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, 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 expected_sig = self.obligations_for_self_ty(expected_vid)
 223             .find_map(|(_, obligation)| {
 224                 debug!(
 225                     "deduce_expectations_from_obligations: obligation.predicate={:?}",
 226                     obligation.predicate
 227                 );
 228
 229                 if let ty::Predicate::Projection(ref proj_predicate) = obligation.predicate {
 230                     // Given a Projection predicate, we can potentially infer
 231                     // the complete signature.
 232                     self.deduce_sig_from_projection(
 233                         Some(obligation.cause.span),
 234                         proj_predicate
 235                     )
 236                 } else {
 237                     None
 238                 }
 239             });
 240
 241         // Even if we can't infer the full signature, we may be able to
 242         // infer the kind. This can occur if there is a trait-reference
 243         // like `F : Fn<A>`. Note that due to subtyping we could encounter
 244         // many viable options, so pick the most restrictive.
 245         let expected_kind = self.obligations_for_self_ty(expected_vid)
 246             .filter_map(|(tr, _)| self.tcx.lang_items().fn_trait_kind(tr.def_id()))
 247             .fold(None, |best, cur| {
 248                 Some(best.map_or(cur, |best| cmp::min(best, cur)))
 249             });
 250
 251         (expected_sig, expected_kind)
 252     }
 253
 254     /// Given a projection like "<F as Fn(X)>::Result == Y", we can deduce
 255     /// everything we need to know about a closure.
 256     ///
 257     /// The `cause_span` should be the span that caused us to
 258     /// have this expected signature, or `None` if we can't readily
 259     /// know that.
 260     fn deduce_sig_from_projection(
 261         &self,
 262         cause_span: Option<Span>,
 263         projection: &ty::PolyProjectionPredicate<'tcx>,
 264     ) -> Option<ExpectedSig<'tcx>> {
 265         let tcx = self.tcx;
 266
 267         debug!("deduce_sig_from_projection({:?})", projection);
 268
 269         let trait_ref = projection.to_poly_trait_ref(tcx);
 270
 271         if tcx.lang_items().fn_trait_kind(trait_ref.def_id()).is_none() {
 272             return None;
 273         }
 274
 275         let arg_param_ty = trait_ref.skip_binder().substs.type_at(1);
 276         let arg_param_ty = self.resolve_type_vars_if_possible(&arg_param_ty);
 277         debug!(
 278             "deduce_sig_from_projection: arg_param_ty {:?}",
 279             arg_param_ty
 280         );
 281
 282         let input_tys = match arg_param_ty.sty {
 283             ty::Tuple(tys) => tys.into_iter(),
 284             _ => return None
 285         };
 286
 287         let ret_param_ty = projection.skip_binder().ty;
 288         let ret_param_ty = self.resolve_type_vars_if_possible(&ret_param_ty);
 289         debug!(
 290             "deduce_sig_from_projection: ret_param_ty {:?}",
 291             ret_param_ty
 292         );
 293
 294         let sig = self.tcx.mk_fn_sig(
 295             input_tys.cloned(),
 296             ret_param_ty,
 297             false,
 298             hir::Unsafety::Normal,
 299             Abi::Rust,
 300         );
 301         debug!("deduce_sig_from_projection: sig {:?}", sig);
 302
 303         Some(ExpectedSig { cause_span, sig })
 304     }
 305
 306     fn sig_of_closure(
 307         &self,
 308         expr_def_id: DefId,
 309         decl: &hir::FnDecl,
 310         body: &hir::Body,
 311         expected_sig: Option<ExpectedSig<'tcx>>,
 312     ) -> ClosureSignatures<'tcx> {
 313         if let Some(e) = expected_sig {
 314             self.sig_of_closure_with_expectation(expr_def_id, decl, body, e)
 315         } else {
 316             self.sig_of_closure_no_expectation(expr_def_id, decl, body)
 317         }
 318     }
 319
 320     /// If there is no expected signature, then we will convert the
 321     /// types that the user gave into a signature.
 322     fn sig_of_closure_no_expectation(
 323         &self,
 324         expr_def_id: DefId,
 325         decl: &hir::FnDecl,
 326         body: &hir::Body,
 327     ) -> ClosureSignatures<'tcx> {
 328         debug!("sig_of_closure_no_expectation()");
 329
 330         let bound_sig = self.supplied_sig_of_closure(expr_def_id, decl);
 331
 332         self.closure_sigs(expr_def_id, body, bound_sig)
 333     }
 334
 335     /// Invoked to compute the signature of a closure expression. This
 336     /// combines any user-provided type annotations (e.g., `|x: u32|
 337     /// -> u32 { .. }`) with the expected signature.
 338     ///
 339     /// The approach is as follows:
 340     ///
 341     /// - Let `S` be the (higher-ranked) signature that we derive from the user's annotations.
 342     /// - Let `E` be the (higher-ranked) signature that we derive from the expectations, if any.
 343     ///   - If we have no expectation `E`, then the signature of the closure is `S`.
 344     ///   - Otherwise, the signature of the closure is E. Moreover:
 345     ///     - Skolemize the late-bound regions in `E`, yielding `E'`.
 346     ///     - Instantiate all the late-bound regions bound in the closure within `S`
 347     ///       with fresh (existential) variables, yielding `S'`
 348     ///     - Require that `E' = S'`
 349     ///       - We could use some kind of subtyping relationship here,
 350     ///         I imagine, but equality is easier and works fine for
 351     ///         our purposes.
 352     ///
 353     /// The key intuition here is that the user's types must be valid
 354     /// from "the inside" of the closure, but the expectation
 355     /// ultimately drives the overall signature.
 356     ///
 357     /// # Examples
 358     ///
 359     /// ```
 360     /// fn with_closure<F>(_: F)
 361     ///   where F: Fn(&u32) -> &u32 { .. }
 362     ///
 363     /// with_closure(|x: &u32| { ... })
 364     /// ```
 365     ///
 366     /// Here:
 367     /// - E would be `fn(&u32) -> &u32`.
 368     /// - S would be `fn(&u32) ->
 369     /// - E' is `&'!0 u32 -> &'!0 u32`
 370     /// - S' is `&'?0 u32 -> ?T`
 371     ///
 372     /// S' can be unified with E' with `['?0 = '!0, ?T = &'!10 u32]`.
 373     ///
 374     /// # Arguments
 375     ///
 376     /// - `expr_def_id`: the def-id of the closure expression
 377     /// - `decl`: the HIR declaration of the closure
 378     /// - `body`: the body of the closure
 379     /// - `expected_sig`: the expected signature (if any). Note that
 380     ///   this is missing a binder: that is, there may be late-bound
 381     ///   regions with depth 1, which are bound then by the closure.
 382     fn sig_of_closure_with_expectation(
 383         &self,
 384         expr_def_id: DefId,
 385         decl: &hir::FnDecl,
 386         body: &hir::Body,
 387         expected_sig: ExpectedSig<'tcx>,
 388     ) -> ClosureSignatures<'tcx> {
 389         debug!(
 390             "sig_of_closure_with_expectation(expected_sig={:?})",
 391             expected_sig
 392         );
 393
 394         // Watch out for some surprises and just ignore the
 395         // expectation if things don't see to match up with what we
 396         // expect.
 397         if expected_sig.sig.variadic != decl.variadic {
 398             return self.sig_of_closure_no_expectation(expr_def_id, decl, body);
 399         } else if expected_sig.sig.inputs_and_output.len() != decl.inputs.len() + 1 {
 400             return self.sig_of_closure_with_mismatched_number_of_arguments(
 401                 expr_def_id,
 402                 decl,
 403                 body,
 404                 expected_sig,
 405             );
 406         }
 407
 408         // Create a `PolyFnSig`. Note the oddity that late bound
 409         // regions appearing free in `expected_sig` are now bound up
 410         // in this binder we are creating.
 411         assert!(!expected_sig.sig.has_vars_bound_above(ty::INNERMOST));
 412         let bound_sig = ty::Binder::bind(self.tcx.mk_fn_sig(
 413             expected_sig.sig.inputs().iter().cloned(),
 414             expected_sig.sig.output(),
 415             decl.variadic,
 416             hir::Unsafety::Normal,
 417             Abi::RustCall,
 418         ));
 419
 420         // `deduce_expectations_from_expected_type` introduces
 421         // late-bound lifetimes defined elsewhere, which we now
 422         // anonymize away, so as not to confuse the user.
 423         let bound_sig = self.tcx.anonymize_late_bound_regions(&bound_sig);
 424
 425         let closure_sigs = self.closure_sigs(expr_def_id, body, bound_sig);
 426
 427         // Up till this point, we have ignored the annotations that the user
 428         // gave. This function will check that they unify successfully.
 429         // Along the way, it also writes out entries for types that the user
 430         // wrote into our tables, which are then later used by the privacy
 431         // check.
 432         match self.check_supplied_sig_against_expectation(expr_def_id, decl, body, &closure_sigs) {
 433             Ok(infer_ok) => self.register_infer_ok_obligations(infer_ok),
 434             Err(_) => return self.sig_of_closure_no_expectation(expr_def_id, decl, body),
 435         }
 436
 437         closure_sigs
 438     }
 439
 440     fn sig_of_closure_with_mismatched_number_of_arguments(
 441         &self,
 442         expr_def_id: DefId,
 443         decl: &hir::FnDecl,
 444         body: &hir::Body,
 445         expected_sig: ExpectedSig<'tcx>,
 446     ) -> ClosureSignatures<'tcx> {
 447         let expr_map_node = self.tcx.hir().get_if_local(expr_def_id).unwrap();
 448         let expected_args: Vec<_> = expected_sig
 449             .sig
 450             .inputs()
 451             .iter()
 452             .map(|ty| ArgKind::from_expected_ty(ty, None))
 453             .collect();
 454         let (closure_span, found_args) = self.get_fn_like_arguments(expr_map_node);
 455         let expected_span = expected_sig.cause_span.unwrap_or(closure_span);
 456         self.report_arg_count_mismatch(
 457             expected_span,
 458             Some(closure_span),
 459             expected_args,
 460             found_args,
 461             true,
 462         ).emit();
 463
 464         let error_sig = self.error_sig_of_closure(decl);
 465
 466         self.closure_sigs(expr_def_id, body, error_sig)
 467     }
 468
 469     /// Enforce the user's types against the expectation.  See
 470     /// `sig_of_closure_with_expectation` for details on the overall
 471     /// strategy.
 472     fn check_supplied_sig_against_expectation(
 473         &self,
 474         expr_def_id: DefId,
 475         decl: &hir::FnDecl,
 476         body: &hir::Body,
 477         expected_sigs: &ClosureSignatures<'tcx>,
 478     ) -> InferResult<'tcx, ()> {
 479         // Get the signature S that the user gave.
 480         //
 481         // (See comment on `sig_of_closure_with_expectation` for the
 482         // meaning of these letters.)
 483         let supplied_sig = self.supplied_sig_of_closure(expr_def_id, decl);
 484
 485         debug!(
 486             "check_supplied_sig_against_expectation: supplied_sig={:?}",
 487             supplied_sig
 488         );
 489
 490         // FIXME(#45727): As discussed in [this comment][c1], naively
 491         // forcing equality here actually results in suboptimal error
 492         // messages in some cases.  For now, if there would have been
 493         // an obvious error, we fallback to declaring the type of the
 494         // closure to be the one the user gave, which allows other
 495         // error message code to trigger.
 496         //
 497         // However, I think [there is potential to do even better
 498         // here][c2], since in *this* code we have the precise span of
 499         // the type parameter in question in hand when we report the
 500         // error.
 501         //
 502         // [c1]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341089706
 503         // [c2]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341096796
 504         self.infcx.commit_if_ok(|_| {
 505             let mut all_obligations = vec![];
 506
 507             // The liberated version of this signature should be be a subtype
 508             // of the liberated form of the expectation.
 509             for ((hir_ty, &supplied_ty), expected_ty) in decl.inputs.iter()
 510                .zip(*supplied_sig.inputs().skip_binder()) // binder moved to (*) below
 511                .zip(expected_sigs.liberated_sig.inputs())
 512             // `liberated_sig` is E'.
 513             {
 514                 // Instantiate (this part of..) S to S', i.e., with fresh variables.
 515                 let (supplied_ty, _) = self.infcx.replace_bound_vars_with_fresh_vars(
 516                     hir_ty.span,
 517                     LateBoundRegionConversionTime::FnCall,
 518                     &ty::Binder::bind(supplied_ty),
 519                 ); // recreated from (*) above
 520
 521                 // Check that E' = S'.
 522                 let cause = &self.misc(hir_ty.span);
 523                 let InferOk {
 524                     value: (),
 525                     obligations,
 526                 } = self.at(cause, self.param_env)
 527                     .eq(*expected_ty, supplied_ty)?;
 528                 all_obligations.extend(obligations);
 529
 530                 // Also, require that the supplied type must outlive
 531                 // the closure body.
 532                 let closure_body_region = self.tcx.mk_region(
 533                     ty::ReScope(
 534                         region::Scope {
 535                             id: body.value.hir_id.local_id,
 536                             data: region::ScopeData::Node,
 537                         },
 538                     ),
 539                 );
 540                 all_obligations.push(
 541                     Obligation::new(
 542                         cause.clone(),
 543                         self.param_env,
 544                         ty::Predicate::TypeOutlives(
 545                             ty::Binder::dummy(
 546                                 ty::OutlivesPredicate(
 547                                     supplied_ty,
 548                                     closure_body_region,
 549                                 ),
 550                             ),
 551                         ),
 552                     ),
 553                 );
 554             }
 555
 556             let (supplied_output_ty, _) = self.infcx.replace_bound_vars_with_fresh_vars(
 557                 decl.output.span(),
 558                 LateBoundRegionConversionTime::FnCall,
 559                 &supplied_sig.output(),
 560             );
 561             let cause = &self.misc(decl.output.span());
 562             let InferOk {
 563                 value: (),
 564                 obligations,
 565             } = self.at(cause, self.param_env)
 566                 .eq(expected_sigs.liberated_sig.output(), supplied_output_ty)?;
 567             all_obligations.extend(obligations);
 568
 569             Ok(InferOk {
 570                 value: (),
 571                 obligations: all_obligations,
 572             })
 573         })
 574     }
 575
 576     /// If there is no expected signature, then we will convert the
 577     /// types that the user gave into a signature.
 578     ///
 579     /// Also, record this closure signature for later.
 580     fn supplied_sig_of_closure(
 581         &self,
 582         expr_def_id: DefId,
 583         decl: &hir::FnDecl,
 584     ) -> ty::PolyFnSig<'tcx> {
 585         let astconv: &dyn AstConv = self;
 586
 587         // First, convert the types that the user supplied (if any).
 588         let supplied_arguments = decl.inputs.iter().map(|a| astconv.ast_ty_to_ty(a));
 589         let supplied_return = match decl.output {
 590             hir::Return(ref output) => astconv.ast_ty_to_ty(&output),
 591             hir::DefaultReturn(_) => astconv.ty_infer(decl.output.span()),
 592         };
 593
 594         let result = ty::Binder::bind(self.tcx.mk_fn_sig(
 595             supplied_arguments,
 596             supplied_return,
 597             decl.variadic,
 598             hir::Unsafety::Normal,
 599             Abi::RustCall,
 600         ));
 601
 602         debug!("supplied_sig_of_closure: result={:?}", result);
 603
 604         let c_result = self.inh.infcx.canonicalize_response(&result);
 605         self.tables.borrow_mut().user_provided_sigs.insert(
 606             expr_def_id,
 607             c_result,
 608         );
 609
 610         result
 611     }
 612
 613     /// Converts the types that the user supplied, in case that doing
 614     /// so should yield an error, but returns back a signature where
 615     /// all parameters are of type `TyErr`.
 616     fn error_sig_of_closure(&self, decl: &hir::FnDecl) -> ty::PolyFnSig<'tcx> {
 617         let astconv: &dyn AstConv = self;
 618
 619         let supplied_arguments = decl.inputs.iter().map(|a| {
 620             // Convert the types that the user supplied (if any), but ignore them.
 621             astconv.ast_ty_to_ty(a);
 622             self.tcx.types.err
 623         });
 624
 625         if let hir::Return(ref output) = decl.output {
 626             astconv.ast_ty_to_ty(&output);
 627         }
 628
 629         let result = ty::Binder::bind(self.tcx.mk_fn_sig(
 630             supplied_arguments,
 631             self.tcx.types.err,
 632             decl.variadic,
 633             hir::Unsafety::Normal,
 634             Abi::RustCall,
 635         ));
 636
 637         debug!("supplied_sig_of_closure: result={:?}", result);
 638
 639         result
 640     }
 641
 642     fn closure_sigs(
 643         &self,
 644         expr_def_id: DefId,
 645         body: &hir::Body,
 646         bound_sig: ty::PolyFnSig<'tcx>,
 647     ) -> ClosureSignatures<'tcx> {
 648         let liberated_sig = self.tcx()
 649             .liberate_late_bound_regions(expr_def_id, &bound_sig);
 650         let liberated_sig = self.inh.normalize_associated_types_in(
 651             body.value.span,
 652             body.value.id,
 653             self.param_env,
 654             &liberated_sig,
 655         );
 656         ClosureSignatures {
 657             bound_sig,
 658             liberated_sig,
 659         }
 660     }
 661 }