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