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.
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.
11 use super::MethodError;
12 use super::NoMatchData;
13 use super::{CandidateSource, ImplSource, TraitSource};
17 use hir::def_id::DefId;
19 use namespace::Namespace;
20 use rustc::ty::subst::{Subst, Substs};
21 use rustc::traits::{self, ObligationCause};
22 use rustc::ty::{self, Ty, ToPolyTraitRef, ToPredicate, TraitRef, TypeFoldable};
23 use rustc::infer::type_variable::TypeVariableOrigin;
24 use rustc::util::nodemap::FxHashSet;
25 use rustc::infer::{self, InferOk};
27 use syntax::util::lev_distance::{lev_distance, find_best_match_for_name};
36 use self::CandidateKind::*;
37 pub use self::PickKind::*;
39 /// Boolean flag used to indicate if this search is for a suggestion
40 /// or not. If true, we can allow ambiguity and so forth.
41 pub struct IsSuggestion(pub bool);
43 struct ProbeContext<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
44 fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
47 method_name: Option<ast::Name>,
48 return_type: Option<Ty<'tcx>>,
49 steps: Rc<Vec<CandidateStep<'tcx>>>,
50 inherent_candidates: Vec<Candidate<'tcx>>,
51 extension_candidates: Vec<Candidate<'tcx>>,
52 impl_dups: FxHashSet<DefId>,
54 /// Collects near misses when the candidate functions are missing a `self` keyword and is only
55 /// used for error reporting
56 static_candidates: Vec<CandidateSource>,
58 /// When probing for names, include names that are close to the
59 /// requested name (by Levensthein distance)
60 allow_similar_names: bool,
62 /// Some(candidate) if there is a private candidate
63 private_candidate: Option<Def>,
65 /// Collects near misses when trait bounds for type parameters are unsatisfied and is only used
66 /// for error reporting
67 unsatisfied_predicates: Vec<TraitRef<'tcx>>,
70 impl<'a, 'gcx, 'tcx> Deref for ProbeContext<'a, 'gcx, 'tcx> {
71 type Target = FnCtxt<'a, 'gcx, 'tcx>;
72 fn deref(&self) -> &Self::Target {
78 struct CandidateStep<'tcx> {
81 // true if the type results from a dereference of a raw pointer.
82 // when assembling candidates, we include these steps, but not when
83 // picking methods. This so that if we have `foo: *const Foo` and `Foo` has methods
84 // `fn by_raw_ptr(self: *const Self)` and `fn by_ref(&self)`, then
85 // `foo.by_raw_ptr()` will work and `foo.by_ref()` won't.
86 from_unsafe_deref: bool,
91 struct Candidate<'tcx> {
92 xform_self_ty: Ty<'tcx>,
93 xform_ret_ty: Option<Ty<'tcx>>,
94 item: ty::AssociatedItem,
95 kind: CandidateKind<'tcx>,
96 import_id: Option<ast::NodeId>,
100 enum CandidateKind<'tcx> {
101 InherentImplCandidate(&'tcx Substs<'tcx>,
102 // Normalize obligations
103 Vec<traits::PredicateObligation<'tcx>>),
105 TraitCandidate(ty::TraitRef<'tcx>),
106 WhereClauseCandidate(// Trait
107 ty::PolyTraitRef<'tcx>),
110 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
117 #[derive(Debug, PartialEq, Eq, Clone)]
118 pub struct Pick<'tcx> {
119 pub item: ty::AssociatedItem,
120 pub kind: PickKind<'tcx>,
121 pub import_id: Option<ast::NodeId>,
123 // Indicates that the source expression should be autoderef'd N times
125 // A = expr | *expr | **expr | ...
126 pub autoderefs: usize,
128 // Indicates that an autoref is applied after the optional autoderefs
130 // B = A | &A | &mut A
131 pub autoref: Option<hir::Mutability>,
133 // Indicates that the source expression should be "unsized" to a
134 // target type. This should probably eventually go away in favor
135 // of just coercing method receivers.
138 pub unsize: Option<Ty<'tcx>>,
141 #[derive(Clone, Debug, PartialEq, Eq)]
142 pub enum PickKind<'tcx> {
146 WhereClausePick(// Trait
147 ty::PolyTraitRef<'tcx>),
150 pub type PickResult<'tcx> = Result<Pick<'tcx>, MethodError<'tcx>>;
152 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
154 // An expression of the form `receiver.method_name(...)`.
155 // Autoderefs are performed on `receiver`, lookup is done based on the
156 // `self` argument of the method, and static methods aren't considered.
158 // An expression of the form `Type::item` or `<T>::item`.
159 // No autoderefs are performed, lookup is done based on the type each
160 // implementation is for, and static methods are included.
164 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
165 pub enum ProbeScope {
166 // Assemble candidates coming only from traits in scope.
169 // Assemble candidates coming from all traits.
173 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
174 /// This is used to offer suggestions to users. It returns methods
175 /// that could have been called which have the desired return
176 /// type. Some effort is made to rule out methods that, if called,
177 /// would result in an error (basically, the same criteria we
178 /// would use to decide if a method is a plausible fit for
179 /// ambiguity purposes).
180 pub fn probe_for_return_type(&self,
183 return_type: Ty<'tcx>,
185 scope_expr_id: ast::NodeId)
186 -> Vec<ty::AssociatedItem> {
187 debug!("probe(self_ty={:?}, return_type={}, scope_expr_id={})",
192 self.probe_op(span, mode, None, Some(return_type), IsSuggestion(true),
193 self_ty, scope_expr_id, ProbeScope::AllTraits,
194 |probe_cx| Ok(probe_cx.candidate_method_names()))
198 .flat_map(|&method_name| {
200 span, mode, Some(method_name), Some(return_type),
201 IsSuggestion(true), self_ty, scope_expr_id,
202 ProbeScope::AllTraits, |probe_cx| probe_cx.pick()
203 ).ok().map(|pick| pick.item)
208 pub fn probe_for_name(&self,
211 item_name: ast::Name,
212 is_suggestion: IsSuggestion,
214 scope_expr_id: ast::NodeId,
216 -> PickResult<'tcx> {
217 debug!("probe(self_ty={:?}, item_name={}, scope_expr_id={})",
229 |probe_cx| probe_cx.pick())
232 fn probe_op<OP,R>(&'a self,
235 method_name: Option<ast::Name>,
236 return_type: Option<Ty<'tcx>>,
237 is_suggestion: IsSuggestion,
239 scope_expr_id: ast::NodeId,
242 -> Result<R, MethodError<'tcx>>
243 where OP: FnOnce(ProbeContext<'a, 'gcx, 'tcx>) -> Result<R, MethodError<'tcx>>
245 // FIXME(#18741) -- right now, creating the steps involves evaluating the
246 // `*` operator, which registers obligations that then escape into
247 // the global fulfillment context and thus has global
248 // side-effects. This is a bit of a pain to refactor. So just let
249 // it ride, although it's really not great, and in fact could I
250 // think cause spurious errors. Really though this part should
251 // take place in the `self.probe` below.
252 let steps = if mode == Mode::MethodCall {
253 match self.create_steps(span, scope_expr_id, self_ty, is_suggestion) {
254 Some(steps) => steps,
256 return Err(MethodError::NoMatch(NoMatchData::new(Vec::new(),
267 from_unsafe_deref: false,
272 debug!("ProbeContext: steps for self_ty={:?} are {:?}",
276 // this creates one big transaction so that all type variables etc
277 // that we create during the probe process are removed later
280 ProbeContext::new(self, span, mode, method_name, return_type, Rc::new(steps));
282 probe_cx.assemble_inherent_candidates();
284 ProbeScope::TraitsInScope =>
285 probe_cx.assemble_extension_candidates_for_traits_in_scope(scope_expr_id)?,
286 ProbeScope::AllTraits =>
287 probe_cx.assemble_extension_candidates_for_all_traits()?,
293 fn create_steps(&self,
295 scope_expr_id: ast::NodeId,
297 is_suggestion: IsSuggestion)
298 -> Option<Vec<CandidateStep<'tcx>>> {
299 // FIXME: we don't need to create the entire steps in one pass
301 let mut autoderef = self.autoderef(span, self_ty).include_raw_pointers();
302 let mut reached_raw_pointer = false;
303 let mut steps: Vec<_> = autoderef.by_ref()
305 let step = CandidateStep {
308 from_unsafe_deref: reached_raw_pointer,
311 if let ty::TyRawPtr(_) = ty.sty {
312 // all the subsequent steps will be from_unsafe_deref
313 reached_raw_pointer = true;
319 let final_ty = autoderef.maybe_ambiguous_final_ty();
321 ty::TyInfer(ty::TyVar(_)) => {
322 // Ended in an inference variable. If we are doing
323 // a real method lookup, this is a hard error because it's
324 // possible that there will be multiple applicable methods.
325 if !is_suggestion.0 {
326 if reached_raw_pointer
327 && !self.tcx.sess.features.borrow().arbitrary_self_types {
328 // this case used to be allowed by the compiler,
329 // so we do a future-compat lint here
330 // (see https://github.com/rust-lang/rust/issues/46906)
332 lint::builtin::TYVAR_BEHIND_RAW_POINTER,
335 &format!("the type of this value must be known in this context"));
337 let t = self.structurally_resolved_type(span, final_ty);
338 assert_eq!(t, self.tcx.types.err);
342 // If we're just looking for suggestions,
343 // though, ambiguity is no big thing, we can
347 ty::TyArray(elem_ty, _) => {
348 let dereferences = steps.len() - 1;
350 steps.push(CandidateStep {
351 self_ty: self.tcx.mk_slice(elem_ty),
352 autoderefs: dereferences,
353 // this could be from an unsafe deref if we had
354 // a *mut/const [T; N]
355 from_unsafe_deref: reached_raw_pointer,
359 ty::TyError => return None,
363 debug!("create_steps: steps={:?}", steps);
369 impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
370 fn new(fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
373 method_name: Option<ast::Name>,
374 return_type: Option<Ty<'tcx>>,
375 steps: Rc<Vec<CandidateStep<'tcx>>>)
376 -> ProbeContext<'a, 'gcx, 'tcx> {
383 inherent_candidates: Vec::new(),
384 extension_candidates: Vec::new(),
385 impl_dups: FxHashSet(),
387 static_candidates: Vec::new(),
388 allow_similar_names: false,
389 private_candidate: None,
390 unsatisfied_predicates: Vec::new(),
394 fn reset(&mut self) {
395 self.inherent_candidates.clear();
396 self.extension_candidates.clear();
397 self.impl_dups.clear();
398 self.static_candidates.clear();
399 self.private_candidate = None;
402 ///////////////////////////////////////////////////////////////////////////
403 // CANDIDATE ASSEMBLY
405 fn push_candidate(&mut self,
406 candidate: Candidate<'tcx>,
409 let is_accessible = if let Some(name) = self.method_name {
410 let item = candidate.item;
411 let def_scope = self.tcx.adjust(name, item.container.id(), self.body_id).1;
412 item.vis.is_accessible_from(def_scope, self.tcx)
418 self.inherent_candidates.push(candidate);
420 self.extension_candidates.push(candidate);
422 } else if self.private_candidate.is_none() {
423 self.private_candidate = Some(candidate.item.def());
427 fn assemble_inherent_candidates(&mut self) {
428 let steps = self.steps.clone();
429 for step in steps.iter() {
430 self.assemble_probe(step.self_ty);
434 fn assemble_probe(&mut self, self_ty: Ty<'tcx>) {
435 debug!("assemble_probe: self_ty={:?}", self_ty);
436 let lang_items = self.tcx.lang_items();
439 ty::TyDynamic(ref data, ..) => {
440 if let Some(p) = data.principal() {
441 self.assemble_inherent_candidates_from_object(self_ty, p);
442 self.assemble_inherent_impl_candidates_for_type(p.def_id());
445 ty::TyAdt(def, _) => {
446 self.assemble_inherent_impl_candidates_for_type(def.did);
448 ty::TyForeign(did) => {
449 self.assemble_inherent_impl_candidates_for_type(did);
452 self.assemble_inherent_candidates_from_param(self_ty, p);
455 let lang_def_id = lang_items.char_impl();
456 self.assemble_inherent_impl_for_primitive(lang_def_id);
459 let lang_def_id = lang_items.str_impl();
460 self.assemble_inherent_impl_for_primitive(lang_def_id);
463 let lang_def_id = lang_items.slice_impl();
464 self.assemble_inherent_impl_for_primitive(lang_def_id);
466 let lang_def_id = lang_items.slice_u8_impl();
467 self.assemble_inherent_impl_for_primitive(lang_def_id);
469 ty::TyRawPtr(ty::TypeAndMut { ty: _, mutbl: hir::MutImmutable }) => {
470 let lang_def_id = lang_items.const_ptr_impl();
471 self.assemble_inherent_impl_for_primitive(lang_def_id);
473 ty::TyRawPtr(ty::TypeAndMut { ty: _, mutbl: hir::MutMutable }) => {
474 let lang_def_id = lang_items.mut_ptr_impl();
475 self.assemble_inherent_impl_for_primitive(lang_def_id);
477 ty::TyInt(ast::IntTy::I8) => {
478 let lang_def_id = lang_items.i8_impl();
479 self.assemble_inherent_impl_for_primitive(lang_def_id);
481 ty::TyInt(ast::IntTy::I16) => {
482 let lang_def_id = lang_items.i16_impl();
483 self.assemble_inherent_impl_for_primitive(lang_def_id);
485 ty::TyInt(ast::IntTy::I32) => {
486 let lang_def_id = lang_items.i32_impl();
487 self.assemble_inherent_impl_for_primitive(lang_def_id);
489 ty::TyInt(ast::IntTy::I64) => {
490 let lang_def_id = lang_items.i64_impl();
491 self.assemble_inherent_impl_for_primitive(lang_def_id);
493 ty::TyInt(ast::IntTy::I128) => {
494 let lang_def_id = lang_items.i128_impl();
495 self.assemble_inherent_impl_for_primitive(lang_def_id);
497 ty::TyInt(ast::IntTy::Isize) => {
498 let lang_def_id = lang_items.isize_impl();
499 self.assemble_inherent_impl_for_primitive(lang_def_id);
501 ty::TyUint(ast::UintTy::U8) => {
502 let lang_def_id = lang_items.u8_impl();
503 self.assemble_inherent_impl_for_primitive(lang_def_id);
505 ty::TyUint(ast::UintTy::U16) => {
506 let lang_def_id = lang_items.u16_impl();
507 self.assemble_inherent_impl_for_primitive(lang_def_id);
509 ty::TyUint(ast::UintTy::U32) => {
510 let lang_def_id = lang_items.u32_impl();
511 self.assemble_inherent_impl_for_primitive(lang_def_id);
513 ty::TyUint(ast::UintTy::U64) => {
514 let lang_def_id = lang_items.u64_impl();
515 self.assemble_inherent_impl_for_primitive(lang_def_id);
517 ty::TyUint(ast::UintTy::U128) => {
518 let lang_def_id = lang_items.u128_impl();
519 self.assemble_inherent_impl_for_primitive(lang_def_id);
521 ty::TyUint(ast::UintTy::Usize) => {
522 let lang_def_id = lang_items.usize_impl();
523 self.assemble_inherent_impl_for_primitive(lang_def_id);
525 ty::TyFloat(ast::FloatTy::F32) => {
526 let lang_def_id = lang_items.f32_impl();
527 self.assemble_inherent_impl_for_primitive(lang_def_id);
529 ty::TyFloat(ast::FloatTy::F64) => {
530 let lang_def_id = lang_items.f64_impl();
531 self.assemble_inherent_impl_for_primitive(lang_def_id);
537 fn assemble_inherent_impl_for_primitive(&mut self, lang_def_id: Option<DefId>) {
538 if let Some(impl_def_id) = lang_def_id {
539 self.assemble_inherent_impl_probe(impl_def_id);
543 fn assemble_inherent_impl_candidates_for_type(&mut self, def_id: DefId) {
544 let impl_def_ids = self.tcx.at(self.span).inherent_impls(def_id);
545 for &impl_def_id in impl_def_ids.iter() {
546 self.assemble_inherent_impl_probe(impl_def_id);
550 fn assemble_inherent_impl_probe(&mut self, impl_def_id: DefId) {
551 if !self.impl_dups.insert(impl_def_id) {
552 return; // already visited
555 debug!("assemble_inherent_impl_probe {:?}", impl_def_id);
557 for item in self.impl_or_trait_item(impl_def_id) {
558 if !self.has_applicable_self(&item) {
559 // No receiver declared. Not a candidate.
560 self.record_static_candidate(ImplSource(impl_def_id));
564 let (impl_ty, impl_substs) = self.impl_ty_and_substs(impl_def_id);
565 let impl_ty = impl_ty.subst(self.tcx, impl_substs);
567 // Determine the receiver type that the method itself expects.
568 let xform_tys = self.xform_self_ty(&item, impl_ty, impl_substs);
570 // We can't use normalize_associated_types_in as it will pollute the
571 // fcx's fulfillment context after this probe is over.
572 let cause = traits::ObligationCause::misc(self.span, self.body_id);
573 let selcx = &mut traits::SelectionContext::new(self.fcx);
574 let traits::Normalized { value: (xform_self_ty, xform_ret_ty), obligations } =
575 traits::normalize(selcx, self.param_env, cause, &xform_tys);
576 debug!("assemble_inherent_impl_probe: xform_self_ty = {:?}/{:?}",
577 xform_self_ty, xform_ret_ty);
579 self.push_candidate(Candidate {
580 xform_self_ty, xform_ret_ty, item,
581 kind: InherentImplCandidate(impl_substs, obligations),
587 fn assemble_inherent_candidates_from_object(&mut self,
589 principal: ty::PolyExistentialTraitRef<'tcx>) {
590 debug!("assemble_inherent_candidates_from_object(self_ty={:?})",
593 // It is illegal to invoke a method on a trait instance that
594 // refers to the `Self` type. An error will be reported by
595 // `enforce_object_limitations()` if the method refers to the
596 // `Self` type anywhere other than the receiver. Here, we use
597 // a substitution that replaces `Self` with the object type
598 // itself. Hence, a `&self` method will wind up with an
599 // argument type like `&Trait`.
600 let trait_ref = principal.with_self_ty(self.tcx, self_ty);
601 self.elaborate_bounds(&[trait_ref], |this, new_trait_ref, item| {
602 let new_trait_ref = this.erase_late_bound_regions(&new_trait_ref);
604 let (xform_self_ty, xform_ret_ty) =
605 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
606 this.push_candidate(Candidate {
607 xform_self_ty, xform_ret_ty, item,
608 kind: ObjectCandidate,
614 fn assemble_inherent_candidates_from_param(&mut self,
616 param_ty: ty::ParamTy) {
617 // FIXME -- Do we want to commit to this behavior for param bounds?
619 let bounds: Vec<_> = self.param_env
622 .filter_map(|predicate| {
624 ty::Predicate::Trait(ref trait_predicate) => {
625 match trait_predicate.0.trait_ref.self_ty().sty {
626 ty::TyParam(ref p) if *p == param_ty => {
627 Some(trait_predicate.to_poly_trait_ref())
632 ty::Predicate::Equate(..) |
633 ty::Predicate::Subtype(..) |
634 ty::Predicate::Projection(..) |
635 ty::Predicate::RegionOutlives(..) |
636 ty::Predicate::WellFormed(..) |
637 ty::Predicate::ObjectSafe(..) |
638 ty::Predicate::ClosureKind(..) |
639 ty::Predicate::TypeOutlives(..) |
640 ty::Predicate::ConstEvaluatable(..) => None,
645 self.elaborate_bounds(&bounds, |this, poly_trait_ref, item| {
646 let trait_ref = this.erase_late_bound_regions(&poly_trait_ref);
648 let (xform_self_ty, xform_ret_ty) =
649 this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs);
651 // Because this trait derives from a where-clause, it
652 // should not contain any inference variables or other
653 // artifacts. This means it is safe to put into the
654 // `WhereClauseCandidate` and (eventually) into the
655 // `WhereClausePick`.
656 assert!(!trait_ref.substs.needs_infer());
658 this.push_candidate(Candidate {
659 xform_self_ty, xform_ret_ty, item,
660 kind: WhereClauseCandidate(poly_trait_ref),
666 // Do a search through a list of bounds, using a callback to actually
667 // create the candidates.
668 fn elaborate_bounds<F>(&mut self, bounds: &[ty::PolyTraitRef<'tcx>], mut mk_cand: F)
669 where F: for<'b> FnMut(&mut ProbeContext<'b, 'gcx, 'tcx>,
670 ty::PolyTraitRef<'tcx>,
673 debug!("elaborate_bounds(bounds={:?})", bounds);
676 for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
677 for item in self.impl_or_trait_item(bound_trait_ref.def_id()) {
678 if !self.has_applicable_self(&item) {
679 self.record_static_candidate(TraitSource(bound_trait_ref.def_id()));
681 mk_cand(self, bound_trait_ref, item);
687 fn assemble_extension_candidates_for_traits_in_scope(&mut self,
688 expr_id: ast::NodeId)
689 -> Result<(), MethodError<'tcx>> {
690 if expr_id == ast::DUMMY_NODE_ID {
693 let mut duplicates = FxHashSet();
694 let expr_hir_id = self.tcx.hir.node_to_hir_id(expr_id);
695 let opt_applicable_traits = self.tcx.in_scope_traits(expr_hir_id);
696 if let Some(applicable_traits) = opt_applicable_traits {
697 for trait_candidate in applicable_traits.iter() {
698 let trait_did = trait_candidate.def_id;
699 if duplicates.insert(trait_did) {
700 let import_id = trait_candidate.import_id;
701 let result = self.assemble_extension_candidates_for_trait(import_id, trait_did);
709 fn assemble_extension_candidates_for_all_traits(&mut self) -> Result<(), MethodError<'tcx>> {
710 let mut duplicates = FxHashSet();
711 for trait_info in suggest::all_traits(self.tcx) {
712 if duplicates.insert(trait_info.def_id) {
713 self.assemble_extension_candidates_for_trait(None, trait_info.def_id)?;
719 pub fn matches_return_type(&self,
720 method: &ty::AssociatedItem,
721 self_ty: Option<Ty<'tcx>>,
722 expected: Ty<'tcx>) -> bool {
724 Def::Method(def_id) => {
725 let fty = self.tcx.fn_sig(def_id);
727 let substs = self.fresh_substs_for_item(self.span, method.def_id);
728 let fty = fty.subst(self.tcx, substs);
729 let (fty, _) = self.replace_late_bound_regions_with_fresh_var(
730 self.span, infer::FnCall, &fty);
732 if let Some(self_ty) = self_ty {
733 if let Err(_) = self.at(&ObligationCause::dummy(), self.param_env)
734 .sup(fty.inputs()[0], self_ty)
739 self.can_sub(self.param_env, fty.output(), expected).is_ok()
746 fn assemble_extension_candidates_for_trait(&mut self,
747 import_id: Option<ast::NodeId>,
749 -> Result<(), MethodError<'tcx>> {
750 debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})",
752 let trait_substs = self.fresh_item_substs(trait_def_id);
753 let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
755 for item in self.impl_or_trait_item(trait_def_id) {
756 // Check whether `trait_def_id` defines a method with suitable name:
757 if !self.has_applicable_self(&item) {
758 debug!("method has inapplicable self");
759 self.record_static_candidate(TraitSource(trait_def_id));
763 let (xform_self_ty, xform_ret_ty) =
764 self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
765 self.push_candidate(Candidate {
766 xform_self_ty, xform_ret_ty, item, import_id,
767 kind: TraitCandidate(trait_ref),
773 fn candidate_method_names(&self) -> Vec<ast::Name> {
774 let mut set = FxHashSet();
775 let mut names: Vec<_> = self.inherent_candidates
777 .chain(&self.extension_candidates)
778 .filter(|candidate| {
779 if let Some(return_ty) = self.return_type {
780 self.matches_return_type(&candidate.item, None, return_ty)
785 .map(|candidate| candidate.item.name)
786 .filter(|&name| set.insert(name))
789 // sort them by the name so we have a stable result
790 names.sort_by_key(|n| n.as_str());
794 ///////////////////////////////////////////////////////////////////////////
797 fn pick(mut self) -> PickResult<'tcx> {
798 assert!(self.method_name.is_some());
800 if let Some(r) = self.pick_core() {
804 let static_candidates = mem::replace(&mut self.static_candidates, vec![]);
805 let private_candidate = mem::replace(&mut self.private_candidate, None);
806 let unsatisfied_predicates = mem::replace(&mut self.unsatisfied_predicates, vec![]);
808 // things failed, so lets look at all traits, for diagnostic purposes now:
811 let span = self.span;
814 self.assemble_extension_candidates_for_all_traits()?;
816 let out_of_scope_traits = match self.pick_core() {
817 Some(Ok(p)) => vec![p.item.container.id()],
818 //Some(Ok(p)) => p.iter().map(|p| p.item.container().id()).collect(),
819 Some(Err(MethodError::Ambiguity(v))) => {
823 TraitSource(id) => id,
824 ImplSource(impl_id) => {
825 match tcx.trait_id_of_impl(impl_id) {
829 "found inherent method when looking at traits")
837 Some(Err(MethodError::NoMatch(NoMatchData { out_of_scope_traits: others, .. }))) => {
838 assert!(others.is_empty());
844 if let Some(def) = private_candidate {
845 return Err(MethodError::PrivateMatch(def, out_of_scope_traits));
847 let lev_candidate = self.probe_for_lev_candidate()?;
849 Err(MethodError::NoMatch(NoMatchData::new(static_candidates,
850 unsatisfied_predicates,
856 fn pick_core(&mut self) -> Option<PickResult<'tcx>> {
857 let steps = self.steps.clone();
859 // find the first step that works
863 debug!("pick_core: step={:?}", step);
864 // skip types that are from a type error or that would require dereferencing
866 !step.self_ty.references_error() && !step.from_unsafe_deref
868 self.pick_by_value_method(step).or_else(|| {
869 self.pick_autorefd_method(step, hir::MutImmutable).or_else(|| {
870 self.pick_autorefd_method(step, hir::MutMutable)
875 fn pick_by_value_method(&mut self, step: &CandidateStep<'tcx>) -> Option<PickResult<'tcx>> {
876 //! For each type `T` in the step list, this attempts to find a
877 //! method where the (transformed) self type is exactly `T`. We
878 //! do however do one transformation on the adjustment: if we
879 //! are passing a region pointer in, we will potentially
880 //! *reborrow* it to a shorter lifetime. This allows us to
881 //! transparently pass `&mut` pointers, in particular, without
882 //! consuming them for their entire lifetime.
888 self.pick_method(step.self_ty).map(|r| {
890 pick.autoderefs = step.autoderefs;
892 // Insert a `&*` or `&mut *` if this is a reference type:
893 if let ty::TyRef(_, mt) = step.self_ty.sty {
894 pick.autoderefs += 1;
895 pick.autoref = Some(mt.mutbl);
903 fn pick_autorefd_method(&mut self, step: &CandidateStep<'tcx>, mutbl: hir::Mutability)
904 -> Option<PickResult<'tcx>> {
907 // In general, during probing we erase regions. See
908 // `impl_self_ty()` for an explanation.
909 let region = tcx.types.re_erased;
911 let autoref_ty = tcx.mk_ref(region,
913 ty: step.self_ty, mutbl
915 self.pick_method(autoref_ty).map(|r| {
917 pick.autoderefs = step.autoderefs;
918 pick.autoref = Some(mutbl);
919 pick.unsize = if step.unsize {
929 fn pick_method(&mut self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
930 debug!("pick_method(self_ty={})", self.ty_to_string(self_ty));
932 let mut possibly_unsatisfied_predicates = Vec::new();
934 debug!("searching inherent candidates");
935 if let Some(pick) = self.consider_candidates(self_ty,
936 &self.inherent_candidates,
937 &mut possibly_unsatisfied_predicates) {
941 debug!("searching extension candidates");
942 let res = self.consider_candidates(self_ty,
943 &self.extension_candidates,
944 &mut possibly_unsatisfied_predicates);
946 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
951 fn consider_candidates(&self,
953 probes: &[Candidate<'tcx>],
954 possibly_unsatisfied_predicates: &mut Vec<TraitRef<'tcx>>)
955 -> Option<PickResult<'tcx>> {
956 let mut applicable_candidates: Vec<_> = probes.iter()
958 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
960 .filter(|&(_, status)| status != ProbeResult::NoMatch)
963 debug!("applicable_candidates: {:?}", applicable_candidates);
965 if applicable_candidates.len() > 1 {
966 if let Some(pick) = self.collapse_candidates_to_trait_pick(&applicable_candidates[..]) {
967 return Some(Ok(pick));
971 if applicable_candidates.len() > 1 {
972 let sources = probes.iter()
973 .map(|p| self.candidate_source(p, self_ty))
975 return Some(Err(MethodError::Ambiguity(sources)));
978 applicable_candidates.pop().map(|(probe, status)| {
979 if status == ProbeResult::Match {
980 Ok(probe.to_unadjusted_pick())
982 Err(MethodError::BadReturnType)
987 fn select_trait_candidate(&self, trait_ref: ty::TraitRef<'tcx>)
988 -> traits::SelectionResult<'tcx, traits::Selection<'tcx>>
990 let cause = traits::ObligationCause::misc(self.span, self.body_id);
992 trait_ref.to_poly_trait_ref().to_poly_trait_predicate();
993 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
994 traits::SelectionContext::new(self).select(&obligation)
997 fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>)
1000 match candidate.kind {
1001 InherentImplCandidate(..) => ImplSource(candidate.item.container.id()),
1003 WhereClauseCandidate(_) => TraitSource(candidate.item.container.id()),
1004 TraitCandidate(trait_ref) => self.probe(|_| {
1005 let _ = self.at(&ObligationCause::dummy(), self.param_env)
1006 .sup(candidate.xform_self_ty, self_ty);
1007 match self.select_trait_candidate(trait_ref) {
1008 Ok(Some(traits::Vtable::VtableImpl(ref impl_data))) => {
1009 // If only a single impl matches, make the error message point
1011 ImplSource(impl_data.impl_def_id)
1014 TraitSource(candidate.item.container.id())
1021 fn consider_probe(&self,
1023 probe: &Candidate<'tcx>,
1024 possibly_unsatisfied_predicates: &mut Vec<TraitRef<'tcx>>)
1026 debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe);
1029 // First check that the self type can be related.
1030 let sub_obligations = match self.at(&ObligationCause::dummy(), self.param_env)
1031 .sup(probe.xform_self_ty, self_ty) {
1032 Ok(InferOk { obligations, value: () }) => obligations,
1034 debug!("--> cannot relate self-types");
1035 return ProbeResult::NoMatch;
1039 let mut result = ProbeResult::Match;
1040 let selcx = &mut traits::SelectionContext::new(self);
1041 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1043 // If so, impls may carry other conditions (e.g., where
1044 // clauses) that must be considered. Make sure that those
1045 // match as well (or at least may match, sometimes we
1046 // don't have enough information to fully evaluate).
1047 let candidate_obligations : Vec<_> = match probe.kind {
1048 InherentImplCandidate(ref substs, ref ref_obligations) => {
1049 // Check whether the impl imposes obligations we have to worry about.
1050 let impl_def_id = probe.item.container.id();
1051 let impl_bounds = self.tcx.predicates_of(impl_def_id);
1052 let impl_bounds = impl_bounds.instantiate(self.tcx, substs);
1053 let traits::Normalized { value: impl_bounds, obligations: norm_obligations } =
1054 traits::normalize(selcx, self.param_env, cause.clone(), &impl_bounds);
1056 // Convert the bounds into obligations.
1057 let impl_obligations = traits::predicates_for_generics(
1058 cause.clone(), self.param_env, &impl_bounds);
1060 debug!("impl_obligations={:?}", impl_obligations);
1061 impl_obligations.into_iter()
1062 .chain(norm_obligations.into_iter())
1063 .chain(ref_obligations.iter().cloned())
1068 WhereClauseCandidate(..) => {
1069 // These have no additional conditions to check.
1073 TraitCandidate(trait_ref) => {
1074 let predicate = trait_ref.to_predicate();
1076 traits::Obligation::new(cause.clone(), self.param_env, predicate);
1077 if !selcx.evaluate_obligation(&obligation) {
1078 if self.probe(|_| self.select_trait_candidate(trait_ref).is_err()) {
1079 // This candidate's primary obligation doesn't even
1080 // select - don't bother registering anything in
1081 // `potentially_unsatisfied_predicates`.
1082 return ProbeResult::NoMatch;
1084 // Some nested subobligation of this predicate
1087 // FIXME: try to find the exact nested subobligation
1088 // and point at it rather than reporting the entire
1090 result = ProbeResult::NoMatch;
1091 let trait_ref = self.resolve_type_vars_if_possible(&trait_ref);
1092 possibly_unsatisfied_predicates.push(trait_ref);
1099 debug!("consider_probe - candidate_obligations={:?} sub_obligations={:?}",
1100 candidate_obligations, sub_obligations);
1102 // Evaluate those obligations to see if they might possibly hold.
1103 for o in candidate_obligations.into_iter().chain(sub_obligations) {
1104 let o = self.resolve_type_vars_if_possible(&o);
1105 if !selcx.evaluate_obligation(&o) {
1106 result = ProbeResult::NoMatch;
1107 if let &ty::Predicate::Trait(ref pred) = &o.predicate {
1108 possibly_unsatisfied_predicates.push(pred.0.trait_ref);
1113 if let ProbeResult::Match = result {
1114 if let (Some(return_ty), Some(xform_ret_ty)) =
1115 (self.return_type, probe.xform_ret_ty)
1117 let xform_ret_ty = self.resolve_type_vars_if_possible(&xform_ret_ty);
1118 debug!("comparing return_ty {:?} with xform ret ty {:?}",
1120 probe.xform_ret_ty);
1121 if self.at(&ObligationCause::dummy(), self.param_env)
1122 .sup(return_ty, xform_ret_ty)
1125 return ProbeResult::BadReturnType;
1134 /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1135 /// same trait, but we don't know which impl to use. In this case, since in all cases the
1136 /// external interface of the method can be determined from the trait, it's ok not to decide.
1137 /// We can basically just collapse all of the probes for various impls into one where-clause
1138 /// probe. This will result in a pending obligation so when more type-info is available we can
1139 /// make the final decision.
1141 /// Example (`src/test/run-pass/method-two-trait-defer-resolution-1.rs`):
1144 /// trait Foo { ... }
1145 /// impl Foo for Vec<int> { ... }
1146 /// impl Foo for Vec<usize> { ... }
1149 /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1150 /// use, so it's ok to just commit to "using the method from the trait Foo".
1151 fn collapse_candidates_to_trait_pick(&self, probes: &[(&Candidate<'tcx>, ProbeResult)])
1152 -> Option<Pick<'tcx>>
1154 // Do all probes correspond to the same trait?
1155 let container = probes[0].0.item.container;
1157 ty::TraitContainer(_) => {}
1158 ty::ImplContainer(_) => return None,
1160 if probes[1..].iter().any(|&(p, _)| p.item.container != container) {
1164 // FIXME: check the return type here somehow.
1165 // If so, just use this trait and call it a day.
1167 item: probes[0].0.item.clone(),
1169 import_id: probes[0].0.import_id,
1176 /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
1177 /// candidate method where the method name may have been misspelt. Similarly to other
1178 /// Levenshtein based suggestions, we provide at most one such suggestion.
1179 fn probe_for_lev_candidate(&mut self) -> Result<Option<ty::AssociatedItem>, MethodError<'tcx>> {
1180 debug!("Probing for method names similar to {:?}",
1183 let steps = self.steps.clone();
1185 let mut pcx = ProbeContext::new(self.fcx, self.span, self.mode, self.method_name,
1186 self.return_type, steps);
1187 pcx.allow_similar_names = true;
1188 pcx.assemble_inherent_candidates();
1189 pcx.assemble_extension_candidates_for_traits_in_scope(ast::DUMMY_NODE_ID)?;
1191 let method_names = pcx.candidate_method_names();
1192 pcx.allow_similar_names = false;
1193 let applicable_close_candidates: Vec<ty::AssociatedItem> = method_names
1195 .filter_map(|&method_name| {
1197 pcx.method_name = Some(method_name);
1198 pcx.assemble_inherent_candidates();
1199 pcx.assemble_extension_candidates_for_traits_in_scope(ast::DUMMY_NODE_ID)
1200 .ok().map_or(None, |_| {
1202 .and_then(|pick| pick.ok())
1203 .and_then(|pick| Some(pick.item))
1208 if applicable_close_candidates.is_empty() {
1212 let names = applicable_close_candidates.iter().map(|cand| &cand.name);
1213 find_best_match_for_name(names,
1214 &self.method_name.unwrap().as_str(),
1217 Ok(applicable_close_candidates
1219 .find(|method| method.name == best_name))
1224 ///////////////////////////////////////////////////////////////////////////
1226 fn has_applicable_self(&self, item: &ty::AssociatedItem) -> bool {
1227 // "Fast track" -- check for usage of sugar when in method call
1230 // In Path mode (i.e., resolving a value like `T::next`), consider any
1231 // associated value (i.e., methods, constants) but not types.
1233 Mode::MethodCall => item.method_has_self_argument,
1234 Mode::Path => match item.kind {
1235 ty::AssociatedKind::Type => false,
1236 ty::AssociatedKind::Method | ty::AssociatedKind::Const => true
1239 // FIXME -- check for types that deref to `Self`,
1240 // like `Rc<Self>` and so on.
1242 // Note also that the current code will break if this type
1243 // includes any of the type parameters defined on the method
1244 // -- but this could be overcome.
1247 fn record_static_candidate(&mut self, source: CandidateSource) {
1248 self.static_candidates.push(source);
1251 fn xform_self_ty(&self,
1252 item: &ty::AssociatedItem,
1254 substs: &Substs<'tcx>)
1255 -> (Ty<'tcx>, Option<Ty<'tcx>>) {
1256 if item.kind == ty::AssociatedKind::Method && self.mode == Mode::MethodCall {
1257 let sig = self.xform_method_sig(item.def_id, substs);
1258 (sig.inputs()[0], Some(sig.output()))
1264 fn xform_method_sig(&self,
1266 substs: &Substs<'tcx>)
1269 let fn_sig = self.tcx.fn_sig(method);
1270 debug!("xform_self_ty(fn_sig={:?}, substs={:?})",
1274 assert!(!substs.has_escaping_regions());
1276 // It is possible for type parameters or early-bound lifetimes
1277 // to appear in the signature of `self`. The substitutions we
1278 // are given do not include type/lifetime parameters for the
1279 // method yet. So create fresh variables here for those too,
1280 // if there are any.
1281 let generics = self.tcx.generics_of(method);
1282 assert_eq!(substs.types().count(), generics.parent_types as usize);
1283 assert_eq!(substs.regions().count(), generics.parent_regions as usize);
1285 // Erase any late-bound regions from the method and substitute
1286 // in the values from the substitution.
1287 let xform_fn_sig = self.erase_late_bound_regions(&fn_sig);
1289 if generics.types.is_empty() && generics.regions.is_empty() {
1290 xform_fn_sig.subst(self.tcx, substs)
1292 let substs = Substs::for_item(self.tcx, method, |def, _| {
1293 let i = def.index as usize;
1294 if i < substs.len() {
1297 // In general, during probe we erase regions. See
1298 // `impl_self_ty()` for an explanation.
1299 self.tcx.types.re_erased
1301 }, |def, cur_substs| {
1302 let i = def.index as usize;
1303 if i < substs.len() {
1306 self.type_var_for_def(self.span, def, cur_substs)
1309 xform_fn_sig.subst(self.tcx, substs)
1313 /// Get the type of an impl and generate substitutions with placeholders.
1314 fn impl_ty_and_substs(&self, impl_def_id: DefId) -> (Ty<'tcx>, &'tcx Substs<'tcx>) {
1315 (self.tcx.type_of(impl_def_id), self.fresh_item_substs(impl_def_id))
1318 fn fresh_item_substs(&self, def_id: DefId) -> &'tcx Substs<'tcx> {
1319 Substs::for_item(self.tcx,
1321 |_, _| self.tcx.types.re_erased,
1322 |_, _| self.next_ty_var(
1323 TypeVariableOrigin::SubstitutionPlaceholder(
1324 self.tcx.def_span(def_id))))
1327 /// Replace late-bound-regions bound by `value` with `'static` using
1328 /// `ty::erase_late_bound_regions`.
1330 /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1331 /// method matching. It is reasonable during the probe phase because we don't consider region
1332 /// relationships at all. Therefore, we can just replace all the region variables with 'static
1333 /// rather than creating fresh region variables. This is nice for two reasons:
1335 /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1336 /// particular method call, it winds up creating fewer types overall, which helps for memory
1337 /// usage. (Admittedly, this is a rather small effect, though measureable.)
1339 /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1340 /// late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1341 /// regions with actual region variables as is proper, we'd have to ensure that the same
1342 /// region got replaced with the same variable, which requires a bit more coordination
1343 /// and/or tracking the substitution and
1345 fn erase_late_bound_regions<T>(&self, value: &ty::Binder<T>) -> T
1346 where T: TypeFoldable<'tcx>
1348 self.tcx.erase_late_bound_regions(value)
1351 /// Find the method with the appropriate name (or return type, as the case may be). If
1352 /// `allow_similar_names` is set, find methods with close-matching names.
1353 fn impl_or_trait_item(&self, def_id: DefId) -> Vec<ty::AssociatedItem> {
1354 if let Some(name) = self.method_name {
1355 if self.allow_similar_names {
1356 let max_dist = max(name.as_str().len(), 3) / 3;
1357 self.tcx.associated_items(def_id)
1359 let dist = lev_distance(&*name.as_str(), &x.name.as_str());
1360 Namespace::from(x.kind) == Namespace::Value && dist > 0
1366 .associated_item(def_id, name, Namespace::Value)
1367 .map_or(Vec::new(), |x| vec![x])
1370 self.tcx.associated_items(def_id).collect()
1375 impl<'tcx> Candidate<'tcx> {
1376 fn to_unadjusted_pick(&self) -> Pick<'tcx> {
1378 item: self.item.clone(),
1379 kind: match self.kind {
1380 InherentImplCandidate(..) => InherentImplPick,
1381 ObjectCandidate => ObjectPick,
1382 TraitCandidate(_) => TraitPick,
1383 WhereClauseCandidate(ref trait_ref) => {
1384 // Only trait derived from where-clauses should
1385 // appear here, so they should not contain any
1386 // inference variables or other artifacts. This
1387 // means they are safe to put into the
1388 // `WhereClausePick`.
1389 assert!(!trait_ref.substs().needs_infer());
1391 WhereClausePick(trait_ref.clone())
1394 import_id: self.import_id,