2 use super::MethodError;
3 use super::NoMatchData;
4 use super::{CandidateSource, ImplSource, TraitSource};
6 use crate::check::FnCtxt;
7 use crate::hir::def::DefKind;
8 use crate::hir::def_id::DefId;
11 use rustc_ast::util::lev_distance::{find_best_match_for_name, lev_distance};
12 use rustc_data_structures::fx::FxHashSet;
13 use rustc_data_structures::sync::Lrc;
14 use rustc_errors::struct_span_err;
16 use rustc_hir::def::Namespace;
17 use rustc_infer::infer::canonical::OriginalQueryValues;
18 use rustc_infer::infer::canonical::{Canonical, QueryResponse};
19 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
20 use rustc_infer::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
21 use rustc_infer::infer::{self, InferOk, TyCtxtInferExt};
22 use rustc_middle::middle::stability;
23 use rustc_middle::ty::subst::{InternalSubsts, Subst, SubstsRef};
24 use rustc_middle::ty::GenericParamDefKind;
25 use rustc_middle::ty::{
26 self, ParamEnvAnd, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
28 use rustc_session::config::nightly_options;
29 use rustc_session::lint;
30 use rustc_span::def_id::LocalDefId;
31 use rustc_span::{symbol::Ident, Span, Symbol, DUMMY_SP};
32 use rustc_trait_selection::autoderef::{self, Autoderef};
33 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
34 use rustc_trait_selection::traits::query::method_autoderef::MethodAutoderefBadTy;
35 use rustc_trait_selection::traits::query::method_autoderef::{
36 CandidateStep, MethodAutoderefStepsResult,
38 use rustc_trait_selection::traits::query::CanonicalTyGoal;
39 use rustc_trait_selection::traits::{self, ObligationCause};
45 use smallvec::{smallvec, SmallVec};
47 use self::CandidateKind::*;
48 pub use self::PickKind::*;
50 /// Boolean flag used to indicate if this search is for a suggestion
51 /// or not. If true, we can allow ambiguity and so forth.
52 #[derive(Clone, Copy)]
53 pub struct IsSuggestion(pub bool);
55 struct ProbeContext<'a, 'tcx> {
56 fcx: &'a FnCtxt<'a, 'tcx>,
59 method_name: Option<Ident>,
60 return_type: Option<Ty<'tcx>>,
62 /// This is the OriginalQueryValues for the steps queries
63 /// that are answered in steps.
64 orig_steps_var_values: OriginalQueryValues<'tcx>,
65 steps: Lrc<Vec<CandidateStep<'tcx>>>,
67 inherent_candidates: Vec<Candidate<'tcx>>,
68 extension_candidates: Vec<Candidate<'tcx>>,
69 impl_dups: FxHashSet<DefId>,
71 /// Collects near misses when the candidate functions are missing a `self` keyword and is only
72 /// used for error reporting
73 static_candidates: Vec<CandidateSource>,
75 /// When probing for names, include names that are close to the
76 /// requested name (by Levensthein distance)
77 allow_similar_names: bool,
79 /// Some(candidate) if there is a private candidate
80 private_candidate: Option<(DefKind, DefId)>,
82 /// Collects near misses when trait bounds for type parameters are unsatisfied and is only used
83 /// for error reporting
84 unsatisfied_predicates: Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>)>,
86 is_suggestion: IsSuggestion,
89 impl<'a, 'tcx> Deref for ProbeContext<'a, 'tcx> {
90 type Target = FnCtxt<'a, 'tcx>;
91 fn deref(&self) -> &Self::Target {
97 struct Candidate<'tcx> {
98 // Candidates are (I'm not quite sure, but they are mostly) basically
99 // some metadata on top of a `ty::AssocItem` (without substs).
101 // However, method probing wants to be able to evaluate the predicates
102 // for a function with the substs applied - for example, if a function
103 // has `where Self: Sized`, we don't want to consider it unless `Self`
104 // is actually `Sized`, and similarly, return-type suggestions want
105 // to consider the "actual" return type.
107 // The way this is handled is through `xform_self_ty`. It contains
108 // the receiver type of this candidate, but `xform_self_ty`,
109 // `xform_ret_ty` and `kind` (which contains the predicates) have the
110 // generic parameters of this candidate substituted with the *same set*
111 // of inference variables, which acts as some weird sort of "query".
113 // When we check out a candidate, we require `xform_self_ty` to be
114 // a subtype of the passed-in self-type, and this equates the type
115 // variables in the rest of the fields.
117 // For example, if we have this candidate:
120 // fn foo(&self) where Self: Sized;
124 // Then `xform_self_ty` will be `&'erased ?X` and `kind` will contain
125 // the predicate `?X: Sized`, so if we are evaluating `Foo` for a
126 // the receiver `&T`, we'll do the subtyping which will make `?X`
127 // get the right value, then when we evaluate the predicate we'll check
129 xform_self_ty: Ty<'tcx>,
130 xform_ret_ty: Option<Ty<'tcx>>,
132 kind: CandidateKind<'tcx>,
133 import_ids: SmallVec<[LocalDefId; 1]>,
137 enum CandidateKind<'tcx> {
138 InherentImplCandidate(
140 // Normalize obligations
141 Vec<traits::PredicateObligation<'tcx>>,
144 TraitCandidate(ty::TraitRef<'tcx>),
145 WhereClauseCandidate(
147 ty::PolyTraitRef<'tcx>,
151 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
158 #[derive(Debug, PartialEq, Clone)]
159 pub struct Pick<'tcx> {
160 pub item: ty::AssocItem,
161 pub kind: PickKind<'tcx>,
162 pub import_ids: SmallVec<[LocalDefId; 1]>,
164 // Indicates that the source expression should be autoderef'd N times
166 // A = expr | *expr | **expr | ...
167 pub autoderefs: usize,
169 // Indicates that an autoref is applied after the optional autoderefs
171 // B = A | &A | &mut A
172 pub autoref: Option<hir::Mutability>,
174 // Indicates that the source expression should be "unsized" to a
175 // target type. This should probably eventually go away in favor
176 // of just coercing method receivers.
179 pub unsize: Option<Ty<'tcx>>,
182 #[derive(Clone, Debug, PartialEq, Eq)]
183 pub enum PickKind<'tcx> {
189 ty::PolyTraitRef<'tcx>,
193 pub type PickResult<'tcx> = Result<Pick<'tcx>, MethodError<'tcx>>;
195 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
197 // An expression of the form `receiver.method_name(...)`.
198 // Autoderefs are performed on `receiver`, lookup is done based on the
199 // `self` argument of the method, and static methods aren't considered.
201 // An expression of the form `Type::item` or `<T>::item`.
202 // No autoderefs are performed, lookup is done based on the type each
203 // implementation is for, and static methods are included.
207 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
208 pub enum ProbeScope {
209 // Assemble candidates coming only from traits in scope.
212 // Assemble candidates coming from all traits.
216 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
217 /// This is used to offer suggestions to users. It returns methods
218 /// that could have been called which have the desired return
219 /// type. Some effort is made to rule out methods that, if called,
220 /// would result in an error (basically, the same criteria we
221 /// would use to decide if a method is a plausible fit for
222 /// ambiguity purposes).
223 pub fn probe_for_return_type(
227 return_type: Ty<'tcx>,
229 scope_expr_id: hir::HirId,
230 ) -> Vec<ty::AssocItem> {
232 "probe(self_ty={:?}, return_type={}, scope_expr_id={})",
233 self_ty, return_type, scope_expr_id
235 let method_names = self
244 ProbeScope::AllTraits,
245 |probe_cx| Ok(probe_cx.candidate_method_names()),
250 .flat_map(|&method_name| {
259 ProbeScope::AllTraits,
260 |probe_cx| probe_cx.pick(),
263 .map(|pick| pick.item)
268 pub fn probe_for_name(
273 is_suggestion: IsSuggestion,
275 scope_expr_id: hir::HirId,
277 ) -> PickResult<'tcx> {
279 "probe(self_ty={:?}, item_name={}, scope_expr_id={})",
280 self_ty, item_name, scope_expr_id
291 |probe_cx| probe_cx.pick(),
299 method_name: Option<Ident>,
300 return_type: Option<Ty<'tcx>>,
301 is_suggestion: IsSuggestion,
303 scope_expr_id: hir::HirId,
306 ) -> Result<R, MethodError<'tcx>>
308 OP: FnOnce(ProbeContext<'a, 'tcx>) -> Result<R, MethodError<'tcx>>,
310 let mut orig_values = OriginalQueryValues::default();
311 let param_env_and_self_ty = self.infcx.canonicalize_query(
312 &ParamEnvAnd { param_env: self.param_env, value: self_ty },
316 let steps = if mode == Mode::MethodCall {
317 self.tcx.method_autoderef_steps(param_env_and_self_ty)
319 self.infcx.probe(|_| {
320 // Mode::Path - the deref steps is "trivial". This turns
321 // our CanonicalQuery into a "trivial" QueryResponse. This
322 // is a bit inefficient, but I don't think that writing
323 // special handling for this "trivial case" is a good idea.
325 let infcx = &self.infcx;
326 let (ParamEnvAnd { param_env: _, value: self_ty }, canonical_inference_vars) =
327 infcx.instantiate_canonical_with_fresh_inference_vars(
329 ¶m_env_and_self_ty,
332 "probe_op: Mode::Path, param_env_and_self_ty={:?} self_ty={:?}",
333 param_env_and_self_ty, self_ty
335 MethodAutoderefStepsResult {
336 steps: Lrc::new(vec![CandidateStep {
337 self_ty: self.make_query_response_ignoring_pending_obligations(
338 canonical_inference_vars,
342 from_unsafe_deref: false,
346 reached_recursion_limit: false,
351 // If our autoderef loop had reached the recursion limit,
352 // report an overflow error, but continue going on with
353 // the truncated autoderef list.
354 if steps.reached_recursion_limit {
359 .unwrap_or_else(|| span_bug!(span, "reached the recursion limit in 0 steps?"))
362 .probe_instantiate_query_response(span, &orig_values, ty)
363 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
364 autoderef::report_autoderef_recursion_limit_error(self.tcx, span, ty.value);
368 // If we encountered an `_` type or an error type during autoderef, this is
370 if let Some(bad_ty) = &steps.opt_bad_ty {
372 // Ambiguity was encountered during a suggestion. Just keep going.
373 debug!("ProbeContext: encountered ambiguity in suggestion");
374 } else if bad_ty.reached_raw_pointer && !self.tcx.features().arbitrary_self_types {
375 // this case used to be allowed by the compiler,
376 // so we do a future-compat lint here for the 2015 edition
377 // (see https://github.com/rust-lang/rust/issues/46906)
378 if self.tcx.sess.rust_2018() {
383 "the type of this value must be known to call a method on a raw pointer on \
388 self.tcx.struct_span_lint_hir(
389 lint::builtin::TYVAR_BEHIND_RAW_POINTER,
392 |lint| lint.build("type annotations needed").emit(),
396 // Encountered a real ambiguity, so abort the lookup. If `ty` is not
397 // an `Err`, report the right "type annotations needed" error pointing
401 .probe_instantiate_query_response(span, &orig_values, ty)
402 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
403 let ty = self.structurally_resolved_type(span, ty.value);
404 assert!(matches!(ty.kind, ty::Error(_)));
405 return Err(MethodError::NoMatch(NoMatchData::new(
415 debug!("ProbeContext: steps for self_ty={:?} are {:?}", self_ty, steps);
417 // this creates one big transaction so that all type variables etc
418 // that we create during the probe process are removed later
420 let mut probe_cx = ProbeContext::new(
431 probe_cx.assemble_inherent_candidates();
433 ProbeScope::TraitsInScope => {
434 probe_cx.assemble_extension_candidates_for_traits_in_scope(scope_expr_id)?
436 ProbeScope::AllTraits => probe_cx.assemble_extension_candidates_for_all_traits()?,
443 pub fn provide(providers: &mut ty::query::Providers) {
444 providers.method_autoderef_steps = method_autoderef_steps;
447 fn method_autoderef_steps<'tcx>(
449 goal: CanonicalTyGoal<'tcx>,
450 ) -> MethodAutoderefStepsResult<'tcx> {
451 debug!("method_autoderef_steps({:?})", goal);
453 tcx.infer_ctxt().enter_with_canonical(DUMMY_SP, &goal, |ref infcx, goal, inference_vars| {
454 let ParamEnvAnd { param_env, value: self_ty } = goal;
456 let mut autoderef = Autoderef::new(infcx, param_env, hir::CRATE_HIR_ID, DUMMY_SP, self_ty)
457 .include_raw_pointers()
459 let mut reached_raw_pointer = false;
460 let mut steps: Vec<_> = autoderef
463 let step = CandidateStep {
464 self_ty: infcx.make_query_response_ignoring_pending_obligations(
465 inference_vars.clone(),
469 from_unsafe_deref: reached_raw_pointer,
472 if let ty::RawPtr(_) = ty.kind {
473 // all the subsequent steps will be from_unsafe_deref
474 reached_raw_pointer = true;
480 let final_ty = autoderef.final_ty(true);
481 let opt_bad_ty = match final_ty.kind {
482 ty::Infer(ty::TyVar(_)) | ty::Error(_) => Some(MethodAutoderefBadTy {
485 .make_query_response_ignoring_pending_obligations(inference_vars, final_ty),
487 ty::Array(elem_ty, _) => {
488 let dereferences = steps.len() - 1;
490 steps.push(CandidateStep {
491 self_ty: infcx.make_query_response_ignoring_pending_obligations(
493 infcx.tcx.mk_slice(elem_ty),
495 autoderefs: dereferences,
496 // this could be from an unsafe deref if we had
497 // a *mut/const [T; N]
498 from_unsafe_deref: reached_raw_pointer,
507 debug!("method_autoderef_steps: steps={:?} opt_bad_ty={:?}", steps, opt_bad_ty);
509 MethodAutoderefStepsResult {
510 steps: Lrc::new(steps),
511 opt_bad_ty: opt_bad_ty.map(Lrc::new),
512 reached_recursion_limit: autoderef.reached_recursion_limit(),
517 impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
519 fcx: &'a FnCtxt<'a, 'tcx>,
522 method_name: Option<Ident>,
523 return_type: Option<Ty<'tcx>>,
524 orig_steps_var_values: OriginalQueryValues<'tcx>,
525 steps: Lrc<Vec<CandidateStep<'tcx>>>,
526 is_suggestion: IsSuggestion,
527 ) -> ProbeContext<'a, 'tcx> {
534 inherent_candidates: Vec::new(),
535 extension_candidates: Vec::new(),
536 impl_dups: FxHashSet::default(),
537 orig_steps_var_values,
539 static_candidates: Vec::new(),
540 allow_similar_names: false,
541 private_candidate: None,
542 unsatisfied_predicates: Vec::new(),
547 fn reset(&mut self) {
548 self.inherent_candidates.clear();
549 self.extension_candidates.clear();
550 self.impl_dups.clear();
551 self.static_candidates.clear();
552 self.private_candidate = None;
555 ///////////////////////////////////////////////////////////////////////////
556 // CANDIDATE ASSEMBLY
558 fn push_candidate(&mut self, candidate: Candidate<'tcx>, is_inherent: bool) {
559 let is_accessible = if let Some(name) = self.method_name {
560 let item = candidate.item;
562 self.tcx.adjust_ident_and_get_scope(name, item.container.id(), self.body_id).1;
563 item.vis.is_accessible_from(def_scope, self.tcx)
569 self.inherent_candidates.push(candidate);
571 self.extension_candidates.push(candidate);
573 } else if self.private_candidate.is_none() {
574 self.private_candidate =
575 Some((candidate.item.kind.as_def_kind(), candidate.item.def_id));
579 fn assemble_inherent_candidates(&mut self) {
580 let steps = Lrc::clone(&self.steps);
581 for step in steps.iter() {
582 self.assemble_probe(&step.self_ty);
586 fn assemble_probe(&mut self, self_ty: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>) {
587 debug!("assemble_probe: self_ty={:?}", self_ty);
588 let lang_items = self.tcx.lang_items();
590 match self_ty.value.value.kind {
591 ty::Dynamic(ref data, ..) => {
592 if let Some(p) = data.principal() {
593 // Subtle: we can't use `instantiate_query_response` here: using it will
594 // commit to all of the type equalities assumed by inference going through
595 // autoderef (see the `method-probe-no-guessing` test).
597 // However, in this code, it is OK if we end up with an object type that is
598 // "more general" than the object type that we are evaluating. For *every*
599 // object type `MY_OBJECT`, a function call that goes through a trait-ref
600 // of the form `<MY_OBJECT as SuperTraitOf(MY_OBJECT)>::func` is a valid
601 // `ObjectCandidate`, and it should be discoverable "exactly" through one
602 // of the iterations in the autoderef loop, so there is no problem with it
603 // being discoverable in another one of these iterations.
605 // Using `instantiate_canonical_with_fresh_inference_vars` on our
606 // `Canonical<QueryResponse<Ty<'tcx>>>` and then *throwing away* the
607 // `CanonicalVarValues` will exactly give us such a generalization - it
608 // will still match the original object type, but it won't pollute our
609 // type variables in any form, so just do that!
610 let (QueryResponse { value: generalized_self_ty, .. }, _ignored_var_values) =
612 .instantiate_canonical_with_fresh_inference_vars(self.span, &self_ty);
614 self.assemble_inherent_candidates_from_object(generalized_self_ty);
615 self.assemble_inherent_impl_candidates_for_type(p.def_id());
619 self.assemble_inherent_impl_candidates_for_type(def.did);
621 ty::Foreign(did) => {
622 self.assemble_inherent_impl_candidates_for_type(did);
625 self.assemble_inherent_candidates_from_param(p);
628 let lang_def_id = lang_items.bool_impl();
629 self.assemble_inherent_impl_for_primitive(lang_def_id);
632 let lang_def_id = lang_items.char_impl();
633 self.assemble_inherent_impl_for_primitive(lang_def_id);
636 let lang_def_id = lang_items.str_impl();
637 self.assemble_inherent_impl_for_primitive(lang_def_id);
639 let lang_def_id = lang_items.str_alloc_impl();
640 self.assemble_inherent_impl_for_primitive(lang_def_id);
643 for &lang_def_id in &[
644 lang_items.slice_impl(),
645 lang_items.slice_u8_impl(),
646 lang_items.slice_alloc_impl(),
647 lang_items.slice_u8_alloc_impl(),
649 self.assemble_inherent_impl_for_primitive(lang_def_id);
653 let lang_def_id = lang_items.array_impl();
654 self.assemble_inherent_impl_for_primitive(lang_def_id);
656 ty::RawPtr(ty::TypeAndMut { ty: _, mutbl }) => {
657 let (lang_def_id1, lang_def_id2) = match mutbl {
658 hir::Mutability::Not => {
659 (lang_items.const_ptr_impl(), lang_items.const_slice_ptr_impl())
661 hir::Mutability::Mut => {
662 (lang_items.mut_ptr_impl(), lang_items.mut_slice_ptr_impl())
665 self.assemble_inherent_impl_for_primitive(lang_def_id1);
666 self.assemble_inherent_impl_for_primitive(lang_def_id2);
669 let lang_def_id = match i {
670 ast::IntTy::I8 => lang_items.i8_impl(),
671 ast::IntTy::I16 => lang_items.i16_impl(),
672 ast::IntTy::I32 => lang_items.i32_impl(),
673 ast::IntTy::I64 => lang_items.i64_impl(),
674 ast::IntTy::I128 => lang_items.i128_impl(),
675 ast::IntTy::Isize => lang_items.isize_impl(),
677 self.assemble_inherent_impl_for_primitive(lang_def_id);
680 let lang_def_id = match i {
681 ast::UintTy::U8 => lang_items.u8_impl(),
682 ast::UintTy::U16 => lang_items.u16_impl(),
683 ast::UintTy::U32 => lang_items.u32_impl(),
684 ast::UintTy::U64 => lang_items.u64_impl(),
685 ast::UintTy::U128 => lang_items.u128_impl(),
686 ast::UintTy::Usize => lang_items.usize_impl(),
688 self.assemble_inherent_impl_for_primitive(lang_def_id);
691 let (lang_def_id1, lang_def_id2) = match f {
692 ast::FloatTy::F32 => (lang_items.f32_impl(), lang_items.f32_runtime_impl()),
693 ast::FloatTy::F64 => (lang_items.f64_impl(), lang_items.f64_runtime_impl()),
695 self.assemble_inherent_impl_for_primitive(lang_def_id1);
696 self.assemble_inherent_impl_for_primitive(lang_def_id2);
702 fn assemble_inherent_impl_for_primitive(&mut self, lang_def_id: Option<DefId>) {
703 if let Some(impl_def_id) = lang_def_id {
704 self.assemble_inherent_impl_probe(impl_def_id);
708 fn assemble_inherent_impl_candidates_for_type(&mut self, def_id: DefId) {
709 let impl_def_ids = self.tcx.at(self.span).inherent_impls(def_id);
710 for &impl_def_id in impl_def_ids.iter() {
711 self.assemble_inherent_impl_probe(impl_def_id);
715 fn assemble_inherent_impl_probe(&mut self, impl_def_id: DefId) {
716 if !self.impl_dups.insert(impl_def_id) {
717 return; // already visited
720 debug!("assemble_inherent_impl_probe {:?}", impl_def_id);
722 for item in self.impl_or_trait_item(impl_def_id) {
723 if !self.has_applicable_self(&item) {
724 // No receiver declared. Not a candidate.
725 self.record_static_candidate(ImplSource(impl_def_id));
729 let (impl_ty, impl_substs) = self.impl_ty_and_substs(impl_def_id);
730 let impl_ty = impl_ty.subst(self.tcx, impl_substs);
732 // Determine the receiver type that the method itself expects.
733 let xform_tys = self.xform_self_ty(&item, impl_ty, impl_substs);
735 // We can't use normalize_associated_types_in as it will pollute the
736 // fcx's fulfillment context after this probe is over.
737 let cause = traits::ObligationCause::misc(self.span, self.body_id);
738 let selcx = &mut traits::SelectionContext::new(self.fcx);
739 let traits::Normalized { value: (xform_self_ty, xform_ret_ty), obligations } =
740 traits::normalize(selcx, self.param_env, cause, &xform_tys);
742 "assemble_inherent_impl_probe: xform_self_ty = {:?}/{:?}",
743 xform_self_ty, xform_ret_ty
751 kind: InherentImplCandidate(impl_substs, obligations),
752 import_ids: smallvec![],
759 fn assemble_inherent_candidates_from_object(&mut self, self_ty: Ty<'tcx>) {
760 debug!("assemble_inherent_candidates_from_object(self_ty={:?})", self_ty);
762 let principal = match self_ty.kind {
763 ty::Dynamic(ref data, ..) => Some(data),
766 .and_then(|data| data.principal())
770 "non-object {:?} in assemble_inherent_candidates_from_object",
775 // It is illegal to invoke a method on a trait instance that
776 // refers to the `Self` type. An error will be reported by
777 // `enforce_object_limitations()` if the method refers to the
778 // `Self` type anywhere other than the receiver. Here, we use
779 // a substitution that replaces `Self` with the object type
780 // itself. Hence, a `&self` method will wind up with an
781 // argument type like `&Trait`.
782 let trait_ref = principal.with_self_ty(self.tcx, self_ty);
783 self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
784 let new_trait_ref = this.erase_late_bound_regions(&new_trait_ref);
786 let (xform_self_ty, xform_ret_ty) =
787 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
793 kind: ObjectCandidate,
794 import_ids: smallvec![],
801 fn assemble_inherent_candidates_from_param(&mut self, param_ty: ty::ParamTy) {
802 // FIXME: do we want to commit to this behavior for param bounds?
803 debug!("assemble_inherent_candidates_from_param(param_ty={:?})", param_ty);
806 self.param_env.caller_bounds().iter().map(ty::Predicate::skip_binders).filter_map(
807 |predicate| match predicate {
808 ty::PredicateAtom::Trait(trait_predicate, _) => {
809 match trait_predicate.trait_ref.self_ty().kind {
810 ty::Param(ref p) if *p == param_ty => {
811 Some(ty::Binder::bind(trait_predicate.trait_ref))
816 ty::PredicateAtom::Subtype(..)
817 | ty::PredicateAtom::Projection(..)
818 | ty::PredicateAtom::RegionOutlives(..)
819 | ty::PredicateAtom::WellFormed(..)
820 | ty::PredicateAtom::ObjectSafe(..)
821 | ty::PredicateAtom::ClosureKind(..)
822 | ty::PredicateAtom::TypeOutlives(..)
823 | ty::PredicateAtom::ConstEvaluatable(..)
824 | ty::PredicateAtom::ConstEquate(..) => None,
828 self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
829 let trait_ref = this.erase_late_bound_regions(&poly_trait_ref);
831 let (xform_self_ty, xform_ret_ty) =
832 this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs);
834 // Because this trait derives from a where-clause, it
835 // should not contain any inference variables or other
836 // artifacts. This means it is safe to put into the
837 // `WhereClauseCandidate` and (eventually) into the
838 // `WhereClausePick`.
839 assert!(!trait_ref.substs.needs_infer());
846 kind: WhereClauseCandidate(poly_trait_ref),
847 import_ids: smallvec![],
854 // Do a search through a list of bounds, using a callback to actually
855 // create the candidates.
856 fn elaborate_bounds<F>(
858 bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
861 F: for<'b> FnMut(&mut ProbeContext<'b, 'tcx>, ty::PolyTraitRef<'tcx>, ty::AssocItem),
864 for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
865 debug!("elaborate_bounds(bound_trait_ref={:?})", bound_trait_ref);
866 for item in self.impl_or_trait_item(bound_trait_ref.def_id()) {
867 if !self.has_applicable_self(&item) {
868 self.record_static_candidate(TraitSource(bound_trait_ref.def_id()));
870 mk_cand(self, bound_trait_ref, item);
876 fn assemble_extension_candidates_for_traits_in_scope(
878 expr_hir_id: hir::HirId,
879 ) -> Result<(), MethodError<'tcx>> {
880 let mut duplicates = FxHashSet::default();
881 let opt_applicable_traits = self.tcx.in_scope_traits(expr_hir_id);
882 if let Some(applicable_traits) = opt_applicable_traits {
883 for trait_candidate in applicable_traits.iter() {
884 let trait_did = trait_candidate.def_id;
885 if duplicates.insert(trait_did) {
886 let result = self.assemble_extension_candidates_for_trait(
887 &trait_candidate.import_ids,
897 fn assemble_extension_candidates_for_all_traits(&mut self) -> Result<(), MethodError<'tcx>> {
898 let mut duplicates = FxHashSet::default();
899 for trait_info in suggest::all_traits(self.tcx) {
900 if duplicates.insert(trait_info.def_id) {
901 self.assemble_extension_candidates_for_trait(&smallvec![], trait_info.def_id)?;
907 pub fn matches_return_type(
909 method: &ty::AssocItem,
910 self_ty: Option<Ty<'tcx>>,
914 ty::AssocKind::Fn => {
915 let fty = self.tcx.fn_sig(method.def_id);
917 let substs = self.fresh_substs_for_item(self.span, method.def_id);
918 let fty = fty.subst(self.tcx, substs);
920 self.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, &fty);
922 if let Some(self_ty) = self_ty {
924 .at(&ObligationCause::dummy(), self.param_env)
925 .sup(fty.inputs()[0], self_ty)
931 self.can_sub(self.param_env, fty.output(), expected).is_ok()
938 fn assemble_extension_candidates_for_trait(
940 import_ids: &SmallVec<[LocalDefId; 1]>,
942 ) -> Result<(), MethodError<'tcx>> {
943 debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})", trait_def_id);
944 let trait_substs = self.fresh_item_substs(trait_def_id);
945 let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
947 if self.tcx.is_trait_alias(trait_def_id) {
948 // For trait aliases, assume all super-traits are relevant.
949 let bounds = iter::once(trait_ref.to_poly_trait_ref());
950 self.elaborate_bounds(bounds, |this, new_trait_ref, item| {
951 let new_trait_ref = this.erase_late_bound_regions(&new_trait_ref);
953 let (xform_self_ty, xform_ret_ty) =
954 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
960 import_ids: import_ids.clone(),
961 kind: TraitCandidate(new_trait_ref),
967 debug_assert!(self.tcx.is_trait(trait_def_id));
968 for item in self.impl_or_trait_item(trait_def_id) {
969 // Check whether `trait_def_id` defines a method with suitable name.
970 if !self.has_applicable_self(&item) {
971 debug!("method has inapplicable self");
972 self.record_static_candidate(TraitSource(trait_def_id));
976 let (xform_self_ty, xform_ret_ty) =
977 self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
983 import_ids: import_ids.clone(),
984 kind: TraitCandidate(trait_ref),
993 fn candidate_method_names(&self) -> Vec<Ident> {
994 let mut set = FxHashSet::default();
995 let mut names: Vec<_> = self
998 .chain(&self.extension_candidates)
999 .filter(|candidate| {
1000 if let Some(return_ty) = self.return_type {
1001 self.matches_return_type(&candidate.item, None, return_ty)
1006 .map(|candidate| candidate.item.ident)
1007 .filter(|&name| set.insert(name))
1010 // Sort them by the name so we have a stable result.
1011 names.sort_by_cached_key(|n| n.as_str());
1015 ///////////////////////////////////////////////////////////////////////////
1016 // THE ACTUAL SEARCH
1018 fn pick(mut self) -> PickResult<'tcx> {
1019 assert!(self.method_name.is_some());
1021 if let Some(r) = self.pick_core() {
1025 debug!("pick: actual search failed, assemble diagnostics");
1027 let static_candidates = mem::take(&mut self.static_candidates);
1028 let private_candidate = self.private_candidate.take();
1029 let unsatisfied_predicates = mem::take(&mut self.unsatisfied_predicates);
1031 // things failed, so lets look at all traits, for diagnostic purposes now:
1034 let span = self.span;
1037 self.assemble_extension_candidates_for_all_traits()?;
1039 let out_of_scope_traits = match self.pick_core() {
1040 Some(Ok(p)) => vec![p.item.container.id()],
1041 //Some(Ok(p)) => p.iter().map(|p| p.item.container().id()).collect(),
1042 Some(Err(MethodError::Ambiguity(v))) => v
1044 .map(|source| match source {
1045 TraitSource(id) => id,
1046 ImplSource(impl_id) => match tcx.trait_id_of_impl(impl_id) {
1048 None => span_bug!(span, "found inherent method when looking at traits"),
1052 Some(Err(MethodError::NoMatch(NoMatchData {
1053 out_of_scope_traits: others, ..
1055 assert!(others.is_empty());
1061 if let Some((kind, def_id)) = private_candidate {
1062 return Err(MethodError::PrivateMatch(kind, def_id, out_of_scope_traits));
1064 let lev_candidate = self.probe_for_lev_candidate()?;
1066 Err(MethodError::NoMatch(NoMatchData::new(
1068 unsatisfied_predicates,
1069 out_of_scope_traits,
1075 fn pick_core(&mut self) -> Option<PickResult<'tcx>> {
1076 let steps = self.steps.clone();
1078 // find the first step that works
1082 debug!("pick_core: step={:?}", step);
1083 // skip types that are from a type error or that would require dereferencing
1085 !step.self_ty.references_error() && !step.from_unsafe_deref
1088 let InferOk { value: self_ty, obligations: _ } = self
1090 .probe_instantiate_query_response(
1092 &self.orig_steps_var_values,
1095 .unwrap_or_else(|_| {
1096 span_bug!(self.span, "{:?} was applicable but now isn't?", step.self_ty)
1098 self.pick_by_value_method(step, self_ty).or_else(|| {
1099 self.pick_autorefd_method(step, self_ty, hir::Mutability::Not)
1100 .or_else(|| self.pick_autorefd_method(step, self_ty, hir::Mutability::Mut))
1106 fn pick_by_value_method(
1108 step: &CandidateStep<'tcx>,
1110 ) -> Option<PickResult<'tcx>> {
1111 //! For each type `T` in the step list, this attempts to find a
1112 //! method where the (transformed) self type is exactly `T`. We
1113 //! do however do one transformation on the adjustment: if we
1114 //! are passing a region pointer in, we will potentially
1115 //! *reborrow* it to a shorter lifetime. This allows us to
1116 //! transparently pass `&mut` pointers, in particular, without
1117 //! consuming them for their entire lifetime.
1123 self.pick_method(self_ty).map(|r| {
1125 pick.autoderefs = step.autoderefs;
1127 // Insert a `&*` or `&mut *` if this is a reference type:
1128 if let ty::Ref(_, _, mutbl) = step.self_ty.value.value.kind {
1129 pick.autoderefs += 1;
1130 pick.autoref = Some(mutbl);
1138 fn pick_autorefd_method(
1140 step: &CandidateStep<'tcx>,
1142 mutbl: hir::Mutability,
1143 ) -> Option<PickResult<'tcx>> {
1146 // In general, during probing we erase regions.
1147 let region = tcx.lifetimes.re_erased;
1149 let autoref_ty = tcx.mk_ref(region, ty::TypeAndMut { ty: self_ty, mutbl });
1150 self.pick_method(autoref_ty).map(|r| {
1152 pick.autoderefs = step.autoderefs;
1153 pick.autoref = Some(mutbl);
1154 pick.unsize = step.unsize.then_some(self_ty);
1160 fn pick_method(&mut self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
1161 debug!("pick_method(self_ty={})", self.ty_to_string(self_ty));
1163 let mut possibly_unsatisfied_predicates = Vec::new();
1164 let mut unstable_candidates = Vec::new();
1166 for (kind, candidates) in
1167 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1169 debug!("searching {} candidates", kind);
1170 let res = self.consider_candidates(
1173 &mut possibly_unsatisfied_predicates,
1174 Some(&mut unstable_candidates),
1176 if let Some(pick) = res {
1177 if !self.is_suggestion.0 && !unstable_candidates.is_empty() {
1178 if let Ok(p) = &pick {
1179 // Emit a lint if there are unstable candidates alongside the stable ones.
1181 // We suppress warning if we're picking the method only because it is a
1183 self.emit_unstable_name_collision_hint(p, &unstable_candidates);
1190 debug!("searching unstable candidates");
1191 let res = self.consider_candidates(
1193 unstable_candidates.into_iter().map(|(c, _)| c),
1194 &mut possibly_unsatisfied_predicates,
1198 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1203 fn consider_candidates<'b, ProbesIter>(
1207 possibly_unsatisfied_predicates: &mut Vec<(
1208 ty::Predicate<'tcx>,
1209 Option<ty::Predicate<'tcx>>,
1211 unstable_candidates: Option<&mut Vec<(&'b Candidate<'tcx>, Symbol)>>,
1212 ) -> Option<PickResult<'tcx>>
1214 ProbesIter: Iterator<Item = &'b Candidate<'tcx>> + Clone,
1216 let mut applicable_candidates: Vec<_> = probes
1219 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
1221 .filter(|&(_, status)| status != ProbeResult::NoMatch)
1224 debug!("applicable_candidates: {:?}", applicable_candidates);
1226 if applicable_candidates.len() > 1 {
1227 if let Some(pick) = self.collapse_candidates_to_trait_pick(&applicable_candidates[..]) {
1228 return Some(Ok(pick));
1232 if let Some(uc) = unstable_candidates {
1233 applicable_candidates.retain(|&(p, _)| {
1234 if let stability::EvalResult::Deny { feature, .. } =
1235 self.tcx.eval_stability(p.item.def_id, None, self.span)
1237 uc.push((p, feature));
1244 if applicable_candidates.len() > 1 {
1245 let sources = probes.map(|p| self.candidate_source(p, self_ty)).collect();
1246 return Some(Err(MethodError::Ambiguity(sources)));
1249 applicable_candidates.pop().map(|(probe, status)| {
1250 if status == ProbeResult::Match {
1251 Ok(probe.to_unadjusted_pick())
1253 Err(MethodError::BadReturnType)
1258 fn emit_unstable_name_collision_hint(
1260 stable_pick: &Pick<'_>,
1261 unstable_candidates: &[(&Candidate<'tcx>, Symbol)],
1263 self.tcx.struct_span_lint_hir(
1264 lint::builtin::UNSTABLE_NAME_COLLISIONS,
1268 let mut diag = lint.build(
1269 "a method with this name may be added to the standard library in the future",
1271 // FIXME: This should be a `span_suggestion` instead of `help`
1272 // However `self.span` only
1273 // highlights the method name, so we can't use it. Also consider reusing the code from
1274 // `report_method_error()`.
1276 "call with fully qualified syntax `{}(...)` to keep using the current method",
1277 self.tcx.def_path_str(stable_pick.item.def_id),
1280 if nightly_options::is_nightly_build() {
1281 for (candidate, feature) in unstable_candidates {
1283 "add `#![feature({})]` to the crate attributes to enable `{}`",
1285 self.tcx.def_path_str(candidate.item.def_id),
1295 fn select_trait_candidate(
1297 trait_ref: ty::TraitRef<'tcx>,
1298 ) -> traits::SelectionResult<'tcx, traits::Selection<'tcx>> {
1299 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1300 let predicate = trait_ref.to_poly_trait_ref().to_poly_trait_predicate();
1301 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1302 traits::SelectionContext::new(self).select(&obligation)
1305 fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>) -> CandidateSource {
1306 match candidate.kind {
1307 InherentImplCandidate(..) => ImplSource(candidate.item.container.id()),
1308 ObjectCandidate | WhereClauseCandidate(_) => TraitSource(candidate.item.container.id()),
1309 TraitCandidate(trait_ref) => self.probe(|_| {
1311 .at(&ObligationCause::dummy(), self.param_env)
1312 .sup(candidate.xform_self_ty, self_ty);
1313 match self.select_trait_candidate(trait_ref) {
1314 Ok(Some(traits::ImplSource::ImplSourceUserDefined(ref impl_data))) => {
1315 // If only a single impl matches, make the error message point
1317 ImplSource(impl_data.impl_def_id)
1319 _ => TraitSource(candidate.item.container.id()),
1328 probe: &Candidate<'tcx>,
1329 possibly_unsatisfied_predicates: &mut Vec<(
1330 ty::Predicate<'tcx>,
1331 Option<ty::Predicate<'tcx>>,
1334 debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe);
1337 // First check that the self type can be related.
1338 let sub_obligations = match self
1339 .at(&ObligationCause::dummy(), self.param_env)
1340 .sup(probe.xform_self_ty, self_ty)
1342 Ok(InferOk { obligations, value: () }) => obligations,
1344 debug!("--> cannot relate self-types");
1345 return ProbeResult::NoMatch;
1349 let mut result = ProbeResult::Match;
1350 let selcx = &mut traits::SelectionContext::new(self);
1351 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1353 // If so, impls may carry other conditions (e.g., where
1354 // clauses) that must be considered. Make sure that those
1355 // match as well (or at least may match, sometimes we
1356 // don't have enough information to fully evaluate).
1358 InherentImplCandidate(ref substs, ref ref_obligations) => {
1359 // Check whether the impl imposes obligations we have to worry about.
1360 let impl_def_id = probe.item.container.id();
1361 let impl_bounds = self.tcx.predicates_of(impl_def_id);
1362 let impl_bounds = impl_bounds.instantiate(self.tcx, substs);
1363 let traits::Normalized { value: impl_bounds, obligations: norm_obligations } =
1364 traits::normalize(selcx, self.param_env, cause.clone(), &impl_bounds);
1366 // Convert the bounds into obligations.
1367 let impl_obligations =
1368 traits::predicates_for_generics(cause, self.param_env, impl_bounds);
1370 let candidate_obligations = impl_obligations
1371 .chain(norm_obligations.into_iter())
1372 .chain(ref_obligations.iter().cloned());
1373 // Evaluate those obligations to see if they might possibly hold.
1374 for o in candidate_obligations {
1375 let o = self.resolve_vars_if_possible(&o);
1376 if !self.predicate_may_hold(&o) {
1377 result = ProbeResult::NoMatch;
1378 possibly_unsatisfied_predicates.push((o.predicate, None));
1383 ObjectCandidate | WhereClauseCandidate(..) => {
1384 // These have no additional conditions to check.
1387 TraitCandidate(trait_ref) => {
1388 let predicate = trait_ref.without_const().to_predicate(self.tcx);
1389 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1390 if !self.predicate_may_hold(&obligation) {
1391 result = ProbeResult::NoMatch;
1393 match self.select_trait_candidate(trait_ref) {
1394 Err(_) => return true,
1395 Ok(Some(impl_source))
1396 if !impl_source.borrow_nested_obligations().is_empty() =>
1398 for obligation in impl_source.borrow_nested_obligations() {
1399 // Determine exactly which obligation wasn't met, so
1400 // that we can give more context in the error.
1401 if !self.predicate_may_hold(&obligation) {
1402 let o = self.resolve_vars_if_possible(obligation);
1404 self.resolve_vars_if_possible(&predicate);
1405 let p = if predicate == o.predicate {
1406 // Avoid "`MyStruct: Foo` which is required by
1407 // `MyStruct: Foo`" in E0599.
1412 possibly_unsatisfied_predicates.push((o.predicate, p));
1417 // Some nested subobligation of this predicate
1419 let predicate = self.resolve_vars_if_possible(&predicate);
1420 possibly_unsatisfied_predicates.push((predicate, None));
1425 // This candidate's primary obligation doesn't even
1426 // select - don't bother registering anything in
1427 // `potentially_unsatisfied_predicates`.
1428 return ProbeResult::NoMatch;
1434 // Evaluate those obligations to see if they might possibly hold.
1435 for o in sub_obligations {
1436 let o = self.resolve_vars_if_possible(&o);
1437 if !self.predicate_may_hold(&o) {
1438 result = ProbeResult::NoMatch;
1439 possibly_unsatisfied_predicates.push((o.predicate, None));
1443 if let ProbeResult::Match = result {
1444 if let (Some(return_ty), Some(xform_ret_ty)) =
1445 (self.return_type, probe.xform_ret_ty)
1447 let xform_ret_ty = self.resolve_vars_if_possible(&xform_ret_ty);
1449 "comparing return_ty {:?} with xform ret ty {:?}",
1450 return_ty, probe.xform_ret_ty
1453 .at(&ObligationCause::dummy(), self.param_env)
1454 .sup(return_ty, xform_ret_ty)
1457 return ProbeResult::BadReturnType;
1466 /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1467 /// same trait, but we don't know which impl to use. In this case, since in all cases the
1468 /// external interface of the method can be determined from the trait, it's ok not to decide.
1469 /// We can basically just collapse all of the probes for various impls into one where-clause
1470 /// probe. This will result in a pending obligation so when more type-info is available we can
1471 /// make the final decision.
1473 /// Example (`src/test/ui/method-two-trait-defer-resolution-1.rs`):
1476 /// trait Foo { ... }
1477 /// impl Foo for Vec<i32> { ... }
1478 /// impl Foo for Vec<usize> { ... }
1481 /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1482 /// use, so it's ok to just commit to "using the method from the trait Foo".
1483 fn collapse_candidates_to_trait_pick(
1485 probes: &[(&Candidate<'tcx>, ProbeResult)],
1486 ) -> Option<Pick<'tcx>> {
1487 // Do all probes correspond to the same trait?
1488 let container = probes[0].0.item.container;
1489 if let ty::ImplContainer(_) = container {
1492 if probes[1..].iter().any(|&(p, _)| p.item.container != container) {
1496 // FIXME: check the return type here somehow.
1497 // If so, just use this trait and call it a day.
1499 item: probes[0].0.item,
1501 import_ids: probes[0].0.import_ids.clone(),
1508 /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
1509 /// candidate method where the method name may have been misspelt. Similarly to other
1510 /// Levenshtein based suggestions, we provide at most one such suggestion.
1511 fn probe_for_lev_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
1512 debug!("probing for method names similar to {:?}", self.method_name);
1514 let steps = self.steps.clone();
1516 let mut pcx = ProbeContext::new(
1522 self.orig_steps_var_values.clone(),
1526 pcx.allow_similar_names = true;
1527 pcx.assemble_inherent_candidates();
1529 let method_names = pcx.candidate_method_names();
1530 pcx.allow_similar_names = false;
1531 let applicable_close_candidates: Vec<ty::AssocItem> = method_names
1533 .filter_map(|&method_name| {
1535 pcx.method_name = Some(method_name);
1536 pcx.assemble_inherent_candidates();
1537 pcx.pick_core().and_then(|pick| pick.ok()).map(|pick| pick.item)
1541 if applicable_close_candidates.is_empty() {
1545 let names = applicable_close_candidates.iter().map(|cand| &cand.ident.name);
1546 find_best_match_for_name(names, self.method_name.unwrap().name, None)
1549 Ok(applicable_close_candidates
1551 .find(|method| method.ident.name == best_name))
1556 ///////////////////////////////////////////////////////////////////////////
1558 fn has_applicable_self(&self, item: &ty::AssocItem) -> bool {
1559 // "Fast track" -- check for usage of sugar when in method call
1562 // In Path mode (i.e., resolving a value like `T::next`), consider any
1563 // associated value (i.e., methods, constants) but not types.
1565 Mode::MethodCall => item.fn_has_self_parameter,
1566 Mode::Path => match item.kind {
1567 ty::AssocKind::Type => false,
1568 ty::AssocKind::Fn | ty::AssocKind::Const => true,
1571 // FIXME -- check for types that deref to `Self`,
1572 // like `Rc<Self>` and so on.
1574 // Note also that the current code will break if this type
1575 // includes any of the type parameters defined on the method
1576 // -- but this could be overcome.
1579 fn record_static_candidate(&mut self, source: CandidateSource) {
1580 self.static_candidates.push(source);
1585 item: &ty::AssocItem,
1587 substs: SubstsRef<'tcx>,
1588 ) -> (Ty<'tcx>, Option<Ty<'tcx>>) {
1589 if item.kind == ty::AssocKind::Fn && self.mode == Mode::MethodCall {
1590 let sig = self.xform_method_sig(item.def_id, substs);
1591 (sig.inputs()[0], Some(sig.output()))
1597 fn xform_method_sig(&self, method: DefId, substs: SubstsRef<'tcx>) -> ty::FnSig<'tcx> {
1598 let fn_sig = self.tcx.fn_sig(method);
1599 debug!("xform_self_ty(fn_sig={:?}, substs={:?})", fn_sig, substs);
1601 assert!(!substs.has_escaping_bound_vars());
1603 // It is possible for type parameters or early-bound lifetimes
1604 // to appear in the signature of `self`. The substitutions we
1605 // are given do not include type/lifetime parameters for the
1606 // method yet. So create fresh variables here for those too,
1607 // if there are any.
1608 let generics = self.tcx.generics_of(method);
1609 assert_eq!(substs.len(), generics.parent_count as usize);
1611 // Erase any late-bound regions from the method and substitute
1612 // in the values from the substitution.
1613 let xform_fn_sig = self.erase_late_bound_regions(&fn_sig);
1615 if generics.params.is_empty() {
1616 xform_fn_sig.subst(self.tcx, substs)
1618 let substs = InternalSubsts::for_item(self.tcx, method, |param, _| {
1619 let i = param.index as usize;
1620 if i < substs.len() {
1624 GenericParamDefKind::Lifetime => {
1625 // In general, during probe we erase regions.
1626 self.tcx.lifetimes.re_erased.into()
1628 GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => {
1629 self.var_for_def(self.span, param)
1634 xform_fn_sig.subst(self.tcx, substs)
1638 /// Gets the type of an impl and generate substitutions with placeholders.
1639 fn impl_ty_and_substs(&self, impl_def_id: DefId) -> (Ty<'tcx>, SubstsRef<'tcx>) {
1640 (self.tcx.type_of(impl_def_id), self.fresh_item_substs(impl_def_id))
1643 fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx> {
1644 InternalSubsts::for_item(self.tcx, def_id, |param, _| match param.kind {
1645 GenericParamDefKind::Lifetime => self.tcx.lifetimes.re_erased.into(),
1646 GenericParamDefKind::Type { .. } => self
1647 .next_ty_var(TypeVariableOrigin {
1648 kind: TypeVariableOriginKind::SubstitutionPlaceholder,
1649 span: self.tcx.def_span(def_id),
1652 GenericParamDefKind::Const { .. } => {
1653 let span = self.tcx.def_span(def_id);
1654 let origin = ConstVariableOrigin {
1655 kind: ConstVariableOriginKind::SubstitutionPlaceholder,
1658 self.next_const_var(self.tcx.type_of(param.def_id), origin).into()
1663 /// Replaces late-bound-regions bound by `value` with `'static` using
1664 /// `ty::erase_late_bound_regions`.
1666 /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1667 /// method matching. It is reasonable during the probe phase because we don't consider region
1668 /// relationships at all. Therefore, we can just replace all the region variables with 'static
1669 /// rather than creating fresh region variables. This is nice for two reasons:
1671 /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1672 /// particular method call, it winds up creating fewer types overall, which helps for memory
1673 /// usage. (Admittedly, this is a rather small effect, though measurable.)
1675 /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1676 /// late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1677 /// regions with actual region variables as is proper, we'd have to ensure that the same
1678 /// region got replaced with the same variable, which requires a bit more coordination
1679 /// and/or tracking the substitution and
1681 fn erase_late_bound_regions<T>(&self, value: &ty::Binder<T>) -> T
1683 T: TypeFoldable<'tcx>,
1685 self.tcx.erase_late_bound_regions(value)
1688 /// Finds the method with the appropriate name (or return type, as the case may be). If
1689 /// `allow_similar_names` is set, find methods with close-matching names.
1690 fn impl_or_trait_item(&self, def_id: DefId) -> Vec<ty::AssocItem> {
1691 if let Some(name) = self.method_name {
1692 if self.allow_similar_names {
1693 let max_dist = max(name.as_str().len(), 3) / 3;
1695 .associated_items(def_id)
1696 .in_definition_order()
1698 let dist = lev_distance(&*name.as_str(), &x.ident.as_str());
1699 x.kind.namespace() == Namespace::ValueNS && dist > 0 && dist <= max_dist
1705 .associated_item(def_id, name, Namespace::ValueNS)
1706 .map_or(Vec::new(), |x| vec![x])
1709 self.tcx.associated_items(def_id).in_definition_order().copied().collect()
1714 impl<'tcx> Candidate<'tcx> {
1715 fn to_unadjusted_pick(&self) -> Pick<'tcx> {
1718 kind: match self.kind {
1719 InherentImplCandidate(..) => InherentImplPick,
1720 ObjectCandidate => ObjectPick,
1721 TraitCandidate(_) => TraitPick,
1722 WhereClauseCandidate(ref trait_ref) => {
1723 // Only trait derived from where-clauses should
1724 // appear here, so they should not contain any
1725 // inference variables or other artifacts. This
1726 // means they are safe to put into the
1727 // `WhereClausePick`.
1729 !trait_ref.skip_binder().substs.needs_infer()
1730 && !trait_ref.skip_binder().substs.has_placeholders()
1733 WhereClausePick(*trait_ref)
1736 import_ids: self.import_ids.clone(),