approximation. -/// That is, all regions returned by this function are definitely -/// required, but there may be other region bounds that are not -/// returned, as well as requirements like `for<'a> T: 'a`. -/// -/// Requires that trait definitions have been processed so that we can -/// elaborate predicates and walk supertraits. -#[instrument(skip(tcx, predicates), level = "debug")] -pub(crate) fn required_region_bounds<'tcx>( - tcx: TyCtxt<'tcx>, - erased_self_ty: Ty<'tcx>, - predicates: impl Iterator>, -) -> Vec> { - assert!(!erased_self_ty.has_escaping_bound_vars()); - - traits::elaborate_predicates(tcx, predicates) - .filter_map(|obligation| { - debug!(?obligation); - match obligation.predicate.kind().skip_binder() { - ty::PredicateKind::Projection(..) - | ty::PredicateKind::Trait(..) - | ty::PredicateKind::Subtype(..) - | ty::PredicateKind::Coerce(..) - | ty::PredicateKind::WellFormed(..) - | ty::PredicateKind::ObjectSafe(..) - | ty::PredicateKind::ClosureKind(..) - | ty::PredicateKind::RegionOutlives(..) - | ty::PredicateKind::ConstEvaluatable(..) - | ty::PredicateKind::ConstEquate(..) - | ty::PredicateKind::TypeWellFormedFromEnv(..) => None, - ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ref t, ref r)) => { - // Search for a bound of the form `erased_self_ty - // : 'a`, but be wary of something like `for<'a> - // erased_self_ty : 'a` (we interpret a - // higher-ranked bound like that as 'static, - // though at present the code in `fulfill.rs` - // considers such bounds to be unsatisfiable, so - // it's kind of a moot point since you could never - // construct such an object, but this seems - // correct even if that code changes). - if t == &erased_self_ty && !r.has_escaping_bound_vars() { - Some(*r) - } else { - None - } - } - } - }) - .collect() -} diff --git a/compiler/rustc_trait_selection/src/traits/wf.rs b/compiler/rustc_trait_selection/src/traits/wf.rs index d43b3c9091fc6..3dfc7a9cacd97 100644 --- a/compiler/rustc_trait_selection/src/traits/wf.rs +++ b/compiler/rustc_trait_selection/src/traits/wf.rs @@ -1,5 +1,4 @@ use crate::infer::InferCtxt; -use crate::opaque_types::required_region_bounds; use crate::traits; use rustc_hir as hir; use rustc_hir::def_id::DefId; @@ -810,3 +809,63 @@ pub fn object_region_bounds<'tcx>( required_region_bounds(tcx, open_ty, predicates) } + +/// Given a set of predicates that apply to an object type, returns +/// the region bounds that the (erased) `Self` type must +/// outlive. Precisely *because* the `Self` type is erased, the +/// parameter `erased_self_ty` must be supplied to indicate what type +/// has been used to represent `Self` in the predicates +/// themselves. This should really be a unique type; `FreshTy(0)` is a +/// popular choice. +/// +/// N.B., in some cases, particularly around higher-ranked bounds, +/// this function returns a kind of conservative approximation. +/// That is, all regions returned by this function are definitely +/// required, but there may be other region bounds that are not +/// returned, as well as requirements like `for<'a> T: 'a`. +/// +/// Requires that trait definitions have been processed so that we can +/// elaborate predicates and walk supertraits. +#[instrument(skip(tcx, predicates), level = "debug")] +pub(crate) fn required_region_bounds<'tcx>( + tcx: TyCtxt<'tcx>, + erased_self_ty: Ty<'tcx>, + predicates: impl Iterator>, +) -> Vec> { + assert!(!erased_self_ty.has_escaping_bound_vars()); + + traits::elaborate_predicates(tcx, predicates) + .filter_map(|obligation| { + debug!(?obligation); + match obligation.predicate.kind().skip_binder() { + ty::PredicateKind::Projection(..) + | ty::PredicateKind::Trait(..) + | ty::PredicateKind::Subtype(..) + | ty::PredicateKind::Coerce(..) + | ty::PredicateKind::WellFormed(..) + | ty::PredicateKind::ObjectSafe(..) + | ty::PredicateKind::ClosureKind(..) + | ty::PredicateKind::RegionOutlives(..) + | ty::PredicateKind::ConstEvaluatable(..) + | ty::PredicateKind::ConstEquate(..) + | ty::PredicateKind::TypeWellFormedFromEnv(..) => None, + ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ref t, ref r)) => { + // Search for a bound of the form `erased_self_ty + // : 'a`, but be wary of something like `for<'a> + // erased_self_ty : 'a` (we interpret a + // higher-ranked bound like that as 'static, + // though at present the code in `fulfill.rs` + // considers such bounds to be unsatisfiable, so + // it's kind of a moot point since you could never + // construct such an object, but this seems + // correct even if that code changes). + if t == &erased_self_ty && !r.has_escaping_bound_vars() { + Some(*r) + } else { + None + } + } + } + }) + .collect() +}