| use super::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; |
| use super::{DefineOpaqueTypes, InferResult}; |
| use crate::errors::OpaqueHiddenTypeDiag; |
| use crate::infer::{InferCtxt, InferOk}; |
| use crate::traits::{self, PredicateObligation}; |
| use hir::def_id::{DefId, LocalDefId}; |
| use hir::OpaqueTyOrigin; |
| use rustc_data_structures::fx::FxIndexMap; |
| use rustc_data_structures::sync::Lrc; |
| use rustc_hir as hir; |
| use rustc_middle::traits::{DefiningAnchor, ObligationCause}; |
| use rustc_middle::ty::error::{ExpectedFound, TypeError}; |
| use rustc_middle::ty::fold::BottomUpFolder; |
| use rustc_middle::ty::GenericArgKind; |
| use rustc_middle::ty::{ |
| self, OpaqueHiddenType, OpaqueTypeKey, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable, |
| TypeVisitable, TypeVisitableExt, TypeVisitor, |
| }; |
| use rustc_span::Span; |
| use std::ops::ControlFlow; |
| |
| mod table; |
| |
| pub type OpaqueTypeMap<'tcx> = FxIndexMap<OpaqueTypeKey<'tcx>, OpaqueTypeDecl<'tcx>>; |
| pub use table::{OpaqueTypeStorage, OpaqueTypeTable}; |
| |
| /// 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(Clone, Debug)] |
| pub struct OpaqueTypeDecl<'tcx> { |
| /// The hidden types that have been inferred for this opaque type. |
| /// There can be multiple, but they are all `lub`ed together at the end |
| /// to obtain the canonical hidden type. |
| pub hidden_type: OpaqueHiddenType<'tcx>, |
| } |
| |
| impl<'tcx> InferCtxt<'tcx> { |
| /// This is a backwards compatibility hack to prevent breaking changes from |
| /// lazy TAIT around RPIT handling. |
| pub fn replace_opaque_types_with_inference_vars<T: TypeFoldable<TyCtxt<'tcx>>>( |
| &self, |
| value: T, |
| body_id: LocalDefId, |
| span: Span, |
| param_env: ty::ParamEnv<'tcx>, |
| ) -> InferOk<'tcx, T> { |
| // We handle opaque types differently in the new solver. |
| if self.next_trait_solver() { |
| return InferOk { value, obligations: vec![] }; |
| } |
| |
| if !value.has_opaque_types() { |
| return InferOk { value, obligations: vec![] }; |
| } |
| |
| let mut obligations = vec![]; |
| let replace_opaque_type = |def_id: DefId| { |
| def_id.as_local().is_some_and(|def_id| self.opaque_type_origin(def_id).is_some()) |
| }; |
| let value = value.fold_with(&mut BottomUpFolder { |
| tcx: self.tcx, |
| lt_op: |lt| lt, |
| ct_op: |ct| ct, |
| ty_op: |ty| match *ty.kind() { |
| ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }) |
| if replace_opaque_type(def_id) && !ty.has_escaping_bound_vars() => |
| { |
| let def_span = self.tcx.def_span(def_id); |
| let span = if span.contains(def_span) { def_span } else { span }; |
| let code = traits::ObligationCauseCode::OpaqueReturnType(None); |
| let cause = ObligationCause::new(span, body_id, code); |
| // FIXME(compiler-errors): We probably should add a new TypeVariableOriginKind |
| // for opaque types, and then use that kind to fix the spans for type errors |
| // that we see later on. |
| let ty_var = self.next_ty_var(TypeVariableOrigin { |
| kind: TypeVariableOriginKind::OpaqueTypeInference(def_id), |
| span, |
| }); |
| obligations.extend( |
| self.handle_opaque_type(ty, ty_var, true, &cause, param_env) |
| .unwrap() |
| .obligations, |
| ); |
| ty_var |
| } |
| _ => ty, |
| }, |
| }); |
| InferOk { value, obligations } |
| } |
| |
| pub fn handle_opaque_type( |
| &self, |
| a: Ty<'tcx>, |
| b: Ty<'tcx>, |
| a_is_expected: bool, |
| cause: &ObligationCause<'tcx>, |
| param_env: ty::ParamEnv<'tcx>, |
| ) -> InferResult<'tcx, ()> { |
| if a.references_error() || b.references_error() { |
| return Ok(InferOk { value: (), obligations: vec![] }); |
| } |
| let (a, b) = if a_is_expected { (a, b) } else { (b, a) }; |
| let process = |a: Ty<'tcx>, b: Ty<'tcx>, a_is_expected| match *a.kind() { |
| ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) if def_id.is_local() => { |
| let def_id = def_id.expect_local(); |
| match self.defining_use_anchor { |
| DefiningAnchor::Bind(_) => { |
| // 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 an |
| // `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 self.opaque_type_origin(def_id).is_none() { |
| return None; |
| } |
| } |
| DefiningAnchor::Bubble => {} |
| DefiningAnchor::Error => return None, |
| }; |
| if let ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, .. }) = *b.kind() { |
| // We could accept this, but there are various ways to handle this situation, and we don't |
| // want to make a decision on it right now. Likely this case is so super rare anyway, that |
| // no one encounters it in practice. |
| // It does occur however in `fn fut() -> impl Future<Output = i32> { async { 42 } }`, |
| // where it is of no concern, so we only check for TAITs. |
| if let Some(OpaqueTyOrigin::TyAlias { .. }) = |
| b_def_id.as_local().and_then(|b_def_id| self.opaque_type_origin(b_def_id)) |
| { |
| self.tcx.sess.emit_err(OpaqueHiddenTypeDiag { |
| span: cause.span, |
| hidden_type: self.tcx.def_span(b_def_id), |
| opaque_type: self.tcx.def_span(def_id), |
| }); |
| } |
| } |
| Some(self.register_hidden_type( |
| OpaqueTypeKey { def_id, args }, |
| cause.clone(), |
| param_env, |
| b, |
| a_is_expected, |
| )) |
| } |
| _ => None, |
| }; |
| if let Some(res) = process(a, b, true) { |
| res |
| } else if let Some(res) = process(b, a, false) { |
| res |
| } else { |
| let (a, b) = self.resolve_vars_if_possible((a, b)); |
| Err(TypeError::Sorts(ExpectedFound::new(true, a, b))) |
| } |
| } |
| |
| /// 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>) { .. } |
| /// // ^^^^ ^^ |
| /// // | | |
| /// // | args |
| /// // def_id |
| /// ``` |
| /// |
| /// As indicating in the comments above, each of those references |
| /// is (in the compiler) basically a substitution (`args`) |
| /// 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 args: 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` itself. |
| /// For example, if we had a function like this: |
| /// |
| /// ``` |
| /// # #![feature(type_alias_impl_trait)] |
| /// # fn main() {} |
| /// # trait Foo<'a> {} |
| /// # impl<'a, T> Foo<'a> for (&'a u32, T) {} |
| /// fn foo<'a, T>(x: &'a u32, y: T) -> impl Foo<'a> { |
| /// (x, y) |
| /// } |
| /// |
| /// // Equivalent to: |
| /// # mod dummy { use super::*; |
| /// type FooReturn<'a, T> = impl Foo<'a>; |
| /// fn foo<'a, T>(x: &'a u32, y: T) -> FooReturn<'a, T> { |
| /// (x, y) |
| /// } |
| /// # } |
| /// ``` |
| /// |
| /// 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`. |
| #[instrument(level = "debug", skip(self))] |
| pub fn register_member_constraints( |
| &self, |
| param_env: ty::ParamEnv<'tcx>, |
| opaque_type_key: OpaqueTypeKey<'tcx>, |
| concrete_ty: Ty<'tcx>, |
| span: Span, |
| ) { |
| let concrete_ty = self.resolve_vars_if_possible(concrete_ty); |
| debug!(?concrete_ty); |
| |
| let variances = self.tcx.variances_of(opaque_type_key.def_id); |
| debug!(?variances); |
| |
| // For a case like `impl Foo<'a, 'b>`, 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. |
| |
| // 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_type_key |
| .args |
| .iter() |
| .enumerate() |
| .filter(|(i, _)| variances[*i] == ty::Variance::Invariant) |
| .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 { |
| tcx: self.tcx, |
| op: |r| self.member_constraint(opaque_type_key, span, concrete_ty, r, &choice_regions), |
| }); |
| } |
| |
| /// Returns the origin of the opaque type `def_id` if we're currently |
| /// in its defining scope. |
| #[instrument(skip(self), level = "trace", ret)] |
| pub fn opaque_type_origin(&self, def_id: LocalDefId) -> Option<OpaqueTyOrigin> { |
| let opaque_hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id); |
| let parent_def_id = match self.defining_use_anchor { |
| DefiningAnchor::Bubble | DefiningAnchor::Error => return None, |
| DefiningAnchor::Bind(bind) => bind, |
| }; |
| |
| let origin = self.tcx.opaque_type_origin(def_id); |
| let in_definition_scope = match origin { |
| // Async `impl Trait` |
| hir::OpaqueTyOrigin::AsyncFn(parent) => parent == parent_def_id, |
| // Anonymous `impl Trait` |
| hir::OpaqueTyOrigin::FnReturn(parent) => parent == parent_def_id, |
| // Named `type Foo = impl Bar;` |
| hir::OpaqueTyOrigin::TyAlias { in_assoc_ty } => { |
| if in_assoc_ty { |
| self.tcx.opaque_types_defined_by(parent_def_id).contains(&def_id) |
| } else { |
| may_define_opaque_type(self.tcx, parent_def_id, opaque_hir_id) |
| } |
| } |
| }; |
| in_definition_scope.then_some(origin) |
| } |
| } |
| |
| /// 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. |
| pub struct ConstrainOpaqueTypeRegionVisitor<'tcx, OP: FnMut(ty::Region<'tcx>)> { |
| pub tcx: TyCtxt<'tcx>, |
| pub op: OP, |
| } |
| |
| impl<'tcx, OP> TypeVisitor<TyCtxt<'tcx>> for ConstrainOpaqueTypeRegionVisitor<'tcx, OP> |
| where |
| OP: FnMut(ty::Region<'tcx>), |
| { |
| fn visit_binder<T: TypeVisitable<TyCtxt<'tcx>>>( |
| &mut self, |
| t: &ty::Binder<'tcx, T>, |
| ) -> ControlFlow<Self::BreakTy> { |
| t.super_visit_with(self); |
| ControlFlow::Continue(()) |
| } |
| |
| fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> { |
| match *r { |
| // ignore bound regions, keep visiting |
| ty::ReLateBound(_, _) => ControlFlow::Continue(()), |
| _ => { |
| (self.op)(r); |
| ControlFlow::Continue(()) |
| } |
| } |
| } |
| |
| fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> { |
| // We're only interested in types involving regions |
| if !ty.flags().intersects(ty::TypeFlags::HAS_FREE_REGIONS) { |
| return ControlFlow::Continue(()); |
| } |
| |
| match ty.kind() { |
| ty::Closure(_, ref args) => { |
| // Skip lifetime parameters of the enclosing item(s) |
| |
| for upvar in args.as_closure().upvar_tys() { |
| upvar.visit_with(self); |
| } |
| args.as_closure().sig_as_fn_ptr_ty().visit_with(self); |
| } |
| |
| ty::Generator(_, ref args, _) => { |
| // Skip lifetime parameters of the enclosing item(s) |
| // Also skip the witness type, because that has no free regions. |
| |
| for upvar in args.as_generator().upvar_tys() { |
| upvar.visit_with(self); |
| } |
| args.as_generator().return_ty().visit_with(self); |
| args.as_generator().yield_ty().visit_with(self); |
| args.as_generator().resume_ty().visit_with(self); |
| } |
| |
| ty::Alias(ty::Opaque, ty::AliasTy { def_id, ref args, .. }) => { |
| // Skip lifetime parameters that are not captures. |
| let variances = self.tcx.variances_of(*def_id); |
| |
| for (v, s) in std::iter::zip(variances, args.iter()) { |
| if *v != ty::Variance::Bivariant { |
| s.visit_with(self); |
| } |
| } |
| } |
| |
| _ => { |
| ty.super_visit_with(self); |
| } |
| } |
| |
| ControlFlow::Continue(()) |
| } |
| } |
| |
| pub enum UseKind { |
| DefiningUse, |
| OpaqueUse, |
| } |
| |
| impl UseKind { |
| pub fn is_defining(self) -> bool { |
| match self { |
| UseKind::DefiningUse => true, |
| UseKind::OpaqueUse => false, |
| } |
| } |
| } |
| |
| impl<'tcx> InferCtxt<'tcx> { |
| #[instrument(skip(self), level = "debug")] |
| fn register_hidden_type( |
| &self, |
| opaque_type_key: OpaqueTypeKey<'tcx>, |
| cause: ObligationCause<'tcx>, |
| param_env: ty::ParamEnv<'tcx>, |
| hidden_ty: Ty<'tcx>, |
| a_is_expected: bool, |
| ) -> InferResult<'tcx, ()> { |
| let mut obligations = Vec::new(); |
| |
| self.insert_hidden_type( |
| opaque_type_key, |
| &cause, |
| param_env, |
| hidden_ty, |
| a_is_expected, |
| &mut obligations, |
| )?; |
| |
| self.add_item_bounds_for_hidden_type( |
| opaque_type_key.def_id.to_def_id(), |
| opaque_type_key.args, |
| cause, |
| param_env, |
| hidden_ty, |
| &mut obligations, |
| ); |
| |
| Ok(InferOk { value: (), obligations }) |
| } |
| |
| /// Insert a hidden type into the opaque type storage, equating it |
| /// with any previous entries if necessary. |
| /// |
| /// This **does not** add the item bounds of the opaque as nested |
| /// obligations. That is only necessary when normalizing the opaque |
| /// itself, not when getting the opaque type constraints from |
| /// somewhere else. |
| pub fn insert_hidden_type( |
| &self, |
| opaque_type_key: OpaqueTypeKey<'tcx>, |
| cause: &ObligationCause<'tcx>, |
| param_env: ty::ParamEnv<'tcx>, |
| hidden_ty: Ty<'tcx>, |
| a_is_expected: bool, |
| obligations: &mut Vec<PredicateObligation<'tcx>>, |
| ) -> Result<(), TypeError<'tcx>> { |
| // 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 span = cause.span; |
| if self.intercrate { |
| // During intercrate we do not define opaque types but instead always |
| // force ambiguity unless the hidden type is known to not implement |
| // our trait. |
| obligations.push(traits::Obligation::new( |
| self.tcx, |
| cause.clone(), |
| param_env, |
| ty::PredicateKind::Ambiguous, |
| )) |
| } else { |
| let prev = self |
| .inner |
| .borrow_mut() |
| .opaque_types() |
| .register(opaque_type_key, OpaqueHiddenType { ty: hidden_ty, span }); |
| if let Some(prev) = prev { |
| obligations.extend( |
| self.at(&cause, param_env) |
| .eq_exp(DefineOpaqueTypes::Yes, a_is_expected, prev, hidden_ty)? |
| .obligations, |
| ); |
| } |
| }; |
| |
| Ok(()) |
| } |
| |
| pub fn add_item_bounds_for_hidden_type( |
| &self, |
| def_id: DefId, |
| args: ty::GenericArgsRef<'tcx>, |
| cause: ObligationCause<'tcx>, |
| param_env: ty::ParamEnv<'tcx>, |
| hidden_ty: Ty<'tcx>, |
| obligations: &mut Vec<PredicateObligation<'tcx>>, |
| ) { |
| let tcx = self.tcx; |
| let item_bounds = tcx.explicit_item_bounds(def_id); |
| |
| for (predicate, _) in item_bounds.iter_instantiated_copied(tcx, args) { |
| let predicate = predicate.fold_with(&mut BottomUpFolder { |
| tcx, |
| ty_op: |ty| match *ty.kind() { |
| // We can't normalize associated types from `rustc_infer`, |
| // but we can eagerly register inference variables for them. |
| // FIXME(RPITIT): Don't replace RPITITs with inference vars. |
| // FIXME(inherent_associated_types): Extend this to support `ty::Inherent`, too. |
| ty::Alias(ty::Projection, projection_ty) |
| if !projection_ty.has_escaping_bound_vars() |
| && !tcx.is_impl_trait_in_trait(projection_ty.def_id) |
| && !self.next_trait_solver() => |
| { |
| self.infer_projection( |
| param_env, |
| projection_ty, |
| cause.clone(), |
| 0, |
| obligations, |
| ) |
| } |
| // Replace all other mentions of the same opaque type with the hidden type, |
| // as the bounds must hold on the hidden type after all. |
| ty::Alias(ty::Opaque, ty::AliasTy { def_id: def_id2, args: args2, .. }) |
| if def_id == def_id2 && args == args2 => |
| { |
| hidden_ty |
| } |
| _ => ty, |
| }, |
| lt_op: |lt| lt, |
| ct_op: |ct| ct, |
| }); |
| |
| if let ty::ClauseKind::Projection(projection) = predicate.kind().skip_binder() { |
| if projection.term.references_error() { |
| // No point on adding any obligations since there's a type error involved. |
| obligations.clear(); |
| return; |
| } |
| } |
| // Require that the predicate holds for the concrete type. |
| debug!(?predicate); |
| obligations.push(traits::Obligation::new( |
| self.tcx, |
| cause.clone(), |
| param_env, |
| predicate, |
| )); |
| } |
| } |
| } |
| |
| /// Returns `true` if `opaque_hir_id` is a sibling or a child of a sibling of `def_id`. |
| /// |
| /// Example: |
| /// ```ignore UNSOLVED (is this a bug?) |
| /// # #![feature(type_alias_impl_trait)] |
| /// pub mod foo { |
| /// pub mod bar { |
| /// pub trait Bar { /* ... */ } |
| /// pub type Baz = impl Bar; |
| /// |
| /// # impl Bar for () {} |
| /// 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`. |
| 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).into(); |
| } |
| // 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 |
| } |
