2 use super::CandidateSource;
3 use super::MethodError;
4 use super::NoMatchData;
6 use crate::errors::MethodCallOnUnknownType;
8 use rustc_data_structures::fx::FxHashSet;
9 use rustc_errors::Applicability;
11 use rustc_hir::def::DefKind;
12 use rustc_hir::def::Namespace;
13 use rustc_infer::infer::canonical::OriginalQueryValues;
14 use rustc_infer::infer::canonical::{Canonical, QueryResponse};
15 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
16 use rustc_infer::infer::{self, InferOk, TyCtxtInferExt};
17 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
18 use rustc_middle::middle::stability;
19 use rustc_middle::ty::fast_reject::{simplify_type, TreatParams};
20 use rustc_middle::ty::AssocItem;
21 use rustc_middle::ty::GenericParamDefKind;
22 use rustc_middle::ty::ToPredicate;
23 use rustc_middle::ty::{self, ParamEnvAnd, Ty, TyCtxt, TypeFoldable, TypeVisitable};
24 use rustc_middle::ty::{InternalSubsts, SubstsRef};
25 use rustc_session::lint;
26 use rustc_span::def_id::DefId;
27 use rustc_span::def_id::LocalDefId;
28 use rustc_span::lev_distance::{
29 find_best_match_for_name_with_substrings, lev_distance_with_substrings,
31 use rustc_span::symbol::sym;
32 use rustc_span::{symbol::Ident, Span, Symbol, DUMMY_SP};
33 use rustc_trait_selection::autoderef::{self, Autoderef};
34 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
35 use rustc_trait_selection::traits::query::method_autoderef::MethodAutoderefBadTy;
36 use rustc_trait_selection::traits::query::method_autoderef::{
37 CandidateStep, MethodAutoderefStepsResult,
39 use rustc_trait_selection::traits::query::CanonicalTyGoal;
40 use rustc_trait_selection::traits::NormalizeExt;
41 use rustc_trait_selection::traits::{self, ObligationCause};
47 use smallvec::{smallvec, SmallVec};
49 use self::CandidateKind::*;
50 pub use self::PickKind::*;
52 /// Boolean flag used to indicate if this search is for a suggestion
53 /// or not. If true, we can allow ambiguity and so forth.
54 #[derive(Clone, Copy, Debug)]
55 pub struct IsSuggestion(pub bool);
57 struct ProbeContext<'a, 'tcx> {
58 fcx: &'a FnCtxt<'a, 'tcx>,
61 method_name: Option<Ident>,
62 return_type: Option<Ty<'tcx>>,
64 /// This is the OriginalQueryValues for the steps queries
65 /// that are answered in steps.
66 orig_steps_var_values: OriginalQueryValues<'tcx>,
67 steps: &'tcx [CandidateStep<'tcx>],
69 inherent_candidates: Vec<Candidate<'tcx>>,
70 extension_candidates: Vec<Candidate<'tcx>>,
71 impl_dups: FxHashSet<DefId>,
73 /// Collects near misses when the candidate functions are missing a `self` keyword and is only
74 /// used for error reporting
75 static_candidates: Vec<CandidateSource>,
77 /// When probing for names, include names that are close to the
78 /// requested name (by Levensthein distance)
79 allow_similar_names: bool,
81 /// Some(candidate) if there is a private candidate
82 private_candidate: Option<(DefKind, DefId)>,
84 /// Collects near misses when trait bounds for type parameters are unsatisfied and is only used
85 /// for error reporting
86 unsatisfied_predicates:
87 Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>, Option<ObligationCause<'tcx>>)>,
89 scope_expr_id: hir::HirId,
92 impl<'a, 'tcx> Deref for ProbeContext<'a, 'tcx> {
93 type Target = FnCtxt<'a, 'tcx>;
94 fn deref(&self) -> &Self::Target {
99 #[derive(Debug, Clone)]
100 struct Candidate<'tcx> {
101 // Candidates are (I'm not quite sure, but they are mostly) basically
102 // some metadata on top of a `ty::AssocItem` (without substs).
104 // However, method probing wants to be able to evaluate the predicates
105 // for a function with the substs applied - for example, if a function
106 // has `where Self: Sized`, we don't want to consider it unless `Self`
107 // is actually `Sized`, and similarly, return-type suggestions want
108 // to consider the "actual" return type.
110 // The way this is handled is through `xform_self_ty`. It contains
111 // the receiver type of this candidate, but `xform_self_ty`,
112 // `xform_ret_ty` and `kind` (which contains the predicates) have the
113 // generic parameters of this candidate substituted with the *same set*
114 // of inference variables, which acts as some weird sort of "query".
116 // When we check out a candidate, we require `xform_self_ty` to be
117 // a subtype of the passed-in self-type, and this equates the type
118 // variables in the rest of the fields.
120 // For example, if we have this candidate:
123 // fn foo(&self) where Self: Sized;
127 // Then `xform_self_ty` will be `&'erased ?X` and `kind` will contain
128 // the predicate `?X: Sized`, so if we are evaluating `Foo` for a
129 // the receiver `&T`, we'll do the subtyping which will make `?X`
130 // get the right value, then when we evaluate the predicate we'll check
132 xform_self_ty: Ty<'tcx>,
133 xform_ret_ty: Option<Ty<'tcx>>,
135 kind: CandidateKind<'tcx>,
136 import_ids: SmallVec<[LocalDefId; 1]>,
139 #[derive(Debug, Clone)]
140 enum CandidateKind<'tcx> {
141 InherentImplCandidate(
143 // Normalize obligations
144 Vec<traits::PredicateObligation<'tcx>>,
147 TraitCandidate(ty::TraitRef<'tcx>),
148 WhereClauseCandidate(
150 ty::PolyTraitRef<'tcx>,
154 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
161 /// When adjusting a receiver we often want to do one of
163 /// - Add a `&` (or `&mut`), converting the receiver from `T` to `&T` (or `&mut T`)
164 /// - If the receiver has type `*mut T`, convert it to `*const T`
166 /// This type tells us which one to do.
168 /// Note that in principle we could do both at the same time. For example, when the receiver has
169 /// type `T`, we could autoref it to `&T`, then convert to `*const T`. Or, when it has type `*mut
170 /// T`, we could convert it to `*const T`, then autoref to `&*const T`. However, currently we do
171 /// (at most) one of these. Either the receiver has type `T` and we convert it to `&T` (or with
172 /// `mut`), or it has type `*mut T` and we convert it to `*const T`.
173 #[derive(Debug, PartialEq, Copy, Clone)]
174 pub enum AutorefOrPtrAdjustment {
175 /// Receiver has type `T`, add `&` or `&mut` (it `T` is `mut`), and maybe also "unsize" it.
176 /// Unsizing is used to convert a `[T; N]` to `[T]`, which only makes sense when autorefing.
178 mutbl: hir::Mutability,
180 /// Indicates that the source expression should be "unsized" to a target type.
181 /// This is special-cased for just arrays unsizing to slices.
184 /// Receiver has type `*mut T`, convert to `*const T`
188 impl AutorefOrPtrAdjustment {
189 fn get_unsize(&self) -> bool {
191 AutorefOrPtrAdjustment::Autoref { mutbl: _, unsize } => *unsize,
192 AutorefOrPtrAdjustment::ToConstPtr => false,
197 #[derive(Debug, Clone)]
198 pub struct Pick<'tcx> {
199 pub item: ty::AssocItem,
200 pub kind: PickKind<'tcx>,
201 pub import_ids: SmallVec<[LocalDefId; 1]>,
203 /// Indicates that the source expression should be autoderef'd N times
204 /// ```ignore (not-rust)
205 /// A = expr | *expr | **expr | ...
207 pub autoderefs: usize,
209 /// Indicates that we want to add an autoref (and maybe also unsize it), or if the receiver is
210 /// `*mut T`, convert it to `*const T`.
211 pub autoref_or_ptr_adjustment: Option<AutorefOrPtrAdjustment>,
212 pub self_ty: Ty<'tcx>,
214 /// Unstable candidates alongside the stable ones.
215 unstable_candidates: Vec<(Candidate<'tcx>, Symbol)>,
218 #[derive(Clone, Debug, PartialEq, Eq)]
219 pub enum PickKind<'tcx> {
225 ty::PolyTraitRef<'tcx>,
229 pub type PickResult<'tcx> = Result<Pick<'tcx>, MethodError<'tcx>>;
231 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
233 // An expression of the form `receiver.method_name(...)`.
234 // Autoderefs are performed on `receiver`, lookup is done based on the
235 // `self` argument of the method, and static methods aren't considered.
237 // An expression of the form `Type::item` or `<T>::item`.
238 // No autoderefs are performed, lookup is done based on the type each
239 // implementation is for, and static methods are included.
243 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
244 pub enum ProbeScope {
245 // Assemble candidates coming only from traits in scope.
248 // Assemble candidates coming from all traits.
252 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
253 /// This is used to offer suggestions to users. It returns methods
254 /// that could have been called which have the desired return
255 /// type. Some effort is made to rule out methods that, if called,
256 /// would result in an error (basically, the same criteria we
257 /// would use to decide if a method is a plausible fit for
258 /// ambiguity purposes).
259 #[instrument(level = "debug", skip(self, candidate_filter))]
260 pub fn probe_for_return_type(
264 return_type: Ty<'tcx>,
266 scope_expr_id: hir::HirId,
267 candidate_filter: impl Fn(&ty::AssocItem) -> bool,
268 ) -> Vec<ty::AssocItem> {
269 let method_names = self
278 ProbeScope::AllTraits,
279 |probe_cx| Ok(probe_cx.candidate_method_names(candidate_filter)),
281 .unwrap_or_default();
284 .flat_map(|&method_name| {
293 ProbeScope::AllTraits,
294 |probe_cx| probe_cx.pick(),
297 .map(|pick| pick.item)
302 #[instrument(level = "debug", skip(self))]
303 pub fn probe_for_name(
307 is_suggestion: IsSuggestion,
309 scope_expr_id: hir::HirId,
311 ) -> PickResult<'tcx> {
321 |probe_cx| probe_cx.pick(),
329 method_name: Option<Ident>,
330 return_type: Option<Ty<'tcx>>,
331 is_suggestion: IsSuggestion,
333 scope_expr_id: hir::HirId,
336 ) -> Result<R, MethodError<'tcx>>
338 OP: FnOnce(ProbeContext<'a, 'tcx>) -> Result<R, MethodError<'tcx>>,
340 let mut orig_values = OriginalQueryValues::default();
341 let param_env_and_self_ty = self.canonicalize_query(
342 ParamEnvAnd { param_env: self.param_env, value: self_ty },
346 let steps = match mode {
347 Mode::MethodCall => self.tcx.method_autoderef_steps(param_env_and_self_ty),
348 Mode::Path => self.probe(|_| {
349 // Mode::Path - the deref steps is "trivial". This turns
350 // our CanonicalQuery into a "trivial" QueryResponse. This
351 // is a bit inefficient, but I don't think that writing
352 // special handling for this "trivial case" is a good idea.
354 let infcx = &self.infcx;
355 let (ParamEnvAnd { param_env: _, value: self_ty }, canonical_inference_vars) =
356 infcx.instantiate_canonical_with_fresh_inference_vars(
358 ¶m_env_and_self_ty,
361 "probe_op: Mode::Path, param_env_and_self_ty={:?} self_ty={:?}",
362 param_env_and_self_ty, self_ty
364 MethodAutoderefStepsResult {
365 steps: infcx.tcx.arena.alloc_from_iter([CandidateStep {
366 self_ty: self.make_query_response_ignoring_pending_obligations(
367 canonical_inference_vars,
371 from_unsafe_deref: false,
375 reached_recursion_limit: false,
380 // If our autoderef loop had reached the recursion limit,
381 // report an overflow error, but continue going on with
382 // the truncated autoderef list.
383 if steps.reached_recursion_limit {
388 .unwrap_or_else(|| span_bug!(span, "reached the recursion limit in 0 steps?"))
391 .probe_instantiate_query_response(span, &orig_values, ty)
392 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
393 autoderef::report_autoderef_recursion_limit_error(self.tcx, span, ty.value);
397 // If we encountered an `_` type or an error type during autoderef, this is
399 if let Some(bad_ty) = &steps.opt_bad_ty {
401 // Ambiguity was encountered during a suggestion. Just keep going.
402 debug!("ProbeContext: encountered ambiguity in suggestion");
403 } else if bad_ty.reached_raw_pointer && !self.tcx.features().arbitrary_self_types {
404 // this case used to be allowed by the compiler,
405 // so we do a future-compat lint here for the 2015 edition
406 // (see https://github.com/rust-lang/rust/issues/46906)
407 if self.tcx.sess.rust_2018() {
408 self.tcx.sess.emit_err(MethodCallOnUnknownType { span });
410 self.tcx.struct_span_lint_hir(
411 lint::builtin::TYVAR_BEHIND_RAW_POINTER,
414 "type annotations needed",
419 // Encountered a real ambiguity, so abort the lookup. If `ty` is not
420 // an `Err`, report the right "type annotations needed" error pointing
424 .probe_instantiate_query_response(span, &orig_values, ty)
425 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
426 let ty = self.structurally_resolved_type(span, ty.value);
427 assert!(matches!(ty.kind(), ty::Error(_)));
428 return Err(MethodError::NoMatch(NoMatchData {
429 static_candidates: Vec::new(),
430 unsatisfied_predicates: Vec::new(),
431 out_of_scope_traits: Vec::new(),
438 debug!("ProbeContext: steps for self_ty={:?} are {:?}", self_ty, steps);
440 // this creates one big transaction so that all type variables etc
441 // that we create during the probe process are removed later
443 let mut probe_cx = ProbeContext::new(
454 probe_cx.assemble_inherent_candidates();
456 ProbeScope::TraitsInScope => {
457 probe_cx.assemble_extension_candidates_for_traits_in_scope(scope_expr_id)
459 ProbeScope::AllTraits => probe_cx.assemble_extension_candidates_for_all_traits(),
466 pub fn provide(providers: &mut ty::query::Providers) {
467 providers.method_autoderef_steps = method_autoderef_steps;
470 fn method_autoderef_steps<'tcx>(
472 goal: CanonicalTyGoal<'tcx>,
473 ) -> MethodAutoderefStepsResult<'tcx> {
474 debug!("method_autoderef_steps({:?})", goal);
476 let (ref infcx, goal, inference_vars) = tcx.infer_ctxt().build_with_canonical(DUMMY_SP, &goal);
477 let ParamEnvAnd { param_env, value: self_ty } = goal;
479 let mut autoderef = Autoderef::new(infcx, param_env, hir::CRATE_HIR_ID, DUMMY_SP, self_ty)
480 .include_raw_pointers()
482 let mut reached_raw_pointer = false;
483 let mut steps: Vec<_> = autoderef
486 let step = CandidateStep {
488 .make_query_response_ignoring_pending_obligations(inference_vars.clone(), ty),
490 from_unsafe_deref: reached_raw_pointer,
493 if let ty::RawPtr(_) = ty.kind() {
494 // all the subsequent steps will be from_unsafe_deref
495 reached_raw_pointer = true;
501 let final_ty = autoderef.final_ty(true);
502 let opt_bad_ty = match final_ty.kind() {
503 ty::Infer(ty::TyVar(_)) | ty::Error(_) => Some(MethodAutoderefBadTy {
505 ty: infcx.make_query_response_ignoring_pending_obligations(inference_vars, final_ty),
507 ty::Array(elem_ty, _) => {
508 let dereferences = steps.len() - 1;
510 steps.push(CandidateStep {
511 self_ty: infcx.make_query_response_ignoring_pending_obligations(
513 infcx.tcx.mk_slice(*elem_ty),
515 autoderefs: dereferences,
516 // this could be from an unsafe deref if we had
517 // a *mut/const [T; N]
518 from_unsafe_deref: reached_raw_pointer,
527 debug!("method_autoderef_steps: steps={:?} opt_bad_ty={:?}", steps, opt_bad_ty);
529 MethodAutoderefStepsResult {
530 steps: tcx.arena.alloc_from_iter(steps),
531 opt_bad_ty: opt_bad_ty.map(|ty| &*tcx.arena.alloc(ty)),
532 reached_recursion_limit: autoderef.reached_recursion_limit(),
536 impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
538 fcx: &'a FnCtxt<'a, 'tcx>,
541 method_name: Option<Ident>,
542 return_type: Option<Ty<'tcx>>,
543 orig_steps_var_values: OriginalQueryValues<'tcx>,
544 steps: &'tcx [CandidateStep<'tcx>],
545 scope_expr_id: hir::HirId,
546 ) -> ProbeContext<'a, 'tcx> {
553 inherent_candidates: Vec::new(),
554 extension_candidates: Vec::new(),
555 impl_dups: FxHashSet::default(),
556 orig_steps_var_values,
558 static_candidates: Vec::new(),
559 allow_similar_names: false,
560 private_candidate: None,
561 unsatisfied_predicates: Vec::new(),
566 fn reset(&mut self) {
567 self.inherent_candidates.clear();
568 self.extension_candidates.clear();
569 self.impl_dups.clear();
570 self.static_candidates.clear();
571 self.private_candidate = None;
574 ///////////////////////////////////////////////////////////////////////////
575 // CANDIDATE ASSEMBLY
577 fn push_candidate(&mut self, candidate: Candidate<'tcx>, is_inherent: bool) {
578 let is_accessible = if let Some(name) = self.method_name {
579 let item = candidate.item;
582 .adjust_ident_and_get_scope(name, item.container_id(self.tcx), self.body_id)
584 item.visibility(self.tcx).is_accessible_from(def_scope, self.tcx)
590 self.inherent_candidates.push(candidate);
592 self.extension_candidates.push(candidate);
594 } else if self.private_candidate.is_none() {
595 self.private_candidate =
596 Some((candidate.item.kind.as_def_kind(), candidate.item.def_id));
600 fn assemble_inherent_candidates(&mut self) {
601 for step in self.steps.iter() {
602 self.assemble_probe(&step.self_ty);
606 fn assemble_probe(&mut self, self_ty: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>) {
607 debug!("assemble_probe: self_ty={:?}", self_ty);
608 let raw_self_ty = self_ty.value.value;
609 match *raw_self_ty.kind() {
610 ty::Dynamic(data, ..) if let Some(p) = data.principal() => {
611 // Subtle: we can't use `instantiate_query_response` here: using it will
612 // commit to all of the type equalities assumed by inference going through
613 // autoderef (see the `method-probe-no-guessing` test).
615 // However, in this code, it is OK if we end up with an object type that is
616 // "more general" than the object type that we are evaluating. For *every*
617 // object type `MY_OBJECT`, a function call that goes through a trait-ref
618 // of the form `<MY_OBJECT as SuperTraitOf(MY_OBJECT)>::func` is a valid
619 // `ObjectCandidate`, and it should be discoverable "exactly" through one
620 // of the iterations in the autoderef loop, so there is no problem with it
621 // being discoverable in another one of these iterations.
623 // Using `instantiate_canonical_with_fresh_inference_vars` on our
624 // `Canonical<QueryResponse<Ty<'tcx>>>` and then *throwing away* the
625 // `CanonicalVarValues` will exactly give us such a generalization - it
626 // will still match the original object type, but it won't pollute our
627 // type variables in any form, so just do that!
628 let (QueryResponse { value: generalized_self_ty, .. }, _ignored_var_values) =
630 .instantiate_canonical_with_fresh_inference_vars(self.span, self_ty);
632 self.assemble_inherent_candidates_from_object(generalized_self_ty);
633 self.assemble_inherent_impl_candidates_for_type(p.def_id());
634 if self.tcx.has_attr(p.def_id(), sym::rustc_has_incoherent_inherent_impls) {
635 self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
639 let def_id = def.did();
640 self.assemble_inherent_impl_candidates_for_type(def_id);
641 if self.tcx.has_attr(def_id, sym::rustc_has_incoherent_inherent_impls) {
642 self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
645 ty::Foreign(did) => {
646 self.assemble_inherent_impl_candidates_for_type(did);
647 if self.tcx.has_attr(did, sym::rustc_has_incoherent_inherent_impls) {
648 self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
652 self.assemble_inherent_candidates_from_param(p);
665 | ty::Tuple(..) => self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty),
670 fn assemble_inherent_candidates_for_incoherent_ty(&mut self, self_ty: Ty<'tcx>) {
671 let Some(simp) = simplify_type(self.tcx, self_ty, TreatParams::AsInfer) else {
672 bug!("unexpected incoherent type: {:?}", self_ty)
674 for &impl_def_id in self.tcx.incoherent_impls(simp) {
675 self.assemble_inherent_impl_probe(impl_def_id);
679 fn assemble_inherent_impl_candidates_for_type(&mut self, def_id: DefId) {
680 let impl_def_ids = self.tcx.at(self.span).inherent_impls(def_id);
681 for &impl_def_id in impl_def_ids.iter() {
682 self.assemble_inherent_impl_probe(impl_def_id);
686 fn assemble_inherent_impl_probe(&mut self, impl_def_id: DefId) {
687 if !self.impl_dups.insert(impl_def_id) {
688 return; // already visited
691 debug!("assemble_inherent_impl_probe {:?}", impl_def_id);
693 for item in self.impl_or_trait_item(impl_def_id) {
694 if !self.has_applicable_self(&item) {
695 // No receiver declared. Not a candidate.
696 self.record_static_candidate(CandidateSource::Impl(impl_def_id));
700 let (impl_ty, impl_substs) = self.impl_ty_and_substs(impl_def_id);
701 let impl_ty = impl_ty.subst(self.tcx, impl_substs);
703 debug!("impl_ty: {:?}", impl_ty);
705 // Determine the receiver type that the method itself expects.
706 let (xform_self_ty, xform_ret_ty) = self.xform_self_ty(&item, impl_ty, impl_substs);
707 debug!("xform_self_ty: {:?}, xform_ret_ty: {:?}", xform_self_ty, xform_ret_ty);
709 // We can't use normalize_associated_types_in as it will pollute the
710 // fcx's fulfillment context after this probe is over.
711 // Note: we only normalize `xform_self_ty` here since the normalization
712 // of the return type can lead to inference results that prohibit
713 // valid candidates from being found, see issue #85671
714 // FIXME Postponing the normalization of the return type likely only hides a deeper bug,
715 // which might be caused by the `param_env` itself. The clauses of the `param_env`
716 // maybe shouldn't include `Param`s, but rather fresh variables or be canonicalized,
718 let cause = traits::ObligationCause::misc(self.span, self.body_id);
719 let InferOk { value: xform_self_ty, obligations } =
720 self.fcx.at(&cause, self.param_env).normalize(xform_self_ty);
723 "assemble_inherent_impl_probe after normalization: xform_self_ty = {:?}/{:?}",
724 xform_self_ty, xform_ret_ty
732 kind: InherentImplCandidate(impl_substs, obligations),
733 import_ids: smallvec![],
740 fn assemble_inherent_candidates_from_object(&mut self, self_ty: Ty<'tcx>) {
741 debug!("assemble_inherent_candidates_from_object(self_ty={:?})", self_ty);
743 let principal = match self_ty.kind() {
744 ty::Dynamic(ref data, ..) => Some(data),
747 .and_then(|data| data.principal())
751 "non-object {:?} in assemble_inherent_candidates_from_object",
756 // It is illegal to invoke a method on a trait instance that refers to
757 // the `Self` type. An [`ObjectSafetyViolation::SupertraitSelf`] error
758 // will be reported by `object_safety.rs` if the method refers to the
759 // `Self` type anywhere other than the receiver. Here, we use a
760 // substitution that replaces `Self` with the object type itself. Hence,
761 // a `&self` method will wind up with an argument type like `&dyn Trait`.
762 let trait_ref = principal.with_self_ty(self.tcx, self_ty);
763 self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
764 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
766 let (xform_self_ty, xform_ret_ty) =
767 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
773 kind: ObjectCandidate,
774 import_ids: smallvec![],
781 fn assemble_inherent_candidates_from_param(&mut self, param_ty: ty::ParamTy) {
782 // FIXME: do we want to commit to this behavior for param bounds?
783 debug!("assemble_inherent_candidates_from_param(param_ty={:?})", param_ty);
785 let bounds = self.param_env.caller_bounds().iter().filter_map(|predicate| {
786 let bound_predicate = predicate.kind();
787 match bound_predicate.skip_binder() {
788 ty::PredicateKind::Clause(ty::Clause::Trait(trait_predicate)) => {
789 match *trait_predicate.trait_ref.self_ty().kind() {
790 ty::Param(p) if p == param_ty => {
791 Some(bound_predicate.rebind(trait_predicate.trait_ref))
796 ty::PredicateKind::Subtype(..)
797 | ty::PredicateKind::Coerce(..)
798 | ty::PredicateKind::Clause(ty::Clause::Projection(..))
799 | ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..))
800 | ty::PredicateKind::WellFormed(..)
801 | ty::PredicateKind::ObjectSafe(..)
802 | ty::PredicateKind::ClosureKind(..)
803 | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..))
804 | ty::PredicateKind::ConstEvaluatable(..)
805 | ty::PredicateKind::ConstEquate(..)
806 | ty::PredicateKind::Ambiguous
807 | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
811 self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
812 let trait_ref = this.erase_late_bound_regions(poly_trait_ref);
814 let (xform_self_ty, xform_ret_ty) =
815 this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs);
817 // Because this trait derives from a where-clause, it
818 // should not contain any inference variables or other
819 // artifacts. This means it is safe to put into the
820 // `WhereClauseCandidate` and (eventually) into the
821 // `WhereClausePick`.
822 assert!(!trait_ref.substs.needs_infer());
829 kind: WhereClauseCandidate(poly_trait_ref),
830 import_ids: smallvec![],
837 // Do a search through a list of bounds, using a callback to actually
838 // create the candidates.
839 fn elaborate_bounds<F>(
841 bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
844 F: for<'b> FnMut(&mut ProbeContext<'b, 'tcx>, ty::PolyTraitRef<'tcx>, ty::AssocItem),
847 for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
848 debug!("elaborate_bounds(bound_trait_ref={:?})", bound_trait_ref);
849 for item in self.impl_or_trait_item(bound_trait_ref.def_id()) {
850 if !self.has_applicable_self(&item) {
851 self.record_static_candidate(CandidateSource::Trait(bound_trait_ref.def_id()));
853 mk_cand(self, bound_trait_ref, item);
859 fn assemble_extension_candidates_for_traits_in_scope(&mut self, expr_hir_id: hir::HirId) {
860 let mut duplicates = FxHashSet::default();
861 let opt_applicable_traits = self.tcx.in_scope_traits(expr_hir_id);
862 if let Some(applicable_traits) = opt_applicable_traits {
863 for trait_candidate in applicable_traits.iter() {
864 let trait_did = trait_candidate.def_id;
865 if duplicates.insert(trait_did) {
866 self.assemble_extension_candidates_for_trait(
867 &trait_candidate.import_ids,
875 fn assemble_extension_candidates_for_all_traits(&mut self) {
876 let mut duplicates = FxHashSet::default();
877 for trait_info in suggest::all_traits(self.tcx) {
878 if duplicates.insert(trait_info.def_id) {
879 self.assemble_extension_candidates_for_trait(&smallvec![], trait_info.def_id);
884 fn matches_return_type(
886 method: &ty::AssocItem,
887 self_ty: Option<Ty<'tcx>>,
891 ty::AssocKind::Fn => {
892 let fty = self.tcx.bound_fn_sig(method.def_id);
894 let substs = self.fresh_substs_for_item(self.span, method.def_id);
895 let fty = fty.subst(self.tcx, substs);
897 self.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, fty);
899 if let Some(self_ty) = self_ty {
901 .at(&ObligationCause::dummy(), self.param_env)
902 .sup(fty.inputs()[0], self_ty)
908 self.can_sub(self.param_env, fty.output(), expected).is_ok()
915 fn assemble_extension_candidates_for_trait(
917 import_ids: &SmallVec<[LocalDefId; 1]>,
920 debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})", trait_def_id);
921 let trait_substs = self.fresh_item_substs(trait_def_id);
922 let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
924 if self.tcx.is_trait_alias(trait_def_id) {
925 // For trait aliases, assume all supertraits are relevant.
926 let bounds = iter::once(ty::Binder::dummy(trait_ref));
927 self.elaborate_bounds(bounds, |this, new_trait_ref, item| {
928 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
930 let (xform_self_ty, xform_ret_ty) =
931 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
937 import_ids: import_ids.clone(),
938 kind: TraitCandidate(new_trait_ref),
944 debug_assert!(self.tcx.is_trait(trait_def_id));
945 for item in self.impl_or_trait_item(trait_def_id) {
946 // Check whether `trait_def_id` defines a method with suitable name.
947 if !self.has_applicable_self(&item) {
948 debug!("method has inapplicable self");
949 self.record_static_candidate(CandidateSource::Trait(trait_def_id));
953 let (xform_self_ty, xform_ret_ty) =
954 self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
960 import_ids: import_ids.clone(),
961 kind: TraitCandidate(trait_ref),
969 fn candidate_method_names(
971 candidate_filter: impl Fn(&ty::AssocItem) -> bool,
973 let mut set = FxHashSet::default();
974 let mut names: Vec<_> = self
977 .chain(&self.extension_candidates)
978 .filter(|candidate| candidate_filter(&candidate.item))
979 .filter(|candidate| {
980 if let Some(return_ty) = self.return_type {
981 self.matches_return_type(&candidate.item, None, return_ty)
986 .map(|candidate| candidate.item.ident(self.tcx))
987 .filter(|&name| set.insert(name))
990 // Sort them by the name so we have a stable result.
991 names.sort_by(|a, b| a.as_str().partial_cmp(b.as_str()).unwrap());
995 ///////////////////////////////////////////////////////////////////////////
998 fn pick(mut self) -> PickResult<'tcx> {
999 assert!(self.method_name.is_some());
1001 if let Some(r) = self.pick_core() {
1005 debug!("pick: actual search failed, assemble diagnostics");
1007 let static_candidates = mem::take(&mut self.static_candidates);
1008 let private_candidate = self.private_candidate.take();
1009 let unsatisfied_predicates = mem::take(&mut self.unsatisfied_predicates);
1011 // things failed, so lets look at all traits, for diagnostic purposes now:
1014 let span = self.span;
1017 self.assemble_extension_candidates_for_all_traits();
1019 let out_of_scope_traits = match self.pick_core() {
1020 Some(Ok(p)) => vec![p.item.container_id(self.tcx)],
1021 Some(Err(MethodError::Ambiguity(v))) => v
1023 .map(|source| match source {
1024 CandidateSource::Trait(id) => id,
1025 CandidateSource::Impl(impl_id) => match tcx.trait_id_of_impl(impl_id) {
1027 None => span_bug!(span, "found inherent method when looking at traits"),
1031 Some(Err(MethodError::NoMatch(NoMatchData {
1032 out_of_scope_traits: others, ..
1034 assert!(others.is_empty());
1040 if let Some((kind, def_id)) = private_candidate {
1041 return Err(MethodError::PrivateMatch(kind, def_id, out_of_scope_traits));
1043 let lev_candidate = self.probe_for_lev_candidate()?;
1045 Err(MethodError::NoMatch(NoMatchData {
1047 unsatisfied_predicates,
1048 out_of_scope_traits,
1054 fn pick_core(&mut self) -> Option<PickResult<'tcx>> {
1055 let pick = self.pick_all_method(Some(&mut vec![]));
1057 // In this case unstable picking is done by `pick_method`.
1058 if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable {
1063 return self.pick_all_method(None);
1070 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1071 ) -> Option<PickResult<'tcx>> {
1072 let steps = self.steps.clone();
1076 debug!("pick_all_method: step={:?}", step);
1077 // skip types that are from a type error or that would require dereferencing
1079 !step.self_ty.references_error() && !step.from_unsafe_deref
1082 let InferOk { value: self_ty, obligations: _ } = self
1084 .probe_instantiate_query_response(
1086 &self.orig_steps_var_values,
1089 .unwrap_or_else(|_| {
1090 span_bug!(self.span, "{:?} was applicable but now isn't?", step.self_ty)
1092 self.pick_by_value_method(step, self_ty, unstable_candidates.as_deref_mut())
1094 self.pick_autorefd_method(
1097 hir::Mutability::Not,
1098 unstable_candidates.as_deref_mut(),
1101 self.pick_autorefd_method(
1104 hir::Mutability::Mut,
1105 unstable_candidates.as_deref_mut(),
1109 self.pick_const_ptr_method(
1112 unstable_candidates.as_deref_mut(),
1120 /// For each type `T` in the step list, this attempts to find a method where
1121 /// the (transformed) self type is exactly `T`. We do however do one
1122 /// transformation on the adjustment: if we are passing a region pointer in,
1123 /// we will potentially *reborrow* it to a shorter lifetime. This allows us
1124 /// to transparently pass `&mut` pointers, in particular, without consuming
1125 /// them for their entire lifetime.
1126 fn pick_by_value_method(
1128 step: &CandidateStep<'tcx>,
1130 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1131 ) -> Option<PickResult<'tcx>> {
1136 self.pick_method(self_ty, unstable_candidates).map(|r| {
1138 pick.autoderefs = step.autoderefs;
1140 // Insert a `&*` or `&mut *` if this is a reference type:
1141 if let ty::Ref(_, _, mutbl) = *step.self_ty.value.value.kind() {
1142 pick.autoderefs += 1;
1143 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::Autoref {
1145 unsize: pick.autoref_or_ptr_adjustment.map_or(false, |a| a.get_unsize()),
1154 fn pick_autorefd_method(
1156 step: &CandidateStep<'tcx>,
1158 mutbl: hir::Mutability,
1159 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1160 ) -> Option<PickResult<'tcx>> {
1163 // In general, during probing we erase regions.
1164 let region = tcx.lifetimes.re_erased;
1166 let autoref_ty = tcx.mk_ref(region, ty::TypeAndMut { ty: self_ty, mutbl });
1167 self.pick_method(autoref_ty, unstable_candidates).map(|r| {
1169 pick.autoderefs = step.autoderefs;
1170 pick.autoref_or_ptr_adjustment =
1171 Some(AutorefOrPtrAdjustment::Autoref { mutbl, unsize: step.unsize });
1177 /// If `self_ty` is `*mut T` then this picks `*const T` methods. The reason why we have a
1178 /// special case for this is because going from `*mut T` to `*const T` with autoderefs and
1179 /// autorefs would require dereferencing the pointer, which is not safe.
1180 fn pick_const_ptr_method(
1182 step: &CandidateStep<'tcx>,
1184 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1185 ) -> Option<PickResult<'tcx>> {
1186 // Don't convert an unsized reference to ptr
1191 let &ty::RawPtr(ty::TypeAndMut { ty, mutbl: hir::Mutability::Mut }) = self_ty.kind() else {
1195 let const_self_ty = ty::TypeAndMut { ty, mutbl: hir::Mutability::Not };
1196 let const_ptr_ty = self.tcx.mk_ptr(const_self_ty);
1197 self.pick_method(const_ptr_ty, unstable_candidates).map(|r| {
1199 pick.autoderefs = step.autoderefs;
1200 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::ToConstPtr);
1206 fn pick_method_with_unstable(&mut self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
1207 debug!("pick_method_with_unstable(self_ty={})", self.ty_to_string(self_ty));
1209 let mut possibly_unsatisfied_predicates = Vec::new();
1211 for (kind, candidates) in
1212 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1214 debug!("searching {} candidates", kind);
1215 let res = self.consider_candidates(
1218 &mut possibly_unsatisfied_predicates,
1226 debug!("searching unstable candidates");
1227 let res = self.consider_candidates(
1229 self.inherent_candidates.iter().chain(&self.extension_candidates),
1230 &mut possibly_unsatisfied_predicates,
1234 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1242 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1243 ) -> Option<PickResult<'tcx>> {
1244 if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable {
1245 return self.pick_method_with_unstable(self_ty);
1248 debug!("pick_method(self_ty={})", self.ty_to_string(self_ty));
1250 let mut possibly_unsatisfied_predicates = Vec::new();
1252 for (kind, candidates) in
1253 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1255 debug!("searching {} candidates", kind);
1256 let res = self.consider_candidates(
1259 &mut possibly_unsatisfied_predicates,
1260 unstable_candidates.as_deref_mut(),
1262 if let Some(pick) = res {
1267 // `pick_method` may be called twice for the same self_ty if no stable methods
1268 // match. Only extend once.
1269 if unstable_candidates.is_some() {
1270 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1275 fn consider_candidates<'b, ProbesIter>(
1279 possibly_unsatisfied_predicates: &mut Vec<(
1280 ty::Predicate<'tcx>,
1281 Option<ty::Predicate<'tcx>>,
1282 Option<ObligationCause<'tcx>>,
1284 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1285 ) -> Option<PickResult<'tcx>>
1287 ProbesIter: Iterator<Item = &'b Candidate<'tcx>> + Clone,
1290 let mut applicable_candidates: Vec<_> = probes
1293 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
1295 .filter(|&(_, status)| status != ProbeResult::NoMatch)
1298 debug!("applicable_candidates: {:?}", applicable_candidates);
1300 if applicable_candidates.len() > 1 {
1302 self.collapse_candidates_to_trait_pick(self_ty, &applicable_candidates)
1304 return Some(Ok(pick));
1308 if let Some(uc) = &mut unstable_candidates {
1309 applicable_candidates.retain(|&(p, _)| {
1310 if let stability::EvalResult::Deny { feature, .. } =
1311 self.tcx.eval_stability(p.item.def_id, None, self.span, None)
1313 uc.push((p.clone(), feature));
1320 if applicable_candidates.len() > 1 {
1321 let sources = probes.map(|p| self.candidate_source(p, self_ty)).collect();
1322 return Some(Err(MethodError::Ambiguity(sources)));
1325 applicable_candidates.pop().map(|(probe, status)| {
1326 if status == ProbeResult::Match {
1328 .to_unadjusted_pick(self_ty, unstable_candidates.cloned().unwrap_or_default()))
1330 Err(MethodError::BadReturnType)
1336 impl<'tcx> Pick<'tcx> {
1337 /// In case there were unstable name collisions, emit them as a lint.
1338 /// Checks whether two picks do not refer to the same trait item for the same `Self` type.
1339 /// Only useful for comparisons of picks in order to improve diagnostics.
1340 /// Do not use for type checking.
1341 pub fn differs_from(&self, other: &Self) -> bool {
1349 trait_item_def_id: _,
1350 fn_has_self_parameter: _,
1355 autoref_or_ptr_adjustment: _,
1357 unstable_candidates: _,
1359 self_ty != other.self_ty || def_id != other.item.def_id
1362 /// In case there were unstable name collisions, emit them as a lint.
1363 pub fn maybe_emit_unstable_name_collision_hint(
1367 scope_expr_id: hir::HirId,
1369 if self.unstable_candidates.is_empty() {
1372 let def_kind = self.item.kind.as_def_kind();
1373 tcx.struct_span_lint_hir(
1374 lint::builtin::UNSTABLE_NAME_COLLISIONS,
1378 "{} {} with this name may be added to the standard library in the future",
1380 def_kind.descr(self.item.def_id),
1383 match (self.item.kind, self.item.container) {
1384 (ty::AssocKind::Fn, _) => {
1385 // FIXME: This should be a `span_suggestion` instead of `help`
1386 // However `self.span` only
1387 // highlights the method name, so we can't use it. Also consider reusing
1388 // the code from `report_method_error()`.
1390 "call with fully qualified syntax `{}(...)` to keep using the current \
1392 tcx.def_path_str(self.item.def_id),
1395 (ty::AssocKind::Const, ty::AssocItemContainer::TraitContainer) => {
1396 let def_id = self.item.container_id(tcx);
1397 lint.span_suggestion(
1399 "use the fully qualified path to the associated const",
1403 tcx.def_path_str(def_id),
1406 Applicability::MachineApplicable,
1411 if tcx.sess.is_nightly_build() {
1412 for (candidate, feature) in &self.unstable_candidates {
1414 "add `#![feature({})]` to the crate attributes to enable `{}`",
1416 tcx.def_path_str(candidate.item.def_id),
1427 impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
1428 fn select_trait_candidate(
1430 trait_ref: ty::TraitRef<'tcx>,
1431 ) -> traits::SelectionResult<'tcx, traits::Selection<'tcx>> {
1432 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1433 let predicate = ty::Binder::dummy(trait_ref);
1434 let obligation = traits::Obligation::new(self.tcx, cause, self.param_env, predicate);
1435 traits::SelectionContext::new(self).select(&obligation)
1438 fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>) -> CandidateSource {
1439 match candidate.kind {
1440 InherentImplCandidate(..) => {
1441 CandidateSource::Impl(candidate.item.container_id(self.tcx))
1443 ObjectCandidate | WhereClauseCandidate(_) => {
1444 CandidateSource::Trait(candidate.item.container_id(self.tcx))
1446 TraitCandidate(trait_ref) => self.probe(|_| {
1448 .at(&ObligationCause::dummy(), self.param_env)
1449 .define_opaque_types(false)
1450 .sup(candidate.xform_self_ty, self_ty);
1451 match self.select_trait_candidate(trait_ref) {
1452 Ok(Some(traits::ImplSource::UserDefined(ref impl_data))) => {
1453 // If only a single impl matches, make the error message point
1455 CandidateSource::Impl(impl_data.impl_def_id)
1457 _ => CandidateSource::Trait(candidate.item.container_id(self.tcx)),
1466 probe: &Candidate<'tcx>,
1467 possibly_unsatisfied_predicates: &mut Vec<(
1468 ty::Predicate<'tcx>,
1469 Option<ty::Predicate<'tcx>>,
1470 Option<ObligationCause<'tcx>>,
1473 debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe);
1476 // First check that the self type can be related.
1477 let sub_obligations = match self
1478 .at(&ObligationCause::dummy(), self.param_env)
1479 .define_opaque_types(false)
1480 .sup(probe.xform_self_ty, self_ty)
1482 Ok(InferOk { obligations, value: () }) => obligations,
1484 debug!("--> cannot relate self-types {:?}", err);
1485 return ProbeResult::NoMatch;
1489 let mut result = ProbeResult::Match;
1490 let mut xform_ret_ty = probe.xform_ret_ty;
1491 debug!(?xform_ret_ty);
1493 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1495 let mut parent_pred = None;
1497 // If so, impls may carry other conditions (e.g., where
1498 // clauses) that must be considered. Make sure that those
1499 // match as well (or at least may match, sometimes we
1500 // don't have enough information to fully evaluate).
1502 InherentImplCandidate(ref substs, ref ref_obligations) => {
1503 // `xform_ret_ty` hasn't been normalized yet, only `xform_self_ty`,
1504 // see the reasons mentioned in the comments in `assemble_inherent_impl_probe`
1505 // for why this is necessary
1507 value: normalized_xform_ret_ty,
1508 obligations: normalization_obligations,
1509 } = self.fcx.at(&cause, self.param_env).normalize(probe.xform_ret_ty);
1510 xform_ret_ty = normalized_xform_ret_ty;
1511 debug!("xform_ret_ty after normalization: {:?}", xform_ret_ty);
1513 // Check whether the impl imposes obligations we have to worry about.
1514 let impl_def_id = probe.item.container_id(self.tcx);
1515 let impl_bounds = self.tcx.predicates_of(impl_def_id);
1516 let impl_bounds = impl_bounds.instantiate(self.tcx, substs);
1518 let InferOk { value: impl_bounds, obligations: norm_obligations } =
1519 self.fcx.at(&cause, self.param_env).normalize(impl_bounds);
1521 // Convert the bounds into obligations.
1522 let impl_obligations = traits::predicates_for_generics(
1523 move |_, _| cause.clone(),
1528 let candidate_obligations = impl_obligations
1529 .chain(norm_obligations.into_iter())
1530 .chain(ref_obligations.iter().cloned())
1531 .chain(normalization_obligations.into_iter());
1533 // Evaluate those obligations to see if they might possibly hold.
1534 for o in candidate_obligations {
1535 let o = self.resolve_vars_if_possible(o);
1536 if !self.predicate_may_hold(&o) {
1537 result = ProbeResult::NoMatch;
1538 possibly_unsatisfied_predicates.push((
1547 ObjectCandidate | WhereClauseCandidate(..) => {
1548 // These have no additional conditions to check.
1551 TraitCandidate(trait_ref) => {
1552 if let Some(method_name) = self.method_name {
1553 // Some trait methods are excluded for arrays before 2021.
1554 // (`array.into_iter()` wants a slice iterator for compatibility.)
1555 if self_ty.is_array() && !method_name.span.rust_2021() {
1556 let trait_def = self.tcx.trait_def(trait_ref.def_id);
1557 if trait_def.skip_array_during_method_dispatch {
1558 return ProbeResult::NoMatch;
1563 ty::Binder::dummy(trait_ref).without_const().to_predicate(self.tcx);
1564 parent_pred = Some(predicate);
1566 traits::Obligation::new(self.tcx, cause, self.param_env, predicate);
1567 if !self.predicate_may_hold(&obligation) {
1568 result = ProbeResult::NoMatch;
1570 match self.select_trait_candidate(trait_ref) {
1571 Err(_) => return true,
1572 Ok(Some(impl_source))
1573 if !impl_source.borrow_nested_obligations().is_empty() =>
1575 for obligation in impl_source.borrow_nested_obligations() {
1576 // Determine exactly which obligation wasn't met, so
1577 // that we can give more context in the error.
1578 if !self.predicate_may_hold(obligation) {
1579 let nested_predicate =
1580 self.resolve_vars_if_possible(obligation.predicate);
1582 self.resolve_vars_if_possible(predicate);
1583 let p = if predicate == nested_predicate {
1584 // Avoid "`MyStruct: Foo` which is required by
1585 // `MyStruct: Foo`" in E0599.
1590 possibly_unsatisfied_predicates.push((
1593 Some(obligation.cause.clone()),
1599 // Some nested subobligation of this predicate
1601 let predicate = self.resolve_vars_if_possible(predicate);
1602 possibly_unsatisfied_predicates.push((predicate, None, None));
1607 // This candidate's primary obligation doesn't even
1608 // select - don't bother registering anything in
1609 // `potentially_unsatisfied_predicates`.
1610 return ProbeResult::NoMatch;
1616 // Evaluate those obligations to see if they might possibly hold.
1617 for o in sub_obligations {
1618 let o = self.resolve_vars_if_possible(o);
1619 if !self.predicate_may_hold(&o) {
1620 result = ProbeResult::NoMatch;
1621 possibly_unsatisfied_predicates.push((o.predicate, parent_pred, Some(o.cause)));
1625 if let ProbeResult::Match = result {
1626 if let (Some(return_ty), Some(xform_ret_ty)) = (self.return_type, xform_ret_ty) {
1627 let xform_ret_ty = self.resolve_vars_if_possible(xform_ret_ty);
1629 "comparing return_ty {:?} with xform ret ty {:?}",
1630 return_ty, probe.xform_ret_ty
1633 .at(&ObligationCause::dummy(), self.param_env)
1634 .define_opaque_types(false)
1635 .sup(return_ty, xform_ret_ty)
1638 return ProbeResult::BadReturnType;
1647 /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1648 /// same trait, but we don't know which impl to use. In this case, since in all cases the
1649 /// external interface of the method can be determined from the trait, it's ok not to decide.
1650 /// We can basically just collapse all of the probes for various impls into one where-clause
1651 /// probe. This will result in a pending obligation so when more type-info is available we can
1652 /// make the final decision.
1654 /// Example (`src/test/ui/method-two-trait-defer-resolution-1.rs`):
1656 /// ```ignore (illustrative)
1657 /// trait Foo { ... }
1658 /// impl Foo for Vec<i32> { ... }
1659 /// impl Foo for Vec<usize> { ... }
1662 /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1663 /// use, so it's ok to just commit to "using the method from the trait Foo".
1664 fn collapse_candidates_to_trait_pick(
1667 probes: &[(&Candidate<'tcx>, ProbeResult)],
1668 ) -> Option<Pick<'tcx>> {
1669 // Do all probes correspond to the same trait?
1670 let container = probes[0].0.item.trait_container(self.tcx)?;
1671 for (p, _) in &probes[1..] {
1672 let p_container = p.item.trait_container(self.tcx)?;
1673 if p_container != container {
1678 // FIXME: check the return type here somehow.
1679 // If so, just use this trait and call it a day.
1681 item: probes[0].0.item,
1683 import_ids: probes[0].0.import_ids.clone(),
1685 autoref_or_ptr_adjustment: None,
1687 unstable_candidates: vec![],
1691 /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
1692 /// candidate method where the method name may have been misspelled. Similarly to other
1693 /// Levenshtein based suggestions, we provide at most one such suggestion.
1694 fn probe_for_lev_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
1695 debug!("probing for method names similar to {:?}", self.method_name);
1697 let steps = self.steps.clone();
1699 let mut pcx = ProbeContext::new(
1705 self.orig_steps_var_values.clone(),
1709 pcx.allow_similar_names = true;
1710 pcx.assemble_inherent_candidates();
1712 let method_names = pcx.candidate_method_names(|_| true);
1713 pcx.allow_similar_names = false;
1714 let applicable_close_candidates: Vec<ty::AssocItem> = method_names
1716 .filter_map(|&method_name| {
1718 pcx.method_name = Some(method_name);
1719 pcx.assemble_inherent_candidates();
1720 pcx.pick_core().and_then(|pick| pick.ok()).map(|pick| pick.item)
1724 if applicable_close_candidates.is_empty() {
1728 let names = applicable_close_candidates
1730 .map(|cand| cand.name)
1731 .collect::<Vec<Symbol>>();
1732 find_best_match_for_name_with_substrings(
1734 self.method_name.unwrap().name,
1739 Ok(applicable_close_candidates.into_iter().find(|method| method.name == best_name))
1744 ///////////////////////////////////////////////////////////////////////////
1746 fn has_applicable_self(&self, item: &ty::AssocItem) -> bool {
1747 // "Fast track" -- check for usage of sugar when in method call
1750 // In Path mode (i.e., resolving a value like `T::next`), consider any
1751 // associated value (i.e., methods, constants) but not types.
1753 Mode::MethodCall => item.fn_has_self_parameter,
1754 Mode::Path => match item.kind {
1755 ty::AssocKind::Type => false,
1756 ty::AssocKind::Fn | ty::AssocKind::Const => true,
1759 // FIXME -- check for types that deref to `Self`,
1760 // like `Rc<Self>` and so on.
1762 // Note also that the current code will break if this type
1763 // includes any of the type parameters defined on the method
1764 // -- but this could be overcome.
1767 fn record_static_candidate(&mut self, source: CandidateSource) {
1768 self.static_candidates.push(source);
1771 #[instrument(level = "debug", skip(self))]
1774 item: &ty::AssocItem,
1776 substs: SubstsRef<'tcx>,
1777 ) -> (Ty<'tcx>, Option<Ty<'tcx>>) {
1778 if item.kind == ty::AssocKind::Fn && self.mode == Mode::MethodCall {
1779 let sig = self.xform_method_sig(item.def_id, substs);
1780 (sig.inputs()[0], Some(sig.output()))
1786 #[instrument(level = "debug", skip(self))]
1787 fn xform_method_sig(&self, method: DefId, substs: SubstsRef<'tcx>) -> ty::FnSig<'tcx> {
1788 let fn_sig = self.tcx.bound_fn_sig(method);
1791 assert!(!substs.has_escaping_bound_vars());
1793 // It is possible for type parameters or early-bound lifetimes
1794 // to appear in the signature of `self`. The substitutions we
1795 // are given do not include type/lifetime parameters for the
1796 // method yet. So create fresh variables here for those too,
1797 // if there are any.
1798 let generics = self.tcx.generics_of(method);
1799 assert_eq!(substs.len(), generics.parent_count as usize);
1801 let xform_fn_sig = if generics.params.is_empty() {
1802 fn_sig.subst(self.tcx, substs)
1804 let substs = InternalSubsts::for_item(self.tcx, method, |param, _| {
1805 let i = param.index as usize;
1806 if i < substs.len() {
1810 GenericParamDefKind::Lifetime => {
1811 // In general, during probe we erase regions.
1812 self.tcx.lifetimes.re_erased.into()
1814 GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
1815 self.var_for_def(self.span, param)
1820 fn_sig.subst(self.tcx, substs)
1823 self.erase_late_bound_regions(xform_fn_sig)
1826 /// Gets the type of an impl and generate substitutions with inference vars.
1827 fn impl_ty_and_substs(
1830 ) -> (ty::EarlyBinder<Ty<'tcx>>, SubstsRef<'tcx>) {
1831 (self.tcx.bound_type_of(impl_def_id), self.fresh_item_substs(impl_def_id))
1834 fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx> {
1835 InternalSubsts::for_item(self.tcx, def_id, |param, _| match param.kind {
1836 GenericParamDefKind::Lifetime => self.tcx.lifetimes.re_erased.into(),
1837 GenericParamDefKind::Type { .. } => self
1838 .next_ty_var(TypeVariableOrigin {
1839 kind: TypeVariableOriginKind::SubstitutionPlaceholder,
1840 span: self.tcx.def_span(def_id),
1843 GenericParamDefKind::Const { .. } => {
1844 let span = self.tcx.def_span(def_id);
1845 let origin = ConstVariableOrigin {
1846 kind: ConstVariableOriginKind::SubstitutionPlaceholder,
1849 self.next_const_var(self.tcx.type_of(param.def_id), origin).into()
1854 /// Replaces late-bound-regions bound by `value` with `'static` using
1855 /// `ty::erase_late_bound_regions`.
1857 /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1858 /// method matching. It is reasonable during the probe phase because we don't consider region
1859 /// relationships at all. Therefore, we can just replace all the region variables with 'static
1860 /// rather than creating fresh region variables. This is nice for two reasons:
1862 /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1863 /// particular method call, it winds up creating fewer types overall, which helps for memory
1864 /// usage. (Admittedly, this is a rather small effect, though measurable.)
1866 /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1867 /// late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1868 /// regions with actual region variables as is proper, we'd have to ensure that the same
1869 /// region got replaced with the same variable, which requires a bit more coordination
1870 /// and/or tracking the substitution and
1872 fn erase_late_bound_regions<T>(&self, value: ty::Binder<'tcx, T>) -> T
1874 T: TypeFoldable<'tcx>,
1876 self.tcx.erase_late_bound_regions(value)
1879 /// Finds the method with the appropriate name (or return type, as the case may be). If
1880 /// `allow_similar_names` is set, find methods with close-matching names.
1881 // The length of the returned iterator is nearly always 0 or 1 and this
1882 // method is fairly hot.
1883 fn impl_or_trait_item(&self, def_id: DefId) -> SmallVec<[ty::AssocItem; 1]> {
1884 if let Some(name) = self.method_name {
1885 if self.allow_similar_names {
1886 let max_dist = max(name.as_str().len(), 3) / 3;
1888 .associated_items(def_id)
1889 .in_definition_order()
1891 if x.kind.namespace() != Namespace::ValueNS {
1894 match lev_distance_with_substrings(name.as_str(), x.name.as_str(), max_dist)
1904 .associated_value(def_id, name)
1905 .map_or_else(SmallVec::new, |x| SmallVec::from_buf([x]))
1908 self.tcx.associated_items(def_id).in_definition_order().copied().collect()
1913 impl<'tcx> Candidate<'tcx> {
1914 fn to_unadjusted_pick(
1917 unstable_candidates: Vec<(Candidate<'tcx>, Symbol)>,
1921 kind: match self.kind {
1922 InherentImplCandidate(..) => InherentImplPick,
1923 ObjectCandidate => ObjectPick,
1924 TraitCandidate(_) => TraitPick,
1925 WhereClauseCandidate(ref trait_ref) => {
1926 // Only trait derived from where-clauses should
1927 // appear here, so they should not contain any
1928 // inference variables or other artifacts. This
1929 // means they are safe to put into the
1930 // `WhereClausePick`.
1932 !trait_ref.skip_binder().substs.needs_infer()
1933 && !trait_ref.skip_binder().substs.has_placeholders()
1936 WhereClausePick(*trait_ref)
1939 import_ids: self.import_ids.clone(),
1941 autoref_or_ptr_adjustment: None,
1943 unstable_candidates,