src/librustc_typeck/check/compare_method.rs

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