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.
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.
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.
18 use metadata::csearch::{each_impl, get_impl_trait, each_implementation_for_trait};
19 use metadata::csearch;
21 use middle::subst::{Substs};
23 use middle::ty::{ImplContainer, lookup_item_type};
24 use middle::ty::{t, ty_bool, ty_char, ty_bot, ty_box, ty_enum, ty_err};
25 use middle::ty::{ty_str, ty_vec, ty_float, ty_infer, ty_int, ty_nil};
26 use middle::ty::{ty_param, Polytype, ty_ptr};
27 use middle::ty::{ty_rptr, ty_struct, ty_trait, ty_tup};
28 use middle::ty::{ty_uint, ty_uniq, ty_bare_fn, ty_closure};
29 use middle::ty::type_is_ty_var;
30 use middle::subst::Subst;
32 use middle::typeck::CrateCtxt;
33 use middle::typeck::infer::combine::Combine;
34 use middle::typeck::infer::InferCtxt;
35 use middle::typeck::infer::{new_infer_ctxt, resolve_ivar, resolve_type};
36 use middle::typeck::infer;
37 use util::ppaux::Repr;
38 use middle::def::{DefStruct, DefTy};
39 use syntax::ast::{Crate, DefId};
40 use syntax::ast::{Item, ItemEnum, ItemImpl, ItemMod, ItemStruct};
41 use syntax::ast::{LOCAL_CRATE, TraitRef, TyPath};
43 use syntax::ast_map::NodeItem;
45 use syntax::ast_util::{local_def};
46 use syntax::codemap::{Span, DUMMY_SP};
47 use syntax::parse::token;
50 use std::collections::HashSet;
51 use std::cell::RefCell;
54 struct UniversalQuantificationResult {
58 fn get_base_type(inference_context: &InferCtxt,
63 match resolve_type(inference_context,
66 Ok(resulting_type) if !type_is_ty_var(resulting_type) => {
67 resolved_type = resulting_type;
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");
76 match get(resolved_type).sty {
77 ty_enum(..) | ty_struct(..) => {
78 debug!("(getting base type) found base type");
81 // FIXME(14865) I would prefere to use `_` here, but that causes a
83 ty_uniq(_) | ty_rptr(_, _) | ty_trait(..) if ty::type_is_trait(resolved_type) => {
84 debug!("(getting base type) found base type (trait)");
88 ty_nil | ty_bot | ty_bool | ty_char | ty_int(..) | ty_uint(..) | ty_float(..) |
89 ty_str(..) | ty_vec(..) | ty_bare_fn(..) | ty_closure(..) | ty_tup(..) |
90 ty_infer(..) | ty_param(..) | ty_err |
91 ty_box(_) | ty_uniq(_) | ty_ptr(_) | ty_rptr(_, _) => {
92 debug!("(getting base type) no base type; found {:?}",
93 get(original_type).sty);
96 ty_trait(..) => fail!("should have been caught")
100 fn type_is_defined_in_local_crate(tcx: &ty::ctxt, original_type: t) -> bool {
103 * For coherence, when we have `impl Trait for Type`, we need to
104 * guarantee that `Type` is "local" to the
105 * crate. For our purposes, this means that it must contain
106 * some nominal type defined in this crate.
109 let mut found_nominal = false;
110 ty::walk_ty(original_type, |t| {
113 ty_struct(def_id, _) => {
114 if def_id.krate == ast::LOCAL_CRATE {
115 found_nominal = true;
118 ty_trait(box ty::TyTrait { def_id, .. }) => {
119 if def_id.krate == ast::LOCAL_CRATE {
120 found_nominal = true;
124 match tcx.lang_items.owned_box() {
125 Some(did) if did.krate == ast::LOCAL_CRATE => {
126 found_nominal = true;
132 match tcx.lang_items.gc() {
133 Some(did) if did.krate == ast::LOCAL_CRATE => {
134 found_nominal = true;
143 return found_nominal;
146 // Returns the def ID of the base type, if there is one.
147 fn get_base_type_def_id(inference_context: &InferCtxt,
151 match get_base_type(inference_context, span, original_type) {
154 match get(base_type).sty {
156 ty_struct(def_id, _) => {
159 ty_rptr(_, ty::mt {ty, ..}) | ty_uniq(ty) => match ty::get(ty).sty {
160 ty_trait(box ty::TyTrait { def_id, .. }) => {
164 fail!("get_base_type() returned a type that wasn't an \
165 enum, struct, or trait");
169 fail!("get_base_type() returned a type that wasn't an \
170 enum, struct, or trait");
177 struct CoherenceChecker<'a> {
178 crate_context: &'a CrateCtxt<'a>,
179 inference_context: InferCtxt<'a>,
182 struct CoherenceCheckVisitor<'a> {
183 cc: &'a CoherenceChecker<'a>
186 impl<'a> visit::Visitor<()> for CoherenceCheckVisitor<'a> {
187 fn visit_item(&mut self, item: &Item, _: ()) {
189 //debug!("(checking coherence) item '{}'", token::get_ident(item.ident));
192 ItemImpl(_, ref opt_trait, _, _) => {
193 match opt_trait.clone() {
195 self.cc.check_implementation(item, [opt_trait]);
197 None => self.cc.check_implementation(item, [])
205 visit::walk_item(self, item, ());
209 struct PrivilegedScopeVisitor<'a> { cc: &'a CoherenceChecker<'a> }
211 impl<'a> visit::Visitor<()> for PrivilegedScopeVisitor<'a> {
212 fn visit_item(&mut self, item: &Item, _: ()) {
215 ItemMod(ref module_) => {
216 // Then visit the module items.
217 visit::walk_mod(self, module_, ());
219 ItemImpl(_, None, ref ast_ty, _) => {
220 if !self.cc.ast_type_is_defined_in_local_crate(&**ast_ty) {
222 let session = &self.cc.crate_context.tcx.sess;
223 session.span_err(item.span,
224 "cannot associate methods with a type outside the \
225 crate the type is defined in; define and implement \
226 a trait or new type instead");
229 ItemImpl(_, Some(ref trait_ref), _, _) => {
230 let tcx = self.cc.crate_context.tcx;
231 // `for_ty` is `Type` in `impl Trait for Type`
232 let for_ty = ty::node_id_to_type(tcx, item.id);
233 if !type_is_defined_in_local_crate(tcx, for_ty) {
234 // This implementation is not in scope of its base
235 // type. This still might be OK if the trait is
236 // defined in the same crate.
239 self.cc.trait_ref_to_trait_def_id(trait_ref);
241 if trait_def_id.krate != LOCAL_CRATE {
242 let session = &self.cc.crate_context.tcx.sess;
243 session.span_err(item.span,
244 "cannot provide an extension implementation \
245 where both trait and type are not defined in this crate");
249 visit::walk_item(self, item, ());
252 visit::walk_item(self, item, ());
258 impl<'a> CoherenceChecker<'a> {
259 fn check(&self, krate: &Crate) {
260 // Check implementations and traits. This populates the tables
261 // containing the inherent methods and extension methods. It also
262 // builds up the trait inheritance table.
263 let mut visitor = CoherenceCheckVisitor { cc: self };
264 visit::walk_crate(&mut visitor, krate, ());
266 // Check that there are no overlapping trait instances
267 self.check_implementation_coherence();
269 // Check whether traits with base types are in privileged scopes.
270 self.check_privileged_scopes(krate);
272 // Bring in external crates. It's fine for this to happen after the
273 // coherence checks, because we ensure by construction that no errors
274 // can happen at link time.
275 self.add_external_crates();
277 // Populate the table of destructors. It might seem a bit strange to
278 // do this here, but it's actually the most convenient place, since
279 // the coherence tables contain the trait -> type mappings.
280 self.populate_destructor_table();
283 fn check_implementation(&self, item: &Item,
284 associated_traits: &[TraitRef]) {
285 let tcx = self.crate_context.tcx;
286 let impl_did = local_def(item.id);
287 let self_type = ty::lookup_item_type(tcx, impl_did);
289 // If there are no traits, then this implementation must have a
292 if associated_traits.len() == 0 {
293 debug!("(checking implementation) no associated traits for item '{}'",
294 token::get_ident(item.ident));
296 match get_base_type_def_id(&self.inference_context,
300 let session = &self.crate_context.tcx.sess;
301 session.span_err(item.span,
302 "no base type found for inherent implementation; \
303 implement a trait or new type instead");
311 let impl_methods = self.create_impl_from_item(item);
313 for associated_trait in associated_traits.iter() {
314 let trait_ref = ty::node_id_to_trait_ref(
315 self.crate_context.tcx, associated_trait.ref_id);
316 debug!("(checking implementation) adding impl for trait '{}', item '{}'",
317 trait_ref.repr(self.crate_context.tcx),
318 token::get_ident(item.ident));
320 self.add_trait_impl(trait_ref.def_id, impl_did);
323 // Add the implementation to the mapping from implementation to base
324 // type def ID, if there is a base type for this implementation and
325 // the implementation does not have any associated traits.
326 match get_base_type_def_id(&self.inference_context,
332 Some(base_type_def_id) => {
333 // FIXME: Gather up default methods?
334 if associated_traits.len() == 0 {
335 self.add_inherent_impl(base_type_def_id, impl_did);
340 tcx.impl_methods.borrow_mut().insert(impl_did, impl_methods);
343 // Creates default method IDs and performs type substitutions for an impl
344 // and trait pair. Then, for each provided method in the trait, inserts a
345 // `ProvidedMethodInfo` instance into the `provided_method_sources` map.
346 fn instantiate_default_methods(&self,
348 trait_ref: &ty::TraitRef,
349 all_methods: &mut Vec<DefId>) {
350 let tcx = self.crate_context.tcx;
351 debug!("instantiate_default_methods(impl_id={:?}, trait_ref={})",
352 impl_id, trait_ref.repr(tcx));
354 let impl_poly_type = ty::lookup_item_type(tcx, impl_id);
356 let prov = ty::provided_trait_methods(tcx, trait_ref.def_id);
357 for trait_method in prov.iter() {
359 let new_id = tcx.sess.next_node_id();
360 let new_did = local_def(new_id);
362 debug!("new_did={:?} trait_method={}", new_did, trait_method.repr(tcx));
364 // Create substitutions for the various trait parameters.
366 Rc::new(subst_receiver_types_in_method_ty(
373 Some(trait_method.def_id)));
375 debug!("new_method_ty={}", new_method_ty.repr(tcx));
376 all_methods.push(new_did);
378 // construct the polytype for the method based on the
379 // method_ty. it will have all the generics from the
380 // impl, plus its own.
381 let new_polytype = ty::Polytype {
382 generics: new_method_ty.generics.clone(),
383 ty: ty::mk_bare_fn(tcx, new_method_ty.fty.clone())
385 debug!("new_polytype={}", new_polytype.repr(tcx));
387 tcx.tcache.borrow_mut().insert(new_did, new_polytype);
388 tcx.methods.borrow_mut().insert(new_did, new_method_ty);
390 // Pair the new synthesized ID up with the
392 self.crate_context.tcx.provided_method_sources.borrow_mut()
393 .insert(new_did, trait_method.def_id);
397 fn add_inherent_impl(&self, base_def_id: DefId, impl_def_id: DefId) {
398 let tcx = self.crate_context.tcx;
399 match tcx.inherent_impls.borrow().find(&base_def_id) {
400 Some(implementation_list) => {
401 implementation_list.borrow_mut().push(impl_def_id);
407 tcx.inherent_impls.borrow_mut().insert(base_def_id,
408 Rc::new(RefCell::new(vec!(impl_def_id))));
411 fn add_trait_impl(&self, base_def_id: DefId, impl_def_id: DefId) {
412 ty::record_trait_implementation(self.crate_context.tcx,
417 fn check_implementation_coherence(&self) {
418 for &trait_id in self.crate_context.tcx.trait_impls.borrow().keys() {
419 self.check_implementation_coherence_of(trait_id);
423 fn check_implementation_coherence_of(&self, trait_def_id: DefId) {
424 // Unify pairs of polytypes.
425 self.iter_impls_of_trait_local(trait_def_id, |impl_a| {
427 self.get_self_type_for_implementation(impl_a);
429 // "We have an impl of trait <trait_def_id> for type <polytype_a>,
430 // and that impl is <impl_a>"
431 self.iter_impls_of_trait(trait_def_id, |impl_b| {
433 // An impl is coherent with itself
434 if impl_a != impl_b {
435 let polytype_b = self.get_self_type_for_implementation(
438 if self.polytypes_unify(polytype_a.clone(), polytype_b) {
439 let session = &self.crate_context.tcx.sess;
441 self.span_of_impl(impl_a),
442 format!("conflicting implementations for trait `{}`",
444 self.crate_context.tcx,
445 trait_def_id)).as_slice());
446 if impl_b.krate == LOCAL_CRATE {
447 session.span_note(self.span_of_impl(impl_b),
448 "note conflicting implementation here");
450 let crate_store = &self.crate_context.tcx.sess.cstore;
451 let cdata = crate_store.get_crate_data(impl_b.krate);
453 format!("conflicting implementation in crate \
455 cdata.name).as_slice());
463 fn iter_impls_of_trait(&self, trait_def_id: DefId, f: |DefId|) {
464 self.iter_impls_of_trait_local(trait_def_id, |x| f(x));
466 if trait_def_id.krate == LOCAL_CRATE {
470 let crate_store = &self.crate_context.tcx.sess.cstore;
471 csearch::each_implementation_for_trait(crate_store, trait_def_id, |impl_def_id| {
472 // Is this actually necessary?
473 let _ = lookup_item_type(self.crate_context.tcx, impl_def_id);
478 fn iter_impls_of_trait_local(&self, trait_def_id: DefId, f: |DefId|) {
479 match self.crate_context.tcx.trait_impls.borrow().find(&trait_def_id) {
481 for &impl_did in impls.borrow().iter() {
485 None => { /* no impls? */ }
489 fn polytypes_unify(&self,
490 polytype_a: Polytype,
491 polytype_b: Polytype)
493 let universally_quantified_a =
494 self.universally_quantify_polytype(polytype_a);
495 let universally_quantified_b =
496 self.universally_quantify_polytype(polytype_b);
498 return self.can_unify_universally_quantified(
499 &universally_quantified_a, &universally_quantified_b) ||
500 self.can_unify_universally_quantified(
501 &universally_quantified_b, &universally_quantified_a);
504 // Converts a polytype to a monotype by replacing all parameters with
505 // type variables. Returns the monotype and the type variables created.
506 fn universally_quantify_polytype(&self, polytype: Polytype)
507 -> UniversalQuantificationResult
510 self.inference_context.fresh_substs_for_type(DUMMY_SP,
512 let monotype = polytype.ty.subst(self.crate_context.tcx, &substitutions);
514 UniversalQuantificationResult {
519 fn can_unify_universally_quantified<'a>(&self,
520 a: &'a UniversalQuantificationResult,
521 b: &'a UniversalQuantificationResult)
524 infer::can_mk_subty(&self.inference_context,
529 fn get_self_type_for_implementation(&self, impl_did: DefId)
531 self.crate_context.tcx.tcache.borrow().get_copy(&impl_did)
534 // Privileged scope checking
535 fn check_privileged_scopes(&self, krate: &Crate) {
536 let mut visitor = PrivilegedScopeVisitor{ cc: self };
537 visit::walk_crate(&mut visitor, krate, ());
540 fn trait_ref_to_trait_def_id(&self, trait_ref: &TraitRef) -> DefId {
541 let def_map = &self.crate_context.tcx.def_map;
542 let trait_def = def_map.borrow().get_copy(&trait_ref.ref_id);
543 let trait_id = trait_def.def_id();
547 /// For coherence, when we have `impl Type`, we need to guarantee that
548 /// `Type` is "local" to the crate. For our purposes, this means that it
549 /// must precisely name some nominal type defined in this crate.
550 fn ast_type_is_defined_in_local_crate(&self, original_type: &ast::Ty) -> bool {
551 match original_type.node {
552 TyPath(_, _, path_id) => {
553 match self.crate_context.tcx.def_map.borrow().get_copy(&path_id) {
554 DefTy(def_id) | DefStruct(def_id) => {
555 if def_id.krate != LOCAL_CRATE {
559 // Make sure that this type precisely names a nominal
561 match self.crate_context.tcx.map.find(def_id.node) {
563 self.crate_context.tcx.sess.span_bug(
565 "resolve didn't resolve this type?!");
567 Some(NodeItem(item)) => {
569 ItemStruct(..) | ItemEnum(..) => true,
583 // Converts an implementation in the AST to a vector of methods.
584 fn create_impl_from_item(&self, item: &Item) -> Vec<DefId> {
586 ItemImpl(_, ref trait_refs, _, ref ast_methods) => {
587 let mut methods: Vec<DefId> = ast_methods.iter().map(|ast_method| {
588 local_def(ast_method.id)
591 for trait_ref in trait_refs.iter() {
592 let ty_trait_ref = ty::node_id_to_trait_ref(
593 self.crate_context.tcx,
596 self.instantiate_default_methods(local_def(item.id),
604 self.crate_context.tcx.sess.span_bug(item.span,
605 "can't convert a non-impl to an impl");
610 fn span_of_impl(&self, impl_did: DefId) -> Span {
611 assert_eq!(impl_did.krate, LOCAL_CRATE);
612 self.crate_context.tcx.map.span(impl_did.node)
615 // External crate handling
617 fn add_external_impl(&self,
618 impls_seen: &mut HashSet<DefId>,
619 impl_def_id: DefId) {
620 let tcx = self.crate_context.tcx;
621 let methods = csearch::get_impl_methods(&tcx.sess.cstore, impl_def_id);
623 // Make sure we don't visit the same implementation multiple times.
624 if !impls_seen.insert(impl_def_id) {
630 let _ = lookup_item_type(tcx, impl_def_id);
631 let associated_traits = get_impl_trait(tcx, impl_def_id);
633 // Do a sanity check.
634 assert!(associated_traits.is_some());
636 // Record all the trait methods.
637 for trait_ref in associated_traits.iter() {
638 self.add_trait_impl(trait_ref.def_id, impl_def_id);
641 // For any methods that use a default implementation, add them to
642 // the map. This is a bit unfortunate.
643 for &method_def_id in methods.iter() {
644 for &source in ty::method(tcx, method_def_id).provided_source.iter() {
645 tcx.provided_method_sources.borrow_mut().insert(method_def_id, source);
649 tcx.impl_methods.borrow_mut().insert(impl_def_id, methods);
652 // Adds implementations and traits from external crates to the coherence
654 fn add_external_crates(&self) {
655 let mut impls_seen = HashSet::new();
657 let crate_store = &self.crate_context.tcx.sess.cstore;
658 crate_store.iter_crate_data(|crate_number, _crate_metadata| {
659 each_impl(crate_store, crate_number, |def_id| {
660 assert_eq!(crate_number, def_id.krate);
661 self.add_external_impl(&mut impls_seen, def_id)
670 fn populate_destructor_table(&self) {
671 let tcx = self.crate_context.tcx;
672 let drop_trait = match tcx.lang_items.drop_trait() {
673 Some(id) => id, None => { return }
676 let impl_methods = tcx.impl_methods.borrow();
677 let trait_impls = match tcx.trait_impls.borrow().find_copy(&drop_trait) {
678 None => return, // No types with (new-style) dtors present.
679 Some(found_impls) => found_impls
682 for &impl_did in trait_impls.borrow().iter() {
683 let methods = impl_methods.get(&impl_did);
684 if methods.len() < 1 {
685 // We'll error out later. For now, just don't ICE.
688 let method_def_id = *methods.get(0);
690 let self_type = self.get_self_type_for_implementation(impl_did);
691 match ty::get(self_type.ty).sty {
692 ty::ty_enum(type_def_id, _) |
693 ty::ty_struct(type_def_id, _) => {
694 tcx.destructor_for_type.borrow_mut().insert(type_def_id,
696 tcx.destructors.borrow_mut().insert(method_def_id);
699 // Destructors only work on nominal types.
700 if impl_did.krate == ast::LOCAL_CRATE {
702 match tcx.map.find(impl_did.node) {
703 Some(ast_map::NodeItem(item)) => {
704 tcx.sess.span_err((*item).span,
705 "the Drop trait may \
706 only be implemented \
710 tcx.sess.bug("didn't find impl in ast \
716 tcx.sess.bug("found external impl of Drop trait on \
717 something other than a struct");
725 pub fn make_substs_for_receiver_types(tcx: &ty::ctxt,
726 trait_ref: &ty::TraitRef,
731 * Substitutes the values for the receiver's type parameters
732 * that are found in method, leaving the method's type parameters
736 let meth_tps: Vec<ty::t> =
737 method.generics.types.get_vec(subst::FnSpace)
739 .map(|def| ty::mk_param_from_def(tcx, def))
741 let meth_regions: Vec<ty::Region> =
742 method.generics.regions.get_vec(subst::FnSpace)
744 .map(|def| ty::ReEarlyBound(def.def_id.node, def.space,
745 def.index, def.name))
747 trait_ref.substs.clone().with_method(meth_tps, meth_regions)
750 fn subst_receiver_types_in_method_ty(tcx: &ty::ctxt,
752 impl_poly_type: &ty::Polytype,
753 trait_ref: &ty::TraitRef,
754 new_def_id: ast::DefId,
756 provided_source: Option<ast::DefId>)
759 let combined_substs = make_substs_for_receiver_types(tcx, trait_ref, method);
761 debug!("subst_receiver_types_in_method_ty: combined_substs={}",
762 combined_substs.repr(tcx));
764 let mut method_generics = method.generics.subst(tcx, &combined_substs);
766 // replace the type parameters declared on the trait with those
768 for &space in [subst::TypeSpace, subst::SelfSpace].iter() {
769 *method_generics.types.get_mut_vec(space) =
770 impl_poly_type.generics.types.get_vec(space).clone();
771 *method_generics.regions.get_mut_vec(space) =
772 impl_poly_type.generics.regions.get_vec(space).clone();
775 debug!("subst_receiver_types_in_method_ty: method_generics={}",
776 method_generics.repr(tcx));
778 let method_fty = method.fty.subst(tcx, &combined_substs);
780 debug!("subst_receiver_types_in_method_ty: method_ty={}",
781 method.fty.repr(tcx));
787 method.explicit_self,
790 ImplContainer(impl_id),
795 pub fn check_coherence(crate_context: &CrateCtxt, krate: &Crate) {
797 crate_context: crate_context,
798 inference_context: new_infer_ctxt(crate_context.tcx),