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, TypeSuperVisitable, TypeVisitor};
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 _;
24 use std::ops::ControlFlow;
26 /// What signature do we *expect* the closure to have from context?
27 #[derive(Debug, Clone, TypeFoldable, TypeVisitable)]
28 struct ExpectedSig<'tcx> {
29 /// Span that gave us this expectation, if we know that.
30 cause_span: Option<Span>,
31 sig: ty::PolyFnSig<'tcx>,
34 struct ClosureSignatures<'tcx> {
35 /// The signature users of the closure see.
36 bound_sig: ty::PolyFnSig<'tcx>,
37 /// The signature within the function body.
38 /// This mostly differs in the sense that lifetimes are now early bound and any
39 /// opaque types from the signature expectation are overridden in case there are
40 /// explicit hidden types written by the user in the closure signature.
41 liberated_sig: ty::FnSig<'tcx>,
44 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
45 #[instrument(skip(self, closure), level = "debug")]
46 pub fn check_expr_closure(
48 closure: &hir::Closure<'tcx>,
50 expected: Expectation<'tcx>,
52 trace!("decl = {:#?}", closure.fn_decl);
54 // It's always helpful for inference if we know the kind of
55 // closure sooner rather than later, so first examine the expected
56 // type, and see if can glean a closure kind from there.
57 let (expected_sig, expected_kind) = match expected.to_option(self) {
58 Some(ty) => self.deduce_closure_signature(ty),
61 let body = self.tcx.hir().body(closure.body);
62 self.check_closure(closure, expr_span, expected_kind, body, expected_sig)
65 #[instrument(skip(self, closure, body), level = "debug", ret)]
68 closure: &hir::Closure<'tcx>,
70 opt_kind: Option<ty::ClosureKind>,
71 body: &'tcx hir::Body<'tcx>,
72 expected_sig: Option<ExpectedSig<'tcx>>,
74 trace!("decl = {:#?}", closure.fn_decl);
75 let expr_def_id = closure.def_id;
78 let ClosureSignatures { bound_sig, liberated_sig } =
79 self.sig_of_closure(expr_def_id, closure.fn_decl, body, expected_sig);
81 debug!(?bound_sig, ?liberated_sig);
83 let mut fcx = FnCtxt::new(self, self.param_env.without_const(), body.value.hir_id);
84 let generator_types = check_fn(
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_closure_signature(
168 expected_ty: Ty<'tcx>,
169 ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
170 match *expected_ty.kind() {
171 ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) => self
172 .deduce_closure_signature_from_predicates(
174 self.tcx.bound_explicit_item_bounds(def_id).subst_iter_copied(self.tcx, substs),
176 ty::Dynamic(ref object_type, ..) => {
177 let sig = object_type.projection_bounds().find_map(|pb| {
178 let pb = pb.with_self_ty(self.tcx, self.tcx.types.trait_object_dummy_self);
179 self.deduce_sig_from_projection(None, pb)
181 let kind = object_type
183 .and_then(|did| self.tcx.fn_trait_kind_from_def_id(did));
186 ty::Infer(ty::TyVar(vid)) => self.deduce_closure_signature_from_predicates(
187 self.tcx.mk_ty_var(self.root_var(vid)),
188 self.obligations_for_self_ty(vid).map(|obl| (obl.predicate, obl.cause.span)),
191 let expected_sig = ExpectedSig { cause_span: None, sig };
192 (Some(expected_sig), Some(ty::ClosureKind::Fn))
198 fn deduce_closure_signature_from_predicates(
200 expected_ty: Ty<'tcx>,
201 predicates: impl DoubleEndedIterator<Item = (ty::Predicate<'tcx>, Span)>,
202 ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
203 let mut expected_sig = None;
204 let mut expected_kind = None;
206 for obligation in traits::elaborate_predicates_with_span(
208 // Reverse the obligations here, since `elaborate_*` uses a stack,
209 // and we want to keep inference generally in the same order of
210 // the registered obligations.
213 debug!(?obligation.predicate);
214 let bound_predicate = obligation.predicate.kind();
216 // Given a Projection predicate, we can potentially infer
217 // the complete signature.
218 if expected_sig.is_none()
219 && let ty::PredicateKind::Clause(ty::Clause::Projection(proj_predicate)) = bound_predicate.skip_binder()
221 let inferred_sig = self.normalize(
222 obligation.cause.span,
223 self.deduce_sig_from_projection(
224 Some(obligation.cause.span),
225 bound_predicate.rebind(proj_predicate),
228 // Make sure that we didn't infer a signature that mentions itself.
229 // This can happen when we elaborate certain supertrait bounds that
230 // mention projections containing the `Self` type. See #105401.
231 struct MentionsTy<'tcx> {
232 expected_ty: Ty<'tcx>,
234 impl<'tcx> TypeVisitor<'tcx> for MentionsTy<'tcx> {
237 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
238 if t == self.expected_ty {
241 t.super_visit_with(self)
245 if inferred_sig.visit_with(&mut MentionsTy { expected_ty }).is_continue() {
246 expected_sig = inferred_sig;
250 // Even if we can't infer the full signature, we may be able to
251 // infer the kind. This can occur when we elaborate a predicate
252 // like `F : Fn<A>`. Note that due to subtyping we could encounter
253 // many viable options, so pick the most restrictive.
254 let trait_def_id = match bound_predicate.skip_binder() {
255 ty::PredicateKind::Clause(ty::Clause::Projection(data)) => {
256 Some(data.projection_ty.trait_def_id(self.tcx))
258 ty::PredicateKind::Clause(ty::Clause::Trait(data)) => Some(data.def_id()),
261 if let Some(closure_kind) =
262 trait_def_id.and_then(|def_id| self.tcx.fn_trait_kind_from_def_id(def_id))
264 expected_kind = Some(
266 .map_or_else(|| closure_kind, |current| cmp::min(current, closure_kind)),
271 (expected_sig, expected_kind)
274 /// Given a projection like "<F as Fn(X)>::Result == Y", we can deduce
275 /// everything we need to know about a closure or generator.
277 /// The `cause_span` should be the span that caused us to
278 /// have this expected signature, or `None` if we can't readily
280 #[instrument(level = "debug", skip(self, cause_span), ret)]
281 fn deduce_sig_from_projection(
283 cause_span: Option<Span>,
284 projection: ty::PolyProjectionPredicate<'tcx>,
285 ) -> Option<ExpectedSig<'tcx>> {
288 let trait_def_id = projection.trait_def_id(tcx);
290 let is_fn = tcx.is_fn_trait(trait_def_id);
291 let gen_trait = tcx.require_lang_item(LangItem::Generator, cause_span);
292 let is_gen = gen_trait == trait_def_id;
293 if !is_fn && !is_gen {
294 debug!("not fn or generator");
299 // Check that we deduce the signature from the `<_ as std::ops::Generator>::Return`
300 // associated item and not yield.
301 let return_assoc_item = self.tcx.associated_item_def_ids(gen_trait)[1];
302 if return_assoc_item != projection.projection_def_id() {
303 debug!("not return assoc item of generator");
308 let input_tys = if is_fn {
309 let arg_param_ty = projection.skip_binder().projection_ty.substs.type_at(1);
310 let arg_param_ty = self.resolve_vars_if_possible(arg_param_ty);
311 debug!(?arg_param_ty);
313 match arg_param_ty.kind() {
314 &ty::Tuple(tys) => tys,
318 // Generators with a `()` resume type may be defined with 0 or 1 explicit arguments,
319 // else they must have exactly 1 argument. For now though, just give up in this case.
323 // Since this is a return parameter type it is safe to unwrap.
324 let ret_param_ty = projection.skip_binder().term.ty().unwrap();
325 let ret_param_ty = self.resolve_vars_if_possible(ret_param_ty);
326 debug!(?ret_param_ty);
328 let sig = projection.rebind(self.tcx.mk_fn_sig(
332 hir::Unsafety::Normal,
336 Some(ExpectedSig { cause_span, sig })
341 expr_def_id: LocalDefId,
342 decl: &hir::FnDecl<'_>,
343 body: &hir::Body<'_>,
344 expected_sig: Option<ExpectedSig<'tcx>>,
345 ) -> ClosureSignatures<'tcx> {
346 if let Some(e) = expected_sig {
347 self.sig_of_closure_with_expectation(expr_def_id, decl, body, e)
349 self.sig_of_closure_no_expectation(expr_def_id, decl, body)
353 /// If there is no expected signature, then we will convert the
354 /// types that the user gave into a signature.
355 #[instrument(skip(self, expr_def_id, decl, body), level = "debug")]
356 fn sig_of_closure_no_expectation(
358 expr_def_id: LocalDefId,
359 decl: &hir::FnDecl<'_>,
360 body: &hir::Body<'_>,
361 ) -> ClosureSignatures<'tcx> {
362 let bound_sig = self.supplied_sig_of_closure(expr_def_id, decl, body);
364 self.closure_sigs(expr_def_id, body, bound_sig)
367 /// Invoked to compute the signature of a closure expression. This
368 /// combines any user-provided type annotations (e.g., `|x: u32|
369 /// -> u32 { .. }`) with the expected signature.
371 /// The approach is as follows:
373 /// - Let `S` be the (higher-ranked) signature that we derive from the user's annotations.
374 /// - Let `E` be the (higher-ranked) signature that we derive from the expectations, if any.
375 /// - If we have no expectation `E`, then the signature of the closure is `S`.
376 /// - Otherwise, the signature of the closure is E. Moreover:
377 /// - Skolemize the late-bound regions in `E`, yielding `E'`.
378 /// - Instantiate all the late-bound regions bound in the closure within `S`
379 /// with fresh (existential) variables, yielding `S'`
380 /// - Require that `E' = S'`
381 /// - We could use some kind of subtyping relationship here,
382 /// I imagine, but equality is easier and works fine for
385 /// The key intuition here is that the user's types must be valid
386 /// from "the inside" of the closure, but the expectation
387 /// ultimately drives the overall signature.
391 /// ```ignore (illustrative)
392 /// fn with_closure<F>(_: F)
393 /// where F: Fn(&u32) -> &u32 { .. }
395 /// with_closure(|x: &u32| { ... })
399 /// - E would be `fn(&u32) -> &u32`.
400 /// - S would be `fn(&u32) ->
401 /// - E' is `&'!0 u32 -> &'!0 u32`
402 /// - S' is `&'?0 u32 -> ?T`
404 /// S' can be unified with E' with `['?0 = '!0, ?T = &'!10 u32]`.
408 /// - `expr_def_id`: the `LocalDefId` of the closure expression
409 /// - `decl`: the HIR declaration of the closure
410 /// - `body`: the body of the closure
411 /// - `expected_sig`: the expected signature (if any). Note that
412 /// this is missing a binder: that is, there may be late-bound
413 /// regions with depth 1, which are bound then by the closure.
414 #[instrument(skip(self, expr_def_id, decl, body), level = "debug")]
415 fn sig_of_closure_with_expectation(
417 expr_def_id: LocalDefId,
418 decl: &hir::FnDecl<'_>,
419 body: &hir::Body<'_>,
420 expected_sig: ExpectedSig<'tcx>,
421 ) -> ClosureSignatures<'tcx> {
422 // Watch out for some surprises and just ignore the
423 // expectation if things don't see to match up with what we
425 if expected_sig.sig.c_variadic() != decl.c_variadic {
426 return self.sig_of_closure_no_expectation(expr_def_id, decl, body);
427 } else if expected_sig.sig.skip_binder().inputs_and_output.len() != decl.inputs.len() + 1 {
428 return self.sig_of_closure_with_mismatched_number_of_arguments(
436 // Create a `PolyFnSig`. Note the oddity that late bound
437 // regions appearing free in `expected_sig` are now bound up
438 // in this binder we are creating.
439 assert!(!expected_sig.sig.skip_binder().has_vars_bound_above(ty::INNERMOST));
440 let bound_sig = expected_sig.sig.map_bound(|sig| {
442 sig.inputs().iter().cloned(),
445 hir::Unsafety::Normal,
450 // `deduce_expectations_from_expected_type` introduces
451 // late-bound lifetimes defined elsewhere, which we now
452 // anonymize away, so as not to confuse the user.
453 let bound_sig = self.tcx.anonymize_bound_vars(bound_sig);
455 let closure_sigs = self.closure_sigs(expr_def_id, body, bound_sig);
457 // Up till this point, we have ignored the annotations that the user
458 // gave. This function will check that they unify successfully.
459 // Along the way, it also writes out entries for types that the user
460 // wrote into our typeck results, which are then later used by the privacy
462 match self.merge_supplied_sig_with_expectation(expr_def_id, decl, body, closure_sigs) {
463 Ok(infer_ok) => self.register_infer_ok_obligations(infer_ok),
464 Err(_) => self.sig_of_closure_no_expectation(expr_def_id, decl, body),
468 fn sig_of_closure_with_mismatched_number_of_arguments(
470 expr_def_id: LocalDefId,
471 decl: &hir::FnDecl<'_>,
472 body: &hir::Body<'_>,
473 expected_sig: ExpectedSig<'tcx>,
474 ) -> ClosureSignatures<'tcx> {
475 let hir = self.tcx.hir();
476 let expr_map_node = hir.get_by_def_id(expr_def_id);
477 let expected_args: Vec<_> = expected_sig
482 .map(|ty| ArgKind::from_expected_ty(*ty, None))
484 let (closure_span, closure_arg_span, found_args) =
485 match self.get_fn_like_arguments(expr_map_node) {
486 Some((sp, arg_sp, args)) => (Some(sp), arg_sp, args),
487 None => (None, None, Vec::new()),
490 expected_sig.cause_span.unwrap_or_else(|| self.tcx.def_span(expr_def_id));
491 self.report_arg_count_mismatch(
501 let error_sig = self.error_sig_of_closure(decl);
503 self.closure_sigs(expr_def_id, body, error_sig)
506 /// Enforce the user's types against the expectation. See
507 /// `sig_of_closure_with_expectation` for details on the overall
509 #[instrument(level = "debug", skip(self, expr_def_id, decl, body, expected_sigs))]
510 fn merge_supplied_sig_with_expectation(
512 expr_def_id: LocalDefId,
513 decl: &hir::FnDecl<'_>,
514 body: &hir::Body<'_>,
515 mut expected_sigs: ClosureSignatures<'tcx>,
516 ) -> InferResult<'tcx, ClosureSignatures<'tcx>> {
517 // Get the signature S that the user gave.
519 // (See comment on `sig_of_closure_with_expectation` for the
520 // meaning of these letters.)
521 let supplied_sig = self.supplied_sig_of_closure(expr_def_id, decl, body);
523 debug!(?supplied_sig);
525 // FIXME(#45727): As discussed in [this comment][c1], naively
526 // forcing equality here actually results in suboptimal error
527 // messages in some cases. For now, if there would have been
528 // an obvious error, we fallback to declaring the type of the
529 // closure to be the one the user gave, which allows other
530 // error message code to trigger.
532 // However, I think [there is potential to do even better
533 // here][c2], since in *this* code we have the precise span of
534 // the type parameter in question in hand when we report the
537 // [c1]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341089706
538 // [c2]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341096796
539 self.commit_if_ok(|_| {
540 let mut all_obligations = vec![];
541 let inputs: Vec<_> = iter::zip(
543 supplied_sig.inputs().skip_binder(), // binder moved to (*) below
545 .map(|(hir_ty, &supplied_ty)| {
546 // Instantiate (this part of..) S to S', i.e., with fresh variables.
547 self.replace_bound_vars_with_fresh_vars(
549 LateBoundRegionConversionTime::FnCall,
550 // (*) binder moved to here
551 supplied_sig.inputs().rebind(supplied_ty),
556 // The liberated version of this signature should be a subtype
557 // of the liberated form of the expectation.
558 for ((hir_ty, &supplied_ty), expected_ty) in iter::zip(
559 iter::zip(decl.inputs, &inputs),
560 expected_sigs.liberated_sig.inputs(), // `liberated_sig` is E'.
562 // Check that E' = S'.
563 let cause = self.misc(hir_ty.span);
564 let InferOk { value: (), obligations } =
565 self.at(&cause, self.param_env).eq(*expected_ty, supplied_ty)?;
566 all_obligations.extend(obligations);
569 let supplied_output_ty = self.replace_bound_vars_with_fresh_vars(
571 LateBoundRegionConversionTime::FnCall,
572 supplied_sig.output(),
574 let cause = &self.misc(decl.output.span());
575 let InferOk { value: (), obligations } = self
576 .at(cause, self.param_env)
577 .eq(expected_sigs.liberated_sig.output(), supplied_output_ty)?;
578 all_obligations.extend(obligations);
580 let inputs = inputs.into_iter().map(|ty| self.resolve_vars_if_possible(ty));
582 expected_sigs.liberated_sig = self.tcx.mk_fn_sig(
585 expected_sigs.liberated_sig.c_variadic,
586 hir::Unsafety::Normal,
590 Ok(InferOk { value: expected_sigs, obligations: all_obligations })
594 /// If there is no expected signature, then we will convert the
595 /// types that the user gave into a signature.
597 /// Also, record this closure signature for later.
598 #[instrument(skip(self, decl, body), level = "debug", ret)]
599 fn supplied_sig_of_closure(
601 expr_def_id: LocalDefId,
602 decl: &hir::FnDecl<'_>,
603 body: &hir::Body<'_>,
604 ) -> ty::PolyFnSig<'tcx> {
605 let astconv: &dyn AstConv<'_> = self;
607 trace!("decl = {:#?}", decl);
608 debug!(?body.generator_kind);
610 let hir_id = self.tcx.hir().local_def_id_to_hir_id(expr_def_id);
611 let bound_vars = self.tcx.late_bound_vars(hir_id);
613 // First, convert the types that the user supplied (if any).
614 let supplied_arguments = decl.inputs.iter().map(|a| astconv.ast_ty_to_ty(a));
615 let supplied_return = match decl.output {
616 hir::FnRetTy::Return(ref output) => astconv.ast_ty_to_ty(&output),
617 hir::FnRetTy::DefaultReturn(_) => match body.generator_kind {
618 // In the case of the async block that we create for a function body,
619 // we expect the return type of the block to match that of the enclosing
621 Some(hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn)) => {
622 debug!("closure is async fn body");
623 self.deduce_future_output_from_obligations(expr_def_id, body.id().hir_id)
625 // AFAIK, deducing the future output
626 // always succeeds *except* in error cases
627 // like #65159. I'd like to return Error
628 // here, but I can't because I can't
629 // easily (and locally) prove that we
630 // *have* reported an
631 // error. --nikomatsakis
632 astconv.ty_infer(None, decl.output.span())
636 _ => astconv.ty_infer(None, decl.output.span()),
640 let result = ty::Binder::bind_with_vars(
645 hir::Unsafety::Normal,
651 let c_result = self.inh.infcx.canonicalize_response(result);
652 self.typeck_results.borrow_mut().user_provided_sigs.insert(expr_def_id, c_result);
654 // Normalize only after registering in `user_provided_sigs`.
655 self.normalize(self.tcx.hir().span(hir_id), result)
658 /// Invoked when we are translating the generator that results
659 /// from desugaring an `async fn`. Returns the "sugared" return
660 /// type of the `async fn` -- that is, the return type that the
661 /// user specified. The "desugared" return type is an `impl
662 /// Future<Output = T>`, so we do this by searching through the
663 /// obligations to extract the `T`.
664 #[instrument(skip(self), level = "debug", ret)]
665 fn deduce_future_output_from_obligations(
667 expr_def_id: LocalDefId,
669 ) -> Option<Ty<'tcx>> {
670 let ret_coercion = self.ret_coercion.as_ref().unwrap_or_else(|| {
671 span_bug!(self.tcx.def_span(expr_def_id), "async fn generator outside of a fn")
674 let ret_ty = ret_coercion.borrow().expected_ty();
675 let ret_ty = self.inh.infcx.shallow_resolve(ret_ty);
677 let get_future_output = |predicate: ty::Predicate<'tcx>, span| {
678 // Search for a pending obligation like
680 // `<R as Future>::Output = T`
682 // where R is the return type we are expecting. This type `T`
683 // will be our output.
684 let bound_predicate = predicate.kind();
685 if let ty::PredicateKind::Clause(ty::Clause::Projection(proj_predicate)) =
686 bound_predicate.skip_binder()
688 self.deduce_future_output_from_projection(
690 bound_predicate.rebind(proj_predicate),
697 let output_ty = match *ret_ty.kind() {
698 ty::Infer(ty::TyVar(ret_vid)) => {
699 self.obligations_for_self_ty(ret_vid).find_map(|obligation| {
700 get_future_output(obligation.predicate, obligation.cause.span)
703 ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) => self
705 .bound_explicit_item_bounds(def_id)
706 .subst_iter_copied(self.tcx, substs)
707 .find_map(|(p, s)| get_future_output(p, s))?,
708 ty::Error(_) => return None,
709 ty::Alias(ty::Projection, proj)
710 if self.tcx.def_kind(proj.def_id) == DefKind::ImplTraitPlaceholder =>
713 .bound_explicit_item_bounds(proj.def_id)
714 .subst_iter_copied(self.tcx, proj.substs)
715 .find_map(|(p, s)| get_future_output(p, s))?
718 self.tcx.def_span(expr_def_id),
719 "async fn generator return type not an inference variable: {ret_ty}"
723 // async fn that have opaque types in their return type need to redo the conversion to inference variables
724 // as they fetch the still opaque version from the signature.
725 let InferOk { value: output_ty, obligations } = self
726 .replace_opaque_types_with_inference_vars(
729 self.tcx.def_span(expr_def_id),
732 self.register_predicates(obligations);
737 /// Given a projection like
739 /// `<X as Future>::Output = T`
741 /// where `X` is some type that has no late-bound regions, returns
742 /// `Some(T)`. If the projection is for some other trait, returns
744 fn deduce_future_output_from_projection(
747 predicate: ty::PolyProjectionPredicate<'tcx>,
748 ) -> Option<Ty<'tcx>> {
749 debug!("deduce_future_output_from_projection(predicate={:?})", predicate);
751 // We do not expect any bound regions in our predicate, so
752 // skip past the bound vars.
753 let Some(predicate) = predicate.no_bound_vars() else {
754 debug!("deduce_future_output_from_projection: has late-bound regions");
758 // Check that this is a projection from the `Future` trait.
759 let trait_def_id = predicate.projection_ty.trait_def_id(self.tcx);
760 let future_trait = self.tcx.require_lang_item(LangItem::Future, Some(cause_span));
761 if trait_def_id != future_trait {
762 debug!("deduce_future_output_from_projection: not a future");
766 // The `Future` trait has only one associated item, `Output`,
767 // so check that this is what we see.
768 let output_assoc_item = self.tcx.associated_item_def_ids(future_trait)[0];
769 if output_assoc_item != predicate.projection_ty.def_id {
772 "projecting associated item `{:?}` from future, which is not Output `{:?}`",
773 predicate.projection_ty.def_id,
778 // Extract the type from the projection. Note that there can
779 // be no bound variables in this type because the "self type"
780 // does not have any regions in it.
781 let output_ty = self.resolve_vars_if_possible(predicate.term);
782 debug!("deduce_future_output_from_projection: output_ty={:?}", output_ty);
783 // This is a projection on a Fn trait so will always be a type.
784 Some(output_ty.ty().unwrap())
787 /// Converts the types that the user supplied, in case that doing
788 /// so should yield an error, but returns back a signature where
789 /// all parameters are of type `TyErr`.
790 fn error_sig_of_closure(&self, decl: &hir::FnDecl<'_>) -> ty::PolyFnSig<'tcx> {
791 let astconv: &dyn AstConv<'_> = self;
793 let supplied_arguments = decl.inputs.iter().map(|a| {
794 // Convert the types that the user supplied (if any), but ignore them.
795 astconv.ast_ty_to_ty(a);
799 if let hir::FnRetTy::Return(ref output) = decl.output {
800 astconv.ast_ty_to_ty(&output);
803 let result = ty::Binder::dummy(self.tcx.mk_fn_sig(
807 hir::Unsafety::Normal,
811 debug!("supplied_sig_of_closure: result={:?}", result);
818 expr_def_id: LocalDefId,
819 body: &hir::Body<'_>,
820 bound_sig: ty::PolyFnSig<'tcx>,
821 ) -> ClosureSignatures<'tcx> {
823 self.tcx().liberate_late_bound_regions(expr_def_id.to_def_id(), bound_sig);
824 let liberated_sig = self.normalize(body.value.span, liberated_sig);
825 ClosureSignatures { bound_sig, liberated_sig }