src/librustc_typeck/coherence/mod.rs

   1 // Copyright 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 // Coherence phase
  12 //
  13 // The job of the coherence phase of typechecking is to ensure that
  14 // each trait has at most one implementation for each type. This is
  15 // done by the orphan and overlap modules. Then we build up various
  16 // mappings. That mapping code resides here.
  17
  18
  19 use middle::def_id::{DefId, LOCAL_CRATE};
  20 use middle::lang_items::UnsizeTraitLangItem;
  21 use middle::subst::{self, Subst};
  22 use middle::traits;
  23 use middle::ty;
  24 use middle::ty::RegionEscape;
  25 use middle::ty::{ImplContainer, ImplOrTraitItemId, ConstTraitItemId};
  26 use middle::ty::{MethodTraitItemId, TypeTraitItemId, ParameterEnvironment};
  27 use middle::ty::{Ty, TyBool, TyChar, TyEnum, TyError};
  28 use middle::ty::{TyParam, TypeScheme, TyRawPtr};
  29 use middle::ty::{TyRef, TyStruct, TyTrait, TyTuple};
  30 use middle::ty::{TyStr, TyArray, TySlice, TyFloat, TyInfer, TyInt};
  31 use middle::ty::{TyUint, TyClosure, TyBox, TyBareFn};
  32 use middle::ty::TyProjection;
  33 use middle::ty::util::CopyImplementationError;
  34 use middle::free_region::FreeRegionMap;
  35 use CrateCtxt;
  36 use middle::infer::{self, InferCtxt, new_infer_ctxt};
  37 use std::cell::RefCell;
  38 use std::rc::Rc;
  39 use syntax::codemap::Span;
  40 use syntax::parse::token;
  41 use util::nodemap::{DefIdMap, FnvHashMap};
  42 use rustc::front::map as hir_map;
  43 use rustc::front::map::NodeItem;
  44 use rustc_front::visit;
  45 use rustc_front::hir::{Item, ItemImpl,Crate};
  46 use rustc_front::hir;
  47
  48 mod orphan;
  49 mod overlap;
  50 mod unsafety;
  51
  52 // Returns the def ID of the base type, if there is one.
  53 fn get_base_type_def_id<'a, 'tcx>(inference_context: &InferCtxt<'a, 'tcx>,
  54                                   span: Span,
  55                                   ty: Ty<'tcx>)
  56                                   -> Option<DefId> {
  57     match ty.sty {
  58         TyEnum(def, _) |
  59         TyStruct(def, _) => {
  60             Some(def.did)
  61         }
  62
  63         TyTrait(ref t) => {
  64             Some(t.principal_def_id())
  65         }
  66
  67         TyBox(_) => {
  68             inference_context.tcx.lang_items.owned_box()
  69         }
  70
  71         TyBool | TyChar | TyInt(..) | TyUint(..) | TyFloat(..) |
  72         TyStr(..) | TyArray(..) | TySlice(..) | TyBareFn(..) | TyTuple(..) |
  73         TyParam(..) | TyError |
  74         TyRawPtr(_) | TyRef(_, _) | TyProjection(..) => {
  75             None
  76         }
  77
  78         TyInfer(..) | TyClosure(..) => {
  79             // `ty` comes from a user declaration so we should only expect types
  80             // that the user can type
  81             inference_context.tcx.sess.span_bug(
  82                 span,
  83                 &format!("coherence encountered unexpected type searching for base type: {}",
  84                          ty));
  85         }
  86     }
  87 }
  88
  89 struct CoherenceChecker<'a, 'tcx: 'a> {
  90     crate_context: &'a CrateCtxt<'a, 'tcx>,
  91     inference_context: InferCtxt<'a, 'tcx>,
  92     inherent_impls: RefCell<DefIdMap<Rc<RefCell<Vec<DefId>>>>>,
  93 }
  94
  95 struct CoherenceCheckVisitor<'a, 'tcx: 'a> {
  96     cc: &'a CoherenceChecker<'a, 'tcx>
  97 }
  98
  99 impl<'a, 'tcx, 'v> visit::Visitor<'v> for CoherenceCheckVisitor<'a, 'tcx> {
 100     fn visit_item(&mut self, item: &Item) {
 101         if let ItemImpl(..) = item.node {
 102             self.cc.check_implementation(item)
 103         }
 104
 105         visit::walk_item(self, item);
 106     }
 107 }
 108
 109 impl<'a, 'tcx> CoherenceChecker<'a, 'tcx> {
 110     fn check(&self, krate: &Crate) {
 111         // Check implementations and traits. This populates the tables
 112         // containing the inherent methods and extension methods. It also
 113         // builds up the trait inheritance table.
 114         let mut visitor = CoherenceCheckVisitor { cc: self };
 115         visit::walk_crate(&mut visitor, krate);
 116
 117         // Copy over the inherent impls we gathered up during the walk into
 118         // the tcx.
 119         let mut tcx_inherent_impls =
 120             self.crate_context.tcx.inherent_impls.borrow_mut();
 121         for (k, v) in self.inherent_impls.borrow().iter() {
 122             tcx_inherent_impls.insert((*k).clone(),
 123                                       Rc::new((*v.borrow()).clone()));
 124         }
 125
 126         // Populate the table of destructors. It might seem a bit strange to
 127         // do this here, but it's actually the most convenient place, since
 128         // the coherence tables contain the trait -> type mappings.
 129         self.populate_destructor_table();
 130
 131         // Check to make sure implementations of `Copy` are legal.
 132         self.check_implementations_of_copy();
 133
 134         // Check to make sure implementations of `CoerceUnsized` are legal
 135         // and collect the necessary information from them.
 136         self.check_implementations_of_coerce_unsized();
 137     }
 138
 139     fn check_implementation(&self, item: &Item) {
 140         let tcx = self.crate_context.tcx;
 141         let impl_did = DefId::local(item.id);
 142         let self_type = tcx.lookup_item_type(impl_did);
 143
 144         // If there are no traits, then this implementation must have a
 145         // base type.
 146
 147         let impl_items = self.create_impl_from_item(item);
 148
 149         if let Some(trait_ref) = self.crate_context.tcx.impl_trait_ref(impl_did) {
 150             debug!("(checking implementation) adding impl for trait '{:?}', item '{}'",
 151                    trait_ref,
 152                    item.ident);
 153
 154             enforce_trait_manually_implementable(self.crate_context.tcx,
 155                                                  item.span,
 156                                                  trait_ref.def_id);
 157             self.add_trait_impl(trait_ref, impl_did);
 158         } else {
 159             // Add the implementation to the mapping from implementation to base
 160             // type def ID, if there is a base type for this implementation and
 161             // the implementation does not have any associated traits.
 162             if let Some(base_type_def_id) = get_base_type_def_id(
 163                     &self.inference_context, item.span, self_type.ty) {
 164                 self.add_inherent_impl(base_type_def_id, impl_did);
 165             }
 166         }
 167
 168         tcx.impl_items.borrow_mut().insert(impl_did, impl_items);
 169     }
 170
 171     // Creates default method IDs and performs type substitutions for an impl
 172     // and trait pair. Then, for each provided method in the trait, inserts a
 173     // `ProvidedMethodInfo` instance into the `provided_method_sources` map.
 174     fn instantiate_default_methods(
 175             &self,
 176             impl_id: DefId,
 177             trait_ref: &ty::TraitRef<'tcx>,
 178             all_impl_items: &mut Vec<ImplOrTraitItemId>) {
 179         let tcx = self.crate_context.tcx;
 180         debug!("instantiate_default_methods(impl_id={:?}, trait_ref={:?})",
 181                impl_id, trait_ref);
 182
 183         let impl_type_scheme = tcx.lookup_item_type(impl_id);
 184
 185         let prov = tcx.provided_trait_methods(trait_ref.def_id);
 186         for trait_method in &prov {
 187             // Synthesize an ID.
 188             let new_id = tcx.sess.next_node_id();
 189             let new_did = DefId::local(new_id);
 190
 191             debug!("new_did={:?} trait_method={:?}", new_did, trait_method);
 192
 193             // Create substitutions for the various trait parameters.
 194             let new_method_ty =
 195                 Rc::new(subst_receiver_types_in_method_ty(
 196                     tcx,
 197                     impl_id,
 198                     &impl_type_scheme,
 199                     trait_ref,
 200                     new_did,
 201                     &**trait_method,
 202                     Some(trait_method.def_id)));
 203
 204             debug!("new_method_ty={:?}", new_method_ty);
 205             all_impl_items.push(MethodTraitItemId(new_did));
 206
 207             // construct the polytype for the method based on the
 208             // method_ty.  it will have all the generics from the
 209             // impl, plus its own.
 210             let new_polytype = ty::TypeScheme {
 211                 generics: new_method_ty.generics.clone(),
 212                 ty: tcx.mk_fn(Some(new_did),
 213                               tcx.mk_bare_fn(new_method_ty.fty.clone()))
 214             };
 215             debug!("new_polytype={:?}", new_polytype);
 216
 217             tcx.register_item_type(new_did, new_polytype);
 218             tcx.predicates.borrow_mut().insert(new_did, new_method_ty.predicates.clone());
 219             tcx.impl_or_trait_items
 220                .borrow_mut()
 221                .insert(new_did, ty::MethodTraitItem(new_method_ty));
 222
 223             // Pair the new synthesized ID up with the
 224             // ID of the method.
 225             self.crate_context.tcx.provided_method_sources.borrow_mut()
 226                 .insert(new_did, trait_method.def_id);
 227         }
 228     }
 229
 230     fn add_inherent_impl(&self, base_def_id: DefId, impl_def_id: DefId) {
 231         match self.inherent_impls.borrow().get(&base_def_id) {
 232             Some(implementation_list) => {
 233                 implementation_list.borrow_mut().push(impl_def_id);
 234                 return;
 235             }
 236             None => {}
 237         }
 238
 239         self.inherent_impls.borrow_mut().insert(
 240             base_def_id,
 241             Rc::new(RefCell::new(vec!(impl_def_id))));
 242     }
 243
 244     fn add_trait_impl(&self, impl_trait_ref: ty::TraitRef<'tcx>, impl_def_id: DefId) {
 245         debug!("add_trait_impl: impl_trait_ref={:?} impl_def_id={:?}",
 246                impl_trait_ref, impl_def_id);
 247         let trait_def = self.crate_context.tcx.lookup_trait_def(impl_trait_ref.def_id);
 248         trait_def.record_impl(self.crate_context.tcx, impl_def_id, impl_trait_ref);
 249     }
 250
 251     // Converts an implementation in the AST to a vector of items.
 252     fn create_impl_from_item(&self, item: &Item) -> Vec<ImplOrTraitItemId> {
 253         match item.node {
 254             ItemImpl(_, _, _, _, _, ref impl_items) => {
 255                 let mut items: Vec<ImplOrTraitItemId> =
 256                         impl_items.iter().map(|impl_item| {
 257                     match impl_item.node {
 258                         hir::ConstImplItem(..) => {
 259                             ConstTraitItemId(DefId::local(impl_item.id))
 260                         }
 261                         hir::MethodImplItem(..) => {
 262                             MethodTraitItemId(DefId::local(impl_item.id))
 263                         }
 264                         hir::TypeImplItem(_) => {
 265                             TypeTraitItemId(DefId::local(impl_item.id))
 266                         }
 267                     }
 268                 }).collect();
 269
 270                 let def_id = DefId::local(item.id);
 271                 if let Some(trait_ref) = self.crate_context.tcx.impl_trait_ref(def_id) {
 272                     self.instantiate_default_methods(def_id, &trait_ref, &mut items);
 273                 }
 274
 275                 items
 276             }
 277             _ => {
 278                 self.crate_context.tcx.sess.span_bug(item.span,
 279                                                      "can't convert a non-impl \
 280                                                       to an impl");
 281             }
 282         }
 283     }
 284
 285     //
 286     // Destructors
 287     //
 288
 289     fn populate_destructor_table(&self) {
 290         let tcx = self.crate_context.tcx;
 291         let drop_trait = match tcx.lang_items.drop_trait() {
 292             Some(id) => id, None => { return }
 293         };
 294         tcx.populate_implementations_for_trait_if_necessary(drop_trait);
 295         let drop_trait = tcx.lookup_trait_def(drop_trait);
 296
 297         let impl_items = tcx.impl_items.borrow();
 298
 299         drop_trait.for_each_impl(tcx, |impl_did| {
 300             let items = impl_items.get(&impl_did).unwrap();
 301             if items.is_empty() {
 302                 // We'll error out later. For now, just don't ICE.
 303                 return;
 304             }
 305             let method_def_id = items[0];
 306
 307             let self_type = tcx.lookup_item_type(impl_did);
 308             match self_type.ty.sty {
 309                 ty::TyEnum(type_def, _) |
 310                 ty::TyStruct(type_def, _) => {
 311                     type_def.set_destructor(method_def_id.def_id());
 312                     tcx.destructors
 313                        .borrow_mut()
 314                        .insert(method_def_id.def_id());
 315                 }
 316                 _ => {
 317                     // Destructors only work on nominal types.
 318                     if impl_did.is_local() {
 319                         {
 320                             match tcx.map.find(impl_did.node) {
 321                                 Some(hir_map::NodeItem(item)) => {
 322                                     span_err!(tcx.sess, item.span, E0120,
 323                                         "the Drop trait may only be implemented on structures");
 324                                 }
 325                                 _ => {
 326                                     tcx.sess.bug("didn't find impl in ast \
 327                                                   map");
 328                                 }
 329                             }
 330                         }
 331                     } else {
 332                         tcx.sess.bug("found external impl of Drop trait on \
 333                                       something other than a struct");
 334                     }
 335                 }
 336             }
 337         });
 338     }
 339
 340     /// Ensures that implementations of the built-in trait `Copy` are legal.
 341     fn check_implementations_of_copy(&self) {
 342         let tcx = self.crate_context.tcx;
 343         let copy_trait = match tcx.lang_items.copy_trait() {
 344             Some(id) => id,
 345             None => return,
 346         };
 347         tcx.populate_implementations_for_trait_if_necessary(copy_trait);
 348         let copy_trait = tcx.lookup_trait_def(copy_trait);
 349
 350         copy_trait.for_each_impl(tcx, |impl_did| {
 351             debug!("check_implementations_of_copy: impl_did={:?}",
 352                    impl_did);
 353
 354             if impl_did.krate != LOCAL_CRATE {
 355                 debug!("check_implementations_of_copy(): impl not in this \
 356                         crate");
 357                 return
 358             }
 359
 360             let self_type = tcx.lookup_item_type(impl_did);
 361             debug!("check_implementations_of_copy: self_type={:?} (bound)",
 362                    self_type);
 363
 364             let span = tcx.map.span(impl_did.node);
 365             let param_env = ParameterEnvironment::for_item(tcx, impl_did.node);
 366             let self_type = self_type.ty.subst(tcx, &param_env.free_substs);
 367             assert!(!self_type.has_escaping_regions());
 368
 369             debug!("check_implementations_of_copy: self_type={:?} (free)",
 370                    self_type);
 371
 372             match param_env.can_type_implement_copy(self_type, span) {
 373                 Ok(()) => {}
 374                 Err(CopyImplementationError::InfrigingField(name)) => {
 375                        span_err!(tcx.sess, span, E0204,
 376                                  "the trait `Copy` may not be \
 377                                           implemented for this type; field \
 378                                           `{}` does not implement `Copy`",
 379                                          name)
 380                 }
 381                 Err(CopyImplementationError::InfrigingVariant(name)) => {
 382                        span_err!(tcx.sess, span, E0205,
 383                                  "the trait `Copy` may not be \
 384                                           implemented for this type; variant \
 385                                           `{}` does not implement `Copy`",
 386                                          name)
 387                 }
 388                 Err(CopyImplementationError::NotAnAdt) => {
 389                        span_err!(tcx.sess, span, E0206,
 390                                  "the trait `Copy` may not be implemented \
 391                                   for this type; type is not a structure or \
 392                                   enumeration")
 393                 }
 394                 Err(CopyImplementationError::HasDestructor) => {
 395                     span_err!(tcx.sess, span, E0184,
 396                               "the trait `Copy` may not be implemented for this type; \
 397                                the type has a destructor");
 398                 }
 399             }
 400         });
 401     }
 402
 403     /// Process implementations of the built-in trait `CoerceUnsized`.
 404     fn check_implementations_of_coerce_unsized(&self) {
 405         let tcx = self.crate_context.tcx;
 406         let coerce_unsized_trait = match tcx.lang_items.coerce_unsized_trait() {
 407             Some(id) => id,
 408             None => return,
 409         };
 410         let unsize_trait = match tcx.lang_items.require(UnsizeTraitLangItem) {
 411             Ok(id) => id,
 412             Err(err) => {
 413                 tcx.sess.fatal(&format!("`CoerceUnsized` implementation {}", err));
 414             }
 415         };
 416
 417         let trait_def = tcx.lookup_trait_def(coerce_unsized_trait);
 418
 419         trait_def.for_each_impl(tcx, |impl_did| {
 420             debug!("check_implementations_of_coerce_unsized: impl_did={:?}",
 421                    impl_did);
 422
 423             if impl_did.krate != LOCAL_CRATE {
 424                 debug!("check_implementations_of_coerce_unsized(): impl not \
 425                         in this crate");
 426                 return;
 427             }
 428
 429             let source = tcx.lookup_item_type(impl_did).ty;
 430             let trait_ref = self.crate_context.tcx.impl_trait_ref(impl_did).unwrap();
 431             let target = *trait_ref.substs.types.get(subst::TypeSpace, 0);
 432             debug!("check_implementations_of_coerce_unsized: {:?} -> {:?} (bound)",
 433                    source, target);
 434
 435             let span = tcx.map.span(impl_did.node);
 436             let param_env = ParameterEnvironment::for_item(tcx, impl_did.node);
 437             let source = source.subst(tcx, &param_env.free_substs);
 438             let target = target.subst(tcx, &param_env.free_substs);
 439             assert!(!source.has_escaping_regions());
 440
 441             debug!("check_implementations_of_coerce_unsized: {:?} -> {:?} (free)",
 442                    source, target);
 443
 444             let infcx = new_infer_ctxt(tcx, &tcx.tables, Some(param_env), true);
 445
 446             let check_mutbl = |mt_a: ty::TypeAndMut<'tcx>, mt_b: ty::TypeAndMut<'tcx>,
 447                                mk_ptr: &Fn(Ty<'tcx>) -> Ty<'tcx>| {
 448                 if (mt_a.mutbl, mt_b.mutbl) == (hir::MutImmutable, hir::MutMutable) {
 449                     infcx.report_mismatched_types(span, mk_ptr(mt_b.ty),
 450                                                   target, &ty::error::TypeError::Mutability);
 451                 }
 452                 (mt_a.ty, mt_b.ty, unsize_trait, None)
 453             };
 454             let (source, target, trait_def_id, kind) = match (&source.sty, &target.sty) {
 455                 (&ty::TyBox(a), &ty::TyBox(b)) => (a, b, unsize_trait, None),
 456
 457                 (&ty::TyRef(r_a, mt_a), &ty::TyRef(r_b, mt_b)) => {
 458                     infer::mk_subr(&infcx, infer::RelateObjectBound(span), *r_b, *r_a);
 459                     check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ref(r_b, ty))
 460                 }
 461
 462                 (&ty::TyRef(_, mt_a), &ty::TyRawPtr(mt_b)) |
 463                 (&ty::TyRawPtr(mt_a), &ty::TyRawPtr(mt_b)) => {
 464                     check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty))
 465                 }
 466
 467                 (&ty::TyStruct(def_a, substs_a), &ty::TyStruct(def_b, substs_b)) => {
 468                     if def_a != def_b {
 469                         let source_path = tcx.item_path_str(def_a.did);
 470                         let target_path = tcx.item_path_str(def_b.did);
 471                         span_err!(tcx.sess, span, E0377,
 472                                   "the trait `CoerceUnsized` may only be implemented \
 473                                    for a coercion between structures with the same \
 474                                    definition; expected {}, found {}",
 475                                   source_path, target_path);
 476                         return;
 477                     }
 478
 479                     let origin = infer::Misc(span);
 480                     let fields = &def_a.struct_variant().fields;
 481                     let diff_fields = fields.iter().enumerate().filter_map(|(i, f)| {
 482                         let (a, b) = (f.ty(tcx, substs_a), f.ty(tcx, substs_b));
 483                         if infcx.sub_types(false, origin, b, a).is_ok() {
 484                             None
 485                         } else {
 486                             Some((i, a, b))
 487                         }
 488                     }).collect::<Vec<_>>();
 489
 490                     if diff_fields.is_empty() {
 491                         span_err!(tcx.sess, span, E0374,
 492                                   "the trait `CoerceUnsized` may only be implemented \
 493                                    for a coercion between structures with one field \
 494                                    being coerced, none found");
 495                         return;
 496                     } else if diff_fields.len() > 1 {
 497                         span_err!(tcx.sess, span, E0375,
 498                                   "the trait `CoerceUnsized` may only be implemented \
 499                                    for a coercion between structures with one field \
 500                                    being coerced, but {} fields need coercions: {}",
 501                                    diff_fields.len(), diff_fields.iter().map(|&(i, a, b)| {
 502                                         let name = fields[i].name;
 503                                         format!("{} ({} to {})",
 504                                                 if name == token::special_names::unnamed_field {
 505                                                     i.to_string()
 506                                                 } else {
 507                                                     name.to_string()
 508                                                 }, a, b)
 509                                    }).collect::<Vec<_>>().join(", "));
 510                         return;
 511                     }
 512
 513                     let (i, a, b) = diff_fields[0];
 514                     let kind = ty::adjustment::CustomCoerceUnsized::Struct(i);
 515                     (a, b, coerce_unsized_trait, Some(kind))
 516                 }
 517
 518                 _ => {
 519                     span_err!(tcx.sess, span, E0376,
 520                               "the trait `CoerceUnsized` may only be implemented \
 521                                for a coercion between structures");
 522                     return;
 523                 }
 524             };
 525
 526             let mut fulfill_cx = infcx.fulfillment_cx.borrow_mut();
 527
 528             // Register an obligation for `A: Trait<B>`.
 529             let cause = traits::ObligationCause::misc(span, impl_did.node);
 530             let predicate = traits::predicate_for_trait_def(tcx, cause, trait_def_id,
 531                                                             0, source, vec![target]);
 532             fulfill_cx.register_predicate_obligation(&infcx, predicate);
 533
 534             // Check that all transitive obligations are satisfied.
 535             if let Err(errors) = fulfill_cx.select_all_or_error(&infcx) {
 536                 traits::report_fulfillment_errors(&infcx, &errors);
 537             }
 538
 539             // Finally, resolve all regions.
 540             let mut free_regions = FreeRegionMap::new();
 541             free_regions.relate_free_regions_from_predicates(tcx, &infcx.parameter_environment
 542                                                                         .caller_bounds);
 543             infcx.resolve_regions_and_report_errors(&free_regions, impl_did.node);
 544
 545             if let Some(kind) = kind {
 546                 tcx.custom_coerce_unsized_kinds.borrow_mut().insert(impl_did, kind);
 547             }
 548         });
 549     }
 550 }
 551
 552 fn enforce_trait_manually_implementable(tcx: &ty::ctxt, sp: Span, trait_def_id: DefId) {
 553     if tcx.sess.features.borrow().unboxed_closures {
 554         // the feature gate allows all of them
 555         return
 556     }
 557     let did = Some(trait_def_id);
 558     let li = &tcx.lang_items;
 559
 560     let trait_name = if did == li.fn_trait() {
 561         "Fn"
 562     } else if did == li.fn_mut_trait() {
 563         "FnMut"
 564     } else if did == li.fn_once_trait() {
 565         "FnOnce"
 566     } else {
 567         return // everything OK
 568     };
 569     span_err!(tcx.sess, sp, E0183, "manual implementations of `{}` are experimental", trait_name);
 570     fileline_help!(tcx.sess, sp,
 571                "add `#![feature(unboxed_closures)]` to the crate attributes to enable");
 572 }
 573
 574 fn subst_receiver_types_in_method_ty<'tcx>(tcx: &ty::ctxt<'tcx>,
 575                                            impl_id: DefId,
 576                                            impl_type_scheme: &ty::TypeScheme<'tcx>,
 577                                            trait_ref: &ty::TraitRef<'tcx>,
 578                                            new_def_id: DefId,
 579                                            method: &ty::Method<'tcx>,
 580                                            provided_source: Option<DefId>)
 581                                            -> ty::Method<'tcx>
 582 {
 583     let combined_substs = tcx.make_substs_for_receiver_types(trait_ref, method);
 584
 585     debug!("subst_receiver_types_in_method_ty: combined_substs={:?}",
 586            combined_substs);
 587
 588     let method_predicates = method.predicates.subst(tcx, &combined_substs);
 589     let mut method_generics = method.generics.subst(tcx, &combined_substs);
 590
 591     // replace the type parameters declared on the trait with those
 592     // from the impl
 593     for &space in &[subst::TypeSpace, subst::SelfSpace] {
 594         method_generics.types.replace(
 595             space,
 596             impl_type_scheme.generics.types.get_slice(space).to_vec());
 597         method_generics.regions.replace(
 598             space,
 599             impl_type_scheme.generics.regions.get_slice(space).to_vec());
 600     }
 601
 602     debug!("subst_receiver_types_in_method_ty: method_generics={:?}",
 603            method_generics);
 604
 605     let method_fty = method.fty.subst(tcx, &combined_substs);
 606
 607     debug!("subst_receiver_types_in_method_ty: method_ty={:?}",
 608            method.fty);
 609
 610     ty::Method::new(
 611         method.name,
 612         method_generics,
 613         method_predicates,
 614         method_fty,
 615         method.explicit_self,
 616         method.vis,
 617         new_def_id,
 618         ImplContainer(impl_id),
 619         provided_source
 620     )
 621 }
 622
 623 pub fn check_coherence(crate_context: &CrateCtxt) {
 624     CoherenceChecker {
 625         crate_context: crate_context,
 626         inference_context: new_infer_ctxt(crate_context.tcx, &crate_context.tcx.tables, None, true),
 627         inherent_impls: RefCell::new(FnvHashMap()),
 628     }.check(crate_context.tcx.map.krate());
 629     unsafety::check(crate_context.tcx);
 630     orphan::check(crate_context.tcx);
 631     overlap::check(crate_context.tcx);
 632 }