| //! Code for type-checking closure expressions. |
| |
| use super::{check_fn, CoroutineTypes, Expectation, FnCtxt}; |
| |
| use rustc_errors::ErrorGuaranteed; |
| use rustc_hir as hir; |
| use rustc_hir::lang_items::LangItem; |
| use rustc_hir_analysis::hir_ty_lowering::HirTyLowerer; |
| use rustc_infer::infer::type_variable::TypeVariableOrigin; |
| use rustc_infer::infer::{BoundRegionConversionTime, DefineOpaqueTypes}; |
| use rustc_infer::infer::{InferOk, InferResult}; |
| use rustc_macros::{TypeFoldable, TypeVisitable}; |
| use rustc_middle::ty::visit::{TypeVisitable, TypeVisitableExt}; |
| use rustc_middle::ty::GenericArgs; |
| use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor}; |
| use rustc_span::def_id::LocalDefId; |
| use rustc_span::Span; |
| use rustc_target::spec::abi::Abi; |
| use rustc_trait_selection::traits; |
| use rustc_trait_selection::traits::error_reporting::ArgKind; |
| use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _; |
| use rustc_type_ir::ClosureKind; |
| use std::iter; |
| use std::ops::ControlFlow; |
| |
| /// What signature do we *expect* the closure to have from context? |
| #[derive(Debug, Clone, TypeFoldable, TypeVisitable)] |
| struct ExpectedSig<'tcx> { |
| /// Span that gave us this expectation, if we know that. |
| cause_span: Option<Span>, |
| sig: ty::PolyFnSig<'tcx>, |
| } |
| |
| #[derive(Debug)] |
| struct ClosureSignatures<'tcx> { |
| /// The signature users of the closure see. |
| bound_sig: ty::PolyFnSig<'tcx>, |
| /// The signature within the function body. |
| /// This mostly differs in the sense that lifetimes are now early bound and any |
| /// opaque types from the signature expectation are overridden in case there are |
| /// explicit hidden types written by the user in the closure signature. |
| liberated_sig: ty::FnSig<'tcx>, |
| } |
| |
| impl<'a, 'tcx> FnCtxt<'a, 'tcx> { |
| #[instrument(skip(self, closure), level = "debug")] |
| pub fn check_expr_closure( |
| &self, |
| closure: &hir::Closure<'tcx>, |
| expr_span: Span, |
| expected: Expectation<'tcx>, |
| ) -> Ty<'tcx> { |
| let tcx = self.tcx; |
| let body = tcx.hir().body(closure.body); |
| let expr_def_id = closure.def_id; |
| |
| // It's always helpful for inference if we know the kind of |
| // closure sooner rather than later, so first examine the expected |
| // type, and see if can glean a closure kind from there. |
| let (expected_sig, expected_kind) = match expected.to_option(self) { |
| Some(ty) => self.deduce_closure_signature( |
| self.try_structurally_resolve_type(expr_span, ty), |
| closure.kind, |
| ), |
| None => (None, None), |
| }; |
| |
| let ClosureSignatures { bound_sig, mut liberated_sig } = |
| self.sig_of_closure(expr_def_id, closure.fn_decl, closure.kind, expected_sig); |
| |
| debug!(?bound_sig, ?liberated_sig); |
| |
| let parent_args = |
| GenericArgs::identity_for_item(tcx, tcx.typeck_root_def_id(expr_def_id.to_def_id())); |
| |
| let tupled_upvars_ty = |
| self.next_ty_var(TypeVariableOrigin { param_def_id: None, span: expr_span }); |
| |
| // FIXME: We could probably actually just unify this further -- |
| // instead of having a `FnSig` and a `Option<CoroutineTypes>`, |
| // we can have a `ClosureSignature { Coroutine { .. }, Closure { .. } }`, |
| // similar to how `ty::GenSig` is a distinct data structure. |
| let (closure_ty, coroutine_types) = match closure.kind { |
| hir::ClosureKind::Closure => { |
| // Tuple up the arguments and insert the resulting function type into |
| // the `closures` table. |
| let sig = bound_sig.map_bound(|sig| { |
| tcx.mk_fn_sig( |
| [Ty::new_tup(tcx, sig.inputs())], |
| sig.output(), |
| sig.c_variadic, |
| sig.unsafety, |
| sig.abi, |
| ) |
| }); |
| |
| debug!(?sig, ?expected_kind); |
| |
| let closure_kind_ty = match expected_kind { |
| Some(kind) => Ty::from_closure_kind(tcx, kind), |
| |
| // Create a type variable (for now) to represent the closure kind. |
| // It will be unified during the upvar inference phase (`upvar.rs`) |
| None => { |
| self.next_ty_var(TypeVariableOrigin { param_def_id: None, span: expr_span }) |
| } |
| }; |
| |
| let closure_args = ty::ClosureArgs::new( |
| tcx, |
| ty::ClosureArgsParts { |
| parent_args, |
| closure_kind_ty, |
| closure_sig_as_fn_ptr_ty: Ty::new_fn_ptr(tcx, sig), |
| tupled_upvars_ty, |
| }, |
| ); |
| |
| (Ty::new_closure(tcx, expr_def_id.to_def_id(), closure_args.args), None) |
| } |
| hir::ClosureKind::Coroutine(kind) => { |
| let yield_ty = match kind { |
| hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Gen, _) |
| | hir::CoroutineKind::Coroutine(_) => { |
| let yield_ty = self.next_ty_var(TypeVariableOrigin { |
| param_def_id: None, |
| span: expr_span, |
| }); |
| self.require_type_is_sized(yield_ty, expr_span, traits::SizedYieldType); |
| yield_ty |
| } |
| // HACK(-Ztrait-solver=next): In the *old* trait solver, we must eagerly |
| // guide inference on the yield type so that we can handle `AsyncIterator` |
| // in this block in projection correctly. In the new trait solver, it is |
| // not a problem. |
| hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::AsyncGen, _) => { |
| let yield_ty = self.next_ty_var(TypeVariableOrigin { |
| param_def_id: None, |
| span: expr_span, |
| }); |
| self.require_type_is_sized(yield_ty, expr_span, traits::SizedYieldType); |
| |
| Ty::new_adt( |
| tcx, |
| tcx.adt_def( |
| tcx.require_lang_item(hir::LangItem::Poll, Some(expr_span)), |
| ), |
| tcx.mk_args(&[Ty::new_adt( |
| tcx, |
| tcx.adt_def( |
| tcx.require_lang_item(hir::LangItem::Option, Some(expr_span)), |
| ), |
| tcx.mk_args(&[yield_ty.into()]), |
| ) |
| .into()]), |
| ) |
| } |
| hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Async, _) => { |
| tcx.types.unit |
| } |
| }; |
| |
| // Resume type defaults to `()` if the coroutine has no argument. |
| let resume_ty = liberated_sig.inputs().get(0).copied().unwrap_or(tcx.types.unit); |
| |
| let interior = |
| self.next_ty_var(TypeVariableOrigin { param_def_id: None, span: expr_span }); |
| self.deferred_coroutine_interiors.borrow_mut().push(( |
| expr_def_id, |
| body.id(), |
| interior, |
| )); |
| |
| // Coroutines that come from coroutine closures have not yet determined |
| // their kind ty, so make a fresh infer var which will be constrained |
| // later during upvar analysis. Regular coroutines always have the kind |
| // ty of `().` |
| let kind_ty = match kind { |
| hir::CoroutineKind::Desugared(_, hir::CoroutineSource::Closure) => { |
| self.next_ty_var(TypeVariableOrigin { param_def_id: None, span: expr_span }) |
| } |
| _ => tcx.types.unit, |
| }; |
| |
| let coroutine_args = ty::CoroutineArgs::new( |
| tcx, |
| ty::CoroutineArgsParts { |
| parent_args, |
| kind_ty, |
| resume_ty, |
| yield_ty, |
| return_ty: liberated_sig.output(), |
| witness: interior, |
| tupled_upvars_ty, |
| }, |
| ); |
| |
| ( |
| Ty::new_coroutine(tcx, expr_def_id.to_def_id(), coroutine_args.args), |
| Some(CoroutineTypes { resume_ty, yield_ty }), |
| ) |
| } |
| hir::ClosureKind::CoroutineClosure(kind) => { |
| // async closures always return the type ascribed after the `->` (if present), |
| // and yield `()`. |
| let (bound_return_ty, bound_yield_ty) = match kind { |
| hir::CoroutineDesugaring::Async => { |
| (bound_sig.skip_binder().output(), tcx.types.unit) |
| } |
| hir::CoroutineDesugaring::Gen | hir::CoroutineDesugaring::AsyncGen => { |
| todo!("`gen` and `async gen` closures not supported yet") |
| } |
| }; |
| // Compute all of the variables that will be used to populate the coroutine. |
| let resume_ty = |
| self.next_ty_var(TypeVariableOrigin { param_def_id: None, span: expr_span }); |
| let interior = |
| self.next_ty_var(TypeVariableOrigin { param_def_id: None, span: expr_span }); |
| |
| let closure_kind_ty = match expected_kind { |
| Some(kind) => Ty::from_closure_kind(tcx, kind), |
| |
| // Create a type variable (for now) to represent the closure kind. |
| // It will be unified during the upvar inference phase (`upvar.rs`) |
| None => { |
| self.next_ty_var(TypeVariableOrigin { param_def_id: None, span: expr_span }) |
| } |
| }; |
| |
| let coroutine_captures_by_ref_ty = |
| self.next_ty_var(TypeVariableOrigin { param_def_id: None, span: expr_span }); |
| let closure_args = ty::CoroutineClosureArgs::new( |
| tcx, |
| ty::CoroutineClosureArgsParts { |
| parent_args, |
| closure_kind_ty, |
| signature_parts_ty: Ty::new_fn_ptr( |
| tcx, |
| bound_sig.map_bound(|sig| { |
| tcx.mk_fn_sig( |
| [ |
| resume_ty, |
| Ty::new_tup_from_iter(tcx, sig.inputs().iter().copied()), |
| ], |
| Ty::new_tup(tcx, &[bound_yield_ty, bound_return_ty]), |
| sig.c_variadic, |
| sig.unsafety, |
| sig.abi, |
| ) |
| }), |
| ), |
| tupled_upvars_ty, |
| coroutine_captures_by_ref_ty, |
| coroutine_witness_ty: interior, |
| }, |
| ); |
| |
| let coroutine_kind_ty = match expected_kind { |
| Some(kind) => Ty::from_coroutine_closure_kind(tcx, kind), |
| |
| // Create a type variable (for now) to represent the closure kind. |
| // It will be unified during the upvar inference phase (`upvar.rs`) |
| None => { |
| self.next_ty_var(TypeVariableOrigin { param_def_id: None, span: expr_span }) |
| } |
| }; |
| |
| let coroutine_upvars_ty = |
| self.next_ty_var(TypeVariableOrigin { param_def_id: None, span: expr_span }); |
| |
| // We need to turn the liberated signature that we got from HIR, which |
| // looks something like `|Args...| -> T`, into a signature that is suitable |
| // for type checking the inner body of the closure, which always returns a |
| // coroutine. To do so, we use the `CoroutineClosureSignature` to compute |
| // the coroutine type, filling in the tupled_upvars_ty and kind_ty with infer |
| // vars which will get constrained during upvar analysis. |
| let coroutine_output_ty = tcx.liberate_late_bound_regions( |
| expr_def_id.to_def_id(), |
| closure_args.coroutine_closure_sig().map_bound(|sig| { |
| sig.to_coroutine( |
| tcx, |
| parent_args, |
| coroutine_kind_ty, |
| tcx.coroutine_for_closure(expr_def_id), |
| coroutine_upvars_ty, |
| ) |
| }), |
| ); |
| liberated_sig = tcx.mk_fn_sig( |
| liberated_sig.inputs().iter().copied(), |
| coroutine_output_ty, |
| liberated_sig.c_variadic, |
| liberated_sig.unsafety, |
| liberated_sig.abi, |
| ); |
| |
| (Ty::new_coroutine_closure(tcx, expr_def_id.to_def_id(), closure_args.args), None) |
| } |
| }; |
| |
| check_fn( |
| &mut FnCtxt::new(self, self.param_env, closure.def_id), |
| liberated_sig, |
| coroutine_types, |
| closure.fn_decl, |
| expr_def_id, |
| body, |
| // Closure "rust-call" ABI doesn't support unsized params |
| false, |
| ); |
| |
| closure_ty |
| } |
| |
| /// Given the expected type, figures out what it can about this closure we |
| /// are about to type check: |
| #[instrument(skip(self), level = "debug")] |
| fn deduce_closure_signature( |
| &self, |
| expected_ty: Ty<'tcx>, |
| closure_kind: hir::ClosureKind, |
| ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) { |
| match *expected_ty.kind() { |
| ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => self |
| .deduce_closure_signature_from_predicates( |
| expected_ty, |
| closure_kind, |
| self.tcx |
| .explicit_item_super_predicates(def_id) |
| .iter_instantiated_copied(self.tcx, args) |
| .map(|(c, s)| (c.as_predicate(), s)), |
| ), |
| ty::Dynamic(object_type, ..) => { |
| let sig = object_type.projection_bounds().find_map(|pb| { |
| let pb = pb.with_self_ty(self.tcx, self.tcx.types.trait_object_dummy_self); |
| self.deduce_sig_from_projection(None, closure_kind, pb) |
| }); |
| let kind = object_type |
| .principal_def_id() |
| .and_then(|did| self.tcx.fn_trait_kind_from_def_id(did)); |
| (sig, kind) |
| } |
| ty::Infer(ty::TyVar(vid)) => self.deduce_closure_signature_from_predicates( |
| Ty::new_var(self.tcx, self.root_var(vid)), |
| closure_kind, |
| self.obligations_for_self_ty(vid) |
| .into_iter() |
| .map(|obl| (obl.predicate, obl.cause.span)), |
| ), |
| ty::FnPtr(sig) => match closure_kind { |
| hir::ClosureKind::Closure => { |
| let expected_sig = ExpectedSig { cause_span: None, sig }; |
| (Some(expected_sig), Some(ty::ClosureKind::Fn)) |
| } |
| hir::ClosureKind::Coroutine(_) | hir::ClosureKind::CoroutineClosure(_) => { |
| (None, None) |
| } |
| }, |
| _ => (None, None), |
| } |
| } |
| |
| fn deduce_closure_signature_from_predicates( |
| &self, |
| expected_ty: Ty<'tcx>, |
| closure_kind: hir::ClosureKind, |
| predicates: impl DoubleEndedIterator<Item = (ty::Predicate<'tcx>, Span)>, |
| ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) { |
| let mut expected_sig = None; |
| let mut expected_kind = None; |
| |
| for (pred, span) in traits::elaborate( |
| self.tcx, |
| // Reverse the obligations here, since `elaborate_*` uses a stack, |
| // and we want to keep inference generally in the same order of |
| // the registered obligations. |
| predicates.rev(), |
| ) |
| // We only care about self bounds |
| .filter_only_self() |
| { |
| debug!(?pred); |
| let bound_predicate = pred.kind(); |
| |
| // Given a Projection predicate, we can potentially infer |
| // the complete signature. |
| if expected_sig.is_none() |
| && let ty::PredicateKind::Clause(ty::ClauseKind::Projection(proj_predicate)) = |
| bound_predicate.skip_binder() |
| { |
| let inferred_sig = self.normalize( |
| span, |
| self.deduce_sig_from_projection( |
| Some(span), |
| closure_kind, |
| bound_predicate.rebind(proj_predicate), |
| ), |
| ); |
| // Make sure that we didn't infer a signature that mentions itself. |
| // This can happen when we elaborate certain supertrait bounds that |
| // mention projections containing the `Self` type. See #105401. |
| struct MentionsTy<'tcx> { |
| expected_ty: Ty<'tcx>, |
| } |
| impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for MentionsTy<'tcx> { |
| type Result = ControlFlow<()>; |
| |
| fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result { |
| if t == self.expected_ty { |
| ControlFlow::Break(()) |
| } else { |
| t.super_visit_with(self) |
| } |
| } |
| } |
| if inferred_sig.visit_with(&mut MentionsTy { expected_ty }).is_continue() { |
| expected_sig = inferred_sig; |
| } |
| } |
| |
| // Even if we can't infer the full signature, we may be able to |
| // infer the kind. This can occur when we elaborate a predicate |
| // like `F : Fn<A>`. Note that due to subtyping we could encounter |
| // many viable options, so pick the most restrictive. |
| let trait_def_id = match bound_predicate.skip_binder() { |
| ty::PredicateKind::Clause(ty::ClauseKind::Projection(data)) => { |
| Some(data.projection_ty.trait_def_id(self.tcx)) |
| } |
| ty::PredicateKind::Clause(ty::ClauseKind::Trait(data)) => Some(data.def_id()), |
| _ => None, |
| }; |
| |
| if let Some(trait_def_id) = trait_def_id { |
| let found_kind = match closure_kind { |
| hir::ClosureKind::Closure => self.tcx.fn_trait_kind_from_def_id(trait_def_id), |
| hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::Async) => { |
| self.tcx.async_fn_trait_kind_from_def_id(trait_def_id) |
| } |
| _ => None, |
| }; |
| |
| if let Some(found_kind) = found_kind { |
| // always use the closure kind that is more permissive. |
| match (expected_kind, found_kind) { |
| (None, _) => expected_kind = Some(found_kind), |
| (Some(ClosureKind::FnMut), ClosureKind::Fn) => { |
| expected_kind = Some(ClosureKind::Fn) |
| } |
| (Some(ClosureKind::FnOnce), ClosureKind::Fn | ClosureKind::FnMut) => { |
| expected_kind = Some(found_kind) |
| } |
| _ => {} |
| } |
| } |
| } |
| } |
| |
| (expected_sig, expected_kind) |
| } |
| |
| /// Given a projection like "<F as Fn(X)>::Result == Y", we can deduce |
| /// everything we need to know about a closure or coroutine. |
| /// |
| /// The `cause_span` should be the span that caused us to |
| /// have this expected signature, or `None` if we can't readily |
| /// know that. |
| #[instrument(level = "debug", skip(self, cause_span), ret)] |
| fn deduce_sig_from_projection( |
| &self, |
| cause_span: Option<Span>, |
| closure_kind: hir::ClosureKind, |
| projection: ty::PolyProjectionPredicate<'tcx>, |
| ) -> Option<ExpectedSig<'tcx>> { |
| let tcx = self.tcx; |
| |
| let trait_def_id = projection.trait_def_id(tcx); |
| |
| // For now, we only do signature deduction based off of the `Fn` and `AsyncFn` traits, |
| // for closures and async closures, respectively. |
| match closure_kind { |
| hir::ClosureKind::Closure |
| if self.tcx.fn_trait_kind_from_def_id(trait_def_id).is_some() => {} |
| hir::ClosureKind::CoroutineClosure(hir::CoroutineDesugaring::Async) |
| if self.tcx.async_fn_trait_kind_from_def_id(trait_def_id).is_some() => {} |
| _ => return None, |
| } |
| |
| let arg_param_ty = projection.skip_binder().projection_ty.args.type_at(1); |
| let arg_param_ty = self.resolve_vars_if_possible(arg_param_ty); |
| debug!(?arg_param_ty); |
| |
| let ty::Tuple(input_tys) = *arg_param_ty.kind() else { |
| return None; |
| }; |
| |
| // Since this is a return parameter type it is safe to unwrap. |
| let ret_param_ty = projection.skip_binder().term.ty().unwrap(); |
| let ret_param_ty = self.resolve_vars_if_possible(ret_param_ty); |
| debug!(?ret_param_ty); |
| |
| let sig = projection.rebind(self.tcx.mk_fn_sig( |
| input_tys, |
| ret_param_ty, |
| false, |
| hir::Unsafety::Normal, |
| Abi::Rust, |
| )); |
| |
| Some(ExpectedSig { cause_span, sig }) |
| } |
| |
| fn sig_of_closure( |
| &self, |
| expr_def_id: LocalDefId, |
| decl: &hir::FnDecl<'tcx>, |
| closure_kind: hir::ClosureKind, |
| expected_sig: Option<ExpectedSig<'tcx>>, |
| ) -> ClosureSignatures<'tcx> { |
| if let Some(e) = expected_sig { |
| self.sig_of_closure_with_expectation(expr_def_id, decl, closure_kind, e) |
| } else { |
| self.sig_of_closure_no_expectation(expr_def_id, decl, closure_kind) |
| } |
| } |
| |
| /// If there is no expected signature, then we will convert the |
| /// types that the user gave into a signature. |
| #[instrument(skip(self, expr_def_id, decl), level = "debug")] |
| fn sig_of_closure_no_expectation( |
| &self, |
| expr_def_id: LocalDefId, |
| decl: &hir::FnDecl<'tcx>, |
| closure_kind: hir::ClosureKind, |
| ) -> ClosureSignatures<'tcx> { |
| let bound_sig = self.supplied_sig_of_closure(expr_def_id, decl, closure_kind); |
| |
| self.closure_sigs(expr_def_id, bound_sig) |
| } |
| |
| /// Invoked to compute the signature of a closure expression. This |
| /// combines any user-provided type annotations (e.g., `|x: u32| |
| /// -> u32 { .. }`) with the expected signature. |
| /// |
| /// The approach is as follows: |
| /// |
| /// - Let `S` be the (higher-ranked) signature that we derive from the user's annotations. |
| /// - Let `E` be the (higher-ranked) signature that we derive from the expectations, if any. |
| /// - If we have no expectation `E`, then the signature of the closure is `S`. |
| /// - Otherwise, the signature of the closure is E. Moreover: |
| /// - Skolemize the late-bound regions in `E`, yielding `E'`. |
| /// - Instantiate all the late-bound regions bound in the closure within `S` |
| /// with fresh (existential) variables, yielding `S'` |
| /// - Require that `E' = S'` |
| /// - We could use some kind of subtyping relationship here, |
| /// I imagine, but equality is easier and works fine for |
| /// our purposes. |
| /// |
| /// The key intuition here is that the user's types must be valid |
| /// from "the inside" of the closure, but the expectation |
| /// ultimately drives the overall signature. |
| /// |
| /// # Examples |
| /// |
| /// ```ignore (illustrative) |
| /// fn with_closure<F>(_: F) |
| /// where F: Fn(&u32) -> &u32 { .. } |
| /// |
| /// with_closure(|x: &u32| { ... }) |
| /// ``` |
| /// |
| /// Here: |
| /// - E would be `fn(&u32) -> &u32`. |
| /// - S would be `fn(&u32) -> ?T` |
| /// - E' is `&'!0 u32 -> &'!0 u32` |
| /// - S' is `&'?0 u32 -> ?T` |
| /// |
| /// S' can be unified with E' with `['?0 = '!0, ?T = &'!10 u32]`. |
| /// |
| /// # Arguments |
| /// |
| /// - `expr_def_id`: the `LocalDefId` of the closure expression |
| /// - `decl`: the HIR declaration of the closure |
| /// - `body`: the body of the closure |
| /// - `expected_sig`: the expected signature (if any). Note that |
| /// this is missing a binder: that is, there may be late-bound |
| /// regions with depth 1, which are bound then by the closure. |
| #[instrument(skip(self, expr_def_id, decl), level = "debug")] |
| fn sig_of_closure_with_expectation( |
| &self, |
| expr_def_id: LocalDefId, |
| decl: &hir::FnDecl<'tcx>, |
| closure_kind: hir::ClosureKind, |
| expected_sig: ExpectedSig<'tcx>, |
| ) -> ClosureSignatures<'tcx> { |
| // Watch out for some surprises and just ignore the |
| // expectation if things don't see to match up with what we |
| // expect. |
| if expected_sig.sig.c_variadic() != decl.c_variadic { |
| return self.sig_of_closure_no_expectation(expr_def_id, decl, closure_kind); |
| } else if expected_sig.sig.skip_binder().inputs_and_output.len() != decl.inputs.len() + 1 { |
| return self.sig_of_closure_with_mismatched_number_of_arguments( |
| expr_def_id, |
| decl, |
| expected_sig, |
| ); |
| } |
| |
| // Create a `PolyFnSig`. Note the oddity that late bound |
| // regions appearing free in `expected_sig` are now bound up |
| // in this binder we are creating. |
| assert!(!expected_sig.sig.skip_binder().has_vars_bound_above(ty::INNERMOST)); |
| let bound_sig = expected_sig.sig.map_bound(|sig| { |
| self.tcx.mk_fn_sig( |
| sig.inputs().iter().cloned(), |
| sig.output(), |
| sig.c_variadic, |
| hir::Unsafety::Normal, |
| Abi::RustCall, |
| ) |
| }); |
| |
| // `deduce_expectations_from_expected_type` introduces |
| // late-bound lifetimes defined elsewhere, which we now |
| // anonymize away, so as not to confuse the user. |
| let bound_sig = self.tcx.anonymize_bound_vars(bound_sig); |
| |
| let closure_sigs = self.closure_sigs(expr_def_id, bound_sig); |
| |
| // Up till this point, we have ignored the annotations that the user |
| // gave. This function will check that they unify successfully. |
| // Along the way, it also writes out entries for types that the user |
| // wrote into our typeck results, which are then later used by the privacy |
| // check. |
| match self.merge_supplied_sig_with_expectation( |
| expr_def_id, |
| decl, |
| closure_kind, |
| closure_sigs, |
| ) { |
| Ok(infer_ok) => self.register_infer_ok_obligations(infer_ok), |
| Err(_) => self.sig_of_closure_no_expectation(expr_def_id, decl, closure_kind), |
| } |
| } |
| |
| fn sig_of_closure_with_mismatched_number_of_arguments( |
| &self, |
| expr_def_id: LocalDefId, |
| decl: &hir::FnDecl<'tcx>, |
| expected_sig: ExpectedSig<'tcx>, |
| ) -> ClosureSignatures<'tcx> { |
| let expr_map_node = self.tcx.hir_node_by_def_id(expr_def_id); |
| let expected_args: Vec<_> = expected_sig |
| .sig |
| .skip_binder() |
| .inputs() |
| .iter() |
| .map(|ty| ArgKind::from_expected_ty(*ty, None)) |
| .collect(); |
| let (closure_span, closure_arg_span, found_args) = |
| match self.get_fn_like_arguments(expr_map_node) { |
| Some((sp, arg_sp, args)) => (Some(sp), arg_sp, args), |
| None => (None, None, Vec::new()), |
| }; |
| let expected_span = |
| expected_sig.cause_span.unwrap_or_else(|| self.tcx.def_span(expr_def_id)); |
| let guar = self |
| .report_arg_count_mismatch( |
| expected_span, |
| closure_span, |
| expected_args, |
| found_args, |
| true, |
| closure_arg_span, |
| ) |
| .emit(); |
| |
| let error_sig = self.error_sig_of_closure(decl, guar); |
| |
| self.closure_sigs(expr_def_id, error_sig) |
| } |
| |
| /// Enforce the user's types against the expectation. See |
| /// `sig_of_closure_with_expectation` for details on the overall |
| /// strategy. |
| #[instrument(level = "debug", skip(self, expr_def_id, decl, expected_sigs))] |
| fn merge_supplied_sig_with_expectation( |
| &self, |
| expr_def_id: LocalDefId, |
| decl: &hir::FnDecl<'tcx>, |
| closure_kind: hir::ClosureKind, |
| mut expected_sigs: ClosureSignatures<'tcx>, |
| ) -> InferResult<'tcx, ClosureSignatures<'tcx>> { |
| // Get the signature S that the user gave. |
| // |
| // (See comment on `sig_of_closure_with_expectation` for the |
| // meaning of these letters.) |
| let supplied_sig = self.supplied_sig_of_closure(expr_def_id, decl, closure_kind); |
| |
| debug!(?supplied_sig); |
| |
| // FIXME(#45727): As discussed in [this comment][c1], naively |
| // forcing equality here actually results in suboptimal error |
| // messages in some cases. For now, if there would have been |
| // an obvious error, we fallback to declaring the type of the |
| // closure to be the one the user gave, which allows other |
| // error message code to trigger. |
| // |
| // However, I think [there is potential to do even better |
| // here][c2], since in *this* code we have the precise span of |
| // the type parameter in question in hand when we report the |
| // error. |
| // |
| // [c1]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341089706 |
| // [c2]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341096796 |
| self.commit_if_ok(|_| { |
| let mut all_obligations = vec![]; |
| let supplied_sig = self.instantiate_binder_with_fresh_vars( |
| self.tcx.def_span(expr_def_id), |
| BoundRegionConversionTime::FnCall, |
| supplied_sig, |
| ); |
| |
| // The liberated version of this signature should be a subtype |
| // of the liberated form of the expectation. |
| for ((hir_ty, &supplied_ty), expected_ty) in iter::zip( |
| iter::zip(decl.inputs, supplied_sig.inputs()), |
| expected_sigs.liberated_sig.inputs(), // `liberated_sig` is E'. |
| ) { |
| // Check that E' = S'. |
| let cause = self.misc(hir_ty.span); |
| let InferOk { value: (), obligations } = self.at(&cause, self.param_env).eq( |
| DefineOpaqueTypes::Yes, |
| *expected_ty, |
| supplied_ty, |
| )?; |
| all_obligations.extend(obligations); |
| } |
| |
| let supplied_output_ty = supplied_sig.output(); |
| let cause = &self.misc(decl.output.span()); |
| let InferOk { value: (), obligations } = self.at(cause, self.param_env).eq( |
| DefineOpaqueTypes::Yes, |
| expected_sigs.liberated_sig.output(), |
| supplied_output_ty, |
| )?; |
| all_obligations.extend(obligations); |
| |
| let inputs = |
| supplied_sig.inputs().into_iter().map(|&ty| self.resolve_vars_if_possible(ty)); |
| |
| expected_sigs.liberated_sig = self.tcx.mk_fn_sig( |
| inputs, |
| supplied_output_ty, |
| expected_sigs.liberated_sig.c_variadic, |
| hir::Unsafety::Normal, |
| Abi::RustCall, |
| ); |
| |
| Ok(InferOk { value: expected_sigs, obligations: all_obligations }) |
| }) |
| } |
| |
| /// If there is no expected signature, then we will convert the |
| /// types that the user gave into a signature. |
| /// |
| /// Also, record this closure signature for later. |
| #[instrument(skip(self, decl), level = "debug", ret)] |
| fn supplied_sig_of_closure( |
| &self, |
| expr_def_id: LocalDefId, |
| decl: &hir::FnDecl<'tcx>, |
| closure_kind: hir::ClosureKind, |
| ) -> ty::PolyFnSig<'tcx> { |
| let lowerer = self.lowerer(); |
| |
| trace!("decl = {:#?}", decl); |
| debug!(?closure_kind); |
| |
| let hir_id = self.tcx.local_def_id_to_hir_id(expr_def_id); |
| let bound_vars = self.tcx.late_bound_vars(hir_id); |
| |
| // First, convert the types that the user supplied (if any). |
| let supplied_arguments = decl.inputs.iter().map(|a| lowerer.lower_ty(a)); |
| let supplied_return = match decl.output { |
| hir::FnRetTy::Return(ref output) => lowerer.lower_ty(output), |
| hir::FnRetTy::DefaultReturn(_) => match closure_kind { |
| // In the case of the async block that we create for a function body, |
| // we expect the return type of the block to match that of the enclosing |
| // function. |
| hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared( |
| hir::CoroutineDesugaring::Async, |
| hir::CoroutineSource::Fn, |
| )) => { |
| debug!("closure is async fn body"); |
| self.deduce_future_output_from_obligations(expr_def_id).unwrap_or_else(|| { |
| // AFAIK, deducing the future output |
| // always succeeds *except* in error cases |
| // like #65159. I'd like to return Error |
| // here, but I can't because I can't |
| // easily (and locally) prove that we |
| // *have* reported an |
| // error. --nikomatsakis |
| lowerer.ty_infer(None, decl.output.span()) |
| }) |
| } |
| // All `gen {}` and `async gen {}` must return unit. |
| hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared( |
| hir::CoroutineDesugaring::Gen | hir::CoroutineDesugaring::AsyncGen, |
| _, |
| )) => self.tcx.types.unit, |
| |
| // For async blocks, we just fall back to `_` here. |
| // For closures/coroutines, we know nothing about the return |
| // type unless it was supplied. |
| hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared( |
| hir::CoroutineDesugaring::Async, |
| _, |
| )) |
| | hir::ClosureKind::Coroutine(hir::CoroutineKind::Coroutine(_)) |
| | hir::ClosureKind::Closure |
| | hir::ClosureKind::CoroutineClosure(_) => { |
| lowerer.ty_infer(None, decl.output.span()) |
| } |
| }, |
| }; |
| |
| let result = ty::Binder::bind_with_vars( |
| self.tcx.mk_fn_sig( |
| supplied_arguments, |
| supplied_return, |
| decl.c_variadic, |
| hir::Unsafety::Normal, |
| Abi::RustCall, |
| ), |
| bound_vars, |
| ); |
| |
| let c_result = self.infcx.canonicalize_response(result); |
| self.typeck_results.borrow_mut().user_provided_sigs.insert(expr_def_id, c_result); |
| |
| // Normalize only after registering in `user_provided_sigs`. |
| self.normalize(self.tcx.hir().span(hir_id), result) |
| } |
| |
| /// Invoked when we are translating the coroutine that results |
| /// from desugaring an `async fn`. Returns the "sugared" return |
| /// type of the `async fn` -- that is, the return type that the |
| /// user specified. The "desugared" return type is an `impl |
| /// Future<Output = T>`, so we do this by searching through the |
| /// obligations to extract the `T`. |
| #[instrument(skip(self), level = "debug", ret)] |
| fn deduce_future_output_from_obligations(&self, body_def_id: LocalDefId) -> Option<Ty<'tcx>> { |
| let ret_coercion = self.ret_coercion.as_ref().unwrap_or_else(|| { |
| span_bug!(self.tcx.def_span(body_def_id), "async fn coroutine outside of a fn") |
| }); |
| |
| let closure_span = self.tcx.def_span(body_def_id); |
| let ret_ty = ret_coercion.borrow().expected_ty(); |
| let ret_ty = self.try_structurally_resolve_type(closure_span, ret_ty); |
| |
| let get_future_output = |predicate: ty::Predicate<'tcx>, span| { |
| // Search for a pending obligation like |
| // |
| // `<R as Future>::Output = T` |
| // |
| // where R is the return type we are expecting. This type `T` |
| // will be our output. |
| let bound_predicate = predicate.kind(); |
| if let ty::PredicateKind::Clause(ty::ClauseKind::Projection(proj_predicate)) = |
| bound_predicate.skip_binder() |
| { |
| self.deduce_future_output_from_projection( |
| span, |
| bound_predicate.rebind(proj_predicate), |
| ) |
| } else { |
| None |
| } |
| }; |
| |
| let output_ty = match *ret_ty.kind() { |
| ty::Infer(ty::TyVar(ret_vid)) => { |
| self.obligations_for_self_ty(ret_vid).into_iter().find_map(|obligation| { |
| get_future_output(obligation.predicate, obligation.cause.span) |
| })? |
| } |
| ty::Alias(ty::Projection, _) => { |
| return Some(Ty::new_error_with_message( |
| self.tcx, |
| closure_span, |
| "this projection should have been projected to an opaque type", |
| )); |
| } |
| ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => self |
| .tcx |
| .explicit_item_super_predicates(def_id) |
| .iter_instantiated_copied(self.tcx, args) |
| .find_map(|(p, s)| get_future_output(p.as_predicate(), s))?, |
| ty::Error(_) => return Some(ret_ty), |
| _ => { |
| span_bug!(closure_span, "invalid async fn coroutine return type: {ret_ty:?}") |
| } |
| }; |
| |
| let output_ty = self.normalize(closure_span, output_ty); |
| |
| // async fn that have opaque types in their return type need to redo the conversion to inference variables |
| // as they fetch the still opaque version from the signature. |
| let InferOk { value: output_ty, obligations } = self |
| .replace_opaque_types_with_inference_vars( |
| output_ty, |
| body_def_id, |
| closure_span, |
| self.param_env, |
| ); |
| self.register_predicates(obligations); |
| |
| Some(output_ty) |
| } |
| |
| /// Given a projection like |
| /// |
| /// `<X as Future>::Output = T` |
| /// |
| /// where `X` is some type that has no late-bound regions, returns |
| /// `Some(T)`. If the projection is for some other trait, returns |
| /// `None`. |
| fn deduce_future_output_from_projection( |
| &self, |
| cause_span: Span, |
| predicate: ty::PolyProjectionPredicate<'tcx>, |
| ) -> Option<Ty<'tcx>> { |
| debug!("deduce_future_output_from_projection(predicate={:?})", predicate); |
| |
| // We do not expect any bound regions in our predicate, so |
| // skip past the bound vars. |
| let Some(predicate) = predicate.no_bound_vars() else { |
| debug!("deduce_future_output_from_projection: has late-bound regions"); |
| return None; |
| }; |
| |
| // Check that this is a projection from the `Future` trait. |
| let trait_def_id = predicate.projection_ty.trait_def_id(self.tcx); |
| let future_trait = self.tcx.require_lang_item(LangItem::Future, Some(cause_span)); |
| if trait_def_id != future_trait { |
| debug!("deduce_future_output_from_projection: not a future"); |
| return None; |
| } |
| |
| // The `Future` trait has only one associated item, `Output`, |
| // so check that this is what we see. |
| let output_assoc_item = self.tcx.associated_item_def_ids(future_trait)[0]; |
| if output_assoc_item != predicate.projection_ty.def_id { |
| span_bug!( |
| cause_span, |
| "projecting associated item `{:?}` from future, which is not Output `{:?}`", |
| predicate.projection_ty.def_id, |
| output_assoc_item, |
| ); |
| } |
| |
| // Extract the type from the projection. Note that there can |
| // be no bound variables in this type because the "self type" |
| // does not have any regions in it. |
| let output_ty = self.resolve_vars_if_possible(predicate.term); |
| debug!("deduce_future_output_from_projection: output_ty={:?}", output_ty); |
| // This is a projection on a Fn trait so will always be a type. |
| Some(output_ty.ty().unwrap()) |
| } |
| |
| /// Converts the types that the user supplied, in case that doing |
| /// so should yield an error, but returns back a signature where |
| /// all parameters are of type `ty::Error`. |
| fn error_sig_of_closure( |
| &self, |
| decl: &hir::FnDecl<'tcx>, |
| guar: ErrorGuaranteed, |
| ) -> ty::PolyFnSig<'tcx> { |
| let lowerer = self.lowerer(); |
| let err_ty = Ty::new_error(self.tcx, guar); |
| |
| let supplied_arguments = decl.inputs.iter().map(|a| { |
| // Convert the types that the user supplied (if any), but ignore them. |
| lowerer.lower_ty(a); |
| err_ty |
| }); |
| |
| if let hir::FnRetTy::Return(ref output) = decl.output { |
| lowerer.lower_ty(output); |
| } |
| |
| let result = ty::Binder::dummy(self.tcx.mk_fn_sig( |
| supplied_arguments, |
| err_ty, |
| decl.c_variadic, |
| hir::Unsafety::Normal, |
| Abi::RustCall, |
| )); |
| |
| debug!("supplied_sig_of_closure: result={:?}", result); |
| |
| result |
| } |
| |
| #[instrument(level = "debug", skip(self), ret)] |
| fn closure_sigs( |
| &self, |
| expr_def_id: LocalDefId, |
| bound_sig: ty::PolyFnSig<'tcx>, |
| ) -> ClosureSignatures<'tcx> { |
| let liberated_sig = |
| self.tcx().liberate_late_bound_regions(expr_def_id.to_def_id(), bound_sig); |
| let liberated_sig = self.normalize(self.tcx.def_span(expr_def_id), liberated_sig); |
| ClosureSignatures { bound_sig, liberated_sig } |
| } |
| } |
