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 check::{FnCtxt, UnresolvedTypeAction};
18 use middle::def_id::DefId;
20 use middle::subst::Subst;
22 use middle::ty::{self, NoPreference, RegionEscape, Ty, ToPolyTraitRef, TraitRef};
23 use middle::ty::HasTypeFlags;
24 use middle::ty::fold::TypeFoldable;
26 use middle::infer::InferCtxt;
28 use syntax::codemap::{Span, DUMMY_SP};
30 use std::collections::HashSet;
34 use self::CandidateKind::*;
35 pub use self::PickKind::*;
37 struct ProbeContext<'a, 'tcx:'a> {
38 fcx: &'a FnCtxt<'a, 'tcx>,
42 steps: Rc<Vec<CandidateStep<'tcx>>>,
43 opt_simplified_steps: Option<Vec<ty::fast_reject::SimplifiedType>>,
44 inherent_candidates: Vec<Candidate<'tcx>>,
45 extension_candidates: Vec<Candidate<'tcx>>,
46 impl_dups: HashSet<DefId>,
48 /// Collects near misses when the candidate functions are missing a `self` keyword and is only
49 /// used for error reporting
50 static_candidates: Vec<CandidateSource>,
52 /// Collects near misses when trait bounds for type parameters are unsatisfied and is only used
53 /// for error reporting
54 unsatisfied_predicates: Vec<TraitRef<'tcx>>
58 struct CandidateStep<'tcx> {
65 struct Candidate<'tcx> {
66 xform_self_ty: Ty<'tcx>,
67 item: ty::ImplOrTraitItem<'tcx>,
68 kind: CandidateKind<'tcx>,
72 enum CandidateKind<'tcx> {
73 InherentImplCandidate(subst::Substs<'tcx>,
74 /* Normalize obligations */ Vec<traits::PredicateObligation<'tcx>>),
75 ExtensionImplCandidate(/* Impl */ DefId, subst::Substs<'tcx>,
76 /* Normalize obligations */ Vec<traits::PredicateObligation<'tcx>>),
79 WhereClauseCandidate(/* Trait */ ty::PolyTraitRef<'tcx>),
83 pub struct Pick<'tcx> {
84 pub item: ty::ImplOrTraitItem<'tcx>,
85 pub kind: PickKind<'tcx>,
87 // Indicates that the source expression should be autoderef'd N times
89 // A = expr | *expr | **expr | ...
90 pub autoderefs: usize,
92 // Indicates that an autoref is applied after the optional autoderefs
94 // B = A | &A | &mut A
95 pub autoref: Option<hir::Mutability>,
97 // Indicates that the source expression should be "unsized" to a
98 // target type. This should probably eventually go away in favor
99 // of just coercing method receivers.
102 pub unsize: Option<Ty<'tcx>>,
105 #[derive(Clone,Debug)]
106 pub enum PickKind<'tcx> {
108 ExtensionImplPick(/* Impl */ DefId),
111 WhereClausePick(/* Trait */ ty::PolyTraitRef<'tcx>),
114 pub type PickResult<'tcx> = Result<Pick<'tcx>, MethodError<'tcx>>;
116 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
118 // An expression of the form `receiver.method_name(...)`.
119 // Autoderefs are performed on `receiver`, lookup is done based on the
120 // `self` argument of the method, and static methods aren't considered.
122 // An expression of the form `Type::item` or `<T>::item`.
123 // No autoderefs are performed, lookup is done based on the type each
124 // implementation is for, and static methods are included.
128 pub fn probe<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
131 item_name: ast::Name,
133 scope_expr_id: ast::NodeId)
136 debug!("probe(self_ty={:?}, item_name={}, scope_expr_id={})",
141 // FIXME(#18741) -- right now, creating the steps involves evaluating the
142 // `*` operator, which registers obligations that then escape into
143 // the global fulfillment context and thus has global
144 // side-effects. This is a bit of a pain to refactor. So just let
145 // it ride, although it's really not great, and in fact could I
146 // think cause spurious errors. Really though this part should
147 // take place in the `fcx.infcx().probe` below.
148 let steps = if mode == Mode::MethodCall {
149 match create_steps(fcx, span, self_ty) {
150 Some(steps) => steps,
151 None =>return Err(MethodError::NoMatch(NoMatchData::new(Vec::new(), Vec::new(),
162 // Create a list of simplified self types, if we can.
163 let mut simplified_steps = Vec::new();
165 match ty::fast_reject::simplify_type(fcx.tcx(), step.self_ty, true) {
167 Some(simplified_type) => { simplified_steps.push(simplified_type); }
170 let opt_simplified_steps =
171 if simplified_steps.len() < steps.len() {
172 None // failed to convert at least one of the steps
174 Some(simplified_steps)
177 debug!("ProbeContext: steps for self_ty={:?} are {:?}",
181 // this creates one big transaction so that all type variables etc
182 // that we create during the probe process are removed later
183 fcx.infcx().probe(|_| {
184 let mut probe_cx = ProbeContext::new(fcx,
189 opt_simplified_steps);
190 probe_cx.assemble_inherent_candidates();
191 try!(probe_cx.assemble_extension_candidates_for_traits_in_scope(scope_expr_id));
196 fn create_steps<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
199 -> Option<Vec<CandidateStep<'tcx>>> {
200 let mut steps = Vec::new();
202 let (final_ty, dereferences, _) = check::autoderef(fcx,
206 UnresolvedTypeAction::Error,
209 steps.push(CandidateStep {
214 None::<()> // keep iterating until we can't anymore
218 ty::TyArray(elem_ty, _) => {
219 steps.push(CandidateStep {
220 self_ty: fcx.tcx().mk_slice(elem_ty),
221 autoderefs: dereferences,
225 ty::TyError => return None,
232 impl<'a,'tcx> ProbeContext<'a,'tcx> {
233 fn new(fcx: &'a FnCtxt<'a,'tcx>,
236 item_name: ast::Name,
237 steps: Vec<CandidateStep<'tcx>>,
238 opt_simplified_steps: Option<Vec<ty::fast_reject::SimplifiedType>>)
239 -> ProbeContext<'a,'tcx>
245 item_name: item_name,
246 inherent_candidates: Vec::new(),
247 extension_candidates: Vec::new(),
248 impl_dups: HashSet::new(),
249 steps: Rc::new(steps),
250 opt_simplified_steps: opt_simplified_steps,
251 static_candidates: Vec::new(),
252 unsatisfied_predicates: Vec::new(),
256 fn reset(&mut self) {
257 self.inherent_candidates.clear();
258 self.extension_candidates.clear();
259 self.impl_dups.clear();
260 self.static_candidates.clear();
263 fn tcx(&self) -> &'a ty::ctxt<'tcx> {
267 fn infcx(&self) -> &'a InferCtxt<'a, 'tcx> {
271 ///////////////////////////////////////////////////////////////////////////
272 // CANDIDATE ASSEMBLY
274 fn assemble_inherent_candidates(&mut self) {
275 let steps = self.steps.clone();
276 for step in steps.iter() {
277 self.assemble_probe(step.self_ty);
281 fn assemble_probe(&mut self, self_ty: Ty<'tcx>) {
282 debug!("assemble_probe: self_ty={:?}",
286 ty::TyTrait(box ref data) => {
287 self.assemble_inherent_candidates_from_object(self_ty, data);
288 self.assemble_inherent_impl_candidates_for_type(data.principal_def_id());
291 ty::TyStruct(def, _) => {
292 self.assemble_inherent_impl_candidates_for_type(def.did);
295 if let Some(box_did) = self.tcx().lang_items.owned_box() {
296 self.assemble_inherent_impl_candidates_for_type(box_did);
300 self.assemble_inherent_candidates_from_param(self_ty, p);
303 let lang_def_id = self.tcx().lang_items.char_impl();
304 self.assemble_inherent_impl_for_primitive(lang_def_id);
307 let lang_def_id = self.tcx().lang_items.str_impl();
308 self.assemble_inherent_impl_for_primitive(lang_def_id);
311 let lang_def_id = self.tcx().lang_items.slice_impl();
312 self.assemble_inherent_impl_for_primitive(lang_def_id);
314 ty::TyRawPtr(ty::TypeAndMut { ty: _, mutbl: hir::MutImmutable }) => {
315 let lang_def_id = self.tcx().lang_items.const_ptr_impl();
316 self.assemble_inherent_impl_for_primitive(lang_def_id);
318 ty::TyRawPtr(ty::TypeAndMut { ty: _, mutbl: hir::MutMutable }) => {
319 let lang_def_id = self.tcx().lang_items.mut_ptr_impl();
320 self.assemble_inherent_impl_for_primitive(lang_def_id);
322 ty::TyInt(hir::TyI8) => {
323 let lang_def_id = self.tcx().lang_items.i8_impl();
324 self.assemble_inherent_impl_for_primitive(lang_def_id);
326 ty::TyInt(hir::TyI16) => {
327 let lang_def_id = self.tcx().lang_items.i16_impl();
328 self.assemble_inherent_impl_for_primitive(lang_def_id);
330 ty::TyInt(hir::TyI32) => {
331 let lang_def_id = self.tcx().lang_items.i32_impl();
332 self.assemble_inherent_impl_for_primitive(lang_def_id);
334 ty::TyInt(hir::TyI64) => {
335 let lang_def_id = self.tcx().lang_items.i64_impl();
336 self.assemble_inherent_impl_for_primitive(lang_def_id);
338 ty::TyInt(hir::TyIs) => {
339 let lang_def_id = self.tcx().lang_items.isize_impl();
340 self.assemble_inherent_impl_for_primitive(lang_def_id);
342 ty::TyUint(hir::TyU8) => {
343 let lang_def_id = self.tcx().lang_items.u8_impl();
344 self.assemble_inherent_impl_for_primitive(lang_def_id);
346 ty::TyUint(hir::TyU16) => {
347 let lang_def_id = self.tcx().lang_items.u16_impl();
348 self.assemble_inherent_impl_for_primitive(lang_def_id);
350 ty::TyUint(hir::TyU32) => {
351 let lang_def_id = self.tcx().lang_items.u32_impl();
352 self.assemble_inherent_impl_for_primitive(lang_def_id);
354 ty::TyUint(hir::TyU64) => {
355 let lang_def_id = self.tcx().lang_items.u64_impl();
356 self.assemble_inherent_impl_for_primitive(lang_def_id);
358 ty::TyUint(hir::TyUs) => {
359 let lang_def_id = self.tcx().lang_items.usize_impl();
360 self.assemble_inherent_impl_for_primitive(lang_def_id);
362 ty::TyFloat(hir::TyF32) => {
363 let lang_def_id = self.tcx().lang_items.f32_impl();
364 self.assemble_inherent_impl_for_primitive(lang_def_id);
366 ty::TyFloat(hir::TyF64) => {
367 let lang_def_id = self.tcx().lang_items.f64_impl();
368 self.assemble_inherent_impl_for_primitive(lang_def_id);
375 fn assemble_inherent_impl_for_primitive(&mut self, lang_def_id: Option<DefId>) {
376 if let Some(impl_def_id) = lang_def_id {
377 self.tcx().populate_implementations_for_primitive_if_necessary(impl_def_id);
379 self.assemble_inherent_impl_probe(impl_def_id);
383 fn assemble_inherent_impl_candidates_for_type(&mut self, def_id: DefId) {
384 // Read the inherent implementation candidates for this type from the
385 // metadata if necessary.
386 self.tcx().populate_inherent_implementations_for_type_if_necessary(def_id);
388 if let Some(impl_infos) = self.tcx().inherent_impls.borrow().get(&def_id) {
389 for &impl_def_id in impl_infos.iter() {
390 self.assemble_inherent_impl_probe(impl_def_id);
395 fn assemble_inherent_impl_probe(&mut self, impl_def_id: DefId) {
396 if !self.impl_dups.insert(impl_def_id) {
397 return; // already visited
400 debug!("assemble_inherent_impl_probe {:?}", impl_def_id);
402 let item = match impl_item(self.tcx(), impl_def_id, self.item_name) {
404 None => { return; } // No method with correct name on this impl
407 if !self.has_applicable_self(&item) {
408 // No receiver declared. Not a candidate.
409 return self.record_static_candidate(ImplSource(impl_def_id));
412 let (impl_ty, impl_substs) = self.impl_ty_and_substs(impl_def_id);
413 let impl_ty = impl_ty.subst(self.tcx(), &impl_substs);
415 // Determine the receiver type that the method itself expects.
416 let xform_self_ty = self.xform_self_ty(&item, impl_ty, &impl_substs);
418 // We can't use normalize_associated_types_in as it will pollute the
419 // fcx's fulfillment context after this probe is over.
420 let cause = traits::ObligationCause::misc(self.span, self.fcx.body_id);
421 let mut selcx = &mut traits::SelectionContext::new(self.fcx.infcx());
422 let traits::Normalized { value: xform_self_ty, obligations } =
423 traits::normalize(selcx, cause, &xform_self_ty);
424 debug!("assemble_inherent_impl_probe: xform_self_ty = {:?}",
427 self.inherent_candidates.push(Candidate {
428 xform_self_ty: xform_self_ty,
430 kind: InherentImplCandidate(impl_substs, obligations)
434 fn assemble_inherent_candidates_from_object(&mut self,
436 data: &ty::TraitTy<'tcx>) {
437 debug!("assemble_inherent_candidates_from_object(self_ty={:?})",
440 // It is illegal to invoke a method on a trait instance that
441 // refers to the `Self` type. An error will be reported by
442 // `enforce_object_limitations()` if the method refers to the
443 // `Self` type anywhere other than the receiver. Here, we use
444 // a substitution that replaces `Self` with the object type
445 // itself. Hence, a `&self` method will wind up with an
446 // argument type like `&Trait`.
447 let trait_ref = data.principal_trait_ref_with_self_ty(self.tcx(), self_ty);
448 self.elaborate_bounds(&[trait_ref], |this, new_trait_ref, item| {
449 let new_trait_ref = this.erase_late_bound_regions(&new_trait_ref);
451 let xform_self_ty = this.xform_self_ty(&item,
452 new_trait_ref.self_ty(),
453 new_trait_ref.substs);
455 this.inherent_candidates.push(Candidate {
456 xform_self_ty: xform_self_ty,
458 kind: ObjectCandidate
463 fn assemble_inherent_candidates_from_param(&mut self,
465 param_ty: ty::ParamTy) {
466 // FIXME -- Do we want to commit to this behavior for param bounds?
469 self.fcx.inh.infcx.parameter_environment.caller_bounds
471 .filter_map(|predicate| {
473 ty::Predicate::Trait(ref trait_predicate) => {
474 match trait_predicate.0.trait_ref.self_ty().sty {
475 ty::TyParam(ref p) if *p == param_ty => {
476 Some(trait_predicate.to_poly_trait_ref())
481 ty::Predicate::Equate(..) |
482 ty::Predicate::Projection(..) |
483 ty::Predicate::RegionOutlives(..) |
484 ty::Predicate::WellFormed(..) |
485 ty::Predicate::ObjectSafe(..) |
486 ty::Predicate::TypeOutlives(..) => {
493 self.elaborate_bounds(&bounds, |this, poly_trait_ref, item| {
495 this.erase_late_bound_regions(&poly_trait_ref);
498 this.xform_self_ty(&item,
502 if let Some(ref m) = item.as_opt_method() {
503 debug!("found match: trait_ref={:?} substs={:?} m={:?}",
507 assert_eq!(m.generics.types.get_slice(subst::TypeSpace).len(),
508 trait_ref.substs.types.get_slice(subst::TypeSpace).len());
509 assert_eq!(m.generics.regions.get_slice(subst::TypeSpace).len(),
510 trait_ref.substs.regions().get_slice(subst::TypeSpace).len());
511 assert_eq!(m.generics.types.get_slice(subst::SelfSpace).len(),
512 trait_ref.substs.types.get_slice(subst::SelfSpace).len());
513 assert_eq!(m.generics.regions.get_slice(subst::SelfSpace).len(),
514 trait_ref.substs.regions().get_slice(subst::SelfSpace).len());
517 // Because this trait derives from a where-clause, it
518 // should not contain any inference variables or other
519 // artifacts. This means it is safe to put into the
520 // `WhereClauseCandidate` and (eventually) into the
521 // `WhereClausePick`.
522 assert!(!trait_ref.substs.types.needs_infer());
524 this.inherent_candidates.push(Candidate {
525 xform_self_ty: xform_self_ty,
527 kind: WhereClauseCandidate(poly_trait_ref)
532 // Do a search through a list of bounds, using a callback to actually
533 // create the candidates.
534 fn elaborate_bounds<F>(
536 bounds: &[ty::PolyTraitRef<'tcx>],
540 &mut ProbeContext<'b, 'tcx>,
541 ty::PolyTraitRef<'tcx>,
542 ty::ImplOrTraitItem<'tcx>,
545 debug!("elaborate_bounds(bounds={:?})", bounds);
547 let tcx = self.tcx();
548 for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
549 let item = match trait_item(tcx,
550 bound_trait_ref.def_id(),
553 None => { continue; }
556 if !self.has_applicable_self(&item) {
557 self.record_static_candidate(TraitSource(bound_trait_ref.def_id()));
559 mk_cand(self, bound_trait_ref, item);
564 fn assemble_extension_candidates_for_traits_in_scope(&mut self,
565 expr_id: ast::NodeId)
566 -> Result<(), MethodError<'tcx>>
568 let mut duplicates = HashSet::new();
569 let opt_applicable_traits = self.fcx.ccx.trait_map.get(&expr_id);
570 if let Some(applicable_traits) = opt_applicable_traits {
571 for &trait_did in applicable_traits {
572 if duplicates.insert(trait_did) {
573 try!(self.assemble_extension_candidates_for_trait(trait_did));
580 fn assemble_extension_candidates_for_all_traits(&mut self) -> Result<(), MethodError<'tcx>> {
581 let mut duplicates = HashSet::new();
582 for trait_info in suggest::all_traits(self.fcx.ccx) {
583 if duplicates.insert(trait_info.def_id) {
584 try!(self.assemble_extension_candidates_for_trait(trait_info.def_id));
590 fn assemble_extension_candidates_for_trait(&mut self,
592 -> Result<(), MethodError<'tcx>>
594 debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})",
597 // Check whether `trait_def_id` defines a method with suitable name:
599 self.tcx().trait_items(trait_def_id);
602 .find(|item| item.name() == self.item_name);
603 let item = match maybe_item {
605 None => { return Ok(()); }
608 // Check whether `trait_def_id` defines a method with suitable name:
609 if !self.has_applicable_self(item) {
610 debug!("method has inapplicable self");
611 self.record_static_candidate(TraitSource(trait_def_id));
615 self.assemble_extension_candidates_for_trait_impls(trait_def_id, item.clone());
617 try!(self.assemble_closure_candidates(trait_def_id, item.clone()));
619 self.assemble_projection_candidates(trait_def_id, item.clone());
621 self.assemble_where_clause_candidates(trait_def_id, item.clone());
626 fn assemble_extension_candidates_for_trait_impls(&mut self,
628 item: ty::ImplOrTraitItem<'tcx>)
630 let trait_def = self.tcx().lookup_trait_def(trait_def_id);
632 // FIXME(arielb1): can we use for_each_relevant_impl here?
633 trait_def.for_each_impl(self.tcx(), |impl_def_id| {
634 debug!("assemble_extension_candidates_for_trait_impl: trait_def_id={:?} \
639 if !self.impl_can_possibly_match(impl_def_id) {
643 let (_, impl_substs) = self.impl_ty_and_substs(impl_def_id);
645 debug!("impl_substs={:?}", impl_substs);
648 self.tcx().impl_trait_ref(impl_def_id)
649 .unwrap() // we know this is a trait impl
650 .subst(self.tcx(), &impl_substs);
652 debug!("impl_trait_ref={:?}", impl_trait_ref);
654 // Determine the receiver type that the method itself expects.
656 self.xform_self_ty(&item,
657 impl_trait_ref.self_ty(),
658 impl_trait_ref.substs);
660 // Normalize the receiver. We can't use normalize_associated_types_in
661 // as it will pollute the fcx's fulfillment context after this probe
663 let cause = traits::ObligationCause::misc(self.span, self.fcx.body_id);
664 let mut selcx = &mut traits::SelectionContext::new(self.fcx.infcx());
665 let traits::Normalized { value: xform_self_ty, obligations } =
666 traits::normalize(selcx, cause, &xform_self_ty);
668 debug!("xform_self_ty={:?}", xform_self_ty);
670 self.extension_candidates.push(Candidate {
671 xform_self_ty: xform_self_ty,
673 kind: ExtensionImplCandidate(impl_def_id, impl_substs, obligations)
678 fn impl_can_possibly_match(&self, impl_def_id: DefId) -> bool {
679 let simplified_steps = match self.opt_simplified_steps {
680 Some(ref simplified_steps) => simplified_steps,
681 None => { return true; }
684 let impl_type = self.tcx().lookup_item_type(impl_def_id);
685 let impl_simplified_type =
686 match ty::fast_reject::simplify_type(self.tcx(), impl_type.ty, false) {
687 Some(simplified_type) => simplified_type,
688 None => { return true; }
691 simplified_steps.contains(&impl_simplified_type)
694 fn assemble_closure_candidates(&mut self,
696 item: ty::ImplOrTraitItem<'tcx>)
697 -> Result<(), MethodError<'tcx>>
699 // Check if this is one of the Fn,FnMut,FnOnce traits.
700 let tcx = self.tcx();
701 let kind = if Some(trait_def_id) == tcx.lang_items.fn_trait() {
703 } else if Some(trait_def_id) == tcx.lang_items.fn_mut_trait() {
705 } else if Some(trait_def_id) == tcx.lang_items.fn_once_trait() {
706 ty::FnOnceClosureKind
711 // Check if there is an unboxed-closure self-type in the list of receivers.
712 // If so, add "synthetic impls".
713 let steps = self.steps.clone();
714 for step in steps.iter() {
715 let closure_def_id = match step.self_ty.sty {
716 ty::TyClosure(a, _) => a,
720 let closure_kinds = &self.fcx.inh.tables.borrow().closure_kinds;
721 let closure_kind = match closure_kinds.get(&closure_def_id) {
724 return Err(MethodError::ClosureAmbiguity(trait_def_id));
728 // this closure doesn't implement the right kind of `Fn` trait
729 if !closure_kind.extends(kind) {
733 // create some substitutions for the argument/return type;
734 // for the purposes of our method lookup, we only take
735 // receiver type into account, so we can just substitute
736 // fresh types here to use during substitution and subtyping.
737 let trait_def = self.tcx().lookup_trait_def(trait_def_id);
738 let substs = self.infcx().fresh_substs_for_trait(self.span,
742 let xform_self_ty = self.xform_self_ty(&item,
745 self.inherent_candidates.push(Candidate {
746 xform_self_ty: xform_self_ty,
755 fn assemble_projection_candidates(&mut self,
757 item: ty::ImplOrTraitItem<'tcx>)
759 debug!("assemble_projection_candidates(\
765 for step in self.steps.iter() {
766 debug!("assemble_projection_candidates: step={:?}",
769 let projection_trait_ref = match step.self_ty.sty {
770 ty::TyProjection(ref data) => &data.trait_ref,
774 debug!("assemble_projection_candidates: projection_trait_ref={:?}",
775 projection_trait_ref);
777 let trait_predicates = self.tcx().lookup_predicates(projection_trait_ref.def_id);
778 let bounds = trait_predicates.instantiate(self.tcx(), projection_trait_ref.substs);
779 let predicates = bounds.predicates.into_vec();
780 debug!("assemble_projection_candidates: predicates={:?}",
783 traits::elaborate_predicates(self.tcx(), predicates)
784 .filter_map(|p| p.to_opt_poly_trait_ref())
785 .filter(|b| b.def_id() == trait_def_id)
787 let bound = self.erase_late_bound_regions(&poly_bound);
789 debug!("assemble_projection_candidates: projection_trait_ref={:?} bound={:?}",
790 projection_trait_ref,
793 if self.infcx().can_equate(&step.self_ty, &bound.self_ty()).is_ok() {
794 let xform_self_ty = self.xform_self_ty(&item,
798 debug!("assemble_projection_candidates: bound={:?} xform_self_ty={:?}",
802 self.extension_candidates.push(Candidate {
803 xform_self_ty: xform_self_ty,
812 fn assemble_where_clause_candidates(&mut self,
814 item: ty::ImplOrTraitItem<'tcx>)
816 debug!("assemble_where_clause_candidates(trait_def_id={:?})",
819 let caller_predicates = self.fcx.inh.infcx.parameter_environment.caller_bounds.clone();
820 for poly_bound in traits::elaborate_predicates(self.tcx(), caller_predicates)
821 .filter_map(|p| p.to_opt_poly_trait_ref())
822 .filter(|b| b.def_id() == trait_def_id)
824 let bound = self.erase_late_bound_regions(&poly_bound);
825 let xform_self_ty = self.xform_self_ty(&item,
829 debug!("assemble_where_clause_candidates: bound={:?} xform_self_ty={:?}",
833 self.extension_candidates.push(Candidate {
834 xform_self_ty: xform_self_ty,
836 kind: WhereClauseCandidate(poly_bound)
841 ///////////////////////////////////////////////////////////////////////////
844 fn pick(mut self) -> PickResult<'tcx> {
845 match self.pick_core() {
850 let static_candidates = mem::replace(&mut self.static_candidates, vec![]);
851 let unsatisfied_predicates = mem::replace(&mut self.unsatisfied_predicates, vec![]);
853 // things failed, so lets look at all traits, for diagnostic purposes now:
856 let span = self.span;
857 let tcx = self.tcx();
859 try!(self.assemble_extension_candidates_for_all_traits());
861 let out_of_scope_traits = match self.pick_core() {
862 Some(Ok(p)) => vec![p.item.container().id()],
863 Some(Err(MethodError::Ambiguity(v))) => v.into_iter().map(|source| {
865 TraitSource(id) => id,
866 ImplSource(impl_id) => {
867 match tcx.trait_id_of_impl(impl_id) {
870 tcx.sess.span_bug(span,
871 "found inherent method when looking at traits")
876 Some(Err(MethodError::NoMatch(NoMatchData { out_of_scope_traits: others, .. }))) => {
877 assert!(others.is_empty());
880 Some(Err(MethodError::ClosureAmbiguity(..))) => {
881 // this error only occurs when assembling candidates
882 tcx.sess.span_bug(span, "encountered ClosureAmbiguity from pick_core");
887 Err(MethodError::NoMatch(NoMatchData::new(static_candidates, unsatisfied_predicates,
888 out_of_scope_traits, self.mode)))
891 fn pick_core(&mut self) -> Option<PickResult<'tcx>> {
892 let steps = self.steps.clone();
894 // find the first step that works
895 steps.iter().filter_map(|step| self.pick_step(step)).next()
898 fn pick_step(&mut self, step: &CandidateStep<'tcx>) -> Option<PickResult<'tcx>> {
899 debug!("pick_step: step={:?}", step);
901 if step.self_ty.references_error() {
905 match self.pick_by_value_method(step) {
906 Some(result) => return Some(result),
910 self.pick_autorefd_method(step)
913 fn pick_by_value_method(&mut self,
914 step: &CandidateStep<'tcx>)
915 -> Option<PickResult<'tcx>>
918 * For each type `T` in the step list, this attempts to find a
919 * method where the (transformed) self type is exactly `T`. We
920 * do however do one transformation on the adjustment: if we
921 * are passing a region pointer in, we will potentially
922 * *reborrow* it to a shorter lifetime. This allows us to
923 * transparently pass `&mut` pointers, in particular, without
924 * consuming them for their entire lifetime.
931 self.pick_method(step.self_ty).map(|r| r.map(|mut pick| {
932 pick.autoderefs = step.autoderefs;
934 // Insert a `&*` or `&mut *` if this is a reference type:
935 if let ty::TyRef(_, mt) = step.self_ty.sty {
936 pick.autoderefs += 1;
937 pick.autoref = Some(mt.mutbl);
944 fn pick_autorefd_method(&mut self,
945 step: &CandidateStep<'tcx>)
946 -> Option<PickResult<'tcx>>
948 let tcx = self.tcx();
950 // In general, during probing we erase regions. See
951 // `impl_self_ty()` for an explanation.
952 let region = tcx.mk_region(ty::ReStatic);
954 // Search through mutabilities in order to find one where pick works:
955 [hir::MutImmutable, hir::MutMutable].iter().filter_map(|&m| {
956 let autoref_ty = tcx.mk_ref(region, ty::TypeAndMut {
960 self.pick_method(autoref_ty).map(|r| r.map(|mut pick| {
961 pick.autoderefs = step.autoderefs;
962 pick.autoref = Some(m);
963 pick.unsize = if step.unsize {
973 fn pick_method(&mut self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
974 debug!("pick_method(self_ty={})", self.infcx().ty_to_string(self_ty));
976 let mut possibly_unsatisfied_predicates = Vec::new();
978 debug!("searching inherent candidates");
979 match self.consider_candidates(self_ty, &self.inherent_candidates,
980 &mut possibly_unsatisfied_predicates) {
987 debug!("searching extension candidates");
988 let res = self.consider_candidates(self_ty, &self.extension_candidates,
989 &mut possibly_unsatisfied_predicates);
991 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
996 fn consider_candidates(&self,
998 probes: &[Candidate<'tcx>],
999 possibly_unsatisfied_predicates: &mut Vec<TraitRef<'tcx>>)
1000 -> Option<PickResult<'tcx>> {
1001 let mut applicable_candidates: Vec<_> =
1003 .filter(|&probe| self.consider_probe(self_ty,
1004 probe,possibly_unsatisfied_predicates))
1007 debug!("applicable_candidates: {:?}", applicable_candidates);
1009 if applicable_candidates.len() > 1 {
1010 match self.collapse_candidates_to_trait_pick(&applicable_candidates[..]) {
1011 Some(pick) => { return Some(Ok(pick)); }
1016 if applicable_candidates.len() > 1 {
1017 let sources = probes.iter().map(|p| p.to_source()).collect();
1018 return Some(Err(MethodError::Ambiguity(sources)));
1021 applicable_candidates.pop().map(|probe| {
1022 Ok(probe.to_unadjusted_pick())
1026 fn consider_probe(&self, self_ty: Ty<'tcx>, probe: &Candidate<'tcx>,
1027 possibly_unsatisfied_predicates: &mut Vec<TraitRef<'tcx>>) -> bool {
1028 debug!("consider_probe: self_ty={:?} probe={:?}",
1032 self.infcx().probe(|_| {
1033 // First check that the self type can be related.
1034 match self.make_sub_ty(self_ty, probe.xform_self_ty) {
1037 debug!("--> cannot relate self-types");
1042 // If so, impls may carry other conditions (e.g., where
1043 // clauses) that must be considered. Make sure that those
1044 // match as well (or at least may match, sometimes we
1045 // don't have enough information to fully evaluate).
1046 let (impl_def_id, substs, ref_obligations) = match probe.kind {
1047 InherentImplCandidate(ref substs, ref ref_obligations) => {
1048 (probe.item.container().id(), substs, ref_obligations)
1051 ExtensionImplCandidate(impl_def_id, ref substs, ref ref_obligations) => {
1052 (impl_def_id, substs, ref_obligations)
1055 ObjectCandidate(..) |
1057 WhereClauseCandidate(..) => {
1058 // These have no additional conditions to check.
1063 let selcx = &mut traits::SelectionContext::new(self.infcx());
1064 let cause = traits::ObligationCause::misc(self.span, self.fcx.body_id);
1066 // Check whether the impl imposes obligations we have to worry about.
1067 let impl_bounds = self.tcx().lookup_predicates(impl_def_id);
1068 let impl_bounds = impl_bounds.instantiate(self.tcx(), substs);
1069 let traits::Normalized { value: impl_bounds,
1070 obligations: norm_obligations } =
1071 traits::normalize(selcx, cause.clone(), &impl_bounds);
1073 // Convert the bounds into obligations.
1075 traits::predicates_for_generics(cause.clone(),
1077 debug!("impl_obligations={:?}", obligations);
1079 // Evaluate those obligations to see if they might possibly hold.
1080 let mut all_true = true;
1081 for o in obligations.iter()
1082 .chain(norm_obligations.iter())
1083 .chain(ref_obligations.iter()) {
1084 if !selcx.evaluate_obligation(o) {
1086 if let &ty::Predicate::Trait(ref pred) = &o.predicate {
1087 possibly_unsatisfied_predicates.push(pred.0.trait_ref);
1095 /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1096 /// same trait, but we don't know which impl to use. In this case, since in all cases the
1097 /// external interface of the method can be determined from the trait, it's ok not to decide.
1098 /// We can basically just collapse all of the probes for various impls into one where-clause
1099 /// probe. This will result in a pending obligation so when more type-info is available we can
1100 /// make the final decision.
1102 /// Example (`src/test/run-pass/method-two-trait-defer-resolution-1.rs`):
1105 /// trait Foo { ... }
1106 /// impl Foo for Vec<int> { ... }
1107 /// impl Foo for Vec<usize> { ... }
1110 /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1111 /// use, so it's ok to just commit to "using the method from the trait Foo".
1112 fn collapse_candidates_to_trait_pick(&self,
1113 probes: &[&Candidate<'tcx>])
1114 -> Option<Pick<'tcx>> {
1115 // Do all probes correspond to the same trait?
1116 let container = probes[0].item.container();
1118 ty::TraitContainer(_) => {}
1119 ty::ImplContainer(_) => return None
1121 if probes[1..].iter().any(|p| p.item.container() != container) {
1125 // If so, just use this trait and call it a day.
1127 item: probes[0].item.clone(),
1135 ///////////////////////////////////////////////////////////////////////////
1138 fn make_sub_ty(&self, sub: Ty<'tcx>, sup: Ty<'tcx>) -> infer::UnitResult<'tcx> {
1139 self.infcx().sub_types(false, infer::Misc(DUMMY_SP), sub, sup)
1142 fn has_applicable_self(&self, item: &ty::ImplOrTraitItem) -> bool {
1143 // "fast track" -- check for usage of sugar
1145 ty::ImplOrTraitItem::MethodTraitItem(ref method) =>
1146 match method.explicit_self {
1147 ty::StaticExplicitSelfCategory => self.mode == Mode::Path,
1148 ty::ByValueExplicitSelfCategory |
1149 ty::ByReferenceExplicitSelfCategory(..) |
1150 ty::ByBoxExplicitSelfCategory => true,
1152 ty::ImplOrTraitItem::ConstTraitItem(..) => self.mode == Mode::Path,
1155 // FIXME -- check for types that deref to `Self`,
1156 // like `Rc<Self>` and so on.
1158 // Note also that the current code will break if this type
1159 // includes any of the type parameters defined on the method
1160 // -- but this could be overcome.
1163 fn record_static_candidate(&mut self, source: CandidateSource) {
1164 self.static_candidates.push(source);
1167 fn xform_self_ty(&self,
1168 item: &ty::ImplOrTraitItem<'tcx>,
1170 substs: &subst::Substs<'tcx>)
1173 match item.as_opt_method() {
1174 Some(ref method) => self.xform_method_self_ty(method, impl_ty,
1180 fn xform_method_self_ty(&self,
1181 method: &Rc<ty::Method<'tcx>>,
1183 substs: &subst::Substs<'tcx>)
1186 debug!("xform_self_ty(impl_ty={:?}, self_ty={:?}, substs={:?})",
1188 method.fty.sig.0.inputs.get(0),
1191 assert!(!substs.has_escaping_regions());
1193 // It is possible for type parameters or early-bound lifetimes
1194 // to appear in the signature of `self`. The substitutions we
1195 // are given do not include type/lifetime parameters for the
1196 // method yet. So create fresh variables here for those too,
1197 // if there are any.
1198 assert_eq!(substs.types.len(subst::FnSpace), 0);
1199 assert_eq!(substs.regions().len(subst::FnSpace), 0);
1201 if self.mode == Mode::Path {
1205 let mut placeholder;
1206 let mut substs = substs;
1208 !method.generics.types.is_empty_in(subst::FnSpace) ||
1209 !method.generics.regions.is_empty_in(subst::FnSpace)
1211 // In general, during probe we erase regions. See
1212 // `impl_self_ty()` for an explanation.
1213 let method_regions =
1214 method.generics.regions.get_slice(subst::FnSpace)
1216 .map(|_| ty::ReStatic)
1219 placeholder = (*substs).clone().with_method(Vec::new(), method_regions);
1221 self.infcx().type_vars_for_defs(
1225 method.generics.types.get_slice(subst::FnSpace));
1227 substs = &placeholder;
1230 // Erase any late-bound regions from the method and substitute
1231 // in the values from the substitution.
1232 let xform_self_ty = method.fty.sig.input(0);
1233 let xform_self_ty = self.erase_late_bound_regions(&xform_self_ty);
1234 let xform_self_ty = xform_self_ty.subst(self.tcx(), substs);
1239 /// Get the type of an impl and generate substitutions with placeholders.
1240 fn impl_ty_and_substs(&self,
1242 -> (Ty<'tcx>, subst::Substs<'tcx>)
1244 let impl_pty = self.tcx().lookup_item_type(impl_def_id);
1247 impl_pty.generics.types.map(
1248 |_| self.infcx().next_ty_var());
1250 let region_placeholders =
1251 impl_pty.generics.regions.map(
1252 |_| ty::ReStatic); // see erase_late_bound_regions() for an expl of why 'static
1254 let substs = subst::Substs::new(type_vars, region_placeholders);
1255 (impl_pty.ty, substs)
1258 /// Replace late-bound-regions bound by `value` with `'static` using
1259 /// `ty::erase_late_bound_regions`.
1261 /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1262 /// method matching. It is reasonable during the probe phase because we don't consider region
1263 /// relationships at all. Therefore, we can just replace all the region variables with 'static
1264 /// rather than creating fresh region variables. This is nice for two reasons:
1266 /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1267 /// particular method call, it winds up creating fewer types overall, which helps for memory
1268 /// usage. (Admittedly, this is a rather small effect, though measureable.)
1270 /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1271 /// late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1272 /// regions with actual region variables as is proper, we'd have to ensure that the same
1273 /// region got replaced with the same variable, which requires a bit more coordination
1274 /// and/or tracking the substitution and
1276 fn erase_late_bound_regions<T>(&self, value: &ty::Binder<T>) -> T
1277 where T : TypeFoldable<'tcx>
1279 self.tcx().erase_late_bound_regions(value)
1283 fn impl_item<'tcx>(tcx: &ty::ctxt<'tcx>,
1285 item_name: ast::Name)
1286 -> Option<ty::ImplOrTraitItem<'tcx>>
1288 let impl_items = tcx.impl_items.borrow();
1289 let impl_items = impl_items.get(&impl_def_id).unwrap();
1292 .map(|&did| tcx.impl_or_trait_item(did.def_id()))
1293 .find(|item| item.name() == item_name)
1296 /// Find item with name `item_name` defined in `trait_def_id`
1297 /// and return it, or `None`, if no such item.
1298 fn trait_item<'tcx>(tcx: &ty::ctxt<'tcx>,
1299 trait_def_id: DefId,
1300 item_name: ast::Name)
1301 -> Option<ty::ImplOrTraitItem<'tcx>>
1303 let trait_items = tcx.trait_items(trait_def_id);
1304 debug!("trait_method; items: {:?}", trait_items);
1306 .find(|item| item.name() == item_name)
1310 impl<'tcx> Candidate<'tcx> {
1311 fn to_unadjusted_pick(&self) -> Pick<'tcx> {
1313 item: self.item.clone(),
1314 kind: match self.kind {
1315 InherentImplCandidate(_, _) => InherentImplPick,
1316 ExtensionImplCandidate(def_id, _, _) => {
1317 ExtensionImplPick(def_id)
1319 ObjectCandidate => ObjectPick,
1320 TraitCandidate => TraitPick,
1321 WhereClauseCandidate(ref trait_ref) => {
1322 // Only trait derived from where-clauses should
1323 // appear here, so they should not contain any
1324 // inference variables or other artifacts. This
1325 // means they are safe to put into the
1326 // `WhereClausePick`.
1327 assert!(!trait_ref.substs().types.needs_infer());
1329 WhereClausePick(trait_ref.clone())
1338 fn to_source(&self) -> CandidateSource {
1340 InherentImplCandidate(_, _) => {
1341 ImplSource(self.item.container().id())
1343 ExtensionImplCandidate(def_id, _, _) => ImplSource(def_id),
1346 WhereClauseCandidate(_) => TraitSource(self.item.container().id()),