src/librustc_typeck/check/compare_method.rs

   1 use errors::{Applicability, DiagnosticId};
   2 use rustc::hir::intravisit;
   3 use rustc::infer::{self, InferOk};
   4 use rustc::traits::{self, ObligationCause, ObligationCauseCode, Reveal};
   5 use rustc::ty::error::{ExpectedFound, TypeError};
   6 use rustc::ty::subst::{InternalSubsts, Subst};
   7 use rustc::ty::util::ExplicitSelf;
   8 use rustc::ty::{self, GenericParamDefKind, TyCtxt};
   9 use rustc::util::common::ErrorReported;
  10 use rustc_hir as hir;
  11 use rustc_hir::def::{DefKind, Res};
  12 use rustc_hir::{GenericParamKind, ImplItemKind, TraitItemKind};
  13 use rustc_span::Span;
  14 use syntax::errors::pluralize;
  15
  16 use super::{potentially_plural_count, FnCtxt, Inherited};
  17
  18 use rustc_error_codes::*;
  19
  20 /// Checks that a method from an impl conforms to the signature of
  21 /// the same method as declared in the trait.
  22 ///
  23 /// # Parameters
  24 ///
  25 /// - `impl_m`: type of the method we are checking
  26 /// - `impl_m_span`: span to use for reporting errors
  27 /// - `trait_m`: the method in the trait
  28 /// - `impl_trait_ref`: the TraitRef corresponding to the trait implementation
  29
  30 crate fn compare_impl_method<'tcx>(
  31     tcx: TyCtxt<'tcx>,
  32     impl_m: &ty::AssocItem,
  33     impl_m_span: Span,
  34     trait_m: &ty::AssocItem,
  35     impl_trait_ref: ty::TraitRef<'tcx>,
  36     trait_item_span: Option<Span>,
  37 ) {
  38     debug!("compare_impl_method(impl_trait_ref={:?})", impl_trait_ref);
  39
  40     let impl_m_span = tcx.sess.source_map().def_span(impl_m_span);
  41
  42     if let Err(ErrorReported) = compare_self_type(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref)
  43     {
  44         return;
  45     }
  46
  47     if let Err(ErrorReported) =
  48         compare_number_of_generics(tcx, impl_m, impl_m_span, trait_m, trait_item_span)
  49     {
  50         return;
  51     }
  52
  53     if let Err(ErrorReported) =
  54         compare_number_of_method_arguments(tcx, impl_m, impl_m_span, trait_m, trait_item_span)
  55     {
  56         return;
  57     }
  58
  59     if let Err(ErrorReported) = compare_synthetic_generics(tcx, impl_m, trait_m) {
  60         return;
  61     }
  62
  63     if let Err(ErrorReported) =
  64         compare_predicate_entailment(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref)
  65     {
  66         return;
  67     }
  68 }
  69
  70 fn compare_predicate_entailment<'tcx>(
  71     tcx: TyCtxt<'tcx>,
  72     impl_m: &ty::AssocItem,
  73     impl_m_span: Span,
  74     trait_m: &ty::AssocItem,
  75     impl_trait_ref: ty::TraitRef<'tcx>,
  76 ) -> Result<(), ErrorReported> {
  77     let trait_to_impl_substs = impl_trait_ref.substs;
  78
  79     // This node-id should be used for the `body_id` field on each
  80     // `ObligationCause` (and the `FnCtxt`). This is what
  81     // `regionck_item` expects.
  82     let impl_m_hir_id = tcx.hir().as_local_hir_id(impl_m.def_id).unwrap();
  83
  84     let cause = ObligationCause {
  85         span: impl_m_span,
  86         body_id: impl_m_hir_id,
  87         code: ObligationCauseCode::CompareImplMethodObligation {
  88             item_name: impl_m.ident.name,
  89             impl_item_def_id: impl_m.def_id,
  90             trait_item_def_id: trait_m.def_id,
  91         },
  92     };
  93
  94     // This code is best explained by example. Consider a trait:
  95     //
  96     //     trait Trait<'t,T> {
  97     //          fn method<'a,M>(t: &'t T, m: &'a M) -> Self;
  98     //     }
  99     //
 100     // And an impl:
 101     //
 102     //     impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
 103     //          fn method<'b,N>(t: &'j &'i U, m: &'b N) -> Foo;
 104     //     }
 105     //
 106     // We wish to decide if those two method types are compatible.
 107     //
 108     // We start out with trait_to_impl_substs, that maps the trait
 109     // type parameters to impl type parameters. This is taken from the
 110     // impl trait reference:
 111     //
 112     //     trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
 113     //
 114     // We create a mapping `dummy_substs` that maps from the impl type
 115     // parameters to fresh types and regions. For type parameters,
 116     // this is the identity transform, but we could as well use any
 117     // placeholder types. For regions, we convert from bound to free
 118     // regions (Note: but only early-bound regions, i.e., those
 119     // declared on the impl or used in type parameter bounds).
 120     //
 121     //     impl_to_skol_substs = {'i => 'i0, U => U0, N => N0 }
 122     //
 123     // Now we can apply skol_substs to the type of the impl method
 124     // to yield a new function type in terms of our fresh, placeholder
 125     // types:
 126     //
 127     //     <'b> fn(t: &'i0 U0, m: &'b) -> Foo
 128     //
 129     // We now want to extract and substitute the type of the *trait*
 130     // method and compare it. To do so, we must create a compound
 131     // substitution by combining trait_to_impl_substs and
 132     // impl_to_skol_substs, and also adding a mapping for the method
 133     // type parameters. We extend the mapping to also include
 134     // the method parameters.
 135     //
 136     //     trait_to_skol_substs = { T => &'i0 U0, Self => Foo, M => N0 }
 137     //
 138     // Applying this to the trait method type yields:
 139     //
 140     //     <'a> fn(t: &'i0 U0, m: &'a) -> Foo
 141     //
 142     // This type is also the same but the name of the bound region ('a
 143     // vs 'b).  However, the normal subtyping rules on fn types handle
 144     // this kind of equivalency just fine.
 145     //
 146     // We now use these substitutions to ensure that all declared bounds are
 147     // satisfied by the implementation's method.
 148     //
 149     // We do this by creating a parameter environment which contains a
 150     // substitution corresponding to impl_to_skol_substs. We then build
 151     // trait_to_skol_substs and use it to convert the predicates contained
 152     // in the trait_m.generics to the placeholder form.
 153     //
 154     // Finally we register each of these predicates as an obligation in
 155     // a fresh FulfillmentCtxt, and invoke select_all_or_error.
 156
 157     // Create mapping from impl to placeholder.
 158     let impl_to_skol_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
 159
 160     // Create mapping from trait to placeholder.
 161     let trait_to_skol_substs =
 162         impl_to_skol_substs.rebase_onto(tcx, impl_m.container.id(), trait_to_impl_substs);
 163     debug!("compare_impl_method: trait_to_skol_substs={:?}", trait_to_skol_substs);
 164
 165     let impl_m_generics = tcx.generics_of(impl_m.def_id);
 166     let trait_m_generics = tcx.generics_of(trait_m.def_id);
 167     let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
 168     let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
 169
 170     // Check region bounds.
 171     check_region_bounds_on_impl_item(
 172         tcx,
 173         impl_m_span,
 174         impl_m,
 175         trait_m,
 176         &trait_m_generics,
 177         &impl_m_generics,
 178     )?;
 179
 180     // Create obligations for each predicate declared by the impl
 181     // definition in the context of the trait's parameter
 182     // environment. We can't just use `impl_env.caller_bounds`,
 183     // however, because we want to replace all late-bound regions with
 184     // region variables.
 185     let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap());
 186     let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
 187
 188     debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
 189
 190     // This is the only tricky bit of the new way we check implementation methods
 191     // We need to build a set of predicates where only the method-level bounds
 192     // are from the trait and we assume all other bounds from the implementation
 193     // to be previously satisfied.
 194     //
 195     // We then register the obligations from the impl_m and check to see
 196     // if all constraints hold.
 197     hybrid_preds
 198         .predicates
 199         .extend(trait_m_predicates.instantiate_own(tcx, trait_to_skol_substs).predicates);
 200
 201     // Construct trait parameter environment and then shift it into the placeholder viewpoint.
 202     // The key step here is to update the caller_bounds's predicates to be
 203     // the new hybrid bounds we computed.
 204     let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_hir_id);
 205     let param_env = ty::ParamEnv::new(
 206         tcx.intern_predicates(&hybrid_preds.predicates),
 207         Reveal::UserFacing,
 208         None,
 209     );
 210     let param_env = traits::normalize_param_env_or_error(
 211         tcx,
 212         impl_m.def_id,
 213         param_env,
 214         normalize_cause.clone(),
 215     );
 216
 217     tcx.infer_ctxt().enter(|infcx| {
 218         let inh = Inherited::new(infcx, impl_m.def_id);
 219         let infcx = &inh.infcx;
 220
 221         debug!("compare_impl_method: caller_bounds={:?}", param_env.caller_bounds);
 222
 223         let mut selcx = traits::SelectionContext::new(&infcx);
 224
 225         let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_skol_substs);
 226         let (impl_m_own_bounds, _) = infcx.replace_bound_vars_with_fresh_vars(
 227             impl_m_span,
 228             infer::HigherRankedType,
 229             &ty::Binder::bind(impl_m_own_bounds.predicates),
 230         );
 231         for predicate in impl_m_own_bounds {
 232             let traits::Normalized { value: predicate, obligations } =
 233                 traits::normalize(&mut selcx, param_env, normalize_cause.clone(), &predicate);
 234
 235             inh.register_predicates(obligations);
 236             inh.register_predicate(traits::Obligation::new(cause.clone(), param_env, predicate));
 237         }
 238
 239         // We now need to check that the signature of the impl method is
 240         // compatible with that of the trait method. We do this by
 241         // checking that `impl_fty <: trait_fty`.
 242         //
 243         // FIXME. Unfortunately, this doesn't quite work right now because
 244         // associated type normalization is not integrated into subtype
 245         // checks. For the comparison to be valid, we need to
 246         // normalize the associated types in the impl/trait methods
 247         // first. However, because function types bind regions, just
 248         // calling `normalize_associated_types_in` would have no effect on
 249         // any associated types appearing in the fn arguments or return
 250         // type.
 251
 252         // Compute placeholder form of impl and trait method tys.
 253         let tcx = infcx.tcx;
 254
 255         let (impl_sig, _) = infcx.replace_bound_vars_with_fresh_vars(
 256             impl_m_span,
 257             infer::HigherRankedType,
 258             &tcx.fn_sig(impl_m.def_id),
 259         );
 260         let impl_sig =
 261             inh.normalize_associated_types_in(impl_m_span, impl_m_hir_id, param_env, &impl_sig);
 262         let impl_fty = tcx.mk_fn_ptr(ty::Binder::bind(impl_sig));
 263         debug!("compare_impl_method: impl_fty={:?}", impl_fty);
 264
 265         let trait_sig = tcx.liberate_late_bound_regions(impl_m.def_id, &tcx.fn_sig(trait_m.def_id));
 266         let trait_sig = trait_sig.subst(tcx, trait_to_skol_substs);
 267         let trait_sig =
 268             inh.normalize_associated_types_in(impl_m_span, impl_m_hir_id, param_env, &trait_sig);
 269         let trait_fty = tcx.mk_fn_ptr(ty::Binder::bind(trait_sig));
 270
 271         debug!("compare_impl_method: trait_fty={:?}", trait_fty);
 272
 273         let sub_result = infcx.at(&cause, param_env).sup(trait_fty, impl_fty).map(
 274             |InferOk { obligations, .. }| {
 275                 inh.register_predicates(obligations);
 276             },
 277         );
 278
 279         if let Err(terr) = sub_result {
 280             debug!("sub_types failed: impl ty {:?}, trait ty {:?}", impl_fty, trait_fty);
 281
 282             let (impl_err_span, trait_err_span) = extract_spans_for_error_reporting(
 283                 &infcx, param_env, &terr, &cause, impl_m, impl_sig, trait_m, trait_sig,
 284             );
 285
 286             let cause = ObligationCause { span: impl_err_span, ..cause };
 287
 288             let mut diag = struct_span_err!(
 289                 tcx.sess,
 290                 cause.span(tcx),
 291                 E0053,
 292                 "method `{}` has an incompatible type for trait",
 293                 trait_m.ident
 294             );
 295             if let TypeError::Mutability = terr {
 296                 if let Some(trait_err_span) = trait_err_span {
 297                     if let Ok(trait_err_str) = tcx.sess.source_map().span_to_snippet(trait_err_span)
 298                     {
 299                         diag.span_suggestion(
 300                             impl_err_span,
 301                             "consider change the type to match the mutability in trait",
 302                             trait_err_str,
 303                             Applicability::MachineApplicable,
 304                         );
 305                     }
 306                 }
 307             }
 308
 309             infcx.note_type_err(
 310                 &mut diag,
 311                 &cause,
 312                 trait_err_span.map(|sp| (sp, "type in trait".to_owned())),
 313                 Some(infer::ValuePairs::Types(ExpectedFound {
 314                     expected: trait_fty,
 315                     found: impl_fty,
 316                 })),
 317                 &terr,
 318             );
 319             diag.emit();
 320             return Err(ErrorReported);
 321         }
 322
 323         // Check that all obligations are satisfied by the implementation's
 324         // version.
 325         if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
 326             infcx.report_fulfillment_errors(errors, None, false);
 327             return Err(ErrorReported);
 328         }
 329
 330         // Finally, resolve all regions. This catches wily misuses of
 331         // lifetime parameters.
 332         let fcx = FnCtxt::new(&inh, param_env, impl_m_hir_id);
 333         fcx.regionck_item(impl_m_hir_id, impl_m_span, &[]);
 334
 335         Ok(())
 336     })
 337 }
 338
 339 fn check_region_bounds_on_impl_item<'tcx>(
 340     tcx: TyCtxt<'tcx>,
 341     span: Span,
 342     impl_m: &ty::AssocItem,
 343     trait_m: &ty::AssocItem,
 344     trait_generics: &ty::Generics,
 345     impl_generics: &ty::Generics,
 346 ) -> Result<(), ErrorReported> {
 347     let trait_params = trait_generics.own_counts().lifetimes;
 348     let impl_params = impl_generics.own_counts().lifetimes;
 349
 350     debug!(
 351         "check_region_bounds_on_impl_item: \
 352             trait_generics={:?} \
 353             impl_generics={:?}",
 354         trait_generics, impl_generics
 355     );
 356
 357     // Must have same number of early-bound lifetime parameters.
 358     // Unfortunately, if the user screws up the bounds, then this
 359     // will change classification between early and late.  E.g.,
 360     // if in trait we have `<'a,'b:'a>`, and in impl we just have
 361     // `<'a,'b>`, then we have 2 early-bound lifetime parameters
 362     // in trait but 0 in the impl. But if we report "expected 2
 363     // but found 0" it's confusing, because it looks like there
 364     // are zero. Since I don't quite know how to phrase things at
 365     // the moment, give a kind of vague error message.
 366     if trait_params != impl_params {
 367         let item_kind = assoc_item_kind_str(impl_m);
 368         let def_span = tcx.sess.source_map().def_span(span);
 369         let span = tcx.hir().get_generics(impl_m.def_id).map(|g| g.span).unwrap_or(def_span);
 370         let mut err = struct_span_err!(
 371             tcx.sess,
 372             span,
 373             E0195,
 374             "lifetime parameters or bounds on {} `{}` do not match the trait declaration",
 375             item_kind,
 376             impl_m.ident,
 377         );
 378         err.span_label(span, &format!("lifetimes do not match {} in trait", item_kind));
 379         if let Some(sp) = tcx.hir().span_if_local(trait_m.def_id) {
 380             let def_sp = tcx.sess.source_map().def_span(sp);
 381             let sp = tcx.hir().get_generics(trait_m.def_id).map(|g| g.span).unwrap_or(def_sp);
 382             err.span_label(
 383                 sp,
 384                 &format!("lifetimes in impl do not match this {} in trait", item_kind),
 385             );
 386         }
 387         err.emit();
 388         return Err(ErrorReported);
 389     }
 390
 391     Ok(())
 392 }
 393
 394 fn extract_spans_for_error_reporting<'a, 'tcx>(
 395     infcx: &infer::InferCtxt<'a, 'tcx>,
 396     param_env: ty::ParamEnv<'tcx>,
 397     terr: &TypeError<'_>,
 398     cause: &ObligationCause<'tcx>,
 399     impl_m: &ty::AssocItem,
 400     impl_sig: ty::FnSig<'tcx>,
 401     trait_m: &ty::AssocItem,
 402     trait_sig: ty::FnSig<'tcx>,
 403 ) -> (Span, Option<Span>) {
 404     let tcx = infcx.tcx;
 405     let impl_m_hir_id = tcx.hir().as_local_hir_id(impl_m.def_id).unwrap();
 406     let (impl_m_output, impl_m_iter) = match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
 407         ImplItemKind::Method(ref impl_m_sig, _) => {
 408             (&impl_m_sig.decl.output, impl_m_sig.decl.inputs.iter())
 409         }
 410         _ => bug!("{:?} is not a method", impl_m),
 411     };
 412
 413     match *terr {
 414         TypeError::Mutability => {
 415             if let Some(trait_m_hir_id) = tcx.hir().as_local_hir_id(trait_m.def_id) {
 416                 let trait_m_iter = match tcx.hir().expect_trait_item(trait_m_hir_id).kind {
 417                     TraitItemKind::Method(ref trait_m_sig, _) => trait_m_sig.decl.inputs.iter(),
 418                     _ => bug!("{:?} is not a TraitItemKind::Method", trait_m),
 419                 };
 420
 421                 impl_m_iter
 422                     .zip(trait_m_iter)
 423                     .find(|&(ref impl_arg, ref trait_arg)| {
 424                         match (&impl_arg.kind, &trait_arg.kind) {
 425                             (
 426                                 &hir::TyKind::Rptr(_, ref impl_mt),
 427                                 &hir::TyKind::Rptr(_, ref trait_mt),
 428                             )
 429                             | (&hir::TyKind::Ptr(ref impl_mt), &hir::TyKind::Ptr(ref trait_mt)) => {
 430                                 impl_mt.mutbl != trait_mt.mutbl
 431                             }
 432                             _ => false,
 433                         }
 434                     })
 435                     .map(|(ref impl_arg, ref trait_arg)| (impl_arg.span, Some(trait_arg.span)))
 436                     .unwrap_or_else(|| (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id)))
 437             } else {
 438                 (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
 439             }
 440         }
 441         TypeError::Sorts(ExpectedFound { .. }) => {
 442             if let Some(trait_m_hir_id) = tcx.hir().as_local_hir_id(trait_m.def_id) {
 443                 let (trait_m_output, trait_m_iter) =
 444                     match tcx.hir().expect_trait_item(trait_m_hir_id).kind {
 445                         TraitItemKind::Method(ref trait_m_sig, _) => {
 446                             (&trait_m_sig.decl.output, trait_m_sig.decl.inputs.iter())
 447                         }
 448                         _ => bug!("{:?} is not a TraitItemKind::Method", trait_m),
 449                     };
 450
 451                 let impl_iter = impl_sig.inputs().iter();
 452                 let trait_iter = trait_sig.inputs().iter();
 453                 impl_iter
 454                     .zip(trait_iter)
 455                     .zip(impl_m_iter)
 456                     .zip(trait_m_iter)
 457                     .filter_map(
 458                         |(((&impl_arg_ty, &trait_arg_ty), impl_arg), trait_arg)| match infcx
 459                             .at(&cause, param_env)
 460                             .sub(trait_arg_ty, impl_arg_ty)
 461                         {
 462                             Ok(_) => None,
 463                             Err(_) => Some((impl_arg.span, Some(trait_arg.span))),
 464                         },
 465                     )
 466                     .next()
 467                     .unwrap_or_else(|| {
 468                         if infcx
 469                             .at(&cause, param_env)
 470                             .sup(trait_sig.output(), impl_sig.output())
 471                             .is_err()
 472                         {
 473                             (impl_m_output.span(), Some(trait_m_output.span()))
 474                         } else {
 475                             (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
 476                         }
 477                     })
 478             } else {
 479                 (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
 480             }
 481         }
 482         _ => (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id)),
 483     }
 484 }
 485
 486 fn compare_self_type<'tcx>(
 487     tcx: TyCtxt<'tcx>,
 488     impl_m: &ty::AssocItem,
 489     impl_m_span: Span,
 490     trait_m: &ty::AssocItem,
 491     impl_trait_ref: ty::TraitRef<'tcx>,
 492 ) -> Result<(), ErrorReported> {
 493     // Try to give more informative error messages about self typing
 494     // mismatches.  Note that any mismatch will also be detected
 495     // below, where we construct a canonical function type that
 496     // includes the self parameter as a normal parameter.  It's just
 497     // that the error messages you get out of this code are a bit more
 498     // inscrutable, particularly for cases where one method has no
 499     // self.
 500
 501     let self_string = |method: &ty::AssocItem| {
 502         let untransformed_self_ty = match method.container {
 503             ty::ImplContainer(_) => impl_trait_ref.self_ty(),
 504             ty::TraitContainer(_) => tcx.types.self_param,
 505         };
 506         let self_arg_ty = *tcx.fn_sig(method.def_id).input(0).skip_binder();
 507         let param_env = ty::ParamEnv::reveal_all();
 508
 509         tcx.infer_ctxt().enter(|infcx| {
 510             let self_arg_ty =
 511                 tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(self_arg_ty));
 512             let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty).is_ok();
 513             match ExplicitSelf::determine(self_arg_ty, can_eq_self) {
 514                 ExplicitSelf::ByValue => "self".to_owned(),
 515                 ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
 516                 ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(),
 517                 _ => format!("self: {}", self_arg_ty),
 518             }
 519         })
 520     };
 521
 522     match (trait_m.method_has_self_argument, impl_m.method_has_self_argument) {
 523         (false, false) | (true, true) => {}
 524
 525         (false, true) => {
 526             let self_descr = self_string(impl_m);
 527             let mut err = struct_span_err!(
 528                 tcx.sess,
 529                 impl_m_span,
 530                 E0185,
 531                 "method `{}` has a `{}` declaration in the impl, but \
 532                                             not in the trait",
 533                 trait_m.ident,
 534                 self_descr
 535             );
 536             err.span_label(impl_m_span, format!("`{}` used in impl", self_descr));
 537             if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
 538                 err.span_label(span, format!("trait method declared without `{}`", self_descr));
 539             } else {
 540                 err.note_trait_signature(trait_m.ident.to_string(), trait_m.signature(tcx));
 541             }
 542             err.emit();
 543             return Err(ErrorReported);
 544         }
 545
 546         (true, false) => {
 547             let self_descr = self_string(trait_m);
 548             let mut err = struct_span_err!(
 549                 tcx.sess,
 550                 impl_m_span,
 551                 E0186,
 552                 "method `{}` has a `{}` declaration in the trait, but \
 553                                             not in the impl",
 554                 trait_m.ident,
 555                 self_descr
 556             );
 557             err.span_label(impl_m_span, format!("expected `{}` in impl", self_descr));
 558             if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
 559                 err.span_label(span, format!("`{}` used in trait", self_descr));
 560             } else {
 561                 err.note_trait_signature(trait_m.ident.to_string(), trait_m.signature(tcx));
 562             }
 563             err.emit();
 564             return Err(ErrorReported);
 565         }
 566     }
 567
 568     Ok(())
 569 }
 570
 571 fn compare_number_of_generics<'tcx>(
 572     tcx: TyCtxt<'tcx>,
 573     impl_: &ty::AssocItem,
 574     _impl_span: Span,
 575     trait_: &ty::AssocItem,
 576     trait_span: Option<Span>,
 577 ) -> Result<(), ErrorReported> {
 578     let trait_own_counts = tcx.generics_of(trait_.def_id).own_counts();
 579     let impl_own_counts = tcx.generics_of(impl_.def_id).own_counts();
 580
 581     let matchings = [
 582         ("type", trait_own_counts.types, impl_own_counts.types),
 583         ("const", trait_own_counts.consts, impl_own_counts.consts),
 584     ];
 585
 586     let item_kind = assoc_item_kind_str(impl_);
 587
 588     let mut err_occurred = false;
 589     for &(kind, trait_count, impl_count) in &matchings {
 590         if impl_count != trait_count {
 591             err_occurred = true;
 592
 593             let (trait_spans, impl_trait_spans) =
 594                 if let Some(trait_hir_id) = tcx.hir().as_local_hir_id(trait_.def_id) {
 595                     let trait_item = tcx.hir().expect_trait_item(trait_hir_id);
 596                     if trait_item.generics.params.is_empty() {
 597                         (Some(vec![trait_item.generics.span]), vec![])
 598                     } else {
 599                         let arg_spans: Vec<Span> =
 600                             trait_item.generics.params.iter().map(|p| p.span).collect();
 601                         let impl_trait_spans: Vec<Span> = trait_item
 602                             .generics
 603                             .params
 604                             .iter()
 605                             .filter_map(|p| match p.kind {
 606                                 GenericParamKind::Type {
 607                                     synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
 608                                     ..
 609                                 } => Some(p.span),
 610                                 _ => None,
 611                             })
 612                             .collect();
 613                         (Some(arg_spans), impl_trait_spans)
 614                     }
 615                 } else {
 616                     (trait_span.map(|s| vec![s]), vec![])
 617                 };
 618
 619             let impl_hir_id = tcx.hir().as_local_hir_id(impl_.def_id).unwrap();
 620             let impl_item = tcx.hir().expect_impl_item(impl_hir_id);
 621             let impl_item_impl_trait_spans: Vec<Span> = impl_item
 622                 .generics
 623                 .params
 624                 .iter()
 625                 .filter_map(|p| match p.kind {
 626                     GenericParamKind::Type {
 627                         synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
 628                         ..
 629                     } => Some(p.span),
 630                     _ => None,
 631                 })
 632                 .collect();
 633             let spans = impl_item.generics.spans();
 634             let span = spans.primary_span();
 635
 636             let mut err = tcx.sess.struct_span_err_with_code(
 637                 spans,
 638                 &format!(
 639                     "{} `{}` has {} {kind} parameter{} but its trait \
 640                      declaration has {} {kind} parameter{}",
 641                     item_kind,
 642                     trait_.ident,
 643                     impl_count,
 644                     pluralize!(impl_count),
 645                     trait_count,
 646                     pluralize!(trait_count),
 647                     kind = kind,
 648                 ),
 649                 DiagnosticId::Error("E0049".into()),
 650             );
 651
 652             let mut suffix = None;
 653
 654             if let Some(spans) = trait_spans {
 655                 let mut spans = spans.iter();
 656                 if let Some(span) = spans.next() {
 657                     err.span_label(
 658                         *span,
 659                         format!(
 660                             "expected {} {} parameter{}",
 661                             trait_count,
 662                             kind,
 663                             pluralize!(trait_count),
 664                         ),
 665                     );
 666                 }
 667                 for span in spans {
 668                     err.span_label(*span, "");
 669                 }
 670             } else {
 671                 suffix = Some(format!(", expected {}", trait_count));
 672             }
 673
 674             if let Some(span) = span {
 675                 err.span_label(
 676                     span,
 677                     format!(
 678                         "found {} {} parameter{}{}",
 679                         impl_count,
 680                         kind,
 681                         pluralize!(impl_count),
 682                         suffix.unwrap_or_else(|| String::new()),
 683                     ),
 684                 );
 685             }
 686
 687             for span in impl_trait_spans.iter().chain(impl_item_impl_trait_spans.iter()) {
 688                 err.span_label(*span, "`impl Trait` introduces an implicit type parameter");
 689             }
 690
 691             err.emit();
 692         }
 693     }
 694
 695     if err_occurred { Err(ErrorReported) } else { Ok(()) }
 696 }
 697
 698 fn compare_number_of_method_arguments<'tcx>(
 699     tcx: TyCtxt<'tcx>,
 700     impl_m: &ty::AssocItem,
 701     impl_m_span: Span,
 702     trait_m: &ty::AssocItem,
 703     trait_item_span: Option<Span>,
 704 ) -> Result<(), ErrorReported> {
 705     let impl_m_fty = tcx.fn_sig(impl_m.def_id);
 706     let trait_m_fty = tcx.fn_sig(trait_m.def_id);
 707     let trait_number_args = trait_m_fty.inputs().skip_binder().len();
 708     let impl_number_args = impl_m_fty.inputs().skip_binder().len();
 709     if trait_number_args != impl_number_args {
 710         let trait_m_hir_id = tcx.hir().as_local_hir_id(trait_m.def_id);
 711         let trait_span = if let Some(trait_id) = trait_m_hir_id {
 712             match tcx.hir().expect_trait_item(trait_id).kind {
 713                 TraitItemKind::Method(ref trait_m_sig, _) => {
 714                     let pos = if trait_number_args > 0 { trait_number_args - 1 } else { 0 };
 715                     if let Some(arg) = trait_m_sig.decl.inputs.get(pos) {
 716                         Some(if pos == 0 {
 717                             arg.span
 718                         } else {
 719                             Span::new(
 720                                 trait_m_sig.decl.inputs[0].span.lo(),
 721                                 arg.span.hi(),
 722                                 arg.span.ctxt(),
 723                             )
 724                         })
 725                     } else {
 726                         trait_item_span
 727                     }
 728                 }
 729                 _ => bug!("{:?} is not a method", impl_m),
 730             }
 731         } else {
 732             trait_item_span
 733         };
 734         let impl_m_hir_id = tcx.hir().as_local_hir_id(impl_m.def_id).unwrap();
 735         let impl_span = match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
 736             ImplItemKind::Method(ref impl_m_sig, _) => {
 737                 let pos = if impl_number_args > 0 { impl_number_args - 1 } else { 0 };
 738                 if let Some(arg) = impl_m_sig.decl.inputs.get(pos) {
 739                     if pos == 0 {
 740                         arg.span
 741                     } else {
 742                         Span::new(
 743                             impl_m_sig.decl.inputs[0].span.lo(),
 744                             arg.span.hi(),
 745                             arg.span.ctxt(),
 746                         )
 747                     }
 748                 } else {
 749                     impl_m_span
 750                 }
 751             }
 752             _ => bug!("{:?} is not a method", impl_m),
 753         };
 754         let mut err = struct_span_err!(
 755             tcx.sess,
 756             impl_span,
 757             E0050,
 758             "method `{}` has {} but the declaration in \
 759                                         trait `{}` has {}",
 760             trait_m.ident,
 761             potentially_plural_count(impl_number_args, "parameter"),
 762             tcx.def_path_str(trait_m.def_id),
 763             trait_number_args
 764         );
 765         if let Some(trait_span) = trait_span {
 766             err.span_label(
 767                 trait_span,
 768                 format!(
 769                     "trait requires {}",
 770                     potentially_plural_count(trait_number_args, "parameter")
 771                 ),
 772             );
 773         } else {
 774             err.note_trait_signature(trait_m.ident.to_string(), trait_m.signature(tcx));
 775         }
 776         err.span_label(
 777             impl_span,
 778             format!(
 779                 "expected {}, found {}",
 780                 potentially_plural_count(trait_number_args, "parameter"),
 781                 impl_number_args
 782             ),
 783         );
 784         err.emit();
 785         return Err(ErrorReported);
 786     }
 787
 788     Ok(())
 789 }
 790
 791 fn compare_synthetic_generics<'tcx>(
 792     tcx: TyCtxt<'tcx>,
 793     impl_m: &ty::AssocItem,
 794     trait_m: &ty::AssocItem,
 795 ) -> Result<(), ErrorReported> {
 796     // FIXME(chrisvittal) Clean up this function, list of FIXME items:
 797     //     1. Better messages for the span labels
 798     //     2. Explanation as to what is going on
 799     // If we get here, we already have the same number of generics, so the zip will
 800     // be okay.
 801     let mut error_found = false;
 802     let impl_m_generics = tcx.generics_of(impl_m.def_id);
 803     let trait_m_generics = tcx.generics_of(trait_m.def_id);
 804     let impl_m_type_params = impl_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     let trait_m_type_params = trait_m_generics.params.iter().filter_map(|param| match param.kind {
 809         GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
 810         GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None,
 811     });
 812     for ((impl_def_id, impl_synthetic), (trait_def_id, trait_synthetic)) in
 813         impl_m_type_params.zip(trait_m_type_params)
 814     {
 815         if impl_synthetic != trait_synthetic {
 816             let impl_hir_id = tcx.hir().as_local_hir_id(impl_def_id).unwrap();
 817             let impl_span = tcx.hir().span(impl_hir_id);
 818             let trait_span = tcx.def_span(trait_def_id);
 819             let mut err = struct_span_err!(
 820                 tcx.sess,
 821                 impl_span,
 822                 E0643,
 823                 "method `{}` has incompatible signature for trait",
 824                 trait_m.ident
 825             );
 826             err.span_label(trait_span, "declaration in trait here");
 827             match (impl_synthetic, trait_synthetic) {
 828                 // The case where the impl method uses `impl Trait` but the trait method uses
 829                 // explicit generics
 830                 (Some(hir::SyntheticTyParamKind::ImplTrait), None) => {
 831                     err.span_label(impl_span, "expected generic parameter, found `impl Trait`");
 832                     (|| {
 833                         // try taking the name from the trait impl
 834                         // FIXME: this is obviously suboptimal since the name can already be used
 835                         // as another generic argument
 836                         let new_name = tcx.sess.source_map().span_to_snippet(trait_span).ok()?;
 837                         let trait_m = tcx.hir().as_local_hir_id(trait_m.def_id)?;
 838                         let trait_m = tcx.hir().trait_item(hir::TraitItemId { hir_id: trait_m });
 839
 840                         let impl_m = tcx.hir().as_local_hir_id(impl_m.def_id)?;
 841                         let impl_m = tcx.hir().impl_item(hir::ImplItemId { hir_id: impl_m });
 842
 843                         // in case there are no generics, take the spot between the function name
 844                         // and the opening paren of the argument list
 845                         let new_generics_span =
 846                             tcx.sess.source_map().generate_fn_name_span(impl_span)?.shrink_to_hi();
 847                         // in case there are generics, just replace them
 848                         let generics_span =
 849                             impl_m.generics.span.substitute_dummy(new_generics_span);
 850                         // replace with the generics from the trait
 851                         let new_generics =
 852                             tcx.sess.source_map().span_to_snippet(trait_m.generics.span).ok()?;
 853
 854                         err.multipart_suggestion(
 855                             "try changing the `impl Trait` argument to a generic parameter",
 856                             vec![
 857                                 // replace `impl Trait` with `T`
 858                                 (impl_span, new_name),
 859                                 // replace impl method generics with trait method generics
 860                                 // This isn't quite right, as users might have changed the names
 861                                 // of the generics, but it works for the common case
 862                                 (generics_span, new_generics),
 863                             ],
 864                             Applicability::MaybeIncorrect,
 865                         );
 866                         Some(())
 867                     })();
 868                 }
 869                 // The case where the trait method uses `impl Trait`, but the impl method uses
 870                 // explicit generics.
 871                 (None, Some(hir::SyntheticTyParamKind::ImplTrait)) => {
 872                     err.span_label(impl_span, "expected `impl Trait`, found generic parameter");
 873                     (|| {
 874                         let impl_m = tcx.hir().as_local_hir_id(impl_m.def_id)?;
 875                         let impl_m = tcx.hir().impl_item(hir::ImplItemId { hir_id: impl_m });
 876                         let input_tys = match impl_m.kind {
 877                             hir::ImplItemKind::Method(ref sig, _) => sig.decl.inputs,
 878                             _ => unreachable!(),
 879                         };
 880                         struct Visitor(Option<Span>, hir::def_id::DefId);
 881                         impl<'v> intravisit::Visitor<'v> for Visitor {
 882                             fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
 883                                 intravisit::walk_ty(self, ty);
 884                                 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) =
 885                                     ty.kind
 886                                 {
 887                                     if let Res::Def(DefKind::TyParam, def_id) = path.res {
 888                                         if def_id == self.1 {
 889                                             self.0 = Some(ty.span);
 890                                         }
 891                                     }
 892                                 }
 893                             }
 894                             fn nested_visit_map<'this>(
 895                                 &'this mut self,
 896                             ) -> intravisit::NestedVisitorMap<'this, 'v>
 897                             {
 898                                 intravisit::NestedVisitorMap::None
 899                             }
 900                         }
 901                         let mut visitor = Visitor(None, impl_def_id);
 902                         for ty in input_tys {
 903                             intravisit::Visitor::visit_ty(&mut visitor, ty);
 904                         }
 905                         let span = visitor.0?;
 906
 907                         let bounds =
 908                             impl_m.generics.params.iter().find_map(|param| match param.kind {
 909                                 GenericParamKind::Lifetime { .. } => None,
 910                                 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
 911                                     if param.hir_id == impl_hir_id {
 912                                         Some(&param.bounds)
 913                                     } else {
 914                                         None
 915                                     }
 916                                 }
 917                             })?;
 918                         let bounds = bounds.first()?.span().to(bounds.last()?.span());
 919                         let bounds = tcx.sess.source_map().span_to_snippet(bounds).ok()?;
 920
 921                         err.multipart_suggestion(
 922                             "try removing the generic parameter and using `impl Trait` instead",
 923                             vec![
 924                                 // delete generic parameters
 925                                 (impl_m.generics.span, String::new()),
 926                                 // replace param usage with `impl Trait`
 927                                 (span, format!("impl {}", bounds)),
 928                             ],
 929                             Applicability::MaybeIncorrect,
 930                         );
 931                         Some(())
 932                     })();
 933                 }
 934                 _ => unreachable!(),
 935             }
 936             err.emit();
 937             error_found = true;
 938         }
 939     }
 940     if error_found { Err(ErrorReported) } else { Ok(()) }
 941 }
 942
 943 crate fn compare_const_impl<'tcx>(
 944     tcx: TyCtxt<'tcx>,
 945     impl_c: &ty::AssocItem,
 946     impl_c_span: Span,
 947     trait_c: &ty::AssocItem,
 948     impl_trait_ref: ty::TraitRef<'tcx>,
 949 ) {
 950     debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref);
 951
 952     tcx.infer_ctxt().enter(|infcx| {
 953         let param_env = tcx.param_env(impl_c.def_id);
 954         let inh = Inherited::new(infcx, impl_c.def_id);
 955         let infcx = &inh.infcx;
 956
 957         // The below is for the most part highly similar to the procedure
 958         // for methods above. It is simpler in many respects, especially
 959         // because we shouldn't really have to deal with lifetimes or
 960         // predicates. In fact some of this should probably be put into
 961         // shared functions because of DRY violations...
 962         let trait_to_impl_substs = impl_trait_ref.substs;
 963
 964         // Create a parameter environment that represents the implementation's
 965         // method.
 966         let impl_c_hir_id = tcx.hir().as_local_hir_id(impl_c.def_id).unwrap();
 967
 968         // Compute placeholder form of impl and trait const tys.
 969         let impl_ty = tcx.type_of(impl_c.def_id);
 970         let trait_ty = tcx.type_of(trait_c.def_id).subst(tcx, trait_to_impl_substs);
 971         let mut cause = ObligationCause::misc(impl_c_span, impl_c_hir_id);
 972
 973         // There is no "body" here, so just pass dummy id.
 974         let impl_ty =
 975             inh.normalize_associated_types_in(impl_c_span, impl_c_hir_id, param_env, &impl_ty);
 976
 977         debug!("compare_const_impl: impl_ty={:?}", impl_ty);
 978
 979         let trait_ty =
 980             inh.normalize_associated_types_in(impl_c_span, impl_c_hir_id, param_env, &trait_ty);
 981
 982         debug!("compare_const_impl: trait_ty={:?}", trait_ty);
 983
 984         let err = infcx
 985             .at(&cause, param_env)
 986             .sup(trait_ty, impl_ty)
 987             .map(|ok| inh.register_infer_ok_obligations(ok));
 988
 989         if let Err(terr) = err {
 990             debug!(
 991                 "checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
 992                 impl_ty, trait_ty
 993             );
 994
 995             // Locate the Span containing just the type of the offending impl
 996             match tcx.hir().expect_impl_item(impl_c_hir_id).kind {
 997                 ImplItemKind::Const(ref ty, _) => cause.span = ty.span,
 998                 _ => bug!("{:?} is not a impl const", impl_c),
 999             }
1000
1001             let mut diag = struct_span_err!(
1002                 tcx.sess,
1003                 cause.span,
1004                 E0326,
1005                 "implemented const `{}` has an incompatible type for \
1006                                              trait",
1007                 trait_c.ident
1008             );
1009
1010             let trait_c_hir_id = tcx.hir().as_local_hir_id(trait_c.def_id);
1011             let trait_c_span = trait_c_hir_id.map(|trait_c_hir_id| {
1012                 // Add a label to the Span containing just the type of the const
1013                 match tcx.hir().expect_trait_item(trait_c_hir_id).kind {
1014                     TraitItemKind::Const(ref ty, _) => ty.span,
1015                     _ => bug!("{:?} is not a trait const", trait_c),
1016                 }
1017             });
1018
1019             infcx.note_type_err(
1020                 &mut diag,
1021                 &cause,
1022                 trait_c_span.map(|span| (span, "type in trait".to_owned())),
1023                 Some(infer::ValuePairs::Types(ExpectedFound {
1024                     expected: trait_ty,
1025                     found: impl_ty,
1026                 })),
1027                 &terr,
1028             );
1029             diag.emit();
1030         }
1031
1032         // Check that all obligations are satisfied by the implementation's
1033         // version.
1034         if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
1035             infcx.report_fulfillment_errors(errors, None, false);
1036             return;
1037         }
1038
1039         let fcx = FnCtxt::new(&inh, param_env, impl_c_hir_id);
1040         fcx.regionck_item(impl_c_hir_id, impl_c_span, &[]);
1041     });
1042 }
1043
1044 crate fn compare_ty_impl<'tcx>(
1045     tcx: TyCtxt<'tcx>,
1046     impl_ty: &ty::AssocItem,
1047     impl_ty_span: Span,
1048     trait_ty: &ty::AssocItem,
1049     impl_trait_ref: ty::TraitRef<'tcx>,
1050     trait_item_span: Option<Span>,
1051 ) {
1052     debug!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref);
1053
1054     let _: Result<(), ErrorReported> = (|| {
1055         compare_number_of_generics(tcx, impl_ty, impl_ty_span, trait_ty, trait_item_span)?;
1056
1057         compare_type_predicate_entailment(tcx, impl_ty, impl_ty_span, trait_ty, impl_trait_ref)
1058     })();
1059 }
1060
1061 /// The equivalent of [compare_predicate_entailment], but for associated types
1062 /// instead of associated functions.
1063 fn compare_type_predicate_entailment(
1064     tcx: TyCtxt<'tcx>,
1065     impl_ty: &ty::AssocItem,
1066     impl_ty_span: Span,
1067     trait_ty: &ty::AssocItem,
1068     impl_trait_ref: ty::TraitRef<'tcx>,
1069 ) -> Result<(), ErrorReported> {
1070     let impl_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1071     let trait_to_impl_substs =
1072         impl_substs.rebase_onto(tcx, impl_ty.container.id(), impl_trait_ref.substs);
1073
1074     let impl_ty_generics = tcx.generics_of(impl_ty.def_id);
1075     let trait_ty_generics = tcx.generics_of(trait_ty.def_id);
1076     let impl_ty_predicates = tcx.predicates_of(impl_ty.def_id);
1077     let trait_ty_predicates = tcx.predicates_of(trait_ty.def_id);
1078
1079     check_region_bounds_on_impl_item(
1080         tcx,
1081         impl_ty_span,
1082         impl_ty,
1083         trait_ty,
1084         &trait_ty_generics,
1085         &impl_ty_generics,
1086     )?;
1087
1088     let impl_ty_own_bounds = impl_ty_predicates.instantiate_own(tcx, impl_substs);
1089
1090     if impl_ty_own_bounds.is_empty() {
1091         // Nothing to check.
1092         return Ok(());
1093     }
1094
1095     // This `HirId` should be used for the `body_id` field on each
1096     // `ObligationCause` (and the `FnCtxt`). This is what
1097     // `regionck_item` expects.
1098     let impl_ty_hir_id = tcx.hir().as_local_hir_id(impl_ty.def_id).unwrap();
1099     let cause = ObligationCause {
1100         span: impl_ty_span,
1101         body_id: impl_ty_hir_id,
1102         code: ObligationCauseCode::CompareImplTypeObligation {
1103             item_name: impl_ty.ident.name,
1104             impl_item_def_id: impl_ty.def_id,
1105             trait_item_def_id: trait_ty.def_id,
1106         },
1107     };
1108
1109     debug!("compare_type_predicate_entailment: trait_to_impl_substs={:?}", trait_to_impl_substs);
1110
1111     // The predicates declared by the impl definition, the trait and the
1112     // associated type in the trait are assumed.
1113     let impl_predicates = tcx.predicates_of(impl_ty_predicates.parent.unwrap());
1114     let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
1115     hybrid_preds
1116         .predicates
1117         .extend(trait_ty_predicates.instantiate_own(tcx, trait_to_impl_substs).predicates);
1118
1119     debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds);
1120
1121     let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_hir_id);
1122     let param_env = ty::ParamEnv::new(
1123         tcx.intern_predicates(&hybrid_preds.predicates),
1124         Reveal::UserFacing,
1125         None,
1126     );
1127     let param_env = traits::normalize_param_env_or_error(
1128         tcx,
1129         impl_ty.def_id,
1130         param_env,
1131         normalize_cause.clone(),
1132     );
1133     tcx.infer_ctxt().enter(|infcx| {
1134         let inh = Inherited::new(infcx, impl_ty.def_id);
1135         let infcx = &inh.infcx;
1136
1137         debug!("compare_type_predicate_entailment: caller_bounds={:?}", param_env.caller_bounds);
1138
1139         let mut selcx = traits::SelectionContext::new(&infcx);
1140
1141         for predicate in impl_ty_own_bounds.predicates {
1142             let traits::Normalized { value: predicate, obligations } =
1143                 traits::normalize(&mut selcx, param_env, normalize_cause.clone(), &predicate);
1144
1145             inh.register_predicates(obligations);
1146             inh.register_predicate(traits::Obligation::new(cause.clone(), param_env, predicate));
1147         }
1148
1149         // Check that all obligations are satisfied by the implementation's
1150         // version.
1151         if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
1152             infcx.report_fulfillment_errors(errors, None, false);
1153             return Err(ErrorReported);
1154         }
1155
1156         // Finally, resolve all regions. This catches wily misuses of
1157         // lifetime parameters.
1158         let fcx = FnCtxt::new(&inh, param_env, impl_ty_hir_id);
1159         fcx.regionck_item(impl_ty_hir_id, impl_ty_span, &[]);
1160
1161         Ok(())
1162     })
1163 }
1164
1165 fn assoc_item_kind_str(impl_item: &ty::AssocItem) -> &'static str {
1166     match impl_item.kind {
1167         ty::AssocKind::Const => "const",
1168         ty::AssocKind::Method => "method",
1169         ty::AssocKind::Type | ty::AssocKind::OpaqueTy => "type",
1170     }
1171 }