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, TypeVariableOriginKind};
  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 lifetime param")
 103                 }
 104                 GenericParamDefKind::Type { .. } => {
 105                     self.infcx.next_ty_var(TypeVariableOrigin {
 106                         kind: TypeVariableOriginKind::ClosureSynthetic,
 107                         span: expr.span,
 108                     }).into()
 109                 }
 110                 GenericParamDefKind::Const => {
 111                     span_bug!(expr.span, "closure has const param")
 112                 }
 113             }
 114         });
 115         if let Some(GeneratorTypes { yield_ty, interior, movability }) = generator_types {
 116             let substs = ty::GeneratorSubsts { substs };
 117             self.demand_eqtype(
 118                 expr.span,
 119                 yield_ty,
 120                 substs.yield_ty(expr_def_id, self.tcx),
 121             );
 122             self.demand_eqtype(
 123                 expr.span,
 124                 liberated_sig.output(),
 125                 substs.return_ty(expr_def_id, self.tcx),
 126             );
 127             self.demand_eqtype(
 128                 expr.span,
 129                 interior,
 130                 substs.witness(expr_def_id, self.tcx),
 131             );
 132             return self.tcx.mk_generator(expr_def_id, substs, movability);
 133         }
 134
 135         let substs = ty::ClosureSubsts { substs };
 136         let closure_type = self.tcx.mk_closure(expr_def_id, substs);
 137
 138         debug!(
 139             "check_closure: expr.hir_id={:?} closure_type={:?}",
 140             expr.hir_id, closure_type
 141         );
 142
 143         // Tuple up the arguments and insert the resulting function type into
 144         // the `closures` table.
 145         let sig = bound_sig.map_bound(|sig| {
 146             self.tcx.mk_fn_sig(
 147                 iter::once(self.tcx.intern_tup(sig.inputs())),
 148                 sig.output(),
 149                 sig.c_variadic,
 150                 sig.unsafety,
 151                 sig.abi,
 152             )
 153         });
 154
 155         debug!(
 156             "check_closure: expr_def_id={:?}, sig={:?}, opt_kind={:?}",
 157             expr_def_id, sig, opt_kind
 158         );
 159
 160         let sig_fn_ptr_ty = self.tcx.mk_fn_ptr(sig);
 161         self.demand_eqtype(
 162             expr.span,
 163             sig_fn_ptr_ty,
 164             substs.closure_sig_ty(expr_def_id, self.tcx),
 165         );
 166
 167         if let Some(kind) = opt_kind {
 168             self.demand_eqtype(
 169                 expr.span,
 170                 kind.to_ty(self.tcx),
 171                 substs.closure_kind_ty(expr_def_id, self.tcx),
 172             );
 173         }
 174
 175         closure_type
 176     }
 177
 178     /// Given the expected type, figures out what it can about this closure we
 179     /// are about to type check:
 180     fn deduce_expectations_from_expected_type(
 181         &self,
 182         expected_ty: Ty<'tcx>,
 183     ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
 184         debug!(
 185             "deduce_expectations_from_expected_type(expected_ty={:?})",
 186             expected_ty
 187         );
 188
 189         match expected_ty.sty {
 190             ty::Dynamic(ref object_type, ..) => {
 191                 let sig = object_type
 192                     .projection_bounds()
 193                     .filter_map(|pb| {
 194                         let pb = pb.with_self_ty(self.tcx, self.tcx.types.err);
 195                         self.deduce_sig_from_projection(None, &pb)
 196                     })
 197                     .next();
 198                 let kind = object_type.principal_def_id().and_then(|did| {
 199                     self.tcx.lang_items().fn_trait_kind(did)
 200                 });
 201                 (sig, kind)
 202             }
 203             ty::Infer(ty::TyVar(vid)) => self.deduce_expectations_from_obligations(vid),
 204             ty::FnPtr(sig) => {
 205                 let expected_sig = ExpectedSig {
 206                     cause_span: None,
 207                     sig: sig.skip_binder().clone(),
 208                 };
 209                 (Some(expected_sig), Some(ty::ClosureKind::Fn))
 210             }
 211             _ => (None, None),
 212         }
 213     }
 214
 215     fn deduce_expectations_from_obligations(
 216         &self,
 217         expected_vid: ty::TyVid,
 218     ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
 219         let expected_sig = self.obligations_for_self_ty(expected_vid)
 220             .find_map(|(_, obligation)| {
 221                 debug!(
 222                     "deduce_expectations_from_obligations: obligation.predicate={:?}",
 223                     obligation.predicate
 224                 );
 225
 226                 if let ty::Predicate::Projection(ref proj_predicate) = obligation.predicate {
 227                     // Given a Projection predicate, we can potentially infer
 228                     // the complete signature.
 229                     self.deduce_sig_from_projection(
 230                         Some(obligation.cause.span),
 231                         proj_predicate
 232                     )
 233                 } else {
 234                     None
 235                 }
 236             });
 237
 238         // Even if we can't infer the full signature, we may be able to
 239         // infer the kind. This can occur if there is a trait-reference
 240         // like `F : Fn<A>`. Note that due to subtyping we could encounter
 241         // many viable options, so pick the most restrictive.
 242         let expected_kind = self.obligations_for_self_ty(expected_vid)
 243             .filter_map(|(tr, _)| self.tcx.lang_items().fn_trait_kind(tr.def_id()))
 244             .fold(None, |best, cur| {
 245                 Some(best.map_or(cur, |best| cmp::min(best, cur)))
 246             });
 247
 248         (expected_sig, expected_kind)
 249     }
 250
 251     /// Given a projection like "<F as Fn(X)>::Result == Y", we can deduce
 252     /// everything we need to know about a closure or generator.
 253     ///
 254     /// The `cause_span` should be the span that caused us to
 255     /// have this expected signature, or `None` if we can't readily
 256     /// know that.
 257     fn deduce_sig_from_projection(
 258         &self,
 259         cause_span: Option<Span>,
 260         projection: &ty::PolyProjectionPredicate<'tcx>,
 261     ) -> Option<ExpectedSig<'tcx>> {
 262         let tcx = self.tcx;
 263
 264         debug!("deduce_sig_from_projection({:?})", projection);
 265
 266         let trait_ref = projection.to_poly_trait_ref(tcx);
 267
 268         let is_fn = tcx.lang_items().fn_trait_kind(trait_ref.def_id()).is_some();
 269         let gen_trait = tcx.lang_items().gen_trait().unwrap();
 270         let is_gen = gen_trait == trait_ref.def_id();
 271         if !is_fn && !is_gen {
 272             debug!("deduce_sig_from_projection: not fn or generator");
 273             return None;
 274         }
 275
 276         if is_gen {
 277             // Check that we deduce the signature from the `<_ as std::ops::Generator>::Return`
 278             // associated item and not yield.
 279             let return_assoc_item = self.tcx.associated_items(gen_trait).nth(1).unwrap().def_id;
 280             if return_assoc_item != projection.projection_def_id() {
 281                 debug!("deduce_sig_from_projection: not return assoc item of generator");
 282                 return None;
 283             }
 284         }
 285
 286         let input_tys = if is_fn {
 287             let arg_param_ty = trait_ref.skip_binder().substs.type_at(1);
 288             let arg_param_ty = self.resolve_vars_if_possible(&arg_param_ty);
 289             debug!("deduce_sig_from_projection: arg_param_ty={:?}", arg_param_ty);
 290
 291             match arg_param_ty.sty {
 292                 ty::Tuple(tys) => tys.into_iter().map(|k| k.expect_ty()).collect::<Vec<_>>(),
 293                 _ => return None,
 294             }
 295         } else {
 296             // Generators cannot have explicit arguments.
 297             vec![]
 298         };
 299
 300         let ret_param_ty = projection.skip_binder().ty;
 301         let ret_param_ty = self.resolve_vars_if_possible(&ret_param_ty);
 302         debug!("deduce_sig_from_projection: ret_param_ty={:?}", ret_param_ty);
 303
 304         let sig = self.tcx.mk_fn_sig(
 305             input_tys.iter(),
 306             &ret_param_ty,
 307             false,
 308             hir::Unsafety::Normal,
 309             Abi::Rust,
 310         );
 311         debug!("deduce_sig_from_projection: sig={:?}", sig);
 312
 313         Some(ExpectedSig { cause_span, sig })
 314     }
 315
 316     fn sig_of_closure(
 317         &self,
 318         expr_def_id: DefId,
 319         decl: &hir::FnDecl,
 320         body: &hir::Body,
 321         expected_sig: Option<ExpectedSig<'tcx>>,
 322     ) -> ClosureSignatures<'tcx> {
 323         if let Some(e) = expected_sig {
 324             self.sig_of_closure_with_expectation(expr_def_id, decl, body, e)
 325         } else {
 326             self.sig_of_closure_no_expectation(expr_def_id, decl, body)
 327         }
 328     }
 329
 330     /// If there is no expected signature, then we will convert the
 331     /// types that the user gave into a signature.
 332     fn sig_of_closure_no_expectation(
 333         &self,
 334         expr_def_id: DefId,
 335         decl: &hir::FnDecl,
 336         body: &hir::Body,
 337     ) -> ClosureSignatures<'tcx> {
 338         debug!("sig_of_closure_no_expectation()");
 339
 340         let bound_sig = self.supplied_sig_of_closure(expr_def_id, decl);
 341
 342         self.closure_sigs(expr_def_id, body, bound_sig)
 343     }
 344
 345     /// Invoked to compute the signature of a closure expression. This
 346     /// combines any user-provided type annotations (e.g., `|x: u32|
 347     /// -> u32 { .. }`) with the expected signature.
 348     ///
 349     /// The approach is as follows:
 350     ///
 351     /// - Let `S` be the (higher-ranked) signature that we derive from the user's annotations.
 352     /// - Let `E` be the (higher-ranked) signature that we derive from the expectations, if any.
 353     ///   - If we have no expectation `E`, then the signature of the closure is `S`.
 354     ///   - Otherwise, the signature of the closure is E. Moreover:
 355     ///     - Skolemize the late-bound regions in `E`, yielding `E'`.
 356     ///     - Instantiate all the late-bound regions bound in the closure within `S`
 357     ///       with fresh (existential) variables, yielding `S'`
 358     ///     - Require that `E' = S'`
 359     ///       - We could use some kind of subtyping relationship here,
 360     ///         I imagine, but equality is easier and works fine for
 361     ///         our purposes.
 362     ///
 363     /// The key intuition here is that the user's types must be valid
 364     /// from "the inside" of the closure, but the expectation
 365     /// ultimately drives the overall signature.
 366     ///
 367     /// # Examples
 368     ///
 369     /// ```
 370     /// fn with_closure<F>(_: F)
 371     ///   where F: Fn(&u32) -> &u32 { .. }
 372     ///
 373     /// with_closure(|x: &u32| { ... })
 374     /// ```
 375     ///
 376     /// Here:
 377     /// - E would be `fn(&u32) -> &u32`.
 378     /// - S would be `fn(&u32) ->
 379     /// - E' is `&'!0 u32 -> &'!0 u32`
 380     /// - S' is `&'?0 u32 -> ?T`
 381     ///
 382     /// S' can be unified with E' with `['?0 = '!0, ?T = &'!10 u32]`.
 383     ///
 384     /// # Arguments
 385     ///
 386     /// - `expr_def_id`: the `DefId` of the closure expression
 387     /// - `decl`: the HIR declaration of the closure
 388     /// - `body`: the body of the closure
 389     /// - `expected_sig`: the expected signature (if any). Note that
 390     ///   this is missing a binder: that is, there may be late-bound
 391     ///   regions with depth 1, which are bound then by the closure.
 392     fn sig_of_closure_with_expectation(
 393         &self,
 394         expr_def_id: DefId,
 395         decl: &hir::FnDecl,
 396         body: &hir::Body,
 397         expected_sig: ExpectedSig<'tcx>,
 398     ) -> ClosureSignatures<'tcx> {
 399         debug!(
 400             "sig_of_closure_with_expectation(expected_sig={:?})",
 401             expected_sig
 402         );
 403
 404         // Watch out for some surprises and just ignore the
 405         // expectation if things don't see to match up with what we
 406         // expect.
 407         if expected_sig.sig.c_variadic != decl.c_variadic {
 408             return self.sig_of_closure_no_expectation(expr_def_id, decl, body);
 409         } else if expected_sig.sig.inputs_and_output.len() != decl.inputs.len() + 1 {
 410             return self.sig_of_closure_with_mismatched_number_of_arguments(
 411                 expr_def_id,
 412                 decl,
 413                 body,
 414                 expected_sig,
 415             );
 416         }
 417
 418         // Create a `PolyFnSig`. Note the oddity that late bound
 419         // regions appearing free in `expected_sig` are now bound up
 420         // in this binder we are creating.
 421         assert!(!expected_sig.sig.has_vars_bound_above(ty::INNERMOST));
 422         let bound_sig = ty::Binder::bind(self.tcx.mk_fn_sig(
 423             expected_sig.sig.inputs().iter().cloned(),
 424             expected_sig.sig.output(),
 425             decl.c_variadic,
 426             hir::Unsafety::Normal,
 427             Abi::RustCall,
 428         ));
 429
 430         // `deduce_expectations_from_expected_type` introduces
 431         // late-bound lifetimes defined elsewhere, which we now
 432         // anonymize away, so as not to confuse the user.
 433         let bound_sig = self.tcx.anonymize_late_bound_regions(&bound_sig);
 434
 435         let closure_sigs = self.closure_sigs(expr_def_id, body, bound_sig);
 436
 437         // Up till this point, we have ignored the annotations that the user
 438         // gave. This function will check that they unify successfully.
 439         // Along the way, it also writes out entries for types that the user
 440         // wrote into our tables, which are then later used by the privacy
 441         // check.
 442         match self.check_supplied_sig_against_expectation(expr_def_id, decl, body, &closure_sigs) {
 443             Ok(infer_ok) => self.register_infer_ok_obligations(infer_ok),
 444             Err(_) => return self.sig_of_closure_no_expectation(expr_def_id, decl, body),
 445         }
 446
 447         closure_sigs
 448     }
 449
 450     fn sig_of_closure_with_mismatched_number_of_arguments(
 451         &self,
 452         expr_def_id: DefId,
 453         decl: &hir::FnDecl,
 454         body: &hir::Body,
 455         expected_sig: ExpectedSig<'tcx>,
 456     ) -> ClosureSignatures<'tcx> {
 457         let expr_map_node = self.tcx.hir().get_if_local(expr_def_id).unwrap();
 458         let expected_args: Vec<_> = expected_sig
 459             .sig
 460             .inputs()
 461             .iter()
 462             .map(|ty| ArgKind::from_expected_ty(ty, None))
 463             .collect();
 464         let (closure_span, found_args) = self.get_fn_like_arguments(expr_map_node);
 465         let expected_span = expected_sig.cause_span.unwrap_or(closure_span);
 466         self.report_arg_count_mismatch(
 467             expected_span,
 468             Some(closure_span),
 469             expected_args,
 470             found_args,
 471             true,
 472         ).emit();
 473
 474         let error_sig = self.error_sig_of_closure(decl);
 475
 476         self.closure_sigs(expr_def_id, body, error_sig)
 477     }
 478
 479     /// Enforce the user's types against the expectation. See
 480     /// `sig_of_closure_with_expectation` for details on the overall
 481     /// strategy.
 482     fn check_supplied_sig_against_expectation(
 483         &self,
 484         expr_def_id: DefId,
 485         decl: &hir::FnDecl,
 486         body: &hir::Body,
 487         expected_sigs: &ClosureSignatures<'tcx>,
 488     ) -> InferResult<'tcx, ()> {
 489         // Get the signature S that the user gave.
 490         //
 491         // (See comment on `sig_of_closure_with_expectation` for the
 492         // meaning of these letters.)
 493         let supplied_sig = self.supplied_sig_of_closure(expr_def_id, decl);
 494
 495         debug!(
 496             "check_supplied_sig_against_expectation: supplied_sig={:?}",
 497             supplied_sig
 498         );
 499
 500         // FIXME(#45727): As discussed in [this comment][c1], naively
 501         // forcing equality here actually results in suboptimal error
 502         // messages in some cases.  For now, if there would have been
 503         // an obvious error, we fallback to declaring the type of the
 504         // closure to be the one the user gave, which allows other
 505         // error message code to trigger.
 506         //
 507         // However, I think [there is potential to do even better
 508         // here][c2], since in *this* code we have the precise span of
 509         // the type parameter in question in hand when we report the
 510         // error.
 511         //
 512         // [c1]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341089706
 513         // [c2]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341096796
 514         self.infcx.commit_if_ok(|_| {
 515             let mut all_obligations = vec![];
 516
 517             // The liberated version of this signature should be a subtype
 518             // of the liberated form of the expectation.
 519             for ((hir_ty, &supplied_ty), expected_ty) in decl.inputs.iter()
 520                .zip(*supplied_sig.inputs().skip_binder()) // binder moved to (*) below
 521                .zip(expected_sigs.liberated_sig.inputs())
 522             // `liberated_sig` is E'.
 523             {
 524                 // Instantiate (this part of..) S to S', i.e., with fresh variables.
 525                 let (supplied_ty, _) = self.infcx.replace_bound_vars_with_fresh_vars(
 526                     hir_ty.span,
 527                     LateBoundRegionConversionTime::FnCall,
 528                     &ty::Binder::bind(supplied_ty),
 529                 ); // recreated from (*) above
 530
 531                 // Check that E' = S'.
 532                 let cause = &self.misc(hir_ty.span);
 533                 let InferOk {
 534                     value: (),
 535                     obligations,
 536                 } = self.at(cause, self.param_env)
 537                     .eq(*expected_ty, supplied_ty)?;
 538                 all_obligations.extend(obligations);
 539
 540                 // Also, require that the supplied type must outlive
 541                 // the closure body.
 542                 let closure_body_region = self.tcx.mk_region(
 543                     ty::ReScope(
 544                         region::Scope {
 545                             id: body.value.hir_id.local_id,
 546                             data: region::ScopeData::Node,
 547                         },
 548                     ),
 549                 );
 550                 all_obligations.push(
 551                     Obligation::new(
 552                         cause.clone(),
 553                         self.param_env,
 554                         ty::Predicate::TypeOutlives(
 555                             ty::Binder::dummy(
 556                                 ty::OutlivesPredicate(
 557                                     supplied_ty,
 558                                     closure_body_region,
 559                                 ),
 560                             ),
 561                         ),
 562                     ),
 563                 );
 564             }
 565
 566             let (supplied_output_ty, _) = self.infcx.replace_bound_vars_with_fresh_vars(
 567                 decl.output.span(),
 568                 LateBoundRegionConversionTime::FnCall,
 569                 &supplied_sig.output(),
 570             );
 571             let cause = &self.misc(decl.output.span());
 572             let InferOk {
 573                 value: (),
 574                 obligations,
 575             } = self.at(cause, self.param_env)
 576                 .eq(expected_sigs.liberated_sig.output(), supplied_output_ty)?;
 577             all_obligations.extend(obligations);
 578
 579             Ok(InferOk {
 580                 value: (),
 581                 obligations: all_obligations,
 582             })
 583         })
 584     }
 585
 586     /// If there is no expected signature, then we will convert the
 587     /// types that the user gave into a signature.
 588     ///
 589     /// Also, record this closure signature for later.
 590     fn supplied_sig_of_closure(
 591         &self,
 592         expr_def_id: DefId,
 593         decl: &hir::FnDecl,
 594     ) -> ty::PolyFnSig<'tcx> {
 595         let astconv: &dyn AstConv<'_, '_> = self;
 596
 597         // First, convert the types that the user supplied (if any).
 598         let supplied_arguments = decl.inputs.iter().map(|a| astconv.ast_ty_to_ty(a));
 599         let supplied_return = match decl.output {
 600             hir::Return(ref output) => astconv.ast_ty_to_ty(&output),
 601             hir::DefaultReturn(_) => astconv.ty_infer(None, decl.output.span()),
 602         };
 603
 604         let result = ty::Binder::bind(self.tcx.mk_fn_sig(
 605             supplied_arguments,
 606             supplied_return,
 607             decl.c_variadic,
 608             hir::Unsafety::Normal,
 609             Abi::RustCall,
 610         ));
 611
 612         debug!("supplied_sig_of_closure: result={:?}", result);
 613
 614         let c_result = self.inh.infcx.canonicalize_response(&result);
 615         self.tables.borrow_mut().user_provided_sigs.insert(
 616             expr_def_id,
 617             c_result,
 618         );
 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: &dyn 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         if let hir::Return(ref output) = decl.output {
 636             astconv.ast_ty_to_ty(&output);
 637         }
 638
 639         let result = ty::Binder::bind(self.tcx.mk_fn_sig(
 640             supplied_arguments,
 641             self.tcx.types.err,
 642             decl.c_variadic,
 643             hir::Unsafety::Normal,
 644             Abi::RustCall,
 645         ));
 646
 647         debug!("supplied_sig_of_closure: result={:?}", result);
 648
 649         result
 650     }
 651
 652     fn closure_sigs(
 653         &self,
 654         expr_def_id: DefId,
 655         body: &hir::Body,
 656         bound_sig: ty::PolyFnSig<'tcx>,
 657     ) -> ClosureSignatures<'tcx> {
 658         let liberated_sig = self.tcx()
 659             .liberate_late_bound_regions(expr_def_id, &bound_sig);
 660         let liberated_sig = self.inh.normalize_associated_types_in(
 661             body.value.span,
 662             body.value.hir_id,
 663             self.param_env,
 664             &liberated_sig,
 665         );
 666         ClosureSignatures {
 667             bound_sig,
 668             liberated_sig,
 669         }
 670     }
 671 }