| use crate::infer::InferCtxtExt as _; |
| use crate::traits::{self, PredicateObligation}; |
| use rustc_data_structures::fx::FxHashMap; |
| use rustc_data_structures::sync::Lrc; |
| use rustc_hir as hir; |
| use rustc_hir::def_id::{DefId, DefIdMap, LocalDefId}; |
| use rustc_hir::Node; |
| use rustc_infer::infer::error_reporting::unexpected_hidden_region_diagnostic; |
| use rustc_infer::infer::free_regions::FreeRegionRelations; |
| use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; |
| use rustc_infer::infer::{self, InferCtxt, InferOk}; |
| use rustc_middle::ty::fold::{BottomUpFolder, TypeFoldable, TypeFolder, TypeVisitor}; |
| use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, SubstsRef}; |
| use rustc_middle::ty::{self, Ty, TyCtxt}; |
| use rustc_session::config::nightly_options; |
| use rustc_span::Span; |
| |
| pub type OpaqueTypeMap<'tcx> = DefIdMap<OpaqueTypeDecl<'tcx>>; |
| |
| /// Information about the opaque types whose values we |
| /// are inferring in this function (these are the `impl Trait` that |
| /// appear in the return type). |
| #[derive(Copy, Clone, Debug)] |
| pub struct OpaqueTypeDecl<'tcx> { |
| /// The opaque type (`ty::Opaque`) for this declaration. |
| pub opaque_type: Ty<'tcx>, |
| |
| /// The substitutions that we apply to the opaque type that this |
| /// `impl Trait` desugars to. e.g., if: |
| /// |
| /// fn foo<'a, 'b, T>() -> impl Trait<'a> |
| /// |
| /// winds up desugared to: |
| /// |
| /// type Foo<'x, X> = impl Trait<'x> |
| /// fn foo<'a, 'b, T>() -> Foo<'a, T> |
| /// |
| /// then `substs` would be `['a, T]`. |
| pub substs: SubstsRef<'tcx>, |
| |
| /// The span of this particular definition of the opaque type. So |
| /// for example: |
| /// |
| /// ``` |
| /// type Foo = impl Baz; |
| /// fn bar() -> Foo { |
| /// ^^^ This is the span we are looking for! |
| /// ``` |
| /// |
| /// In cases where the fn returns `(impl Trait, impl Trait)` or |
| /// other such combinations, the result is currently |
| /// over-approximated, but better than nothing. |
| pub definition_span: Span, |
| |
| /// The type variable that represents the value of the opaque type |
| /// that we require. In other words, after we compile this function, |
| /// we will be created a constraint like: |
| /// |
| /// Foo<'a, T> = ?C |
| /// |
| /// where `?C` is the value of this type variable. =) It may |
| /// naturally refer to the type and lifetime parameters in scope |
| /// in this function, though ultimately it should only reference |
| /// those that are arguments to `Foo` in the constraint above. (In |
| /// other words, `?C` should not include `'b`, even though it's a |
| /// lifetime parameter on `foo`.) |
| pub concrete_ty: Ty<'tcx>, |
| |
| /// Returns `true` if the `impl Trait` bounds include region bounds. |
| /// For example, this would be true for: |
| /// |
| /// fn foo<'a, 'b, 'c>() -> impl Trait<'c> + 'a + 'b |
| /// |
| /// but false for: |
| /// |
| /// fn foo<'c>() -> impl Trait<'c> |
| /// |
| /// unless `Trait` was declared like: |
| /// |
| /// trait Trait<'c>: 'c |
| /// |
| /// in which case it would be true. |
| /// |
| /// This is used during regionck to decide whether we need to |
| /// impose any additional constraints to ensure that region |
| /// variables in `concrete_ty` wind up being constrained to |
| /// something from `substs` (or, at minimum, things that outlive |
| /// the fn body). (Ultimately, writeback is responsible for this |
| /// check.) |
| pub has_required_region_bounds: bool, |
| |
| /// The origin of the opaque type. |
| pub origin: hir::OpaqueTyOrigin, |
| } |
| |
| /// Whether member constraints should be generated for all opaque types |
| pub enum GenerateMemberConstraints { |
| /// The default, used by typeck |
| WhenRequired, |
| /// The borrow checker needs member constraints in any case where we don't |
| /// have a `'static` bound. This is because the borrow checker has more |
| /// flexibility in the values of regions. For example, given `f<'a, 'b>` |
| /// the borrow checker can have an inference variable outlive `'a` and `'b`, |
| /// but not be equal to `'static`. |
| IfNoStaticBound, |
| } |
| |
| pub trait InferCtxtExt<'tcx> { |
| fn instantiate_opaque_types<T: TypeFoldable<'tcx>>( |
| &self, |
| parent_def_id: LocalDefId, |
| body_id: hir::HirId, |
| param_env: ty::ParamEnv<'tcx>, |
| value: &T, |
| value_span: Span, |
| ) -> InferOk<'tcx, (T, OpaqueTypeMap<'tcx>)>; |
| |
| fn constrain_opaque_types<FRR: FreeRegionRelations<'tcx>>( |
| &self, |
| opaque_types: &OpaqueTypeMap<'tcx>, |
| free_region_relations: &FRR, |
| ); |
| |
| fn constrain_opaque_type<FRR: FreeRegionRelations<'tcx>>( |
| &self, |
| def_id: DefId, |
| opaque_defn: &OpaqueTypeDecl<'tcx>, |
| mode: GenerateMemberConstraints, |
| free_region_relations: &FRR, |
| ); |
| |
| /*private*/ |
| fn generate_member_constraint( |
| &self, |
| concrete_ty: Ty<'tcx>, |
| opaque_defn: &OpaqueTypeDecl<'tcx>, |
| opaque_type_def_id: DefId, |
| first_own_region_index: usize, |
| ); |
| |
| /*private*/ |
| fn member_constraint_feature_gate( |
| &self, |
| opaque_defn: &OpaqueTypeDecl<'tcx>, |
| opaque_type_def_id: DefId, |
| conflict1: ty::Region<'tcx>, |
| conflict2: ty::Region<'tcx>, |
| ) -> bool; |
| |
| fn infer_opaque_definition_from_instantiation( |
| &self, |
| def_id: DefId, |
| substs: SubstsRef<'tcx>, |
| instantiated_ty: Ty<'tcx>, |
| span: Span, |
| ) -> Ty<'tcx>; |
| } |
| |
| impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> { |
| /// Replaces all opaque types in `value` with fresh inference variables |
| /// and creates appropriate obligations. For example, given the input: |
| /// |
| /// impl Iterator<Item = impl Debug> |
| /// |
| /// this method would create two type variables, `?0` and `?1`. It would |
| /// return the type `?0` but also the obligations: |
| /// |
| /// ?0: Iterator<Item = ?1> |
| /// ?1: Debug |
| /// |
| /// Moreover, it returns a `OpaqueTypeMap` that would map `?0` to |
| /// info about the `impl Iterator<..>` type and `?1` to info about |
| /// the `impl Debug` type. |
| /// |
| /// # Parameters |
| /// |
| /// - `parent_def_id` -- the `DefId` of the function in which the opaque type |
| /// is defined |
| /// - `body_id` -- the body-id with which the resulting obligations should |
| /// be associated |
| /// - `param_env` -- the in-scope parameter environment to be used for |
| /// obligations |
| /// - `value` -- the value within which we are instantiating opaque types |
| /// - `value_span` -- the span where the value came from, used in error reporting |
| fn instantiate_opaque_types<T: TypeFoldable<'tcx>>( |
| &self, |
| parent_def_id: LocalDefId, |
| body_id: hir::HirId, |
| param_env: ty::ParamEnv<'tcx>, |
| value: &T, |
| value_span: Span, |
| ) -> InferOk<'tcx, (T, OpaqueTypeMap<'tcx>)> { |
| debug!( |
| "instantiate_opaque_types(value={:?}, parent_def_id={:?}, body_id={:?}, \ |
| param_env={:?}, value_span={:?})", |
| value, parent_def_id, body_id, param_env, value_span, |
| ); |
| let mut instantiator = Instantiator { |
| infcx: self, |
| parent_def_id, |
| body_id, |
| param_env, |
| value_span, |
| opaque_types: Default::default(), |
| obligations: vec![], |
| }; |
| let value = instantiator.instantiate_opaque_types_in_map(value); |
| InferOk { value: (value, instantiator.opaque_types), obligations: instantiator.obligations } |
| } |
| |
| /// Given the map `opaque_types` containing the opaque |
| /// `impl Trait` types whose underlying, hidden types are being |
| /// inferred, this method adds constraints to the regions |
| /// appearing in those underlying hidden types to ensure that they |
| /// at least do not refer to random scopes within the current |
| /// function. These constraints are not (quite) sufficient to |
| /// guarantee that the regions are actually legal values; that |
| /// final condition is imposed after region inference is done. |
| /// |
| /// # The Problem |
| /// |
| /// Let's work through an example to explain how it works. Assume |
| /// the current function is as follows: |
| /// |
| /// ```text |
| /// fn foo<'a, 'b>(..) -> (impl Bar<'a>, impl Bar<'b>) |
| /// ``` |
| /// |
| /// Here, we have two `impl Trait` types whose values are being |
| /// inferred (the `impl Bar<'a>` and the `impl |
| /// Bar<'b>`). Conceptually, this is sugar for a setup where we |
| /// define underlying opaque types (`Foo1`, `Foo2`) and then, in |
| /// the return type of `foo`, we *reference* those definitions: |
| /// |
| /// ```text |
| /// type Foo1<'x> = impl Bar<'x>; |
| /// type Foo2<'x> = impl Bar<'x>; |
| /// fn foo<'a, 'b>(..) -> (Foo1<'a>, Foo2<'b>) { .. } |
| /// // ^^^^ ^^ |
| /// // | | |
| /// // | substs |
| /// // def_id |
| /// ``` |
| /// |
| /// As indicating in the comments above, each of those references |
| /// is (in the compiler) basically a substitution (`substs`) |
| /// applied to the type of a suitable `def_id` (which identifies |
| /// `Foo1` or `Foo2`). |
| /// |
| /// Now, at this point in compilation, what we have done is to |
| /// replace each of the references (`Foo1<'a>`, `Foo2<'b>`) with |
| /// fresh inference variables C1 and C2. We wish to use the values |
| /// of these variables to infer the underlying types of `Foo1` and |
| /// `Foo2`. That is, this gives rise to higher-order (pattern) unification |
| /// constraints like: |
| /// |
| /// ```text |
| /// for<'a> (Foo1<'a> = C1) |
| /// for<'b> (Foo1<'b> = C2) |
| /// ``` |
| /// |
| /// For these equation to be satisfiable, the types `C1` and `C2` |
| /// can only refer to a limited set of regions. For example, `C1` |
| /// can only refer to `'static` and `'a`, and `C2` can only refer |
| /// to `'static` and `'b`. The job of this function is to impose that |
| /// constraint. |
| /// |
| /// Up to this point, C1 and C2 are basically just random type |
| /// inference variables, and hence they may contain arbitrary |
| /// regions. In fact, it is fairly likely that they do! Consider |
| /// this possible definition of `foo`: |
| /// |
| /// ```text |
| /// fn foo<'a, 'b>(x: &'a i32, y: &'b i32) -> (impl Bar<'a>, impl Bar<'b>) { |
| /// (&*x, &*y) |
| /// } |
| /// ``` |
| /// |
| /// Here, the values for the concrete types of the two impl |
| /// traits will include inference variables: |
| /// |
| /// ```text |
| /// &'0 i32 |
| /// &'1 i32 |
| /// ``` |
| /// |
| /// Ordinarily, the subtyping rules would ensure that these are |
| /// sufficiently large. But since `impl Bar<'a>` isn't a specific |
| /// type per se, we don't get such constraints by default. This |
| /// is where this function comes into play. It adds extra |
| /// constraints to ensure that all the regions which appear in the |
| /// inferred type are regions that could validly appear. |
| /// |
| /// This is actually a bit of a tricky constraint in general. We |
| /// want to say that each variable (e.g., `'0`) can only take on |
| /// values that were supplied as arguments to the opaque type |
| /// (e.g., `'a` for `Foo1<'a>`) or `'static`, which is always in |
| /// scope. We don't have a constraint quite of this kind in the current |
| /// region checker. |
| /// |
| /// # The Solution |
| /// |
| /// We generally prefer to make `<=` constraints, since they |
| /// integrate best into the region solver. To do that, we find the |
| /// "minimum" of all the arguments that appear in the substs: that |
| /// is, some region which is less than all the others. In the case |
| /// of `Foo1<'a>`, that would be `'a` (it's the only choice, after |
| /// all). Then we apply that as a least bound to the variables |
| /// (e.g., `'a <= '0`). |
| /// |
| /// In some cases, there is no minimum. Consider this example: |
| /// |
| /// ```text |
| /// fn baz<'a, 'b>() -> impl Trait<'a, 'b> { ... } |
| /// ``` |
| /// |
| /// Here we would report a more complex "in constraint", like `'r |
| /// in ['a, 'b, 'static]` (where `'r` is some region appearing in |
| /// the hidden type). |
| /// |
| /// # Constrain regions, not the hidden concrete type |
| /// |
| /// Note that generating constraints on each region `Rc` is *not* |
| /// the same as generating an outlives constraint on `Tc` iself. |
| /// For example, if we had a function like this: |
| /// |
| /// ```rust |
| /// fn foo<'a, T>(x: &'a u32, y: T) -> impl Foo<'a> { |
| /// (x, y) |
| /// } |
| /// |
| /// // Equivalent to: |
| /// type FooReturn<'a, T> = impl Foo<'a>; |
| /// fn foo<'a, T>(..) -> FooReturn<'a, T> { .. } |
| /// ``` |
| /// |
| /// then the hidden type `Tc` would be `(&'0 u32, T)` (where `'0` |
| /// is an inference variable). If we generated a constraint that |
| /// `Tc: 'a`, then this would incorrectly require that `T: 'a` -- |
| /// but this is not necessary, because the opaque type we |
| /// create will be allowed to reference `T`. So we only generate a |
| /// constraint that `'0: 'a`. |
| /// |
| /// # The `free_region_relations` parameter |
| /// |
| /// The `free_region_relations` argument is used to find the |
| /// "minimum" of the regions supplied to a given opaque type. |
| /// It must be a relation that can answer whether `'a <= 'b`, |
| /// where `'a` and `'b` are regions that appear in the "substs" |
| /// for the opaque type references (the `<'a>` in `Foo1<'a>`). |
| /// |
| /// Note that we do not impose the constraints based on the |
| /// generic regions from the `Foo1` definition (e.g., `'x`). This |
| /// is because the constraints we are imposing here is basically |
| /// the concern of the one generating the constraining type C1, |
| /// which is the current function. It also means that we can |
| /// take "implied bounds" into account in some cases: |
| /// |
| /// ```text |
| /// trait SomeTrait<'a, 'b> { } |
| /// fn foo<'a, 'b>(_: &'a &'b u32) -> impl SomeTrait<'a, 'b> { .. } |
| /// ``` |
| /// |
| /// Here, the fact that `'b: 'a` is known only because of the |
| /// implied bounds from the `&'a &'b u32` parameter, and is not |
| /// "inherent" to the opaque type definition. |
| /// |
| /// # Parameters |
| /// |
| /// - `opaque_types` -- the map produced by `instantiate_opaque_types` |
| /// - `free_region_relations` -- something that can be used to relate |
| /// the free regions (`'a`) that appear in the impl trait. |
| fn constrain_opaque_types<FRR: FreeRegionRelations<'tcx>>( |
| &self, |
| opaque_types: &OpaqueTypeMap<'tcx>, |
| free_region_relations: &FRR, |
| ) { |
| debug!("constrain_opaque_types()"); |
| |
| for (&def_id, opaque_defn) in opaque_types { |
| self.constrain_opaque_type( |
| def_id, |
| opaque_defn, |
| GenerateMemberConstraints::WhenRequired, |
| free_region_relations, |
| ); |
| } |
| } |
| |
| /// See `constrain_opaque_types` for documentation. |
| fn constrain_opaque_type<FRR: FreeRegionRelations<'tcx>>( |
| &self, |
| def_id: DefId, |
| opaque_defn: &OpaqueTypeDecl<'tcx>, |
| mode: GenerateMemberConstraints, |
| free_region_relations: &FRR, |
| ) { |
| debug!("constrain_opaque_type()"); |
| debug!("constrain_opaque_type: def_id={:?}", def_id); |
| debug!("constrain_opaque_type: opaque_defn={:#?}", opaque_defn); |
| |
| let tcx = self.tcx; |
| |
| let concrete_ty = self.resolve_vars_if_possible(&opaque_defn.concrete_ty); |
| |
| debug!("constrain_opaque_type: concrete_ty={:?}", concrete_ty); |
| |
| let first_own_region = match opaque_defn.origin { |
| hir::OpaqueTyOrigin::FnReturn | hir::OpaqueTyOrigin::AsyncFn => { |
| // We lower |
| // |
| // fn foo<'l0..'ln>() -> impl Trait<'l0..'lm> |
| // |
| // into |
| // |
| // type foo::<'p0..'pn>::Foo<'q0..'qm> |
| // fn foo<l0..'ln>() -> foo::<'static..'static>::Foo<'l0..'lm>. |
| // |
| // For these types we onlt iterate over `'l0..lm` below. |
| tcx.generics_of(def_id).parent_count |
| } |
| // These opaque type inherit all lifetime parameters from their |
| // parent, so we have to check them all. |
| hir::OpaqueTyOrigin::Binding | hir::OpaqueTyOrigin::Misc => 0, |
| }; |
| |
| let span = tcx.def_span(def_id); |
| |
| // If there are required region bounds, we can use them. |
| if opaque_defn.has_required_region_bounds { |
| let predicates_of = tcx.predicates_of(def_id); |
| debug!("constrain_opaque_type: predicates: {:#?}", predicates_of,); |
| let bounds = predicates_of.instantiate(tcx, opaque_defn.substs); |
| debug!("constrain_opaque_type: bounds={:#?}", bounds); |
| let opaque_type = tcx.mk_opaque(def_id, opaque_defn.substs); |
| |
| let required_region_bounds = |
| required_region_bounds(tcx, opaque_type, bounds.predicates.into_iter()); |
| debug_assert!(!required_region_bounds.is_empty()); |
| |
| for required_region in required_region_bounds { |
| concrete_ty.visit_with(&mut ConstrainOpaqueTypeRegionVisitor { |
| op: |r| self.sub_regions(infer::CallReturn(span), required_region, r), |
| }); |
| } |
| if let GenerateMemberConstraints::IfNoStaticBound = mode { |
| self.generate_member_constraint(concrete_ty, opaque_defn, def_id, first_own_region); |
| } |
| return; |
| } |
| |
| // There were no `required_region_bounds`, |
| // so we have to search for a `least_region`. |
| // Go through all the regions used as arguments to the |
| // opaque type. These are the parameters to the opaque |
| // type; so in our example above, `substs` would contain |
| // `['a]` for the first impl trait and `'b` for the |
| // second. |
| let mut least_region = None; |
| |
| for subst_arg in &opaque_defn.substs[first_own_region..] { |
| let subst_region = match subst_arg.unpack() { |
| GenericArgKind::Lifetime(r) => r, |
| GenericArgKind::Type(_) | GenericArgKind::Const(_) => continue, |
| }; |
| |
| // Compute the least upper bound of it with the other regions. |
| debug!("constrain_opaque_types: least_region={:?}", least_region); |
| debug!("constrain_opaque_types: subst_region={:?}", subst_region); |
| match least_region { |
| None => least_region = Some(subst_region), |
| Some(lr) => { |
| if free_region_relations.sub_free_regions(self.tcx, lr, subst_region) { |
| // keep the current least region |
| } else if free_region_relations.sub_free_regions(self.tcx, subst_region, lr) { |
| // switch to `subst_region` |
| least_region = Some(subst_region); |
| } else { |
| // There are two regions (`lr` and |
| // `subst_region`) which are not relatable. We |
| // can't find a best choice. Therefore, |
| // instead of creating a single bound like |
| // `'r: 'a` (which is our preferred choice), |
| // we will create a "in bound" like `'r in |
| // ['a, 'b, 'c]`, where `'a..'c` are the |
| // regions that appear in the impl trait. |
| |
| // For now, enforce a feature gate outside of async functions. |
| self.member_constraint_feature_gate(opaque_defn, def_id, lr, subst_region); |
| |
| return self.generate_member_constraint( |
| concrete_ty, |
| opaque_defn, |
| def_id, |
| first_own_region, |
| ); |
| } |
| } |
| } |
| } |
| |
| let least_region = least_region.unwrap_or(tcx.lifetimes.re_static); |
| debug!("constrain_opaque_types: least_region={:?}", least_region); |
| |
| if let GenerateMemberConstraints::IfNoStaticBound = mode { |
| if least_region != tcx.lifetimes.re_static { |
| self.generate_member_constraint(concrete_ty, opaque_defn, def_id, first_own_region); |
| } |
| } |
| concrete_ty.visit_with(&mut ConstrainOpaqueTypeRegionVisitor { |
| op: |r| self.sub_regions(infer::CallReturn(span), least_region, r), |
| }); |
| } |
| |
| /// As a fallback, we sometimes generate an "in constraint". For |
| /// a case like `impl Foo<'a, 'b>`, where `'a` and `'b` cannot be |
| /// related, we would generate a constraint `'r in ['a, 'b, |
| /// 'static]` for each region `'r` that appears in the hidden type |
| /// (i.e., it must be equal to `'a`, `'b`, or `'static`). |
| /// |
| /// `conflict1` and `conflict2` are the two region bounds that we |
| /// detected which were unrelated. They are used for diagnostics. |
| fn generate_member_constraint( |
| &self, |
| concrete_ty: Ty<'tcx>, |
| opaque_defn: &OpaqueTypeDecl<'tcx>, |
| opaque_type_def_id: DefId, |
| first_own_region: usize, |
| ) { |
| // Create the set of choice regions: each region in the hidden |
| // type can be equal to any of the region parameters of the |
| // opaque type definition. |
| let choice_regions: Lrc<Vec<ty::Region<'tcx>>> = Lrc::new( |
| opaque_defn.substs[first_own_region..] |
| .iter() |
| .filter_map(|arg| match arg.unpack() { |
| GenericArgKind::Lifetime(r) => Some(r), |
| GenericArgKind::Type(_) | GenericArgKind::Const(_) => None, |
| }) |
| .chain(std::iter::once(self.tcx.lifetimes.re_static)) |
| .collect(), |
| ); |
| |
| concrete_ty.visit_with(&mut ConstrainOpaqueTypeRegionVisitor { |
| op: |r| { |
| self.member_constraint( |
| opaque_type_def_id, |
| opaque_defn.definition_span, |
| concrete_ty, |
| r, |
| &choice_regions, |
| ) |
| }, |
| }); |
| } |
| |
| /// Member constraints are presently feature-gated except for |
| /// async-await. We expect to lift this once we've had a bit more |
| /// time. |
| fn member_constraint_feature_gate( |
| &self, |
| opaque_defn: &OpaqueTypeDecl<'tcx>, |
| opaque_type_def_id: DefId, |
| conflict1: ty::Region<'tcx>, |
| conflict2: ty::Region<'tcx>, |
| ) -> bool { |
| // If we have `#![feature(member_constraints)]`, no problems. |
| if self.tcx.features().member_constraints { |
| return false; |
| } |
| |
| let span = self.tcx.def_span(opaque_type_def_id); |
| |
| // Without a feature-gate, we only generate member-constraints for async-await. |
| let context_name = match opaque_defn.origin { |
| // No feature-gate required for `async fn`. |
| hir::OpaqueTyOrigin::AsyncFn => return false, |
| |
| // Otherwise, generate the label we'll use in the error message. |
| hir::OpaqueTyOrigin::Binding |
| | hir::OpaqueTyOrigin::FnReturn |
| | hir::OpaqueTyOrigin::Misc => "impl Trait", |
| }; |
| let msg = format!("ambiguous lifetime bound in `{}`", context_name); |
| let mut err = self.tcx.sess.struct_span_err(span, &msg); |
| |
| let conflict1_name = conflict1.to_string(); |
| let conflict2_name = conflict2.to_string(); |
| let label_owned; |
| let label = match (&*conflict1_name, &*conflict2_name) { |
| ("'_", "'_") => "the elided lifetimes here do not outlive one another", |
| _ => { |
| label_owned = format!( |
| "neither `{}` nor `{}` outlives the other", |
| conflict1_name, conflict2_name, |
| ); |
| &label_owned |
| } |
| }; |
| err.span_label(span, label); |
| |
| if nightly_options::is_nightly_build() { |
| err.help("add #![feature(member_constraints)] to the crate attributes to enable"); |
| } |
| |
| err.emit(); |
| true |
| } |
| |
| /// 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: |
| /// |
| /// 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 |
| /// `constrain_opaque_types`. 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` |
| fn infer_opaque_definition_from_instantiation( |
| &self, |
| def_id: DefId, |
| substs: SubstsRef<'tcx>, |
| instantiated_ty: Ty<'tcx>, |
| span: Span, |
| ) -> Ty<'tcx> { |
| debug!( |
| "infer_opaque_definition_from_instantiation(def_id={:?}, instantiated_ty={:?})", |
| def_id, instantiated_ty |
| ); |
| |
| // 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); |
| let map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>> = |
| substs.iter().enumerate().map(|(index, subst)| (subst, id_substs[index])).collect(); |
| |
| // 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.fold_with(&mut ReverseMapper::new( |
| self.tcx, |
| self.is_tainted_by_errors(), |
| def_id, |
| map, |
| instantiated_ty, |
| span, |
| )); |
| debug!("infer_opaque_definition_from_instantiation: definition_ty={:?}", definition_ty); |
| |
| definition_ty |
| } |
| } |
| |
| // Visitor that requires that (almost) all regions in the type visited outlive |
| // `least_region`. We cannot use `push_outlives_components` because regions in |
| // closure signatures are not included in their outlives components. We need to |
| // ensure all regions outlive the given bound so that we don't end up with, |
| // say, `ReVar` appearing in a return type and causing ICEs when other |
| // functions end up with region constraints involving regions from other |
| // functions. |
| // |
| // We also cannot use `for_each_free_region` because for closures it includes |
| // the regions parameters from the enclosing item. |
| // |
| // We ignore any type parameters because impl trait values are assumed to |
| // capture all the in-scope type parameters. |
| struct ConstrainOpaqueTypeRegionVisitor<OP> { |
| op: OP, |
| } |
| |
| impl<'tcx, OP> TypeVisitor<'tcx> for ConstrainOpaqueTypeRegionVisitor<OP> |
| where |
| OP: FnMut(ty::Region<'tcx>), |
| { |
| fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> bool { |
| t.as_ref().skip_binder().visit_with(self); |
| false // keep visiting |
| } |
| |
| fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool { |
| match *r { |
| // ignore bound regions, keep visiting |
| ty::ReLateBound(_, _) => false, |
| _ => { |
| (self.op)(r); |
| false |
| } |
| } |
| } |
| |
| fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool { |
| // We're only interested in types involving regions |
| if !ty.flags().intersects(ty::TypeFlags::HAS_FREE_REGIONS) { |
| return false; // keep visiting |
| } |
| |
| match ty.kind() { |
| ty::Closure(_, ref substs) => { |
| // Skip lifetime parameters of the enclosing item(s) |
| |
| for upvar_ty in substs.as_closure().upvar_tys() { |
| upvar_ty.visit_with(self); |
| } |
| |
| substs.as_closure().sig_as_fn_ptr_ty().visit_with(self); |
| } |
| |
| ty::Generator(_, ref substs, _) => { |
| // Skip lifetime parameters of the enclosing item(s) |
| // Also skip the witness type, because that has no free regions. |
| |
| for upvar_ty in substs.as_generator().upvar_tys() { |
| upvar_ty.visit_with(self); |
| } |
| |
| substs.as_generator().return_ty().visit_with(self); |
| substs.as_generator().yield_ty().visit_with(self); |
| substs.as_generator().resume_ty().visit_with(self); |
| } |
| _ => { |
| ty.super_visit_with(self); |
| } |
| } |
| |
| false |
| } |
| } |
| |
| struct ReverseMapper<'tcx> { |
| tcx: TyCtxt<'tcx>, |
| |
| /// If errors have already been reported in this fn, we suppress |
| /// our own errors because they are sometimes derivative. |
| tainted_by_errors: bool, |
| |
| opaque_type_def_id: DefId, |
| map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>>, |
| map_missing_regions_to_empty: bool, |
| |
| /// initially `Some`, set to `None` once error has been reported |
| hidden_ty: Option<Ty<'tcx>>, |
| |
| /// Span of function being checked. |
| span: Span, |
| } |
| |
| impl ReverseMapper<'tcx> { |
| fn new( |
| tcx: TyCtxt<'tcx>, |
| tainted_by_errors: bool, |
| opaque_type_def_id: DefId, |
| map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>>, |
| hidden_ty: Ty<'tcx>, |
| span: Span, |
| ) -> Self { |
| Self { |
| tcx, |
| tainted_by_errors, |
| 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 TypeFolder<'tcx> for ReverseMapper<'tcx> { |
| fn tcx(&self) -> TyCtxt<'tcx> { |
| self.tcx |
| } |
| |
| 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 declaraion. |
| // 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.tainted_by_errors => { |
| 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(..) => { |
| // 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 => { |
| 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: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> { |
| trace!("checking const {:?}", ct); |
| // Find a const parameter |
| match ct.val { |
| 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, |
| } |
| } |
| } |
| |
| struct Instantiator<'a, 'tcx> { |
| infcx: &'a InferCtxt<'a, 'tcx>, |
| parent_def_id: LocalDefId, |
| body_id: hir::HirId, |
| param_env: ty::ParamEnv<'tcx>, |
| value_span: Span, |
| opaque_types: OpaqueTypeMap<'tcx>, |
| obligations: Vec<PredicateObligation<'tcx>>, |
| } |
| |
| impl<'a, 'tcx> Instantiator<'a, 'tcx> { |
| fn instantiate_opaque_types_in_map<T: TypeFoldable<'tcx>>(&mut self, value: &T) -> T { |
| debug!("instantiate_opaque_types_in_map(value={:?})", value); |
| let tcx = self.infcx.tcx; |
| value.fold_with(&mut BottomUpFolder { |
| tcx, |
| ty_op: |ty| { |
| if ty.references_error() { |
| return tcx.ty_error(); |
| } else if let ty::Opaque(def_id, substs) = ty.kind() { |
| // Check that this is `impl Trait` type is |
| // declared by `parent_def_id` -- i.e., one whose |
| // value we are inferring. At present, this is |
| // always true during the first phase of |
| // type-check, but not always true later on during |
| // NLL. Once we support named opaque types more fully, |
| // this same scenario will be able to arise during all phases. |
| // |
| // Here is an example using type alias `impl Trait` |
| // that indicates the distinction we are checking for: |
| // |
| // ```rust |
| // mod a { |
| // pub type Foo = impl Iterator; |
| // pub fn make_foo() -> Foo { .. } |
| // } |
| // |
| // mod b { |
| // fn foo() -> a::Foo { a::make_foo() } |
| // } |
| // ``` |
| // |
| // Here, the return type of `foo` references a |
| // `Opaque` indeed, but not one whose value is |
| // presently being inferred. You can get into a |
| // similar situation with closure return types |
| // today: |
| // |
| // ```rust |
| // fn foo() -> impl Iterator { .. } |
| // fn bar() { |
| // let x = || foo(); // returns the Opaque assoc with `foo` |
| // } |
| // ``` |
| if let Some(def_id) = def_id.as_local() { |
| let opaque_hir_id = tcx.hir().local_def_id_to_hir_id(def_id); |
| let parent_def_id = self.parent_def_id; |
| let def_scope_default = || { |
| let opaque_parent_hir_id = tcx.hir().get_parent_item(opaque_hir_id); |
| parent_def_id == tcx.hir().local_def_id(opaque_parent_hir_id) |
| }; |
| let (in_definition_scope, origin) = match tcx.hir().find(opaque_hir_id) { |
| Some(Node::Item(item)) => match item.kind { |
| // Anonymous `impl Trait` |
| hir::ItemKind::OpaqueTy(hir::OpaqueTy { |
| impl_trait_fn: Some(parent), |
| origin, |
| .. |
| }) => (parent == self.parent_def_id.to_def_id(), origin), |
| // Named `type Foo = impl Bar;` |
| hir::ItemKind::OpaqueTy(hir::OpaqueTy { |
| impl_trait_fn: None, |
| origin, |
| .. |
| }) => ( |
| may_define_opaque_type(tcx, self.parent_def_id, opaque_hir_id), |
| origin, |
| ), |
| _ => (def_scope_default(), hir::OpaqueTyOrigin::Misc), |
| }, |
| _ => bug!( |
| "expected item, found {}", |
| tcx.hir().node_to_string(opaque_hir_id), |
| ), |
| }; |
| if in_definition_scope { |
| return self.fold_opaque_ty(ty, def_id.to_def_id(), substs, origin); |
| } |
| |
| debug!( |
| "instantiate_opaque_types_in_map: \ |
| encountered opaque outside its definition scope \ |
| def_id={:?}", |
| def_id, |
| ); |
| } |
| } |
| |
| ty |
| }, |
| lt_op: |lt| lt, |
| ct_op: |ct| ct, |
| }) |
| } |
| |
| fn fold_opaque_ty( |
| &mut self, |
| ty: Ty<'tcx>, |
| def_id: DefId, |
| substs: SubstsRef<'tcx>, |
| origin: hir::OpaqueTyOrigin, |
| ) -> Ty<'tcx> { |
| let infcx = self.infcx; |
| let tcx = infcx.tcx; |
| |
| debug!("instantiate_opaque_types: Opaque(def_id={:?}, substs={:?})", def_id, substs); |
| |
| // Use the same type variable if the exact same opaque type appears more |
| // than once in the return type (e.g., if it's passed to a type alias). |
| if let Some(opaque_defn) = self.opaque_types.get(&def_id) { |
| debug!("instantiate_opaque_types: returning concrete ty {:?}", opaque_defn.concrete_ty); |
| return opaque_defn.concrete_ty; |
| } |
| let span = tcx.def_span(def_id); |
| debug!("fold_opaque_ty {:?} {:?}", self.value_span, span); |
| let ty_var = infcx |
| .next_ty_var(TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span }); |
| |
| let predicates_of = tcx.predicates_of(def_id); |
| debug!("instantiate_opaque_types: predicates={:#?}", predicates_of,); |
| let bounds = predicates_of.instantiate(tcx, substs); |
| |
| let param_env = tcx.param_env(def_id); |
| let InferOk { value: bounds, obligations } = |
| infcx.partially_normalize_associated_types_in(span, self.body_id, param_env, &bounds); |
| self.obligations.extend(obligations); |
| |
| debug!("instantiate_opaque_types: bounds={:?}", bounds); |
| |
| let required_region_bounds = |
| required_region_bounds(tcx, ty, bounds.predicates.iter().cloned()); |
| debug!("instantiate_opaque_types: required_region_bounds={:?}", required_region_bounds); |
| |
| // Make sure that we are in fact defining the *entire* type |
| // (e.g., `type Foo<T: Bound> = impl Bar;` needs to be |
| // defined by a function like `fn foo<T: Bound>() -> Foo<T>`). |
| debug!("instantiate_opaque_types: param_env={:#?}", self.param_env,); |
| debug!("instantiate_opaque_types: generics={:#?}", tcx.generics_of(def_id),); |
| |
| // Ideally, we'd get the span where *this specific `ty` came |
| // from*, but right now we just use the span from the overall |
| // value being folded. In simple cases like `-> impl Foo`, |
| // these are the same span, but not in cases like `-> (impl |
| // Foo, impl Bar)`. |
| let definition_span = self.value_span; |
| |
| self.opaque_types.insert( |
| def_id, |
| OpaqueTypeDecl { |
| opaque_type: ty, |
| substs, |
| definition_span, |
| concrete_ty: ty_var, |
| has_required_region_bounds: !required_region_bounds.is_empty(), |
| origin, |
| }, |
| ); |
| debug!("instantiate_opaque_types: ty_var={:?}", ty_var); |
| |
| for predicate in &bounds.predicates { |
| if let ty::PredicateAtom::Projection(projection) = predicate.skip_binders() { |
| if projection.ty.references_error() { |
| // No point on adding these obligations since there's a type error involved. |
| return ty_var; |
| } |
| } |
| } |
| |
| self.obligations.reserve(bounds.predicates.len()); |
| for predicate in bounds.predicates { |
| // Change the predicate to refer to the type variable, |
| // which will be the concrete type instead of the opaque type. |
| // This also instantiates nested instances of `impl Trait`. |
| let predicate = self.instantiate_opaque_types_in_map(&predicate); |
| |
| let cause = traits::ObligationCause::new(span, self.body_id, traits::SizedReturnType); |
| |
| // Require that the predicate holds for the concrete type. |
| debug!("instantiate_opaque_types: predicate={:?}", predicate); |
| self.obligations.push(traits::Obligation::new(cause, self.param_env, predicate)); |
| } |
| |
| ty_var |
| } |
| } |
| |
| /// Returns `true` if `opaque_hir_id` is a sibling or a child of a sibling of `def_id`. |
| /// |
| /// Example: |
| /// ```rust |
| /// pub mod foo { |
| /// pub mod bar { |
| /// pub trait Bar { .. } |
| /// |
| /// pub type Baz = impl Bar; |
| /// |
| /// fn f1() -> Baz { .. } |
| /// } |
| /// |
| /// fn f2() -> bar::Baz { .. } |
| /// } |
| /// ``` |
| /// |
| /// Here, `def_id` is the `LocalDefId` of the defining use of the opaque type (e.g., `f1` or `f2`), |
| /// and `opaque_hir_id` is the `HirId` of the definition of the opaque type `Baz`. |
| /// For the above example, this function returns `true` for `f1` and `false` for `f2`. |
| pub fn may_define_opaque_type( |
| tcx: TyCtxt<'_>, |
| def_id: LocalDefId, |
| opaque_hir_id: hir::HirId, |
| ) -> bool { |
| let mut hir_id = tcx.hir().local_def_id_to_hir_id(def_id); |
| |
| // Named opaque types can be defined by any siblings or children of siblings. |
| let scope = tcx.hir().get_defining_scope(opaque_hir_id); |
| // We walk up the node tree until we hit the root or the scope of the opaque type. |
| while hir_id != scope && hir_id != hir::CRATE_HIR_ID { |
| hir_id = tcx.hir().get_parent_item(hir_id); |
| } |
| // Syntactically, we are allowed to define the concrete type if: |
| let res = hir_id == scope; |
| trace!( |
| "may_define_opaque_type(def={:?}, opaque_node={:?}) = {}", |
| tcx.hir().find(hir_id), |
| tcx.hir().get(opaque_hir_id), |
| res |
| ); |
| res |
| } |
| |
| /// 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. |
| crate fn required_region_bounds( |
| tcx: TyCtxt<'tcx>, |
| erased_self_ty: Ty<'tcx>, |
| predicates: impl Iterator<Item = ty::Predicate<'tcx>>, |
| ) -> Vec<ty::Region<'tcx>> { |
| debug!("required_region_bounds(erased_self_ty={:?})", erased_self_ty); |
| |
| assert!(!erased_self_ty.has_escaping_bound_vars()); |
| |
| traits::elaborate_predicates(tcx, predicates) |
| .filter_map(|obligation| { |
| debug!("required_region_bounds(obligation={:?})", obligation); |
| match obligation.predicate.skip_binders() { |
| ty::PredicateAtom::Projection(..) |
| | ty::PredicateAtom::Trait(..) |
| | ty::PredicateAtom::Subtype(..) |
| | ty::PredicateAtom::WellFormed(..) |
| | ty::PredicateAtom::ObjectSafe(..) |
| | ty::PredicateAtom::ClosureKind(..) |
| | ty::PredicateAtom::RegionOutlives(..) |
| | ty::PredicateAtom::ConstEvaluatable(..) |
| | ty::PredicateAtom::ConstEquate(..) |
| | ty::PredicateAtom::TypeWellFormedFromEnv(..) => None, |
| ty::PredicateAtom::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() |
| } |
