src/librustc_typeck/check/compare_method.rs

   1 use errors::{pluralize, struct_span_err, 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
  15 use super::{potentially_plural_count, FnCtxt, Inherited};
  16
  17 use rustc_error_codes::*;
  18
  19 /// Checks that a method from an impl conforms to the signature of
  20 /// the same method as declared in the trait.
  21 ///
  22 /// # Parameters
  23 ///
  24 /// - `impl_m`: type of the method we are checking
  25 /// - `impl_m_span`: span to use for reporting errors
  26 /// - `trait_m`: the method in the trait
  27 /// - `impl_trait_ref`: the TraitRef corresponding to the trait implementation
  28
  29 crate fn compare_impl_method<'tcx>(
  30     tcx: TyCtxt<'tcx>,
  31     impl_m: &ty::AssocItem,
  32     impl_m_span: Span,
  33     trait_m: &ty::AssocItem,
  34     impl_trait_ref: ty::TraitRef<'tcx>,
  35     trait_item_span: Option<Span>,
  36 ) {
  37     debug!("compare_impl_method(impl_trait_ref={:?})", impl_trait_ref);
  38
  39     let impl_m_span = tcx.sess.source_map().def_span(impl_m_span);
  40
  41     if let Err(ErrorReported) = compare_self_type(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref)
  42     {
  43         return;
  44     }
  45
  46     if let Err(ErrorReported) =
  47         compare_number_of_generics(tcx, impl_m, impl_m_span, trait_m, trait_item_span)
  48     {
  49         return;
  50     }
  51
  52     if let Err(ErrorReported) =
  53         compare_number_of_method_arguments(tcx, impl_m, impl_m_span, trait_m, trait_item_span)
  54     {
  55         return;
  56     }
  57
  58     if let Err(ErrorReported) = compare_synthetic_generics(tcx, impl_m, trait_m) {
  59         return;
  60     }
  61
  62     if let Err(ErrorReported) =
  63         compare_predicate_entailment(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref)
  64     {
  65         return;
  66     }
  67 }
  68
  69 fn compare_predicate_entailment<'tcx>(
  70     tcx: TyCtxt<'tcx>,
  71     impl_m: &ty::AssocItem,
  72     impl_m_span: Span,
  73     trait_m: &ty::AssocItem,
  74     impl_trait_ref: ty::TraitRef<'tcx>,
  75 ) -> Result<(), ErrorReported> {
  76     let trait_to_impl_substs = impl_trait_ref.substs;
  77
  78     // This node-id should be used for the `body_id` field on each
  79     // `ObligationCause` (and the `FnCtxt`). This is what
  80     // `regionck_item` expects.
  81     let impl_m_hir_id = tcx.hir().as_local_hir_id(impl_m.def_id).unwrap();
  82
  83     let cause = ObligationCause {
  84         span: impl_m_span,
  85         body_id: impl_m_hir_id,
  86         code: ObligationCauseCode::CompareImplMethodObligation {
  87             item_name: impl_m.ident.name,
  88             impl_item_def_id: impl_m.def_id,
  89             trait_item_def_id: trait_m.def_id,
  90         },
  91     };
  92
  93     // This code is best explained by example. Consider a trait:
  94     //
  95     //     trait Trait<'t,T> {
  96     //          fn method<'a,M>(t: &'t T, m: &'a M) -> Self;
  97     //     }
  98     //
  99     // And an impl:
 100     //
 101     //     impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
 102     //          fn method<'b,N>(t: &'j &'i U, m: &'b N) -> Foo;
 103     //     }
 104     //
 105     // We wish to decide if those two method types are compatible.
 106     //
 107     // We start out with trait_to_impl_substs, that maps the trait
 108     // type parameters to impl type parameters. This is taken from the
 109     // impl trait reference:
 110     //
 111     //     trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
 112     //
 113     // We create a mapping `dummy_substs` that maps from the impl type
 114     // parameters to fresh types and regions. For type parameters,
 115     // this is the identity transform, but we could as well use any
 116     // placeholder types. For regions, we convert from bound to free
 117     // regions (Note: but only early-bound regions, i.e., those
 118     // declared on the impl or used in type parameter bounds).
 119     //
 120     //     impl_to_skol_substs = {'i => 'i0, U => U0, N => N0 }
 121     //
 122     // Now we can apply skol_substs to the type of the impl method
 123     // to yield a new function type in terms of our fresh, placeholder
 124     // types:
 125     //
 126     //     <'b> fn(t: &'i0 U0, m: &'b) -> Foo
 127     //
 128     // We now want to extract and substitute the type of the *trait*
 129     // method and compare it. To do so, we must create a compound
 130     // substitution by combining trait_to_impl_substs and
 131     // impl_to_skol_substs, and also adding a mapping for the method
 132     // type parameters. We extend the mapping to also include
 133     // the method parameters.
 134     //
 135     //     trait_to_skol_substs = { T => &'i0 U0, Self => Foo, M => N0 }
 136     //
 137     // Applying this to the trait method type yields:
 138     //
 139     //     <'a> fn(t: &'i0 U0, m: &'a) -> Foo
 140     //
 141     // This type is also the same but the name of the bound region ('a
 142     // vs 'b).  However, the normal subtyping rules on fn types handle
 143     // this kind of equivalency just fine.
 144     //
 145     // We now use these substitutions to ensure that all declared bounds are
 146     // satisfied by the implementation's method.
 147     //
 148     // We do this by creating a parameter environment which contains a
 149     // substitution corresponding to impl_to_skol_substs. We then build
 150     // trait_to_skol_substs and use it to convert the predicates contained
 151     // in the trait_m.generics to the placeholder form.
 152     //
 153     // Finally we register each of these predicates as an obligation in
 154     // a fresh FulfillmentCtxt, and invoke select_all_or_error.
 155
 156     // Create mapping from impl to placeholder.
 157     let impl_to_skol_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
 158
 159     // Create mapping from trait to placeholder.
 160     let trait_to_skol_substs =
 161         impl_to_skol_substs.rebase_onto(tcx, impl_m.container.id(), trait_to_impl_substs);
 162     debug!("compare_impl_method: trait_to_skol_substs={:?}", trait_to_skol_substs);
 163
 164     let impl_m_generics = tcx.generics_of(impl_m.def_id);
 165     let trait_m_generics = tcx.generics_of(trait_m.def_id);
 166     let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
 167     let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
 168
 169     // Check region bounds.
 170     check_region_bounds_on_impl_item(
 171         tcx,
 172         impl_m_span,
 173         impl_m,
 174         trait_m,
 175         &trait_m_generics,
 176         &impl_m_generics,
 177     )?;
 178
 179     // Create obligations for each predicate declared by the impl
 180     // definition in the context of the trait's parameter
 181     // environment. We can't just use `impl_env.caller_bounds`,
 182     // however, because we want to replace all late-bound regions with
 183     // region variables.
 184     let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap());
 185     let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
 186
 187     debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
 188
 189     // This is the only tricky bit of the new way we check implementation methods
 190     // We need to build a set of predicates where only the method-level bounds
 191     // are from the trait and we assume all other bounds from the implementation
 192     // to be previously satisfied.
 193     //
 194     // We then register the obligations from the impl_m and check to see
 195     // if all constraints hold.
 196     hybrid_preds
 197         .predicates
 198         .extend(trait_m_predicates.instantiate_own(tcx, trait_to_skol_substs).predicates);
 199
 200     // Construct trait parameter environment and then shift it into the placeholder viewpoint.
 201     // The key step here is to update the caller_bounds's predicates to be
 202     // the new hybrid bounds we computed.
 203     let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_hir_id);
 204     let param_env = ty::ParamEnv::new(
 205         tcx.intern_predicates(&hybrid_preds.predicates),
 206         Reveal::UserFacing,
 207         None,
 208     );
 209     let param_env = traits::normalize_param_env_or_error(
 210         tcx,
 211         impl_m.def_id,
 212         param_env,
 213         normalize_cause.clone(),
 214     );
 215
 216     tcx.infer_ctxt().enter(|infcx| {
 217         let inh = Inherited::new(infcx, impl_m.def_id);
 218         let infcx = &inh.infcx;
 219
 220         debug!("compare_impl_method: caller_bounds={:?}", param_env.caller_bounds);
 221
 222         let mut selcx = traits::SelectionContext::new(&infcx);
 223
 224         let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_skol_substs);
 225         let (impl_m_own_bounds, _) = infcx.replace_bound_vars_with_fresh_vars(
 226             impl_m_span,
 227             infer::HigherRankedType,
 228             &ty::Binder::bind(impl_m_own_bounds.predicates),
 229         );
 230         for predicate in impl_m_own_bounds {
 231             let traits::Normalized { value: predicate, obligations } =
 232                 traits::normalize(&mut selcx, param_env, normalize_cause.clone(), &predicate);
 233
 234             inh.register_predicates(obligations);
 235             inh.register_predicate(traits::Obligation::new(cause.clone(), param_env, predicate));
 236         }
 237
 238         // We now need to check that the signature of the impl method is
 239         // compatible with that of the trait method. We do this by
 240         // checking that `impl_fty <: trait_fty`.
 241         //
 242         // FIXME. Unfortunately, this doesn't quite work right now because
 243         // associated type normalization is not integrated into subtype
 244         // checks. For the comparison to be valid, we need to
 245         // normalize the associated types in the impl/trait methods
 246         // first. However, because function types bind regions, just
 247         // calling `normalize_associated_types_in` would have no effect on
 248         // any associated types appearing in the fn arguments or return
 249         // type.
 250
 251         // Compute placeholder form of impl and trait method tys.
 252         let tcx = infcx.tcx;
 253
 254         let (impl_sig, _) = infcx.replace_bound_vars_with_fresh_vars(
 255             impl_m_span,
 256             infer::HigherRankedType,
 257             &tcx.fn_sig(impl_m.def_id),
 258         );
 259         let impl_sig =
 260             inh.normalize_associated_types_in(impl_m_span, impl_m_hir_id, param_env, &impl_sig);
 261         let impl_fty = tcx.mk_fn_ptr(ty::Binder::bind(impl_sig));
 262         debug!("compare_impl_method: impl_fty={:?}", impl_fty);
 263
 264         let trait_sig = tcx.liberate_late_bound_regions(impl_m.def_id, &tcx.fn_sig(trait_m.def_id));
 265         let trait_sig = trait_sig.subst(tcx, trait_to_skol_substs);
 266         let trait_sig =
 267             inh.normalize_associated_types_in(impl_m_span, impl_m_hir_id, param_env, &trait_sig);
 268         let trait_fty = tcx.mk_fn_ptr(ty::Binder::bind(trait_sig));
 269
 270         debug!("compare_impl_method: trait_fty={:?}", trait_fty);
 271
 272         let sub_result = infcx.at(&cause, param_env).sup(trait_fty, impl_fty).map(
 273             |InferOk { obligations, .. }| {
 274                 inh.register_predicates(obligations);
 275             },
 276         );
 277
 278         if let Err(terr) = sub_result {
 279             debug!("sub_types failed: impl ty {:?}, trait ty {:?}", impl_fty, trait_fty);
 280
 281             let (impl_err_span, trait_err_span) = extract_spans_for_error_reporting(
 282                 &infcx, param_env, &terr, &cause, impl_m, impl_sig, trait_m, trait_sig,
 283             );
 284
 285             let cause = ObligationCause { span: impl_err_span, ..cause };
 286
 287             let mut diag = struct_span_err!(
 288                 tcx.sess,
 289                 cause.span(tcx),
 290                 E0053,
 291                 "method `{}` has an incompatible type for trait",
 292                 trait_m.ident
 293             );
 294             if let TypeError::Mutability = terr {
 295                 if let Some(trait_err_span) = trait_err_span {
 296                     if let Ok(trait_err_str) = tcx.sess.source_map().span_to_snippet(trait_err_span)
 297                     {
 298                         diag.span_suggestion(
 299                             impl_err_span,
 300                             "consider change the type to match the mutability in trait",
 301                             trait_err_str,
 302                             Applicability::MachineApplicable,
 303                         );
 304                     }
 305                 }
 306             }
 307
 308             infcx.note_type_err(
 309                 &mut diag,
 310                 &cause,
 311                 trait_err_span.map(|sp| (sp, "type in trait".to_owned())),
 312                 Some(infer::ValuePairs::Types(ExpectedFound {
 313                     expected: trait_fty,
 314                     found: impl_fty,
 315                 })),
 316                 &terr,
 317             );
 318             diag.emit();
 319             return Err(ErrorReported);
 320         }
 321
 322         // Check that all obligations are satisfied by the implementation's
 323         // version.
 324         if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
 325             infcx.report_fulfillment_errors(errors, None, false);
 326             return Err(ErrorReported);
 327         }
 328
 329         // Finally, resolve all regions. This catches wily misuses of
 330         // lifetime parameters.
 331         let fcx = FnCtxt::new(&inh, param_env, impl_m_hir_id);
 332         fcx.regionck_item(impl_m_hir_id, impl_m_span, &[]);
 333
 334         Ok(())
 335     })
 336 }
 337
 338 fn check_region_bounds_on_impl_item<'tcx>(
 339     tcx: TyCtxt<'tcx>,
 340     span: Span,
 341     impl_m: &ty::AssocItem,
 342     trait_m: &ty::AssocItem,
 343     trait_generics: &ty::Generics,
 344     impl_generics: &ty::Generics,
 345 ) -> Result<(), ErrorReported> {
 346     let trait_params = trait_generics.own_counts().lifetimes;
 347     let impl_params = impl_generics.own_counts().lifetimes;
 348
 349     debug!(
 350         "check_region_bounds_on_impl_item: \
 351             trait_generics={:?} \
 352             impl_generics={:?}",
 353         trait_generics, impl_generics
 354     );
 355
 356     // Must have same number of early-bound lifetime parameters.
 357     // Unfortunately, if the user screws up the bounds, then this
 358     // will change classification between early and late.  E.g.,
 359     // if in trait we have `<'a,'b:'a>`, and in impl we just have
 360     // `<'a,'b>`, then we have 2 early-bound lifetime parameters
 361     // in trait but 0 in the impl. But if we report "expected 2
 362     // but found 0" it's confusing, because it looks like there
 363     // are zero. Since I don't quite know how to phrase things at
 364     // the moment, give a kind of vague error message.
 365     if trait_params != impl_params {
 366         let item_kind = assoc_item_kind_str(impl_m);
 367         let def_span = tcx.sess.source_map().def_span(span);
 368         let span = tcx.hir().get_generics(impl_m.def_id).map(|g| g.span).unwrap_or(def_span);
 369         let mut err = struct_span_err!(
 370             tcx.sess,
 371             span,
 372             E0195,
 373             "lifetime parameters or bounds on {} `{}` do not match the trait declaration",
 374             item_kind,
 375             impl_m.ident,
 376         );
 377         err.span_label(span, &format!("lifetimes do not match {} in trait", item_kind));
 378         if let Some(sp) = tcx.hir().span_if_local(trait_m.def_id) {
 379             let def_sp = tcx.sess.source_map().def_span(sp);
 380             let sp = tcx.hir().get_generics(trait_m.def_id).map(|g| g.span).unwrap_or(def_sp);
 381             err.span_label(
 382                 sp,
 383                 &format!("lifetimes in impl do not match this {} in trait", item_kind),
 384             );
 385         }
 386         err.emit();
 387         return Err(ErrorReported);
 388     }
 389
 390     Ok(())
 391 }
 392
 393 fn extract_spans_for_error_reporting<'a, 'tcx>(
 394     infcx: &infer::InferCtxt<'a, 'tcx>,
 395     param_env: ty::ParamEnv<'tcx>,
 396     terr: &TypeError<'_>,
 397     cause: &ObligationCause<'tcx>,
 398     impl_m: &ty::AssocItem,
 399     impl_sig: ty::FnSig<'tcx>,
 400     trait_m: &ty::AssocItem,
 401     trait_sig: ty::FnSig<'tcx>,
 402 ) -> (Span, Option<Span>) {
 403     let tcx = infcx.tcx;
 404     let impl_m_hir_id = tcx.hir().as_local_hir_id(impl_m.def_id).unwrap();
 405     let (impl_m_output, impl_m_iter) = match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
 406         ImplItemKind::Method(ref impl_m_sig, _) => {
 407             (&impl_m_sig.decl.output, impl_m_sig.decl.inputs.iter())
 408         }
 409         _ => bug!("{:?} is not a method", impl_m),
 410     };
 411
 412     match *terr {
 413         TypeError::Mutability => {
 414             if let Some(trait_m_hir_id) = tcx.hir().as_local_hir_id(trait_m.def_id) {
 415                 let trait_m_iter = match tcx.hir().expect_trait_item(trait_m_hir_id).kind {
 416                     TraitItemKind::Method(ref trait_m_sig, _) => trait_m_sig.decl.inputs.iter(),
 417                     _ => bug!("{:?} is not a TraitItemKind::Method", trait_m),
 418                 };
 419
 420                 impl_m_iter
 421                     .zip(trait_m_iter)
 422                     .find(|&(ref impl_arg, ref trait_arg)| {
 423                         match (&impl_arg.kind, &trait_arg.kind) {
 424                             (
 425                                 &hir::TyKind::Rptr(_, ref impl_mt),
 426                                 &hir::TyKind::Rptr(_, ref trait_mt),
 427                             )
 428                             | (&hir::TyKind::Ptr(ref impl_mt), &hir::TyKind::Ptr(ref trait_mt)) => {
 429                                 impl_mt.mutbl != trait_mt.mutbl
 430                             }
 431                             _ => false,
 432                         }
 433                     })
 434                     .map(|(ref impl_arg, ref trait_arg)| (impl_arg.span, Some(trait_arg.span)))
 435                     .unwrap_or_else(|| (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id)))
 436             } else {
 437                 (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
 438             }
 439         }
 440         TypeError::Sorts(ExpectedFound { .. }) => {
 441             if let Some(trait_m_hir_id) = tcx.hir().as_local_hir_id(trait_m.def_id) {
 442                 let (trait_m_output, trait_m_iter) =
 443                     match tcx.hir().expect_trait_item(trait_m_hir_id).kind {
 444                         TraitItemKind::Method(ref trait_m_sig, _) => {
 445                             (&trait_m_sig.decl.output, trait_m_sig.decl.inputs.iter())
 446                         }
 447                         _ => bug!("{:?} is not a TraitItemKind::Method", 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                     .filter_map(
 457                         |(((&impl_arg_ty, &trait_arg_ty), impl_arg), trait_arg)| match infcx
 458                             .at(&cause, param_env)
 459                             .sub(trait_arg_ty, impl_arg_ty)
 460                         {
 461                             Ok(_) => None,
 462                             Err(_) => Some((impl_arg.span, Some(trait_arg.span))),
 463                         },
 464                     )
 465                     .next()
 466                     .unwrap_or_else(|| {
 467                         if infcx
 468                             .at(&cause, param_env)
 469                             .sup(trait_sig.output(), impl_sig.output())
 470                             .is_err()
 471                         {
 472                             (impl_m_output.span(), Some(trait_m_output.span()))
 473                         } else {
 474                             (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
 475                         }
 476                     })
 477             } else {
 478                 (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
 479             }
 480         }
 481         _ => (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id)),
 482     }
 483 }
 484
 485 fn compare_self_type<'tcx>(
 486     tcx: TyCtxt<'tcx>,
 487     impl_m: &ty::AssocItem,
 488     impl_m_span: Span,
 489     trait_m: &ty::AssocItem,
 490     impl_trait_ref: ty::TraitRef<'tcx>,
 491 ) -> Result<(), ErrorReported> {
 492     // Try to give more informative error messages about self typing
 493     // mismatches.  Note that any mismatch will also be detected
 494     // below, where we construct a canonical function type that
 495     // includes the self parameter as a normal parameter.  It's just
 496     // that the error messages you get out of this code are a bit more
 497     // inscrutable, particularly for cases where one method has no
 498     // self.
 499
 500     let self_string = |method: &ty::AssocItem| {
 501         let untransformed_self_ty = match method.container {
 502             ty::ImplContainer(_) => impl_trait_ref.self_ty(),
 503             ty::TraitContainer(_) => tcx.types.self_param,
 504         };
 505         let self_arg_ty = *tcx.fn_sig(method.def_id).input(0).skip_binder();
 506         let param_env = ty::ParamEnv::reveal_all();
 507
 508         tcx.infer_ctxt().enter(|infcx| {
 509             let self_arg_ty =
 510                 tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(self_arg_ty));
 511             let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty).is_ok();
 512             match ExplicitSelf::determine(self_arg_ty, can_eq_self) {
 513                 ExplicitSelf::ByValue => "self".to_owned(),
 514                 ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
 515                 ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(),
 516                 _ => format!("self: {}", self_arg_ty),
 517             }
 518         })
 519     };
 520
 521     match (trait_m.method_has_self_argument, impl_m.method_has_self_argument) {
 522         (false, false) | (true, true) => {}
 523
 524         (false, true) => {
 525             let self_descr = self_string(impl_m);
 526             let mut err = struct_span_err!(
 527                 tcx.sess,
 528                 impl_m_span,
 529                 E0185,
 530                 "method `{}` has a `{}` declaration in the impl, but \
 531                                             not in the trait",
 532                 trait_m.ident,
 533                 self_descr
 534             );
 535             err.span_label(impl_m_span, format!("`{}` used in impl", self_descr));
 536             if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
 537                 err.span_label(span, format!("trait method declared without `{}`", self_descr));
 538             } else {
 539                 err.note_trait_signature(trait_m.ident.to_string(), trait_m.signature(tcx));
 540             }
 541             err.emit();
 542             return Err(ErrorReported);
 543         }
 544
 545         (true, false) => {
 546             let self_descr = self_string(trait_m);
 547             let mut err = struct_span_err!(
 548                 tcx.sess,
 549                 impl_m_span,
 550                 E0186,
 551                 "method `{}` has a `{}` declaration in the trait, but \
 552                                             not in the impl",
 553                 trait_m.ident,
 554                 self_descr
 555             );
 556             err.span_label(impl_m_span, format!("expected `{}` in impl", self_descr));
 557             if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
 558                 err.span_label(span, format!("`{}` used in trait", self_descr));
 559             } else {
 560                 err.note_trait_signature(trait_m.ident.to_string(), trait_m.signature(tcx));
 561             }
 562             err.emit();
 563             return Err(ErrorReported);
 564         }
 565     }
 566
 567     Ok(())
 568 }
 569
 570 fn compare_number_of_generics<'tcx>(
 571     tcx: TyCtxt<'tcx>,
 572     impl_: &ty::AssocItem,
 573     _impl_span: Span,
 574     trait_: &ty::AssocItem,
 575     trait_span: Option<Span>,
 576 ) -> Result<(), ErrorReported> {
 577     let trait_own_counts = tcx.generics_of(trait_.def_id).own_counts();
 578     let impl_own_counts = tcx.generics_of(impl_.def_id).own_counts();
 579
 580     let matchings = [
 581         ("type", trait_own_counts.types, impl_own_counts.types),
 582         ("const", trait_own_counts.consts, impl_own_counts.consts),
 583     ];
 584
 585     let item_kind = assoc_item_kind_str(impl_);
 586
 587     let mut err_occurred = false;
 588     for &(kind, trait_count, impl_count) in &matchings {
 589         if impl_count != trait_count {
 590             err_occurred = true;
 591
 592             let (trait_spans, impl_trait_spans) =
 593                 if let Some(trait_hir_id) = tcx.hir().as_local_hir_id(trait_.def_id) {
 594                     let trait_item = tcx.hir().expect_trait_item(trait_hir_id);
 595                     if trait_item.generics.params.is_empty() {
 596                         (Some(vec![trait_item.generics.span]), vec![])
 597                     } else {
 598                         let arg_spans: Vec<Span> =
 599                             trait_item.generics.params.iter().map(|p| p.span).collect();
 600                         let impl_trait_spans: Vec<Span> = trait_item
 601                             .generics
 602                             .params
 603                             .iter()
 604                             .filter_map(|p| match p.kind {
 605                                 GenericParamKind::Type {
 606                                     synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
 607                                     ..
 608                                 } => Some(p.span),
 609                                 _ => None,
 610                             })
 611                             .collect();
 612                         (Some(arg_spans), impl_trait_spans)
 613                     }
 614                 } else {
 615                     (trait_span.map(|s| vec![s]), vec![])
 616                 };
 617
 618             let impl_hir_id = tcx.hir().as_local_hir_id(impl_.def_id).unwrap();
 619             let impl_item = tcx.hir().expect_impl_item(impl_hir_id);
 620             let impl_item_impl_trait_spans: Vec<Span> = impl_item
 621                 .generics
 622                 .params
 623                 .iter()
 624                 .filter_map(|p| match p.kind {
 625                     GenericParamKind::Type {
 626                         synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
 627                         ..
 628                     } => Some(p.span),
 629                     _ => None,
 630                 })
 631                 .collect();
 632             let spans = impl_item.generics.spans();
 633             let span = spans.primary_span();
 634
 635             let mut err = tcx.sess.struct_span_err_with_code(
 636                 spans,
 637                 &format!(
 638                     "{} `{}` has {} {kind} parameter{} but its trait \
 639                      declaration has {} {kind} parameter{}",
 640                     item_kind,
 641                     trait_.ident,
 642                     impl_count,
 643                     pluralize!(impl_count),
 644                     trait_count,
 645                     pluralize!(trait_count),
 646                     kind = kind,
 647                 ),
 648                 DiagnosticId::Error("E0049".into()),
 649             );
 650
 651             let mut suffix = None;
 652
 653             if let Some(spans) = trait_spans {
 654                 let mut spans = spans.iter();
 655                 if let Some(span) = spans.next() {
 656                     err.span_label(
 657                         *span,
 658                         format!(
 659                             "expected {} {} parameter{}",
 660                             trait_count,
 661                             kind,
 662                             pluralize!(trait_count),
 663                         ),
 664                     );
 665                 }
 666                 for span in spans {
 667                     err.span_label(*span, "");
 668                 }
 669             } else {
 670                 suffix = Some(format!(", expected {}", trait_count));
 671             }
 672
 673             if let Some(span) = span {
 674                 err.span_label(
 675                     span,
 676                     format!(
 677                         "found {} {} parameter{}{}",
 678                         impl_count,
 679                         kind,
 680                         pluralize!(impl_count),
 681                         suffix.unwrap_or_else(|| String::new()),
 682                     ),
 683                 );
 684             }
 685
 686             for span in impl_trait_spans.iter().chain(impl_item_impl_trait_spans.iter()) {
 687                 err.span_label(*span, "`impl Trait` introduces an implicit type parameter");
 688             }
 689
 690             err.emit();
 691         }
 692     }
 693
 694     if err_occurred { Err(ErrorReported) } else { Ok(()) }
 695 }
 696
 697 fn compare_number_of_method_arguments<'tcx>(
 698     tcx: TyCtxt<'tcx>,
 699     impl_m: &ty::AssocItem,
 700     impl_m_span: Span,
 701     trait_m: &ty::AssocItem,
 702     trait_item_span: Option<Span>,
 703 ) -> Result<(), ErrorReported> {
 704     let impl_m_fty = tcx.fn_sig(impl_m.def_id);
 705     let trait_m_fty = tcx.fn_sig(trait_m.def_id);
 706     let trait_number_args = trait_m_fty.inputs().skip_binder().len();
 707     let impl_number_args = impl_m_fty.inputs().skip_binder().len();
 708     if trait_number_args != impl_number_args {
 709         let trait_m_hir_id = tcx.hir().as_local_hir_id(trait_m.def_id);
 710         let trait_span = if let Some(trait_id) = trait_m_hir_id {
 711             match tcx.hir().expect_trait_item(trait_id).kind {
 712                 TraitItemKind::Method(ref trait_m_sig, _) => {
 713                     let pos = if trait_number_args > 0 { trait_number_args - 1 } else { 0 };
 714                     if let Some(arg) = trait_m_sig.decl.inputs.get(pos) {
 715                         Some(if pos == 0 {
 716                             arg.span
 717                         } else {
 718                             Span::new(
 719                                 trait_m_sig.decl.inputs[0].span.lo(),
 720                                 arg.span.hi(),
 721                                 arg.span.ctxt(),
 722                             )
 723                         })
 724                     } else {
 725                         trait_item_span
 726                     }
 727                 }
 728                 _ => bug!("{:?} is not a method", impl_m),
 729             }
 730         } else {
 731             trait_item_span
 732         };
 733         let impl_m_hir_id = tcx.hir().as_local_hir_id(impl_m.def_id).unwrap();
 734         let impl_span = match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
 735             ImplItemKind::Method(ref impl_m_sig, _) => {
 736                 let pos = if impl_number_args > 0 { impl_number_args - 1 } else { 0 };
 737                 if let Some(arg) = impl_m_sig.decl.inputs.get(pos) {
 738                     if pos == 0 {
 739                         arg.span
 740                     } else {
 741                         Span::new(
 742                             impl_m_sig.decl.inputs[0].span.lo(),
 743                             arg.span.hi(),
 744                             arg.span.ctxt(),
 745                         )
 746                     }
 747                 } else {
 748                     impl_m_span
 749                 }
 750             }
 751             _ => bug!("{:?} is not a method", impl_m),
 752         };
 753         let mut err = struct_span_err!(
 754             tcx.sess,
 755             impl_span,
 756             E0050,
 757             "method `{}` has {} but the declaration in \
 758                                         trait `{}` has {}",
 759             trait_m.ident,
 760             potentially_plural_count(impl_number_args, "parameter"),
 761             tcx.def_path_str(trait_m.def_id),
 762             trait_number_args
 763         );
 764         if let Some(trait_span) = trait_span {
 765             err.span_label(
 766                 trait_span,
 767                 format!(
 768                     "trait requires {}",
 769                     potentially_plural_count(trait_number_args, "parameter")
 770                 ),
 771             );
 772         } else {
 773             err.note_trait_signature(trait_m.ident.to_string(), trait_m.signature(tcx));
 774         }
 775         err.span_label(
 776             impl_span,
 777             format!(
 778                 "expected {}, found {}",
 779                 potentially_plural_count(trait_number_args, "parameter"),
 780                 impl_number_args
 781             ),
 782         );
 783         err.emit();
 784         return Err(ErrorReported);
 785     }
 786
 787     Ok(())
 788 }
 789
 790 fn compare_synthetic_generics<'tcx>(
 791     tcx: TyCtxt<'tcx>,
 792     impl_m: &ty::AssocItem,
 793     trait_m: &ty::AssocItem,
 794 ) -> Result<(), ErrorReported> {
 795     // FIXME(chrisvittal) Clean up this function, list of FIXME items:
 796     //     1. Better messages for the span labels
 797     //     2. Explanation as to what is going on
 798     // If we get here, we already have the same number of generics, so the zip will
 799     // be okay.
 800     let mut error_found = false;
 801     let impl_m_generics = tcx.generics_of(impl_m.def_id);
 802     let trait_m_generics = tcx.generics_of(trait_m.def_id);
 803     let impl_m_type_params = impl_m_generics.params.iter().filter_map(|param| match param.kind {
 804         GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
 805         GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None,
 806     });
 807     let trait_m_type_params = trait_m_generics.params.iter().filter_map(|param| match param.kind {
 808         GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
 809         GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None,
 810     });
 811     for ((impl_def_id, impl_synthetic), (trait_def_id, trait_synthetic)) in
 812         impl_m_type_params.zip(trait_m_type_params)
 813     {
 814         if impl_synthetic != trait_synthetic {
 815             let impl_hir_id = tcx.hir().as_local_hir_id(impl_def_id).unwrap();
 816             let impl_span = tcx.hir().span(impl_hir_id);
 817             let trait_span = tcx.def_span(trait_def_id);
 818             let mut err = struct_span_err!(
 819                 tcx.sess,
 820                 impl_span,
 821                 E0643,
 822                 "method `{}` has incompatible signature for trait",
 823                 trait_m.ident
 824             );
 825             err.span_label(trait_span, "declaration in trait here");
 826             match (impl_synthetic, trait_synthetic) {
 827                 // The case where the impl method uses `impl Trait` but the trait method uses
 828                 // explicit generics
 829                 (Some(hir::SyntheticTyParamKind::ImplTrait), None) => {
 830                     err.span_label(impl_span, "expected generic parameter, found `impl Trait`");
 831                     (|| {
 832                         // try taking the name from the trait impl
 833                         // FIXME: this is obviously suboptimal since the name can already be used
 834                         // as another generic argument
 835                         let new_name = tcx.sess.source_map().span_to_snippet(trait_span).ok()?;
 836                         let trait_m = tcx.hir().as_local_hir_id(trait_m.def_id)?;
 837                         let trait_m = tcx.hir().trait_item(hir::TraitItemId { hir_id: trait_m });
 838
 839                         let impl_m = tcx.hir().as_local_hir_id(impl_m.def_id)?;
 840                         let impl_m = tcx.hir().impl_item(hir::ImplItemId { hir_id: impl_m });
 841
 842                         // in case there are no generics, take the spot between the function name
 843                         // and the opening paren of the argument list
 844                         let new_generics_span =
 845                             tcx.sess.source_map().generate_fn_name_span(impl_span)?.shrink_to_hi();
 846                         // in case there are generics, just replace them
 847                         let generics_span =
 848                             impl_m.generics.span.substitute_dummy(new_generics_span);
 849                         // replace with the generics from the trait
 850                         let new_generics =
 851                             tcx.sess.source_map().span_to_snippet(trait_m.generics.span).ok()?;
 852
 853                         err.multipart_suggestion(
 854                             "try changing the `impl Trait` argument to a generic parameter",
 855                             vec![
 856                                 // replace `impl Trait` with `T`
 857                                 (impl_span, new_name),
 858                                 // replace impl method generics with trait method generics
 859                                 // This isn't quite right, as users might have changed the names
 860                                 // of the generics, but it works for the common case
 861                                 (generics_span, new_generics),
 862                             ],
 863                             Applicability::MaybeIncorrect,
 864                         );
 865                         Some(())
 866                     })();
 867                 }
 868                 // The case where the trait method uses `impl Trait`, but the impl method uses
 869                 // explicit generics.
 870                 (None, Some(hir::SyntheticTyParamKind::ImplTrait)) => {
 871                     err.span_label(impl_span, "expected `impl Trait`, found generic parameter");
 872                     (|| {
 873                         let impl_m = tcx.hir().as_local_hir_id(impl_m.def_id)?;
 874                         let impl_m = tcx.hir().impl_item(hir::ImplItemId { hir_id: impl_m });
 875                         let input_tys = match impl_m.kind {
 876                             hir::ImplItemKind::Method(ref sig, _) => sig.decl.inputs,
 877                             _ => unreachable!(),
 878                         };
 879                         struct Visitor(Option<Span>, hir::def_id::DefId);
 880                         impl<'v> intravisit::Visitor<'v> for Visitor {
 881                             fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
 882                                 intravisit::walk_ty(self, ty);
 883                                 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) =
 884                                     ty.kind
 885                                 {
 886                                     if let Res::Def(DefKind::TyParam, def_id) = path.res {
 887                                         if def_id == self.1 {
 888                                             self.0 = Some(ty.span);
 889                                         }
 890                                     }
 891                                 }
 892                             }
 893                             fn nested_visit_map<'this>(
 894                                 &'this mut self,
 895                             ) -> intravisit::NestedVisitorMap<'this, 'v>
 896                             {
 897                                 intravisit::NestedVisitorMap::None
 898                             }
 899                         }
 900                         let mut visitor = Visitor(None, impl_def_id);
 901                         for ty in input_tys {
 902                             intravisit::Visitor::visit_ty(&mut visitor, ty);
 903                         }
 904                         let span = visitor.0?;
 905
 906                         let bounds =
 907                             impl_m.generics.params.iter().find_map(|param| match param.kind {
 908                                 GenericParamKind::Lifetime { .. } => None,
 909                                 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
 910                                     if param.hir_id == impl_hir_id {
 911                                         Some(&param.bounds)
 912                                     } else {
 913                                         None
 914                                     }
 915                                 }
 916                             })?;
 917                         let bounds = bounds.first()?.span().to(bounds.last()?.span());
 918                         let bounds = tcx.sess.source_map().span_to_snippet(bounds).ok()?;
 919
 920                         err.multipart_suggestion(
 921                             "try removing the generic parameter and using `impl Trait` instead",
 922                             vec![
 923                                 // delete generic parameters
 924                                 (impl_m.generics.span, String::new()),
 925                                 // replace param usage with `impl Trait`
 926                                 (span, format!("impl {}", bounds)),
 927                             ],
 928                             Applicability::MaybeIncorrect,
 929                         );
 930                         Some(())
 931                     })();
 932                 }
 933                 _ => unreachable!(),
 934             }
 935             err.emit();
 936             error_found = true;
 937         }
 938     }
 939     if error_found { Err(ErrorReported) } else { Ok(()) }
 940 }
 941
 942 crate fn compare_const_impl<'tcx>(
 943     tcx: TyCtxt<'tcx>,
 944     impl_c: &ty::AssocItem,
 945     impl_c_span: Span,
 946     trait_c: &ty::AssocItem,
 947     impl_trait_ref: ty::TraitRef<'tcx>,
 948 ) {
 949     debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref);
 950
 951     tcx.infer_ctxt().enter(|infcx| {
 952         let param_env = tcx.param_env(impl_c.def_id);
 953         let inh = Inherited::new(infcx, impl_c.def_id);
 954         let infcx = &inh.infcx;
 955
 956         // The below is for the most part highly similar to the procedure
 957         // for methods above. It is simpler in many respects, especially
 958         // because we shouldn't really have to deal with lifetimes or
 959         // predicates. In fact some of this should probably be put into
 960         // shared functions because of DRY violations...
 961         let trait_to_impl_substs = impl_trait_ref.substs;
 962
 963         // Create a parameter environment that represents the implementation's
 964         // method.
 965         let impl_c_hir_id = tcx.hir().as_local_hir_id(impl_c.def_id).unwrap();
 966
 967         // Compute placeholder form of impl and trait const tys.
 968         let impl_ty = tcx.type_of(impl_c.def_id);
 969         let trait_ty = tcx.type_of(trait_c.def_id).subst(tcx, trait_to_impl_substs);
 970         let mut cause = ObligationCause::misc(impl_c_span, impl_c_hir_id);
 971
 972         // There is no "body" here, so just pass dummy id.
 973         let impl_ty =
 974             inh.normalize_associated_types_in(impl_c_span, impl_c_hir_id, param_env, &impl_ty);
 975
 976         debug!("compare_const_impl: impl_ty={:?}", impl_ty);
 977
 978         let trait_ty =
 979             inh.normalize_associated_types_in(impl_c_span, impl_c_hir_id, param_env, &trait_ty);
 980
 981         debug!("compare_const_impl: trait_ty={:?}", trait_ty);
 982
 983         let err = infcx
 984             .at(&cause, param_env)
 985             .sup(trait_ty, impl_ty)
 986             .map(|ok| inh.register_infer_ok_obligations(ok));
 987
 988         if let Err(terr) = err {
 989             debug!(
 990                 "checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
 991                 impl_ty, trait_ty
 992             );
 993
 994             // Locate the Span containing just the type of the offending impl
 995             match tcx.hir().expect_impl_item(impl_c_hir_id).kind {
 996                 ImplItemKind::Const(ref ty, _) => cause.span = ty.span,
 997                 _ => bug!("{:?} is not a impl const", impl_c),
 998             }
 999
1000             let mut diag = struct_span_err!(
1001                 tcx.sess,
1002                 cause.span,
1003                 E0326,
1004                 "implemented const `{}` has an incompatible type for \
1005                                              trait",
1006                 trait_c.ident
1007             );
1008
1009             let trait_c_hir_id = tcx.hir().as_local_hir_id(trait_c.def_id);
1010             let trait_c_span = trait_c_hir_id.map(|trait_c_hir_id| {
1011                 // Add a label to the Span containing just the type of the const
1012                 match tcx.hir().expect_trait_item(trait_c_hir_id).kind {
1013                     TraitItemKind::Const(ref ty, _) => ty.span,
1014                     _ => bug!("{:?} is not a trait const", trait_c),
1015                 }
1016             });
1017
1018             infcx.note_type_err(
1019                 &mut diag,
1020                 &cause,
1021                 trait_c_span.map(|span| (span, "type in trait".to_owned())),
1022                 Some(infer::ValuePairs::Types(ExpectedFound {
1023                     expected: trait_ty,
1024                     found: impl_ty,
1025                 })),
1026                 &terr,
1027             );
1028             diag.emit();
1029         }
1030
1031         // Check that all obligations are satisfied by the implementation's
1032         // version.
1033         if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
1034             infcx.report_fulfillment_errors(errors, None, false);
1035             return;
1036         }
1037
1038         let fcx = FnCtxt::new(&inh, param_env, impl_c_hir_id);
1039         fcx.regionck_item(impl_c_hir_id, impl_c_span, &[]);
1040     });
1041 }
1042
1043 crate fn compare_ty_impl<'tcx>(
1044     tcx: TyCtxt<'tcx>,
1045     impl_ty: &ty::AssocItem,
1046     impl_ty_span: Span,
1047     trait_ty: &ty::AssocItem,
1048     impl_trait_ref: ty::TraitRef<'tcx>,
1049     trait_item_span: Option<Span>,
1050 ) {
1051     debug!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref);
1052
1053     let _: Result<(), ErrorReported> = (|| {
1054         compare_number_of_generics(tcx, impl_ty, impl_ty_span, trait_ty, trait_item_span)?;
1055
1056         compare_type_predicate_entailment(tcx, impl_ty, impl_ty_span, trait_ty, impl_trait_ref)
1057     })();
1058 }
1059
1060 /// The equivalent of [compare_predicate_entailment], but for associated types
1061 /// instead of associated functions.
1062 fn compare_type_predicate_entailment(
1063     tcx: TyCtxt<'tcx>,
1064     impl_ty: &ty::AssocItem,
1065     impl_ty_span: Span,
1066     trait_ty: &ty::AssocItem,
1067     impl_trait_ref: ty::TraitRef<'tcx>,
1068 ) -> Result<(), ErrorReported> {
1069     let impl_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1070     let trait_to_impl_substs =
1071         impl_substs.rebase_onto(tcx, impl_ty.container.id(), impl_trait_ref.substs);
1072
1073     let impl_ty_generics = tcx.generics_of(impl_ty.def_id);
1074     let trait_ty_generics = tcx.generics_of(trait_ty.def_id);
1075     let impl_ty_predicates = tcx.predicates_of(impl_ty.def_id);
1076     let trait_ty_predicates = tcx.predicates_of(trait_ty.def_id);
1077
1078     check_region_bounds_on_impl_item(
1079         tcx,
1080         impl_ty_span,
1081         impl_ty,
1082         trait_ty,
1083         &trait_ty_generics,
1084         &impl_ty_generics,
1085     )?;
1086
1087     let impl_ty_own_bounds = impl_ty_predicates.instantiate_own(tcx, impl_substs);
1088
1089     if impl_ty_own_bounds.is_empty() {
1090         // Nothing to check.
1091         return Ok(());
1092     }
1093
1094     // This `HirId` should be used for the `body_id` field on each
1095     // `ObligationCause` (and the `FnCtxt`). This is what
1096     // `regionck_item` expects.
1097     let impl_ty_hir_id = tcx.hir().as_local_hir_id(impl_ty.def_id).unwrap();
1098     let cause = ObligationCause {
1099         span: impl_ty_span,
1100         body_id: impl_ty_hir_id,
1101         code: ObligationCauseCode::CompareImplTypeObligation {
1102             item_name: impl_ty.ident.name,
1103             impl_item_def_id: impl_ty.def_id,
1104             trait_item_def_id: trait_ty.def_id,
1105         },
1106     };
1107
1108     debug!("compare_type_predicate_entailment: trait_to_impl_substs={:?}", trait_to_impl_substs);
1109
1110     // The predicates declared by the impl definition, the trait and the
1111     // associated type in the trait are assumed.
1112     let impl_predicates = tcx.predicates_of(impl_ty_predicates.parent.unwrap());
1113     let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
1114     hybrid_preds
1115         .predicates
1116         .extend(trait_ty_predicates.instantiate_own(tcx, trait_to_impl_substs).predicates);
1117
1118     debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds);
1119
1120     let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_hir_id);
1121     let param_env = ty::ParamEnv::new(
1122         tcx.intern_predicates(&hybrid_preds.predicates),
1123         Reveal::UserFacing,
1124         None,
1125     );
1126     let param_env = traits::normalize_param_env_or_error(
1127         tcx,
1128         impl_ty.def_id,
1129         param_env,
1130         normalize_cause.clone(),
1131     );
1132     tcx.infer_ctxt().enter(|infcx| {
1133         let inh = Inherited::new(infcx, impl_ty.def_id);
1134         let infcx = &inh.infcx;
1135
1136         debug!("compare_type_predicate_entailment: caller_bounds={:?}", param_env.caller_bounds);
1137
1138         let mut selcx = traits::SelectionContext::new(&infcx);
1139
1140         for predicate in impl_ty_own_bounds.predicates {
1141             let traits::Normalized { value: predicate, obligations } =
1142                 traits::normalize(&mut selcx, param_env, normalize_cause.clone(), &predicate);
1143
1144             inh.register_predicates(obligations);
1145             inh.register_predicate(traits::Obligation::new(cause.clone(), param_env, predicate));
1146         }
1147
1148         // Check that all obligations are satisfied by the implementation's
1149         // version.
1150         if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
1151             infcx.report_fulfillment_errors(errors, None, false);
1152             return Err(ErrorReported);
1153         }
1154
1155         // Finally, resolve all regions. This catches wily misuses of
1156         // lifetime parameters.
1157         let fcx = FnCtxt::new(&inh, param_env, impl_ty_hir_id);
1158         fcx.regionck_item(impl_ty_hir_id, impl_ty_span, &[]);
1159
1160         Ok(())
1161     })
1162 }
1163
1164 fn assoc_item_kind_str(impl_item: &ty::AssocItem) -> &'static str {
1165     match impl_item.kind {
1166         ty::AssocKind::Const => "const",
1167         ty::AssocKind::Method => "method",
1168         ty::AssocKind::Type | ty::AssocKind::OpaqueTy => "type",
1169     }
1170 }