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