2 use super::MethodError;
3 use super::NoMatchData;
4 use super::{CandidateSource, ImplSource, TraitSource};
6 use crate::check::FnCtxt;
7 use crate::errors::MethodCallOnUnknownType;
8 use crate::hir::def::DefKind;
9 use crate::hir::def_id::DefId;
11 use rustc_data_structures::fx::FxHashSet;
12 use rustc_data_structures::sync::Lrc;
13 use rustc_errors::Applicability;
15 use rustc_hir::def::Namespace;
16 use rustc_infer::infer::canonical::OriginalQueryValues;
17 use rustc_infer::infer::canonical::{Canonical, QueryResponse};
18 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
19 use rustc_infer::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
20 use rustc_infer::infer::{self, InferOk, TyCtxtInferExt};
21 use rustc_middle::middle::stability;
22 use rustc_middle::ty::subst::{InternalSubsts, Subst, SubstsRef};
23 use rustc_middle::ty::GenericParamDefKind;
24 use rustc_middle::ty::{
25 self, ParamEnvAnd, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
27 use rustc_session::lint;
28 use rustc_span::def_id::LocalDefId;
29 use rustc_span::lev_distance::{find_best_match_for_name, lev_distance};
30 use rustc_span::{symbol::Ident, Span, Symbol, DUMMY_SP};
31 use rustc_trait_selection::autoderef::{self, Autoderef};
32 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
33 use rustc_trait_selection::traits::query::method_autoderef::MethodAutoderefBadTy;
34 use rustc_trait_selection::traits::query::method_autoderef::{
35 CandidateStep, MethodAutoderefStepsResult,
37 use rustc_trait_selection::traits::query::CanonicalTyGoal;
38 use rustc_trait_selection::traits::{self, ObligationCause};
44 use smallvec::{smallvec, SmallVec};
46 use self::CandidateKind::*;
47 pub use self::PickKind::*;
49 /// Boolean flag used to indicate if this search is for a suggestion
50 /// or not. If true, we can allow ambiguity and so forth.
51 #[derive(Clone, Copy, Debug)]
52 pub struct IsSuggestion(pub bool);
54 struct ProbeContext<'a, 'tcx> {
55 fcx: &'a FnCtxt<'a, 'tcx>,
58 method_name: Option<Ident>,
59 return_type: Option<Ty<'tcx>>,
61 /// This is the OriginalQueryValues for the steps queries
62 /// that are answered in steps.
63 orig_steps_var_values: OriginalQueryValues<'tcx>,
64 steps: Lrc<Vec<CandidateStep<'tcx>>>,
66 inherent_candidates: Vec<Candidate<'tcx>>,
67 extension_candidates: Vec<Candidate<'tcx>>,
68 impl_dups: FxHashSet<DefId>,
70 /// Collects near misses when the candidate functions are missing a `self` keyword and is only
71 /// used for error reporting
72 static_candidates: Vec<CandidateSource>,
74 /// When probing for names, include names that are close to the
75 /// requested name (by Levensthein distance)
76 allow_similar_names: bool,
78 /// Some(candidate) if there is a private candidate
79 private_candidate: Option<(DefKind, DefId)>,
81 /// Collects near misses when trait bounds for type parameters are unsatisfied and is only used
82 /// for error reporting
83 unsatisfied_predicates: Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>)>,
85 is_suggestion: IsSuggestion,
87 scope_expr_id: hir::HirId,
90 impl<'a, 'tcx> Deref for ProbeContext<'a, 'tcx> {
91 type Target = FnCtxt<'a, 'tcx>;
92 fn deref(&self) -> &Self::Target {
98 struct Candidate<'tcx> {
99 // Candidates are (I'm not quite sure, but they are mostly) basically
100 // some metadata on top of a `ty::AssocItem` (without substs).
102 // However, method probing wants to be able to evaluate the predicates
103 // for a function with the substs applied - for example, if a function
104 // has `where Self: Sized`, we don't want to consider it unless `Self`
105 // is actually `Sized`, and similarly, return-type suggestions want
106 // to consider the "actual" return type.
108 // The way this is handled is through `xform_self_ty`. It contains
109 // the receiver type of this candidate, but `xform_self_ty`,
110 // `xform_ret_ty` and `kind` (which contains the predicates) have the
111 // generic parameters of this candidate substituted with the *same set*
112 // of inference variables, which acts as some weird sort of "query".
114 // When we check out a candidate, we require `xform_self_ty` to be
115 // a subtype of the passed-in self-type, and this equates the type
116 // variables in the rest of the fields.
118 // For example, if we have this candidate:
121 // fn foo(&self) where Self: Sized;
125 // Then `xform_self_ty` will be `&'erased ?X` and `kind` will contain
126 // the predicate `?X: Sized`, so if we are evaluating `Foo` for a
127 // the receiver `&T`, we'll do the subtyping which will make `?X`
128 // get the right value, then when we evaluate the predicate we'll check
130 xform_self_ty: Ty<'tcx>,
131 xform_ret_ty: Option<Ty<'tcx>>,
133 kind: CandidateKind<'tcx>,
134 import_ids: SmallVec<[LocalDefId; 1]>,
138 enum CandidateKind<'tcx> {
139 InherentImplCandidate(
141 // Normalize obligations
142 Vec<traits::PredicateObligation<'tcx>>,
145 TraitCandidate(ty::TraitRef<'tcx>),
146 WhereClauseCandidate(
148 ty::PolyTraitRef<'tcx>,
152 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
159 /// When adjusting a receiver we often want to do one of
161 /// - Add a `&` (or `&mut`), converting the receiver from `T` to `&T` (or `&mut T`)
162 /// - If the receiver has type `*mut T`, convert it to `*const T`
164 /// This type tells us which one to do.
166 /// Note that in principle we could do both at the same time. For example, when the receiver has
167 /// type `T`, we could autoref it to `&T`, then convert to `*const T`. Or, when it has type `*mut
168 /// T`, we could convert it to `*const T`, then autoref to `&*const T`. However, currently we do
169 /// (at most) one of these. Either the receiver has type `T` and we convert it to `&T` (or with
170 /// `mut`), or it has type `*mut T` and we convert it to `*const T`.
171 #[derive(Debug, PartialEq, Clone)]
172 pub enum AutorefOrPtrAdjustment<'tcx> {
173 /// Receiver has type `T`, add `&` or `&mut` (it `T` is `mut`), and maybe also "unsize" it.
174 /// Unsizing is used to convert a `[T; N]` to `[T]`, which only makes sense when autorefing.
176 mutbl: hir::Mutability,
178 /// Indicates that the source expression should be "unsized" to a target type. This should
179 /// probably eventually go away in favor of just coercing method receivers.
180 unsize: Option<Ty<'tcx>>,
182 /// Receiver has type `*mut T`, convert to `*const T`
186 impl<'tcx> AutorefOrPtrAdjustment<'tcx> {
187 fn get_unsize(&self) -> Option<Ty<'tcx>> {
189 AutorefOrPtrAdjustment::Autoref { mutbl: _, unsize } => unsize.clone(),
190 AutorefOrPtrAdjustment::ToConstPtr => None,
195 #[derive(Debug, PartialEq, Clone)]
196 pub struct Pick<'tcx> {
197 pub item: ty::AssocItem,
198 pub kind: PickKind<'tcx>,
199 pub import_ids: SmallVec<[LocalDefId; 1]>,
201 /// Indicates that the source expression should be autoderef'd N times
203 /// A = expr | *expr | **expr | ...
204 pub autoderefs: usize,
206 /// Indicates that we want to add an autoref (and maybe also unsize it), or if the receiver is
207 /// `*mut T`, convert it to `*const T`.
208 pub autoref_or_ptr_adjustment: Option<AutorefOrPtrAdjustment<'tcx>>,
211 #[derive(Clone, Debug, PartialEq, Eq)]
212 pub enum PickKind<'tcx> {
218 ty::PolyTraitRef<'tcx>,
222 pub type PickResult<'tcx> = Result<Pick<'tcx>, MethodError<'tcx>>;
224 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
226 // An expression of the form `receiver.method_name(...)`.
227 // Autoderefs are performed on `receiver`, lookup is done based on the
228 // `self` argument of the method, and static methods aren't considered.
230 // An expression of the form `Type::item` or `<T>::item`.
231 // No autoderefs are performed, lookup is done based on the type each
232 // implementation is for, and static methods are included.
236 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
237 pub enum ProbeScope {
238 // Assemble candidates coming only from traits in scope.
241 // Assemble candidates coming from all traits.
245 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
246 /// This is used to offer suggestions to users. It returns methods
247 /// that could have been called which have the desired return
248 /// type. Some effort is made to rule out methods that, if called,
249 /// would result in an error (basically, the same criteria we
250 /// would use to decide if a method is a plausible fit for
251 /// ambiguity purposes).
252 #[instrument(level = "debug", skip(self, scope_expr_id))]
253 pub fn probe_for_return_type(
257 return_type: Ty<'tcx>,
259 scope_expr_id: hir::HirId,
260 ) -> Vec<ty::AssocItem> {
262 "probe(self_ty={:?}, return_type={}, scope_expr_id={})",
263 self_ty, return_type, scope_expr_id
265 let method_names = self
274 ProbeScope::AllTraits,
275 |probe_cx| Ok(probe_cx.candidate_method_names()),
277 .unwrap_or_default();
280 .flat_map(|&method_name| {
289 ProbeScope::AllTraits,
290 |probe_cx| probe_cx.pick(),
293 .map(|pick| pick.item)
298 #[instrument(level = "debug", skip(self, scope_expr_id))]
299 pub fn probe_for_name(
304 is_suggestion: IsSuggestion,
306 scope_expr_id: hir::HirId,
308 ) -> PickResult<'tcx> {
310 "probe(self_ty={:?}, item_name={}, scope_expr_id={})",
311 self_ty, item_name, scope_expr_id
322 |probe_cx| probe_cx.pick(),
330 method_name: Option<Ident>,
331 return_type: Option<Ty<'tcx>>,
332 is_suggestion: IsSuggestion,
334 scope_expr_id: hir::HirId,
337 ) -> Result<R, MethodError<'tcx>>
339 OP: FnOnce(ProbeContext<'a, 'tcx>) -> Result<R, MethodError<'tcx>>,
341 let mut orig_values = OriginalQueryValues::default();
342 let param_env_and_self_ty = self.infcx.canonicalize_query(
343 ParamEnvAnd { param_env: self.param_env, value: self_ty },
347 let steps = if mode == Mode::MethodCall {
348 self.tcx.method_autoderef_steps(param_env_and_self_ty)
350 self.infcx.probe(|_| {
351 // Mode::Path - the deref steps is "trivial". This turns
352 // our CanonicalQuery into a "trivial" QueryResponse. This
353 // is a bit inefficient, but I don't think that writing
354 // special handling for this "trivial case" is a good idea.
356 let infcx = &self.infcx;
357 let (ParamEnvAnd { param_env: _, value: self_ty }, canonical_inference_vars) =
358 infcx.instantiate_canonical_with_fresh_inference_vars(
360 ¶m_env_and_self_ty,
363 "probe_op: Mode::Path, param_env_and_self_ty={:?} self_ty={:?}",
364 param_env_and_self_ty, self_ty
366 MethodAutoderefStepsResult {
367 steps: Lrc::new(vec![CandidateStep {
368 self_ty: self.make_query_response_ignoring_pending_obligations(
369 canonical_inference_vars,
373 from_unsafe_deref: false,
377 reached_recursion_limit: false,
382 // If our autoderef loop had reached the recursion limit,
383 // report an overflow error, but continue going on with
384 // the truncated autoderef list.
385 if steps.reached_recursion_limit {
390 .unwrap_or_else(|| span_bug!(span, "reached the recursion limit in 0 steps?"))
393 .probe_instantiate_query_response(span, &orig_values, ty)
394 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
395 autoderef::report_autoderef_recursion_limit_error(self.tcx, span, ty.value);
399 // If we encountered an `_` type or an error type during autoderef, this is
401 if let Some(bad_ty) = &steps.opt_bad_ty {
403 // Ambiguity was encountered during a suggestion. Just keep going.
404 debug!("ProbeContext: encountered ambiguity in suggestion");
405 } else if bad_ty.reached_raw_pointer && !self.tcx.features().arbitrary_self_types {
406 // this case used to be allowed by the compiler,
407 // so we do a future-compat lint here for the 2015 edition
408 // (see https://github.com/rust-lang/rust/issues/46906)
409 if self.tcx.sess.rust_2018() {
410 self.tcx.sess.emit_err(MethodCallOnUnknownType { span });
412 self.tcx.struct_span_lint_hir(
413 lint::builtin::TYVAR_BEHIND_RAW_POINTER,
416 |lint| lint.build("type annotations needed").emit(),
420 // Encountered a real ambiguity, so abort the lookup. If `ty` is not
421 // an `Err`, report the right "type annotations needed" error pointing
425 .probe_instantiate_query_response(span, &orig_values, ty)
426 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
427 let ty = self.structurally_resolved_type(span, ty.value);
428 assert!(matches!(ty.kind(), ty::Error(_)));
429 return Err(MethodError::NoMatch(NoMatchData::new(
439 debug!("ProbeContext: steps for self_ty={:?} are {:?}", self_ty, steps);
441 // this creates one big transaction so that all type variables etc
442 // that we create during the probe process are removed later
444 let mut probe_cx = ProbeContext::new(
456 probe_cx.assemble_inherent_candidates();
458 ProbeScope::TraitsInScope => {
459 probe_cx.assemble_extension_candidates_for_traits_in_scope(scope_expr_id)
461 ProbeScope::AllTraits => probe_cx.assemble_extension_candidates_for_all_traits(),
468 pub fn provide(providers: &mut ty::query::Providers) {
469 providers.method_autoderef_steps = method_autoderef_steps;
472 fn method_autoderef_steps<'tcx>(
474 goal: CanonicalTyGoal<'tcx>,
475 ) -> MethodAutoderefStepsResult<'tcx> {
476 debug!("method_autoderef_steps({:?})", goal);
478 tcx.infer_ctxt().enter_with_canonical(DUMMY_SP, &goal, |ref infcx, goal, inference_vars| {
479 let ParamEnvAnd { param_env, value: self_ty } = goal;
482 Autoderef::new(infcx, param_env, hir::CRATE_HIR_ID, DUMMY_SP, self_ty, DUMMY_SP)
483 .include_raw_pointers()
485 let mut reached_raw_pointer = false;
486 let mut steps: Vec<_> = autoderef
489 let step = CandidateStep {
490 self_ty: infcx.make_query_response_ignoring_pending_obligations(
491 inference_vars.clone(),
495 from_unsafe_deref: reached_raw_pointer,
498 if let ty::RawPtr(_) = ty.kind() {
499 // all the subsequent steps will be from_unsafe_deref
500 reached_raw_pointer = true;
506 let final_ty = autoderef.final_ty(true);
507 let opt_bad_ty = match final_ty.kind() {
508 ty::Infer(ty::TyVar(_)) | ty::Error(_) => Some(MethodAutoderefBadTy {
511 .make_query_response_ignoring_pending_obligations(inference_vars, final_ty),
513 ty::Array(elem_ty, _) => {
514 let dereferences = steps.len() - 1;
516 steps.push(CandidateStep {
517 self_ty: infcx.make_query_response_ignoring_pending_obligations(
519 infcx.tcx.mk_slice(elem_ty),
521 autoderefs: dereferences,
522 // this could be from an unsafe deref if we had
523 // a *mut/const [T; N]
524 from_unsafe_deref: reached_raw_pointer,
533 debug!("method_autoderef_steps: steps={:?} opt_bad_ty={:?}", steps, opt_bad_ty);
535 MethodAutoderefStepsResult {
536 steps: Lrc::new(steps),
537 opt_bad_ty: opt_bad_ty.map(Lrc::new),
538 reached_recursion_limit: autoderef.reached_recursion_limit(),
543 impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
545 fcx: &'a FnCtxt<'a, 'tcx>,
548 method_name: Option<Ident>,
549 return_type: Option<Ty<'tcx>>,
550 orig_steps_var_values: OriginalQueryValues<'tcx>,
551 steps: Lrc<Vec<CandidateStep<'tcx>>>,
552 is_suggestion: IsSuggestion,
553 scope_expr_id: hir::HirId,
554 ) -> ProbeContext<'a, 'tcx> {
561 inherent_candidates: Vec::new(),
562 extension_candidates: Vec::new(),
563 impl_dups: FxHashSet::default(),
564 orig_steps_var_values,
566 static_candidates: Vec::new(),
567 allow_similar_names: false,
568 private_candidate: None,
569 unsatisfied_predicates: Vec::new(),
575 fn reset(&mut self) {
576 self.inherent_candidates.clear();
577 self.extension_candidates.clear();
578 self.impl_dups.clear();
579 self.static_candidates.clear();
580 self.private_candidate = None;
583 ///////////////////////////////////////////////////////////////////////////
584 // CANDIDATE ASSEMBLY
586 fn push_candidate(&mut self, candidate: Candidate<'tcx>, is_inherent: bool) {
587 let is_accessible = if let Some(name) = self.method_name {
588 let item = candidate.item;
590 self.tcx.adjust_ident_and_get_scope(name, item.container.id(), self.body_id).1;
591 item.vis.is_accessible_from(def_scope, self.tcx)
597 self.inherent_candidates.push(candidate);
599 self.extension_candidates.push(candidate);
601 } else if self.private_candidate.is_none() {
602 self.private_candidate =
603 Some((candidate.item.kind.as_def_kind(), candidate.item.def_id));
607 fn assemble_inherent_candidates(&mut self) {
608 let steps = Lrc::clone(&self.steps);
609 for step in steps.iter() {
610 self.assemble_probe(&step.self_ty);
614 fn assemble_probe(&mut self, self_ty: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>) {
615 debug!("assemble_probe: self_ty={:?}", self_ty);
616 let lang_items = self.tcx.lang_items();
618 match *self_ty.value.value.kind() {
619 ty::Dynamic(ref data, ..) => {
620 if let Some(p) = data.principal() {
621 // Subtle: we can't use `instantiate_query_response` here: using it will
622 // commit to all of the type equalities assumed by inference going through
623 // autoderef (see the `method-probe-no-guessing` test).
625 // However, in this code, it is OK if we end up with an object type that is
626 // "more general" than the object type that we are evaluating. For *every*
627 // object type `MY_OBJECT`, a function call that goes through a trait-ref
628 // of the form `<MY_OBJECT as SuperTraitOf(MY_OBJECT)>::func` is a valid
629 // `ObjectCandidate`, and it should be discoverable "exactly" through one
630 // of the iterations in the autoderef loop, so there is no problem with it
631 // being discoverable in another one of these iterations.
633 // Using `instantiate_canonical_with_fresh_inference_vars` on our
634 // `Canonical<QueryResponse<Ty<'tcx>>>` and then *throwing away* the
635 // `CanonicalVarValues` will exactly give us such a generalization - it
636 // will still match the original object type, but it won't pollute our
637 // type variables in any form, so just do that!
638 let (QueryResponse { value: generalized_self_ty, .. }, _ignored_var_values) =
640 .instantiate_canonical_with_fresh_inference_vars(self.span, &self_ty);
642 self.assemble_inherent_candidates_from_object(generalized_self_ty);
643 self.assemble_inherent_impl_candidates_for_type(p.def_id());
647 self.assemble_inherent_impl_candidates_for_type(def.did);
649 ty::Foreign(did) => {
650 self.assemble_inherent_impl_candidates_for_type(did);
653 self.assemble_inherent_candidates_from_param(p);
656 let lang_def_id = lang_items.bool_impl();
657 self.assemble_inherent_impl_for_primitive(lang_def_id);
660 let lang_def_id = lang_items.char_impl();
661 self.assemble_inherent_impl_for_primitive(lang_def_id);
664 let lang_def_id = lang_items.str_impl();
665 self.assemble_inherent_impl_for_primitive(lang_def_id);
667 let lang_def_id = lang_items.str_alloc_impl();
668 self.assemble_inherent_impl_for_primitive(lang_def_id);
671 for &lang_def_id in &[
672 lang_items.slice_impl(),
673 lang_items.slice_u8_impl(),
674 lang_items.slice_alloc_impl(),
675 lang_items.slice_u8_alloc_impl(),
677 self.assemble_inherent_impl_for_primitive(lang_def_id);
681 let lang_def_id = lang_items.array_impl();
682 self.assemble_inherent_impl_for_primitive(lang_def_id);
684 ty::RawPtr(ty::TypeAndMut { ty: _, mutbl }) => {
685 let (lang_def_id1, lang_def_id2) = match mutbl {
686 hir::Mutability::Not => {
687 (lang_items.const_ptr_impl(), lang_items.const_slice_ptr_impl())
689 hir::Mutability::Mut => {
690 (lang_items.mut_ptr_impl(), lang_items.mut_slice_ptr_impl())
693 self.assemble_inherent_impl_for_primitive(lang_def_id1);
694 self.assemble_inherent_impl_for_primitive(lang_def_id2);
697 let lang_def_id = match i {
698 ty::IntTy::I8 => lang_items.i8_impl(),
699 ty::IntTy::I16 => lang_items.i16_impl(),
700 ty::IntTy::I32 => lang_items.i32_impl(),
701 ty::IntTy::I64 => lang_items.i64_impl(),
702 ty::IntTy::I128 => lang_items.i128_impl(),
703 ty::IntTy::Isize => lang_items.isize_impl(),
705 self.assemble_inherent_impl_for_primitive(lang_def_id);
708 let lang_def_id = match i {
709 ty::UintTy::U8 => lang_items.u8_impl(),
710 ty::UintTy::U16 => lang_items.u16_impl(),
711 ty::UintTy::U32 => lang_items.u32_impl(),
712 ty::UintTy::U64 => lang_items.u64_impl(),
713 ty::UintTy::U128 => lang_items.u128_impl(),
714 ty::UintTy::Usize => lang_items.usize_impl(),
716 self.assemble_inherent_impl_for_primitive(lang_def_id);
719 let (lang_def_id1, lang_def_id2) = match f {
720 ty::FloatTy::F32 => (lang_items.f32_impl(), lang_items.f32_runtime_impl()),
721 ty::FloatTy::F64 => (lang_items.f64_impl(), lang_items.f64_runtime_impl()),
723 self.assemble_inherent_impl_for_primitive(lang_def_id1);
724 self.assemble_inherent_impl_for_primitive(lang_def_id2);
730 fn assemble_inherent_impl_for_primitive(&mut self, lang_def_id: Option<DefId>) {
731 if let Some(impl_def_id) = lang_def_id {
732 self.assemble_inherent_impl_probe(impl_def_id);
736 fn assemble_inherent_impl_candidates_for_type(&mut self, def_id: DefId) {
737 let impl_def_ids = self.tcx.at(self.span).inherent_impls(def_id);
738 for &impl_def_id in impl_def_ids.iter() {
739 self.assemble_inherent_impl_probe(impl_def_id);
743 fn assemble_inherent_impl_probe(&mut self, impl_def_id: DefId) {
744 if !self.impl_dups.insert(impl_def_id) {
745 return; // already visited
748 debug!("assemble_inherent_impl_probe {:?}", impl_def_id);
750 for item in self.impl_or_trait_item(impl_def_id) {
751 if !self.has_applicable_self(&item) {
752 // No receiver declared. Not a candidate.
753 self.record_static_candidate(ImplSource(impl_def_id));
757 let (impl_ty, impl_substs) = self.impl_ty_and_substs(impl_def_id);
758 let impl_ty = impl_ty.subst(self.tcx, impl_substs);
760 // Determine the receiver type that the method itself expects.
761 let xform_tys = self.xform_self_ty(&item, impl_ty, impl_substs);
763 // We can't use normalize_associated_types_in as it will pollute the
764 // fcx's fulfillment context after this probe is over.
765 let cause = traits::ObligationCause::misc(self.span, self.body_id);
766 let selcx = &mut traits::SelectionContext::new(self.fcx);
767 let traits::Normalized { value: (xform_self_ty, xform_ret_ty), obligations } =
768 traits::normalize(selcx, self.param_env, cause, xform_tys);
770 "assemble_inherent_impl_probe: xform_self_ty = {:?}/{:?}",
771 xform_self_ty, xform_ret_ty
779 kind: InherentImplCandidate(impl_substs, obligations),
780 import_ids: smallvec![],
787 fn assemble_inherent_candidates_from_object(&mut self, self_ty: Ty<'tcx>) {
788 debug!("assemble_inherent_candidates_from_object(self_ty={:?})", self_ty);
790 let principal = match self_ty.kind() {
791 ty::Dynamic(ref data, ..) => Some(data),
794 .and_then(|data| data.principal())
798 "non-object {:?} in assemble_inherent_candidates_from_object",
803 // It is illegal to invoke a method on a trait instance that refers to
804 // the `Self` type. An [`ObjectSafetyViolation::SupertraitSelf`] error
805 // will be reported by `object_safety.rs` if the method refers to the
806 // `Self` type anywhere other than the receiver. Here, we use a
807 // substitution that replaces `Self` with the object type itself. Hence,
808 // a `&self` method will wind up with an argument type like `&dyn Trait`.
809 let trait_ref = principal.with_self_ty(self.tcx, self_ty);
810 self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
811 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
813 let (xform_self_ty, xform_ret_ty) =
814 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
820 kind: ObjectCandidate,
821 import_ids: smallvec![],
828 fn assemble_inherent_candidates_from_param(&mut self, param_ty: ty::ParamTy) {
829 // FIXME: do we want to commit to this behavior for param bounds?
830 debug!("assemble_inherent_candidates_from_param(param_ty={:?})", param_ty);
832 let bounds = self.param_env.caller_bounds().iter().filter_map(|predicate| {
833 let bound_predicate = predicate.kind();
834 match bound_predicate.skip_binder() {
835 ty::PredicateKind::Trait(trait_predicate, _) => {
836 match *trait_predicate.trait_ref.self_ty().kind() {
837 ty::Param(p) if p == param_ty => {
838 Some(bound_predicate.rebind(trait_predicate.trait_ref))
843 ty::PredicateKind::Subtype(..)
844 | ty::PredicateKind::Projection(..)
845 | ty::PredicateKind::RegionOutlives(..)
846 | ty::PredicateKind::WellFormed(..)
847 | ty::PredicateKind::ObjectSafe(..)
848 | ty::PredicateKind::ClosureKind(..)
849 | ty::PredicateKind::TypeOutlives(..)
850 | ty::PredicateKind::ConstEvaluatable(..)
851 | ty::PredicateKind::ConstEquate(..)
852 | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
856 self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
857 let trait_ref = this.erase_late_bound_regions(poly_trait_ref);
859 let (xform_self_ty, xform_ret_ty) =
860 this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs);
862 // Because this trait derives from a where-clause, it
863 // should not contain any inference variables or other
864 // artifacts. This means it is safe to put into the
865 // `WhereClauseCandidate` and (eventually) into the
866 // `WhereClausePick`.
867 assert!(!trait_ref.substs.needs_infer());
874 kind: WhereClauseCandidate(poly_trait_ref),
875 import_ids: smallvec![],
882 // Do a search through a list of bounds, using a callback to actually
883 // create the candidates.
884 fn elaborate_bounds<F>(
886 bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
889 F: for<'b> FnMut(&mut ProbeContext<'b, 'tcx>, ty::PolyTraitRef<'tcx>, ty::AssocItem),
892 for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
893 debug!("elaborate_bounds(bound_trait_ref={:?})", bound_trait_ref);
894 for item in self.impl_or_trait_item(bound_trait_ref.def_id()) {
895 if !self.has_applicable_self(&item) {
896 self.record_static_candidate(TraitSource(bound_trait_ref.def_id()));
898 mk_cand(self, bound_trait_ref, item);
904 fn assemble_extension_candidates_for_traits_in_scope(&mut self, expr_hir_id: hir::HirId) {
905 let mut duplicates = FxHashSet::default();
906 let opt_applicable_traits = self.tcx.in_scope_traits(expr_hir_id);
907 if let Some(applicable_traits) = opt_applicable_traits {
908 for trait_candidate in applicable_traits.iter() {
909 let trait_did = trait_candidate.def_id;
910 if duplicates.insert(trait_did) {
911 self.assemble_extension_candidates_for_trait(
912 &trait_candidate.import_ids,
920 fn assemble_extension_candidates_for_all_traits(&mut self) {
921 let mut duplicates = FxHashSet::default();
922 for trait_info in suggest::all_traits(self.tcx) {
923 if duplicates.insert(trait_info.def_id) {
924 self.assemble_extension_candidates_for_trait(&smallvec![], trait_info.def_id);
929 pub fn matches_return_type(
931 method: &ty::AssocItem,
932 self_ty: Option<Ty<'tcx>>,
936 ty::AssocKind::Fn => {
937 let fty = self.tcx.fn_sig(method.def_id);
939 let substs = self.fresh_substs_for_item(self.span, method.def_id);
940 let fty = fty.subst(self.tcx, substs);
942 self.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, fty);
944 if let Some(self_ty) = self_ty {
946 .at(&ObligationCause::dummy(), self.param_env)
947 .sup(fty.inputs()[0], self_ty)
953 self.can_sub(self.param_env, fty.output(), expected).is_ok()
960 fn assemble_extension_candidates_for_trait(
962 import_ids: &SmallVec<[LocalDefId; 1]>,
965 debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})", trait_def_id);
966 let trait_substs = self.fresh_item_substs(trait_def_id);
967 let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
969 if self.tcx.is_trait_alias(trait_def_id) {
970 // For trait aliases, assume all super-traits are relevant.
971 let bounds = iter::once(trait_ref.to_poly_trait_ref());
972 self.elaborate_bounds(bounds, |this, new_trait_ref, item| {
973 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
975 let (xform_self_ty, xform_ret_ty) =
976 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
982 import_ids: import_ids.clone(),
983 kind: TraitCandidate(new_trait_ref),
989 debug_assert!(self.tcx.is_trait(trait_def_id));
990 for item in self.impl_or_trait_item(trait_def_id) {
991 // Check whether `trait_def_id` defines a method with suitable name.
992 if !self.has_applicable_self(&item) {
993 debug!("method has inapplicable self");
994 self.record_static_candidate(TraitSource(trait_def_id));
998 let (xform_self_ty, xform_ret_ty) =
999 self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
1000 self.push_candidate(
1005 import_ids: import_ids.clone(),
1006 kind: TraitCandidate(trait_ref),
1014 fn candidate_method_names(&self) -> Vec<Ident> {
1015 let mut set = FxHashSet::default();
1016 let mut names: Vec<_> = self
1017 .inherent_candidates
1019 .chain(&self.extension_candidates)
1020 .filter(|candidate| {
1021 if let Some(return_ty) = self.return_type {
1022 self.matches_return_type(&candidate.item, None, return_ty)
1027 .map(|candidate| candidate.item.ident)
1028 .filter(|&name| set.insert(name))
1031 // Sort them by the name so we have a stable result.
1032 names.sort_by_cached_key(|n| n.as_str());
1036 ///////////////////////////////////////////////////////////////////////////
1037 // THE ACTUAL SEARCH
1039 fn pick(mut self) -> PickResult<'tcx> {
1040 assert!(self.method_name.is_some());
1042 if let Some(r) = self.pick_core() {
1046 debug!("pick: actual search failed, assemble diagnostics");
1048 let static_candidates = mem::take(&mut self.static_candidates);
1049 let private_candidate = self.private_candidate.take();
1050 let unsatisfied_predicates = mem::take(&mut self.unsatisfied_predicates);
1052 // things failed, so lets look at all traits, for diagnostic purposes now:
1055 let span = self.span;
1058 self.assemble_extension_candidates_for_all_traits();
1060 let out_of_scope_traits = match self.pick_core() {
1061 Some(Ok(p)) => vec![p.item.container.id()],
1062 //Some(Ok(p)) => p.iter().map(|p| p.item.container().id()).collect(),
1063 Some(Err(MethodError::Ambiguity(v))) => v
1065 .map(|source| match source {
1066 TraitSource(id) => id,
1067 ImplSource(impl_id) => match tcx.trait_id_of_impl(impl_id) {
1069 None => span_bug!(span, "found inherent method when looking at traits"),
1073 Some(Err(MethodError::NoMatch(NoMatchData {
1074 out_of_scope_traits: others, ..
1076 assert!(others.is_empty());
1082 if let Some((kind, def_id)) = private_candidate {
1083 return Err(MethodError::PrivateMatch(kind, def_id, out_of_scope_traits));
1085 let lev_candidate = self.probe_for_lev_candidate()?;
1087 Err(MethodError::NoMatch(NoMatchData::new(
1089 unsatisfied_predicates,
1090 out_of_scope_traits,
1096 fn pick_core(&mut self) -> Option<PickResult<'tcx>> {
1097 let steps = self.steps.clone();
1099 // find the first step that works
1103 debug!("pick_core: step={:?}", step);
1104 // skip types that are from a type error or that would require dereferencing
1106 !step.self_ty.references_error() && !step.from_unsafe_deref
1109 let InferOk { value: self_ty, obligations: _ } = self
1111 .probe_instantiate_query_response(
1113 &self.orig_steps_var_values,
1116 .unwrap_or_else(|_| {
1117 span_bug!(self.span, "{:?} was applicable but now isn't?", step.self_ty)
1119 self.pick_by_value_method(step, self_ty).or_else(|| {
1120 self.pick_autorefd_method(step, self_ty, hir::Mutability::Not)
1121 .or_else(|| self.pick_autorefd_method(step, self_ty, hir::Mutability::Mut))
1122 .or_else(|| self.pick_const_ptr_method(step, self_ty))
1128 /// For each type `T` in the step list, this attempts to find a method where
1129 /// the (transformed) self type is exactly `T`. We do however do one
1130 /// transformation on the adjustment: if we are passing a region pointer in,
1131 /// we will potentially *reborrow* it to a shorter lifetime. This allows us
1132 /// to transparently pass `&mut` pointers, in particular, without consuming
1133 /// them for their entire lifetime.
1134 fn pick_by_value_method(
1136 step: &CandidateStep<'tcx>,
1138 ) -> Option<PickResult<'tcx>> {
1143 self.pick_method(self_ty).map(|r| {
1145 pick.autoderefs = step.autoderefs;
1147 // Insert a `&*` or `&mut *` if this is a reference type:
1148 if let ty::Ref(_, _, mutbl) = *step.self_ty.value.value.kind() {
1149 pick.autoderefs += 1;
1150 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::Autoref {
1152 unsize: pick.autoref_or_ptr_adjustment.and_then(|a| a.get_unsize()),
1161 fn pick_autorefd_method(
1163 step: &CandidateStep<'tcx>,
1165 mutbl: hir::Mutability,
1166 ) -> Option<PickResult<'tcx>> {
1169 // In general, during probing we erase regions.
1170 let region = tcx.lifetimes.re_erased;
1172 let autoref_ty = tcx.mk_ref(region, ty::TypeAndMut { ty: self_ty, mutbl });
1173 self.pick_method(autoref_ty).map(|r| {
1175 pick.autoderefs = step.autoderefs;
1176 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::Autoref {
1178 unsize: step.unsize.then_some(self_ty),
1185 /// If `self_ty` is `*mut T` then this picks `*const T` methods. The reason why we have a
1186 /// special case for this is because going from `*mut T` to `*const T` with autoderefs and
1187 /// autorefs would require dereferencing the pointer, which is not safe.
1188 fn pick_const_ptr_method(
1190 step: &CandidateStep<'tcx>,
1192 ) -> Option<PickResult<'tcx>> {
1193 // Don't convert an unsized reference to ptr
1198 let ty = match self_ty.kind() {
1199 ty::RawPtr(ty::TypeAndMut { ty, mutbl: hir::Mutability::Mut }) => ty,
1203 let const_self_ty = ty::TypeAndMut { ty, mutbl: hir::Mutability::Not };
1204 let const_ptr_ty = self.tcx.mk_ptr(const_self_ty);
1205 self.pick_method(const_ptr_ty).map(|r| {
1207 pick.autoderefs = step.autoderefs;
1208 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::ToConstPtr);
1214 fn pick_method(&mut self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
1215 debug!("pick_method(self_ty={})", self.ty_to_string(self_ty));
1217 let mut possibly_unsatisfied_predicates = Vec::new();
1218 let mut unstable_candidates = Vec::new();
1220 for (kind, candidates) in
1221 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1223 debug!("searching {} candidates", kind);
1224 let res = self.consider_candidates(
1227 &mut possibly_unsatisfied_predicates,
1228 Some(&mut unstable_candidates),
1230 if let Some(pick) = res {
1231 if !self.is_suggestion.0 && !unstable_candidates.is_empty() {
1232 if let Ok(p) = &pick {
1233 // Emit a lint if there are unstable candidates alongside the stable ones.
1235 // We suppress warning if we're picking the method only because it is a
1237 self.emit_unstable_name_collision_hint(p, &unstable_candidates, self_ty);
1244 debug!("searching unstable candidates");
1245 let res = self.consider_candidates(
1247 unstable_candidates.into_iter().map(|(c, _)| c),
1248 &mut possibly_unsatisfied_predicates,
1252 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1257 fn consider_candidates<'b, ProbesIter>(
1261 possibly_unsatisfied_predicates: &mut Vec<(
1262 ty::Predicate<'tcx>,
1263 Option<ty::Predicate<'tcx>>,
1265 unstable_candidates: Option<&mut Vec<(&'b Candidate<'tcx>, Symbol)>>,
1266 ) -> Option<PickResult<'tcx>>
1268 ProbesIter: Iterator<Item = &'b Candidate<'tcx>> + Clone,
1270 let mut applicable_candidates: Vec<_> = probes
1273 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
1275 .filter(|&(_, status)| status != ProbeResult::NoMatch)
1278 debug!("applicable_candidates: {:?}", applicable_candidates);
1280 if applicable_candidates.len() > 1 {
1281 if let Some(pick) = self.collapse_candidates_to_trait_pick(&applicable_candidates[..]) {
1282 return Some(Ok(pick));
1286 if let Some(uc) = unstable_candidates {
1287 applicable_candidates.retain(|&(p, _)| {
1288 if let stability::EvalResult::Deny { feature, .. } =
1289 self.tcx.eval_stability(p.item.def_id, None, self.span)
1291 uc.push((p, feature));
1298 if applicable_candidates.len() > 1 {
1299 let sources = probes.map(|p| self.candidate_source(p, self_ty)).collect();
1300 return Some(Err(MethodError::Ambiguity(sources)));
1303 applicable_candidates.pop().map(|(probe, status)| {
1304 if status == ProbeResult::Match {
1305 Ok(probe.to_unadjusted_pick())
1307 Err(MethodError::BadReturnType)
1312 fn emit_unstable_name_collision_hint(
1314 stable_pick: &Pick<'_>,
1315 unstable_candidates: &[(&Candidate<'tcx>, Symbol)],
1318 self.tcx.struct_span_lint_hir(
1319 lint::builtin::UNSTABLE_NAME_COLLISIONS,
1323 let def_kind = stable_pick.item.kind.as_def_kind();
1324 let mut diag = lint.build(&format!(
1325 "{} {} with this name may be added to the standard library in the future",
1327 def_kind.descr(stable_pick.item.def_id),
1329 match (stable_pick.item.kind, stable_pick.item.container) {
1330 (ty::AssocKind::Fn, _) => {
1331 // FIXME: This should be a `span_suggestion` instead of `help`
1332 // However `self.span` only
1333 // highlights the method name, so we can't use it. Also consider reusing
1334 // the code from `report_method_error()`.
1336 "call with fully qualified syntax `{}(...)` to keep using the current \
1338 self.tcx.def_path_str(stable_pick.item.def_id),
1341 (ty::AssocKind::Const, ty::AssocItemContainer::TraitContainer(def_id)) => {
1342 diag.span_suggestion(
1344 "use the fully qualified path to the associated const",
1348 self.tcx.def_path_str(def_id),
1349 stable_pick.item.ident
1351 Applicability::MachineApplicable,
1356 if self.tcx.sess.is_nightly_build() {
1357 for (candidate, feature) in unstable_candidates {
1359 "add `#![feature({})]` to the crate attributes to enable `{}`",
1361 self.tcx.def_path_str(candidate.item.def_id),
1371 fn select_trait_candidate(
1373 trait_ref: ty::TraitRef<'tcx>,
1374 ) -> traits::SelectionResult<'tcx, traits::Selection<'tcx>> {
1375 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1376 let predicate = trait_ref.to_poly_trait_ref().to_poly_trait_predicate();
1377 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1378 traits::SelectionContext::new(self).select(&obligation)
1381 fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>) -> CandidateSource {
1382 match candidate.kind {
1383 InherentImplCandidate(..) => ImplSource(candidate.item.container.id()),
1384 ObjectCandidate | WhereClauseCandidate(_) => TraitSource(candidate.item.container.id()),
1385 TraitCandidate(trait_ref) => self.probe(|_| {
1387 .at(&ObligationCause::dummy(), self.param_env)
1388 .sup(candidate.xform_self_ty, self_ty);
1389 match self.select_trait_candidate(trait_ref) {
1390 Ok(Some(traits::ImplSource::UserDefined(ref impl_data))) => {
1391 // If only a single impl matches, make the error message point
1393 ImplSource(impl_data.impl_def_id)
1395 _ => TraitSource(candidate.item.container.id()),
1404 probe: &Candidate<'tcx>,
1405 possibly_unsatisfied_predicates: &mut Vec<(
1406 ty::Predicate<'tcx>,
1407 Option<ty::Predicate<'tcx>>,
1410 debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe);
1413 // First check that the self type can be related.
1414 let sub_obligations = match self
1415 .at(&ObligationCause::dummy(), self.param_env)
1416 .sup(probe.xform_self_ty, self_ty)
1418 Ok(InferOk { obligations, value: () }) => obligations,
1420 debug!("--> cannot relate self-types");
1421 return ProbeResult::NoMatch;
1425 let mut result = ProbeResult::Match;
1426 let selcx = &mut traits::SelectionContext::new(self);
1427 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1429 // If so, impls may carry other conditions (e.g., where
1430 // clauses) that must be considered. Make sure that those
1431 // match as well (or at least may match, sometimes we
1432 // don't have enough information to fully evaluate).
1434 InherentImplCandidate(ref substs, ref ref_obligations) => {
1435 // Check whether the impl imposes obligations we have to worry about.
1436 let impl_def_id = probe.item.container.id();
1437 let impl_bounds = self.tcx.predicates_of(impl_def_id);
1438 let impl_bounds = impl_bounds.instantiate(self.tcx, substs);
1439 let traits::Normalized { value: impl_bounds, obligations: norm_obligations } =
1440 traits::normalize(selcx, self.param_env, cause.clone(), impl_bounds);
1442 // Convert the bounds into obligations.
1443 let impl_obligations =
1444 traits::predicates_for_generics(cause, self.param_env, impl_bounds);
1446 let candidate_obligations = impl_obligations
1447 .chain(norm_obligations.into_iter())
1448 .chain(ref_obligations.iter().cloned());
1449 // Evaluate those obligations to see if they might possibly hold.
1450 for o in candidate_obligations {
1451 let o = self.resolve_vars_if_possible(o);
1452 if !self.predicate_may_hold(&o) {
1453 result = ProbeResult::NoMatch;
1454 possibly_unsatisfied_predicates.push((o.predicate, None));
1459 ObjectCandidate | WhereClauseCandidate(..) => {
1460 // These have no additional conditions to check.
1463 TraitCandidate(trait_ref) => {
1464 if let Some(method_name) = self.method_name {
1465 // Some trait methods are excluded for arrays before 2021.
1466 // (`array.into_iter()` wants a slice iterator for compatibility.)
1467 if self_ty.is_array() && !method_name.span.rust_2021() {
1468 let trait_def = self.tcx.trait_def(trait_ref.def_id);
1469 if trait_def.skip_array_during_method_dispatch {
1470 return ProbeResult::NoMatch;
1474 let predicate = trait_ref.without_const().to_predicate(self.tcx);
1475 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1476 if !self.predicate_may_hold(&obligation) {
1477 result = ProbeResult::NoMatch;
1479 match self.select_trait_candidate(trait_ref) {
1480 Err(_) => return true,
1481 Ok(Some(impl_source))
1482 if !impl_source.borrow_nested_obligations().is_empty() =>
1484 for obligation in impl_source.borrow_nested_obligations() {
1485 // Determine exactly which obligation wasn't met, so
1486 // that we can give more context in the error.
1487 if !self.predicate_may_hold(obligation) {
1488 let nested_predicate =
1489 self.resolve_vars_if_possible(obligation.predicate);
1491 self.resolve_vars_if_possible(predicate);
1492 let p = if predicate == nested_predicate {
1493 // Avoid "`MyStruct: Foo` which is required by
1494 // `MyStruct: Foo`" in E0599.
1499 possibly_unsatisfied_predicates
1500 .push((nested_predicate, p));
1505 // Some nested subobligation of this predicate
1507 let predicate = self.resolve_vars_if_possible(predicate);
1508 possibly_unsatisfied_predicates.push((predicate, None));
1513 // This candidate's primary obligation doesn't even
1514 // select - don't bother registering anything in
1515 // `potentially_unsatisfied_predicates`.
1516 return ProbeResult::NoMatch;
1522 // Evaluate those obligations to see if they might possibly hold.
1523 for o in sub_obligations {
1524 let o = self.resolve_vars_if_possible(o);
1525 if !self.predicate_may_hold(&o) {
1526 result = ProbeResult::NoMatch;
1527 possibly_unsatisfied_predicates.push((o.predicate, None));
1531 if let ProbeResult::Match = result {
1532 if let (Some(return_ty), Some(xform_ret_ty)) =
1533 (self.return_type, probe.xform_ret_ty)
1535 let xform_ret_ty = self.resolve_vars_if_possible(xform_ret_ty);
1537 "comparing return_ty {:?} with xform ret ty {:?}",
1538 return_ty, probe.xform_ret_ty
1541 .at(&ObligationCause::dummy(), self.param_env)
1542 .sup(return_ty, xform_ret_ty)
1545 return ProbeResult::BadReturnType;
1554 /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1555 /// same trait, but we don't know which impl to use. In this case, since in all cases the
1556 /// external interface of the method can be determined from the trait, it's ok not to decide.
1557 /// We can basically just collapse all of the probes for various impls into one where-clause
1558 /// probe. This will result in a pending obligation so when more type-info is available we can
1559 /// make the final decision.
1561 /// Example (`src/test/ui/method-two-trait-defer-resolution-1.rs`):
1564 /// trait Foo { ... }
1565 /// impl Foo for Vec<i32> { ... }
1566 /// impl Foo for Vec<usize> { ... }
1569 /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1570 /// use, so it's ok to just commit to "using the method from the trait Foo".
1571 fn collapse_candidates_to_trait_pick(
1573 probes: &[(&Candidate<'tcx>, ProbeResult)],
1574 ) -> Option<Pick<'tcx>> {
1575 // Do all probes correspond to the same trait?
1576 let container = probes[0].0.item.container;
1577 if let ty::ImplContainer(_) = container {
1580 if probes[1..].iter().any(|&(p, _)| p.item.container != container) {
1584 // FIXME: check the return type here somehow.
1585 // If so, just use this trait and call it a day.
1587 item: probes[0].0.item,
1589 import_ids: probes[0].0.import_ids.clone(),
1591 autoref_or_ptr_adjustment: None,
1595 /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
1596 /// candidate method where the method name may have been misspelt. Similarly to other
1597 /// Levenshtein based suggestions, we provide at most one such suggestion.
1598 fn probe_for_lev_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
1599 debug!("probing for method names similar to {:?}", self.method_name);
1601 let steps = self.steps.clone();
1603 let mut pcx = ProbeContext::new(
1609 self.orig_steps_var_values.clone(),
1614 pcx.allow_similar_names = true;
1615 pcx.assemble_inherent_candidates();
1617 let method_names = pcx.candidate_method_names();
1618 pcx.allow_similar_names = false;
1619 let applicable_close_candidates: Vec<ty::AssocItem> = method_names
1621 .filter_map(|&method_name| {
1623 pcx.method_name = Some(method_name);
1624 pcx.assemble_inherent_candidates();
1625 pcx.pick_core().and_then(|pick| pick.ok()).map(|pick| pick.item)
1629 if applicable_close_candidates.is_empty() {
1633 let names = applicable_close_candidates
1635 .map(|cand| cand.ident.name)
1636 .collect::<Vec<Symbol>>();
1637 find_best_match_for_name(&names, self.method_name.unwrap().name, None)
1640 Ok(applicable_close_candidates
1642 .find(|method| method.ident.name == best_name))
1647 ///////////////////////////////////////////////////////////////////////////
1649 fn has_applicable_self(&self, item: &ty::AssocItem) -> bool {
1650 // "Fast track" -- check for usage of sugar when in method call
1653 // In Path mode (i.e., resolving a value like `T::next`), consider any
1654 // associated value (i.e., methods, constants) but not types.
1656 Mode::MethodCall => item.fn_has_self_parameter,
1657 Mode::Path => match item.kind {
1658 ty::AssocKind::Type => false,
1659 ty::AssocKind::Fn | ty::AssocKind::Const => true,
1662 // FIXME -- check for types that deref to `Self`,
1663 // like `Rc<Self>` and so on.
1665 // Note also that the current code will break if this type
1666 // includes any of the type parameters defined on the method
1667 // -- but this could be overcome.
1670 fn record_static_candidate(&mut self, source: CandidateSource) {
1671 self.static_candidates.push(source);
1676 item: &ty::AssocItem,
1678 substs: SubstsRef<'tcx>,
1679 ) -> (Ty<'tcx>, Option<Ty<'tcx>>) {
1680 if item.kind == ty::AssocKind::Fn && self.mode == Mode::MethodCall {
1681 let sig = self.xform_method_sig(item.def_id, substs);
1682 (sig.inputs()[0], Some(sig.output()))
1688 fn xform_method_sig(&self, method: DefId, substs: SubstsRef<'tcx>) -> ty::FnSig<'tcx> {
1689 let fn_sig = self.tcx.fn_sig(method);
1690 debug!("xform_self_ty(fn_sig={:?}, substs={:?})", fn_sig, substs);
1692 assert!(!substs.has_escaping_bound_vars());
1694 // It is possible for type parameters or early-bound lifetimes
1695 // to appear in the signature of `self`. The substitutions we
1696 // are given do not include type/lifetime parameters for the
1697 // method yet. So create fresh variables here for those too,
1698 // if there are any.
1699 let generics = self.tcx.generics_of(method);
1700 assert_eq!(substs.len(), generics.parent_count as usize);
1702 // Erase any late-bound regions from the method and substitute
1703 // in the values from the substitution.
1704 let xform_fn_sig = self.erase_late_bound_regions(fn_sig);
1706 if generics.params.is_empty() {
1707 xform_fn_sig.subst(self.tcx, substs)
1709 let substs = InternalSubsts::for_item(self.tcx, method, |param, _| {
1710 let i = param.index as usize;
1711 if i < substs.len() {
1715 GenericParamDefKind::Lifetime => {
1716 // In general, during probe we erase regions.
1717 self.tcx.lifetimes.re_erased.into()
1719 GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
1720 self.var_for_def(self.span, param)
1725 xform_fn_sig.subst(self.tcx, substs)
1729 /// Gets the type of an impl and generate substitutions with placeholders.
1730 fn impl_ty_and_substs(&self, impl_def_id: DefId) -> (Ty<'tcx>, SubstsRef<'tcx>) {
1731 (self.tcx.type_of(impl_def_id), self.fresh_item_substs(impl_def_id))
1734 fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx> {
1735 InternalSubsts::for_item(self.tcx, def_id, |param, _| match param.kind {
1736 GenericParamDefKind::Lifetime => self.tcx.lifetimes.re_erased.into(),
1737 GenericParamDefKind::Type { .. } => self
1738 .next_ty_var(TypeVariableOrigin {
1739 kind: TypeVariableOriginKind::SubstitutionPlaceholder,
1740 span: self.tcx.def_span(def_id),
1743 GenericParamDefKind::Const { .. } => {
1744 let span = self.tcx.def_span(def_id);
1745 let origin = ConstVariableOrigin {
1746 kind: ConstVariableOriginKind::SubstitutionPlaceholder,
1749 self.next_const_var(self.tcx.type_of(param.def_id), origin).into()
1754 /// Replaces late-bound-regions bound by `value` with `'static` using
1755 /// `ty::erase_late_bound_regions`.
1757 /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1758 /// method matching. It is reasonable during the probe phase because we don't consider region
1759 /// relationships at all. Therefore, we can just replace all the region variables with 'static
1760 /// rather than creating fresh region variables. This is nice for two reasons:
1762 /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1763 /// particular method call, it winds up creating fewer types overall, which helps for memory
1764 /// usage. (Admittedly, this is a rather small effect, though measurable.)
1766 /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1767 /// late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1768 /// regions with actual region variables as is proper, we'd have to ensure that the same
1769 /// region got replaced with the same variable, which requires a bit more coordination
1770 /// and/or tracking the substitution and
1772 fn erase_late_bound_regions<T>(&self, value: ty::Binder<'tcx, T>) -> T
1774 T: TypeFoldable<'tcx>,
1776 self.tcx.erase_late_bound_regions(value)
1779 /// Finds the method with the appropriate name (or return type, as the case may be). If
1780 /// `allow_similar_names` is set, find methods with close-matching names.
1781 // The length of the returned iterator is nearly always 0 or 1 and this
1782 // method is fairly hot.
1783 fn impl_or_trait_item(&self, def_id: DefId) -> SmallVec<[ty::AssocItem; 1]> {
1784 if let Some(name) = self.method_name {
1785 if self.allow_similar_names {
1786 let max_dist = max(name.as_str().len(), 3) / 3;
1788 .associated_items(def_id)
1789 .in_definition_order()
1791 let dist = lev_distance(&*name.as_str(), &x.ident.as_str());
1792 x.kind.namespace() == Namespace::ValueNS && dist > 0 && dist <= max_dist
1798 .associated_item(def_id, name, Namespace::ValueNS)
1799 .map_or_else(SmallVec::new, |x| SmallVec::from_buf([x]))
1802 self.tcx.associated_items(def_id).in_definition_order().copied().collect()
1807 impl<'tcx> Candidate<'tcx> {
1808 fn to_unadjusted_pick(&self) -> Pick<'tcx> {
1811 kind: match self.kind {
1812 InherentImplCandidate(..) => InherentImplPick,
1813 ObjectCandidate => ObjectPick,
1814 TraitCandidate(_) => TraitPick,
1815 WhereClauseCandidate(ref trait_ref) => {
1816 // Only trait derived from where-clauses should
1817 // appear here, so they should not contain any
1818 // inference variables or other artifacts. This
1819 // means they are safe to put into the
1820 // `WhereClausePick`.
1822 !trait_ref.skip_binder().substs.needs_infer()
1823 && !trait_ref.skip_binder().substs.has_placeholders()
1826 WhereClausePick(*trait_ref)
1829 import_ids: self.import_ids.clone(),
1831 autoref_or_ptr_adjustment: None,