1 //! Code for type-checking closure expressions.
3 use super::{check_fn, Expectation, FnCtxt, GeneratorTypes};
7 use rustc_hir::def_id::LocalDefId;
8 use rustc_hir::lang_items::LangItem;
9 use rustc_hir_analysis::astconv::AstConv;
10 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
11 use rustc_infer::infer::LateBoundRegionConversionTime;
12 use rustc_infer::infer::{InferOk, InferResult};
13 use rustc_macros::{TypeFoldable, TypeVisitable};
14 use rustc_middle::ty::subst::InternalSubsts;
15 use rustc_middle::ty::visit::TypeVisitable;
16 use rustc_middle::ty::{self, Ty};
17 use rustc_span::source_map::Span;
18 use rustc_target::spec::abi::Abi;
19 use rustc_trait_selection::traits;
20 use rustc_trait_selection::traits::error_reporting::ArgKind;
21 use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
25 /// What signature do we *expect* the closure to have from context?
26 #[derive(Debug, Clone, TypeFoldable, TypeVisitable)]
27 struct ExpectedSig<'tcx> {
28 /// Span that gave us this expectation, if we know that.
29 cause_span: Option<Span>,
30 sig: ty::PolyFnSig<'tcx>,
33 struct ClosureSignatures<'tcx> {
34 /// The signature users of the closure see.
35 bound_sig: ty::PolyFnSig<'tcx>,
36 /// The signature within the function body.
37 /// This mostly differs in the sense that lifetimes are now early bound and any
38 /// opaque types from the signature expectation are overridden in case there are
39 /// explicit hidden types written by the user in the closure signature.
40 liberated_sig: ty::FnSig<'tcx>,
43 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
44 #[instrument(skip(self, closure), level = "debug")]
45 pub fn check_expr_closure(
47 closure: &hir::Closure<'tcx>,
49 expected: Expectation<'tcx>,
51 trace!("decl = {:#?}", closure.fn_decl);
53 // It's always helpful for inference if we know the kind of
54 // closure sooner rather than later, so first examine the expected
55 // type, and see if can glean a closure kind from there.
56 let (expected_sig, expected_kind) = match expected.to_option(self) {
57 Some(ty) => self.deduce_expectations_from_expected_type(ty),
60 let body = self.tcx.hir().body(closure.body);
61 self.check_closure(closure, expr_span, expected_kind, body, expected_sig)
64 #[instrument(skip(self, closure, body), level = "debug", ret)]
67 closure: &hir::Closure<'tcx>,
69 opt_kind: Option<ty::ClosureKind>,
70 body: &'tcx hir::Body<'tcx>,
71 expected_sig: Option<ExpectedSig<'tcx>>,
73 trace!("decl = {:#?}", closure.fn_decl);
74 let expr_def_id = closure.def_id;
77 let ClosureSignatures { bound_sig, liberated_sig } =
78 self.sig_of_closure(expr_def_id, closure.fn_decl, body, expected_sig);
80 debug!(?bound_sig, ?liberated_sig);
82 let generator_types = check_fn(
84 self.param_env.without_const(),
93 let parent_substs = InternalSubsts::identity_for_item(
95 self.tcx.typeck_root_def_id(expr_def_id.to_def_id()),
98 let tupled_upvars_ty = self.next_ty_var(TypeVariableOrigin {
99 kind: TypeVariableOriginKind::ClosureSynthetic,
100 span: self.tcx.def_span(expr_def_id),
103 if let Some(GeneratorTypes { resume_ty, yield_ty, interior, movability }) = generator_types
105 let generator_substs = ty::GeneratorSubsts::new(
107 ty::GeneratorSubstsParts {
111 return_ty: liberated_sig.output(),
117 return self.tcx.mk_generator(
118 expr_def_id.to_def_id(),
119 generator_substs.substs,
124 // Tuple up the arguments and insert the resulting function type into
125 // the `closures` table.
126 let sig = bound_sig.map_bound(|sig| {
128 iter::once(self.tcx.intern_tup(sig.inputs())),
136 debug!(?sig, ?opt_kind);
138 let closure_kind_ty = match opt_kind {
139 Some(kind) => kind.to_ty(self.tcx),
141 // Create a type variable (for now) to represent the closure kind.
142 // It will be unified during the upvar inference phase (`upvar.rs`)
143 None => self.next_ty_var(TypeVariableOrigin {
144 // FIXME(eddyb) distinguish closure kind inference variables from the rest.
145 kind: TypeVariableOriginKind::ClosureSynthetic,
150 let closure_substs = ty::ClosureSubsts::new(
152 ty::ClosureSubstsParts {
155 closure_sig_as_fn_ptr_ty: self.tcx.mk_fn_ptr(sig),
160 self.tcx.mk_closure(expr_def_id.to_def_id(), closure_substs.substs)
163 /// Given the expected type, figures out what it can about this closure we
164 /// are about to type check:
165 #[instrument(skip(self), level = "debug")]
166 fn deduce_expectations_from_expected_type(
168 expected_ty: Ty<'tcx>,
169 ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
170 match *expected_ty.kind() {
171 ty::Opaque(def_id, substs) => self.deduce_signature_from_predicates(
172 self.tcx.bound_explicit_item_bounds(def_id).subst_iter_copied(self.tcx, substs),
174 ty::Dynamic(ref object_type, ..) => {
175 let sig = object_type.projection_bounds().find_map(|pb| {
176 let pb = pb.with_self_ty(self.tcx, self.tcx.types.trait_object_dummy_self);
177 self.deduce_sig_from_projection(None, pb)
179 let kind = object_type
181 .and_then(|did| self.tcx.fn_trait_kind_from_def_id(did));
184 ty::Infer(ty::TyVar(vid)) => self.deduce_signature_from_predicates(
185 self.obligations_for_self_ty(vid).map(|obl| (obl.predicate, obl.cause.span)),
188 let expected_sig = ExpectedSig { cause_span: None, sig };
189 (Some(expected_sig), Some(ty::ClosureKind::Fn))
195 fn deduce_signature_from_predicates(
197 predicates: impl DoubleEndedIterator<Item = (ty::Predicate<'tcx>, Span)>,
198 ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
199 let mut expected_sig = None;
200 let mut expected_kind = None;
202 for obligation in traits::elaborate_predicates_with_span(
204 // Reverse the obligations here, since `elaborate_*` uses a stack,
205 // and we want to keep inference generally in the same order of
206 // the registered obligations.
209 debug!(?obligation.predicate);
210 let bound_predicate = obligation.predicate.kind();
212 // Given a Projection predicate, we can potentially infer
213 // the complete signature.
214 if expected_sig.is_none()
215 && let ty::PredicateKind::Clause(ty::Clause::Projection(proj_predicate)) = bound_predicate.skip_binder()
217 expected_sig = self.normalize_associated_types_in(
218 obligation.cause.span,
219 self.deduce_sig_from_projection(
220 Some(obligation.cause.span),
221 bound_predicate.rebind(proj_predicate),
226 // Even if we can't infer the full signature, we may be able to
227 // infer the kind. This can occur when we elaborate a predicate
228 // like `F : Fn<A>`. Note that due to subtyping we could encounter
229 // many viable options, so pick the most restrictive.
230 let trait_def_id = match bound_predicate.skip_binder() {
231 ty::PredicateKind::Clause(ty::Clause::Projection(data)) => {
232 Some(data.projection_ty.trait_def_id(self.tcx))
234 ty::PredicateKind::Clause(ty::Clause::Trait(data)) => Some(data.def_id()),
237 if let Some(closure_kind) =
238 trait_def_id.and_then(|def_id| self.tcx.fn_trait_kind_from_def_id(def_id))
240 expected_kind = Some(
242 .map_or_else(|| closure_kind, |current| cmp::min(current, closure_kind)),
247 (expected_sig, expected_kind)
250 /// Given a projection like "<F as Fn(X)>::Result == Y", we can deduce
251 /// everything we need to know about a closure or generator.
253 /// The `cause_span` should be the span that caused us to
254 /// have this expected signature, or `None` if we can't readily
256 #[instrument(level = "debug", skip(self, cause_span), ret)]
257 fn deduce_sig_from_projection(
259 cause_span: Option<Span>,
260 projection: ty::PolyProjectionPredicate<'tcx>,
261 ) -> Option<ExpectedSig<'tcx>> {
264 let trait_def_id = projection.trait_def_id(tcx);
266 let is_fn = tcx.fn_trait_kind_from_def_id(trait_def_id).is_some();
267 let gen_trait = tcx.require_lang_item(LangItem::Generator, cause_span);
268 let is_gen = gen_trait == trait_def_id;
269 if !is_fn && !is_gen {
270 debug!("not fn or generator");
275 // Check that we deduce the signature from the `<_ as std::ops::Generator>::Return`
276 // associated item and not yield.
277 let return_assoc_item = self.tcx.associated_item_def_ids(gen_trait)[1];
278 if return_assoc_item != projection.projection_def_id() {
279 debug!("not return assoc item of generator");
284 let input_tys = if is_fn {
285 let arg_param_ty = projection.skip_binder().projection_ty.substs.type_at(1);
286 let arg_param_ty = self.resolve_vars_if_possible(arg_param_ty);
287 debug!(?arg_param_ty);
289 match arg_param_ty.kind() {
290 &ty::Tuple(tys) => tys,
294 // Generators with a `()` resume type may be defined with 0 or 1 explicit arguments,
295 // else they must have exactly 1 argument. For now though, just give up in this case.
299 // Since this is a return parameter type it is safe to unwrap.
300 let ret_param_ty = projection.skip_binder().term.ty().unwrap();
301 let ret_param_ty = self.resolve_vars_if_possible(ret_param_ty);
302 debug!(?ret_param_ty);
304 let sig = projection.rebind(self.tcx.mk_fn_sig(
308 hir::Unsafety::Normal,
312 Some(ExpectedSig { cause_span, sig })
317 expr_def_id: LocalDefId,
318 decl: &hir::FnDecl<'_>,
319 body: &hir::Body<'_>,
320 expected_sig: Option<ExpectedSig<'tcx>>,
321 ) -> ClosureSignatures<'tcx> {
322 if let Some(e) = expected_sig {
323 self.sig_of_closure_with_expectation(expr_def_id, decl, body, e)
325 self.sig_of_closure_no_expectation(expr_def_id, decl, body)
329 /// If there is no expected signature, then we will convert the
330 /// types that the user gave into a signature.
331 #[instrument(skip(self, expr_def_id, decl, body), level = "debug")]
332 fn sig_of_closure_no_expectation(
334 expr_def_id: LocalDefId,
335 decl: &hir::FnDecl<'_>,
336 body: &hir::Body<'_>,
337 ) -> ClosureSignatures<'tcx> {
338 let bound_sig = self.supplied_sig_of_closure(expr_def_id, decl, body);
340 self.closure_sigs(expr_def_id, body, bound_sig)
343 /// Invoked to compute the signature of a closure expression. This
344 /// combines any user-provided type annotations (e.g., `|x: u32|
345 /// -> u32 { .. }`) with the expected signature.
347 /// The approach is as follows:
349 /// - Let `S` be the (higher-ranked) signature that we derive from the user's annotations.
350 /// - Let `E` be the (higher-ranked) signature that we derive from the expectations, if any.
351 /// - If we have no expectation `E`, then the signature of the closure is `S`.
352 /// - Otherwise, the signature of the closure is E. Moreover:
353 /// - Skolemize the late-bound regions in `E`, yielding `E'`.
354 /// - Instantiate all the late-bound regions bound in the closure within `S`
355 /// with fresh (existential) variables, yielding `S'`
356 /// - Require that `E' = S'`
357 /// - We could use some kind of subtyping relationship here,
358 /// I imagine, but equality is easier and works fine for
361 /// The key intuition here is that the user's types must be valid
362 /// from "the inside" of the closure, but the expectation
363 /// ultimately drives the overall signature.
367 /// ```ignore (illustrative)
368 /// fn with_closure<F>(_: F)
369 /// where F: Fn(&u32) -> &u32 { .. }
371 /// with_closure(|x: &u32| { ... })
375 /// - E would be `fn(&u32) -> &u32`.
376 /// - S would be `fn(&u32) ->
377 /// - E' is `&'!0 u32 -> &'!0 u32`
378 /// - S' is `&'?0 u32 -> ?T`
380 /// S' can be unified with E' with `['?0 = '!0, ?T = &'!10 u32]`.
384 /// - `expr_def_id`: the `LocalDefId` of the closure expression
385 /// - `decl`: the HIR declaration of the closure
386 /// - `body`: the body of the closure
387 /// - `expected_sig`: the expected signature (if any). Note that
388 /// this is missing a binder: that is, there may be late-bound
389 /// regions with depth 1, which are bound then by the closure.
390 #[instrument(skip(self, expr_def_id, decl, body), level = "debug")]
391 fn sig_of_closure_with_expectation(
393 expr_def_id: LocalDefId,
394 decl: &hir::FnDecl<'_>,
395 body: &hir::Body<'_>,
396 expected_sig: ExpectedSig<'tcx>,
397 ) -> ClosureSignatures<'tcx> {
398 // Watch out for some surprises and just ignore the
399 // expectation if things don't see to match up with what we
401 if expected_sig.sig.c_variadic() != decl.c_variadic {
402 return self.sig_of_closure_no_expectation(expr_def_id, decl, body);
403 } else if expected_sig.sig.skip_binder().inputs_and_output.len() != decl.inputs.len() + 1 {
404 return self.sig_of_closure_with_mismatched_number_of_arguments(
412 // Create a `PolyFnSig`. Note the oddity that late bound
413 // regions appearing free in `expected_sig` are now bound up
414 // in this binder we are creating.
415 assert!(!expected_sig.sig.skip_binder().has_vars_bound_above(ty::INNERMOST));
416 let bound_sig = expected_sig.sig.map_bound(|sig| {
418 sig.inputs().iter().cloned(),
421 hir::Unsafety::Normal,
426 // `deduce_expectations_from_expected_type` introduces
427 // late-bound lifetimes defined elsewhere, which we now
428 // anonymize away, so as not to confuse the user.
429 let bound_sig = self.tcx.anonymize_late_bound_regions(bound_sig);
431 let closure_sigs = self.closure_sigs(expr_def_id, body, bound_sig);
433 // Up till this point, we have ignored the annotations that the user
434 // gave. This function will check that they unify successfully.
435 // Along the way, it also writes out entries for types that the user
436 // wrote into our typeck results, which are then later used by the privacy
438 match self.merge_supplied_sig_with_expectation(expr_def_id, decl, body, closure_sigs) {
439 Ok(infer_ok) => self.register_infer_ok_obligations(infer_ok),
440 Err(_) => self.sig_of_closure_no_expectation(expr_def_id, decl, body),
444 fn sig_of_closure_with_mismatched_number_of_arguments(
446 expr_def_id: LocalDefId,
447 decl: &hir::FnDecl<'_>,
448 body: &hir::Body<'_>,
449 expected_sig: ExpectedSig<'tcx>,
450 ) -> ClosureSignatures<'tcx> {
451 let hir = self.tcx.hir();
452 let expr_map_node = hir.get_by_def_id(expr_def_id);
453 let expected_args: Vec<_> = expected_sig
458 .map(|ty| ArgKind::from_expected_ty(*ty, None))
460 let (closure_span, found_args) = match self.get_fn_like_arguments(expr_map_node) {
461 Some((sp, args)) => (Some(sp), args),
462 None => (None, Vec::new()),
465 expected_sig.cause_span.unwrap_or_else(|| self.tcx.def_span(expr_def_id));
466 self.report_arg_count_mismatch(
475 let error_sig = self.error_sig_of_closure(decl);
477 self.closure_sigs(expr_def_id, body, error_sig)
480 /// Enforce the user's types against the expectation. See
481 /// `sig_of_closure_with_expectation` for details on the overall
483 #[instrument(level = "debug", skip(self, expr_def_id, decl, body, expected_sigs))]
484 fn merge_supplied_sig_with_expectation(
486 expr_def_id: LocalDefId,
487 decl: &hir::FnDecl<'_>,
488 body: &hir::Body<'_>,
489 mut expected_sigs: ClosureSignatures<'tcx>,
490 ) -> InferResult<'tcx, ClosureSignatures<'tcx>> {
491 // Get the signature S that the user gave.
493 // (See comment on `sig_of_closure_with_expectation` for the
494 // meaning of these letters.)
495 let supplied_sig = self.supplied_sig_of_closure(expr_def_id, decl, body);
497 debug!(?supplied_sig);
499 // FIXME(#45727): As discussed in [this comment][c1], naively
500 // forcing equality here actually results in suboptimal error
501 // messages in some cases. For now, if there would have been
502 // an obvious error, we fallback to declaring the type of the
503 // closure to be the one the user gave, which allows other
504 // error message code to trigger.
506 // However, I think [there is potential to do even better
507 // here][c2], since in *this* code we have the precise span of
508 // the type parameter in question in hand when we report the
511 // [c1]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341089706
512 // [c2]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341096796
513 self.commit_if_ok(|_| {
514 let mut all_obligations = vec![];
515 let inputs: Vec<_> = iter::zip(
517 supplied_sig.inputs().skip_binder(), // binder moved to (*) below
519 .map(|(hir_ty, &supplied_ty)| {
520 // Instantiate (this part of..) S to S', i.e., with fresh variables.
521 self.replace_bound_vars_with_fresh_vars(
523 LateBoundRegionConversionTime::FnCall,
524 // (*) binder moved to here
525 supplied_sig.inputs().rebind(supplied_ty),
530 // The liberated version of this signature should be a subtype
531 // of the liberated form of the expectation.
532 for ((hir_ty, &supplied_ty), expected_ty) in iter::zip(
533 iter::zip(decl.inputs, &inputs),
534 expected_sigs.liberated_sig.inputs(), // `liberated_sig` is E'.
536 // Check that E' = S'.
537 let cause = self.misc(hir_ty.span);
538 let InferOk { value: (), obligations } =
539 self.at(&cause, self.param_env).eq(*expected_ty, supplied_ty)?;
540 all_obligations.extend(obligations);
543 let supplied_output_ty = self.replace_bound_vars_with_fresh_vars(
545 LateBoundRegionConversionTime::FnCall,
546 supplied_sig.output(),
548 let cause = &self.misc(decl.output.span());
549 let InferOk { value: (), obligations } = self
550 .at(cause, self.param_env)
551 .eq(expected_sigs.liberated_sig.output(), supplied_output_ty)?;
552 all_obligations.extend(obligations);
554 let inputs = inputs.into_iter().map(|ty| self.resolve_vars_if_possible(ty));
556 expected_sigs.liberated_sig = self.tcx.mk_fn_sig(
559 expected_sigs.liberated_sig.c_variadic,
560 hir::Unsafety::Normal,
564 Ok(InferOk { value: expected_sigs, obligations: all_obligations })
568 /// If there is no expected signature, then we will convert the
569 /// types that the user gave into a signature.
571 /// Also, record this closure signature for later.
572 #[instrument(skip(self, decl, body), level = "debug", ret)]
573 fn supplied_sig_of_closure(
575 expr_def_id: LocalDefId,
576 decl: &hir::FnDecl<'_>,
577 body: &hir::Body<'_>,
578 ) -> ty::PolyFnSig<'tcx> {
579 let astconv: &dyn AstConv<'_> = self;
581 trace!("decl = {:#?}", decl);
582 debug!(?body.generator_kind);
584 let hir_id = self.tcx.hir().local_def_id_to_hir_id(expr_def_id);
585 let bound_vars = self.tcx.late_bound_vars(hir_id);
587 // First, convert the types that the user supplied (if any).
588 let supplied_arguments = decl.inputs.iter().map(|a| astconv.ast_ty_to_ty(a));
589 let supplied_return = match decl.output {
590 hir::FnRetTy::Return(ref output) => astconv.ast_ty_to_ty(&output),
591 hir::FnRetTy::DefaultReturn(_) => match body.generator_kind {
592 // In the case of the async block that we create for a function body,
593 // we expect the return type of the block to match that of the enclosing
595 Some(hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn)) => {
596 debug!("closure is async fn body");
597 self.deduce_future_output_from_obligations(expr_def_id, body.id().hir_id)
599 // AFAIK, deducing the future output
600 // always succeeds *except* in error cases
601 // like #65159. I'd like to return Error
602 // here, but I can't because I can't
603 // easily (and locally) prove that we
604 // *have* reported an
605 // error. --nikomatsakis
606 astconv.ty_infer(None, decl.output.span())
610 _ => astconv.ty_infer(None, decl.output.span()),
614 let result = ty::Binder::bind_with_vars(
619 hir::Unsafety::Normal,
624 // Astconv can't normalize inputs or outputs with escaping bound vars,
625 // so normalize them here, after we've wrapped them in a binder.
626 let result = self.normalize_associated_types_in(self.tcx.hir().span(hir_id), result);
628 let c_result = self.inh.infcx.canonicalize_response(result);
629 self.typeck_results.borrow_mut().user_provided_sigs.insert(expr_def_id, c_result);
634 /// Invoked when we are translating the generator that results
635 /// from desugaring an `async fn`. Returns the "sugared" return
636 /// type of the `async fn` -- that is, the return type that the
637 /// user specified. The "desugared" return type is an `impl
638 /// Future<Output = T>`, so we do this by searching through the
639 /// obligations to extract the `T`.
640 #[instrument(skip(self), level = "debug", ret)]
641 fn deduce_future_output_from_obligations(
643 expr_def_id: LocalDefId,
645 ) -> Option<Ty<'tcx>> {
646 let ret_coercion = self.ret_coercion.as_ref().unwrap_or_else(|| {
647 span_bug!(self.tcx.def_span(expr_def_id), "async fn generator outside of a fn")
650 let ret_ty = ret_coercion.borrow().expected_ty();
651 let ret_ty = self.inh.infcx.shallow_resolve(ret_ty);
653 let get_future_output = |predicate: ty::Predicate<'tcx>, span| {
654 // Search for a pending obligation like
656 // `<R as Future>::Output = T`
658 // where R is the return type we are expecting. This type `T`
659 // will be our output.
660 let bound_predicate = predicate.kind();
661 if let ty::PredicateKind::Clause(ty::Clause::Projection(proj_predicate)) =
662 bound_predicate.skip_binder()
664 self.deduce_future_output_from_projection(
666 bound_predicate.rebind(proj_predicate),
673 let output_ty = match *ret_ty.kind() {
674 ty::Infer(ty::TyVar(ret_vid)) => {
675 self.obligations_for_self_ty(ret_vid).find_map(|obligation| {
676 get_future_output(obligation.predicate, obligation.cause.span)
679 ty::Opaque(def_id, substs) => self
681 .bound_explicit_item_bounds(def_id)
682 .subst_iter_copied(self.tcx, substs)
683 .find_map(|(p, s)| get_future_output(p, s))?,
684 ty::Error(_) => return None,
686 if self.tcx.def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder =>
689 .bound_explicit_item_bounds(proj.item_def_id)
690 .subst_iter_copied(self.tcx, proj.substs)
691 .find_map(|(p, s)| get_future_output(p, s))?
694 self.tcx.def_span(expr_def_id),
695 "async fn generator return type not an inference variable: {ret_ty}"
699 // async fn that have opaque types in their return type need to redo the conversion to inference variables
700 // as they fetch the still opaque version from the signature.
701 let InferOk { value: output_ty, obligations } = self
702 .replace_opaque_types_with_inference_vars(
705 self.tcx.def_span(expr_def_id),
708 self.register_predicates(obligations);
713 /// Given a projection like
715 /// `<X as Future>::Output = T`
717 /// where `X` is some type that has no late-bound regions, returns
718 /// `Some(T)`. If the projection is for some other trait, returns
720 fn deduce_future_output_from_projection(
723 predicate: ty::PolyProjectionPredicate<'tcx>,
724 ) -> Option<Ty<'tcx>> {
725 debug!("deduce_future_output_from_projection(predicate={:?})", predicate);
727 // We do not expect any bound regions in our predicate, so
728 // skip past the bound vars.
729 let Some(predicate) = predicate.no_bound_vars() else {
730 debug!("deduce_future_output_from_projection: has late-bound regions");
734 // Check that this is a projection from the `Future` trait.
735 let trait_def_id = predicate.projection_ty.trait_def_id(self.tcx);
736 let future_trait = self.tcx.require_lang_item(LangItem::Future, Some(cause_span));
737 if trait_def_id != future_trait {
738 debug!("deduce_future_output_from_projection: not a future");
742 // The `Future` trait has only one associated item, `Output`,
743 // so check that this is what we see.
744 let output_assoc_item = self.tcx.associated_item_def_ids(future_trait)[0];
745 if output_assoc_item != predicate.projection_ty.item_def_id {
748 "projecting associated item `{:?}` from future, which is not Output `{:?}`",
749 predicate.projection_ty.item_def_id,
754 // Extract the type from the projection. Note that there can
755 // be no bound variables in this type because the "self type"
756 // does not have any regions in it.
757 let output_ty = self.resolve_vars_if_possible(predicate.term);
758 debug!("deduce_future_output_from_projection: output_ty={:?}", output_ty);
759 // This is a projection on a Fn trait so will always be a type.
760 Some(output_ty.ty().unwrap())
763 /// Converts the types that the user supplied, in case that doing
764 /// so should yield an error, but returns back a signature where
765 /// all parameters are of type `TyErr`.
766 fn error_sig_of_closure(&self, decl: &hir::FnDecl<'_>) -> ty::PolyFnSig<'tcx> {
767 let astconv: &dyn AstConv<'_> = self;
769 let supplied_arguments = decl.inputs.iter().map(|a| {
770 // Convert the types that the user supplied (if any), but ignore them.
771 astconv.ast_ty_to_ty(a);
775 if let hir::FnRetTy::Return(ref output) = decl.output {
776 astconv.ast_ty_to_ty(&output);
779 let result = ty::Binder::dummy(self.tcx.mk_fn_sig(
783 hir::Unsafety::Normal,
787 debug!("supplied_sig_of_closure: result={:?}", result);
794 expr_def_id: LocalDefId,
795 body: &hir::Body<'_>,
796 bound_sig: ty::PolyFnSig<'tcx>,
797 ) -> ClosureSignatures<'tcx> {
799 self.tcx().liberate_late_bound_regions(expr_def_id.to_def_id(), bound_sig);
800 let liberated_sig = self.inh.normalize_associated_types_in(
802 self.tcx.hir().local_def_id_to_hir_id(expr_def_id),
806 ClosureSignatures { bound_sig, liberated_sig }