| //! Code for type-checking closure expressions. |
| |
| use super::{check_fn, Expectation, FnCtxt, GeneratorTypes}; |
| |
| use crate::astconv::AstConv; |
| use rustc_hir as hir; |
| use rustc_hir::def_id::DefId; |
| use rustc_hir::lang_items::LangItem; |
| use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; |
| use rustc_infer::infer::LateBoundRegionConversionTime; |
| use rustc_infer::infer::{InferOk, InferResult}; |
| use rustc_middle::ty::fold::TypeFoldable; |
| use rustc_middle::ty::subst::InternalSubsts; |
| use rustc_middle::ty::{self, Ty}; |
| use rustc_span::source_map::Span; |
| use rustc_target::spec::abi::Abi; |
| use rustc_trait_selection::traits::error_reporting::ArgKind; |
| use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _; |
| use std::cmp; |
| use std::iter; |
| |
| /// What signature do we *expect* the closure to have from context? |
| #[derive(Debug)] |
| struct ExpectedSig<'tcx> { |
| /// Span that gave us this expectation, if we know that. |
| cause_span: Option<Span>, |
| sig: ty::FnSig<'tcx>, |
| } |
| |
| struct ClosureSignatures<'tcx> { |
| bound_sig: ty::PolyFnSig<'tcx>, |
| liberated_sig: ty::FnSig<'tcx>, |
| } |
| |
| impl<'a, 'tcx> FnCtxt<'a, 'tcx> { |
| pub fn check_expr_closure( |
| &self, |
| expr: &hir::Expr<'_>, |
| _capture: hir::CaptureBy, |
| decl: &'tcx hir::FnDecl<'tcx>, |
| body_id: hir::BodyId, |
| gen: Option<hir::Movability>, |
| expected: Expectation<'tcx>, |
| ) -> Ty<'tcx> { |
| debug!("check_expr_closure(expr={:?},expected={:?})", expr, expected); |
| |
| // 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_expectations_from_expected_type(ty), |
| None => (None, None), |
| }; |
| let body = self.tcx.hir().body(body_id); |
| self.check_closure(expr, expected_kind, decl, body, gen, expected_sig) |
| } |
| |
| fn check_closure( |
| &self, |
| expr: &hir::Expr<'_>, |
| opt_kind: Option<ty::ClosureKind>, |
| decl: &'tcx hir::FnDecl<'tcx>, |
| body: &'tcx hir::Body<'tcx>, |
| gen: Option<hir::Movability>, |
| expected_sig: Option<ExpectedSig<'tcx>>, |
| ) -> Ty<'tcx> { |
| debug!("check_closure(opt_kind={:?}, expected_sig={:?})", opt_kind, expected_sig); |
| |
| let expr_def_id = self.tcx.hir().local_def_id(expr.hir_id); |
| |
| let ClosureSignatures { bound_sig, liberated_sig } = |
| self.sig_of_closure(expr_def_id.to_def_id(), decl, body, expected_sig); |
| |
| debug!("check_closure: ty_of_closure returns {:?}", liberated_sig); |
| |
| let generator_types = |
| check_fn(self, self.param_env, liberated_sig, decl, expr.hir_id, body, gen).1; |
| |
| let parent_substs = InternalSubsts::identity_for_item( |
| self.tcx, |
| self.tcx.closure_base_def_id(expr_def_id.to_def_id()), |
| ); |
| |
| let tupled_upvars_ty = |
| self.tcx.mk_tup(self.tcx.upvars_mentioned(expr_def_id).iter().flat_map(|upvars| { |
| upvars.iter().map(|(&var_hir_id, _)| { |
| // Create type variables (for now) to represent the transformed |
| // types of upvars. These will be unified during the upvar |
| // inference phase (`upvar.rs`). |
| self.infcx.next_ty_var(TypeVariableOrigin { |
| // FIXME(eddyb) distinguish upvar inference variables from the rest. |
| kind: TypeVariableOriginKind::ClosureSynthetic, |
| span: self.tcx.hir().span(var_hir_id), |
| }) |
| }) |
| })); |
| |
| if let Some(GeneratorTypes { resume_ty, yield_ty, interior, movability }) = generator_types |
| { |
| let generator_substs = ty::GeneratorSubsts::new( |
| self.tcx, |
| ty::GeneratorSubstsParts { |
| parent_substs, |
| resume_ty, |
| yield_ty, |
| return_ty: liberated_sig.output(), |
| witness: interior, |
| tupled_upvars_ty, |
| }, |
| ); |
| |
| return self.tcx.mk_generator( |
| expr_def_id.to_def_id(), |
| generator_substs.substs, |
| movability, |
| ); |
| } |
| |
| // Tuple up the arguments and insert the resulting function type into |
| // the `closures` table. |
| let sig = bound_sig.map_bound(|sig| { |
| self.tcx.mk_fn_sig( |
| iter::once(self.tcx.intern_tup(sig.inputs())), |
| sig.output(), |
| sig.c_variadic, |
| sig.unsafety, |
| sig.abi, |
| ) |
| }); |
| |
| debug!( |
| "check_closure: expr_def_id={:?}, sig={:?}, opt_kind={:?}", |
| expr_def_id, sig, opt_kind |
| ); |
| |
| let closure_kind_ty = match opt_kind { |
| Some(kind) => kind.to_ty(self.tcx), |
| |
| // Create a type variable (for now) to represent the closure kind. |
| // It will be unified during the upvar inference phase (`upvar.rs`) |
| None => self.infcx.next_ty_var(TypeVariableOrigin { |
| // FIXME(eddyb) distinguish closure kind inference variables from the rest. |
| kind: TypeVariableOriginKind::ClosureSynthetic, |
| span: expr.span, |
| }), |
| }; |
| |
| let closure_substs = ty::ClosureSubsts::new( |
| self.tcx, |
| ty::ClosureSubstsParts { |
| parent_substs, |
| closure_kind_ty, |
| closure_sig_as_fn_ptr_ty: self.tcx.mk_fn_ptr(sig), |
| tupled_upvars_ty, |
| }, |
| ); |
| |
| let closure_type = self.tcx.mk_closure(expr_def_id.to_def_id(), closure_substs.substs); |
| |
| debug!("check_closure: expr.hir_id={:?} closure_type={:?}", expr.hir_id, closure_type); |
| |
| closure_type |
| } |
| |
| /// Given the expected type, figures out what it can about this closure we |
| /// are about to type check: |
| fn deduce_expectations_from_expected_type( |
| &self, |
| expected_ty: Ty<'tcx>, |
| ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) { |
| debug!("deduce_expectations_from_expected_type(expected_ty={:?})", expected_ty); |
| |
| match *expected_ty.kind() { |
| ty::Dynamic(ref 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, pb) |
| }); |
| let kind = object_type |
| .principal_def_id() |
| .and_then(|did| self.tcx.fn_trait_kind_from_lang_item(did)); |
| (sig, kind) |
| } |
| ty::Infer(ty::TyVar(vid)) => self.deduce_expectations_from_obligations(vid), |
| ty::FnPtr(sig) => { |
| let expected_sig = ExpectedSig { cause_span: None, sig: sig.skip_binder() }; |
| (Some(expected_sig), Some(ty::ClosureKind::Fn)) |
| } |
| _ => (None, None), |
| } |
| } |
| |
| fn deduce_expectations_from_obligations( |
| &self, |
| expected_vid: ty::TyVid, |
| ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) { |
| let expected_sig = |
| self.obligations_for_self_ty(expected_vid).find_map(|(_, obligation)| { |
| debug!( |
| "deduce_expectations_from_obligations: obligation.predicate={:?}", |
| obligation.predicate |
| ); |
| |
| if let ty::PredicateAtom::Projection(proj_predicate) = |
| obligation.predicate.skip_binders() |
| { |
| // Given a Projection predicate, we can potentially infer |
| // the complete signature. |
| self.deduce_sig_from_projection( |
| Some(obligation.cause.span), |
| ty::Binder::bind(proj_predicate), |
| ) |
| } else { |
| None |
| } |
| }); |
| |
| // Even if we can't infer the full signature, we may be able to |
| // infer the kind. This can occur if there is a trait-reference |
| // like `F : Fn<A>`. Note that due to subtyping we could encounter |
| // many viable options, so pick the most restrictive. |
| let expected_kind = self |
| .obligations_for_self_ty(expected_vid) |
| .filter_map(|(tr, _)| self.tcx.fn_trait_kind_from_lang_item(tr.def_id())) |
| .fold(None, |best, cur| Some(best.map_or(cur, |best| cmp::min(best, cur)))); |
| |
| (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 generator. |
| /// |
| /// The `cause_span` should be the span that caused us to |
| /// have this expected signature, or `None` if we can't readily |
| /// know that. |
| fn deduce_sig_from_projection( |
| &self, |
| cause_span: Option<Span>, |
| projection: ty::PolyProjectionPredicate<'tcx>, |
| ) -> Option<ExpectedSig<'tcx>> { |
| let tcx = self.tcx; |
| |
| debug!("deduce_sig_from_projection({:?})", projection); |
| |
| let trait_ref = projection.to_poly_trait_ref(tcx); |
| |
| let is_fn = tcx.fn_trait_kind_from_lang_item(trait_ref.def_id()).is_some(); |
| let gen_trait = tcx.require_lang_item(LangItem::Generator, cause_span); |
| let is_gen = gen_trait == trait_ref.def_id(); |
| if !is_fn && !is_gen { |
| debug!("deduce_sig_from_projection: not fn or generator"); |
| return None; |
| } |
| |
| if is_gen { |
| // Check that we deduce the signature from the `<_ as std::ops::Generator>::Return` |
| // associated item and not yield. |
| let return_assoc_item = |
| self.tcx.associated_items(gen_trait).in_definition_order().nth(1).unwrap().def_id; |
| if return_assoc_item != projection.projection_def_id() { |
| debug!("deduce_sig_from_projection: not return assoc item of generator"); |
| return None; |
| } |
| } |
| |
| let input_tys = if is_fn { |
| let arg_param_ty = trait_ref.skip_binder().substs.type_at(1); |
| let arg_param_ty = self.resolve_vars_if_possible(&arg_param_ty); |
| debug!("deduce_sig_from_projection: arg_param_ty={:?}", arg_param_ty); |
| |
| match arg_param_ty.kind() { |
| ty::Tuple(tys) => tys.into_iter().map(|k| k.expect_ty()).collect::<Vec<_>>(), |
| _ => return None, |
| } |
| } else { |
| // Generators with a `()` resume type may be defined with 0 or 1 explicit arguments, |
| // else they must have exactly 1 argument. For now though, just give up in this case. |
| return None; |
| }; |
| |
| let ret_param_ty = projection.skip_binder().ty; |
| let ret_param_ty = self.resolve_vars_if_possible(&ret_param_ty); |
| debug!("deduce_sig_from_projection: ret_param_ty={:?}", ret_param_ty); |
| |
| let sig = self.tcx.mk_fn_sig( |
| input_tys.iter(), |
| &ret_param_ty, |
| false, |
| hir::Unsafety::Normal, |
| Abi::Rust, |
| ); |
| debug!("deduce_sig_from_projection: sig={:?}", sig); |
| |
| Some(ExpectedSig { cause_span, sig }) |
| } |
| |
| fn sig_of_closure( |
| &self, |
| expr_def_id: DefId, |
| decl: &hir::FnDecl<'_>, |
| body: &hir::Body<'_>, |
| expected_sig: Option<ExpectedSig<'tcx>>, |
| ) -> ClosureSignatures<'tcx> { |
| if let Some(e) = expected_sig { |
| self.sig_of_closure_with_expectation(expr_def_id, decl, body, e) |
| } else { |
| self.sig_of_closure_no_expectation(expr_def_id, decl, body) |
| } |
| } |
| |
| /// If there is no expected signature, then we will convert the |
| /// types that the user gave into a signature. |
| fn sig_of_closure_no_expectation( |
| &self, |
| expr_def_id: DefId, |
| decl: &hir::FnDecl<'_>, |
| body: &hir::Body<'_>, |
| ) -> ClosureSignatures<'tcx> { |
| debug!("sig_of_closure_no_expectation()"); |
| |
| let bound_sig = self.supplied_sig_of_closure(expr_def_id, decl, body); |
| |
| self.closure_sigs(expr_def_id, body, 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 |
| /// |
| /// ``` |
| /// 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) -> |
| /// - 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 `DefId` 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. |
| fn sig_of_closure_with_expectation( |
| &self, |
| expr_def_id: DefId, |
| decl: &hir::FnDecl<'_>, |
| body: &hir::Body<'_>, |
| expected_sig: ExpectedSig<'tcx>, |
| ) -> ClosureSignatures<'tcx> { |
| debug!("sig_of_closure_with_expectation(expected_sig={:?})", expected_sig); |
| |
| // 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, body); |
| } else if expected_sig.sig.inputs_and_output.len() != decl.inputs.len() + 1 { |
| return self.sig_of_closure_with_mismatched_number_of_arguments( |
| expr_def_id, |
| decl, |
| body, |
| 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.has_vars_bound_above(ty::INNERMOST)); |
| let bound_sig = ty::Binder::bind(self.tcx.mk_fn_sig( |
| expected_sig.sig.inputs().iter().cloned(), |
| expected_sig.sig.output(), |
| decl.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_late_bound_regions(&bound_sig); |
| |
| let closure_sigs = self.closure_sigs(expr_def_id, body, 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.check_supplied_sig_against_expectation(expr_def_id, decl, body, &closure_sigs) { |
| Ok(infer_ok) => self.register_infer_ok_obligations(infer_ok), |
| Err(_) => return self.sig_of_closure_no_expectation(expr_def_id, decl, body), |
| } |
| |
| closure_sigs |
| } |
| |
| fn sig_of_closure_with_mismatched_number_of_arguments( |
| &self, |
| expr_def_id: DefId, |
| decl: &hir::FnDecl<'_>, |
| body: &hir::Body<'_>, |
| expected_sig: ExpectedSig<'tcx>, |
| ) -> ClosureSignatures<'tcx> { |
| let hir = self.tcx.hir(); |
| let expr_map_node = hir.get_if_local(expr_def_id).unwrap(); |
| let expected_args: Vec<_> = expected_sig |
| .sig |
| .inputs() |
| .iter() |
| .map(|ty| ArgKind::from_expected_ty(ty, None)) |
| .collect(); |
| let (closure_span, found_args) = match self.get_fn_like_arguments(expr_map_node) { |
| Some((sp, args)) => (Some(sp), args), |
| None => (None, Vec::new()), |
| }; |
| let expected_span = |
| expected_sig.cause_span.unwrap_or_else(|| hir.span_if_local(expr_def_id).unwrap()); |
| self.report_arg_count_mismatch( |
| expected_span, |
| closure_span, |
| expected_args, |
| found_args, |
| true, |
| ) |
| .emit(); |
| |
| let error_sig = self.error_sig_of_closure(decl); |
| |
| self.closure_sigs(expr_def_id, body, error_sig) |
| } |
| |
| /// Enforce the user's types against the expectation. See |
| /// `sig_of_closure_with_expectation` for details on the overall |
| /// strategy. |
| fn check_supplied_sig_against_expectation( |
| &self, |
| expr_def_id: DefId, |
| decl: &hir::FnDecl<'_>, |
| body: &hir::Body<'_>, |
| expected_sigs: &ClosureSignatures<'tcx>, |
| ) -> InferResult<'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, body); |
| |
| debug!("check_supplied_sig_against_expectation: supplied_sig={:?}", 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.infcx.commit_if_ok(|_| { |
| let mut all_obligations = vec![]; |
| |
| // 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 decl |
| .inputs |
| .iter() |
| .zip(supplied_sig.inputs().skip_binder()) // binder moved to (*) below |
| .zip(expected_sigs.liberated_sig.inputs()) |
| // `liberated_sig` is E'. |
| { |
| // Instantiate (this part of..) S to S', i.e., with fresh variables. |
| let (supplied_ty, _) = self.infcx.replace_bound_vars_with_fresh_vars( |
| hir_ty.span, |
| LateBoundRegionConversionTime::FnCall, |
| &ty::Binder::bind(supplied_ty), |
| ); // recreated from (*) above |
| |
| // Check that E' = S'. |
| let cause = self.misc(hir_ty.span); |
| let InferOk { value: (), obligations } = |
| self.at(&cause, self.param_env).eq(*expected_ty, supplied_ty)?; |
| all_obligations.extend(obligations); |
| } |
| |
| let (supplied_output_ty, _) = self.infcx.replace_bound_vars_with_fresh_vars( |
| decl.output.span(), |
| LateBoundRegionConversionTime::FnCall, |
| &supplied_sig.output(), |
| ); |
| let cause = &self.misc(decl.output.span()); |
| let InferOk { value: (), obligations } = self |
| .at(cause, self.param_env) |
| .eq(expected_sigs.liberated_sig.output(), supplied_output_ty)?; |
| all_obligations.extend(obligations); |
| |
| Ok(InferOk { value: (), 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. |
| fn supplied_sig_of_closure( |
| &self, |
| expr_def_id: DefId, |
| decl: &hir::FnDecl<'_>, |
| body: &hir::Body<'_>, |
| ) -> ty::PolyFnSig<'tcx> { |
| let astconv: &dyn AstConv<'_> = self; |
| |
| debug!( |
| "supplied_sig_of_closure(decl={:?}, body.generator_kind={:?})", |
| decl, body.generator_kind, |
| ); |
| |
| // First, convert the types that the user supplied (if any). |
| let supplied_arguments = decl.inputs.iter().map(|a| astconv.ast_ty_to_ty(a)); |
| let supplied_return = match decl.output { |
| hir::FnRetTy::Return(ref output) => astconv.ast_ty_to_ty(&output), |
| hir::FnRetTy::DefaultReturn(_) => match body.generator_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. |
| Some(hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn)) => { |
| debug!("supplied_sig_of_closure: 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 |
| astconv.ty_infer(None, decl.output.span()) |
| }) |
| } |
| |
| _ => astconv.ty_infer(None, decl.output.span()), |
| }, |
| }; |
| |
| let result = ty::Binder::bind(self.tcx.mk_fn_sig( |
| supplied_arguments, |
| supplied_return, |
| decl.c_variadic, |
| hir::Unsafety::Normal, |
| Abi::RustCall, |
| )); |
| |
| debug!("supplied_sig_of_closure: result={:?}", result); |
| |
| let c_result = self.inh.infcx.canonicalize_response(&result); |
| self.typeck_results.borrow_mut().user_provided_sigs.insert(expr_def_id, c_result); |
| |
| result |
| } |
| |
| /// Invoked when we are translating the generator 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 a `impl |
| /// Future<Output = T>`, so we do this by searching through the |
| /// obligations to extract the `T`. |
| fn deduce_future_output_from_obligations(&self, expr_def_id: DefId) -> Option<Ty<'tcx>> { |
| debug!("deduce_future_output_from_obligations(expr_def_id={:?})", expr_def_id); |
| |
| let ret_coercion = self.ret_coercion.as_ref().unwrap_or_else(|| { |
| span_bug!(self.tcx.def_span(expr_def_id), "async fn generator outside of a fn") |
| }); |
| |
| // In practice, the return type of the surrounding function is |
| // always a (not yet resolved) inference variable, because it |
| // is the hidden type for an `impl Trait` that we are going to |
| // be inferring. |
| let ret_ty = ret_coercion.borrow().expected_ty(); |
| let ret_ty = self.inh.infcx.shallow_resolve(ret_ty); |
| let ret_vid = match *ret_ty.kind() { |
| ty::Infer(ty::TyVar(ret_vid)) => ret_vid, |
| _ => span_bug!( |
| self.tcx.def_span(expr_def_id), |
| "async fn generator return type not an inference variable" |
| ), |
| }; |
| |
| // 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 output_ty = self.obligations_for_self_ty(ret_vid).find_map(|(_, obligation)| { |
| if let ty::PredicateAtom::Projection(proj_predicate) = |
| obligation.predicate.skip_binders() |
| { |
| self.deduce_future_output_from_projection( |
| obligation.cause.span, |
| ty::Binder::bind(proj_predicate), |
| ) |
| } else { |
| None |
| } |
| }); |
| |
| debug!("deduce_future_output_from_obligations: output_ty={:?}", output_ty); |
| 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 predicate = match predicate.no_bound_vars() { |
| Some(p) => p, |
| None => { |
| debug!("deduce_future_output_from_projection: has late-bound regions"); |
| return None; |
| } |
| }; |
| |
| // Check that this is a projection from the `Future` trait. |
| let trait_ref = predicate.projection_ty.trait_ref(self.tcx); |
| let future_trait = self.tcx.require_lang_item(LangItem::Future, Some(cause_span)); |
| if trait_ref.def_id != future_trait { |
| debug!("deduce_future_output_from_projection: not a future"); |
| return None; |
| } |
| |
| // The `Future` trait has only one associted item, `Output`, |
| // so check that this is what we see. |
| let output_assoc_item = |
| self.tcx.associated_items(future_trait).in_definition_order().next().unwrap().def_id; |
| if output_assoc_item != predicate.projection_ty.item_def_id { |
| span_bug!( |
| cause_span, |
| "projecting associated item `{:?}` from future, which is not Output `{:?}`", |
| predicate.projection_ty.item_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.ty); |
| debug!("deduce_future_output_from_projection: output_ty={:?}", output_ty); |
| Some(output_ty) |
| } |
| |
| /// 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 `TyErr`. |
| fn error_sig_of_closure(&self, decl: &hir::FnDecl<'_>) -> ty::PolyFnSig<'tcx> { |
| let astconv: &dyn AstConv<'_> = self; |
| |
| let supplied_arguments = decl.inputs.iter().map(|a| { |
| // Convert the types that the user supplied (if any), but ignore them. |
| astconv.ast_ty_to_ty(a); |
| self.tcx.ty_error() |
| }); |
| |
| if let hir::FnRetTy::Return(ref output) = decl.output { |
| astconv.ast_ty_to_ty(&output); |
| } |
| |
| let result = ty::Binder::bind(self.tcx.mk_fn_sig( |
| supplied_arguments, |
| self.tcx.ty_error(), |
| decl.c_variadic, |
| hir::Unsafety::Normal, |
| Abi::RustCall, |
| )); |
| |
| debug!("supplied_sig_of_closure: result={:?}", result); |
| |
| result |
| } |
| |
| fn closure_sigs( |
| &self, |
| expr_def_id: DefId, |
| body: &hir::Body<'_>, |
| bound_sig: ty::PolyFnSig<'tcx>, |
| ) -> ClosureSignatures<'tcx> { |
| let liberated_sig = self.tcx().liberate_late_bound_regions(expr_def_id, &bound_sig); |
| let liberated_sig = self.inh.normalize_associated_types_in( |
| body.value.span, |
| body.value.hir_id, |
| self.param_env, |
| &liberated_sig, |
| ); |
| ClosureSignatures { bound_sig, liberated_sig } |
| } |
| } |
