src/librustc_typeck/check/closure.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Code for type-checking closure expressions.
  12
  13 use super::{check_fn, Expectation, FnCtxt, GeneratorTypes};
  14
  15 use astconv::AstConv;
  16 use middle::region;
  17 use rustc::hir::def_id::DefId;
  18 use rustc::infer::{InferOk, InferResult};
  19 use rustc::infer::LateBoundRegionConversionTime;
  20 use rustc::infer::type_variable::TypeVariableOrigin;
  21 use rustc::traits::Obligation;
  22 use rustc::traits::error_reporting::ArgKind;
  23 use rustc::ty::{self, ToPolyTraitRef, Ty, GenericParamDefKind};
  24 use rustc::ty::fold::TypeFoldable;
  25 use rustc::ty::subst::Substs;
  26 use std::cmp;
  27 use std::iter;
  28 use rustc_target::spec::abi::Abi;
  29 use syntax::source_map::Span;
  30 use rustc::hir;
  31
  32 /// What signature do we *expect* the closure to have from context?
  33 #[derive(Debug)]
  34 struct ExpectedSig<'tcx> {
  35     /// Span that gave us this expectation, if we know that.
  36     cause_span: Option<Span>,
  37     sig: ty::FnSig<'tcx>,
  38 }
  39
  40 struct ClosureSignatures<'tcx> {
  41     bound_sig: ty::PolyFnSig<'tcx>,
  42     liberated_sig: ty::FnSig<'tcx>,
  43 }
  44
  45 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
  46     pub fn check_expr_closure(
  47         &self,
  48         expr: &hir::Expr,
  49         _capture: hir::CaptureClause,
  50         decl: &'gcx hir::FnDecl,
  51         body_id: hir::BodyId,
  52         gen: Option<hir::GeneratorMovability>,
  53         expected: Expectation<'tcx>,
  54     ) -> Ty<'tcx> {
  55         debug!(
  56             "check_expr_closure(expr={:?},expected={:?})",
  57             expr, expected
  58         );
  59
  60         // It's always helpful for inference if we know the kind of
  61         // closure sooner rather than later, so first examine the expected
  62         // type, and see if can glean a closure kind from there.
  63         let (expected_sig, expected_kind) = match expected.to_option(self) {
  64             Some(ty) => self.deduce_expectations_from_expected_type(ty),
  65             None => (None, None),
  66         };
  67         let body = self.tcx.hir.body(body_id);
  68         self.check_closure(expr, expected_kind, decl, body, gen, expected_sig)
  69     }
  70
  71     fn check_closure(
  72         &self,
  73         expr: &hir::Expr,
  74         opt_kind: Option<ty::ClosureKind>,
  75         decl: &'gcx hir::FnDecl,
  76         body: &'gcx hir::Body,
  77         gen: Option<hir::GeneratorMovability>,
  78         expected_sig: Option<ExpectedSig<'tcx>>,
  79     ) -> Ty<'tcx> {
  80         debug!(
  81             "check_closure(opt_kind={:?}, expected_sig={:?})",
  82             opt_kind, expected_sig
  83         );
  84
  85         let expr_def_id = self.tcx.hir.local_def_id(expr.id);
  86
  87         let ClosureSignatures {
  88             bound_sig,
  89             liberated_sig,
  90         } = self.sig_of_closure(expr_def_id, decl, body, expected_sig);
  91
  92         debug!("check_closure: ty_of_closure returns {:?}", liberated_sig);
  93
  94         let generator_types = check_fn(
  95             self,
  96             self.param_env,
  97             liberated_sig,
  98             decl,
  99             expr.id,
 100             body,
 101             gen,
 102         ).1;
 103
 104         // Create type variables (for now) to represent the transformed
 105         // types of upvars. These will be unified during the upvar
 106         // inference phase (`upvar.rs`).
 107         let base_substs =
 108             Substs::identity_for_item(self.tcx, self.tcx.closure_base_def_id(expr_def_id));
 109         let substs = base_substs.extend_to(self.tcx,expr_def_id, |param, _| {
 110             match param.kind {
 111                 GenericParamDefKind::Lifetime => {
 112                     span_bug!(expr.span, "closure has region param")
 113                 }
 114                 GenericParamDefKind::Type {..} => {
 115                     self.infcx
 116                         .next_ty_var(TypeVariableOrigin::ClosureSynthetic(expr.span)).into()
 117                 }
 118             }
 119         });
 120         if let Some(GeneratorTypes { yield_ty, interior, movability }) = generator_types {
 121             let substs = ty::GeneratorSubsts { substs };
 122             self.demand_eqtype(
 123                 expr.span,
 124                 yield_ty,
 125                 substs.yield_ty(expr_def_id, self.tcx),
 126             );
 127             self.demand_eqtype(
 128                 expr.span,
 129                 liberated_sig.output(),
 130                 substs.return_ty(expr_def_id, self.tcx),
 131             );
 132             self.demand_eqtype(
 133                 expr.span,
 134                 interior,
 135                 substs.witness(expr_def_id, self.tcx),
 136             );
 137             return self.tcx.mk_generator(expr_def_id, substs, movability);
 138         }
 139
 140         let substs = ty::ClosureSubsts { substs };
 141         let closure_type = self.tcx.mk_closure(expr_def_id, substs);
 142
 143         debug!(
 144             "check_closure: expr.id={:?} closure_type={:?}",
 145             expr.id, closure_type
 146         );
 147
 148         // Tuple up the arguments and insert the resulting function type into
 149         // the `closures` table.
 150         let sig = bound_sig.map_bound(|sig| {
 151             self.tcx.mk_fn_sig(
 152                 iter::once(self.tcx.intern_tup(sig.inputs())),
 153                 sig.output(),
 154                 sig.variadic,
 155                 sig.unsafety,
 156                 sig.abi,
 157             )
 158         });
 159
 160         debug!(
 161             "check_closure: expr_def_id={:?}, sig={:?}, opt_kind={:?}",
 162             expr_def_id, sig, opt_kind
 163         );
 164
 165         let sig_fn_ptr_ty = self.tcx.mk_fn_ptr(sig);
 166         self.demand_eqtype(
 167             expr.span,
 168             sig_fn_ptr_ty,
 169             substs.closure_sig_ty(expr_def_id, self.tcx),
 170         );
 171
 172         if let Some(kind) = opt_kind {
 173             self.demand_eqtype(
 174                 expr.span,
 175                 kind.to_ty(self.tcx),
 176                 substs.closure_kind_ty(expr_def_id, self.tcx),
 177             );
 178         }
 179
 180         closure_type
 181     }
 182
 183     /// Given the expected type, figures out what it can about this closure we
 184     /// are about to type check:
 185     fn deduce_expectations_from_expected_type(
 186         &self,
 187         expected_ty: Ty<'tcx>,
 188     ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
 189         debug!(
 190             "deduce_expectations_from_expected_type(expected_ty={:?})",
 191             expected_ty
 192         );
 193
 194         match expected_ty.sty {
 195             ty::Dynamic(ref object_type, ..) => {
 196                 let sig = object_type
 197                     .projection_bounds()
 198                     .filter_map(|pb| {
 199                         let pb = pb.with_self_ty(self.tcx, self.tcx.types.err);
 200                         self.deduce_sig_from_projection(None, &pb)
 201                     })
 202                     .next();
 203                 let kind = self.tcx.lang_items().fn_trait_kind(object_type.principal().def_id());
 204                 (sig, kind)
 205             }
 206             ty::Infer(ty::TyVar(vid)) => self.deduce_expectations_from_obligations(vid),
 207             ty::FnPtr(sig) => {
 208                 let expected_sig = ExpectedSig {
 209                     cause_span: None,
 210                     sig: sig.skip_binder().clone(),
 211                 };
 212                 (Some(expected_sig), Some(ty::ClosureKind::Fn))
 213             }
 214             _ => (None, None),
 215         }
 216     }
 217
 218     fn deduce_expectations_from_obligations(
 219         &self,
 220         expected_vid: ty::TyVid,
 221     ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
 222         let fulfillment_cx = self.fulfillment_cx.borrow();
 223         // Here `expected_ty` is known to be a type inference variable.
 224
 225         let expected_sig = fulfillment_cx
 226             .pending_obligations()
 227             .iter()
 228             .filter_map(|obligation| {
 229                 debug!(
 230                     "deduce_expectations_from_obligations: obligation.predicate={:?}",
 231                     obligation.predicate
 232                 );
 233
 234                 if let ty::Predicate::Projection(ref proj_predicate) = obligation.predicate {
 235                     // Given a Projection predicate, we can potentially infer
 236                     // the complete signature.
 237                     let trait_ref = proj_predicate.to_poly_trait_ref(self.tcx);
 238                     self.self_type_matches_expected_vid(trait_ref, expected_vid)
 239                         .and_then(|_| {
 240                             self.deduce_sig_from_projection(
 241                                 Some(obligation.cause.span),
 242                                 proj_predicate
 243                             )
 244                         })
 245                 } else {
 246                     None
 247                 }
 248             })
 249             .next();
 250
 251         // Even if we can't infer the full signature, we may be able to
 252         // infer the kind. This can occur if there is a trait-reference
 253         // like `F : Fn<A>`. Note that due to subtyping we could encounter
 254         // many viable options, so pick the most restrictive.
 255         let expected_kind = fulfillment_cx
 256             .pending_obligations()
 257             .iter()
 258             .filter_map(|obligation| {
 259                 let opt_trait_ref = match obligation.predicate {
 260                     ty::Predicate::Projection(ref data) => Some(data.to_poly_trait_ref(self.tcx)),
 261                     ty::Predicate::Trait(ref data) => Some(data.to_poly_trait_ref()),
 262                     ty::Predicate::Subtype(..) => None,
 263                     ty::Predicate::RegionOutlives(..) => None,
 264                     ty::Predicate::TypeOutlives(..) => None,
 265                     ty::Predicate::WellFormed(..) => None,
 266                     ty::Predicate::ObjectSafe(..) => None,
 267                     ty::Predicate::ConstEvaluatable(..) => None,
 268
 269                     // NB: This predicate is created by breaking down a
 270                     // `ClosureType: FnFoo()` predicate, where
 271                     // `ClosureType` represents some `Closure`. It can't
 272                     // possibly be referring to the current closure,
 273                     // because we haven't produced the `Closure` for
 274                     // this closure yet; this is exactly why the other
 275                     // code is looking for a self type of a unresolved
 276                     // inference variable.
 277                     ty::Predicate::ClosureKind(..) => None,
 278                 };
 279                 opt_trait_ref
 280                     .and_then(|tr| self.self_type_matches_expected_vid(tr, expected_vid))
 281                     .and_then(|tr| self.tcx.lang_items().fn_trait_kind(tr.def_id()))
 282             })
 283             .fold(None, |best, cur| {
 284                 Some(best.map_or(cur, |best| cmp::min(best, cur)))
 285             });
 286
 287         (expected_sig, expected_kind)
 288     }
 289
 290     /// Given a projection like "<F as Fn(X)>::Result == Y", we can deduce
 291     /// everything we need to know about a closure.
 292     ///
 293     /// The `cause_span` should be the span that caused us to
 294     /// have this expected signature, or `None` if we can't readily
 295     /// know that.
 296     fn deduce_sig_from_projection(
 297         &self,
 298         cause_span: Option<Span>,
 299         projection: &ty::PolyProjectionPredicate<'tcx>,
 300     ) -> Option<ExpectedSig<'tcx>> {
 301         let tcx = self.tcx;
 302
 303         debug!("deduce_sig_from_projection({:?})", projection);
 304
 305         let trait_ref = projection.to_poly_trait_ref(tcx);
 306
 307         if tcx.lang_items().fn_trait_kind(trait_ref.def_id()).is_none() {
 308             return None;
 309         }
 310
 311         let arg_param_ty = trait_ref.skip_binder().substs.type_at(1);
 312         let arg_param_ty = self.resolve_type_vars_if_possible(&arg_param_ty);
 313         debug!(
 314             "deduce_sig_from_projection: arg_param_ty {:?}",
 315             arg_param_ty
 316         );
 317
 318         let input_tys = match arg_param_ty.sty {
 319             ty::Tuple(tys) => tys.into_iter(),
 320             _ => return None
 321         };
 322
 323         let ret_param_ty = projection.skip_binder().ty;
 324         let ret_param_ty = self.resolve_type_vars_if_possible(&ret_param_ty);
 325         debug!(
 326             "deduce_sig_from_projection: ret_param_ty {:?}",
 327             ret_param_ty
 328         );
 329
 330         let sig = self.tcx.mk_fn_sig(
 331             input_tys.cloned(),
 332             ret_param_ty,
 333             false,
 334             hir::Unsafety::Normal,
 335             Abi::Rust,
 336         );
 337         debug!("deduce_sig_from_projection: sig {:?}", sig);
 338
 339         Some(ExpectedSig { cause_span, sig })
 340     }
 341
 342     fn self_type_matches_expected_vid(
 343         &self,
 344         trait_ref: ty::PolyTraitRef<'tcx>,
 345         expected_vid: ty::TyVid,
 346     ) -> Option<ty::PolyTraitRef<'tcx>> {
 347         let self_ty = self.shallow_resolve(trait_ref.self_ty());
 348         debug!(
 349             "self_type_matches_expected_vid(trait_ref={:?}, self_ty={:?})",
 350             trait_ref, self_ty
 351         );
 352         match self_ty.sty {
 353             ty::Infer(ty::TyVar(v)) if expected_vid == v => Some(trait_ref),
 354             _ => None,
 355         }
 356     }
 357
 358     fn sig_of_closure(
 359         &self,
 360         expr_def_id: DefId,
 361         decl: &hir::FnDecl,
 362         body: &hir::Body,
 363         expected_sig: Option<ExpectedSig<'tcx>>,
 364     ) -> ClosureSignatures<'tcx> {
 365         if let Some(e) = expected_sig {
 366             self.sig_of_closure_with_expectation(expr_def_id, decl, body, e)
 367         } else {
 368             self.sig_of_closure_no_expectation(expr_def_id, decl, body)
 369         }
 370     }
 371
 372     /// If there is no expected signature, then we will convert the
 373     /// types that the user gave into a signature.
 374     fn sig_of_closure_no_expectation(
 375         &self,
 376         expr_def_id: DefId,
 377         decl: &hir::FnDecl,
 378         body: &hir::Body,
 379     ) -> ClosureSignatures<'tcx> {
 380         debug!("sig_of_closure_no_expectation()");
 381
 382         let bound_sig = self.supplied_sig_of_closure(expr_def_id, decl);
 383
 384         self.closure_sigs(expr_def_id, body, bound_sig)
 385     }
 386
 387     /// Invoked to compute the signature of a closure expression. This
 388     /// combines any user-provided type annotations (e.g., `|x: u32|
 389     /// -> u32 { .. }`) with the expected signature.
 390     ///
 391     /// The approach is as follows:
 392     ///
 393     /// - Let `S` be the (higher-ranked) signature that we derive from the user's annotations.
 394     /// - Let `E` be the (higher-ranked) signature that we derive from the expectations, if any.
 395     ///   - If we have no expectation `E`, then the signature of the closure is `S`.
 396     ///   - Otherwise, the signature of the closure is E. Moreover:
 397     ///     - Skolemize the late-bound regions in `E`, yielding `E'`.
 398     ///     - Instantiate all the late-bound regions bound in the closure within `S`
 399     ///       with fresh (existential) variables, yielding `S'`
 400     ///     - Require that `E' = S'`
 401     ///       - We could use some kind of subtyping relationship here,
 402     ///         I imagine, but equality is easier and works fine for
 403     ///         our purposes.
 404     ///
 405     /// The key intuition here is that the user's types must be valid
 406     /// from "the inside" of the closure, but the expectation
 407     /// ultimately drives the overall signature.
 408     ///
 409     /// # Examples
 410     ///
 411     /// ```
 412     /// fn with_closure<F>(_: F)
 413     ///   where F: Fn(&u32) -> &u32 { .. }
 414     ///
 415     /// with_closure(|x: &u32| { ... })
 416     /// ```
 417     ///
 418     /// Here:
 419     /// - E would be `fn(&u32) -> &u32`.
 420     /// - S would be `fn(&u32) ->
 421     /// - E' is `&'!0 u32 -> &'!0 u32`
 422     /// - S' is `&'?0 u32 -> ?T`
 423     ///
 424     /// S' can be unified with E' with `['?0 = '!0, ?T = &'!10 u32]`.
 425     ///
 426     /// # Arguments
 427     ///
 428     /// - `expr_def_id`: the def-id of the closure expression
 429     /// - `decl`: the HIR declaration of the closure
 430     /// - `body`: the body of the closure
 431     /// - `expected_sig`: the expected signature (if any). Note that
 432     ///   this is missing a binder: that is, there may be late-bound
 433     ///   regions with depth 1, which are bound then by the closure.
 434     fn sig_of_closure_with_expectation(
 435         &self,
 436         expr_def_id: DefId,
 437         decl: &hir::FnDecl,
 438         body: &hir::Body,
 439         expected_sig: ExpectedSig<'tcx>,
 440     ) -> ClosureSignatures<'tcx> {
 441         debug!(
 442             "sig_of_closure_with_expectation(expected_sig={:?})",
 443             expected_sig
 444         );
 445
 446         // Watch out for some surprises and just ignore the
 447         // expectation if things don't see to match up with what we
 448         // expect.
 449         if expected_sig.sig.variadic != decl.variadic {
 450             return self.sig_of_closure_no_expectation(expr_def_id, decl, body);
 451         } else if expected_sig.sig.inputs_and_output.len() != decl.inputs.len() + 1 {
 452             return self.sig_of_closure_with_mismatched_number_of_arguments(
 453                 expr_def_id,
 454                 decl,
 455                 body,
 456                 expected_sig,
 457             );
 458         }
 459
 460         // Create a `PolyFnSig`. Note the oddity that late bound
 461         // regions appearing free in `expected_sig` are now bound up
 462         // in this binder we are creating.
 463         assert!(!expected_sig.sig.has_vars_bound_above(ty::INNERMOST));
 464         let bound_sig = ty::Binder::bind(self.tcx.mk_fn_sig(
 465             expected_sig.sig.inputs().iter().cloned(),
 466             expected_sig.sig.output(),
 467             decl.variadic,
 468             hir::Unsafety::Normal,
 469             Abi::RustCall,
 470         ));
 471
 472         // `deduce_expectations_from_expected_type` introduces
 473         // late-bound lifetimes defined elsewhere, which we now
 474         // anonymize away, so as not to confuse the user.
 475         let bound_sig = self.tcx.anonymize_late_bound_regions(&bound_sig);
 476
 477         let closure_sigs = self.closure_sigs(expr_def_id, body, bound_sig);
 478
 479         // Up till this point, we have ignored the annotations that the user
 480         // gave. This function will check that they unify successfully.
 481         // Along the way, it also writes out entries for types that the user
 482         // wrote into our tables, which are then later used by the privacy
 483         // check.
 484         match self.check_supplied_sig_against_expectation(expr_def_id, decl, body, &closure_sigs) {
 485             Ok(infer_ok) => self.register_infer_ok_obligations(infer_ok),
 486             Err(_) => return self.sig_of_closure_no_expectation(expr_def_id, decl, body),
 487         }
 488
 489         closure_sigs
 490     }
 491
 492     fn sig_of_closure_with_mismatched_number_of_arguments(
 493         &self,
 494         expr_def_id: DefId,
 495         decl: &hir::FnDecl,
 496         body: &hir::Body,
 497         expected_sig: ExpectedSig<'tcx>,
 498     ) -> ClosureSignatures<'tcx> {
 499         let expr_map_node = self.tcx.hir.get_if_local(expr_def_id).unwrap();
 500         let expected_args: Vec<_> = expected_sig
 501             .sig
 502             .inputs()
 503             .iter()
 504             .map(|ty| ArgKind::from_expected_ty(ty, None))
 505             .collect();
 506         let (closure_span, found_args) = self.get_fn_like_arguments(expr_map_node);
 507         let expected_span = expected_sig.cause_span.unwrap_or(closure_span);
 508         self.report_arg_count_mismatch(
 509             expected_span,
 510             Some(closure_span),
 511             expected_args,
 512             found_args,
 513             true,
 514         ).emit();
 515
 516         let error_sig = self.error_sig_of_closure(decl);
 517
 518         self.closure_sigs(expr_def_id, body, error_sig)
 519     }
 520
 521     /// Enforce the user's types against the expectation.  See
 522     /// `sig_of_closure_with_expectation` for details on the overall
 523     /// strategy.
 524     fn check_supplied_sig_against_expectation(
 525         &self,
 526         expr_def_id: DefId,
 527         decl: &hir::FnDecl,
 528         body: &hir::Body,
 529         expected_sigs: &ClosureSignatures<'tcx>,
 530     ) -> InferResult<'tcx, ()> {
 531         // Get the signature S that the user gave.
 532         //
 533         // (See comment on `sig_of_closure_with_expectation` for the
 534         // meaning of these letters.)
 535         let supplied_sig = self.supplied_sig_of_closure(expr_def_id, decl);
 536
 537         debug!(
 538             "check_supplied_sig_against_expectation: supplied_sig={:?}",
 539             supplied_sig
 540         );
 541
 542         // FIXME(#45727): As discussed in [this comment][c1], naively
 543         // forcing equality here actually results in suboptimal error
 544         // messages in some cases.  For now, if there would have been
 545         // an obvious error, we fallback to declaring the type of the
 546         // closure to be the one the user gave, which allows other
 547         // error message code to trigger.
 548         //
 549         // However, I think [there is potential to do even better
 550         // here][c2], since in *this* code we have the precise span of
 551         // the type parameter in question in hand when we report the
 552         // error.
 553         //
 554         // [c1]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341089706
 555         // [c2]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341096796
 556         self.infcx.commit_if_ok(|_| {
 557             let mut all_obligations = vec![];
 558
 559             // The liberated version of this signature should be be a subtype
 560             // of the liberated form of the expectation.
 561             for ((hir_ty, &supplied_ty), expected_ty) in decl.inputs.iter()
 562                .zip(*supplied_sig.inputs().skip_binder()) // binder moved to (*) below
 563                .zip(expected_sigs.liberated_sig.inputs())
 564             // `liberated_sig` is E'.
 565             {
 566                 // Instantiate (this part of..) S to S', i.e., with fresh variables.
 567                 let (supplied_ty, _) = self.infcx.replace_late_bound_regions_with_fresh_var(
 568                     hir_ty.span,
 569                     LateBoundRegionConversionTime::FnCall,
 570                     &ty::Binder::bind(supplied_ty),
 571                 ); // recreated from (*) above
 572
 573                 // Check that E' = S'.
 574                 let cause = &self.misc(hir_ty.span);
 575                 let InferOk {
 576                     value: (),
 577                     obligations,
 578                 } = self.at(cause, self.param_env)
 579                     .eq(*expected_ty, supplied_ty)?;
 580                 all_obligations.extend(obligations);
 581
 582                 // Also, require that the supplied type must outlive
 583                 // the closure body.
 584                 let closure_body_region = self.tcx.mk_region(
 585                     ty::ReScope(
 586                         region::Scope {
 587                             id: body.value.hir_id.local_id,
 588                             data: region::ScopeData::Node,
 589                         },
 590                     ),
 591                 );
 592                 all_obligations.push(
 593                     Obligation::new(
 594                         cause.clone(),
 595                         self.param_env,
 596                         ty::Predicate::TypeOutlives(
 597                             ty::Binder::dummy(
 598                                 ty::OutlivesPredicate(
 599                                     supplied_ty,
 600                                     closure_body_region,
 601                                 ),
 602                             ),
 603                         ),
 604                     ),
 605                 );
 606             }
 607
 608             let (supplied_output_ty, _) = self.infcx.replace_late_bound_regions_with_fresh_var(
 609                 decl.output.span(),
 610                 LateBoundRegionConversionTime::FnCall,
 611                 &supplied_sig.output(),
 612             );
 613             let cause = &self.misc(decl.output.span());
 614             let InferOk {
 615                 value: (),
 616                 obligations,
 617             } = self.at(cause, self.param_env)
 618                 .eq(expected_sigs.liberated_sig.output(), supplied_output_ty)?;
 619             all_obligations.extend(obligations);
 620
 621             Ok(InferOk {
 622                 value: (),
 623                 obligations: all_obligations,
 624             })
 625         })
 626     }
 627
 628     /// If there is no expected signature, then we will convert the
 629     /// types that the user gave into a signature.
 630     ///
 631     /// Also, record this closure signature for later.
 632     fn supplied_sig_of_closure(
 633         &self,
 634         expr_def_id: DefId,
 635         decl: &hir::FnDecl,
 636     ) -> ty::PolyFnSig<'tcx> {
 637         let astconv: &dyn AstConv = self;
 638
 639         // First, convert the types that the user supplied (if any).
 640         let supplied_arguments = decl.inputs.iter().map(|a| astconv.ast_ty_to_ty(a));
 641         let supplied_return = match decl.output {
 642             hir::Return(ref output) => astconv.ast_ty_to_ty(&output),
 643             hir::DefaultReturn(_) => astconv.ty_infer(decl.output.span()),
 644         };
 645
 646         let result = ty::Binder::bind(self.tcx.mk_fn_sig(
 647             supplied_arguments,
 648             supplied_return,
 649             decl.variadic,
 650             hir::Unsafety::Normal,
 651             Abi::RustCall,
 652         ));
 653
 654         debug!("supplied_sig_of_closure: result={:?}", result);
 655
 656         let c_result = self.inh.infcx.canonicalize_response(&result);
 657         self.tables.borrow_mut().user_provided_sigs.insert(
 658             expr_def_id,
 659             c_result,
 660         );
 661
 662         result
 663     }
 664
 665     /// Converts the types that the user supplied, in case that doing
 666     /// so should yield an error, but returns back a signature where
 667     /// all parameters are of type `TyErr`.
 668     fn error_sig_of_closure(&self, decl: &hir::FnDecl) -> ty::PolyFnSig<'tcx> {
 669         let astconv: &dyn AstConv = self;
 670
 671         let supplied_arguments = decl.inputs.iter().map(|a| {
 672             // Convert the types that the user supplied (if any), but ignore them.
 673             astconv.ast_ty_to_ty(a);
 674             self.tcx.types.err
 675         });
 676
 677         if let hir::Return(ref output) = decl.output {
 678             astconv.ast_ty_to_ty(&output);
 679         }
 680
 681         let result = ty::Binder::bind(self.tcx.mk_fn_sig(
 682             supplied_arguments,
 683             self.tcx.types.err,
 684             decl.variadic,
 685             hir::Unsafety::Normal,
 686             Abi::RustCall,
 687         ));
 688
 689         debug!("supplied_sig_of_closure: result={:?}", result);
 690
 691         result
 692     }
 693
 694     fn closure_sigs(
 695         &self,
 696         expr_def_id: DefId,
 697         body: &hir::Body,
 698         bound_sig: ty::PolyFnSig<'tcx>,
 699     ) -> ClosureSignatures<'tcx> {
 700         let liberated_sig = self.tcx()
 701             .liberate_late_bound_regions(expr_def_id, &bound_sig);
 702         let liberated_sig = self.inh.normalize_associated_types_in(
 703             body.value.span,
 704             body.value.id,
 705             self.param_env,
 706             &liberated_sig,
 707         );
 708         ClosureSignatures {
 709             bound_sig,
 710             liberated_sig,
 711         }
 712     }
 713 }