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 mut fcx = FnCtxt::new(self, self.param_env.without_const(), body.value.hir_id);
83 let generator_types = check_fn(
92 let parent_substs = InternalSubsts::identity_for_item(
94 self.tcx.typeck_root_def_id(expr_def_id.to_def_id()),
97 let tupled_upvars_ty = self.next_ty_var(TypeVariableOrigin {
98 kind: TypeVariableOriginKind::ClosureSynthetic,
99 span: self.tcx.def_span(expr_def_id),
102 if let Some(GeneratorTypes { resume_ty, yield_ty, interior, movability }) = generator_types
104 let generator_substs = ty::GeneratorSubsts::new(
106 ty::GeneratorSubstsParts {
110 return_ty: liberated_sig.output(),
116 return self.tcx.mk_generator(
117 expr_def_id.to_def_id(),
118 generator_substs.substs,
123 // Tuple up the arguments and insert the resulting function type into
124 // the `closures` table.
125 let sig = bound_sig.map_bound(|sig| {
127 iter::once(self.tcx.intern_tup(sig.inputs())),
135 debug!(?sig, ?opt_kind);
137 let closure_kind_ty = match opt_kind {
138 Some(kind) => kind.to_ty(self.tcx),
140 // Create a type variable (for now) to represent the closure kind.
141 // It will be unified during the upvar inference phase (`upvar.rs`)
142 None => self.next_ty_var(TypeVariableOrigin {
143 // FIXME(eddyb) distinguish closure kind inference variables from the rest.
144 kind: TypeVariableOriginKind::ClosureSynthetic,
149 let closure_substs = ty::ClosureSubsts::new(
151 ty::ClosureSubstsParts {
154 closure_sig_as_fn_ptr_ty: self.tcx.mk_fn_ptr(sig),
159 self.tcx.mk_closure(expr_def_id.to_def_id(), closure_substs.substs)
162 /// Given the expected type, figures out what it can about this closure we
163 /// are about to type check:
164 #[instrument(skip(self), level = "debug")]
165 fn deduce_expectations_from_expected_type(
167 expected_ty: Ty<'tcx>,
168 ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
169 match *expected_ty.kind() {
170 ty::Opaque(def_id, substs) => self.deduce_signature_from_predicates(
171 self.tcx.bound_explicit_item_bounds(def_id).subst_iter_copied(self.tcx, substs),
173 ty::Dynamic(ref object_type, ..) => {
174 let sig = object_type.projection_bounds().find_map(|pb| {
175 let pb = pb.with_self_ty(self.tcx, self.tcx.types.trait_object_dummy_self);
176 self.deduce_sig_from_projection(None, pb)
178 let kind = object_type
180 .and_then(|did| self.tcx.fn_trait_kind_from_def_id(did));
183 ty::Infer(ty::TyVar(vid)) => self.deduce_signature_from_predicates(
184 self.obligations_for_self_ty(vid).map(|obl| (obl.predicate, obl.cause.span)),
187 let expected_sig = ExpectedSig { cause_span: None, sig };
188 (Some(expected_sig), Some(ty::ClosureKind::Fn))
194 fn deduce_signature_from_predicates(
196 predicates: impl DoubleEndedIterator<Item = (ty::Predicate<'tcx>, Span)>,
197 ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
198 let mut expected_sig = None;
199 let mut expected_kind = None;
201 for obligation in traits::elaborate_predicates_with_span(
203 // Reverse the obligations here, since `elaborate_*` uses a stack,
204 // and we want to keep inference generally in the same order of
205 // the registered obligations.
208 debug!(?obligation.predicate);
209 let bound_predicate = obligation.predicate.kind();
211 // Given a Projection predicate, we can potentially infer
212 // the complete signature.
213 if expected_sig.is_none()
214 && let ty::PredicateKind::Clause(ty::Clause::Projection(proj_predicate)) = bound_predicate.skip_binder()
216 expected_sig = self.normalize(
217 obligation.cause.span,
218 self.deduce_sig_from_projection(
219 Some(obligation.cause.span),
220 bound_predicate.rebind(proj_predicate),
225 // Even if we can't infer the full signature, we may be able to
226 // infer the kind. This can occur when we elaborate a predicate
227 // like `F : Fn<A>`. Note that due to subtyping we could encounter
228 // many viable options, so pick the most restrictive.
229 let trait_def_id = match bound_predicate.skip_binder() {
230 ty::PredicateKind::Clause(ty::Clause::Projection(data)) => {
231 Some(data.projection_ty.trait_def_id(self.tcx))
233 ty::PredicateKind::Clause(ty::Clause::Trait(data)) => Some(data.def_id()),
236 if let Some(closure_kind) =
237 trait_def_id.and_then(|def_id| self.tcx.fn_trait_kind_from_def_id(def_id))
239 expected_kind = Some(
241 .map_or_else(|| closure_kind, |current| cmp::min(current, closure_kind)),
246 (expected_sig, expected_kind)
249 /// Given a projection like "<F as Fn(X)>::Result == Y", we can deduce
250 /// everything we need to know about a closure or generator.
252 /// The `cause_span` should be the span that caused us to
253 /// have this expected signature, or `None` if we can't readily
255 #[instrument(level = "debug", skip(self, cause_span), ret)]
256 fn deduce_sig_from_projection(
258 cause_span: Option<Span>,
259 projection: ty::PolyProjectionPredicate<'tcx>,
260 ) -> Option<ExpectedSig<'tcx>> {
263 let trait_def_id = projection.trait_def_id(tcx);
265 let is_fn = tcx.is_fn_trait(trait_def_id);
266 let gen_trait = tcx.require_lang_item(LangItem::Generator, cause_span);
267 let is_gen = gen_trait == trait_def_id;
268 if !is_fn && !is_gen {
269 debug!("not fn or generator");
274 // Check that we deduce the signature from the `<_ as std::ops::Generator>::Return`
275 // associated item and not yield.
276 let return_assoc_item = self.tcx.associated_item_def_ids(gen_trait)[1];
277 if return_assoc_item != projection.projection_def_id() {
278 debug!("not return assoc item of generator");
283 let input_tys = if is_fn {
284 let arg_param_ty = projection.skip_binder().projection_ty.substs.type_at(1);
285 let arg_param_ty = self.resolve_vars_if_possible(arg_param_ty);
286 debug!(?arg_param_ty);
288 match arg_param_ty.kind() {
289 &ty::Tuple(tys) => tys,
293 // Generators with a `()` resume type may be defined with 0 or 1 explicit arguments,
294 // else they must have exactly 1 argument. For now though, just give up in this case.
298 // Since this is a return parameter type it is safe to unwrap.
299 let ret_param_ty = projection.skip_binder().term.ty().unwrap();
300 let ret_param_ty = self.resolve_vars_if_possible(ret_param_ty);
301 debug!(?ret_param_ty);
303 let sig = projection.rebind(self.tcx.mk_fn_sig(
307 hir::Unsafety::Normal,
311 Some(ExpectedSig { cause_span, sig })
316 expr_def_id: LocalDefId,
317 decl: &hir::FnDecl<'_>,
318 body: &hir::Body<'_>,
319 expected_sig: Option<ExpectedSig<'tcx>>,
320 ) -> ClosureSignatures<'tcx> {
321 if let Some(e) = expected_sig {
322 self.sig_of_closure_with_expectation(expr_def_id, decl, body, e)
324 self.sig_of_closure_no_expectation(expr_def_id, decl, body)
328 /// If there is no expected signature, then we will convert the
329 /// types that the user gave into a signature.
330 #[instrument(skip(self, expr_def_id, decl, body), level = "debug")]
331 fn sig_of_closure_no_expectation(
333 expr_def_id: LocalDefId,
334 decl: &hir::FnDecl<'_>,
335 body: &hir::Body<'_>,
336 ) -> ClosureSignatures<'tcx> {
337 let bound_sig = self.supplied_sig_of_closure(expr_def_id, decl, body);
339 self.closure_sigs(expr_def_id, body, bound_sig)
342 /// Invoked to compute the signature of a closure expression. This
343 /// combines any user-provided type annotations (e.g., `|x: u32|
344 /// -> u32 { .. }`) with the expected signature.
346 /// The approach is as follows:
348 /// - Let `S` be the (higher-ranked) signature that we derive from the user's annotations.
349 /// - Let `E` be the (higher-ranked) signature that we derive from the expectations, if any.
350 /// - If we have no expectation `E`, then the signature of the closure is `S`.
351 /// - Otherwise, the signature of the closure is E. Moreover:
352 /// - Skolemize the late-bound regions in `E`, yielding `E'`.
353 /// - Instantiate all the late-bound regions bound in the closure within `S`
354 /// with fresh (existential) variables, yielding `S'`
355 /// - Require that `E' = S'`
356 /// - We could use some kind of subtyping relationship here,
357 /// I imagine, but equality is easier and works fine for
360 /// The key intuition here is that the user's types must be valid
361 /// from "the inside" of the closure, but the expectation
362 /// ultimately drives the overall signature.
366 /// ```ignore (illustrative)
367 /// fn with_closure<F>(_: F)
368 /// where F: Fn(&u32) -> &u32 { .. }
370 /// with_closure(|x: &u32| { ... })
374 /// - E would be `fn(&u32) -> &u32`.
375 /// - S would be `fn(&u32) ->
376 /// - E' is `&'!0 u32 -> &'!0 u32`
377 /// - S' is `&'?0 u32 -> ?T`
379 /// S' can be unified with E' with `['?0 = '!0, ?T = &'!10 u32]`.
383 /// - `expr_def_id`: the `LocalDefId` of the closure expression
384 /// - `decl`: the HIR declaration of the closure
385 /// - `body`: the body of the closure
386 /// - `expected_sig`: the expected signature (if any). Note that
387 /// this is missing a binder: that is, there may be late-bound
388 /// regions with depth 1, which are bound then by the closure.
389 #[instrument(skip(self, expr_def_id, decl, body), level = "debug")]
390 fn sig_of_closure_with_expectation(
392 expr_def_id: LocalDefId,
393 decl: &hir::FnDecl<'_>,
394 body: &hir::Body<'_>,
395 expected_sig: ExpectedSig<'tcx>,
396 ) -> ClosureSignatures<'tcx> {
397 // Watch out for some surprises and just ignore the
398 // expectation if things don't see to match up with what we
400 if expected_sig.sig.c_variadic() != decl.c_variadic {
401 return self.sig_of_closure_no_expectation(expr_def_id, decl, body);
402 } else if expected_sig.sig.skip_binder().inputs_and_output.len() != decl.inputs.len() + 1 {
403 return self.sig_of_closure_with_mismatched_number_of_arguments(
411 // Create a `PolyFnSig`. Note the oddity that late bound
412 // regions appearing free in `expected_sig` are now bound up
413 // in this binder we are creating.
414 assert!(!expected_sig.sig.skip_binder().has_vars_bound_above(ty::INNERMOST));
415 let bound_sig = expected_sig.sig.map_bound(|sig| {
417 sig.inputs().iter().cloned(),
420 hir::Unsafety::Normal,
425 // `deduce_expectations_from_expected_type` introduces
426 // late-bound lifetimes defined elsewhere, which we now
427 // anonymize away, so as not to confuse the user.
428 let bound_sig = self.tcx.anonymize_late_bound_regions(bound_sig);
430 let closure_sigs = self.closure_sigs(expr_def_id, body, bound_sig);
432 // Up till this point, we have ignored the annotations that the user
433 // gave. This function will check that they unify successfully.
434 // Along the way, it also writes out entries for types that the user
435 // wrote into our typeck results, which are then later used by the privacy
437 match self.merge_supplied_sig_with_expectation(expr_def_id, decl, body, closure_sigs) {
438 Ok(infer_ok) => self.register_infer_ok_obligations(infer_ok),
439 Err(_) => self.sig_of_closure_no_expectation(expr_def_id, decl, body),
443 fn sig_of_closure_with_mismatched_number_of_arguments(
445 expr_def_id: LocalDefId,
446 decl: &hir::FnDecl<'_>,
447 body: &hir::Body<'_>,
448 expected_sig: ExpectedSig<'tcx>,
449 ) -> ClosureSignatures<'tcx> {
450 let hir = self.tcx.hir();
451 let expr_map_node = hir.get_by_def_id(expr_def_id);
452 let expected_args: Vec<_> = expected_sig
457 .map(|ty| ArgKind::from_expected_ty(*ty, None))
459 let (closure_span, found_args) = match self.get_fn_like_arguments(expr_map_node) {
460 Some((sp, args)) => (Some(sp), args),
461 None => (None, Vec::new()),
464 expected_sig.cause_span.unwrap_or_else(|| self.tcx.def_span(expr_def_id));
465 self.report_arg_count_mismatch(
474 let error_sig = self.error_sig_of_closure(decl);
476 self.closure_sigs(expr_def_id, body, error_sig)
479 /// Enforce the user's types against the expectation. See
480 /// `sig_of_closure_with_expectation` for details on the overall
482 #[instrument(level = "debug", skip(self, expr_def_id, decl, body, expected_sigs))]
483 fn merge_supplied_sig_with_expectation(
485 expr_def_id: LocalDefId,
486 decl: &hir::FnDecl<'_>,
487 body: &hir::Body<'_>,
488 mut expected_sigs: ClosureSignatures<'tcx>,
489 ) -> InferResult<'tcx, ClosureSignatures<'tcx>> {
490 // Get the signature S that the user gave.
492 // (See comment on `sig_of_closure_with_expectation` for the
493 // meaning of these letters.)
494 let supplied_sig = self.supplied_sig_of_closure(expr_def_id, decl, body);
496 debug!(?supplied_sig);
498 // FIXME(#45727): As discussed in [this comment][c1], naively
499 // forcing equality here actually results in suboptimal error
500 // messages in some cases. For now, if there would have been
501 // an obvious error, we fallback to declaring the type of the
502 // closure to be the one the user gave, which allows other
503 // error message code to trigger.
505 // However, I think [there is potential to do even better
506 // here][c2], since in *this* code we have the precise span of
507 // the type parameter in question in hand when we report the
510 // [c1]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341089706
511 // [c2]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341096796
512 self.commit_if_ok(|_| {
513 let mut all_obligations = vec![];
514 let inputs: Vec<_> = iter::zip(
516 supplied_sig.inputs().skip_binder(), // binder moved to (*) below
518 .map(|(hir_ty, &supplied_ty)| {
519 // Instantiate (this part of..) S to S', i.e., with fresh variables.
520 self.replace_bound_vars_with_fresh_vars(
522 LateBoundRegionConversionTime::FnCall,
523 // (*) binder moved to here
524 supplied_sig.inputs().rebind(supplied_ty),
529 // The liberated version of this signature should be a subtype
530 // of the liberated form of the expectation.
531 for ((hir_ty, &supplied_ty), expected_ty) in iter::zip(
532 iter::zip(decl.inputs, &inputs),
533 expected_sigs.liberated_sig.inputs(), // `liberated_sig` is E'.
535 // Check that E' = S'.
536 let cause = self.misc(hir_ty.span);
537 let InferOk { value: (), obligations } =
538 self.at(&cause, self.param_env).eq(*expected_ty, supplied_ty)?;
539 all_obligations.extend(obligations);
542 let supplied_output_ty = self.replace_bound_vars_with_fresh_vars(
544 LateBoundRegionConversionTime::FnCall,
545 supplied_sig.output(),
547 let cause = &self.misc(decl.output.span());
548 let InferOk { value: (), obligations } = self
549 .at(cause, self.param_env)
550 .eq(expected_sigs.liberated_sig.output(), supplied_output_ty)?;
551 all_obligations.extend(obligations);
553 let inputs = inputs.into_iter().map(|ty| self.resolve_vars_if_possible(ty));
555 expected_sigs.liberated_sig = self.tcx.mk_fn_sig(
558 expected_sigs.liberated_sig.c_variadic,
559 hir::Unsafety::Normal,
563 Ok(InferOk { value: expected_sigs, obligations: all_obligations })
567 /// If there is no expected signature, then we will convert the
568 /// types that the user gave into a signature.
570 /// Also, record this closure signature for later.
571 #[instrument(skip(self, decl, body), level = "debug", ret)]
572 fn supplied_sig_of_closure(
574 expr_def_id: LocalDefId,
575 decl: &hir::FnDecl<'_>,
576 body: &hir::Body<'_>,
577 ) -> ty::PolyFnSig<'tcx> {
578 let astconv: &dyn AstConv<'_> = self;
580 trace!("decl = {:#?}", decl);
581 debug!(?body.generator_kind);
583 let hir_id = self.tcx.hir().local_def_id_to_hir_id(expr_def_id);
584 let bound_vars = self.tcx.late_bound_vars(hir_id);
586 // First, convert the types that the user supplied (if any).
587 let supplied_arguments = decl.inputs.iter().map(|a| astconv.ast_ty_to_ty(a));
588 let supplied_return = match decl.output {
589 hir::FnRetTy::Return(ref output) => astconv.ast_ty_to_ty(&output),
590 hir::FnRetTy::DefaultReturn(_) => match body.generator_kind {
591 // In the case of the async block that we create for a function body,
592 // we expect the return type of the block to match that of the enclosing
594 Some(hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn)) => {
595 debug!("closure is async fn body");
596 self.deduce_future_output_from_obligations(expr_def_id, body.id().hir_id)
598 // AFAIK, deducing the future output
599 // always succeeds *except* in error cases
600 // like #65159. I'd like to return Error
601 // here, but I can't because I can't
602 // easily (and locally) prove that we
603 // *have* reported an
604 // error. --nikomatsakis
605 astconv.ty_infer(None, decl.output.span())
609 _ => astconv.ty_infer(None, decl.output.span()),
613 let result = ty::Binder::bind_with_vars(
618 hir::Unsafety::Normal,
623 // Astconv can't normalize inputs or outputs with escaping bound vars,
624 // so normalize them here, after we've wrapped them in a binder.
625 let result = self.normalize(self.tcx.hir().span(hir_id), result);
627 let c_result = self.inh.infcx.canonicalize_response(result);
628 self.typeck_results.borrow_mut().user_provided_sigs.insert(expr_def_id, c_result);
633 /// Invoked when we are translating the generator that results
634 /// from desugaring an `async fn`. Returns the "sugared" return
635 /// type of the `async fn` -- that is, the return type that the
636 /// user specified. The "desugared" return type is an `impl
637 /// Future<Output = T>`, so we do this by searching through the
638 /// obligations to extract the `T`.
639 #[instrument(skip(self), level = "debug", ret)]
640 fn deduce_future_output_from_obligations(
642 expr_def_id: LocalDefId,
644 ) -> Option<Ty<'tcx>> {
645 let ret_coercion = self.ret_coercion.as_ref().unwrap_or_else(|| {
646 span_bug!(self.tcx.def_span(expr_def_id), "async fn generator outside of a fn")
649 let ret_ty = ret_coercion.borrow().expected_ty();
650 let ret_ty = self.inh.infcx.shallow_resolve(ret_ty);
652 let get_future_output = |predicate: ty::Predicate<'tcx>, span| {
653 // Search for a pending obligation like
655 // `<R as Future>::Output = T`
657 // where R is the return type we are expecting. This type `T`
658 // will be our output.
659 let bound_predicate = predicate.kind();
660 if let ty::PredicateKind::Clause(ty::Clause::Projection(proj_predicate)) =
661 bound_predicate.skip_binder()
663 self.deduce_future_output_from_projection(
665 bound_predicate.rebind(proj_predicate),
672 let output_ty = match *ret_ty.kind() {
673 ty::Infer(ty::TyVar(ret_vid)) => {
674 self.obligations_for_self_ty(ret_vid).find_map(|obligation| {
675 get_future_output(obligation.predicate, obligation.cause.span)
678 ty::Opaque(def_id, substs) => self
680 .bound_explicit_item_bounds(def_id)
681 .subst_iter_copied(self.tcx, substs)
682 .find_map(|(p, s)| get_future_output(p, s))?,
683 ty::Error(_) => return None,
685 if self.tcx.def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder =>
688 .bound_explicit_item_bounds(proj.item_def_id)
689 .subst_iter_copied(self.tcx, proj.substs)
690 .find_map(|(p, s)| get_future_output(p, s))?
693 self.tcx.def_span(expr_def_id),
694 "async fn generator return type not an inference variable: {ret_ty}"
698 // async fn that have opaque types in their return type need to redo the conversion to inference variables
699 // as they fetch the still opaque version from the signature.
700 let InferOk { value: output_ty, obligations } = self
701 .replace_opaque_types_with_inference_vars(
704 self.tcx.def_span(expr_def_id),
707 self.register_predicates(obligations);
712 /// Given a projection like
714 /// `<X as Future>::Output = T`
716 /// where `X` is some type that has no late-bound regions, returns
717 /// `Some(T)`. If the projection is for some other trait, returns
719 fn deduce_future_output_from_projection(
722 predicate: ty::PolyProjectionPredicate<'tcx>,
723 ) -> Option<Ty<'tcx>> {
724 debug!("deduce_future_output_from_projection(predicate={:?})", predicate);
726 // We do not expect any bound regions in our predicate, so
727 // skip past the bound vars.
728 let Some(predicate) = predicate.no_bound_vars() else {
729 debug!("deduce_future_output_from_projection: has late-bound regions");
733 // Check that this is a projection from the `Future` trait.
734 let trait_def_id = predicate.projection_ty.trait_def_id(self.tcx);
735 let future_trait = self.tcx.require_lang_item(LangItem::Future, Some(cause_span));
736 if trait_def_id != future_trait {
737 debug!("deduce_future_output_from_projection: not a future");
741 // The `Future` trait has only one associated item, `Output`,
742 // so check that this is what we see.
743 let output_assoc_item = self.tcx.associated_item_def_ids(future_trait)[0];
744 if output_assoc_item != predicate.projection_ty.item_def_id {
747 "projecting associated item `{:?}` from future, which is not Output `{:?}`",
748 predicate.projection_ty.item_def_id,
753 // Extract the type from the projection. Note that there can
754 // be no bound variables in this type because the "self type"
755 // does not have any regions in it.
756 let output_ty = self.resolve_vars_if_possible(predicate.term);
757 debug!("deduce_future_output_from_projection: output_ty={:?}", output_ty);
758 // This is a projection on a Fn trait so will always be a type.
759 Some(output_ty.ty().unwrap())
762 /// Converts the types that the user supplied, in case that doing
763 /// so should yield an error, but returns back a signature where
764 /// all parameters are of type `TyErr`.
765 fn error_sig_of_closure(&self, decl: &hir::FnDecl<'_>) -> ty::PolyFnSig<'tcx> {
766 let astconv: &dyn AstConv<'_> = self;
768 let supplied_arguments = decl.inputs.iter().map(|a| {
769 // Convert the types that the user supplied (if any), but ignore them.
770 astconv.ast_ty_to_ty(a);
774 if let hir::FnRetTy::Return(ref output) = decl.output {
775 astconv.ast_ty_to_ty(&output);
778 let result = ty::Binder::dummy(self.tcx.mk_fn_sig(
782 hir::Unsafety::Normal,
786 debug!("supplied_sig_of_closure: result={:?}", result);
793 expr_def_id: LocalDefId,
794 body: &hir::Body<'_>,
795 bound_sig: ty::PolyFnSig<'tcx>,
796 ) -> ClosureSignatures<'tcx> {
798 self.tcx().liberate_late_bound_regions(expr_def_id.to_def_id(), bound_sig);
799 let liberated_sig = self.normalize(body.value.span, liberated_sig);
800 ClosureSignatures { bound_sig, liberated_sig }