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;
22 use rustc::session::config::nightly_options;
23 use rustc::ty::subst::{Subst, Substs};
24 use rustc::traits::{self, ObligationCause};
25 use rustc::ty::{self, Ty, ToPolyTraitRef, ToPredicate, TraitRef, TypeFoldable};
26 use rustc::ty::GenericParamDefKind;
27 use rustc::infer::type_variable::TypeVariableOrigin;
28 use rustc::util::nodemap::FxHashSet;
29 use rustc::infer::{self, InferOk};
30 use rustc::middle::stability;
32 use syntax::util::lev_distance::{lev_distance, find_best_match_for_name};
33 use syntax_pos::{Span, symbol::Symbol};
40 use self::CandidateKind::*;
41 pub use self::PickKind::*;
43 /// Boolean flag used to indicate if this search is for a suggestion
44 /// or not. If true, we can allow ambiguity and so forth.
45 #[derive(Clone, Copy)]
46 pub struct IsSuggestion(pub bool);
48 struct ProbeContext<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
49 fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
52 method_name: Option<ast::Ident>,
53 return_type: Option<Ty<'tcx>>,
54 steps: Rc<Vec<CandidateStep<'tcx>>>,
55 inherent_candidates: Vec<Candidate<'tcx>>,
56 extension_candidates: Vec<Candidate<'tcx>>,
57 impl_dups: FxHashSet<DefId>,
59 /// Collects near misses when the candidate functions are missing a `self` keyword and is only
60 /// used for error reporting
61 static_candidates: Vec<CandidateSource>,
63 /// When probing for names, include names that are close to the
64 /// requested name (by Levensthein distance)
65 allow_similar_names: bool,
67 /// Some(candidate) if there is a private candidate
68 private_candidate: Option<Def>,
70 /// Collects near misses when trait bounds for type parameters are unsatisfied and is only used
71 /// for error reporting
72 unsatisfied_predicates: Vec<TraitRef<'tcx>>,
74 is_suggestion: IsSuggestion,
77 impl<'a, 'gcx, 'tcx> Deref for ProbeContext<'a, 'gcx, 'tcx> {
78 type Target = FnCtxt<'a, 'gcx, 'tcx>;
79 fn deref(&self) -> &Self::Target {
85 struct CandidateStep<'tcx> {
88 // true if the type results from a dereference of a raw pointer.
89 // when assembling candidates, we include these steps, but not when
90 // picking methods. This so that if we have `foo: *const Foo` and `Foo` has methods
91 // `fn by_raw_ptr(self: *const Self)` and `fn by_ref(&self)`, then
92 // `foo.by_raw_ptr()` will work and `foo.by_ref()` won't.
93 from_unsafe_deref: bool,
98 struct Candidate<'tcx> {
99 xform_self_ty: Ty<'tcx>,
100 xform_ret_ty: Option<Ty<'tcx>>,
101 item: ty::AssociatedItem,
102 kind: CandidateKind<'tcx>,
103 import_id: Option<ast::NodeId>,
107 enum CandidateKind<'tcx> {
108 InherentImplCandidate(&'tcx Substs<'tcx>,
109 // Normalize obligations
110 Vec<traits::PredicateObligation<'tcx>>),
112 TraitCandidate(ty::TraitRef<'tcx>),
113 WhereClauseCandidate(// Trait
114 ty::PolyTraitRef<'tcx>),
117 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
124 #[derive(Debug, PartialEq, Clone)]
125 pub struct Pick<'tcx> {
126 pub item: ty::AssociatedItem,
127 pub kind: PickKind<'tcx>,
128 pub import_id: Option<ast::NodeId>,
130 // Indicates that the source expression should be autoderef'd N times
132 // A = expr | *expr | **expr | ...
133 pub autoderefs: usize,
135 // Indicates that an autoref is applied after the optional autoderefs
137 // B = A | &A | &mut A
138 pub autoref: Option<hir::Mutability>,
140 // Indicates that the source expression should be "unsized" to a
141 // target type. This should probably eventually go away in favor
142 // of just coercing method receivers.
145 pub unsize: Option<Ty<'tcx>>,
148 #[derive(Clone, Debug, PartialEq, Eq)]
149 pub enum PickKind<'tcx> {
153 WhereClausePick(// Trait
154 ty::PolyTraitRef<'tcx>),
157 pub type PickResult<'tcx> = Result<Pick<'tcx>, MethodError<'tcx>>;
159 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
161 // An expression of the form `receiver.method_name(...)`.
162 // Autoderefs are performed on `receiver`, lookup is done based on the
163 // `self` argument of the method, and static methods aren't considered.
165 // An expression of the form `Type::item` or `<T>::item`.
166 // No autoderefs are performed, lookup is done based on the type each
167 // implementation is for, and static methods are included.
171 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
172 pub enum ProbeScope {
173 // Assemble candidates coming only from traits in scope.
176 // Assemble candidates coming from all traits.
180 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
181 /// This is used to offer suggestions to users. It returns methods
182 /// that could have been called which have the desired return
183 /// type. Some effort is made to rule out methods that, if called,
184 /// would result in an error (basically, the same criteria we
185 /// would use to decide if a method is a plausible fit for
186 /// ambiguity purposes).
187 pub fn probe_for_return_type(&self,
190 return_type: Ty<'tcx>,
192 scope_expr_id: ast::NodeId)
193 -> Vec<ty::AssociatedItem> {
194 debug!("probe(self_ty={:?}, return_type={}, scope_expr_id={})",
199 self.probe_op(span, mode, None, Some(return_type), IsSuggestion(true),
200 self_ty, scope_expr_id, ProbeScope::AllTraits,
201 |probe_cx| Ok(probe_cx.candidate_method_names()))
205 .flat_map(|&method_name| {
207 span, mode, Some(method_name), Some(return_type),
208 IsSuggestion(true), self_ty, scope_expr_id,
209 ProbeScope::AllTraits, |probe_cx| probe_cx.pick()
210 ).ok().map(|pick| pick.item)
215 pub fn probe_for_name(&self,
218 item_name: ast::Ident,
219 is_suggestion: IsSuggestion,
221 scope_expr_id: ast::NodeId,
223 -> PickResult<'tcx> {
224 debug!("probe(self_ty={:?}, item_name={}, scope_expr_id={})",
236 |probe_cx| probe_cx.pick())
239 fn probe_op<OP,R>(&'a self,
242 method_name: Option<ast::Ident>,
243 return_type: Option<Ty<'tcx>>,
244 is_suggestion: IsSuggestion,
246 scope_expr_id: ast::NodeId,
249 -> Result<R, MethodError<'tcx>>
250 where OP: FnOnce(ProbeContext<'a, 'gcx, 'tcx>) -> Result<R, MethodError<'tcx>>
252 // FIXME(#18741) -- right now, creating the steps involves evaluating the
253 // `*` operator, which registers obligations that then escape into
254 // the global fulfillment context and thus has global
255 // side-effects. This is a bit of a pain to refactor. So just let
256 // it ride, although it's really not great, and in fact could I
257 // think cause spurious errors. Really though this part should
258 // take place in the `self.probe` below.
259 let steps = if mode == Mode::MethodCall {
260 match self.create_steps(span, scope_expr_id, self_ty, is_suggestion) {
261 Some(steps) => steps,
263 return Err(MethodError::NoMatch(NoMatchData::new(Vec::new(),
274 from_unsafe_deref: false,
279 debug!("ProbeContext: steps for self_ty={:?} are {:?}",
283 // this creates one big transaction so that all type variables etc
284 // that we create during the probe process are removed later
286 let mut probe_cx = ProbeContext::new(
287 self, span, mode, method_name, return_type, Rc::new(steps), is_suggestion,
290 probe_cx.assemble_inherent_candidates();
292 ProbeScope::TraitsInScope =>
293 probe_cx.assemble_extension_candidates_for_traits_in_scope(scope_expr_id)?,
294 ProbeScope::AllTraits =>
295 probe_cx.assemble_extension_candidates_for_all_traits()?,
301 fn create_steps(&self,
303 scope_expr_id: ast::NodeId,
305 is_suggestion: IsSuggestion)
306 -> Option<Vec<CandidateStep<'tcx>>> {
307 // FIXME: we don't need to create the entire steps in one pass
309 let mut autoderef = self.autoderef(span, self_ty).include_raw_pointers();
310 let mut reached_raw_pointer = false;
311 let mut steps: Vec<_> = autoderef.by_ref()
313 let step = CandidateStep {
316 from_unsafe_deref: reached_raw_pointer,
319 if let ty::RawPtr(_) = ty.sty {
320 // all the subsequent steps will be from_unsafe_deref
321 reached_raw_pointer = true;
327 let final_ty = autoderef.maybe_ambiguous_final_ty();
329 ty::Infer(ty::TyVar(_)) => {
330 // Ended in an inference variable. If we are doing
331 // a real method lookup, this is a hard error because it's
332 // possible that there will be multiple applicable methods.
333 if !is_suggestion.0 {
334 if reached_raw_pointer
335 && !self.tcx.features().arbitrary_self_types {
336 // this case used to be allowed by the compiler,
337 // so we do a future-compat lint here for the 2015 edition
338 // (see https://github.com/rust-lang/rust/issues/46906)
339 if self.tcx.sess.rust_2018() {
340 span_err!(self.tcx.sess, span, E0699,
341 "the type of this value must be known \
342 to call a method on a raw pointer on it");
345 lint::builtin::TYVAR_BEHIND_RAW_POINTER,
348 "type annotations needed");
351 let t = self.structurally_resolved_type(span, final_ty);
352 assert_eq!(t, self.tcx.types.err);
356 // If we're just looking for suggestions,
357 // though, ambiguity is no big thing, we can
361 ty::Array(elem_ty, _) => {
362 let dereferences = steps.len() - 1;
364 steps.push(CandidateStep {
365 self_ty: self.tcx.mk_slice(elem_ty),
366 autoderefs: dereferences,
367 // this could be from an unsafe deref if we had
368 // a *mut/const [T; N]
369 from_unsafe_deref: reached_raw_pointer,
373 ty::Error => return None,
377 debug!("create_steps: steps={:?}", steps);
383 impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
384 fn new(fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
387 method_name: Option<ast::Ident>,
388 return_type: Option<Ty<'tcx>>,
389 steps: Rc<Vec<CandidateStep<'tcx>>>,
390 is_suggestion: IsSuggestion)
391 -> ProbeContext<'a, 'gcx, 'tcx> {
398 inherent_candidates: Vec::new(),
399 extension_candidates: Vec::new(),
400 impl_dups: FxHashSet::default(),
402 static_candidates: Vec::new(),
403 allow_similar_names: false,
404 private_candidate: None,
405 unsatisfied_predicates: Vec::new(),
410 fn reset(&mut self) {
411 self.inherent_candidates.clear();
412 self.extension_candidates.clear();
413 self.impl_dups.clear();
414 self.static_candidates.clear();
415 self.private_candidate = None;
418 ///////////////////////////////////////////////////////////////////////////
419 // CANDIDATE ASSEMBLY
421 fn push_candidate(&mut self,
422 candidate: Candidate<'tcx>,
425 let is_accessible = if let Some(name) = self.method_name {
426 let item = candidate.item;
427 let def_scope = self.tcx.adjust_ident(name, item.container.id(), self.body_id).1;
428 item.vis.is_accessible_from(def_scope, self.tcx)
434 self.inherent_candidates.push(candidate);
436 self.extension_candidates.push(candidate);
438 } else if self.private_candidate.is_none() {
439 self.private_candidate = Some(candidate.item.def());
443 fn assemble_inherent_candidates(&mut self) {
444 let steps = self.steps.clone();
445 for step in steps.iter() {
446 self.assemble_probe(step.self_ty);
450 fn assemble_probe(&mut self, self_ty: Ty<'tcx>) {
451 debug!("assemble_probe: self_ty={:?}", self_ty);
452 let lang_items = self.tcx.lang_items();
455 ty::Dynamic(ref data, ..) => {
456 let p = data.principal();
457 self.assemble_inherent_candidates_from_object(self_ty, p);
458 self.assemble_inherent_impl_candidates_for_type(p.def_id());
461 self.assemble_inherent_impl_candidates_for_type(def.did);
463 ty::Foreign(did) => {
464 self.assemble_inherent_impl_candidates_for_type(did);
467 self.assemble_inherent_candidates_from_param(self_ty, p);
470 let lang_def_id = lang_items.char_impl();
471 self.assemble_inherent_impl_for_primitive(lang_def_id);
474 let lang_def_id = lang_items.str_impl();
475 self.assemble_inherent_impl_for_primitive(lang_def_id);
477 let lang_def_id = lang_items.str_alloc_impl();
478 self.assemble_inherent_impl_for_primitive(lang_def_id);
481 let lang_def_id = lang_items.slice_impl();
482 self.assemble_inherent_impl_for_primitive(lang_def_id);
484 let lang_def_id = lang_items.slice_u8_impl();
485 self.assemble_inherent_impl_for_primitive(lang_def_id);
487 let lang_def_id = lang_items.slice_alloc_impl();
488 self.assemble_inherent_impl_for_primitive(lang_def_id);
490 let lang_def_id = lang_items.slice_u8_alloc_impl();
491 self.assemble_inherent_impl_for_primitive(lang_def_id);
493 ty::RawPtr(ty::TypeAndMut { ty: _, mutbl: hir::MutImmutable }) => {
494 let lang_def_id = lang_items.const_ptr_impl();
495 self.assemble_inherent_impl_for_primitive(lang_def_id);
497 ty::RawPtr(ty::TypeAndMut { ty: _, mutbl: hir::MutMutable }) => {
498 let lang_def_id = lang_items.mut_ptr_impl();
499 self.assemble_inherent_impl_for_primitive(lang_def_id);
501 ty::Int(ast::IntTy::I8) => {
502 let lang_def_id = lang_items.i8_impl();
503 self.assemble_inherent_impl_for_primitive(lang_def_id);
505 ty::Int(ast::IntTy::I16) => {
506 let lang_def_id = lang_items.i16_impl();
507 self.assemble_inherent_impl_for_primitive(lang_def_id);
509 ty::Int(ast::IntTy::I32) => {
510 let lang_def_id = lang_items.i32_impl();
511 self.assemble_inherent_impl_for_primitive(lang_def_id);
513 ty::Int(ast::IntTy::I64) => {
514 let lang_def_id = lang_items.i64_impl();
515 self.assemble_inherent_impl_for_primitive(lang_def_id);
517 ty::Int(ast::IntTy::I128) => {
518 let lang_def_id = lang_items.i128_impl();
519 self.assemble_inherent_impl_for_primitive(lang_def_id);
521 ty::Int(ast::IntTy::Isize) => {
522 let lang_def_id = lang_items.isize_impl();
523 self.assemble_inherent_impl_for_primitive(lang_def_id);
525 ty::Uint(ast::UintTy::U8) => {
526 let lang_def_id = lang_items.u8_impl();
527 self.assemble_inherent_impl_for_primitive(lang_def_id);
529 ty::Uint(ast::UintTy::U16) => {
530 let lang_def_id = lang_items.u16_impl();
531 self.assemble_inherent_impl_for_primitive(lang_def_id);
533 ty::Uint(ast::UintTy::U32) => {
534 let lang_def_id = lang_items.u32_impl();
535 self.assemble_inherent_impl_for_primitive(lang_def_id);
537 ty::Uint(ast::UintTy::U64) => {
538 let lang_def_id = lang_items.u64_impl();
539 self.assemble_inherent_impl_for_primitive(lang_def_id);
541 ty::Uint(ast::UintTy::U128) => {
542 let lang_def_id = lang_items.u128_impl();
543 self.assemble_inherent_impl_for_primitive(lang_def_id);
545 ty::Uint(ast::UintTy::Usize) => {
546 let lang_def_id = lang_items.usize_impl();
547 self.assemble_inherent_impl_for_primitive(lang_def_id);
549 ty::Float(ast::FloatTy::F32) => {
550 let lang_def_id = lang_items.f32_impl();
551 self.assemble_inherent_impl_for_primitive(lang_def_id);
553 let lang_def_id = lang_items.f32_runtime_impl();
554 self.assemble_inherent_impl_for_primitive(lang_def_id);
556 ty::Float(ast::FloatTy::F64) => {
557 let lang_def_id = lang_items.f64_impl();
558 self.assemble_inherent_impl_for_primitive(lang_def_id);
560 let lang_def_id = lang_items.f64_runtime_impl();
561 self.assemble_inherent_impl_for_primitive(lang_def_id);
567 fn assemble_inherent_impl_for_primitive(&mut self, lang_def_id: Option<DefId>) {
568 if let Some(impl_def_id) = lang_def_id {
569 self.assemble_inherent_impl_probe(impl_def_id);
573 fn assemble_inherent_impl_candidates_for_type(&mut self, def_id: DefId) {
574 let impl_def_ids = self.tcx.at(self.span).inherent_impls(def_id);
575 for &impl_def_id in impl_def_ids.iter() {
576 self.assemble_inherent_impl_probe(impl_def_id);
580 fn assemble_inherent_impl_probe(&mut self, impl_def_id: DefId) {
581 if !self.impl_dups.insert(impl_def_id) {
582 return; // already visited
585 debug!("assemble_inherent_impl_probe {:?}", impl_def_id);
587 for item in self.impl_or_trait_item(impl_def_id) {
588 if !self.has_applicable_self(&item) {
589 // No receiver declared. Not a candidate.
590 self.record_static_candidate(ImplSource(impl_def_id));
594 let (impl_ty, impl_substs) = self.impl_ty_and_substs(impl_def_id);
595 let impl_ty = impl_ty.subst(self.tcx, impl_substs);
597 // Determine the receiver type that the method itself expects.
598 let xform_tys = self.xform_self_ty(&item, impl_ty, impl_substs);
600 // We can't use normalize_associated_types_in as it will pollute the
601 // fcx's fulfillment context after this probe is over.
602 let cause = traits::ObligationCause::misc(self.span, self.body_id);
603 let selcx = &mut traits::SelectionContext::new(self.fcx);
604 let traits::Normalized { value: (xform_self_ty, xform_ret_ty), obligations } =
605 traits::normalize(selcx, self.param_env, cause, &xform_tys);
606 debug!("assemble_inherent_impl_probe: xform_self_ty = {:?}/{:?}",
607 xform_self_ty, xform_ret_ty);
609 self.push_candidate(Candidate {
610 xform_self_ty, xform_ret_ty, item,
611 kind: InherentImplCandidate(impl_substs, obligations),
617 fn assemble_inherent_candidates_from_object(&mut self,
619 principal: ty::PolyExistentialTraitRef<'tcx>) {
620 debug!("assemble_inherent_candidates_from_object(self_ty={:?})",
623 // It is illegal to invoke a method on a trait instance that
624 // refers to the `Self` type. An error will be reported by
625 // `enforce_object_limitations()` if the method refers to the
626 // `Self` type anywhere other than the receiver. Here, we use
627 // a substitution that replaces `Self` with the object type
628 // itself. Hence, a `&self` method will wind up with an
629 // argument type like `&Trait`.
630 let trait_ref = principal.with_self_ty(self.tcx, self_ty);
631 self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
632 let new_trait_ref = this.erase_late_bound_regions(&new_trait_ref);
634 let (xform_self_ty, xform_ret_ty) =
635 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
636 this.push_candidate(Candidate {
637 xform_self_ty, xform_ret_ty, item,
638 kind: ObjectCandidate,
644 fn assemble_inherent_candidates_from_param(&mut self,
646 param_ty: ty::ParamTy) {
647 // FIXME -- Do we want to commit to this behavior for param bounds?
649 let bounds = self.param_env
652 .filter_map(|predicate| {
654 ty::Predicate::Trait(ref trait_predicate) => {
655 match trait_predicate.skip_binder().trait_ref.self_ty().sty {
656 ty::Param(ref p) if *p == param_ty => {
657 Some(trait_predicate.to_poly_trait_ref())
662 ty::Predicate::Subtype(..) |
663 ty::Predicate::Projection(..) |
664 ty::Predicate::RegionOutlives(..) |
665 ty::Predicate::WellFormed(..) |
666 ty::Predicate::ObjectSafe(..) |
667 ty::Predicate::ClosureKind(..) |
668 ty::Predicate::TypeOutlives(..) |
669 ty::Predicate::ConstEvaluatable(..) => None,
673 self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
674 let trait_ref = this.erase_late_bound_regions(&poly_trait_ref);
676 let (xform_self_ty, xform_ret_ty) =
677 this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs);
679 // Because this trait derives from a where-clause, it
680 // should not contain any inference variables or other
681 // artifacts. This means it is safe to put into the
682 // `WhereClauseCandidate` and (eventually) into the
683 // `WhereClausePick`.
684 assert!(!trait_ref.substs.needs_infer());
686 this.push_candidate(Candidate {
687 xform_self_ty, xform_ret_ty, item,
688 kind: WhereClauseCandidate(poly_trait_ref),
694 // Do a search through a list of bounds, using a callback to actually
695 // create the candidates.
696 fn elaborate_bounds<F>(&mut self,
697 bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
699 where F: for<'b> FnMut(&mut ProbeContext<'b, 'gcx, 'tcx>,
700 ty::PolyTraitRef<'tcx>,
704 for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
705 debug!("elaborate_bounds(bound_trait_ref={:?})", bound_trait_ref);
706 for item in self.impl_or_trait_item(bound_trait_ref.def_id()) {
707 if !self.has_applicable_self(&item) {
708 self.record_static_candidate(TraitSource(bound_trait_ref.def_id()));
710 mk_cand(self, bound_trait_ref, item);
716 fn assemble_extension_candidates_for_traits_in_scope(&mut self,
717 expr_id: ast::NodeId)
718 -> Result<(), MethodError<'tcx>> {
719 if expr_id == ast::DUMMY_NODE_ID {
722 let mut duplicates = FxHashSet::default();
723 let expr_hir_id = self.tcx.hir.node_to_hir_id(expr_id);
724 let opt_applicable_traits = self.tcx.in_scope_traits(expr_hir_id);
725 if let Some(applicable_traits) = opt_applicable_traits {
726 for trait_candidate in applicable_traits.iter() {
727 let trait_did = trait_candidate.def_id;
728 if duplicates.insert(trait_did) {
729 let import_id = trait_candidate.import_id;
730 let result = self.assemble_extension_candidates_for_trait(import_id, trait_did);
738 fn assemble_extension_candidates_for_all_traits(&mut self) -> Result<(), MethodError<'tcx>> {
739 let mut duplicates = FxHashSet::default();
740 for trait_info in suggest::all_traits(self.tcx) {
741 if duplicates.insert(trait_info.def_id) {
742 self.assemble_extension_candidates_for_trait(None, trait_info.def_id)?;
748 pub fn matches_return_type(&self,
749 method: &ty::AssociatedItem,
750 self_ty: Option<Ty<'tcx>>,
751 expected: Ty<'tcx>) -> bool {
753 Def::Method(def_id) => {
754 let fty = self.tcx.fn_sig(def_id);
756 let substs = self.fresh_substs_for_item(self.span, method.def_id);
757 let fty = fty.subst(self.tcx, substs);
758 let (fty, _) = self.replace_bound_vars_with_fresh_vars(
764 if let Some(self_ty) = self_ty {
765 if self.at(&ObligationCause::dummy(), self.param_env)
766 .sup(fty.inputs()[0], self_ty)
772 self.can_sub(self.param_env, fty.output(), expected).is_ok()
779 fn assemble_extension_candidates_for_trait(&mut self,
780 import_id: Option<ast::NodeId>,
782 -> Result<(), MethodError<'tcx>> {
783 debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})",
785 let trait_substs = self.fresh_item_substs(trait_def_id);
786 let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
788 for item in self.impl_or_trait_item(trait_def_id) {
789 // Check whether `trait_def_id` defines a method with suitable name:
790 if !self.has_applicable_self(&item) {
791 debug!("method has inapplicable self");
792 self.record_static_candidate(TraitSource(trait_def_id));
796 let (xform_self_ty, xform_ret_ty) =
797 self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
798 self.push_candidate(Candidate {
799 xform_self_ty, xform_ret_ty, item, import_id,
800 kind: TraitCandidate(trait_ref),
806 fn candidate_method_names(&self) -> Vec<ast::Ident> {
807 let mut set = FxHashSet::default();
808 let mut names: Vec<_> = self.inherent_candidates
810 .chain(&self.extension_candidates)
811 .filter(|candidate| {
812 if let Some(return_ty) = self.return_type {
813 self.matches_return_type(&candidate.item, None, return_ty)
818 .map(|candidate| candidate.item.ident)
819 .filter(|&name| set.insert(name))
822 // sort them by the name so we have a stable result
823 names.sort_by_cached_key(|n| n.as_str());
827 ///////////////////////////////////////////////////////////////////////////
830 fn pick(mut self) -> PickResult<'tcx> {
831 assert!(self.method_name.is_some());
833 if let Some(r) = self.pick_core() {
837 let static_candidates = mem::replace(&mut self.static_candidates, vec![]);
838 let private_candidate = self.private_candidate.take();
839 let unsatisfied_predicates = mem::replace(&mut self.unsatisfied_predicates, vec![]);
841 // things failed, so lets look at all traits, for diagnostic purposes now:
844 let span = self.span;
847 self.assemble_extension_candidates_for_all_traits()?;
849 let out_of_scope_traits = match self.pick_core() {
850 Some(Ok(p)) => vec![p.item.container.id()],
851 //Some(Ok(p)) => p.iter().map(|p| p.item.container().id()).collect(),
852 Some(Err(MethodError::Ambiguity(v))) => {
856 TraitSource(id) => id,
857 ImplSource(impl_id) => {
858 match tcx.trait_id_of_impl(impl_id) {
862 "found inherent method when looking at traits")
870 Some(Err(MethodError::NoMatch(NoMatchData { out_of_scope_traits: others, .. }))) => {
871 assert!(others.is_empty());
877 if let Some(def) = private_candidate {
878 return Err(MethodError::PrivateMatch(def, out_of_scope_traits));
880 let lev_candidate = self.probe_for_lev_candidate()?;
882 Err(MethodError::NoMatch(NoMatchData::new(static_candidates,
883 unsatisfied_predicates,
889 fn pick_core(&mut self) -> Option<PickResult<'tcx>> {
890 let steps = self.steps.clone();
892 // find the first step that works
896 debug!("pick_core: step={:?}", step);
897 // skip types that are from a type error or that would require dereferencing
899 !step.self_ty.references_error() && !step.from_unsafe_deref
901 self.pick_by_value_method(step).or_else(|| {
902 self.pick_autorefd_method(step, hir::MutImmutable).or_else(|| {
903 self.pick_autorefd_method(step, hir::MutMutable)
908 fn pick_by_value_method(&mut self, step: &CandidateStep<'tcx>) -> Option<PickResult<'tcx>> {
909 //! For each type `T` in the step list, this attempts to find a
910 //! method where the (transformed) self type is exactly `T`. We
911 //! do however do one transformation on the adjustment: if we
912 //! are passing a region pointer in, we will potentially
913 //! *reborrow* it to a shorter lifetime. This allows us to
914 //! transparently pass `&mut` pointers, in particular, without
915 //! consuming them for their entire lifetime.
921 self.pick_method(step.self_ty).map(|r| {
923 pick.autoderefs = step.autoderefs;
925 // Insert a `&*` or `&mut *` if this is a reference type:
926 if let ty::Ref(_, _, mutbl) = step.self_ty.sty {
927 pick.autoderefs += 1;
928 pick.autoref = Some(mutbl);
936 fn pick_autorefd_method(&mut self, step: &CandidateStep<'tcx>, mutbl: hir::Mutability)
937 -> Option<PickResult<'tcx>> {
940 // In general, during probing we erase regions. See
941 // `impl_self_ty()` for an explanation.
942 let region = tcx.types.re_erased;
944 let autoref_ty = tcx.mk_ref(region,
946 ty: step.self_ty, mutbl
948 self.pick_method(autoref_ty).map(|r| {
950 pick.autoderefs = step.autoderefs;
951 pick.autoref = Some(mutbl);
952 pick.unsize = if step.unsize {
962 fn pick_method(&mut self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
963 debug!("pick_method(self_ty={})", self.ty_to_string(self_ty));
965 let mut possibly_unsatisfied_predicates = Vec::new();
966 let mut unstable_candidates = Vec::new();
968 for (kind, candidates) in &[
969 ("inherent", &self.inherent_candidates),
970 ("extension", &self.extension_candidates),
972 debug!("searching {} candidates", kind);
973 let res = self.consider_candidates(
976 &mut possibly_unsatisfied_predicates,
977 Some(&mut unstable_candidates),
979 if let Some(pick) = res {
980 if !self.is_suggestion.0 && !unstable_candidates.is_empty() {
981 if let Ok(p) = &pick {
982 // Emit a lint if there are unstable candidates alongside the stable ones.
984 // We suppress warning if we're picking the method only because it is a
986 self.emit_unstable_name_collision_hint(p, &unstable_candidates);
993 debug!("searching unstable candidates");
994 let res = self.consider_candidates(
996 unstable_candidates.into_iter().map(|(c, _)| c),
997 &mut possibly_unsatisfied_predicates,
1001 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1006 fn consider_candidates<'b, ProbesIter>(
1010 possibly_unsatisfied_predicates: &mut Vec<TraitRef<'tcx>>,
1011 unstable_candidates: Option<&mut Vec<(&'b Candidate<'tcx>, Symbol)>>,
1012 ) -> Option<PickResult<'tcx>>
1014 ProbesIter: Iterator<Item = &'b Candidate<'tcx>> + Clone,
1016 let mut applicable_candidates: Vec<_> = probes.clone()
1018 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
1020 .filter(|&(_, status)| status != ProbeResult::NoMatch)
1023 debug!("applicable_candidates: {:?}", applicable_candidates);
1025 if applicable_candidates.len() > 1 {
1026 if let Some(pick) = self.collapse_candidates_to_trait_pick(&applicable_candidates[..]) {
1027 return Some(Ok(pick));
1031 if let Some(uc) = unstable_candidates {
1032 applicable_candidates.retain(|&(p, _)| {
1033 if let stability::EvalResult::Deny { feature, .. } =
1034 self.tcx.eval_stability(p.item.def_id, None, self.span)
1036 uc.push((p, feature));
1043 if applicable_candidates.len() > 1 {
1044 let sources = probes
1045 .map(|p| self.candidate_source(p, self_ty))
1047 return Some(Err(MethodError::Ambiguity(sources)));
1050 applicable_candidates.pop().map(|(probe, status)| {
1051 if status == ProbeResult::Match {
1052 Ok(probe.to_unadjusted_pick())
1054 Err(MethodError::BadReturnType)
1059 fn emit_unstable_name_collision_hint(
1062 unstable_candidates: &[(&Candidate<'tcx>, Symbol)],
1064 let mut diag = self.tcx.struct_span_lint_node(
1065 lint::builtin::UNSTABLE_NAME_COLLISIONS,
1068 "a method with this name may be added to the standard library in the future",
1071 // FIXME: This should be a `span_suggestion_with_applicability` instead of `help`
1072 // However `self.span` only
1073 // highlights the method name, so we can't use it. Also consider reusing the code from
1074 // `report_method_error()`.
1076 "call with fully qualified syntax `{}(...)` to keep using the current method",
1077 self.tcx.item_path_str(stable_pick.item.def_id),
1080 if nightly_options::is_nightly_build() {
1081 for (candidate, feature) in unstable_candidates {
1083 "add #![feature({})] to the crate attributes to enable `{}`",
1085 self.tcx.item_path_str(candidate.item.def_id),
1093 fn select_trait_candidate(&self, trait_ref: ty::TraitRef<'tcx>)
1094 -> traits::SelectionResult<'tcx, traits::Selection<'tcx>>
1096 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1098 trait_ref.to_poly_trait_ref().to_poly_trait_predicate();
1099 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1100 traits::SelectionContext::new(self).select(&obligation)
1103 fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>)
1106 match candidate.kind {
1107 InherentImplCandidate(..) => ImplSource(candidate.item.container.id()),
1109 WhereClauseCandidate(_) => TraitSource(candidate.item.container.id()),
1110 TraitCandidate(trait_ref) => self.probe(|_| {
1111 let _ = self.at(&ObligationCause::dummy(), self.param_env)
1112 .sup(candidate.xform_self_ty, self_ty);
1113 match self.select_trait_candidate(trait_ref) {
1114 Ok(Some(traits::Vtable::VtableImpl(ref impl_data))) => {
1115 // If only a single impl matches, make the error message point
1117 ImplSource(impl_data.impl_def_id)
1120 TraitSource(candidate.item.container.id())
1127 fn consider_probe(&self,
1129 probe: &Candidate<'tcx>,
1130 possibly_unsatisfied_predicates: &mut Vec<TraitRef<'tcx>>)
1132 debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe);
1135 // First check that the self type can be related.
1136 let sub_obligations = match self.at(&ObligationCause::dummy(), self.param_env)
1137 .sup(probe.xform_self_ty, self_ty) {
1138 Ok(InferOk { obligations, value: () }) => obligations,
1140 debug!("--> cannot relate self-types");
1141 return ProbeResult::NoMatch;
1145 let mut result = ProbeResult::Match;
1146 let selcx = &mut traits::SelectionContext::new(self);
1147 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1149 // If so, impls may carry other conditions (e.g., where
1150 // clauses) that must be considered. Make sure that those
1151 // match as well (or at least may match, sometimes we
1152 // don't have enough information to fully evaluate).
1153 let candidate_obligations : Vec<_> = match probe.kind {
1154 InherentImplCandidate(ref substs, ref ref_obligations) => {
1155 // Check whether the impl imposes obligations we have to worry about.
1156 let impl_def_id = probe.item.container.id();
1157 let impl_bounds = self.tcx.predicates_of(impl_def_id);
1158 let impl_bounds = impl_bounds.instantiate(self.tcx, substs);
1159 let traits::Normalized { value: impl_bounds, obligations: norm_obligations } =
1160 traits::normalize(selcx, self.param_env, cause.clone(), &impl_bounds);
1162 // Convert the bounds into obligations.
1163 let impl_obligations = traits::predicates_for_generics(
1164 cause, self.param_env, &impl_bounds);
1166 debug!("impl_obligations={:?}", impl_obligations);
1167 impl_obligations.into_iter()
1168 .chain(norm_obligations.into_iter())
1169 .chain(ref_obligations.iter().cloned())
1174 WhereClauseCandidate(..) => {
1175 // These have no additional conditions to check.
1179 TraitCandidate(trait_ref) => {
1180 let predicate = trait_ref.to_predicate();
1182 traits::Obligation::new(cause, self.param_env, predicate);
1183 if !self.predicate_may_hold(&obligation) {
1184 if self.probe(|_| self.select_trait_candidate(trait_ref).is_err()) {
1185 // This candidate's primary obligation doesn't even
1186 // select - don't bother registering anything in
1187 // `potentially_unsatisfied_predicates`.
1188 return ProbeResult::NoMatch;
1190 // Some nested subobligation of this predicate
1193 // FIXME: try to find the exact nested subobligation
1194 // and point at it rather than reporting the entire
1196 result = ProbeResult::NoMatch;
1197 let trait_ref = self.resolve_type_vars_if_possible(&trait_ref);
1198 possibly_unsatisfied_predicates.push(trait_ref);
1205 debug!("consider_probe - candidate_obligations={:?} sub_obligations={:?}",
1206 candidate_obligations, sub_obligations);
1208 // Evaluate those obligations to see if they might possibly hold.
1209 for o in candidate_obligations.into_iter().chain(sub_obligations) {
1210 let o = self.resolve_type_vars_if_possible(&o);
1211 if !self.predicate_may_hold(&o) {
1212 result = ProbeResult::NoMatch;
1213 if let &ty::Predicate::Trait(ref pred) = &o.predicate {
1214 possibly_unsatisfied_predicates.push(pred.skip_binder().trait_ref);
1219 if let ProbeResult::Match = result {
1220 if let (Some(return_ty), Some(xform_ret_ty)) =
1221 (self.return_type, probe.xform_ret_ty)
1223 let xform_ret_ty = self.resolve_type_vars_if_possible(&xform_ret_ty);
1224 debug!("comparing return_ty {:?} with xform ret ty {:?}",
1226 probe.xform_ret_ty);
1227 if self.at(&ObligationCause::dummy(), self.param_env)
1228 .sup(return_ty, xform_ret_ty)
1231 return ProbeResult::BadReturnType;
1240 /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1241 /// same trait, but we don't know which impl to use. In this case, since in all cases the
1242 /// external interface of the method can be determined from the trait, it's ok not to decide.
1243 /// We can basically just collapse all of the probes for various impls into one where-clause
1244 /// probe. This will result in a pending obligation so when more type-info is available we can
1245 /// make the final decision.
1247 /// Example (`src/test/run-pass/method-two-trait-defer-resolution-1.rs`):
1250 /// trait Foo { ... }
1251 /// impl Foo for Vec<int> { ... }
1252 /// impl Foo for Vec<usize> { ... }
1255 /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1256 /// use, so it's ok to just commit to "using the method from the trait Foo".
1257 fn collapse_candidates_to_trait_pick(&self, probes: &[(&Candidate<'tcx>, ProbeResult)])
1258 -> Option<Pick<'tcx>>
1260 // Do all probes correspond to the same trait?
1261 let container = probes[0].0.item.container;
1262 if let ty::ImplContainer(_) = container {
1265 if probes[1..].iter().any(|&(p, _)| p.item.container != container) {
1269 // FIXME: check the return type here somehow.
1270 // If so, just use this trait and call it a day.
1272 item: probes[0].0.item.clone(),
1274 import_id: probes[0].0.import_id,
1281 /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
1282 /// candidate method where the method name may have been misspelt. Similarly to other
1283 /// Levenshtein based suggestions, we provide at most one such suggestion.
1284 fn probe_for_lev_candidate(&mut self) -> Result<Option<ty::AssociatedItem>, MethodError<'tcx>> {
1285 debug!("Probing for method names similar to {:?}",
1288 let steps = self.steps.clone();
1290 let mut pcx = ProbeContext::new(self.fcx, self.span, self.mode, self.method_name,
1291 self.return_type, steps, IsSuggestion(true));
1292 pcx.allow_similar_names = true;
1293 pcx.assemble_inherent_candidates();
1294 pcx.assemble_extension_candidates_for_traits_in_scope(ast::DUMMY_NODE_ID)?;
1296 let method_names = pcx.candidate_method_names();
1297 pcx.allow_similar_names = false;
1298 let applicable_close_candidates: Vec<ty::AssociatedItem> = method_names
1300 .filter_map(|&method_name| {
1302 pcx.method_name = Some(method_name);
1303 pcx.assemble_inherent_candidates();
1304 pcx.assemble_extension_candidates_for_traits_in_scope(ast::DUMMY_NODE_ID)
1305 .ok().map_or(None, |_| {
1307 .and_then(|pick| pick.ok())
1308 .and_then(|pick| Some(pick.item))
1313 if applicable_close_candidates.is_empty() {
1317 let names = applicable_close_candidates.iter().map(|cand| &cand.ident.name);
1318 find_best_match_for_name(names,
1319 &self.method_name.unwrap().as_str(),
1322 Ok(applicable_close_candidates
1324 .find(|method| method.ident.name == best_name))
1329 ///////////////////////////////////////////////////////////////////////////
1331 fn has_applicable_self(&self, item: &ty::AssociatedItem) -> bool {
1332 // "Fast track" -- check for usage of sugar when in method call
1335 // In Path mode (i.e., resolving a value like `T::next`), consider any
1336 // associated value (i.e., methods, constants) but not types.
1338 Mode::MethodCall => item.method_has_self_argument,
1339 Mode::Path => match item.kind {
1340 ty::AssociatedKind::Existential |
1341 ty::AssociatedKind::Type => false,
1342 ty::AssociatedKind::Method | ty::AssociatedKind::Const => true
1345 // FIXME -- check for types that deref to `Self`,
1346 // like `Rc<Self>` and so on.
1348 // Note also that the current code will break if this type
1349 // includes any of the type parameters defined on the method
1350 // -- but this could be overcome.
1353 fn record_static_candidate(&mut self, source: CandidateSource) {
1354 self.static_candidates.push(source);
1357 fn xform_self_ty(&self,
1358 item: &ty::AssociatedItem,
1360 substs: &Substs<'tcx>)
1361 -> (Ty<'tcx>, Option<Ty<'tcx>>) {
1362 if item.kind == ty::AssociatedKind::Method && self.mode == Mode::MethodCall {
1363 let sig = self.xform_method_sig(item.def_id, substs);
1364 (sig.inputs()[0], Some(sig.output()))
1370 fn xform_method_sig(&self,
1372 substs: &Substs<'tcx>)
1375 let fn_sig = self.tcx.fn_sig(method);
1376 debug!("xform_self_ty(fn_sig={:?}, substs={:?})",
1380 assert!(!substs.has_escaping_bound_vars());
1382 // It is possible for type parameters or early-bound lifetimes
1383 // to appear in the signature of `self`. The substitutions we
1384 // are given do not include type/lifetime parameters for the
1385 // method yet. So create fresh variables here for those too,
1386 // if there are any.
1387 let generics = self.tcx.generics_of(method);
1388 assert_eq!(substs.len(), generics.parent_count as usize);
1390 // Erase any late-bound regions from the method and substitute
1391 // in the values from the substitution.
1392 let xform_fn_sig = self.erase_late_bound_regions(&fn_sig);
1394 if generics.params.is_empty() {
1395 xform_fn_sig.subst(self.tcx, substs)
1397 let substs = Substs::for_item(self.tcx, method, |param, _| {
1398 let i = param.index as usize;
1399 if i < substs.len() {
1403 GenericParamDefKind::Lifetime => {
1404 // In general, during probe we erase regions. See
1405 // `impl_self_ty()` for an explanation.
1406 self.tcx.types.re_erased.into()
1408 GenericParamDefKind::Type {..} => self.var_for_def(self.span, param),
1412 xform_fn_sig.subst(self.tcx, substs)
1416 /// Get the type of an impl and generate substitutions with placeholders.
1417 fn impl_ty_and_substs(&self, impl_def_id: DefId) -> (Ty<'tcx>, &'tcx Substs<'tcx>) {
1418 (self.tcx.type_of(impl_def_id), self.fresh_item_substs(impl_def_id))
1421 fn fresh_item_substs(&self, def_id: DefId) -> &'tcx Substs<'tcx> {
1422 Substs::for_item(self.tcx, def_id, |param, _| {
1424 GenericParamDefKind::Lifetime => self.tcx.types.re_erased.into(),
1425 GenericParamDefKind::Type {..} => {
1426 self.next_ty_var(TypeVariableOrigin::SubstitutionPlaceholder(
1427 self.tcx.def_span(def_id))).into()
1433 /// Replace late-bound-regions bound by `value` with `'static` using
1434 /// `ty::erase_late_bound_regions`.
1436 /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1437 /// method matching. It is reasonable during the probe phase because we don't consider region
1438 /// relationships at all. Therefore, we can just replace all the region variables with 'static
1439 /// rather than creating fresh region variables. This is nice for two reasons:
1441 /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1442 /// particular method call, it winds up creating fewer types overall, which helps for memory
1443 /// usage. (Admittedly, this is a rather small effect, though measurable.)
1445 /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1446 /// late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1447 /// regions with actual region variables as is proper, we'd have to ensure that the same
1448 /// region got replaced with the same variable, which requires a bit more coordination
1449 /// and/or tracking the substitution and
1451 fn erase_late_bound_regions<T>(&self, value: &ty::Binder<T>) -> T
1452 where T: TypeFoldable<'tcx>
1454 self.tcx.erase_late_bound_regions(value)
1457 /// Find the method with the appropriate name (or return type, as the case may be). If
1458 /// `allow_similar_names` is set, find methods with close-matching names.
1459 fn impl_or_trait_item(&self, def_id: DefId) -> Vec<ty::AssociatedItem> {
1460 if let Some(name) = self.method_name {
1461 if self.allow_similar_names {
1462 let max_dist = max(name.as_str().len(), 3) / 3;
1463 self.tcx.associated_items(def_id)
1465 let dist = lev_distance(&*name.as_str(), &x.ident.as_str());
1466 Namespace::from(x.kind) == Namespace::Value && dist > 0
1472 .associated_item(def_id, name, Namespace::Value)
1473 .map_or(Vec::new(), |x| vec![x])
1476 self.tcx.associated_items(def_id).collect()
1481 impl<'tcx> Candidate<'tcx> {
1482 fn to_unadjusted_pick(&self) -> Pick<'tcx> {
1484 item: self.item.clone(),
1485 kind: match self.kind {
1486 InherentImplCandidate(..) => InherentImplPick,
1487 ObjectCandidate => ObjectPick,
1488 TraitCandidate(_) => TraitPick,
1489 WhereClauseCandidate(ref trait_ref) => {
1490 // Only trait derived from where-clauses should
1491 // appear here, so they should not contain any
1492 // inference variables or other artifacts. This
1493 // means they are safe to put into the
1494 // `WhereClausePick`.
1496 !trait_ref.skip_binder().substs.needs_infer()
1497 && !trait_ref.skip_binder().substs.has_placeholders()
1500 WhereClausePick(trait_ref.clone())
1503 import_id: self.import_id,