src/librustc_typeck/check/compare_method.rs

   1 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId, ErrorReported};
   2 use rustc_hir as hir;
   3 use rustc_hir::def::{DefKind, Res};
   4 use rustc_hir::intravisit;
   5 use rustc_hir::{GenericParamKind, ImplItemKind, TraitItemKind};
   6 use rustc_infer::infer::{self, InferOk, TyCtxtInferExt};
   7 use rustc_middle::ty::error::{ExpectedFound, TypeError};
   8 use rustc_middle::ty::subst::{InternalSubsts, Subst};
   9 use rustc_middle::ty::util::ExplicitSelf;
  10 use rustc_middle::ty::{self, GenericParamDefKind, TyCtxt};
  11 use rustc_span::Span;
  12 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
  13 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode, Reveal};
  14
  15 use super::{potentially_plural_count, FnCtxt, Inherited};
  16
  17 /// Checks that a method from an impl conforms to the signature of
  18 /// the same method as declared in the trait.
  19 ///
  20 /// # Parameters
  21 ///
  22 /// - `impl_m`: type of the method we are checking
  23 /// - `impl_m_span`: span to use for reporting errors
  24 /// - `trait_m`: the method in the trait
  25 /// - `impl_trait_ref`: the TraitRef corresponding to the trait implementation
  26
  27 crate fn compare_impl_method<'tcx>(
  28     tcx: TyCtxt<'tcx>,
  29     impl_m: &ty::AssocItem,
  30     impl_m_span: Span,
  31     trait_m: &ty::AssocItem,
  32     impl_trait_ref: ty::TraitRef<'tcx>,
  33     trait_item_span: Option<Span>,
  34 ) {
  35     debug!("compare_impl_method(impl_trait_ref={:?})", impl_trait_ref);
  36
  37     let impl_m_span = tcx.sess.source_map().guess_head_span(impl_m_span);
  38
  39     if let Err(ErrorReported) = compare_self_type(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref)
  40     {
  41         return;
  42     }
  43
  44     if let Err(ErrorReported) =
  45         compare_number_of_generics(tcx, impl_m, impl_m_span, trait_m, trait_item_span)
  46     {
  47         return;
  48     }
  49
  50     if let Err(ErrorReported) =
  51         compare_number_of_method_arguments(tcx, impl_m, impl_m_span, trait_m, trait_item_span)
  52     {
  53         return;
  54     }
  55
  56     if let Err(ErrorReported) = compare_synthetic_generics(tcx, impl_m, trait_m) {
  57         return;
  58     }
  59
  60     if let Err(ErrorReported) =
  61         compare_predicate_entailment(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref)
  62     {
  63         return;
  64     }
  65 }
  66
  67 fn compare_predicate_entailment<'tcx>(
  68     tcx: TyCtxt<'tcx>,
  69     impl_m: &ty::AssocItem,
  70     impl_m_span: Span,
  71     trait_m: &ty::AssocItem,
  72     impl_trait_ref: ty::TraitRef<'tcx>,
  73 ) -> Result<(), ErrorReported> {
  74     let trait_to_impl_substs = impl_trait_ref.substs;
  75
  76     // This node-id should be used for the `body_id` field on each
  77     // `ObligationCause` (and the `FnCtxt`). This is what
  78     // `regionck_item` expects.
  79     let impl_m_hir_id = tcx.hir().as_local_hir_id(impl_m.def_id.expect_local());
  80
  81     let cause = ObligationCause {
  82         span: impl_m_span,
  83         body_id: impl_m_hir_id,
  84         code: ObligationCauseCode::CompareImplMethodObligation {
  85             item_name: impl_m.ident.name,
  86             impl_item_def_id: impl_m.def_id,
  87             trait_item_def_id: trait_m.def_id,
  88         },
  89     };
  90
  91     // This code is best explained by example. Consider a trait:
  92     //
  93     //     trait Trait<'t,T> {
  94     //          fn method<'a,M>(t: &'t T, m: &'a M) -> Self;
  95     //     }
  96     //
  97     // And an impl:
  98     //
  99     //     impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
 100     //          fn method<'b,N>(t: &'j &'i U, m: &'b N) -> Foo;
 101     //     }
 102     //
 103     // We wish to decide if those two method types are compatible.
 104     //
 105     // We start out with trait_to_impl_substs, that maps the trait
 106     // type parameters to impl type parameters. This is taken from the
 107     // impl trait reference:
 108     //
 109     //     trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
 110     //
 111     // We create a mapping `dummy_substs` that maps from the impl type
 112     // parameters to fresh types and regions. For type parameters,
 113     // this is the identity transform, but we could as well use any
 114     // placeholder types. For regions, we convert from bound to free
 115     // regions (Note: but only early-bound regions, i.e., those
 116     // declared on the impl or used in type parameter bounds).
 117     //
 118     //     impl_to_skol_substs = {'i => 'i0, U => U0, N => N0 }
 119     //
 120     // Now we can apply skol_substs to the type of the impl method
 121     // to yield a new function type in terms of our fresh, placeholder
 122     // types:
 123     //
 124     //     <'b> fn(t: &'i0 U0, m: &'b) -> Foo
 125     //
 126     // We now want to extract and substitute the type of the *trait*
 127     // method and compare it. To do so, we must create a compound
 128     // substitution by combining trait_to_impl_substs and
 129     // impl_to_skol_substs, and also adding a mapping for the method
 130     // type parameters. We extend the mapping to also include
 131     // the method parameters.
 132     //
 133     //     trait_to_skol_substs = { T => &'i0 U0, Self => Foo, M => N0 }
 134     //
 135     // Applying this to the trait method type yields:
 136     //
 137     //     <'a> fn(t: &'i0 U0, m: &'a) -> Foo
 138     //
 139     // This type is also the same but the name of the bound region ('a
 140     // vs 'b).  However, the normal subtyping rules on fn types handle
 141     // this kind of equivalency just fine.
 142     //
 143     // We now use these substitutions to ensure that all declared bounds are
 144     // satisfied by the implementation's method.
 145     //
 146     // We do this by creating a parameter environment which contains a
 147     // substitution corresponding to impl_to_skol_substs. We then build
 148     // trait_to_skol_substs and use it to convert the predicates contained
 149     // in the trait_m.generics to the placeholder form.
 150     //
 151     // Finally we register each of these predicates as an obligation in
 152     // a fresh FulfillmentCtxt, and invoke select_all_or_error.
 153
 154     // Create mapping from impl to placeholder.
 155     let impl_to_skol_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
 156
 157     // Create mapping from trait to placeholder.
 158     let trait_to_skol_substs =
 159         impl_to_skol_substs.rebase_onto(tcx, impl_m.container.id(), trait_to_impl_substs);
 160     debug!("compare_impl_method: trait_to_skol_substs={:?}", trait_to_skol_substs);
 161
 162     let impl_m_generics = tcx.generics_of(impl_m.def_id);
 163     let trait_m_generics = tcx.generics_of(trait_m.def_id);
 164     let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
 165     let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
 166
 167     // Check region bounds.
 168     check_region_bounds_on_impl_item(
 169         tcx,
 170         impl_m_span,
 171         impl_m,
 172         trait_m,
 173         &trait_m_generics,
 174         &impl_m_generics,
 175     )?;
 176
 177     // Create obligations for each predicate declared by the impl
 178     // definition in the context of the trait's parameter
 179     // environment. We can't just use `impl_env.caller_bounds`,
 180     // however, because we want to replace all late-bound regions with
 181     // region variables.
 182     let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap());
 183     let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
 184
 185     debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
 186
 187     // This is the only tricky bit of the new way we check implementation methods
 188     // We need to build a set of predicates where only the method-level bounds
 189     // are from the trait and we assume all other bounds from the implementation
 190     // to be previously satisfied.
 191     //
 192     // We then register the obligations from the impl_m and check to see
 193     // if all constraints hold.
 194     hybrid_preds
 195         .predicates
 196         .extend(trait_m_predicates.instantiate_own(tcx, trait_to_skol_substs).predicates);
 197
 198     // Construct trait parameter environment and then shift it into the placeholder viewpoint.
 199     // The key step here is to update the caller_bounds's predicates to be
 200     // the new hybrid bounds we computed.
 201     let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_hir_id);
 202     let param_env = ty::ParamEnv::new(
 203         tcx.intern_predicates(&hybrid_preds.predicates),
 204         Reveal::UserFacing,
 205         None,
 206     );
 207     let param_env = traits::normalize_param_env_or_error(
 208         tcx,
 209         impl_m.def_id,
 210         param_env,
 211         normalize_cause.clone(),
 212     );
 213
 214     tcx.infer_ctxt().enter(|infcx| {
 215         let inh = Inherited::new(infcx, impl_m.def_id.expect_local());
 216         let infcx = &inh.infcx;
 217
 218         debug!("compare_impl_method: caller_bounds={:?}", param_env.caller_bounds);
 219
 220         let mut selcx = traits::SelectionContext::new(&infcx);
 221
 222         let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_skol_substs);
 223         let (impl_m_own_bounds, _) = infcx.replace_bound_vars_with_fresh_vars(
 224             impl_m_span,
 225             infer::HigherRankedType,
 226             &ty::Binder::bind(impl_m_own_bounds.predicates),
 227         );
 228         for predicate in impl_m_own_bounds {
 229             let traits::Normalized { value: predicate, obligations } =
 230                 traits::normalize(&mut selcx, param_env, normalize_cause.clone(), &predicate);
 231
 232             inh.register_predicates(obligations);
 233             inh.register_predicate(traits::Obligation::new(cause.clone(), param_env, predicate));
 234         }
 235
 236         // We now need to check that the signature of the impl method is
 237         // compatible with that of the trait method. We do this by
 238         // checking that `impl_fty <: trait_fty`.
 239         //
 240         // FIXME. Unfortunately, this doesn't quite work right now because
 241         // associated type normalization is not integrated into subtype
 242         // checks. For the comparison to be valid, we need to
 243         // normalize the associated types in the impl/trait methods
 244         // first. However, because function types bind regions, just
 245         // calling `normalize_associated_types_in` would have no effect on
 246         // any associated types appearing in the fn arguments or return
 247         // type.
 248
 249         // Compute placeholder form of impl and trait method tys.
 250         let tcx = infcx.tcx;
 251
 252         let (impl_sig, _) = infcx.replace_bound_vars_with_fresh_vars(
 253             impl_m_span,
 254             infer::HigherRankedType,
 255             &tcx.fn_sig(impl_m.def_id),
 256         );
 257         let impl_sig =
 258             inh.normalize_associated_types_in(impl_m_span, impl_m_hir_id, param_env, &impl_sig);
 259         let impl_fty = tcx.mk_fn_ptr(ty::Binder::bind(impl_sig));
 260         debug!("compare_impl_method: impl_fty={:?}", impl_fty);
 261
 262         let trait_sig = tcx.liberate_late_bound_regions(impl_m.def_id, &tcx.fn_sig(trait_m.def_id));
 263         let trait_sig = trait_sig.subst(tcx, trait_to_skol_substs);
 264         let trait_sig =
 265             inh.normalize_associated_types_in(impl_m_span, impl_m_hir_id, param_env, &trait_sig);
 266         let trait_fty = tcx.mk_fn_ptr(ty::Binder::bind(trait_sig));
 267
 268         debug!("compare_impl_method: trait_fty={:?}", trait_fty);
 269
 270         let sub_result = infcx.at(&cause, param_env).sup(trait_fty, impl_fty).map(
 271             |InferOk { obligations, .. }| {
 272                 inh.register_predicates(obligations);
 273             },
 274         );
 275
 276         if let Err(terr) = sub_result {
 277             debug!("sub_types failed: impl ty {:?}, trait ty {:?}", impl_fty, trait_fty);
 278
 279             let (impl_err_span, trait_err_span) = extract_spans_for_error_reporting(
 280                 &infcx, param_env, &terr, &cause, impl_m, impl_sig, trait_m, trait_sig,
 281             );
 282
 283             let cause = ObligationCause { span: impl_err_span, ..cause };
 284
 285             let mut diag = struct_span_err!(
 286                 tcx.sess,
 287                 cause.span(tcx),
 288                 E0053,
 289                 "method `{}` has an incompatible type for trait",
 290                 trait_m.ident
 291             );
 292             if let TypeError::Mutability = terr {
 293                 if let Some(trait_err_span) = trait_err_span {
 294                     if let Ok(trait_err_str) = tcx.sess.source_map().span_to_snippet(trait_err_span)
 295                     {
 296                         diag.span_suggestion(
 297                             impl_err_span,
 298                             "consider change the type to match the mutability in trait",
 299                             trait_err_str,
 300                             Applicability::MachineApplicable,
 301                         );
 302                     }
 303                 }
 304             }
 305
 306             infcx.note_type_err(
 307                 &mut diag,
 308                 &cause,
 309                 trait_err_span.map(|sp| (sp, "type in trait".to_owned())),
 310                 Some(infer::ValuePairs::Types(ExpectedFound {
 311                     expected: trait_fty,
 312                     found: impl_fty,
 313                 })),
 314                 &terr,
 315             );
 316             diag.emit();
 317             return Err(ErrorReported);
 318         }
 319
 320         // Check that all obligations are satisfied by the implementation's
 321         // version.
 322         if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
 323             infcx.report_fulfillment_errors(errors, None, false);
 324             return Err(ErrorReported);
 325         }
 326
 327         // Finally, resolve all regions. This catches wily misuses of
 328         // lifetime parameters.
 329         let fcx = FnCtxt::new(&inh, param_env, impl_m_hir_id);
 330         fcx.regionck_item(impl_m_hir_id, impl_m_span, &[]);
 331
 332         Ok(())
 333     })
 334 }
 335
 336 fn check_region_bounds_on_impl_item<'tcx>(
 337     tcx: TyCtxt<'tcx>,
 338     span: Span,
 339     impl_m: &ty::AssocItem,
 340     trait_m: &ty::AssocItem,
 341     trait_generics: &ty::Generics,
 342     impl_generics: &ty::Generics,
 343 ) -> Result<(), ErrorReported> {
 344     let trait_params = trait_generics.own_counts().lifetimes;
 345     let impl_params = impl_generics.own_counts().lifetimes;
 346
 347     debug!(
 348         "check_region_bounds_on_impl_item: \
 349             trait_generics={:?} \
 350             impl_generics={:?}",
 351         trait_generics, impl_generics
 352     );
 353
 354     // Must have same number of early-bound lifetime parameters.
 355     // Unfortunately, if the user screws up the bounds, then this
 356     // will change classification between early and late.  E.g.,
 357     // if in trait we have `<'a,'b:'a>`, and in impl we just have
 358     // `<'a,'b>`, then we have 2 early-bound lifetime parameters
 359     // in trait but 0 in the impl. But if we report "expected 2
 360     // but found 0" it's confusing, because it looks like there
 361     // are zero. Since I don't quite know how to phrase things at
 362     // the moment, give a kind of vague error message.
 363     if trait_params != impl_params {
 364         let item_kind = assoc_item_kind_str(impl_m);
 365         let def_span = tcx.sess.source_map().guess_head_span(span);
 366         let span = tcx.hir().get_generics(impl_m.def_id).map(|g| g.span).unwrap_or(def_span);
 367         let mut err = struct_span_err!(
 368             tcx.sess,
 369             span,
 370             E0195,
 371             "lifetime parameters or bounds on {} `{}` do not match the trait declaration",
 372             item_kind,
 373             impl_m.ident,
 374         );
 375         err.span_label(span, &format!("lifetimes do not match {} in trait", item_kind));
 376         if let Some(sp) = tcx.hir().span_if_local(trait_m.def_id) {
 377             let def_sp = tcx.sess.source_map().guess_head_span(sp);
 378             let sp = tcx.hir().get_generics(trait_m.def_id).map(|g| g.span).unwrap_or(def_sp);
 379             err.span_label(
 380                 sp,
 381                 &format!("lifetimes in impl do not match this {} in trait", item_kind),
 382             );
 383         }
 384         err.emit();
 385         return Err(ErrorReported);
 386     }
 387
 388     Ok(())
 389 }
 390
 391 fn extract_spans_for_error_reporting<'a, 'tcx>(
 392     infcx: &infer::InferCtxt<'a, 'tcx>,
 393     param_env: ty::ParamEnv<'tcx>,
 394     terr: &TypeError<'_>,
 395     cause: &ObligationCause<'tcx>,
 396     impl_m: &ty::AssocItem,
 397     impl_sig: ty::FnSig<'tcx>,
 398     trait_m: &ty::AssocItem,
 399     trait_sig: ty::FnSig<'tcx>,
 400 ) -> (Span, Option<Span>) {
 401     let tcx = infcx.tcx;
 402     let impl_m_hir_id = tcx.hir().as_local_hir_id(impl_m.def_id.expect_local());
 403     let (impl_m_output, impl_m_iter) = match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
 404         ImplItemKind::Fn(ref impl_m_sig, _) => {
 405             (&impl_m_sig.decl.output, impl_m_sig.decl.inputs.iter())
 406         }
 407         _ => bug!("{:?} is not a method", impl_m),
 408     };
 409
 410     match *terr {
 411         TypeError::Mutability => {
 412             if let Some(def_id) = trait_m.def_id.as_local() {
 413                 let trait_m_hir_id = tcx.hir().as_local_hir_id(def_id);
 414                 let trait_m_iter = match tcx.hir().expect_trait_item(trait_m_hir_id).kind {
 415                     TraitItemKind::Fn(ref trait_m_sig, _) => trait_m_sig.decl.inputs.iter(),
 416                     _ => bug!("{:?} is not a TraitItemKind::Fn", trait_m),
 417                 };
 418
 419                 impl_m_iter
 420                     .zip(trait_m_iter)
 421                     .find(|&(ref impl_arg, ref trait_arg)| {
 422                         match (&impl_arg.kind, &trait_arg.kind) {
 423                             (
 424                                 &hir::TyKind::Rptr(_, ref impl_mt),
 425                                 &hir::TyKind::Rptr(_, ref trait_mt),
 426                             )
 427                             | (&hir::TyKind::Ptr(ref impl_mt), &hir::TyKind::Ptr(ref trait_mt)) => {
 428                                 impl_mt.mutbl != trait_mt.mutbl
 429                             }
 430                             _ => false,
 431                         }
 432                     })
 433                     .map(|(ref impl_arg, ref trait_arg)| (impl_arg.span, Some(trait_arg.span)))
 434                     .unwrap_or_else(|| (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id)))
 435             } else {
 436                 (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
 437             }
 438         }
 439         TypeError::Sorts(ExpectedFound { .. }) => {
 440             if let Some(def_id) = trait_m.def_id.as_local() {
 441                 let trait_m_hir_id = tcx.hir().as_local_hir_id(def_id);
 442                 let (trait_m_output, trait_m_iter) =
 443                     match tcx.hir().expect_trait_item(trait_m_hir_id).kind {
 444                         TraitItemKind::Fn(ref trait_m_sig, _) => {
 445                             (&trait_m_sig.decl.output, trait_m_sig.decl.inputs.iter())
 446                         }
 447                         _ => bug!("{:?} is not a TraitItemKind::Fn", trait_m),
 448                     };
 449
 450                 let impl_iter = impl_sig.inputs().iter();
 451                 let trait_iter = trait_sig.inputs().iter();
 452                 impl_iter
 453                     .zip(trait_iter)
 454                     .zip(impl_m_iter)
 455                     .zip(trait_m_iter)
 456                     .find_map(|(((&impl_arg_ty, &trait_arg_ty), impl_arg), trait_arg)| match infcx
 457                         .at(&cause, param_env)
 458                         .sub(trait_arg_ty, impl_arg_ty)
 459                     {
 460                         Ok(_) => None,
 461                         Err(_) => Some((impl_arg.span, Some(trait_arg.span))),
 462                     })
 463                     .unwrap_or_else(|| {
 464                         if infcx
 465                             .at(&cause, param_env)
 466                             .sup(trait_sig.output(), impl_sig.output())
 467                             .is_err()
 468                         {
 469                             (impl_m_output.span(), Some(trait_m_output.span()))
 470                         } else {
 471                             (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
 472                         }
 473                     })
 474             } else {
 475                 (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
 476             }
 477         }
 478         _ => (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id)),
 479     }
 480 }
 481
 482 fn compare_self_type<'tcx>(
 483     tcx: TyCtxt<'tcx>,
 484     impl_m: &ty::AssocItem,
 485     impl_m_span: Span,
 486     trait_m: &ty::AssocItem,
 487     impl_trait_ref: ty::TraitRef<'tcx>,
 488 ) -> Result<(), ErrorReported> {
 489     // Try to give more informative error messages about self typing
 490     // mismatches.  Note that any mismatch will also be detected
 491     // below, where we construct a canonical function type that
 492     // includes the self parameter as a normal parameter.  It's just
 493     // that the error messages you get out of this code are a bit more
 494     // inscrutable, particularly for cases where one method has no
 495     // self.
 496
 497     let self_string = |method: &ty::AssocItem| {
 498         let untransformed_self_ty = match method.container {
 499             ty::ImplContainer(_) => impl_trait_ref.self_ty(),
 500             ty::TraitContainer(_) => tcx.types.self_param,
 501         };
 502         let self_arg_ty = *tcx.fn_sig(method.def_id).input(0).skip_binder();
 503         let param_env = ty::ParamEnv::reveal_all();
 504
 505         tcx.infer_ctxt().enter(|infcx| {
 506             let self_arg_ty =
 507                 tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(self_arg_ty));
 508             let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty).is_ok();
 509             match ExplicitSelf::determine(self_arg_ty, can_eq_self) {
 510                 ExplicitSelf::ByValue => "self".to_owned(),
 511                 ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
 512                 ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(),
 513                 _ => format!("self: {}", self_arg_ty),
 514             }
 515         })
 516     };
 517
 518     match (trait_m.fn_has_self_parameter, impl_m.fn_has_self_parameter) {
 519         (false, false) | (true, true) => {}
 520
 521         (false, true) => {
 522             let self_descr = self_string(impl_m);
 523             let mut err = struct_span_err!(
 524                 tcx.sess,
 525                 impl_m_span,
 526                 E0185,
 527                 "method `{}` has a `{}` declaration in the impl, but \
 528                                             not in the trait",
 529                 trait_m.ident,
 530                 self_descr
 531             );
 532             err.span_label(impl_m_span, format!("`{}` used in impl", self_descr));
 533             if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
 534                 err.span_label(span, format!("trait method declared without `{}`", self_descr));
 535             } else {
 536                 err.note_trait_signature(trait_m.ident.to_string(), trait_m.signature(tcx));
 537             }
 538             err.emit();
 539             return Err(ErrorReported);
 540         }
 541
 542         (true, false) => {
 543             let self_descr = self_string(trait_m);
 544             let mut err = struct_span_err!(
 545                 tcx.sess,
 546                 impl_m_span,
 547                 E0186,
 548                 "method `{}` has a `{}` declaration in the trait, but \
 549                                             not in the impl",
 550                 trait_m.ident,
 551                 self_descr
 552             );
 553             err.span_label(impl_m_span, format!("expected `{}` in impl", self_descr));
 554             if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
 555                 err.span_label(span, format!("`{}` used in trait", self_descr));
 556             } else {
 557                 err.note_trait_signature(trait_m.ident.to_string(), trait_m.signature(tcx));
 558             }
 559             err.emit();
 560             return Err(ErrorReported);
 561         }
 562     }
 563
 564     Ok(())
 565 }
 566
 567 fn compare_number_of_generics<'tcx>(
 568     tcx: TyCtxt<'tcx>,
 569     impl_: &ty::AssocItem,
 570     _impl_span: Span,
 571     trait_: &ty::AssocItem,
 572     trait_span: Option<Span>,
 573 ) -> Result<(), ErrorReported> {
 574     let trait_own_counts = tcx.generics_of(trait_.def_id).own_counts();
 575     let impl_own_counts = tcx.generics_of(impl_.def_id).own_counts();
 576
 577     let matchings = [
 578         ("type", trait_own_counts.types, impl_own_counts.types),
 579         ("const", trait_own_counts.consts, impl_own_counts.consts),
 580     ];
 581
 582     let item_kind = assoc_item_kind_str(impl_);
 583
 584     let mut err_occurred = false;
 585     for &(kind, trait_count, impl_count) in &matchings {
 586         if impl_count != trait_count {
 587             err_occurred = true;
 588
 589             let (trait_spans, impl_trait_spans) = if let Some(def_id) = trait_.def_id.as_local() {
 590                 let trait_hir_id = tcx.hir().as_local_hir_id(def_id);
 591                 let trait_item = tcx.hir().expect_trait_item(trait_hir_id);
 592                 if trait_item.generics.params.is_empty() {
 593                     (Some(vec![trait_item.generics.span]), vec![])
 594                 } else {
 595                     let arg_spans: Vec<Span> =
 596                         trait_item.generics.params.iter().map(|p| p.span).collect();
 597                     let impl_trait_spans: Vec<Span> = trait_item
 598                         .generics
 599                         .params
 600                         .iter()
 601                         .filter_map(|p| match p.kind {
 602                             GenericParamKind::Type {
 603                                 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
 604                                 ..
 605                             } => Some(p.span),
 606                             _ => None,
 607                         })
 608                         .collect();
 609                     (Some(arg_spans), impl_trait_spans)
 610                 }
 611             } else {
 612                 (trait_span.map(|s| vec![s]), vec![])
 613             };
 614
 615             let impl_hir_id = tcx.hir().as_local_hir_id(impl_.def_id.expect_local());
 616             let impl_item = tcx.hir().expect_impl_item(impl_hir_id);
 617             let impl_item_impl_trait_spans: Vec<Span> = impl_item
 618                 .generics
 619                 .params
 620                 .iter()
 621                 .filter_map(|p| match p.kind {
 622                     GenericParamKind::Type {
 623                         synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
 624                         ..
 625                     } => Some(p.span),
 626                     _ => None,
 627                 })
 628                 .collect();
 629             let spans = impl_item.generics.spans();
 630             let span = spans.primary_span();
 631
 632             let mut err = tcx.sess.struct_span_err_with_code(
 633                 spans,
 634                 &format!(
 635                     "{} `{}` has {} {kind} parameter{} but its trait \
 636                      declaration has {} {kind} parameter{}",
 637                     item_kind,
 638                     trait_.ident,
 639                     impl_count,
 640                     pluralize!(impl_count),
 641                     trait_count,
 642                     pluralize!(trait_count),
 643                     kind = kind,
 644                 ),
 645                 DiagnosticId::Error("E0049".into()),
 646             );
 647
 648             let mut suffix = None;
 649
 650             if let Some(spans) = trait_spans {
 651                 let mut spans = spans.iter();
 652                 if let Some(span) = spans.next() {
 653                     err.span_label(
 654                         *span,
 655                         format!(
 656                             "expected {} {} parameter{}",
 657                             trait_count,
 658                             kind,
 659                             pluralize!(trait_count),
 660                         ),
 661                     );
 662                 }
 663                 for span in spans {
 664                     err.span_label(*span, "");
 665                 }
 666             } else {
 667                 suffix = Some(format!(", expected {}", trait_count));
 668             }
 669
 670             if let Some(span) = span {
 671                 err.span_label(
 672                     span,
 673                     format!(
 674                         "found {} {} parameter{}{}",
 675                         impl_count,
 676                         kind,
 677                         pluralize!(impl_count),
 678                         suffix.unwrap_or_else(String::new),
 679                     ),
 680                 );
 681             }
 682
 683             for span in impl_trait_spans.iter().chain(impl_item_impl_trait_spans.iter()) {
 684                 err.span_label(*span, "`impl Trait` introduces an implicit type parameter");
 685             }
 686
 687             err.emit();
 688         }
 689     }
 690
 691     if err_occurred { Err(ErrorReported) } else { Ok(()) }
 692 }
 693
 694 fn compare_number_of_method_arguments<'tcx>(
 695     tcx: TyCtxt<'tcx>,
 696     impl_m: &ty::AssocItem,
 697     impl_m_span: Span,
 698     trait_m: &ty::AssocItem,
 699     trait_item_span: Option<Span>,
 700 ) -> Result<(), ErrorReported> {
 701     let impl_m_fty = tcx.fn_sig(impl_m.def_id);
 702     let trait_m_fty = tcx.fn_sig(trait_m.def_id);
 703     let trait_number_args = trait_m_fty.inputs().skip_binder().len();
 704     let impl_number_args = impl_m_fty.inputs().skip_binder().len();
 705     if trait_number_args != impl_number_args {
 706         let trait_span = if let Some(def_id) = trait_m.def_id.as_local() {
 707             let trait_id = tcx.hir().as_local_hir_id(def_id);
 708             match tcx.hir().expect_trait_item(trait_id).kind {
 709                 TraitItemKind::Fn(ref trait_m_sig, _) => {
 710                     let pos = if trait_number_args > 0 { trait_number_args - 1 } else { 0 };
 711                     if let Some(arg) = trait_m_sig.decl.inputs.get(pos) {
 712                         Some(if pos == 0 {
 713                             arg.span
 714                         } else {
 715                             Span::new(
 716                                 trait_m_sig.decl.inputs[0].span.lo(),
 717                                 arg.span.hi(),
 718                                 arg.span.ctxt(),
 719                             )
 720                         })
 721                     } else {
 722                         trait_item_span
 723                     }
 724                 }
 725                 _ => bug!("{:?} is not a method", impl_m),
 726             }
 727         } else {
 728             trait_item_span
 729         };
 730         let impl_m_hir_id = tcx.hir().as_local_hir_id(impl_m.def_id.expect_local());
 731         let impl_span = match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
 732             ImplItemKind::Fn(ref impl_m_sig, _) => {
 733                 let pos = if impl_number_args > 0 { impl_number_args - 1 } else { 0 };
 734                 if let Some(arg) = impl_m_sig.decl.inputs.get(pos) {
 735                     if pos == 0 {
 736                         arg.span
 737                     } else {
 738                         Span::new(
 739                             impl_m_sig.decl.inputs[0].span.lo(),
 740                             arg.span.hi(),
 741                             arg.span.ctxt(),
 742                         )
 743                     }
 744                 } else {
 745                     impl_m_span
 746                 }
 747             }
 748             _ => bug!("{:?} is not a method", impl_m),
 749         };
 750         let mut err = struct_span_err!(
 751             tcx.sess,
 752             impl_span,
 753             E0050,
 754             "method `{}` has {} but the declaration in \
 755                                         trait `{}` has {}",
 756             trait_m.ident,
 757             potentially_plural_count(impl_number_args, "parameter"),
 758             tcx.def_path_str(trait_m.def_id),
 759             trait_number_args
 760         );
 761         if let Some(trait_span) = trait_span {
 762             err.span_label(
 763                 trait_span,
 764                 format!(
 765                     "trait requires {}",
 766                     potentially_plural_count(trait_number_args, "parameter")
 767                 ),
 768             );
 769         } else {
 770             err.note_trait_signature(trait_m.ident.to_string(), trait_m.signature(tcx));
 771         }
 772         err.span_label(
 773             impl_span,
 774             format!(
 775                 "expected {}, found {}",
 776                 potentially_plural_count(trait_number_args, "parameter"),
 777                 impl_number_args
 778             ),
 779         );
 780         err.emit();
 781         return Err(ErrorReported);
 782     }
 783
 784     Ok(())
 785 }
 786
 787 fn compare_synthetic_generics<'tcx>(
 788     tcx: TyCtxt<'tcx>,
 789     impl_m: &ty::AssocItem,
 790     trait_m: &ty::AssocItem,
 791 ) -> Result<(), ErrorReported> {
 792     // FIXME(chrisvittal) Clean up this function, list of FIXME items:
 793     //     1. Better messages for the span labels
 794     //     2. Explanation as to what is going on
 795     // If we get here, we already have the same number of generics, so the zip will
 796     // be okay.
 797     let mut error_found = false;
 798     let impl_m_generics = tcx.generics_of(impl_m.def_id);
 799     let trait_m_generics = tcx.generics_of(trait_m.def_id);
 800     let impl_m_type_params = impl_m_generics.params.iter().filter_map(|param| match param.kind {
 801         GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
 802         GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None,
 803     });
 804     let trait_m_type_params = trait_m_generics.params.iter().filter_map(|param| match param.kind {
 805         GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
 806         GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None,
 807     });
 808     for ((impl_def_id, impl_synthetic), (trait_def_id, trait_synthetic)) in
 809         impl_m_type_params.zip(trait_m_type_params)
 810     {
 811         if impl_synthetic != trait_synthetic {
 812             let impl_hir_id = tcx.hir().as_local_hir_id(impl_def_id.expect_local());
 813             let impl_span = tcx.hir().span(impl_hir_id);
 814             let trait_span = tcx.def_span(trait_def_id);
 815             let mut err = struct_span_err!(
 816                 tcx.sess,
 817                 impl_span,
 818                 E0643,
 819                 "method `{}` has incompatible signature for trait",
 820                 trait_m.ident
 821             );
 822             err.span_label(trait_span, "declaration in trait here");
 823             match (impl_synthetic, trait_synthetic) {
 824                 // The case where the impl method uses `impl Trait` but the trait method uses
 825                 // explicit generics
 826                 (Some(hir::SyntheticTyParamKind::ImplTrait), None) => {
 827                     err.span_label(impl_span, "expected generic parameter, found `impl Trait`");
 828                     (|| {
 829                         // try taking the name from the trait impl
 830                         // FIXME: this is obviously suboptimal since the name can already be used
 831                         // as another generic argument
 832                         let new_name = tcx.sess.source_map().span_to_snippet(trait_span).ok()?;
 833                         let trait_m = tcx.hir().as_local_hir_id(trait_m.def_id.as_local()?);
 834                         let trait_m = tcx.hir().trait_item(hir::TraitItemId { hir_id: trait_m });
 835
 836                         let impl_m = tcx.hir().as_local_hir_id(impl_m.def_id.as_local()?);
 837                         let impl_m = tcx.hir().impl_item(hir::ImplItemId { hir_id: impl_m });
 838
 839                         // in case there are no generics, take the spot between the function name
 840                         // and the opening paren of the argument list
 841                         let new_generics_span =
 842                             tcx.sess.source_map().generate_fn_name_span(impl_span)?.shrink_to_hi();
 843                         // in case there are generics, just replace them
 844                         let generics_span =
 845                             impl_m.generics.span.substitute_dummy(new_generics_span);
 846                         // replace with the generics from the trait
 847                         let new_generics =
 848                             tcx.sess.source_map().span_to_snippet(trait_m.generics.span).ok()?;
 849
 850                         err.multipart_suggestion(
 851                             "try changing the `impl Trait` argument to a generic parameter",
 852                             vec![
 853                                 // replace `impl Trait` with `T`
 854                                 (impl_span, new_name),
 855                                 // replace impl method generics with trait method generics
 856                                 // This isn't quite right, as users might have changed the names
 857                                 // of the generics, but it works for the common case
 858                                 (generics_span, new_generics),
 859                             ],
 860                             Applicability::MaybeIncorrect,
 861                         );
 862                         Some(())
 863                     })();
 864                 }
 865                 // The case where the trait method uses `impl Trait`, but the impl method uses
 866                 // explicit generics.
 867                 (None, Some(hir::SyntheticTyParamKind::ImplTrait)) => {
 868                     err.span_label(impl_span, "expected `impl Trait`, found generic parameter");
 869                     (|| {
 870                         let impl_m = tcx.hir().as_local_hir_id(impl_m.def_id.as_local()?);
 871                         let impl_m = tcx.hir().impl_item(hir::ImplItemId { hir_id: impl_m });
 872                         let input_tys = match impl_m.kind {
 873                             hir::ImplItemKind::Fn(ref sig, _) => sig.decl.inputs,
 874                             _ => unreachable!(),
 875                         };
 876                         struct Visitor(Option<Span>, hir::def_id::DefId);
 877                         impl<'v> intravisit::Visitor<'v> for Visitor {
 878                             fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
 879                                 intravisit::walk_ty(self, ty);
 880                                 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) =
 881                                     ty.kind
 882                                 {
 883                                     if let Res::Def(DefKind::TyParam, def_id) = path.res {
 884                                         if def_id == self.1 {
 885                                             self.0 = Some(ty.span);
 886                                         }
 887                                     }
 888                                 }
 889                             }
 890                             type Map = intravisit::ErasedMap<'v>;
 891                             fn nested_visit_map(
 892                                 &mut self,
 893                             ) -> intravisit::NestedVisitorMap<Self::Map>
 894                             {
 895                                 intravisit::NestedVisitorMap::None
 896                             }
 897                         }
 898                         let mut visitor = Visitor(None, impl_def_id);
 899                         for ty in input_tys {
 900                             intravisit::Visitor::visit_ty(&mut visitor, ty);
 901                         }
 902                         let span = visitor.0?;
 903
 904                         let bounds =
 905                             impl_m.generics.params.iter().find_map(|param| match param.kind {
 906                                 GenericParamKind::Lifetime { .. } => None,
 907                                 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
 908                                     if param.hir_id == impl_hir_id {
 909                                         Some(&param.bounds)
 910                                     } else {
 911                                         None
 912                                     }
 913                                 }
 914                             })?;
 915                         let bounds = bounds.first()?.span().to(bounds.last()?.span());
 916                         let bounds = tcx.sess.source_map().span_to_snippet(bounds).ok()?;
 917
 918                         err.multipart_suggestion(
 919                             "try removing the generic parameter and using `impl Trait` instead",
 920                             vec![
 921                                 // delete generic parameters
 922                                 (impl_m.generics.span, String::new()),
 923                                 // replace param usage with `impl Trait`
 924                                 (span, format!("impl {}", bounds)),
 925                             ],
 926                             Applicability::MaybeIncorrect,
 927                         );
 928                         Some(())
 929                     })();
 930                 }
 931                 _ => unreachable!(),
 932             }
 933             err.emit();
 934             error_found = true;
 935         }
 936     }
 937     if error_found { Err(ErrorReported) } else { Ok(()) }
 938 }
 939
 940 crate fn compare_const_impl<'tcx>(
 941     tcx: TyCtxt<'tcx>,
 942     impl_c: &ty::AssocItem,
 943     impl_c_span: Span,
 944     trait_c: &ty::AssocItem,
 945     impl_trait_ref: ty::TraitRef<'tcx>,
 946 ) {
 947     debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref);
 948
 949     tcx.infer_ctxt().enter(|infcx| {
 950         let param_env = tcx.param_env(impl_c.def_id);
 951         let inh = Inherited::new(infcx, impl_c.def_id.expect_local());
 952         let infcx = &inh.infcx;
 953
 954         // The below is for the most part highly similar to the procedure
 955         // for methods above. It is simpler in many respects, especially
 956         // because we shouldn't really have to deal with lifetimes or
 957         // predicates. In fact some of this should probably be put into
 958         // shared functions because of DRY violations...
 959         let trait_to_impl_substs = impl_trait_ref.substs;
 960
 961         // Create a parameter environment that represents the implementation's
 962         // method.
 963         let impl_c_hir_id = tcx.hir().as_local_hir_id(impl_c.def_id.expect_local());
 964
 965         // Compute placeholder form of impl and trait const tys.
 966         let impl_ty = tcx.type_of(impl_c.def_id);
 967         let trait_ty = tcx.type_of(trait_c.def_id).subst(tcx, trait_to_impl_substs);
 968         let mut cause = ObligationCause::misc(impl_c_span, impl_c_hir_id);
 969
 970         // There is no "body" here, so just pass dummy id.
 971         let impl_ty =
 972             inh.normalize_associated_types_in(impl_c_span, impl_c_hir_id, param_env, &impl_ty);
 973
 974         debug!("compare_const_impl: impl_ty={:?}", impl_ty);
 975
 976         let trait_ty =
 977             inh.normalize_associated_types_in(impl_c_span, impl_c_hir_id, param_env, &trait_ty);
 978
 979         debug!("compare_const_impl: trait_ty={:?}", trait_ty);
 980
 981         let err = infcx
 982             .at(&cause, param_env)
 983             .sup(trait_ty, impl_ty)
 984             .map(|ok| inh.register_infer_ok_obligations(ok));
 985
 986         if let Err(terr) = err {
 987             debug!(
 988                 "checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
 989                 impl_ty, trait_ty
 990             );
 991
 992             // Locate the Span containing just the type of the offending impl
 993             match tcx.hir().expect_impl_item(impl_c_hir_id).kind {
 994                 ImplItemKind::Const(ref ty, _) => cause.span = ty.span,
 995                 _ => bug!("{:?} is not a impl const", impl_c),
 996             }
 997
 998             let mut diag = struct_span_err!(
 999                 tcx.sess,
1000                 cause.span,
1001                 E0326,
1002                 "implemented const `{}` has an incompatible type for \
1003                                              trait",
1004                 trait_c.ident
1005             );
1006
1007             let trait_c_hir_id =
1008                 trait_c.def_id.as_local().map(|def_id| tcx.hir().as_local_hir_id(def_id));
1009             let trait_c_span = trait_c_hir_id.map(|trait_c_hir_id| {
1010                 // Add a label to the Span containing just the type of the const
1011                 match tcx.hir().expect_trait_item(trait_c_hir_id).kind {
1012                     TraitItemKind::Const(ref ty, _) => ty.span,
1013                     _ => bug!("{:?} is not a trait const", trait_c),
1014                 }
1015             });
1016
1017             infcx.note_type_err(
1018                 &mut diag,
1019                 &cause,
1020                 trait_c_span.map(|span| (span, "type in trait".to_owned())),
1021                 Some(infer::ValuePairs::Types(ExpectedFound {
1022                     expected: trait_ty,
1023                     found: impl_ty,
1024                 })),
1025                 &terr,
1026             );
1027             diag.emit();
1028         }
1029
1030         // Check that all obligations are satisfied by the implementation's
1031         // version.
1032         if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
1033             infcx.report_fulfillment_errors(errors, None, false);
1034             return;
1035         }
1036
1037         let fcx = FnCtxt::new(&inh, param_env, impl_c_hir_id);
1038         fcx.regionck_item(impl_c_hir_id, impl_c_span, &[]);
1039     });
1040 }
1041
1042 crate fn compare_ty_impl<'tcx>(
1043     tcx: TyCtxt<'tcx>,
1044     impl_ty: &ty::AssocItem,
1045     impl_ty_span: Span,
1046     trait_ty: &ty::AssocItem,
1047     impl_trait_ref: ty::TraitRef<'tcx>,
1048     trait_item_span: Option<Span>,
1049 ) {
1050     debug!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref);
1051
1052     let _: Result<(), ErrorReported> = (|| {
1053         compare_number_of_generics(tcx, impl_ty, impl_ty_span, trait_ty, trait_item_span)?;
1054
1055         compare_type_predicate_entailment(tcx, impl_ty, impl_ty_span, trait_ty, impl_trait_ref)
1056     })();
1057 }
1058
1059 /// The equivalent of [compare_predicate_entailment], but for associated types
1060 /// instead of associated functions.
1061 fn compare_type_predicate_entailment(
1062     tcx: TyCtxt<'tcx>,
1063     impl_ty: &ty::AssocItem,
1064     impl_ty_span: Span,
1065     trait_ty: &ty::AssocItem,
1066     impl_trait_ref: ty::TraitRef<'tcx>,
1067 ) -> Result<(), ErrorReported> {
1068     let impl_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1069     let trait_to_impl_substs =
1070         impl_substs.rebase_onto(tcx, impl_ty.container.id(), impl_trait_ref.substs);
1071
1072     let impl_ty_generics = tcx.generics_of(impl_ty.def_id);
1073     let trait_ty_generics = tcx.generics_of(trait_ty.def_id);
1074     let impl_ty_predicates = tcx.predicates_of(impl_ty.def_id);
1075     let trait_ty_predicates = tcx.predicates_of(trait_ty.def_id);
1076
1077     check_region_bounds_on_impl_item(
1078         tcx,
1079         impl_ty_span,
1080         impl_ty,
1081         trait_ty,
1082         &trait_ty_generics,
1083         &impl_ty_generics,
1084     )?;
1085
1086     let impl_ty_own_bounds = impl_ty_predicates.instantiate_own(tcx, impl_substs);
1087
1088     if impl_ty_own_bounds.is_empty() {
1089         // Nothing to check.
1090         return Ok(());
1091     }
1092
1093     // This `HirId` should be used for the `body_id` field on each
1094     // `ObligationCause` (and the `FnCtxt`). This is what
1095     // `regionck_item` expects.
1096     let impl_ty_hir_id = tcx.hir().as_local_hir_id(impl_ty.def_id.expect_local());
1097     let cause = ObligationCause {
1098         span: impl_ty_span,
1099         body_id: impl_ty_hir_id,
1100         code: ObligationCauseCode::CompareImplTypeObligation {
1101             item_name: impl_ty.ident.name,
1102             impl_item_def_id: impl_ty.def_id,
1103             trait_item_def_id: trait_ty.def_id,
1104         },
1105     };
1106
1107     debug!("compare_type_predicate_entailment: trait_to_impl_substs={:?}", trait_to_impl_substs);
1108
1109     // The predicates declared by the impl definition, the trait and the
1110     // associated type in the trait are assumed.
1111     let impl_predicates = tcx.predicates_of(impl_ty_predicates.parent.unwrap());
1112     let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
1113     hybrid_preds
1114         .predicates
1115         .extend(trait_ty_predicates.instantiate_own(tcx, trait_to_impl_substs).predicates);
1116
1117     debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds);
1118
1119     let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_hir_id);
1120     let param_env = ty::ParamEnv::new(
1121         tcx.intern_predicates(&hybrid_preds.predicates),
1122         Reveal::UserFacing,
1123         None,
1124     );
1125     let param_env = traits::normalize_param_env_or_error(
1126         tcx,
1127         impl_ty.def_id,
1128         param_env,
1129         normalize_cause.clone(),
1130     );
1131     tcx.infer_ctxt().enter(|infcx| {
1132         let inh = Inherited::new(infcx, impl_ty.def_id.expect_local());
1133         let infcx = &inh.infcx;
1134
1135         debug!("compare_type_predicate_entailment: caller_bounds={:?}", param_env.caller_bounds);
1136
1137         let mut selcx = traits::SelectionContext::new(&infcx);
1138
1139         for predicate in impl_ty_own_bounds.predicates {
1140             let traits::Normalized { value: predicate, obligations } =
1141                 traits::normalize(&mut selcx, param_env, normalize_cause.clone(), &predicate);
1142
1143             inh.register_predicates(obligations);
1144             inh.register_predicate(traits::Obligation::new(cause.clone(), param_env, predicate));
1145         }
1146
1147         // Check that all obligations are satisfied by the implementation's
1148         // version.
1149         if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
1150             infcx.report_fulfillment_errors(errors, None, false);
1151             return Err(ErrorReported);
1152         }
1153
1154         // Finally, resolve all regions. This catches wily misuses of
1155         // lifetime parameters.
1156         let fcx = FnCtxt::new(&inh, param_env, impl_ty_hir_id);
1157         fcx.regionck_item(impl_ty_hir_id, impl_ty_span, &[]);
1158
1159         Ok(())
1160     })
1161 }
1162
1163 fn assoc_item_kind_str(impl_item: &ty::AssocItem) -> &'static str {
1164     match impl_item.kind {
1165         ty::AssocKind::Const => "const",
1166         ty::AssocKind::Fn => "method",
1167         ty::AssocKind::Type | ty::AssocKind::OpaqueTy => "type",
1168     }
1169 }