src/librustc/middle/typeck/coherence.rs

   1 // Copyright 2012-2013 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 each trait
  14 // has at most one implementation for each type. Then we build a mapping from
  15 // each trait in the system to its implementations.
  16
  17
  18 use metadata::csearch::{each_impl, get_impl_trait, each_implementation_for_trait};
  19 use metadata::csearch;
  20 use middle::subst;
  21 use middle::subst::{Substs};
  22 use middle::ty::get;
  23 use middle::ty::{ImplContainer, ImplOrTraitItemId, MethodTraitItemId};
  24 use middle::ty::{lookup_item_type};
  25 use middle::ty::{t, ty_bool, ty_char, ty_bot, ty_box, ty_enum, ty_err};
  26 use middle::ty::{ty_str, ty_vec, ty_float, ty_infer, ty_int, ty_nil, ty_open};
  27 use middle::ty::{ty_param, Polytype, ty_ptr};
  28 use middle::ty::{ty_rptr, ty_struct, ty_trait, ty_tup};
  29 use middle::ty::{ty_uint, ty_unboxed_closure, ty_uniq, ty_bare_fn};
  30 use middle::ty::{ty_closure};
  31 use middle::ty::type_is_ty_var;
  32 use middle::subst::Subst;
  33 use middle::ty;
  34 use middle::typeck::CrateCtxt;
  35 use middle::typeck::infer::combine::Combine;
  36 use middle::typeck::infer::InferCtxt;
  37 use middle::typeck::infer::{new_infer_ctxt, resolve_ivar, resolve_type};
  38 use middle::typeck::infer;
  39 use util::ppaux::Repr;
  40 use middle::def::{DefStruct, DefTy};
  41 use syntax::ast::{Crate, DefId};
  42 use syntax::ast::{Item, ItemEnum, ItemImpl, ItemMod, ItemStruct};
  43 use syntax::ast::{LOCAL_CRATE, TraitRef, TyPath};
  44 use syntax::ast;
  45 use syntax::ast_map::NodeItem;
  46 use syntax::ast_map;
  47 use syntax::ast_util::{local_def};
  48 use syntax::codemap::{Span, DUMMY_SP};
  49 use syntax::parse::token;
  50 use syntax::visit;
  51
  52 use std::collections::HashSet;
  53 use std::cell::RefCell;
  54 use std::rc::Rc;
  55
  56 struct UniversalQuantificationResult {
  57     monotype: t
  58 }
  59
  60 fn get_base_type(inference_context: &InferCtxt,
  61                  span: Span,
  62                  original_type: t)
  63                  -> Option<t> {
  64     let resolved_type = match resolve_type(inference_context,
  65                                            Some(span),
  66                                            original_type,
  67                                            resolve_ivar) {
  68         Ok(resulting_type) if !type_is_ty_var(resulting_type) => resulting_type,
  69         _ => {
  70             inference_context.tcx.sess.span_fatal(span,
  71                                                   "the type of this value must be known in order \
  72                                                    to determine the base type");
  73         }
  74     };
  75
  76     match get(resolved_type).sty {
  77         ty_enum(..) | ty_struct(..) | ty_unboxed_closure(..) => {
  78             debug!("(getting base type) found base type");
  79             Some(resolved_type)
  80         }
  81
  82         _ if ty::type_is_trait(resolved_type) => {
  83             debug!("(getting base type) found base type (trait)");
  84             Some(resolved_type)
  85         }
  86
  87         ty_nil | ty_bot | ty_bool | ty_char | ty_int(..) | ty_uint(..) | ty_float(..) |
  88         ty_str(..) | ty_vec(..) | ty_bare_fn(..) | ty_closure(..) | ty_tup(..) |
  89         ty_infer(..) | ty_param(..) | ty_err | ty_open(..) |
  90         ty_box(_) | ty_uniq(_) | ty_ptr(_) | ty_rptr(_, _) => {
  91             debug!("(getting base type) no base type; found {:?}",
  92                    get(original_type).sty);
  93             None
  94         }
  95         ty_trait(..) => fail!("should have been caught")
  96     }
  97 }
  98
  99 fn type_is_defined_in_local_crate(tcx: &ty::ctxt, original_type: t) -> bool {
 100     /*!
 101      *
 102      * For coherence, when we have `impl Trait for Type`, we need to
 103      * guarantee that `Type` is "local" to the
 104      * crate.  For our purposes, this means that it must contain
 105      * some nominal type defined in this crate.
 106      */
 107
 108     let mut found_nominal = false;
 109     ty::walk_ty(original_type, |t| {
 110         match get(t).sty {
 111             ty_enum(def_id, _) |
 112             ty_struct(def_id, _) |
 113             ty_unboxed_closure(def_id, _) => {
 114                 if def_id.krate == ast::LOCAL_CRATE {
 115                     found_nominal = true;
 116                 }
 117             }
 118             ty_trait(box ty::TyTrait { def_id, .. }) => {
 119                 if def_id.krate == ast::LOCAL_CRATE {
 120                     found_nominal = true;
 121                 }
 122             }
 123             ty_uniq(..) => {
 124                 match tcx.lang_items.owned_box() {
 125                     Some(did) if did.krate == ast::LOCAL_CRATE => {
 126                         found_nominal = true;
 127                     }
 128                     _ => {}
 129                 }
 130             }
 131             ty_box(..) => {
 132                 match tcx.lang_items.gc() {
 133                     Some(did) if did.krate == ast::LOCAL_CRATE => {
 134                         found_nominal = true;
 135                     }
 136                     _ => {}
 137                 }
 138             }
 139
 140             _ => { }
 141         }
 142     });
 143     return found_nominal;
 144 }
 145
 146 // Returns the def ID of the base type, if there is one.
 147 fn get_base_type_def_id(inference_context: &InferCtxt,
 148                         span: Span,
 149                         original_type: t)
 150                         -> Option<DefId> {
 151     match get_base_type(inference_context, span, original_type) {
 152         None => None,
 153         Some(base_type) => {
 154             match get(base_type).sty {
 155                 ty_enum(def_id, _) |
 156                 ty_struct(def_id, _) |
 157                 ty_unboxed_closure(def_id, _) => {
 158                     Some(def_id)
 159                 }
 160                 ty_ptr(ty::mt {ty, ..}) |
 161                 ty_rptr(_, ty::mt {ty, ..}) |
 162                 ty_uniq(ty) => {
 163                     match ty::get(ty).sty {
 164                         ty_trait(box ty::TyTrait { def_id, .. }) => {
 165                             Some(def_id)
 166                         }
 167                         _ => {
 168                             fail!("get_base_type() returned a type that wasn't an \
 169                                    enum, struct, or trait");
 170                         }
 171                     }
 172                 }
 173                 ty_trait(box ty::TyTrait { def_id, .. }) => {
 174                     Some(def_id)
 175                 }
 176                 _ => {
 177                     fail!("get_base_type() returned a type that wasn't an \
 178                            enum, struct, or trait");
 179                 }
 180             }
 181         }
 182     }
 183 }
 184
 185 struct CoherenceChecker<'a> {
 186     crate_context: &'a CrateCtxt<'a>,
 187     inference_context: InferCtxt<'a>,
 188 }
 189
 190 struct CoherenceCheckVisitor<'a> {
 191     cc: &'a CoherenceChecker<'a>
 192 }
 193
 194 impl<'a> visit::Visitor<()> for CoherenceCheckVisitor<'a> {
 195     fn visit_item(&mut self, item: &Item, _: ()) {
 196
 197         //debug!("(checking coherence) item '{}'", token::get_ident(item.ident));
 198
 199         match item.node {
 200             ItemImpl(_, ref opt_trait, _, _) => {
 201                 match opt_trait.clone() {
 202                     Some(opt_trait) => {
 203                         self.cc.check_implementation(item, [opt_trait]);
 204                     }
 205                     None => self.cc.check_implementation(item, [])
 206                 }
 207             }
 208             _ => {
 209                 // Nothing to do.
 210             }
 211         };
 212
 213         visit::walk_item(self, item, ());
 214     }
 215 }
 216
 217 struct PrivilegedScopeVisitor<'a> { cc: &'a CoherenceChecker<'a> }
 218
 219 impl<'a> visit::Visitor<()> for PrivilegedScopeVisitor<'a> {
 220     fn visit_item(&mut self, item: &Item, _: ()) {
 221
 222         match item.node {
 223             ItemMod(ref module_) => {
 224                 // Then visit the module items.
 225                 visit::walk_mod(self, module_, ());
 226             }
 227             ItemImpl(_, None, ref ast_ty, _) => {
 228                 if !self.cc.ast_type_is_defined_in_local_crate(&**ast_ty) {
 229                     // This is an error.
 230                     let session = &self.cc.crate_context.tcx.sess;
 231                     span_err!(session, item.span, E0116,
 232                               "cannot associate methods with a type outside the \
 233                                crate the type is defined in; define and implement \
 234                                a trait or new type instead");
 235                 }
 236             }
 237             ItemImpl(_, Some(ref trait_ref), _, _) => {
 238                 let tcx = self.cc.crate_context.tcx;
 239                 // `for_ty` is `Type` in `impl Trait for Type`
 240                 let for_ty = ty::node_id_to_type(tcx, item.id);
 241                 if !type_is_defined_in_local_crate(tcx, for_ty) {
 242                     // This implementation is not in scope of its base
 243                     // type. This still might be OK if the trait is
 244                     // defined in the same crate.
 245
 246                     let trait_def_id =
 247                         self.cc.trait_ref_to_trait_def_id(trait_ref);
 248
 249                     if trait_def_id.krate != LOCAL_CRATE {
 250                         let session = &self.cc.crate_context.tcx.sess;
 251                         span_err!(session, item.span, E0117,
 252                                   "cannot provide an extension implementation \
 253                                    where both trait and type are not defined in this crate");
 254                     }
 255                 }
 256
 257                 visit::walk_item(self, item, ());
 258             }
 259             _ => {
 260                 visit::walk_item(self, item, ());
 261             }
 262         }
 263     }
 264 }
 265
 266 impl<'a> CoherenceChecker<'a> {
 267     fn check(&self, krate: &Crate) {
 268         // Check implementations and traits. This populates the tables
 269         // containing the inherent methods and extension methods. It also
 270         // builds up the trait inheritance table.
 271         let mut visitor = CoherenceCheckVisitor { cc: self };
 272         visit::walk_crate(&mut visitor, krate, ());
 273
 274         // Check that there are no overlapping trait instances
 275         self.check_implementation_coherence();
 276
 277         // Check whether traits with base types are in privileged scopes.
 278         self.check_privileged_scopes(krate);
 279
 280         // Bring in external crates. It's fine for this to happen after the
 281         // coherence checks, because we ensure by construction that no errors
 282         // can happen at link time.
 283         self.add_external_crates();
 284
 285         // Populate the table of destructors. It might seem a bit strange to
 286         // do this here, but it's actually the most convenient place, since
 287         // the coherence tables contain the trait -> type mappings.
 288         self.populate_destructor_table();
 289     }
 290
 291     fn check_implementation(&self, item: &Item,
 292                             associated_traits: &[TraitRef]) {
 293         let tcx = self.crate_context.tcx;
 294         let impl_did = local_def(item.id);
 295         let self_type = ty::lookup_item_type(tcx, impl_did);
 296
 297         // If there are no traits, then this implementation must have a
 298         // base type.
 299
 300         if associated_traits.len() == 0 {
 301             debug!("(checking implementation) no associated traits for item '{}'",
 302                    token::get_ident(item.ident));
 303
 304             match get_base_type_def_id(&self.inference_context,
 305                                        item.span,
 306                                        self_type.ty) {
 307                 None => {
 308                     let session = &self.crate_context.tcx.sess;
 309                     span_err!(session, item.span, E0118,
 310                               "no base type found for inherent implementation; \
 311                                implement a trait or new type instead");
 312                 }
 313                 Some(_) => {
 314                     // Nothing to do.
 315                 }
 316             }
 317         }
 318
 319         let impl_items = self.create_impl_from_item(item);
 320
 321         for associated_trait in associated_traits.iter() {
 322             let trait_ref = ty::node_id_to_trait_ref(
 323                 self.crate_context.tcx, associated_trait.ref_id);
 324             debug!("(checking implementation) adding impl for trait '{}', item '{}'",
 325                    trait_ref.repr(self.crate_context.tcx),
 326                    token::get_ident(item.ident));
 327
 328             self.add_trait_impl(trait_ref.def_id, impl_did);
 329         }
 330
 331         // Add the implementation to the mapping from implementation to base
 332         // type def ID, if there is a base type for this implementation and
 333         // the implementation does not have any associated traits.
 334         match get_base_type_def_id(&self.inference_context,
 335                                    item.span,
 336                                    self_type.ty) {
 337             None => {
 338                 // Nothing to do.
 339             }
 340             Some(base_type_def_id) => {
 341                 // FIXME: Gather up default methods?
 342                 if associated_traits.len() == 0 {
 343                     self.add_inherent_impl(base_type_def_id, impl_did);
 344                 }
 345             }
 346         }
 347
 348         tcx.impl_items.borrow_mut().insert(impl_did, impl_items);
 349     }
 350
 351     // Creates default method IDs and performs type substitutions for an impl
 352     // and trait pair. Then, for each provided method in the trait, inserts a
 353     // `ProvidedMethodInfo` instance into the `provided_method_sources` map.
 354     fn instantiate_default_methods(
 355             &self,
 356             impl_id: DefId,
 357             trait_ref: &ty::TraitRef,
 358             all_impl_items: &mut Vec<ImplOrTraitItemId>) {
 359         let tcx = self.crate_context.tcx;
 360         debug!("instantiate_default_methods(impl_id={:?}, trait_ref={})",
 361                impl_id, trait_ref.repr(tcx));
 362
 363         let impl_poly_type = ty::lookup_item_type(tcx, impl_id);
 364
 365         let prov = ty::provided_trait_methods(tcx, trait_ref.def_id);
 366         for trait_method in prov.iter() {
 367             // Synthesize an ID.
 368             let new_id = tcx.sess.next_node_id();
 369             let new_did = local_def(new_id);
 370
 371             debug!("new_did={:?} trait_method={}", new_did, trait_method.repr(tcx));
 372
 373             // Create substitutions for the various trait parameters.
 374             let new_method_ty =
 375                 Rc::new(subst_receiver_types_in_method_ty(
 376                     tcx,
 377                     impl_id,
 378                     &impl_poly_type,
 379                     trait_ref,
 380                     new_did,
 381                     &**trait_method,
 382                     Some(trait_method.def_id)));
 383
 384             debug!("new_method_ty={}", new_method_ty.repr(tcx));
 385             all_impl_items.push(MethodTraitItemId(new_did));
 386
 387             // construct the polytype for the method based on the
 388             // method_ty.  it will have all the generics from the
 389             // impl, plus its own.
 390             let new_polytype = ty::Polytype {
 391                 generics: new_method_ty.generics.clone(),
 392                 ty: ty::mk_bare_fn(tcx, new_method_ty.fty.clone())
 393             };
 394             debug!("new_polytype={}", new_polytype.repr(tcx));
 395
 396             tcx.tcache.borrow_mut().insert(new_did, new_polytype);
 397             tcx.impl_or_trait_items
 398                .borrow_mut()
 399                .insert(new_did, ty::MethodTraitItem(new_method_ty));
 400
 401             // Pair the new synthesized ID up with the
 402             // ID of the method.
 403             self.crate_context.tcx.provided_method_sources.borrow_mut()
 404                 .insert(new_did, trait_method.def_id);
 405         }
 406     }
 407
 408     fn add_inherent_impl(&self, base_def_id: DefId, impl_def_id: DefId) {
 409         let tcx = self.crate_context.tcx;
 410         match tcx.inherent_impls.borrow().find(&base_def_id) {
 411             Some(implementation_list) => {
 412                 implementation_list.borrow_mut().push(impl_def_id);
 413                 return;
 414             }
 415             None => {}
 416         }
 417
 418         tcx.inherent_impls.borrow_mut().insert(base_def_id,
 419                                                Rc::new(RefCell::new(vec!(impl_def_id))));
 420     }
 421
 422     fn add_trait_impl(&self, base_def_id: DefId, impl_def_id: DefId) {
 423         ty::record_trait_implementation(self.crate_context.tcx,
 424                                         base_def_id,
 425                                         impl_def_id);
 426     }
 427
 428     fn check_implementation_coherence(&self) {
 429         for trait_id in self.crate_context.tcx.trait_impls.borrow().keys() {
 430             self.check_implementation_coherence_of(*trait_id);
 431         }
 432     }
 433
 434     fn check_implementation_coherence_of(&self, trait_def_id: DefId) {
 435         // Unify pairs of polytypes.
 436         self.iter_impls_of_trait_local(trait_def_id, |impl_a| {
 437             let polytype_a =
 438                 self.get_self_type_for_implementation(impl_a);
 439
 440             // "We have an impl of trait <trait_def_id> for type <polytype_a>,
 441             // and that impl is <impl_a>"
 442             self.iter_impls_of_trait(trait_def_id, |impl_b| {
 443
 444                 // An impl is coherent with itself
 445                 if impl_a != impl_b {
 446                     let polytype_b = self.get_self_type_for_implementation(
 447                             impl_b);
 448
 449                     if self.polytypes_unify(polytype_a.clone(), polytype_b) {
 450                         let session = &self.crate_context.tcx.sess;
 451                         span_err!(session, self.span_of_impl(impl_a), E0119,
 452                                   "conflicting implementations for trait `{}`",
 453                                   ty::item_path_str(self.crate_context.tcx, trait_def_id));
 454                         if impl_b.krate == LOCAL_CRATE {
 455                             span_note!(session, self.span_of_impl(impl_b),
 456                                        "note conflicting implementation here");
 457                         } else {
 458                             let crate_store = &self.crate_context.tcx.sess.cstore;
 459                             let cdata = crate_store.get_crate_data(impl_b.krate);
 460                             span_note!(session, self.span_of_impl(impl_a),
 461                                        "conflicting implementation in crate `{}`",
 462                                        cdata.name);
 463                         }
 464                     }
 465                 }
 466             })
 467         })
 468     }
 469
 470     fn iter_impls_of_trait(&self, trait_def_id: DefId, f: |DefId|) {
 471         self.iter_impls_of_trait_local(trait_def_id, |x| f(x));
 472
 473         if trait_def_id.krate == LOCAL_CRATE {
 474             return;
 475         }
 476
 477         let crate_store = &self.crate_context.tcx.sess.cstore;
 478         csearch::each_implementation_for_trait(crate_store, trait_def_id, |impl_def_id| {
 479             // Is this actually necessary?
 480             let _ = lookup_item_type(self.crate_context.tcx, impl_def_id);
 481             f(impl_def_id);
 482         });
 483     }
 484
 485     fn iter_impls_of_trait_local(&self, trait_def_id: DefId, f: |DefId|) {
 486         match self.crate_context.tcx.trait_impls.borrow().find(&trait_def_id) {
 487             Some(impls) => {
 488                 for &impl_did in impls.borrow().iter() {
 489                     f(impl_did);
 490                 }
 491             }
 492             None => { /* no impls? */ }
 493         }
 494     }
 495
 496     fn polytypes_unify(&self,
 497                        polytype_a: Polytype,
 498                        polytype_b: Polytype)
 499                        -> bool {
 500         let universally_quantified_a =
 501             self.universally_quantify_polytype(polytype_a);
 502         let universally_quantified_b =
 503             self.universally_quantify_polytype(polytype_b);
 504
 505         return self.can_unify_universally_quantified(
 506             &universally_quantified_a, &universally_quantified_b) ||
 507             self.can_unify_universally_quantified(
 508             &universally_quantified_b, &universally_quantified_a);
 509     }
 510
 511     // Converts a polytype to a monotype by replacing all parameters with
 512     // type variables. Returns the monotype and the type variables created.
 513     fn universally_quantify_polytype(&self, polytype: Polytype)
 514                                      -> UniversalQuantificationResult
 515     {
 516         let substitutions =
 517             self.inference_context.fresh_substs_for_type(DUMMY_SP,
 518                                                          &polytype.generics);
 519         let monotype = polytype.ty.subst(self.crate_context.tcx, &substitutions);
 520
 521         UniversalQuantificationResult {
 522             monotype: monotype
 523         }
 524     }
 525
 526     fn can_unify_universally_quantified<'a>(&self,
 527                                             a: &'a UniversalQuantificationResult,
 528                                             b: &'a UniversalQuantificationResult)
 529                                             -> bool
 530     {
 531         infer::can_mk_subty(&self.inference_context,
 532                             a.monotype,
 533                             b.monotype).is_ok()
 534     }
 535
 536     fn get_self_type_for_implementation(&self, impl_did: DefId)
 537                                         -> Polytype {
 538         self.crate_context.tcx.tcache.borrow().get_copy(&impl_did)
 539     }
 540
 541     // Privileged scope checking
 542     fn check_privileged_scopes(&self, krate: &Crate) {
 543         let mut visitor = PrivilegedScopeVisitor{ cc: self };
 544         visit::walk_crate(&mut visitor, krate, ());
 545     }
 546
 547     fn trait_ref_to_trait_def_id(&self, trait_ref: &TraitRef) -> DefId {
 548         let def_map = &self.crate_context.tcx.def_map;
 549         let trait_def = def_map.borrow().get_copy(&trait_ref.ref_id);
 550         let trait_id = trait_def.def_id();
 551         return trait_id;
 552     }
 553
 554     /// For coherence, when we have `impl Type`, we need to guarantee that
 555     /// `Type` is "local" to the crate. For our purposes, this means that it
 556     /// must precisely name some nominal type defined in this crate.
 557     fn ast_type_is_defined_in_local_crate(&self, original_type: &ast::Ty) -> bool {
 558         match original_type.node {
 559             TyPath(_, _, path_id) => {
 560                 match self.crate_context.tcx.def_map.borrow().get_copy(&path_id) {
 561                     DefTy(def_id) | DefStruct(def_id) => {
 562                         if def_id.krate != LOCAL_CRATE {
 563                             return false;
 564                         }
 565
 566                         // Make sure that this type precisely names a nominal
 567                         // type.
 568                         match self.crate_context.tcx.map.find(def_id.node) {
 569                             None => {
 570                                 self.crate_context.tcx.sess.span_bug(
 571                                     original_type.span,
 572                                     "resolve didn't resolve this type?!");
 573                             }
 574                             Some(NodeItem(item)) => {
 575                                 match item.node {
 576                                     ItemStruct(..) | ItemEnum(..) => true,
 577                                     _ => false,
 578                                 }
 579                             }
 580                             Some(_) => false,
 581                         }
 582                     }
 583                     _ => false
 584                 }
 585             }
 586             _ => false
 587         }
 588     }
 589
 590     // Converts an implementation in the AST to a vector of items.
 591     fn create_impl_from_item(&self, item: &Item) -> Vec<ImplOrTraitItemId> {
 592         match item.node {
 593             ItemImpl(_, ref trait_refs, _, ref ast_items) => {
 594                 let mut items: Vec<ImplOrTraitItemId> =
 595                         ast_items.iter()
 596                                  .map(|ast_item| {
 597                             match *ast_item {
 598                                 ast::MethodImplItem(ast_method) => {
 599                                     MethodTraitItemId(
 600                                         local_def(ast_method.id))
 601                                 }
 602                             }
 603                         }).collect();
 604
 605                 for trait_ref in trait_refs.iter() {
 606                     let ty_trait_ref = ty::node_id_to_trait_ref(
 607                         self.crate_context.tcx,
 608                         trait_ref.ref_id);
 609
 610                     self.instantiate_default_methods(local_def(item.id),
 611                                                      &*ty_trait_ref,
 612                                                      &mut items);
 613                 }
 614
 615                 items
 616             }
 617             _ => {
 618                 self.crate_context.tcx.sess.span_bug(item.span,
 619                                                      "can't convert a non-impl to an impl");
 620             }
 621         }
 622     }
 623
 624     fn span_of_impl(&self, impl_did: DefId) -> Span {
 625         assert_eq!(impl_did.krate, LOCAL_CRATE);
 626         self.crate_context.tcx.map.span(impl_did.node)
 627     }
 628
 629     // External crate handling
 630
 631     fn add_external_impl(&self,
 632                          impls_seen: &mut HashSet<DefId>,
 633                          impl_def_id: DefId) {
 634         let tcx = self.crate_context.tcx;
 635         let impl_items = csearch::get_impl_items(&tcx.sess.cstore,
 636                                                  impl_def_id);
 637
 638         // Make sure we don't visit the same implementation multiple times.
 639         if !impls_seen.insert(impl_def_id) {
 640             // Skip this one.
 641             return
 642         }
 643         // Good. Continue.
 644
 645         let _ = lookup_item_type(tcx, impl_def_id);
 646         let associated_traits = get_impl_trait(tcx, impl_def_id);
 647
 648         // Do a sanity check.
 649         assert!(associated_traits.is_some());
 650
 651         // Record all the trait items.
 652         for trait_ref in associated_traits.iter() {
 653             self.add_trait_impl(trait_ref.def_id, impl_def_id);
 654         }
 655
 656         // For any methods that use a default implementation, add them to
 657         // the map. This is a bit unfortunate.
 658         for item_def_id in impl_items.iter() {
 659             let impl_item = ty::impl_or_trait_item(tcx, item_def_id.def_id());
 660             match impl_item {
 661                 ty::MethodTraitItem(ref method) => {
 662                     for &source in method.provided_source.iter() {
 663                         tcx.provided_method_sources
 664                            .borrow_mut()
 665                            .insert(item_def_id.def_id(), source);
 666                     }
 667                 }
 668             }
 669         }
 670
 671         tcx.impl_items.borrow_mut().insert(impl_def_id, impl_items);
 672     }
 673
 674     // Adds implementations and traits from external crates to the coherence
 675     // info.
 676     fn add_external_crates(&self) {
 677         let mut impls_seen = HashSet::new();
 678
 679         let crate_store = &self.crate_context.tcx.sess.cstore;
 680         crate_store.iter_crate_data(|crate_number, _crate_metadata| {
 681             each_impl(crate_store, crate_number, |def_id| {
 682                 assert_eq!(crate_number, def_id.krate);
 683                 self.add_external_impl(&mut impls_seen, def_id)
 684             })
 685         })
 686     }
 687
 688     //
 689     // Destructors
 690     //
 691
 692     fn populate_destructor_table(&self) {
 693         let tcx = self.crate_context.tcx;
 694         let drop_trait = match tcx.lang_items.drop_trait() {
 695             Some(id) => id, None => { return }
 696         };
 697
 698         let impl_items = tcx.impl_items.borrow();
 699         let trait_impls = match tcx.trait_impls.borrow().find_copy(&drop_trait) {
 700             None => return, // No types with (new-style) dtors present.
 701             Some(found_impls) => found_impls
 702         };
 703
 704         for &impl_did in trait_impls.borrow().iter() {
 705             let items = impl_items.get(&impl_did);
 706             if items.len() < 1 {
 707                 // We'll error out later. For now, just don't ICE.
 708                 continue;
 709             }
 710             let method_def_id = *items.get(0);
 711
 712             let self_type = self.get_self_type_for_implementation(impl_did);
 713             match ty::get(self_type.ty).sty {
 714                 ty::ty_enum(type_def_id, _) |
 715                 ty::ty_struct(type_def_id, _) |
 716                 ty::ty_unboxed_closure(type_def_id, _) => {
 717                     tcx.destructor_for_type
 718                        .borrow_mut()
 719                        .insert(type_def_id, method_def_id.def_id());
 720                     tcx.destructors
 721                        .borrow_mut()
 722                        .insert(method_def_id.def_id());
 723                 }
 724                 _ => {
 725                     // Destructors only work on nominal types.
 726                     if impl_did.krate == ast::LOCAL_CRATE {
 727                         {
 728                             match tcx.map.find(impl_did.node) {
 729                                 Some(ast_map::NodeItem(item)) => {
 730                                     span_err!(tcx.sess, item.span, E0120,
 731                                         "the Drop trait may only be implemented on structures");
 732                                 }
 733                                 _ => {
 734                                     tcx.sess.bug("didn't find impl in ast \
 735                                                   map");
 736                                 }
 737                             }
 738                         }
 739                     } else {
 740                         tcx.sess.bug("found external impl of Drop trait on \
 741                                       something other than a struct");
 742                     }
 743                 }
 744             }
 745         }
 746     }
 747 }
 748
 749 pub fn make_substs_for_receiver_types(tcx: &ty::ctxt,
 750                                       trait_ref: &ty::TraitRef,
 751                                       method: &ty::Method)
 752                                       -> subst::Substs
 753 {
 754     /*!
 755      * Substitutes the values for the receiver's type parameters
 756      * that are found in method, leaving the method's type parameters
 757      * intact.
 758      */
 759
 760     let meth_tps: Vec<ty::t> =
 761         method.generics.types.get_slice(subst::FnSpace)
 762               .iter()
 763               .map(|def| ty::mk_param_from_def(tcx, def))
 764               .collect();
 765     let meth_regions: Vec<ty::Region> =
 766         method.generics.regions.get_slice(subst::FnSpace)
 767               .iter()
 768               .map(|def| ty::ReEarlyBound(def.def_id.node, def.space,
 769                                           def.index, def.name))
 770               .collect();
 771     trait_ref.substs.clone().with_method(meth_tps, meth_regions)
 772 }
 773
 774 fn subst_receiver_types_in_method_ty(tcx: &ty::ctxt,
 775                                      impl_id: ast::DefId,
 776                                      impl_poly_type: &ty::Polytype,
 777                                      trait_ref: &ty::TraitRef,
 778                                      new_def_id: ast::DefId,
 779                                      method: &ty::Method,
 780                                      provided_source: Option<ast::DefId>)
 781                                      -> ty::Method
 782 {
 783     let combined_substs = make_substs_for_receiver_types(tcx, trait_ref, method);
 784
 785     debug!("subst_receiver_types_in_method_ty: combined_substs={}",
 786            combined_substs.repr(tcx));
 787
 788     let mut method_generics = method.generics.subst(tcx, &combined_substs);
 789
 790     // replace the type parameters declared on the trait with those
 791     // from the impl
 792     for &space in [subst::TypeSpace, subst::SelfSpace].iter() {
 793         method_generics.types.replace(
 794             space,
 795             Vec::from_slice(impl_poly_type.generics.types.get_slice(space)));
 796         method_generics.regions.replace(
 797             space,
 798             Vec::from_slice(impl_poly_type.generics.regions.get_slice(space)));
 799     }
 800
 801     debug!("subst_receiver_types_in_method_ty: method_generics={}",
 802            method_generics.repr(tcx));
 803
 804     let method_fty = method.fty.subst(tcx, &combined_substs);
 805
 806     debug!("subst_receiver_types_in_method_ty: method_ty={}",
 807            method.fty.repr(tcx));
 808
 809     ty::Method::new(
 810         method.ident,
 811         method_generics,
 812         method_fty,
 813         method.explicit_self,
 814         method.vis,
 815         new_def_id,
 816         ImplContainer(impl_id),
 817         provided_source
 818     )
 819 }
 820
 821 pub fn check_coherence(crate_context: &CrateCtxt, krate: &Crate) {
 822     CoherenceChecker {
 823         crate_context: crate_context,
 824         inference_context: new_infer_ctxt(crate_context.tcx),
 825     }.check(krate);
 826 }