src/librustc_typeck/check/compare_method.rs

   1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use rustc::hir::{self, ImplItemKind, TraitItemKind};
  12 use rustc::infer::{self, InferOk};
  13 use rustc::ty::{self, TyCtxt};
  14 use rustc::ty::util::ExplicitSelf;
  15 use rustc::traits::{self, ObligationCause, ObligationCauseCode, Reveal};
  16 use rustc::ty::error::{ExpectedFound, TypeError};
  17 use rustc::ty::subst::{Subst, Substs};
  18 use rustc::util::common::ErrorReported;
  19
  20 use syntax_pos::Span;
  21
  22 use super::{Inherited, FnCtxt};
  23
  24 /// Checks that a method from an impl conforms to the signature of
  25 /// the same method as declared in the trait.
  26 ///
  27 /// # Parameters
  28 ///
  29 /// - impl_m: type of the method we are checking
  30 /// - impl_m_span: span to use for reporting errors
  31 /// - trait_m: the method in the trait
  32 /// - impl_trait_ref: the TraitRef corresponding to the trait implementation
  33
  34 pub fn compare_impl_method<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
  35                                      impl_m: &ty::AssociatedItem,
  36                                      impl_m_span: Span,
  37                                      trait_m: &ty::AssociatedItem,
  38                                      impl_trait_ref: ty::TraitRef<'tcx>,
  39                                      trait_item_span: Option<Span>) {
  40     debug!("compare_impl_method(impl_trait_ref={:?})",
  41            impl_trait_ref);
  42
  43     let impl_m_span = tcx.sess.codemap().def_span(impl_m_span);
  44
  45     if let Err(ErrorReported) = compare_self_type(tcx,
  46                                                   impl_m,
  47                                                   impl_m_span,
  48                                                   trait_m,
  49                                                   impl_trait_ref) {
  50         return;
  51     }
  52
  53     if let Err(ErrorReported) = compare_number_of_generics(tcx,
  54                                                            impl_m,
  55                                                            impl_m_span,
  56                                                            trait_m,
  57                                                            trait_item_span) {
  58         return;
  59     }
  60
  61     if let Err(ErrorReported) = compare_number_of_method_arguments(tcx,
  62                                                                    impl_m,
  63                                                                    impl_m_span,
  64                                                                    trait_m,
  65                                                                    trait_item_span) {
  66         return;
  67     }
  68
  69     if let Err(ErrorReported) = compare_synthetic_generics(tcx,
  70                                                            impl_m,
  71                                                            impl_m_span,
  72                                                            trait_m,
  73                                                            trait_item_span) {
  74         return;
  75     }
  76
  77     if let Err(ErrorReported) = compare_predicate_entailment(tcx,
  78                                                              impl_m,
  79                                                              impl_m_span,
  80                                                              trait_m,
  81                                                              impl_trait_ref) {
  82         return;
  83     }
  84 }
  85
  86 fn compare_predicate_entailment<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
  87                                           impl_m: &ty::AssociatedItem,
  88                                           impl_m_span: Span,
  89                                           trait_m: &ty::AssociatedItem,
  90                                           impl_trait_ref: ty::TraitRef<'tcx>)
  91                                           -> Result<(), ErrorReported> {
  92     let trait_to_impl_substs = impl_trait_ref.substs;
  93
  94     // This node-id should be used for the `body_id` field on each
  95     // `ObligationCause` (and the `FnCtxt`). This is what
  96     // `regionck_item` expects.
  97     let impl_m_node_id = tcx.hir.as_local_node_id(impl_m.def_id).unwrap();
  98
  99     let cause = ObligationCause {
 100         span: impl_m_span,
 101         body_id: impl_m_node_id,
 102         code: ObligationCauseCode::CompareImplMethodObligation {
 103             item_name: impl_m.name,
 104             impl_item_def_id: impl_m.def_id,
 105             trait_item_def_id: trait_m.def_id,
 106         },
 107     };
 108
 109     // This code is best explained by example. Consider a trait:
 110     //
 111     //     trait Trait<'t,T> {
 112     //          fn method<'a,M>(t: &'t T, m: &'a M) -> Self;
 113     //     }
 114     //
 115     // And an impl:
 116     //
 117     //     impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
 118     //          fn method<'b,N>(t: &'j &'i U, m: &'b N) -> Foo;
 119     //     }
 120     //
 121     // We wish to decide if those two method types are compatible.
 122     //
 123     // We start out with trait_to_impl_substs, that maps the trait
 124     // type parameters to impl type parameters. This is taken from the
 125     // impl trait reference:
 126     //
 127     //     trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
 128     //
 129     // We create a mapping `dummy_substs` that maps from the impl type
 130     // parameters to fresh types and regions. For type parameters,
 131     // this is the identity transform, but we could as well use any
 132     // skolemized types. For regions, we convert from bound to free
 133     // regions (Note: but only early-bound regions, i.e., those
 134     // declared on the impl or used in type parameter bounds).
 135     //
 136     //     impl_to_skol_substs = {'i => 'i0, U => U0, N => N0 }
 137     //
 138     // Now we can apply skol_substs to the type of the impl method
 139     // to yield a new function type in terms of our fresh, skolemized
 140     // types:
 141     //
 142     //     <'b> fn(t: &'i0 U0, m: &'b) -> Foo
 143     //
 144     // We now want to extract and substitute the type of the *trait*
 145     // method and compare it. To do so, we must create a compound
 146     // substitution by combining trait_to_impl_substs and
 147     // impl_to_skol_substs, and also adding a mapping for the method
 148     // type parameters. We extend the mapping to also include
 149     // the method parameters.
 150     //
 151     //     trait_to_skol_substs = { T => &'i0 U0, Self => Foo, M => N0 }
 152     //
 153     // Applying this to the trait method type yields:
 154     //
 155     //     <'a> fn(t: &'i0 U0, m: &'a) -> Foo
 156     //
 157     // This type is also the same but the name of the bound region ('a
 158     // vs 'b).  However, the normal subtyping rules on fn types handle
 159     // this kind of equivalency just fine.
 160     //
 161     // We now use these substitutions to ensure that all declared bounds are
 162     // satisfied by the implementation's method.
 163     //
 164     // We do this by creating a parameter environment which contains a
 165     // substitution corresponding to impl_to_skol_substs. We then build
 166     // trait_to_skol_substs and use it to convert the predicates contained
 167     // in the trait_m.generics to the skolemized form.
 168     //
 169     // Finally we register each of these predicates as an obligation in
 170     // a fresh FulfillmentCtxt, and invoke select_all_or_error.
 171
 172     // Create mapping from impl to skolemized.
 173     let impl_to_skol_substs = Substs::identity_for_item(tcx, impl_m.def_id);
 174
 175     // Create mapping from trait to skolemized.
 176     let trait_to_skol_substs = impl_to_skol_substs.rebase_onto(tcx,
 177                                                                impl_m.container.id(),
 178                                                                trait_to_impl_substs);
 179     debug!("compare_impl_method: trait_to_skol_substs={:?}",
 180            trait_to_skol_substs);
 181
 182     let impl_m_generics = tcx.generics_of(impl_m.def_id);
 183     let trait_m_generics = tcx.generics_of(trait_m.def_id);
 184     let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
 185     let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
 186
 187     // Check region bounds.
 188     check_region_bounds_on_impl_method(tcx,
 189                                        impl_m_span,
 190                                        impl_m,
 191                                        trait_m,
 192                                        &trait_m_generics,
 193                                        &impl_m_generics,
 194                                        trait_to_skol_substs)?;
 195
 196     // Create obligations for each predicate declared by the impl
 197     // definition in the context of the trait's parameter
 198     // environment. We can't just use `impl_env.caller_bounds`,
 199     // however, because we want to replace all late-bound regions with
 200     // region variables.
 201     let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap());
 202     let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
 203
 204     debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
 205
 206     // This is the only tricky bit of the new way we check implementation methods
 207     // We need to build a set of predicates where only the method-level bounds
 208     // are from the trait and we assume all other bounds from the implementation
 209     // to be previously satisfied.
 210     //
 211     // We then register the obligations from the impl_m and check to see
 212     // if all constraints hold.
 213     hybrid_preds.predicates
 214                 .extend(trait_m_predicates.instantiate_own(tcx, trait_to_skol_substs).predicates);
 215
 216     // Construct trait parameter environment and then shift it into the skolemized viewpoint.
 217     // The key step here is to update the caller_bounds's predicates to be
 218     // the new hybrid bounds we computed.
 219     let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_node_id);
 220     let param_env = ty::ParamEnv::new(tcx.intern_predicates(&hybrid_preds.predicates),
 221                                       Reveal::UserFacing,
 222                                       ty::UniverseIndex::ROOT);
 223     let param_env = traits::normalize_param_env_or_error(tcx,
 224                                                          impl_m.def_id,
 225                                                          param_env,
 226                                                          normalize_cause.clone());
 227
 228     tcx.infer_ctxt().enter(|infcx| {
 229         let inh = Inherited::new(infcx, impl_m.def_id);
 230         let infcx = &inh.infcx;
 231
 232         debug!("compare_impl_method: caller_bounds={:?}",
 233                param_env.caller_bounds);
 234
 235         let mut selcx = traits::SelectionContext::new(&infcx);
 236
 237         let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_skol_substs);
 238         let (impl_m_own_bounds, _) = infcx.replace_late_bound_regions_with_fresh_var(impl_m_span,
 239                                                        infer::HigherRankedType,
 240                                                        &ty::Binder(impl_m_own_bounds.predicates));
 241         for predicate in impl_m_own_bounds {
 242             let traits::Normalized { value: predicate, obligations } =
 243                 traits::normalize(&mut selcx, param_env, normalize_cause.clone(), &predicate);
 244
 245             inh.register_predicates(obligations);
 246             inh.register_predicate(traits::Obligation::new(cause.clone(), param_env, predicate));
 247         }
 248
 249         // We now need to check that the signature of the impl method is
 250         // compatible with that of the trait method. We do this by
 251         // checking that `impl_fty <: trait_fty`.
 252         //
 253         // FIXME. Unfortunately, this doesn't quite work right now because
 254         // associated type normalization is not integrated into subtype
 255         // checks. For the comparison to be valid, we need to
 256         // normalize the associated types in the impl/trait methods
 257         // first. However, because function types bind regions, just
 258         // calling `normalize_associated_types_in` would have no effect on
 259         // any associated types appearing in the fn arguments or return
 260         // type.
 261
 262         // Compute skolemized form of impl and trait method tys.
 263         let tcx = infcx.tcx;
 264
 265         let (impl_sig, _) =
 266             infcx.replace_late_bound_regions_with_fresh_var(impl_m_span,
 267                                                             infer::HigherRankedType,
 268                                                             &tcx.fn_sig(impl_m.def_id));
 269         let impl_sig =
 270             inh.normalize_associated_types_in(impl_m_span,
 271                                               impl_m_node_id,
 272                                               param_env,
 273                                               &impl_sig);
 274         let impl_fty = tcx.mk_fn_ptr(ty::Binder(impl_sig));
 275         debug!("compare_impl_method: impl_fty={:?}", impl_fty);
 276
 277         let trait_sig = tcx.liberate_late_bound_regions(
 278             impl_m.def_id,
 279             &tcx.fn_sig(trait_m.def_id));
 280         let trait_sig =
 281             trait_sig.subst(tcx, trait_to_skol_substs);
 282         let trait_sig =
 283             inh.normalize_associated_types_in(impl_m_span,
 284                                               impl_m_node_id,
 285                                               param_env,
 286                                               &trait_sig);
 287         let trait_fty = tcx.mk_fn_ptr(ty::Binder(trait_sig));
 288
 289         debug!("compare_impl_method: trait_fty={:?}", trait_fty);
 290
 291         let sub_result = infcx.at(&cause, param_env)
 292                               .sup(trait_fty, impl_fty)
 293                               .map(|InferOk { obligations, .. }| {
 294                                   inh.register_predicates(obligations);
 295                               });
 296
 297         if let Err(terr) = sub_result {
 298             debug!("sub_types failed: impl ty {:?}, trait ty {:?}",
 299                    impl_fty,
 300                    trait_fty);
 301
 302             let (impl_err_span, trait_err_span) = extract_spans_for_error_reporting(&infcx,
 303                                                                                     param_env,
 304                                                                                     &terr,
 305                                                                                     &cause,
 306                                                                                     impl_m,
 307                                                                                     impl_sig,
 308                                                                                     trait_m,
 309                                                                                     trait_sig);
 310
 311             let cause = ObligationCause {
 312                 span: impl_err_span,
 313                 ..cause.clone()
 314             };
 315
 316             let mut diag = struct_span_err!(tcx.sess,
 317                                             cause.span(&tcx),
 318                                             E0053,
 319                                             "method `{}` has an incompatible type for trait",
 320                                             trait_m.name);
 321
 322             infcx.note_type_err(&mut diag,
 323                                 &cause,
 324                                 trait_err_span.map(|sp| (sp, format!("type in trait"))),
 325                                 Some(infer::ValuePairs::Types(ExpectedFound {
 326                                     expected: trait_fty,
 327                                     found: impl_fty,
 328                                 })),
 329                                 &terr);
 330             diag.emit();
 331             return Err(ErrorReported);
 332         }
 333
 334         // Check that all obligations are satisfied by the implementation's
 335         // version.
 336         if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
 337             infcx.report_fulfillment_errors(errors, None);
 338             return Err(ErrorReported);
 339         }
 340
 341         // Finally, resolve all regions. This catches wily misuses of
 342         // lifetime parameters.
 343         let fcx = FnCtxt::new(&inh, param_env, impl_m_node_id);
 344         fcx.regionck_item(impl_m_node_id, impl_m_span, &[]);
 345
 346         Ok(())
 347     })
 348 }
 349
 350 fn check_region_bounds_on_impl_method<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 351                                                 span: Span,
 352                                                 impl_m: &ty::AssociatedItem,
 353                                                 trait_m: &ty::AssociatedItem,
 354                                                 trait_generics: &ty::Generics,
 355                                                 impl_generics: &ty::Generics,
 356                                                 trait_to_skol_substs: &Substs<'tcx>)
 357                                                 -> Result<(), ErrorReported> {
 358     let span = tcx.sess.codemap().def_span(span);
 359     let trait_params = &trait_generics.regions[..];
 360     let impl_params = &impl_generics.regions[..];
 361
 362     debug!("check_region_bounds_on_impl_method: \
 363             trait_generics={:?} \
 364             impl_generics={:?} \
 365             trait_to_skol_substs={:?}",
 366            trait_generics,
 367            impl_generics,
 368            trait_to_skol_substs);
 369
 370     // Must have same number of early-bound lifetime parameters.
 371     // Unfortunately, if the user screws up the bounds, then this
 372     // will change classification between early and late.  E.g.,
 373     // if in trait we have `<'a,'b:'a>`, and in impl we just have
 374     // `<'a,'b>`, then we have 2 early-bound lifetime parameters
 375     // in trait but 0 in the impl. But if we report "expected 2
 376     // but found 0" it's confusing, because it looks like there
 377     // are zero. Since I don't quite know how to phrase things at
 378     // the moment, give a kind of vague error message.
 379     if trait_params.len() != impl_params.len() {
 380         let mut err = struct_span_err!(tcx.sess,
 381                                        span,
 382                                        E0195,
 383                                        "lifetime parameters or bounds on method `{}` do not match \
 384                                         the trait declaration",
 385                                        impl_m.name);
 386         err.span_label(span, "lifetimes do not match method in trait");
 387         if let Some(sp) = tcx.hir.span_if_local(trait_m.def_id) {
 388             err.span_label(tcx.sess.codemap().def_span(sp),
 389                            "lifetimes in impl do not match this method in trait");
 390         }
 391         err.emit();
 392         return Err(ErrorReported);
 393     }
 394
 395     return Ok(());
 396 }
 397
 398 fn extract_spans_for_error_reporting<'a, 'gcx, 'tcx>(infcx: &infer::InferCtxt<'a, 'gcx, 'tcx>,
 399                                                      param_env: ty::ParamEnv<'tcx>,
 400                                                      terr: &TypeError,
 401                                                      cause: &ObligationCause<'tcx>,
 402                                                      impl_m: &ty::AssociatedItem,
 403                                                      impl_sig: ty::FnSig<'tcx>,
 404                                                      trait_m: &ty::AssociatedItem,
 405                                                      trait_sig: ty::FnSig<'tcx>)
 406                                                      -> (Span, Option<Span>) {
 407     let tcx = infcx.tcx;
 408     let impl_m_node_id = tcx.hir.as_local_node_id(impl_m.def_id).unwrap();
 409     let (impl_m_output, impl_m_iter) = match tcx.hir.expect_impl_item(impl_m_node_id).node {
 410         ImplItemKind::Method(ref impl_m_sig, _) => {
 411             (&impl_m_sig.decl.output, impl_m_sig.decl.inputs.iter())
 412         }
 413         _ => bug!("{:?} is not a method", impl_m),
 414     };
 415
 416     match *terr {
 417         TypeError::Mutability => {
 418             if let Some(trait_m_node_id) = tcx.hir.as_local_node_id(trait_m.def_id) {
 419                 let trait_m_iter = match tcx.hir.expect_trait_item(trait_m_node_id).node {
 420                     TraitItemKind::Method(ref trait_m_sig, _) => {
 421                         trait_m_sig.decl.inputs.iter()
 422                     }
 423                     _ => bug!("{:?} is not a TraitItemKind::Method", trait_m),
 424                 };
 425
 426                 impl_m_iter.zip(trait_m_iter).find(|&(ref impl_arg, ref trait_arg)| {
 427                     match (&impl_arg.node, &trait_arg.node) {
 428                         (&hir::TyRptr(_, ref impl_mt), &hir::TyRptr(_, ref trait_mt)) |
 429                         (&hir::TyPtr(ref impl_mt), &hir::TyPtr(ref trait_mt)) => {
 430                             impl_mt.mutbl != trait_mt.mutbl
 431                         }
 432                         _ => false,
 433                     }
 434                 }).map(|(ref impl_arg, ref trait_arg)| {
 435                     (impl_arg.span, Some(trait_arg.span))
 436                 })
 437                 .unwrap_or_else(|| (cause.span(&tcx), tcx.hir.span_if_local(trait_m.def_id)))
 438             } else {
 439                 (cause.span(&tcx), tcx.hir.span_if_local(trait_m.def_id))
 440             }
 441         }
 442         TypeError::Sorts(ExpectedFound { .. }) => {
 443             if let Some(trait_m_node_id) = tcx.hir.as_local_node_id(trait_m.def_id) {
 444                 let (trait_m_output, trait_m_iter) =
 445                     match tcx.hir.expect_trait_item(trait_m_node_id).node {
 446                         TraitItemKind::Method(ref trait_m_sig, _) => {
 447                             (&trait_m_sig.decl.output, trait_m_sig.decl.inputs.iter())
 448                         }
 449                         _ => bug!("{:?} is not a TraitItemKind::Method", trait_m),
 450                     };
 451
 452                 let impl_iter = impl_sig.inputs().iter();
 453                 let trait_iter = trait_sig.inputs().iter();
 454                 impl_iter.zip(trait_iter)
 455                          .zip(impl_m_iter)
 456                          .zip(trait_m_iter)
 457                          .filter_map(|(((&impl_arg_ty, &trait_arg_ty), impl_arg), trait_arg)| {
 458                              match infcx.at(&cause, param_env).sub(trait_arg_ty, impl_arg_ty) {
 459                                  Ok(_) => None,
 460                                  Err(_) => Some((impl_arg.span, Some(trait_arg.span))),
 461                              }
 462                          })
 463                          .next()
 464                          .unwrap_or_else(|| {
 465                              if
 466                                  infcx.at(&cause, param_env)
 467                                       .sup(trait_sig.output(), impl_sig.output())
 468                                       .is_err()
 469                              {
 470                                  (impl_m_output.span(), Some(trait_m_output.span()))
 471                              } else {
 472                                  (cause.span(&tcx), tcx.hir.span_if_local(trait_m.def_id))
 473                              }
 474                          })
 475             } else {
 476                 (cause.span(&tcx), tcx.hir.span_if_local(trait_m.def_id))
 477             }
 478         }
 479         _ => (cause.span(&tcx), tcx.hir.span_if_local(trait_m.def_id)),
 480     }
 481 }
 482
 483 fn compare_self_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 484                                impl_m: &ty::AssociatedItem,
 485                                impl_m_span: Span,
 486                                trait_m: &ty::AssociatedItem,
 487                                impl_trait_ref: ty::TraitRef<'tcx>)
 488                                -> Result<(), ErrorReported>
 489 {
 490     // Try to give more informative error messages about self typing
 491     // mismatches.  Note that any mismatch will also be detected
 492     // below, where we construct a canonical function type that
 493     // includes the self parameter as a normal parameter.  It's just
 494     // that the error messages you get out of this code are a bit more
 495     // inscrutable, particularly for cases where one method has no
 496     // self.
 497
 498     let self_string = |method: &ty::AssociatedItem| {
 499         let untransformed_self_ty = match method.container {
 500             ty::ImplContainer(_) => impl_trait_ref.self_ty(),
 501             ty::TraitContainer(_) => tcx.mk_self_type()
 502         };
 503         let self_arg_ty = *tcx.fn_sig(method.def_id).input(0).skip_binder();
 504         let param_env = ty::ParamEnv::empty(Reveal::All);
 505
 506         tcx.infer_ctxt().enter(|infcx| {
 507             let self_arg_ty = tcx.liberate_late_bound_regions(
 508                 method.def_id,
 509                 &ty::Binder(self_arg_ty)
 510             );
 511             let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty).is_ok();
 512             match ExplicitSelf::determine(self_arg_ty, can_eq_self) {
 513                 ExplicitSelf::ByValue => "self".to_string(),
 514                 ExplicitSelf::ByReference(_, hir::MutImmutable) => "&self".to_string(),
 515                 ExplicitSelf::ByReference(_, hir::MutMutable) => "&mut self".to_string(),
 516                 _ => format!("self: {}", self_arg_ty)
 517             }
 518         })
 519     };
 520
 521     match (trait_m.method_has_self_argument, impl_m.method_has_self_argument) {
 522         (false, false) | (true, true) => {}
 523
 524         (false, true) => {
 525             let self_descr = self_string(impl_m);
 526             let mut err = struct_span_err!(tcx.sess,
 527                                            impl_m_span,
 528                                            E0185,
 529                                            "method `{}` has a `{}` declaration in the impl, but \
 530                                             not in the trait",
 531                                            trait_m.name,
 532                                            self_descr);
 533             err.span_label(impl_m_span, format!("`{}` used in impl", self_descr));
 534             if let Some(span) = tcx.hir.span_if_local(trait_m.def_id) {
 535                 err.span_label(span, format!("trait method declared without `{}`", self_descr));
 536             } else {
 537                 err.note_trait_signature(trait_m.name.to_string(),
 538                                          trait_m.signature(&tcx));
 539             }
 540             err.emit();
 541             return Err(ErrorReported);
 542         }
 543
 544         (true, false) => {
 545             let self_descr = self_string(trait_m);
 546             let mut err = struct_span_err!(tcx.sess,
 547                                            impl_m_span,
 548                                            E0186,
 549                                            "method `{}` has a `{}` declaration in the trait, but \
 550                                             not in the impl",
 551                                            trait_m.name,
 552                                            self_descr);
 553             err.span_label(impl_m_span, format!("expected `{}` in impl", self_descr));
 554             if let Some(span) = tcx.hir.span_if_local(trait_m.def_id) {
 555                 err.span_label(span, format!("`{}` used in trait", self_descr));
 556             } else {
 557                 err.note_trait_signature(trait_m.name.to_string(),
 558                                          trait_m.signature(&tcx));
 559             }
 560             err.emit();
 561             return Err(ErrorReported);
 562         }
 563     }
 564
 565     Ok(())
 566 }
 567
 568 fn compare_number_of_generics<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 569                                         impl_m: &ty::AssociatedItem,
 570                                         impl_m_span: Span,
 571                                         trait_m: &ty::AssociatedItem,
 572                                         trait_item_span: Option<Span>)
 573                                         -> Result<(), ErrorReported> {
 574     let impl_m_generics = tcx.generics_of(impl_m.def_id);
 575     let trait_m_generics = tcx.generics_of(trait_m.def_id);
 576     let num_impl_m_type_params = impl_m_generics.types.len();
 577     let num_trait_m_type_params = trait_m_generics.types.len();
 578     if num_impl_m_type_params != num_trait_m_type_params {
 579         let impl_m_node_id = tcx.hir.as_local_node_id(impl_m.def_id).unwrap();
 580         let impl_m_item = tcx.hir.expect_impl_item(impl_m_node_id);
 581         let span = if impl_m_item.generics.params.is_empty() {
 582             impl_m_span
 583         } else {
 584             impl_m_item.generics.span
 585         };
 586
 587         let mut err = struct_span_err!(tcx.sess,
 588                                        span,
 589                                        E0049,
 590                                        "method `{}` has {} type parameter{} but its trait \
 591                                         declaration has {} type parameter{}",
 592                                        trait_m.name,
 593                                        num_impl_m_type_params,
 594                                        if num_impl_m_type_params == 1 { "" } else { "s" },
 595                                        num_trait_m_type_params,
 596                                        if num_trait_m_type_params == 1 {
 597                                            ""
 598                                        } else {
 599                                            "s"
 600                                        });
 601
 602         let mut suffix = None;
 603
 604         if let Some(span) = trait_item_span {
 605             err.span_label(span,
 606                            format!("expected {}",
 607                                     &if num_trait_m_type_params != 1 {
 608                                         format!("{} type parameters", num_trait_m_type_params)
 609                                     } else {
 610                                         format!("{} type parameter", num_trait_m_type_params)
 611                                     }));
 612         } else {
 613             suffix = Some(format!(", expected {}", num_trait_m_type_params));
 614         }
 615
 616         err.span_label(span,
 617                        format!("found {}{}",
 618                                 &if num_impl_m_type_params != 1 {
 619                                     format!("{} type parameters", num_impl_m_type_params)
 620                                 } else {
 621                                     format!("1 type parameter")
 622                                 },
 623                                 suffix.as_ref().map(|s| &s[..]).unwrap_or("")));
 624
 625         err.emit();
 626
 627         return Err(ErrorReported);
 628     }
 629
 630     Ok(())
 631 }
 632
 633 fn compare_number_of_method_arguments<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 634                                                 impl_m: &ty::AssociatedItem,
 635                                                 impl_m_span: Span,
 636                                                 trait_m: &ty::AssociatedItem,
 637                                                 trait_item_span: Option<Span>)
 638                                                 -> Result<(), ErrorReported> {
 639     let impl_m_fty = tcx.fn_sig(impl_m.def_id);
 640     let trait_m_fty = tcx.fn_sig(trait_m.def_id);
 641     let trait_number_args = trait_m_fty.inputs().skip_binder().len();
 642     let impl_number_args = impl_m_fty.inputs().skip_binder().len();
 643     if trait_number_args != impl_number_args {
 644         let trait_m_node_id = tcx.hir.as_local_node_id(trait_m.def_id);
 645         let trait_span = if let Some(trait_id) = trait_m_node_id {
 646             match tcx.hir.expect_trait_item(trait_id).node {
 647                 TraitItemKind::Method(ref trait_m_sig, _) => {
 648                     if let Some(arg) = trait_m_sig.decl.inputs.get(if trait_number_args > 0 {
 649                         trait_number_args - 1
 650                     } else {
 651                         0
 652                     }) {
 653                         Some(arg.span)
 654                     } else {
 655                         trait_item_span
 656                     }
 657                 }
 658                 _ => bug!("{:?} is not a method", impl_m),
 659             }
 660         } else {
 661             trait_item_span
 662         };
 663         let impl_m_node_id = tcx.hir.as_local_node_id(impl_m.def_id).unwrap();
 664         let impl_span = match tcx.hir.expect_impl_item(impl_m_node_id).node {
 665             ImplItemKind::Method(ref impl_m_sig, _) => {
 666                 if let Some(arg) = impl_m_sig.decl.inputs.get(if impl_number_args > 0 {
 667                     impl_number_args - 1
 668                 } else {
 669                     0
 670                 }) {
 671                     arg.span
 672                 } else {
 673                     impl_m_span
 674                 }
 675             }
 676             _ => bug!("{:?} is not a method", impl_m),
 677         };
 678         let mut err = struct_span_err!(tcx.sess,
 679                                        impl_span,
 680                                        E0050,
 681                                        "method `{}` has {} parameter{} but the declaration in \
 682                                         trait `{}` has {}",
 683                                        trait_m.name,
 684                                        impl_number_args,
 685                                        if impl_number_args == 1 { "" } else { "s" },
 686                                        tcx.item_path_str(trait_m.def_id),
 687                                        trait_number_args);
 688         if let Some(trait_span) = trait_span {
 689             err.span_label(trait_span,
 690                            format!("trait requires {}",
 691                                     &if trait_number_args != 1 {
 692                                         format!("{} parameters", trait_number_args)
 693                                     } else {
 694                                         format!("{} parameter", trait_number_args)
 695                                     }));
 696         } else {
 697             err.note_trait_signature(trait_m.name.to_string(),
 698                                      trait_m.signature(&tcx));
 699         }
 700         err.span_label(impl_span,
 701                        format!("expected {}, found {}",
 702                                 &if trait_number_args != 1 {
 703                                     format!("{} parameters", trait_number_args)
 704                                 } else {
 705                                     format!("{} parameter", trait_number_args)
 706                                 },
 707                                 impl_number_args));
 708         err.emit();
 709         return Err(ErrorReported);
 710     }
 711
 712     Ok(())
 713 }
 714
 715 fn compare_synthetic_generics<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 716                                         impl_m: &ty::AssociatedItem,
 717                                         _impl_m_span: Span, // FIXME necessary?
 718                                         trait_m: &ty::AssociatedItem,
 719                                         _trait_item_span: Option<Span>) // FIXME necessary?
 720                                         -> Result<(), ErrorReported> {
 721     // FIXME(chrisvittal) Clean up this function, list of FIXME items:
 722     //     1. Better messages for the span lables
 723     //     2. Explanation as to what is going on
 724     //     3. Correct the function signature for what we actually use
 725     // If we get here, we already have the same number of generics, so the zip will
 726     // be okay.
 727     let mut error_found = false;
 728     let impl_m_generics = tcx.generics_of(impl_m.def_id);
 729     let trait_m_generics = tcx.generics_of(trait_m.def_id);
 730     for (impl_ty, trait_ty) in impl_m_generics.types.iter().zip(trait_m_generics.types.iter()) {
 731         if impl_ty.synthetic != trait_ty.synthetic {
 732             let impl_node_id = tcx.hir.as_local_node_id(impl_ty.def_id).unwrap();
 733             let impl_span = tcx.hir.span(impl_node_id);
 734             let trait_node_id = tcx.hir.as_local_node_id(trait_ty.def_id).unwrap();
 735             let trait_span = tcx.hir.span(trait_node_id);
 736             let mut err = struct_span_err!(tcx.sess,
 737                                            impl_span,
 738                                            E0643,
 739                                            "method `{}` has incompatible signature for trait",
 740                                            trait_m.name);
 741             err.span_label(trait_span, "annotation in trait");
 742             err.span_label(impl_span, "annotation in impl");
 743             err.emit();
 744             error_found = true;
 745         }
 746     }
 747     if error_found {
 748         Err(ErrorReported)
 749     } else {
 750         Ok(())
 751     }
 752 }
 753
 754 pub fn compare_const_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 755                                     impl_c: &ty::AssociatedItem,
 756                                     impl_c_span: Span,
 757                                     trait_c: &ty::AssociatedItem,
 758                                     impl_trait_ref: ty::TraitRef<'tcx>) {
 759     debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref);
 760
 761     tcx.infer_ctxt().enter(|infcx| {
 762         let param_env = ty::ParamEnv::empty(Reveal::UserFacing);
 763         let inh = Inherited::new(infcx, impl_c.def_id);
 764         let infcx = &inh.infcx;
 765
 766         // The below is for the most part highly similar to the procedure
 767         // for methods above. It is simpler in many respects, especially
 768         // because we shouldn't really have to deal with lifetimes or
 769         // predicates. In fact some of this should probably be put into
 770         // shared functions because of DRY violations...
 771         let trait_to_impl_substs = impl_trait_ref.substs;
 772
 773         // Create a parameter environment that represents the implementation's
 774         // method.
 775         let impl_c_node_id = tcx.hir.as_local_node_id(impl_c.def_id).unwrap();
 776
 777         // Compute skolemized form of impl and trait const tys.
 778         let impl_ty = tcx.type_of(impl_c.def_id);
 779         let trait_ty = tcx.type_of(trait_c.def_id).subst(tcx, trait_to_impl_substs);
 780         let mut cause = ObligationCause::misc(impl_c_span, impl_c_node_id);
 781
 782         // There is no "body" here, so just pass dummy id.
 783         let impl_ty = inh.normalize_associated_types_in(impl_c_span,
 784                                                         impl_c_node_id,
 785                                                         param_env,
 786                                                         &impl_ty);
 787
 788         debug!("compare_const_impl: impl_ty={:?}", impl_ty);
 789
 790         let trait_ty = inh.normalize_associated_types_in(impl_c_span,
 791                                                          impl_c_node_id,
 792                                                          param_env,
 793                                                          &trait_ty);
 794
 795         debug!("compare_const_impl: trait_ty={:?}", trait_ty);
 796
 797         let err = infcx.at(&cause, param_env)
 798                        .sup(trait_ty, impl_ty)
 799                        .map(|ok| inh.register_infer_ok_obligations(ok));
 800
 801         if let Err(terr) = err {
 802             debug!("checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
 803                    impl_ty,
 804                    trait_ty);
 805
 806             // Locate the Span containing just the type of the offending impl
 807             match tcx.hir.expect_impl_item(impl_c_node_id).node {
 808                 ImplItemKind::Const(ref ty, _) => cause.span = ty.span,
 809                 _ => bug!("{:?} is not a impl const", impl_c),
 810             }
 811
 812             let mut diag = struct_span_err!(tcx.sess,
 813                                             cause.span,
 814                                             E0326,
 815                                             "implemented const `{}` has an incompatible type for \
 816                                              trait",
 817                                             trait_c.name);
 818
 819             let trait_c_node_id = tcx.hir.as_local_node_id(trait_c.def_id);
 820             let trait_c_span = trait_c_node_id.map(|trait_c_node_id| {
 821                 // Add a label to the Span containing just the type of the const
 822                 match tcx.hir.expect_trait_item(trait_c_node_id).node {
 823                     TraitItemKind::Const(ref ty, _) => ty.span,
 824                     _ => bug!("{:?} is not a trait const", trait_c),
 825                 }
 826             });
 827
 828             infcx.note_type_err(&mut diag,
 829                                 &cause,
 830                                 trait_c_span.map(|span| (span, format!("type in trait"))),
 831                                 Some(infer::ValuePairs::Types(ExpectedFound {
 832                                     expected: trait_ty,
 833                                     found: impl_ty,
 834                                 })),
 835                                 &terr);
 836             diag.emit();
 837         }
 838
 839         // Check that all obligations are satisfied by the implementation's
 840         // version.
 841         if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
 842             infcx.report_fulfillment_errors(errors, None);
 843             return;
 844         }
 845
 846         let fcx = FnCtxt::new(&inh, param_env, impl_c_node_id);
 847         fcx.regionck_item(impl_c_node_id, impl_c_span, &[]);
 848     });
 849 }