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