2 use super::MethodError;
3 use super::NoMatchData;
4 use super::{CandidateSource, ImplSource, TraitSource};
6 use crate::check::autoderef::{self, Autoderef};
7 use crate::check::FnCtxt;
8 use crate::hir::def::DefKind;
9 use crate::hir::def_id::DefId;
12 use rustc::middle::stability;
13 use rustc::session::config::nightly_options;
14 use rustc::ty::subst::{InternalSubsts, Subst, SubstsRef};
15 use rustc::ty::GenericParamDefKind;
17 self, ParamEnvAnd, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
20 use rustc_ast::util::lev_distance::{find_best_match_for_name, lev_distance};
21 use rustc_data_structures::fx::FxHashSet;
22 use rustc_data_structures::sync::Lrc;
23 use rustc_errors::struct_span_err;
25 use rustc_hir::def::Namespace;
26 use rustc_infer::infer::canonical::OriginalQueryValues;
27 use rustc_infer::infer::canonical::{Canonical, QueryResponse};
28 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
29 use rustc_infer::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
30 use rustc_infer::infer::{self, InferOk, TyCtxtInferExt};
31 use rustc_infer::traits::query::method_autoderef::MethodAutoderefBadTy;
32 use rustc_infer::traits::query::method_autoderef::{CandidateStep, MethodAutoderefStepsResult};
33 use rustc_infer::traits::query::CanonicalTyGoal;
34 use rustc_infer::traits::{self, ObligationCause};
35 use rustc_span::{symbol::Symbol, Span, DUMMY_SP};
41 use smallvec::{smallvec, SmallVec};
43 use self::CandidateKind::*;
44 pub use self::PickKind::*;
46 /// Boolean flag used to indicate if this search is for a suggestion
47 /// or not. If true, we can allow ambiguity and so forth.
48 #[derive(Clone, Copy)]
49 pub struct IsSuggestion(pub bool);
51 struct ProbeContext<'a, 'tcx> {
52 fcx: &'a FnCtxt<'a, 'tcx>,
55 method_name: Option<ast::Ident>,
56 return_type: Option<Ty<'tcx>>,
58 /// This is the OriginalQueryValues for the steps queries
59 /// that are answered in steps.
60 orig_steps_var_values: OriginalQueryValues<'tcx>,
61 steps: Lrc<Vec<CandidateStep<'tcx>>>,
63 inherent_candidates: Vec<Candidate<'tcx>>,
64 extension_candidates: Vec<Candidate<'tcx>>,
65 impl_dups: FxHashSet<DefId>,
67 /// Collects near misses when the candidate functions are missing a `self` keyword and is only
68 /// used for error reporting
69 static_candidates: Vec<CandidateSource>,
71 /// When probing for names, include names that are close to the
72 /// requested name (by Levensthein distance)
73 allow_similar_names: bool,
75 /// Some(candidate) if there is a private candidate
76 private_candidate: Option<(DefKind, DefId)>,
78 /// Collects near misses when trait bounds for type parameters are unsatisfied and is only used
79 /// for error reporting
80 unsatisfied_predicates: Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>)>,
82 is_suggestion: IsSuggestion,
85 impl<'a, 'tcx> Deref for ProbeContext<'a, 'tcx> {
86 type Target = FnCtxt<'a, 'tcx>;
87 fn deref(&self) -> &Self::Target {
93 struct Candidate<'tcx> {
94 // Candidates are (I'm not quite sure, but they are mostly) basically
95 // some metadata on top of a `ty::AssocItem` (without substs).
97 // However, method probing wants to be able to evaluate the predicates
98 // for a function with the substs applied - for example, if a function
99 // has `where Self: Sized`, we don't want to consider it unless `Self`
100 // is actually `Sized`, and similarly, return-type suggestions want
101 // to consider the "actual" return type.
103 // The way this is handled is through `xform_self_ty`. It contains
104 // the receiver type of this candidate, but `xform_self_ty`,
105 // `xform_ret_ty` and `kind` (which contains the predicates) have the
106 // generic parameters of this candidate substituted with the *same set*
107 // of inference variables, which acts as some weird sort of "query".
109 // When we check out a candidate, we require `xform_self_ty` to be
110 // a subtype of the passed-in self-type, and this equates the type
111 // variables in the rest of the fields.
113 // For example, if we have this candidate:
116 // fn foo(&self) where Self: Sized;
120 // Then `xform_self_ty` will be `&'erased ?X` and `kind` will contain
121 // the predicate `?X: Sized`, so if we are evaluating `Foo` for a
122 // the receiver `&T`, we'll do the subtyping which will make `?X`
123 // get the right value, then when we evaluate the predicate we'll check
125 xform_self_ty: Ty<'tcx>,
126 xform_ret_ty: Option<Ty<'tcx>>,
128 kind: CandidateKind<'tcx>,
129 import_ids: SmallVec<[hir::HirId; 1]>,
133 enum CandidateKind<'tcx> {
134 InherentImplCandidate(
136 // Normalize obligations
137 Vec<traits::PredicateObligation<'tcx>>,
140 TraitCandidate(ty::TraitRef<'tcx>),
141 WhereClauseCandidate(
143 ty::PolyTraitRef<'tcx>,
147 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
154 #[derive(Debug, PartialEq, Clone)]
155 pub struct Pick<'tcx> {
156 pub item: ty::AssocItem,
157 pub kind: PickKind<'tcx>,
158 pub import_ids: SmallVec<[hir::HirId; 1]>,
160 // Indicates that the source expression should be autoderef'd N times
162 // A = expr | *expr | **expr | ...
163 pub autoderefs: usize,
165 // Indicates that an autoref is applied after the optional autoderefs
167 // B = A | &A | &mut A
168 pub autoref: Option<hir::Mutability>,
170 // Indicates that the source expression should be "unsized" to a
171 // target type. This should probably eventually go away in favor
172 // of just coercing method receivers.
175 pub unsize: Option<Ty<'tcx>>,
178 #[derive(Clone, Debug, PartialEq, Eq)]
179 pub enum PickKind<'tcx> {
185 ty::PolyTraitRef<'tcx>,
189 pub type PickResult<'tcx> = Result<Pick<'tcx>, MethodError<'tcx>>;
191 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
193 // An expression of the form `receiver.method_name(...)`.
194 // Autoderefs are performed on `receiver`, lookup is done based on the
195 // `self` argument of the method, and static methods aren't considered.
197 // An expression of the form `Type::item` or `<T>::item`.
198 // No autoderefs are performed, lookup is done based on the type each
199 // implementation is for, and static methods are included.
203 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
204 pub enum ProbeScope {
205 // Assemble candidates coming only from traits in scope.
208 // Assemble candidates coming from all traits.
212 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
213 /// This is used to offer suggestions to users. It returns methods
214 /// that could have been called which have the desired return
215 /// type. Some effort is made to rule out methods that, if called,
216 /// would result in an error (basically, the same criteria we
217 /// would use to decide if a method is a plausible fit for
218 /// ambiguity purposes).
219 pub fn probe_for_return_type(
223 return_type: Ty<'tcx>,
225 scope_expr_id: hir::HirId,
226 ) -> Vec<ty::AssocItem> {
228 "probe(self_ty={:?}, return_type={}, scope_expr_id={})",
229 self_ty, return_type, scope_expr_id
231 let method_names = self
240 ProbeScope::AllTraits,
241 |probe_cx| Ok(probe_cx.candidate_method_names()),
246 .flat_map(|&method_name| {
255 ProbeScope::AllTraits,
256 |probe_cx| probe_cx.pick(),
259 .map(|pick| pick.item)
264 pub fn probe_for_name(
268 item_name: ast::Ident,
269 is_suggestion: IsSuggestion,
271 scope_expr_id: hir::HirId,
273 ) -> PickResult<'tcx> {
275 "probe(self_ty={:?}, item_name={}, scope_expr_id={})",
276 self_ty, item_name, scope_expr_id
287 |probe_cx| probe_cx.pick(),
295 method_name: Option<ast::Ident>,
296 return_type: Option<Ty<'tcx>>,
297 is_suggestion: IsSuggestion,
299 scope_expr_id: hir::HirId,
302 ) -> Result<R, MethodError<'tcx>>
304 OP: FnOnce(ProbeContext<'a, 'tcx>) -> Result<R, MethodError<'tcx>>,
306 let mut orig_values = OriginalQueryValues::default();
307 let param_env_and_self_ty = self.infcx.canonicalize_query(
308 &ParamEnvAnd { param_env: self.param_env, value: self_ty },
312 let steps = if mode == Mode::MethodCall {
313 self.tcx.method_autoderef_steps(param_env_and_self_ty)
315 self.infcx.probe(|_| {
316 // Mode::Path - the deref steps is "trivial". This turns
317 // our CanonicalQuery into a "trivial" QueryResponse. This
318 // is a bit inefficient, but I don't think that writing
319 // special handling for this "trivial case" is a good idea.
321 let infcx = &self.infcx;
322 let (ParamEnvAnd { param_env: _, value: self_ty }, canonical_inference_vars) =
323 infcx.instantiate_canonical_with_fresh_inference_vars(
325 ¶m_env_and_self_ty,
328 "probe_op: Mode::Path, param_env_and_self_ty={:?} self_ty={:?}",
329 param_env_and_self_ty, self_ty
331 MethodAutoderefStepsResult {
332 steps: Lrc::new(vec![CandidateStep {
333 self_ty: self.make_query_response_ignoring_pending_obligations(
334 canonical_inference_vars,
338 from_unsafe_deref: false,
342 reached_recursion_limit: false,
347 // If our autoderef loop had reached the recursion limit,
348 // report an overflow error, but continue going on with
349 // the truncated autoderef list.
350 if steps.reached_recursion_limit {
355 .unwrap_or_else(|| span_bug!(span, "reached the recursion limit in 0 steps?"))
358 .probe_instantiate_query_response(span, &orig_values, ty)
359 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
360 autoderef::report_autoderef_recursion_limit_error(self.tcx, span, ty.value);
364 // If we encountered an `_` type or an error type during autoderef, this is
366 if let Some(bad_ty) = &steps.opt_bad_ty {
368 // Ambiguity was encountered during a suggestion. Just keep going.
369 debug!("ProbeContext: encountered ambiguity in suggestion");
370 } else if bad_ty.reached_raw_pointer && !self.tcx.features().arbitrary_self_types {
371 // this case used to be allowed by the compiler,
372 // so we do a future-compat lint here for the 2015 edition
373 // (see https://github.com/rust-lang/rust/issues/46906)
374 if self.tcx.sess.rust_2018() {
379 "the type of this value must be known \
380 to call a method on a raw pointer on it"
384 self.tcx.struct_span_lint_hir(
385 lint::builtin::TYVAR_BEHIND_RAW_POINTER,
388 |lint| lint.build("type annotations needed").emit(),
392 // Encountered a real ambiguity, so abort the lookup. If `ty` is not
393 // an `Err`, report the right "type annotations needed" error pointing
397 .probe_instantiate_query_response(span, &orig_values, ty)
398 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
399 let ty = self.structurally_resolved_type(span, ty.value);
400 assert_eq!(ty, self.tcx.types.err);
401 return Err(MethodError::NoMatch(NoMatchData::new(
411 debug!("ProbeContext: steps for self_ty={:?} are {:?}", self_ty, steps);
413 // this creates one big transaction so that all type variables etc
414 // that we create during the probe process are removed later
416 let mut probe_cx = ProbeContext::new(
427 probe_cx.assemble_inherent_candidates();
429 ProbeScope::TraitsInScope => {
430 probe_cx.assemble_extension_candidates_for_traits_in_scope(scope_expr_id)?
432 ProbeScope::AllTraits => probe_cx.assemble_extension_candidates_for_all_traits()?,
439 pub fn provide(providers: &mut ty::query::Providers<'_>) {
440 providers.method_autoderef_steps = method_autoderef_steps;
443 fn method_autoderef_steps<'tcx>(
445 goal: CanonicalTyGoal<'tcx>,
446 ) -> MethodAutoderefStepsResult<'tcx> {
447 debug!("method_autoderef_steps({:?})", goal);
449 tcx.infer_ctxt().enter_with_canonical(DUMMY_SP, &goal, |ref infcx, goal, inference_vars| {
450 let ParamEnvAnd { param_env, value: self_ty } = goal;
452 let mut autoderef = Autoderef::new(infcx, param_env, hir::DUMMY_HIR_ID, DUMMY_SP, self_ty)
453 .include_raw_pointers()
455 let mut reached_raw_pointer = false;
456 let mut steps: Vec<_> = autoderef
459 let step = CandidateStep {
460 self_ty: infcx.make_query_response_ignoring_pending_obligations(
461 inference_vars.clone(),
465 from_unsafe_deref: reached_raw_pointer,
468 if let ty::RawPtr(_) = ty.kind {
469 // all the subsequent steps will be from_unsafe_deref
470 reached_raw_pointer = true;
476 let final_ty = autoderef.maybe_ambiguous_final_ty();
477 let opt_bad_ty = match final_ty.kind {
478 ty::Infer(ty::TyVar(_)) | ty::Error => Some(MethodAutoderefBadTy {
481 .make_query_response_ignoring_pending_obligations(inference_vars, final_ty),
483 ty::Array(elem_ty, _) => {
484 let dereferences = steps.len() - 1;
486 steps.push(CandidateStep {
487 self_ty: infcx.make_query_response_ignoring_pending_obligations(
489 infcx.tcx.mk_slice(elem_ty),
491 autoderefs: dereferences,
492 // this could be from an unsafe deref if we had
493 // a *mut/const [T; N]
494 from_unsafe_deref: reached_raw_pointer,
503 debug!("method_autoderef_steps: steps={:?} opt_bad_ty={:?}", steps, opt_bad_ty);
505 MethodAutoderefStepsResult {
506 steps: Lrc::new(steps),
507 opt_bad_ty: opt_bad_ty.map(Lrc::new),
508 reached_recursion_limit: autoderef.reached_recursion_limit(),
513 impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
515 fcx: &'a FnCtxt<'a, 'tcx>,
518 method_name: Option<ast::Ident>,
519 return_type: Option<Ty<'tcx>>,
520 orig_steps_var_values: OriginalQueryValues<'tcx>,
521 steps: Lrc<Vec<CandidateStep<'tcx>>>,
522 is_suggestion: IsSuggestion,
523 ) -> ProbeContext<'a, 'tcx> {
530 inherent_candidates: Vec::new(),
531 extension_candidates: Vec::new(),
532 impl_dups: FxHashSet::default(),
533 orig_steps_var_values,
535 static_candidates: Vec::new(),
536 allow_similar_names: false,
537 private_candidate: None,
538 unsatisfied_predicates: Vec::new(),
543 fn reset(&mut self) {
544 self.inherent_candidates.clear();
545 self.extension_candidates.clear();
546 self.impl_dups.clear();
547 self.static_candidates.clear();
548 self.private_candidate = None;
551 ///////////////////////////////////////////////////////////////////////////
552 // CANDIDATE ASSEMBLY
554 fn push_candidate(&mut self, candidate: Candidate<'tcx>, is_inherent: bool) {
555 let is_accessible = if let Some(name) = self.method_name {
556 let item = candidate.item;
558 self.tcx.adjust_ident_and_get_scope(name, item.container.id(), self.body_id).1;
559 item.vis.is_accessible_from(def_scope, self.tcx)
565 self.inherent_candidates.push(candidate);
567 self.extension_candidates.push(candidate);
569 } else if self.private_candidate.is_none() {
570 self.private_candidate = Some((candidate.item.def_kind(), candidate.item.def_id));
574 fn assemble_inherent_candidates(&mut self) {
575 let steps = self.steps.clone();
576 for step in steps.iter() {
577 self.assemble_probe(&step.self_ty);
581 fn assemble_probe(&mut self, self_ty: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>) {
582 debug!("assemble_probe: self_ty={:?}", self_ty);
583 let lang_items = self.tcx.lang_items();
585 match self_ty.value.value.kind {
586 ty::Dynamic(ref data, ..) => {
587 if let Some(p) = data.principal() {
588 // Subtle: we can't use `instantiate_query_response` here: using it will
589 // commit to all of the type equalities assumed by inference going through
590 // autoderef (see the `method-probe-no-guessing` test).
592 // However, in this code, it is OK if we end up with an object type that is
593 // "more general" than the object type that we are evaluating. For *every*
594 // object type `MY_OBJECT`, a function call that goes through a trait-ref
595 // of the form `<MY_OBJECT as SuperTraitOf(MY_OBJECT)>::func` is a valid
596 // `ObjectCandidate`, and it should be discoverable "exactly" through one
597 // of the iterations in the autoderef loop, so there is no problem with it
598 // being discoverable in another one of these iterations.
600 // Using `instantiate_canonical_with_fresh_inference_vars` on our
601 // `Canonical<QueryResponse<Ty<'tcx>>>` and then *throwing away* the
602 // `CanonicalVarValues` will exactly give us such a generalization - it
603 // will still match the original object type, but it won't pollute our
604 // type variables in any form, so just do that!
605 let (QueryResponse { value: generalized_self_ty, .. }, _ignored_var_values) =
607 .instantiate_canonical_with_fresh_inference_vars(self.span, &self_ty);
609 self.assemble_inherent_candidates_from_object(generalized_self_ty);
610 self.assemble_inherent_impl_candidates_for_type(p.def_id());
614 self.assemble_inherent_impl_candidates_for_type(def.did);
616 ty::Foreign(did) => {
617 self.assemble_inherent_impl_candidates_for_type(did);
620 self.assemble_inherent_candidates_from_param(p);
623 let lang_def_id = lang_items.bool_impl();
624 self.assemble_inherent_impl_for_primitive(lang_def_id);
627 let lang_def_id = lang_items.char_impl();
628 self.assemble_inherent_impl_for_primitive(lang_def_id);
631 let lang_def_id = lang_items.str_impl();
632 self.assemble_inherent_impl_for_primitive(lang_def_id);
634 let lang_def_id = lang_items.str_alloc_impl();
635 self.assemble_inherent_impl_for_primitive(lang_def_id);
638 let lang_def_id = lang_items.slice_impl();
639 self.assemble_inherent_impl_for_primitive(lang_def_id);
641 let lang_def_id = lang_items.slice_u8_impl();
642 self.assemble_inherent_impl_for_primitive(lang_def_id);
644 let lang_def_id = lang_items.slice_alloc_impl();
645 self.assemble_inherent_impl_for_primitive(lang_def_id);
647 let lang_def_id = lang_items.slice_u8_alloc_impl();
648 self.assemble_inherent_impl_for_primitive(lang_def_id);
650 ty::RawPtr(ty::TypeAndMut { ty: _, mutbl: hir::Mutability::Not }) => {
651 let lang_def_id = lang_items.const_ptr_impl();
652 self.assemble_inherent_impl_for_primitive(lang_def_id);
654 ty::RawPtr(ty::TypeAndMut { ty: _, mutbl: hir::Mutability::Mut }) => {
655 let lang_def_id = lang_items.mut_ptr_impl();
656 self.assemble_inherent_impl_for_primitive(lang_def_id);
658 ty::Int(ast::IntTy::I8) => {
659 let lang_def_id = lang_items.i8_impl();
660 self.assemble_inherent_impl_for_primitive(lang_def_id);
662 ty::Int(ast::IntTy::I16) => {
663 let lang_def_id = lang_items.i16_impl();
664 self.assemble_inherent_impl_for_primitive(lang_def_id);
666 ty::Int(ast::IntTy::I32) => {
667 let lang_def_id = lang_items.i32_impl();
668 self.assemble_inherent_impl_for_primitive(lang_def_id);
670 ty::Int(ast::IntTy::I64) => {
671 let lang_def_id = lang_items.i64_impl();
672 self.assemble_inherent_impl_for_primitive(lang_def_id);
674 ty::Int(ast::IntTy::I128) => {
675 let lang_def_id = lang_items.i128_impl();
676 self.assemble_inherent_impl_for_primitive(lang_def_id);
678 ty::Int(ast::IntTy::Isize) => {
679 let lang_def_id = lang_items.isize_impl();
680 self.assemble_inherent_impl_for_primitive(lang_def_id);
682 ty::Uint(ast::UintTy::U8) => {
683 let lang_def_id = lang_items.u8_impl();
684 self.assemble_inherent_impl_for_primitive(lang_def_id);
686 ty::Uint(ast::UintTy::U16) => {
687 let lang_def_id = lang_items.u16_impl();
688 self.assemble_inherent_impl_for_primitive(lang_def_id);
690 ty::Uint(ast::UintTy::U32) => {
691 let lang_def_id = lang_items.u32_impl();
692 self.assemble_inherent_impl_for_primitive(lang_def_id);
694 ty::Uint(ast::UintTy::U64) => {
695 let lang_def_id = lang_items.u64_impl();
696 self.assemble_inherent_impl_for_primitive(lang_def_id);
698 ty::Uint(ast::UintTy::U128) => {
699 let lang_def_id = lang_items.u128_impl();
700 self.assemble_inherent_impl_for_primitive(lang_def_id);
702 ty::Uint(ast::UintTy::Usize) => {
703 let lang_def_id = lang_items.usize_impl();
704 self.assemble_inherent_impl_for_primitive(lang_def_id);
706 ty::Float(ast::FloatTy::F32) => {
707 let lang_def_id = lang_items.f32_impl();
708 self.assemble_inherent_impl_for_primitive(lang_def_id);
710 let lang_def_id = lang_items.f32_runtime_impl();
711 self.assemble_inherent_impl_for_primitive(lang_def_id);
713 ty::Float(ast::FloatTy::F64) => {
714 let lang_def_id = lang_items.f64_impl();
715 self.assemble_inherent_impl_for_primitive(lang_def_id);
717 let lang_def_id = lang_items.f64_runtime_impl();
718 self.assemble_inherent_impl_for_primitive(lang_def_id);
724 fn assemble_inherent_impl_for_primitive(&mut self, lang_def_id: Option<DefId>) {
725 if let Some(impl_def_id) = lang_def_id {
726 self.assemble_inherent_impl_probe(impl_def_id);
730 fn assemble_inherent_impl_candidates_for_type(&mut self, def_id: DefId) {
731 let impl_def_ids = self.tcx.at(self.span).inherent_impls(def_id);
732 for &impl_def_id in impl_def_ids.iter() {
733 self.assemble_inherent_impl_probe(impl_def_id);
737 fn assemble_inherent_impl_probe(&mut self, impl_def_id: DefId) {
738 if !self.impl_dups.insert(impl_def_id) {
739 return; // already visited
742 debug!("assemble_inherent_impl_probe {:?}", impl_def_id);
744 for item in self.impl_or_trait_item(impl_def_id) {
745 if !self.has_applicable_self(&item) {
746 // No receiver declared. Not a candidate.
747 self.record_static_candidate(ImplSource(impl_def_id));
751 let (impl_ty, impl_substs) = self.impl_ty_and_substs(impl_def_id);
752 let impl_ty = impl_ty.subst(self.tcx, impl_substs);
754 // Determine the receiver type that the method itself expects.
755 let xform_tys = self.xform_self_ty(&item, impl_ty, impl_substs);
757 // We can't use normalize_associated_types_in as it will pollute the
758 // fcx's fulfillment context after this probe is over.
759 let cause = traits::ObligationCause::misc(self.span, self.body_id);
760 let selcx = &mut traits::SelectionContext::new(self.fcx);
761 let traits::Normalized { value: (xform_self_ty, xform_ret_ty), obligations } =
762 traits::normalize(selcx, self.param_env, cause, &xform_tys);
764 "assemble_inherent_impl_probe: xform_self_ty = {:?}/{:?}",
765 xform_self_ty, xform_ret_ty
773 kind: InherentImplCandidate(impl_substs, obligations),
774 import_ids: smallvec![],
781 fn assemble_inherent_candidates_from_object(&mut self, self_ty: Ty<'tcx>) {
782 debug!("assemble_inherent_candidates_from_object(self_ty={:?})", self_ty);
784 let principal = match self_ty.kind {
785 ty::Dynamic(ref data, ..) => Some(data),
788 .and_then(|data| data.principal())
792 "non-object {:?} in assemble_inherent_candidates_from_object",
797 // It is illegal to invoke a method on a trait instance that
798 // refers to the `Self` type. An error will be reported by
799 // `enforce_object_limitations()` if the method refers to the
800 // `Self` type anywhere other than the receiver. Here, we use
801 // a substitution that replaces `Self` with the object type
802 // itself. Hence, a `&self` method will wind up with an
803 // argument type like `&Trait`.
804 let trait_ref = principal.with_self_ty(self.tcx, self_ty);
805 self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
806 let new_trait_ref = this.erase_late_bound_regions(&new_trait_ref);
808 let (xform_self_ty, xform_ret_ty) =
809 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
815 kind: ObjectCandidate,
816 import_ids: smallvec![],
823 fn assemble_inherent_candidates_from_param(&mut self, param_ty: ty::ParamTy) {
824 // FIXME: do we want to commit to this behavior for param bounds?
826 let bounds = self.param_env.caller_bounds.iter().filter_map(|predicate| match *predicate {
827 ty::Predicate::Trait(ref trait_predicate, _) => {
828 match trait_predicate.skip_binder().trait_ref.self_ty().kind {
829 ty::Param(ref p) if *p == param_ty => Some(trait_predicate.to_poly_trait_ref()),
833 ty::Predicate::Subtype(..)
834 | ty::Predicate::Projection(..)
835 | ty::Predicate::RegionOutlives(..)
836 | ty::Predicate::WellFormed(..)
837 | ty::Predicate::ObjectSafe(..)
838 | ty::Predicate::ClosureKind(..)
839 | ty::Predicate::TypeOutlives(..)
840 | ty::Predicate::ConstEvaluatable(..) => None,
843 self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
844 let trait_ref = this.erase_late_bound_regions(&poly_trait_ref);
846 let (xform_self_ty, xform_ret_ty) =
847 this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs);
849 // Because this trait derives from a where-clause, it
850 // should not contain any inference variables or other
851 // artifacts. This means it is safe to put into the
852 // `WhereClauseCandidate` and (eventually) into the
853 // `WhereClausePick`.
854 assert!(!trait_ref.substs.needs_infer());
861 kind: WhereClauseCandidate(poly_trait_ref),
862 import_ids: smallvec![],
869 // Do a search through a list of bounds, using a callback to actually
870 // create the candidates.
871 fn elaborate_bounds<F>(
873 bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
876 F: for<'b> FnMut(&mut ProbeContext<'b, 'tcx>, ty::PolyTraitRef<'tcx>, ty::AssocItem),
879 for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
880 debug!("elaborate_bounds(bound_trait_ref={:?})", bound_trait_ref);
881 for item in self.impl_or_trait_item(bound_trait_ref.def_id()) {
882 if !self.has_applicable_self(&item) {
883 self.record_static_candidate(TraitSource(bound_trait_ref.def_id()));
885 mk_cand(self, bound_trait_ref, item);
891 fn assemble_extension_candidates_for_traits_in_scope(
893 expr_hir_id: hir::HirId,
894 ) -> Result<(), MethodError<'tcx>> {
895 if expr_hir_id == hir::DUMMY_HIR_ID {
898 let mut duplicates = FxHashSet::default();
899 let opt_applicable_traits = self.tcx.in_scope_traits(expr_hir_id);
900 if let Some(applicable_traits) = opt_applicable_traits {
901 for trait_candidate in applicable_traits.iter() {
902 let trait_did = trait_candidate.def_id;
903 if duplicates.insert(trait_did) {
904 let result = self.assemble_extension_candidates_for_trait(
905 &trait_candidate.import_ids,
915 fn assemble_extension_candidates_for_all_traits(&mut self) -> Result<(), MethodError<'tcx>> {
916 let mut duplicates = FxHashSet::default();
917 for trait_info in suggest::all_traits(self.tcx) {
918 if duplicates.insert(trait_info.def_id) {
919 self.assemble_extension_candidates_for_trait(&smallvec![], trait_info.def_id)?;
925 pub fn matches_return_type(
927 method: &ty::AssocItem,
928 self_ty: Option<Ty<'tcx>>,
932 ty::AssocKind::Method => {
933 let fty = self.tcx.fn_sig(method.def_id);
935 let substs = self.fresh_substs_for_item(self.span, method.def_id);
936 let fty = fty.subst(self.tcx, substs);
938 self.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, &fty);
940 if let Some(self_ty) = self_ty {
942 .at(&ObligationCause::dummy(), self.param_env)
943 .sup(fty.inputs()[0], self_ty)
949 self.can_sub(self.param_env, fty.output(), expected).is_ok()
956 fn assemble_extension_candidates_for_trait(
958 import_ids: &SmallVec<[hir::HirId; 1]>,
960 ) -> Result<(), MethodError<'tcx>> {
961 debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})", trait_def_id);
962 let trait_substs = self.fresh_item_substs(trait_def_id);
963 let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
965 if self.tcx.is_trait_alias(trait_def_id) {
966 // For trait aliases, assume all super-traits are relevant.
967 let bounds = iter::once(trait_ref.to_poly_trait_ref());
968 self.elaborate_bounds(bounds, |this, new_trait_ref, item| {
969 let new_trait_ref = this.erase_late_bound_regions(&new_trait_ref);
971 let (xform_self_ty, xform_ret_ty) =
972 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
978 import_ids: import_ids.clone(),
979 kind: TraitCandidate(new_trait_ref),
985 debug_assert!(self.tcx.is_trait(trait_def_id));
986 for item in self.impl_or_trait_item(trait_def_id) {
987 // Check whether `trait_def_id` defines a method with suitable name.
988 if !self.has_applicable_self(&item) {
989 debug!("method has inapplicable self");
990 self.record_static_candidate(TraitSource(trait_def_id));
994 let (xform_self_ty, xform_ret_ty) =
995 self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
1001 import_ids: import_ids.clone(),
1002 kind: TraitCandidate(trait_ref),
1011 fn candidate_method_names(&self) -> Vec<ast::Ident> {
1012 let mut set = FxHashSet::default();
1013 let mut names: Vec<_> = self
1014 .inherent_candidates
1016 .chain(&self.extension_candidates)
1017 .filter(|candidate| {
1018 if let Some(return_ty) = self.return_type {
1019 self.matches_return_type(&candidate.item, None, return_ty)
1024 .map(|candidate| candidate.item.ident)
1025 .filter(|&name| set.insert(name))
1028 // Sort them by the name so we have a stable result.
1029 names.sort_by_cached_key(|n| n.as_str());
1033 ///////////////////////////////////////////////////////////////////////////
1034 // THE ACTUAL SEARCH
1036 fn pick(mut self) -> PickResult<'tcx> {
1037 assert!(self.method_name.is_some());
1039 if let Some(r) = self.pick_core() {
1043 debug!("pick: actual search failed, assemble diagnotics");
1045 let static_candidates = mem::take(&mut self.static_candidates);
1046 let private_candidate = self.private_candidate.take();
1047 let unsatisfied_predicates = mem::take(&mut self.unsatisfied_predicates);
1049 // things failed, so lets look at all traits, for diagnostic purposes now:
1052 let span = self.span;
1055 self.assemble_extension_candidates_for_all_traits()?;
1057 let out_of_scope_traits = match self.pick_core() {
1058 Some(Ok(p)) => vec![p.item.container.id()],
1059 //Some(Ok(p)) => p.iter().map(|p| p.item.container().id()).collect(),
1060 Some(Err(MethodError::Ambiguity(v))) => v
1062 .map(|source| match source {
1063 TraitSource(id) => id,
1064 ImplSource(impl_id) => match tcx.trait_id_of_impl(impl_id) {
1066 None => span_bug!(span, "found inherent method when looking at traits"),
1070 Some(Err(MethodError::NoMatch(NoMatchData {
1071 out_of_scope_traits: others, ..
1073 assert!(others.is_empty());
1079 if let Some((kind, def_id)) = private_candidate {
1080 return Err(MethodError::PrivateMatch(kind, def_id, out_of_scope_traits));
1082 let lev_candidate = self.probe_for_lev_candidate()?;
1084 Err(MethodError::NoMatch(NoMatchData::new(
1086 unsatisfied_predicates,
1087 out_of_scope_traits,
1093 fn pick_core(&mut self) -> Option<PickResult<'tcx>> {
1094 let steps = self.steps.clone();
1096 // find the first step that works
1100 debug!("pick_core: step={:?}", step);
1101 // skip types that are from a type error or that would require dereferencing
1103 !step.self_ty.references_error() && !step.from_unsafe_deref
1106 let InferOk { value: self_ty, obligations: _ } = self
1108 .probe_instantiate_query_response(
1110 &self.orig_steps_var_values,
1113 .unwrap_or_else(|_| {
1114 span_bug!(self.span, "{:?} was applicable but now isn't?", step.self_ty)
1116 self.pick_by_value_method(step, self_ty).or_else(|| {
1117 self.pick_autorefd_method(step, self_ty, hir::Mutability::Not)
1118 .or_else(|| self.pick_autorefd_method(step, self_ty, hir::Mutability::Mut))
1124 fn pick_by_value_method(
1126 step: &CandidateStep<'tcx>,
1128 ) -> Option<PickResult<'tcx>> {
1129 //! For each type `T` in the step list, this attempts to find a
1130 //! method where the (transformed) self type is exactly `T`. We
1131 //! do however do one transformation on the adjustment: if we
1132 //! are passing a region pointer in, we will potentially
1133 //! *reborrow* it to a shorter lifetime. This allows us to
1134 //! transparently pass `&mut` pointers, in particular, without
1135 //! consuming them for their entire lifetime.
1141 self.pick_method(self_ty).map(|r| {
1143 pick.autoderefs = step.autoderefs;
1145 // Insert a `&*` or `&mut *` if this is a reference type:
1146 if let ty::Ref(_, _, mutbl) = step.self_ty.value.value.kind {
1147 pick.autoderefs += 1;
1148 pick.autoref = Some(mutbl);
1156 fn pick_autorefd_method(
1158 step: &CandidateStep<'tcx>,
1160 mutbl: hir::Mutability,
1161 ) -> Option<PickResult<'tcx>> {
1164 // In general, during probing we erase regions. See
1165 // `impl_self_ty()` for an explanation.
1166 let region = tcx.lifetimes.re_erased;
1168 let autoref_ty = tcx.mk_ref(region, ty::TypeAndMut { ty: self_ty, mutbl });
1169 self.pick_method(autoref_ty).map(|r| {
1171 pick.autoderefs = step.autoderefs;
1172 pick.autoref = Some(mutbl);
1173 pick.unsize = step.unsize.then_some(self_ty);
1179 fn pick_method(&mut self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
1180 debug!("pick_method(self_ty={})", self.ty_to_string(self_ty));
1182 let mut possibly_unsatisfied_predicates = Vec::new();
1183 let mut unstable_candidates = Vec::new();
1185 for (kind, candidates) in
1186 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1188 debug!("searching {} candidates", kind);
1189 let res = self.consider_candidates(
1192 &mut possibly_unsatisfied_predicates,
1193 Some(&mut unstable_candidates),
1195 if let Some(pick) = res {
1196 if !self.is_suggestion.0 && !unstable_candidates.is_empty() {
1197 if let Ok(p) = &pick {
1198 // Emit a lint if there are unstable candidates alongside the stable ones.
1200 // We suppress warning if we're picking the method only because it is a
1202 self.emit_unstable_name_collision_hint(p, &unstable_candidates);
1209 debug!("searching unstable candidates");
1210 let res = self.consider_candidates(
1212 unstable_candidates.into_iter().map(|(c, _)| c),
1213 &mut possibly_unsatisfied_predicates,
1217 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1222 fn consider_candidates<'b, ProbesIter>(
1226 possibly_unsatisfied_predicates: &mut Vec<(
1227 ty::Predicate<'tcx>,
1228 Option<ty::Predicate<'tcx>>,
1230 unstable_candidates: Option<&mut Vec<(&'b Candidate<'tcx>, Symbol)>>,
1231 ) -> Option<PickResult<'tcx>>
1233 ProbesIter: Iterator<Item = &'b Candidate<'tcx>> + Clone,
1235 let mut applicable_candidates: Vec<_> = probes
1238 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
1240 .filter(|&(_, status)| status != ProbeResult::NoMatch)
1243 debug!("applicable_candidates: {:?}", applicable_candidates);
1245 if applicable_candidates.len() > 1 {
1246 if let Some(pick) = self.collapse_candidates_to_trait_pick(&applicable_candidates[..]) {
1247 return Some(Ok(pick));
1251 if let Some(uc) = unstable_candidates {
1252 applicable_candidates.retain(|&(p, _)| {
1253 if let stability::EvalResult::Deny { feature, .. } =
1254 self.tcx.eval_stability(p.item.def_id, None, self.span)
1256 uc.push((p, feature));
1263 if applicable_candidates.len() > 1 {
1264 let sources = probes.map(|p| self.candidate_source(p, self_ty)).collect();
1265 return Some(Err(MethodError::Ambiguity(sources)));
1268 applicable_candidates.pop().map(|(probe, status)| {
1269 if status == ProbeResult::Match {
1270 Ok(probe.to_unadjusted_pick())
1272 Err(MethodError::BadReturnType)
1277 fn emit_unstable_name_collision_hint(
1279 stable_pick: &Pick<'_>,
1280 unstable_candidates: &[(&Candidate<'tcx>, Symbol)],
1282 self.tcx.struct_span_lint_hir(
1283 lint::builtin::UNSTABLE_NAME_COLLISIONS,
1287 let mut diag = lint.build(
1288 "a method with this name may be added to the standard library in the future",
1290 // FIXME: This should be a `span_suggestion` instead of `help`
1291 // However `self.span` only
1292 // highlights the method name, so we can't use it. Also consider reusing the code from
1293 // `report_method_error()`.
1295 "call with fully qualified syntax `{}(...)` to keep using the current method",
1296 self.tcx.def_path_str(stable_pick.item.def_id),
1299 if nightly_options::is_nightly_build() {
1300 for (candidate, feature) in unstable_candidates {
1302 "add `#![feature({})]` to the crate attributes to enable `{}`",
1304 self.tcx.def_path_str(candidate.item.def_id),
1314 fn select_trait_candidate(
1316 trait_ref: ty::TraitRef<'tcx>,
1317 ) -> traits::SelectionResult<'tcx, traits::Selection<'tcx>> {
1318 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1319 let predicate = trait_ref.to_poly_trait_ref().to_poly_trait_predicate();
1320 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1321 traits::SelectionContext::new(self).select(&obligation)
1324 fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>) -> CandidateSource {
1325 match candidate.kind {
1326 InherentImplCandidate(..) => ImplSource(candidate.item.container.id()),
1327 ObjectCandidate | WhereClauseCandidate(_) => TraitSource(candidate.item.container.id()),
1328 TraitCandidate(trait_ref) => self.probe(|_| {
1330 .at(&ObligationCause::dummy(), self.param_env)
1331 .sup(candidate.xform_self_ty, self_ty);
1332 match self.select_trait_candidate(trait_ref) {
1333 Ok(Some(traits::Vtable::VtableImpl(ref impl_data))) => {
1334 // If only a single impl matches, make the error message point
1336 ImplSource(impl_data.impl_def_id)
1338 _ => TraitSource(candidate.item.container.id()),
1347 probe: &Candidate<'tcx>,
1348 possibly_unsatisfied_predicates: &mut Vec<(
1349 ty::Predicate<'tcx>,
1350 Option<ty::Predicate<'tcx>>,
1353 debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe);
1356 // First check that the self type can be related.
1357 let sub_obligations = match self
1358 .at(&ObligationCause::dummy(), self.param_env)
1359 .sup(probe.xform_self_ty, self_ty)
1361 Ok(InferOk { obligations, value: () }) => obligations,
1363 debug!("--> cannot relate self-types");
1364 return ProbeResult::NoMatch;
1368 let mut result = ProbeResult::Match;
1369 let selcx = &mut traits::SelectionContext::new(self);
1370 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1372 // If so, impls may carry other conditions (e.g., where
1373 // clauses) that must be considered. Make sure that those
1374 // match as well (or at least may match, sometimes we
1375 // don't have enough information to fully evaluate).
1376 let candidate_obligations: Vec<_> = match probe.kind {
1377 InherentImplCandidate(ref substs, ref ref_obligations) => {
1378 // Check whether the impl imposes obligations we have to worry about.
1379 let impl_def_id = probe.item.container.id();
1380 let impl_bounds = self.tcx.predicates_of(impl_def_id);
1381 let impl_bounds = impl_bounds.instantiate(self.tcx, substs);
1382 let traits::Normalized { value: impl_bounds, obligations: norm_obligations } =
1383 traits::normalize(selcx, self.param_env, cause.clone(), &impl_bounds);
1385 // Convert the bounds into obligations.
1386 let impl_obligations =
1387 traits::predicates_for_generics(cause, self.param_env, &impl_bounds);
1389 debug!("impl_obligations={:?}", impl_obligations);
1392 .chain(norm_obligations.into_iter())
1393 .chain(ref_obligations.iter().cloned())
1397 ObjectCandidate | WhereClauseCandidate(..) => {
1398 // These have no additional conditions to check.
1402 TraitCandidate(trait_ref) => {
1403 let predicate = trait_ref.without_const().to_predicate();
1404 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1405 if !self.predicate_may_hold(&obligation) {
1407 match self.select_trait_candidate(trait_ref) {
1408 Err(_) => return true,
1410 if !vtable.borrow_nested_obligations().is_empty() =>
1412 for obligation in vtable.borrow_nested_obligations() {
1413 // Determine exactly which obligation wasn't met, so
1414 // that we can give more context in the error.
1415 if !self.predicate_may_hold(&obligation) {
1416 result = ProbeResult::NoMatch;
1417 let o = self.resolve_vars_if_possible(obligation);
1419 self.resolve_vars_if_possible(&predicate);
1420 let p = if predicate == o.predicate {
1421 // Avoid "`MyStruct: Foo` which is required by
1422 // `MyStruct: Foo`" in E0599.
1427 possibly_unsatisfied_predicates.push((o.predicate, p));
1432 // Some nested subobligation of this predicate
1434 result = ProbeResult::NoMatch;
1435 let predicate = self.resolve_vars_if_possible(&predicate);
1436 possibly_unsatisfied_predicates.push((predicate, None));
1441 // This candidate's primary obligation doesn't even
1442 // select - don't bother registering anything in
1443 // `potentially_unsatisfied_predicates`.
1444 return ProbeResult::NoMatch;
1452 "consider_probe - candidate_obligations={:?} sub_obligations={:?}",
1453 candidate_obligations, sub_obligations
1456 // Evaluate those obligations to see if they might possibly hold.
1457 for o in candidate_obligations.into_iter().chain(sub_obligations) {
1458 let o = self.resolve_vars_if_possible(&o);
1459 if !self.predicate_may_hold(&o) {
1460 result = ProbeResult::NoMatch;
1461 possibly_unsatisfied_predicates.push((o.predicate, None));
1465 if let ProbeResult::Match = result {
1466 if let (Some(return_ty), Some(xform_ret_ty)) =
1467 (self.return_type, probe.xform_ret_ty)
1469 let xform_ret_ty = self.resolve_vars_if_possible(&xform_ret_ty);
1471 "comparing return_ty {:?} with xform ret ty {:?}",
1472 return_ty, probe.xform_ret_ty
1475 .at(&ObligationCause::dummy(), self.param_env)
1476 .sup(return_ty, xform_ret_ty)
1479 return ProbeResult::BadReturnType;
1488 /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1489 /// same trait, but we don't know which impl to use. In this case, since in all cases the
1490 /// external interface of the method can be determined from the trait, it's ok not to decide.
1491 /// We can basically just collapse all of the probes for various impls into one where-clause
1492 /// probe. This will result in a pending obligation so when more type-info is available we can
1493 /// make the final decision.
1495 /// Example (`src/test/ui/method-two-trait-defer-resolution-1.rs`):
1498 /// trait Foo { ... }
1499 /// impl Foo for Vec<int> { ... }
1500 /// impl Foo for Vec<usize> { ... }
1503 /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1504 /// use, so it's ok to just commit to "using the method from the trait Foo".
1505 fn collapse_candidates_to_trait_pick(
1507 probes: &[(&Candidate<'tcx>, ProbeResult)],
1508 ) -> Option<Pick<'tcx>> {
1509 // Do all probes correspond to the same trait?
1510 let container = probes[0].0.item.container;
1511 if let ty::ImplContainer(_) = container {
1514 if probes[1..].iter().any(|&(p, _)| p.item.container != container) {
1518 // FIXME: check the return type here somehow.
1519 // If so, just use this trait and call it a day.
1521 item: probes[0].0.item,
1523 import_ids: probes[0].0.import_ids.clone(),
1530 /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
1531 /// candidate method where the method name may have been misspelt. Similarly to other
1532 /// Levenshtein based suggestions, we provide at most one such suggestion.
1533 fn probe_for_lev_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
1534 debug!("probing for method names similar to {:?}", self.method_name);
1536 let steps = self.steps.clone();
1538 let mut pcx = ProbeContext::new(
1544 self.orig_steps_var_values.clone(),
1548 pcx.allow_similar_names = true;
1549 pcx.assemble_inherent_candidates();
1550 pcx.assemble_extension_candidates_for_traits_in_scope(hir::DUMMY_HIR_ID)?;
1552 let method_names = pcx.candidate_method_names();
1553 pcx.allow_similar_names = false;
1554 let applicable_close_candidates: Vec<ty::AssocItem> =
1557 .filter_map(|&method_name| {
1559 pcx.method_name = Some(method_name);
1560 pcx.assemble_inherent_candidates();
1561 pcx.assemble_extension_candidates_for_traits_in_scope(hir::DUMMY_HIR_ID)
1564 .and_then(|pick| pick.ok())
1565 .and_then(|pick| Some(pick.item))
1570 if applicable_close_candidates.is_empty() {
1574 let names = applicable_close_candidates.iter().map(|cand| &cand.ident.name);
1575 find_best_match_for_name(names, &self.method_name.unwrap().as_str(), None)
1578 Ok(applicable_close_candidates
1580 .find(|method| method.ident.name == best_name))
1585 ///////////////////////////////////////////////////////////////////////////
1587 fn has_applicable_self(&self, item: &ty::AssocItem) -> bool {
1588 // "Fast track" -- check for usage of sugar when in method call
1591 // In Path mode (i.e., resolving a value like `T::next`), consider any
1592 // associated value (i.e., methods, constants) but not types.
1594 Mode::MethodCall => item.method_has_self_argument,
1595 Mode::Path => match item.kind {
1596 ty::AssocKind::OpaqueTy | ty::AssocKind::Type => false,
1597 ty::AssocKind::Method | ty::AssocKind::Const => true,
1600 // FIXME -- check for types that deref to `Self`,
1601 // like `Rc<Self>` and so on.
1603 // Note also that the current code will break if this type
1604 // includes any of the type parameters defined on the method
1605 // -- but this could be overcome.
1608 fn record_static_candidate(&mut self, source: CandidateSource) {
1609 self.static_candidates.push(source);
1614 item: &ty::AssocItem,
1616 substs: SubstsRef<'tcx>,
1617 ) -> (Ty<'tcx>, Option<Ty<'tcx>>) {
1618 if item.kind == ty::AssocKind::Method && self.mode == Mode::MethodCall {
1619 let sig = self.xform_method_sig(item.def_id, substs);
1620 (sig.inputs()[0], Some(sig.output()))
1626 fn xform_method_sig(&self, method: DefId, substs: SubstsRef<'tcx>) -> ty::FnSig<'tcx> {
1627 let fn_sig = self.tcx.fn_sig(method);
1628 debug!("xform_self_ty(fn_sig={:?}, substs={:?})", fn_sig, substs);
1630 assert!(!substs.has_escaping_bound_vars());
1632 // It is possible for type parameters or early-bound lifetimes
1633 // to appear in the signature of `self`. The substitutions we
1634 // are given do not include type/lifetime parameters for the
1635 // method yet. So create fresh variables here for those too,
1636 // if there are any.
1637 let generics = self.tcx.generics_of(method);
1638 assert_eq!(substs.len(), generics.parent_count as usize);
1640 // Erase any late-bound regions from the method and substitute
1641 // in the values from the substitution.
1642 let xform_fn_sig = self.erase_late_bound_regions(&fn_sig);
1644 if generics.params.is_empty() {
1645 xform_fn_sig.subst(self.tcx, substs)
1647 let substs = InternalSubsts::for_item(self.tcx, method, |param, _| {
1648 let i = param.index as usize;
1649 if i < substs.len() {
1653 GenericParamDefKind::Lifetime => {
1654 // In general, during probe we erase regions. See
1655 // `impl_self_ty()` for an explanation.
1656 self.tcx.lifetimes.re_erased.into()
1658 GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => {
1659 self.var_for_def(self.span, param)
1664 xform_fn_sig.subst(self.tcx, substs)
1668 /// Gets the type of an impl and generate substitutions with placeholders.
1669 fn impl_ty_and_substs(&self, impl_def_id: DefId) -> (Ty<'tcx>, SubstsRef<'tcx>) {
1670 (self.tcx.type_of(impl_def_id), self.fresh_item_substs(impl_def_id))
1673 fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx> {
1674 InternalSubsts::for_item(self.tcx, def_id, |param, _| match param.kind {
1675 GenericParamDefKind::Lifetime => self.tcx.lifetimes.re_erased.into(),
1676 GenericParamDefKind::Type { .. } => self
1677 .next_ty_var(TypeVariableOrigin {
1678 kind: TypeVariableOriginKind::SubstitutionPlaceholder,
1679 span: self.tcx.def_span(def_id),
1682 GenericParamDefKind::Const { .. } => {
1683 let span = self.tcx.def_span(def_id);
1684 let origin = ConstVariableOrigin {
1685 kind: ConstVariableOriginKind::SubstitutionPlaceholder,
1688 self.next_const_var(self.tcx.type_of(param.def_id), origin).into()
1693 /// Replaces late-bound-regions bound by `value` with `'static` using
1694 /// `ty::erase_late_bound_regions`.
1696 /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1697 /// method matching. It is reasonable during the probe phase because we don't consider region
1698 /// relationships at all. Therefore, we can just replace all the region variables with 'static
1699 /// rather than creating fresh region variables. This is nice for two reasons:
1701 /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1702 /// particular method call, it winds up creating fewer types overall, which helps for memory
1703 /// usage. (Admittedly, this is a rather small effect, though measurable.)
1705 /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1706 /// late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1707 /// regions with actual region variables as is proper, we'd have to ensure that the same
1708 /// region got replaced with the same variable, which requires a bit more coordination
1709 /// and/or tracking the substitution and
1711 fn erase_late_bound_regions<T>(&self, value: &ty::Binder<T>) -> T
1713 T: TypeFoldable<'tcx>,
1715 self.tcx.erase_late_bound_regions(value)
1718 /// Finds the method with the appropriate name (or return type, as the case may be). If
1719 /// `allow_similar_names` is set, find methods with close-matching names.
1720 fn impl_or_trait_item(&self, def_id: DefId) -> Vec<ty::AssocItem> {
1721 if let Some(name) = self.method_name {
1722 if self.allow_similar_names {
1723 let max_dist = max(name.as_str().len(), 3) / 3;
1725 .associated_items(def_id)
1726 .in_definition_order()
1728 let dist = lev_distance(&*name.as_str(), &x.ident.as_str());
1729 x.kind.namespace() == Namespace::ValueNS && dist > 0 && dist <= max_dist
1735 .associated_item(def_id, name, Namespace::ValueNS)
1736 .map_or(Vec::new(), |x| vec![x])
1739 self.tcx.associated_items(def_id).in_definition_order().copied().collect()
1744 impl<'tcx> Candidate<'tcx> {
1745 fn to_unadjusted_pick(&self) -> Pick<'tcx> {
1748 kind: match self.kind {
1749 InherentImplCandidate(..) => InherentImplPick,
1750 ObjectCandidate => ObjectPick,
1751 TraitCandidate(_) => TraitPick,
1752 WhereClauseCandidate(ref trait_ref) => {
1753 // Only trait derived from where-clauses should
1754 // appear here, so they should not contain any
1755 // inference variables or other artifacts. This
1756 // means they are safe to put into the
1757 // `WhereClausePick`.
1759 !trait_ref.skip_binder().substs.needs_infer()
1760 && !trait_ref.skip_binder().substs.has_placeholders()
1763 WhereClausePick(*trait_ref)
1766 import_ids: self.import_ids.clone(),