src/librustc_typeck/check/compare_method.rs

   1 use rustc::hir::{self, GenericParamKind, ImplItemKind, TraitItemKind};
   2 use rustc::infer::{self, InferOk};
   3 use rustc::ty::{self, TyCtxt, GenericParamDefKind};
   4 use rustc::ty::util::ExplicitSelf;
   5 use rustc::traits::{self, ObligationCause, ObligationCauseCode, Reveal};
   6 use rustc::ty::error::{ExpectedFound, TypeError};
   7 use rustc::ty::subst::{Subst, InternalSubsts, SubstsRef};
   8 use rustc::util::common::ErrorReported;
   9 use errors::{Applicability, DiagnosticId};
  10
  11 use syntax_pos::Span;
  12
  13 use super::{Inherited, FnCtxt, potentially_plural_count};
  14
  15 /// Checks that a method from an impl conforms to the signature of
  16 /// the same method as declared in the trait.
  17 ///
  18 /// # Parameters
  19 ///
  20 /// - `impl_m`: type of the method we are checking
  21 /// - `impl_m_span`: span to use for reporting errors
  22 /// - `trait_m`: the method in the trait
  23 /// - `impl_trait_ref`: the TraitRef corresponding to the trait implementation
  24
  25 pub fn compare_impl_method<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
  26                                      impl_m: &ty::AssociatedItem,
  27                                      impl_m_span: Span,
  28                                      trait_m: &ty::AssociatedItem,
  29                                      impl_trait_ref: ty::TraitRef<'tcx>,
  30                                      trait_item_span: Option<Span>) {
  31     debug!("compare_impl_method(impl_trait_ref={:?})",
  32            impl_trait_ref);
  33
  34     let impl_m_span = tcx.sess.source_map().def_span(impl_m_span);
  35
  36     if let Err(ErrorReported) = compare_self_type(tcx,
  37                                                   impl_m,
  38                                                   impl_m_span,
  39                                                   trait_m,
  40                                                   impl_trait_ref) {
  41         return;
  42     }
  43
  44     if let Err(ErrorReported) = compare_number_of_generics(tcx,
  45                                                            impl_m,
  46                                                            impl_m_span,
  47                                                            trait_m,
  48                                                            trait_item_span) {
  49         return;
  50     }
  51
  52     if let Err(ErrorReported) = compare_number_of_method_arguments(tcx,
  53                                                                    impl_m,
  54                                                                    impl_m_span,
  55                                                                    trait_m,
  56                                                                    trait_item_span) {
  57         return;
  58     }
  59
  60     if let Err(ErrorReported) = compare_synthetic_generics(tcx,
  61                                                            impl_m,
  62                                                            trait_m) {
  63         return;
  64     }
  65
  66     if let Err(ErrorReported) = compare_predicate_entailment(tcx,
  67                                                              impl_m,
  68                                                              impl_m_span,
  69                                                              trait_m,
  70                                                              impl_trait_ref) {
  71         return;
  72     }
  73 }
  74
  75 fn compare_predicate_entailment<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
  76                                           impl_m: &ty::AssociatedItem,
  77                                           impl_m_span: Span,
  78                                           trait_m: &ty::AssociatedItem,
  79                                           impl_trait_ref: ty::TraitRef<'tcx>)
  80                                           -> Result<(), ErrorReported> {
  81     let trait_to_impl_substs = impl_trait_ref.substs;
  82
  83     // This node-id should be used for the `body_id` field on each
  84     // `ObligationCause` (and the `FnCtxt`). This is what
  85     // `regionck_item` expects.
  86     let impl_m_hir_id = tcx.hir().as_local_hir_id(impl_m.def_id).unwrap();
  87
  88     let cause = ObligationCause {
  89         span: impl_m_span,
  90         body_id: impl_m_hir_id,
  91         code: ObligationCauseCode::CompareImplMethodObligation {
  92             item_name: impl_m.ident.name,
  93             impl_item_def_id: impl_m.def_id,
  94             trait_item_def_id: trait_m.def_id,
  95         },
  96     };
  97
  98     // This code is best explained by example. Consider a trait:
  99     //
 100     //     trait Trait<'t,T> {
 101     //          fn method<'a,M>(t: &'t T, m: &'a M) -> Self;
 102     //     }
 103     //
 104     // And an impl:
 105     //
 106     //     impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
 107     //          fn method<'b,N>(t: &'j &'i U, m: &'b N) -> Foo;
 108     //     }
 109     //
 110     // We wish to decide if those two method types are compatible.
 111     //
 112     // We start out with trait_to_impl_substs, that maps the trait
 113     // type parameters to impl type parameters. This is taken from the
 114     // impl trait reference:
 115     //
 116     //     trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
 117     //
 118     // We create a mapping `dummy_substs` that maps from the impl type
 119     // parameters to fresh types and regions. For type parameters,
 120     // this is the identity transform, but we could as well use any
 121     // placeholder types. For regions, we convert from bound to free
 122     // regions (Note: but only early-bound regions, i.e., those
 123     // declared on the impl or used in type parameter bounds).
 124     //
 125     //     impl_to_skol_substs = {'i => 'i0, U => U0, N => N0 }
 126     //
 127     // Now we can apply skol_substs to the type of the impl method
 128     // to yield a new function type in terms of our fresh, placeholder
 129     // types:
 130     //
 131     //     <'b> fn(t: &'i0 U0, m: &'b) -> Foo
 132     //
 133     // We now want to extract and substitute the type of the *trait*
 134     // method and compare it. To do so, we must create a compound
 135     // substitution by combining trait_to_impl_substs and
 136     // impl_to_skol_substs, and also adding a mapping for the method
 137     // type parameters. We extend the mapping to also include
 138     // the method parameters.
 139     //
 140     //     trait_to_skol_substs = { T => &'i0 U0, Self => Foo, M => N0 }
 141     //
 142     // Applying this to the trait method type yields:
 143     //
 144     //     <'a> fn(t: &'i0 U0, m: &'a) -> Foo
 145     //
 146     // This type is also the same but the name of the bound region ('a
 147     // vs 'b).  However, the normal subtyping rules on fn types handle
 148     // this kind of equivalency just fine.
 149     //
 150     // We now use these substitutions to ensure that all declared bounds are
 151     // satisfied by the implementation's method.
 152     //
 153     // We do this by creating a parameter environment which contains a
 154     // substitution corresponding to impl_to_skol_substs. We then build
 155     // trait_to_skol_substs and use it to convert the predicates contained
 156     // in the trait_m.generics to the placeholder form.
 157     //
 158     // Finally we register each of these predicates as an obligation in
 159     // a fresh FulfillmentCtxt, and invoke select_all_or_error.
 160
 161     // Create mapping from impl to placeholder.
 162     let impl_to_skol_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
 163
 164     // Create mapping from trait to placeholder.
 165     let trait_to_skol_substs = impl_to_skol_substs.rebase_onto(tcx,
 166                                                                impl_m.container.id(),
 167                                                                trait_to_impl_substs);
 168     debug!("compare_impl_method: trait_to_skol_substs={:?}",
 169            trait_to_skol_substs);
 170
 171     let impl_m_generics = tcx.generics_of(impl_m.def_id);
 172     let trait_m_generics = tcx.generics_of(trait_m.def_id);
 173     let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
 174     let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
 175
 176     // Check region bounds.
 177     check_region_bounds_on_impl_method(tcx,
 178                                        impl_m_span,
 179                                        impl_m,
 180                                        trait_m,
 181                                        &trait_m_generics,
 182                                        &impl_m_generics,
 183                                        trait_to_skol_substs)?;
 184
 185     // Create obligations for each predicate declared by the impl
 186     // definition in the context of the trait's parameter
 187     // environment. We can't just use `impl_env.caller_bounds`,
 188     // however, because we want to replace all late-bound regions with
 189     // region variables.
 190     let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap());
 191     let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
 192
 193     debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
 194
 195     // This is the only tricky bit of the new way we check implementation methods
 196     // We need to build a set of predicates where only the method-level bounds
 197     // are from the trait and we assume all other bounds from the implementation
 198     // to be previously satisfied.
 199     //
 200     // We then register the obligations from the impl_m and check to see
 201     // if all constraints hold.
 202     hybrid_preds.predicates.extend(
 203         trait_m_predicates.instantiate_own(tcx, trait_to_skol_substs).predicates);
 204
 205     // Construct trait parameter environment and then shift it into the placeholder viewpoint.
 206     // The key step here is to update the caller_bounds's predicates to be
 207     // the new hybrid bounds we computed.
 208     let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_hir_id);
 209     let param_env = ty::ParamEnv::new(
 210         tcx.intern_predicates(&hybrid_preds.predicates),
 211         Reveal::UserFacing,
 212         None
 213     );
 214     let param_env = traits::normalize_param_env_or_error(tcx,
 215                                                          impl_m.def_id,
 216                                                          param_env,
 217                                                          normalize_cause.clone());
 218
 219     tcx.infer_ctxt().enter(|infcx| {
 220         let inh = Inherited::new(infcx, impl_m.def_id);
 221         let infcx = &inh.infcx;
 222
 223         debug!("compare_impl_method: caller_bounds={:?}",
 224                param_env.caller_bounds);
 225
 226         let mut selcx = traits::SelectionContext::new(&infcx);
 227
 228         let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_skol_substs);
 229         let (impl_m_own_bounds, _) = infcx.replace_bound_vars_with_fresh_vars(
 230             impl_m_span,
 231             infer::HigherRankedType,
 232             &ty::Binder::bind(impl_m_own_bounds.predicates)
 233         );
 234         for predicate in impl_m_own_bounds {
 235             let traits::Normalized { value: predicate, obligations } =
 236                 traits::normalize(&mut selcx, param_env, normalize_cause.clone(), &predicate);
 237
 238             inh.register_predicates(obligations);
 239             inh.register_predicate(traits::Obligation::new(cause.clone(), param_env, predicate));
 240         }
 241
 242         // We now need to check that the signature of the impl method is
 243         // compatible with that of the trait method. We do this by
 244         // checking that `impl_fty <: trait_fty`.
 245         //
 246         // FIXME. Unfortunately, this doesn't quite work right now because
 247         // associated type normalization is not integrated into subtype
 248         // checks. For the comparison to be valid, we need to
 249         // normalize the associated types in the impl/trait methods
 250         // first. However, because function types bind regions, just
 251         // calling `normalize_associated_types_in` would have no effect on
 252         // any associated types appearing in the fn arguments or return
 253         // type.
 254
 255         // Compute placeholder form of impl and trait method tys.
 256         let tcx = infcx.tcx;
 257
 258         let (impl_sig, _) = infcx.replace_bound_vars_with_fresh_vars(
 259             impl_m_span,
 260             infer::HigherRankedType,
 261             &tcx.fn_sig(impl_m.def_id)
 262         );
 263         let impl_sig =
 264             inh.normalize_associated_types_in(impl_m_span,
 265                                               impl_m_hir_id,
 266                                               param_env,
 267                                               &impl_sig);
 268         let impl_fty = tcx.mk_fn_ptr(ty::Binder::bind(impl_sig));
 269         debug!("compare_impl_method: impl_fty={:?}", impl_fty);
 270
 271         let trait_sig = tcx.liberate_late_bound_regions(
 272             impl_m.def_id,
 273             &tcx.fn_sig(trait_m.def_id));
 274         let trait_sig =
 275             trait_sig.subst(tcx, trait_to_skol_substs);
 276         let trait_sig =
 277             inh.normalize_associated_types_in(impl_m_span,
 278                                               impl_m_hir_id,
 279                                               param_env,
 280                                               &trait_sig);
 281         let trait_fty = tcx.mk_fn_ptr(ty::Binder::bind(trait_sig));
 282
 283         debug!("compare_impl_method: trait_fty={:?}", trait_fty);
 284
 285         let sub_result = infcx.at(&cause, param_env)
 286                               .sup(trait_fty, impl_fty)
 287                               .map(|InferOk { obligations, .. }| {
 288                                   inh.register_predicates(obligations);
 289                               });
 290
 291         if let Err(terr) = sub_result {
 292             debug!("sub_types failed: impl ty {:?}, trait ty {:?}",
 293                    impl_fty,
 294                    trait_fty);
 295
 296             let (impl_err_span, trait_err_span) = extract_spans_for_error_reporting(&infcx,
 297                                                                                     param_env,
 298                                                                                     &terr,
 299                                                                                     &cause,
 300                                                                                     impl_m,
 301                                                                                     impl_sig,
 302                                                                                     trait_m,
 303                                                                                     trait_sig);
 304
 305             let cause = ObligationCause {
 306                 span: impl_err_span,
 307                 ..cause.clone()
 308             };
 309
 310             let mut diag = struct_span_err!(tcx.sess,
 311                                             cause.span(tcx),
 312                                             E0053,
 313                                             "method `{}` has an incompatible type for trait",
 314                                             trait_m.ident);
 315             if let TypeError::Mutability = terr {
 316                 if let Some(trait_err_span) = trait_err_span {
 317                     if let Ok(trait_err_str) = tcx.sess.source_map()
 318                                                        .span_to_snippet(trait_err_span) {
 319                         diag.span_suggestion(
 320                             impl_err_span,
 321                             "consider change the type to match the mutability in trait",
 322                             trait_err_str,
 323                             Applicability::MachineApplicable,
 324                         );
 325                     }
 326                 }
 327             }
 328
 329             infcx.note_type_err(&mut diag,
 330                                 &cause,
 331                                 trait_err_span.map(|sp| (sp, "type in trait".to_owned())),
 332                                 Some(infer::ValuePairs::Types(ExpectedFound {
 333                                     expected: trait_fty,
 334                                     found: impl_fty,
 335                                 })),
 336                                 &terr);
 337             diag.emit();
 338             return Err(ErrorReported);
 339         }
 340
 341         // Check that all obligations are satisfied by the implementation's
 342         // version.
 343         if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
 344             infcx.report_fulfillment_errors(errors, None, false);
 345             return Err(ErrorReported);
 346         }
 347
 348         // Finally, resolve all regions. This catches wily misuses of
 349         // lifetime parameters.
 350         let fcx = FnCtxt::new(&inh, param_env, impl_m_hir_id);
 351         fcx.regionck_item(impl_m_hir_id, impl_m_span, &[]);
 352
 353         Ok(())
 354     })
 355 }
 356
 357 fn check_region_bounds_on_impl_method<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 358                                                 span: Span,
 359                                                 impl_m: &ty::AssociatedItem,
 360                                                 trait_m: &ty::AssociatedItem,
 361                                                 trait_generics: &ty::Generics,
 362                                                 impl_generics: &ty::Generics,
 363                                                 trait_to_skol_substs: SubstsRef<'tcx>)
 364                                                 -> Result<(), ErrorReported> {
 365     let trait_params = trait_generics.own_counts().lifetimes;
 366     let impl_params = impl_generics.own_counts().lifetimes;
 367
 368     debug!("check_region_bounds_on_impl_method: \
 369             trait_generics={:?} \
 370             impl_generics={:?} \
 371             trait_to_skol_substs={:?}",
 372            trait_generics,
 373            impl_generics,
 374            trait_to_skol_substs);
 375
 376     // Must have same number of early-bound lifetime parameters.
 377     // Unfortunately, if the user screws up the bounds, then this
 378     // will change classification between early and late.  E.g.,
 379     // if in trait we have `<'a,'b:'a>`, and in impl we just have
 380     // `<'a,'b>`, then we have 2 early-bound lifetime parameters
 381     // in trait but 0 in the impl. But if we report "expected 2
 382     // but found 0" it's confusing, because it looks like there
 383     // are zero. Since I don't quite know how to phrase things at
 384     // the moment, give a kind of vague error message.
 385     if trait_params != impl_params {
 386         let def_span = tcx.sess.source_map().def_span(span);
 387         let span = tcx.hir().get_generics_span(impl_m.def_id).unwrap_or(def_span);
 388         let mut err = struct_span_err!(
 389             tcx.sess,
 390             span,
 391             E0195,
 392             "lifetime parameters or bounds on method `{}` do not match the trait declaration",
 393             impl_m.ident,
 394         );
 395         err.span_label(span, "lifetimes do not match method in trait");
 396         if let Some(sp) = tcx.hir().span_if_local(trait_m.def_id) {
 397             let def_sp = tcx.sess.source_map().def_span(sp);
 398             let sp = tcx.hir().get_generics_span(trait_m.def_id).unwrap_or(def_sp);
 399             err.span_label(sp, "lifetimes in impl do not match this method in trait");
 400         }
 401         err.emit();
 402         return Err(ErrorReported);
 403     }
 404
 405     Ok(())
 406 }
 407
 408 fn extract_spans_for_error_reporting<'a, 'gcx, 'tcx>(infcx: &infer::InferCtxt<'a, 'gcx, 'tcx>,
 409                                                      param_env: ty::ParamEnv<'tcx>,
 410                                                      terr: &TypeError<'_>,
 411                                                      cause: &ObligationCause<'tcx>,
 412                                                      impl_m: &ty::AssociatedItem,
 413                                                      impl_sig: ty::FnSig<'tcx>,
 414                                                      trait_m: &ty::AssociatedItem,
 415                                                      trait_sig: ty::FnSig<'tcx>)
 416                                                      -> (Span, Option<Span>) {
 417     let tcx = infcx.tcx;
 418     let impl_m_hir_id = tcx.hir().as_local_hir_id(impl_m.def_id).unwrap();
 419     let (impl_m_output, impl_m_iter) = match tcx.hir()
 420                                                 .expect_impl_item(impl_m_hir_id)
 421                                                 .node {
 422         ImplItemKind::Method(ref impl_m_sig, _) => {
 423             (&impl_m_sig.decl.output, impl_m_sig.decl.inputs.iter())
 424         }
 425         _ => bug!("{:?} is not a method", impl_m),
 426     };
 427
 428     match *terr {
 429         TypeError::Mutability => {
 430             if let Some(trait_m_hir_id) = tcx.hir().as_local_hir_id(trait_m.def_id) {
 431                 let trait_m_iter = match tcx.hir()
 432                                             .expect_trait_item(trait_m_hir_id)
 433                                             .node {
 434                     TraitItemKind::Method(ref trait_m_sig, _) => {
 435                         trait_m_sig.decl.inputs.iter()
 436                     }
 437                     _ => bug!("{:?} is not a TraitItemKind::Method", trait_m),
 438                 };
 439
 440                 impl_m_iter.zip(trait_m_iter).find(|&(ref impl_arg, ref trait_arg)| {
 441                     match (&impl_arg.node, &trait_arg.node) {
 442                         (&hir::TyKind::Rptr(_, ref impl_mt), &hir::TyKind::Rptr(_, ref trait_mt)) |
 443                         (&hir::TyKind::Ptr(ref impl_mt), &hir::TyKind::Ptr(ref trait_mt)) => {
 444                             impl_mt.mutbl != trait_mt.mutbl
 445                         }
 446                         _ => false,
 447                     }
 448                 }).map(|(ref impl_arg, ref trait_arg)| {
 449                     (impl_arg.span, Some(trait_arg.span))
 450                 })
 451                 .unwrap_or_else(|| (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id)))
 452             } else {
 453                 (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
 454             }
 455         }
 456         TypeError::Sorts(ExpectedFound { .. }) => {
 457             if let Some(trait_m_hir_id) = tcx.hir().as_local_hir_id(trait_m.def_id) {
 458                 let (trait_m_output, trait_m_iter) =
 459                     match tcx.hir().expect_trait_item(trait_m_hir_id).node {
 460                         TraitItemKind::Method(ref trait_m_sig, _) => {
 461                             (&trait_m_sig.decl.output, trait_m_sig.decl.inputs.iter())
 462                         }
 463                         _ => bug!("{:?} is not a TraitItemKind::Method", trait_m),
 464                     };
 465
 466                 let impl_iter = impl_sig.inputs().iter();
 467                 let trait_iter = trait_sig.inputs().iter();
 468                 impl_iter.zip(trait_iter)
 469                          .zip(impl_m_iter)
 470                          .zip(trait_m_iter)
 471                          .filter_map(|(((&impl_arg_ty, &trait_arg_ty), impl_arg), trait_arg)|
 472                              match infcx.at(&cause, param_env).sub(trait_arg_ty, impl_arg_ty) {
 473                                  Ok(_) => None,
 474                                  Err(_) => Some((impl_arg.span, Some(trait_arg.span))),
 475                              }
 476                          )
 477                          .next()
 478                          .unwrap_or_else(||
 479                              if
 480                                  infcx.at(&cause, param_env)
 481                                       .sup(trait_sig.output(), impl_sig.output())
 482                                       .is_err()
 483                              {
 484                                  (impl_m_output.span(), Some(trait_m_output.span()))
 485                              } else {
 486                                  (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
 487                              }
 488                          )
 489             } else {
 490                 (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
 491             }
 492         }
 493         _ => (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id)),
 494     }
 495 }
 496
 497 fn compare_self_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 498                                impl_m: &ty::AssociatedItem,
 499                                impl_m_span: Span,
 500                                trait_m: &ty::AssociatedItem,
 501                                impl_trait_ref: ty::TraitRef<'tcx>)
 502                                -> Result<(), ErrorReported>
 503 {
 504     // Try to give more informative error messages about self typing
 505     // mismatches.  Note that any mismatch will also be detected
 506     // below, where we construct a canonical function type that
 507     // includes the self parameter as a normal parameter.  It's just
 508     // that the error messages you get out of this code are a bit more
 509     // inscrutable, particularly for cases where one method has no
 510     // self.
 511
 512     let self_string = |method: &ty::AssociatedItem| {
 513         let untransformed_self_ty = match method.container {
 514             ty::ImplContainer(_) => impl_trait_ref.self_ty(),
 515             ty::TraitContainer(_) => tcx.mk_self_type()
 516         };
 517         let self_arg_ty = *tcx.fn_sig(method.def_id).input(0).skip_binder();
 518         let param_env = ty::ParamEnv::reveal_all();
 519
 520         tcx.infer_ctxt().enter(|infcx| {
 521             let self_arg_ty = tcx.liberate_late_bound_regions(
 522                 method.def_id,
 523                 &ty::Binder::bind(self_arg_ty)
 524             );
 525             let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty).is_ok();
 526             match ExplicitSelf::determine(self_arg_ty, can_eq_self) {
 527                 ExplicitSelf::ByValue => "self".to_owned(),
 528                 ExplicitSelf::ByReference(_, hir::MutImmutable) => "&self".to_owned(),
 529                 ExplicitSelf::ByReference(_, hir::MutMutable) => "&mut self".to_owned(),
 530                 _ => format!("self: {}", self_arg_ty)
 531             }
 532         })
 533     };
 534
 535     match (trait_m.method_has_self_argument, impl_m.method_has_self_argument) {
 536         (false, false) | (true, true) => {}
 537
 538         (false, true) => {
 539             let self_descr = self_string(impl_m);
 540             let mut err = struct_span_err!(tcx.sess,
 541                                            impl_m_span,
 542                                            E0185,
 543                                            "method `{}` has a `{}` declaration in the impl, but \
 544                                             not in the trait",
 545                                            trait_m.ident,
 546                                            self_descr);
 547             err.span_label(impl_m_span, format!("`{}` used in impl", self_descr));
 548             if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
 549                 err.span_label(span, format!("trait method declared without `{}`", self_descr));
 550             } else {
 551                 err.note_trait_signature(trait_m.ident.to_string(),
 552                                          trait_m.signature(tcx));
 553             }
 554             err.emit();
 555             return Err(ErrorReported);
 556         }
 557
 558         (true, false) => {
 559             let self_descr = self_string(trait_m);
 560             let mut err = struct_span_err!(tcx.sess,
 561                                            impl_m_span,
 562                                            E0186,
 563                                            "method `{}` has a `{}` declaration in the trait, but \
 564                                             not in the impl",
 565                                            trait_m.ident,
 566                                            self_descr);
 567             err.span_label(impl_m_span, format!("expected `{}` in impl", self_descr));
 568             if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
 569                 err.span_label(span, format!("`{}` used in trait", self_descr));
 570             } else {
 571                 err.note_trait_signature(trait_m.ident.to_string(),
 572                                          trait_m.signature(tcx));
 573             }
 574             err.emit();
 575             return Err(ErrorReported);
 576         }
 577     }
 578
 579     Ok(())
 580 }
 581
 582 fn compare_number_of_generics<'a, 'tcx>(
 583     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 584     impl_: &ty::AssociatedItem,
 585     impl_span: Span,
 586     trait_: &ty::AssociatedItem,
 587     trait_span: Option<Span>,
 588 ) -> Result<(), ErrorReported> {
 589     let trait_own_counts = tcx.generics_of(trait_.def_id).own_counts();
 590     let impl_own_counts = tcx.generics_of(impl_.def_id).own_counts();
 591
 592     let matchings = [
 593         ("type", trait_own_counts.types, impl_own_counts.types),
 594         ("const", trait_own_counts.consts, impl_own_counts.consts),
 595     ];
 596
 597     let mut err_occurred = false;
 598     for &(kind, trait_count, impl_count) in &matchings {
 599         if impl_count != trait_count {
 600             err_occurred = true;
 601
 602             let impl_hir_id = tcx.hir().as_local_hir_id(impl_.def_id).unwrap();
 603             let impl_item = tcx.hir().expect_impl_item(impl_hir_id);
 604             let span = if impl_item.generics.params.is_empty()
 605                 || impl_item.generics.span.is_dummy() { // argument position impl Trait (#55374)
 606                 impl_span
 607             } else {
 608                 impl_item.generics.span
 609             };
 610
 611             let mut err = tcx.sess.struct_span_err_with_code(
 612                 span,
 613                 &format!(
 614                     "method `{}` has {} {kind} parameter{} but its trait \
 615                      declaration has {} {kind} parameter{}",
 616                     trait_.ident,
 617                     impl_count,
 618                     if impl_count != 1 { "s" } else { "" },
 619                     trait_count,
 620                     if trait_count != 1 { "s" } else { "" },
 621                     kind = kind,
 622                 ),
 623                 DiagnosticId::Error("E0049".into()),
 624             );
 625
 626             let mut suffix = None;
 627
 628             if let Some(span) = trait_span {
 629                 err.span_label(
 630                     span,
 631                     format!("expected {} {} parameter{}", trait_count, kind,
 632                         if trait_count != 1 { "s" } else { "" })
 633                 );
 634             } else {
 635                 suffix = Some(format!(", expected {}", trait_count));
 636             }
 637
 638             err.span_label(
 639                 span,
 640                 format!("found {} {} parameter{}{}", impl_count, kind,
 641                     if impl_count != 1 { "s" } else { "" },
 642                     suffix.unwrap_or_else(|| String::new())),
 643             );
 644
 645             err.emit();
 646         }
 647     }
 648
 649     if err_occurred {
 650         Err(ErrorReported)
 651     } else {
 652         Ok(())
 653     }
 654 }
 655
 656 fn compare_number_of_method_arguments<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 657                                                 impl_m: &ty::AssociatedItem,
 658                                                 impl_m_span: Span,
 659                                                 trait_m: &ty::AssociatedItem,
 660                                                 trait_item_span: Option<Span>)
 661                                                 -> Result<(), ErrorReported> {
 662     let impl_m_fty = tcx.fn_sig(impl_m.def_id);
 663     let trait_m_fty = tcx.fn_sig(trait_m.def_id);
 664     let trait_number_args = trait_m_fty.inputs().skip_binder().len();
 665     let impl_number_args = impl_m_fty.inputs().skip_binder().len();
 666     if trait_number_args != impl_number_args {
 667         let trait_m_hir_id = tcx.hir().as_local_hir_id(trait_m.def_id);
 668         let trait_span = if let Some(trait_id) = trait_m_hir_id {
 669             match tcx.hir().expect_trait_item(trait_id).node {
 670                 TraitItemKind::Method(ref trait_m_sig, _) => {
 671                     let pos = if trait_number_args > 0 {
 672                         trait_number_args - 1
 673                     } else {
 674                         0
 675                     };
 676                     if let Some(arg) = trait_m_sig.decl.inputs.get(pos) {
 677                         Some(if pos == 0 {
 678                             arg.span
 679                         } else {
 680                             Span::new(trait_m_sig.decl.inputs[0].span.lo(),
 681                                       arg.span.hi(),
 682                                       arg.span.ctxt())
 683                         })
 684                     } else {
 685                         trait_item_span
 686                     }
 687                 }
 688                 _ => bug!("{:?} is not a method", impl_m),
 689             }
 690         } else {
 691             trait_item_span
 692         };
 693         let impl_m_hir_id = tcx.hir().as_local_hir_id(impl_m.def_id).unwrap();
 694         let impl_span = match tcx.hir().expect_impl_item(impl_m_hir_id).node {
 695             ImplItemKind::Method(ref impl_m_sig, _) => {
 696                 let pos = if impl_number_args > 0 {
 697                     impl_number_args - 1
 698                 } else {
 699                     0
 700                 };
 701                 if let Some(arg) = impl_m_sig.decl.inputs.get(pos) {
 702                     if pos == 0 {
 703                         arg.span
 704                     } else {
 705                         Span::new(impl_m_sig.decl.inputs[0].span.lo(),
 706                                   arg.span.hi(),
 707                                   arg.span.ctxt())
 708                     }
 709                 } else {
 710                     impl_m_span
 711                 }
 712             }
 713             _ => bug!("{:?} is not a method", impl_m),
 714         };
 715         let mut err = struct_span_err!(tcx.sess,
 716                                        impl_span,
 717                                        E0050,
 718                                        "method `{}` has {} but the declaration in \
 719                                         trait `{}` has {}",
 720                                        trait_m.ident,
 721                                        potentially_plural_count(impl_number_args, "parameter"),
 722                                        tcx.def_path_str(trait_m.def_id),
 723                                        trait_number_args);
 724         if let Some(trait_span) = trait_span {
 725             err.span_label(trait_span, format!("trait requires {}",
 726                 potentially_plural_count(trait_number_args, "parameter")));
 727         } else {
 728             err.note_trait_signature(trait_m.ident.to_string(),
 729                                      trait_m.signature(tcx));
 730         }
 731         err.span_label(impl_span, format!("expected {}, found {}",
 732             potentially_plural_count(trait_number_args, "parameter"), impl_number_args));
 733         err.emit();
 734         return Err(ErrorReported);
 735     }
 736
 737     Ok(())
 738 }
 739
 740 fn compare_synthetic_generics<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 741                                         impl_m: &ty::AssociatedItem,
 742                                         trait_m: &ty::AssociatedItem)
 743                                         -> Result<(), ErrorReported> {
 744     // FIXME(chrisvittal) Clean up this function, list of FIXME items:
 745     //     1. Better messages for the span labels
 746     //     2. Explanation as to what is going on
 747     // If we get here, we already have the same number of generics, so the zip will
 748     // be okay.
 749     let mut error_found = false;
 750     let impl_m_generics = tcx.generics_of(impl_m.def_id);
 751     let trait_m_generics = tcx.generics_of(trait_m.def_id);
 752     let impl_m_type_params = impl_m_generics.params.iter().filter_map(|param| match param.kind {
 753         GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
 754         GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None,
 755     });
 756     let trait_m_type_params = trait_m_generics.params.iter().filter_map(|param| {
 757         match param.kind {
 758             GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
 759             GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None,
 760         }
 761     });
 762     for ((impl_def_id, impl_synthetic), (trait_def_id, trait_synthetic))
 763         in impl_m_type_params.zip(trait_m_type_params)
 764     {
 765         if impl_synthetic != trait_synthetic {
 766             let impl_hir_id = tcx.hir().as_local_hir_id(impl_def_id).unwrap();
 767             let impl_span = tcx.hir().span_by_hir_id(impl_hir_id);
 768             let trait_span = tcx.def_span(trait_def_id);
 769             let mut err = struct_span_err!(tcx.sess,
 770                                            impl_span,
 771                                            E0643,
 772                                            "method `{}` has incompatible signature for trait",
 773                                            trait_m.ident);
 774             err.span_label(trait_span, "declaration in trait here");
 775             match (impl_synthetic, trait_synthetic) {
 776                 // The case where the impl method uses `impl Trait` but the trait method uses
 777                 // explicit generics
 778                 (Some(hir::SyntheticTyParamKind::ImplTrait), None) => {
 779                     err.span_label(impl_span, "expected generic parameter, found `impl Trait`");
 780                     (|| {
 781                         // try taking the name from the trait impl
 782                         // FIXME: this is obviously suboptimal since the name can already be used
 783                         // as another generic argument
 784                         let new_name = tcx
 785                             .sess
 786                             .source_map()
 787                             .span_to_snippet(trait_span)
 788                             .ok()?;
 789                         let trait_m = tcx.hir().as_local_hir_id(trait_m.def_id)?;
 790                         let trait_m = tcx.hir().trait_item(hir::TraitItemId { hir_id: trait_m });
 791
 792                         let impl_m = tcx.hir().as_local_hir_id(impl_m.def_id)?;
 793                         let impl_m = tcx.hir().impl_item(hir::ImplItemId { hir_id: impl_m });
 794
 795                         // in case there are no generics, take the spot between the function name
 796                         // and the opening paren of the argument list
 797                         let new_generics_span = tcx
 798                             .sess
 799                             .source_map()
 800                             .generate_fn_name_span(impl_span)?
 801                             .shrink_to_hi();
 802                         // in case there are generics, just replace them
 803                         let generics_span = impl_m
 804                             .generics
 805                             .span
 806                             .substitute_dummy(new_generics_span);
 807                         // replace with the generics from the trait
 808                         let new_generics = tcx
 809                             .sess
 810                             .source_map()
 811                             .span_to_snippet(trait_m.generics.span)
 812                             .ok()?;
 813
 814                         err.multipart_suggestion(
 815                             "try changing the `impl Trait` argument to a generic parameter",
 816                             vec![
 817                                 // replace `impl Trait` with `T`
 818                                 (impl_span, new_name),
 819                                 // replace impl method generics with trait method generics
 820                                 // This isn't quite right, as users might have changed the names
 821                                 // of the generics, but it works for the common case
 822                                 (generics_span, new_generics),
 823                             ],
 824                             Applicability::MaybeIncorrect,
 825                         );
 826                         Some(())
 827                     })();
 828                 },
 829                 // The case where the trait method uses `impl Trait`, but the impl method uses
 830                 // explicit generics.
 831                 (None, Some(hir::SyntheticTyParamKind::ImplTrait)) => {
 832                     err.span_label(impl_span, "expected `impl Trait`, found generic parameter");
 833                     (|| {
 834                         let impl_m = tcx.hir().as_local_hir_id(impl_m.def_id)?;
 835                         let impl_m = tcx.hir().impl_item(hir::ImplItemId { hir_id: impl_m });
 836                         let input_tys = match impl_m.node {
 837                             hir::ImplItemKind::Method(ref sig, _) => &sig.decl.inputs,
 838                             _ => unreachable!(),
 839                         };
 840                         struct Visitor(Option<Span>, hir::def_id::DefId);
 841                         impl<'v> hir::intravisit::Visitor<'v> for Visitor {
 842                             fn visit_ty(&mut self, ty: &'v hir::Ty) {
 843                                 hir::intravisit::walk_ty(self, ty);
 844                                 if let hir::TyKind::Path(
 845                                     hir::QPath::Resolved(None, ref path)) = ty.node
 846                                 {
 847                                     if let hir::def::Def::TyParam(def_id) = path.def {
 848                                         if def_id == self.1 {
 849                                             self.0 = Some(ty.span);
 850                                         }
 851                                     }
 852                                 }
 853                             }
 854                             fn nested_visit_map<'this>(
 855                                 &'this mut self
 856                             ) -> hir::intravisit::NestedVisitorMap<'this, 'v> {
 857                                 hir::intravisit::NestedVisitorMap::None
 858                             }
 859                         }
 860                         let mut visitor = Visitor(None, impl_def_id);
 861                         for ty in input_tys {
 862                             hir::intravisit::Visitor::visit_ty(&mut visitor, ty);
 863                         }
 864                         let span = visitor.0?;
 865
 866                         let bounds = impl_m.generics.params.iter().find_map(|param| {
 867                             match param.kind {
 868                                 GenericParamKind::Lifetime { .. } => None,
 869                                 GenericParamKind::Type { .. } |
 870                                 GenericParamKind::Const { .. } => {
 871                                     if param.hir_id == impl_hir_id {
 872                                         Some(&param.bounds)
 873                                     } else {
 874                                         None
 875                                     }
 876                                 }
 877                             }
 878                         })?;
 879                         let bounds = bounds.first()?.span().to(bounds.last()?.span());
 880                         let bounds = tcx
 881                             .sess
 882                             .source_map()
 883                             .span_to_snippet(bounds)
 884                             .ok()?;
 885
 886                         err.multipart_suggestion(
 887                             "try removing the generic parameter and using `impl Trait` instead",
 888                             vec![
 889                                 // delete generic parameters
 890                                 (impl_m.generics.span, String::new()),
 891                                 // replace param usage with `impl Trait`
 892                                 (span, format!("impl {}", bounds)),
 893                             ],
 894                             Applicability::MaybeIncorrect,
 895                         );
 896                         Some(())
 897                     })();
 898                 },
 899                 _ => unreachable!(),
 900             }
 901             err.emit();
 902             error_found = true;
 903         }
 904     }
 905     if error_found {
 906         Err(ErrorReported)
 907     } else {
 908         Ok(())
 909     }
 910 }
 911
 912 pub fn compare_const_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 913                                     impl_c: &ty::AssociatedItem,
 914                                     impl_c_span: Span,
 915                                     trait_c: &ty::AssociatedItem,
 916                                     impl_trait_ref: ty::TraitRef<'tcx>) {
 917     debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref);
 918
 919     tcx.infer_ctxt().enter(|infcx| {
 920         let param_env = tcx.param_env(impl_c.def_id);
 921         let inh = Inherited::new(infcx, impl_c.def_id);
 922         let infcx = &inh.infcx;
 923
 924         // The below is for the most part highly similar to the procedure
 925         // for methods above. It is simpler in many respects, especially
 926         // because we shouldn't really have to deal with lifetimes or
 927         // predicates. In fact some of this should probably be put into
 928         // shared functions because of DRY violations...
 929         let trait_to_impl_substs = impl_trait_ref.substs;
 930
 931         // Create a parameter environment that represents the implementation's
 932         // method.
 933         let impl_c_hir_id = tcx.hir().as_local_hir_id(impl_c.def_id).unwrap();
 934
 935         // Compute placeholder form of impl and trait const tys.
 936         let impl_ty = tcx.type_of(impl_c.def_id);
 937         let trait_ty = tcx.type_of(trait_c.def_id).subst(tcx, trait_to_impl_substs);
 938         let mut cause = ObligationCause::misc(impl_c_span, impl_c_hir_id);
 939
 940         // There is no "body" here, so just pass dummy id.
 941         let impl_ty = inh.normalize_associated_types_in(impl_c_span,
 942                                                         impl_c_hir_id,
 943                                                         param_env,
 944                                                         &impl_ty);
 945
 946         debug!("compare_const_impl: impl_ty={:?}", impl_ty);
 947
 948         let trait_ty = inh.normalize_associated_types_in(impl_c_span,
 949                                                          impl_c_hir_id,
 950                                                          param_env,
 951                                                          &trait_ty);
 952
 953         debug!("compare_const_impl: trait_ty={:?}", trait_ty);
 954
 955         let err = infcx.at(&cause, param_env)
 956                        .sup(trait_ty, impl_ty)
 957                        .map(|ok| inh.register_infer_ok_obligations(ok));
 958
 959         if let Err(terr) = err {
 960             debug!("checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
 961                    impl_ty,
 962                    trait_ty);
 963
 964             // Locate the Span containing just the type of the offending impl
 965             match tcx.hir().expect_impl_item(impl_c_hir_id).node {
 966                 ImplItemKind::Const(ref ty, _) => cause.span = ty.span,
 967                 _ => bug!("{:?} is not a impl const", impl_c),
 968             }
 969
 970             let mut diag = struct_span_err!(tcx.sess,
 971                                             cause.span,
 972                                             E0326,
 973                                             "implemented const `{}` has an incompatible type for \
 974                                              trait",
 975                                             trait_c.ident);
 976
 977             let trait_c_hir_id = tcx.hir().as_local_hir_id(trait_c.def_id);
 978             let trait_c_span = trait_c_hir_id.map(|trait_c_hir_id| {
 979                 // Add a label to the Span containing just the type of the const
 980                 match tcx.hir().expect_trait_item(trait_c_hir_id).node {
 981                     TraitItemKind::Const(ref ty, _) => ty.span,
 982                     _ => bug!("{:?} is not a trait const", trait_c),
 983                 }
 984             });
 985
 986             infcx.note_type_err(&mut diag,
 987                                 &cause,
 988                                 trait_c_span.map(|span| (span, "type in trait".to_owned())),
 989                                 Some(infer::ValuePairs::Types(ExpectedFound {
 990                                     expected: trait_ty,
 991                                     found: impl_ty,
 992                                 })),
 993                                 &terr);
 994             diag.emit();
 995         }
 996
 997         // Check that all obligations are satisfied by the implementation's
 998         // version.
 999         if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
1000             infcx.report_fulfillment_errors(errors, None, false);
1001             return;
1002         }
1003
1004         let fcx = FnCtxt::new(&inh, param_env, impl_c_hir_id);
1005         fcx.regionck_item(impl_c_hir_id, impl_c_span, &[]);
1006     });
1007 }