src/librustc_typeck/check/closure.rs

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