2 use super::CandidateSource;
3 use super::MethodError;
4 use super::NoMatchData;
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_errors::Applicability;
14 use rustc_hir::def::Namespace;
15 use rustc_infer::infer::canonical::OriginalQueryValues;
16 use rustc_infer::infer::canonical::{Canonical, QueryResponse};
17 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
18 use rustc_infer::infer::{self, InferOk, TyCtxtInferExt};
19 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
20 use rustc_middle::middle::stability;
21 use rustc_middle::ty::fast_reject::{simplify_type, TreatParams};
22 use rustc_middle::ty::GenericParamDefKind;
23 use rustc_middle::ty::{self, ParamEnvAnd, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeVisitable};
24 use rustc_middle::ty::{InternalSubsts, SubstsRef};
25 use rustc_session::lint;
26 use rustc_span::def_id::LocalDefId;
27 use rustc_span::lev_distance::{
28 find_best_match_for_name_with_substrings, lev_distance_with_substrings,
30 use rustc_span::symbol::sym;
31 use rustc_span::{symbol::Ident, Span, Symbol, DUMMY_SP};
32 use rustc_trait_selection::autoderef::{self, Autoderef};
33 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
34 use rustc_trait_selection::traits::query::method_autoderef::MethodAutoderefBadTy;
35 use rustc_trait_selection::traits::query::method_autoderef::{
36 CandidateStep, MethodAutoderefStepsResult,
38 use rustc_trait_selection::traits::query::CanonicalTyGoal;
39 use rustc_trait_selection::traits::{self, ObligationCause};
45 use smallvec::{smallvec, SmallVec};
47 use self::CandidateKind::*;
48 pub use self::PickKind::*;
50 /// Boolean flag used to indicate if this search is for a suggestion
51 /// or not. If true, we can allow ambiguity and so forth.
52 #[derive(Clone, Copy, Debug)]
53 pub struct IsSuggestion(pub bool);
55 struct ProbeContext<'a, 'tcx> {
56 fcx: &'a FnCtxt<'a, 'tcx>,
59 method_name: Option<Ident>,
60 return_type: Option<Ty<'tcx>>,
62 /// This is the OriginalQueryValues for the steps queries
63 /// that are answered in steps.
64 orig_steps_var_values: OriginalQueryValues<'tcx>,
65 steps: &'tcx [CandidateStep<'tcx>],
67 inherent_candidates: Vec<Candidate<'tcx>>,
68 extension_candidates: Vec<Candidate<'tcx>>,
69 impl_dups: FxHashSet<DefId>,
71 /// Collects near misses when the candidate functions are missing a `self` keyword and is only
72 /// used for error reporting
73 static_candidates: Vec<CandidateSource>,
75 /// When probing for names, include names that are close to the
76 /// requested name (by Levensthein distance)
77 allow_similar_names: bool,
79 /// Some(candidate) if there is a private candidate
80 private_candidate: Option<(DefKind, DefId)>,
82 /// Collects near misses when trait bounds for type parameters are unsatisfied and is only used
83 /// for error reporting
84 unsatisfied_predicates:
85 Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>, Option<ObligationCause<'tcx>>)>,
87 is_suggestion: IsSuggestion,
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, PartialEq, 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>,
215 #[derive(Clone, Debug, PartialEq, Eq)]
216 pub enum PickKind<'tcx> {
222 ty::PolyTraitRef<'tcx>,
226 pub type PickResult<'tcx> = Result<Pick<'tcx>, MethodError<'tcx>>;
228 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
230 // An expression of the form `receiver.method_name(...)`.
231 // Autoderefs are performed on `receiver`, lookup is done based on the
232 // `self` argument of the method, and static methods aren't considered.
234 // An expression of the form `Type::item` or `<T>::item`.
235 // No autoderefs are performed, lookup is done based on the type each
236 // implementation is for, and static methods are included.
240 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
241 pub enum ProbeScope {
242 // Assemble candidates coming only from traits in scope.
245 // Assemble candidates coming from all traits.
249 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
250 /// This is used to offer suggestions to users. It returns methods
251 /// that could have been called which have the desired return
252 /// type. Some effort is made to rule out methods that, if called,
253 /// would result in an error (basically, the same criteria we
254 /// would use to decide if a method is a plausible fit for
255 /// ambiguity purposes).
256 #[instrument(level = "debug", skip(self))]
257 pub fn probe_for_return_type(
261 return_type: Ty<'tcx>,
263 scope_expr_id: hir::HirId,
264 ) -> Vec<ty::AssocItem> {
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))]
299 pub fn probe_for_name(
304 is_suggestion: IsSuggestion,
306 scope_expr_id: hir::HirId,
308 ) -> PickResult<'tcx> {
318 |probe_cx| probe_cx.pick(),
326 method_name: Option<Ident>,
327 return_type: Option<Ty<'tcx>>,
328 is_suggestion: IsSuggestion,
330 scope_expr_id: hir::HirId,
333 ) -> Result<R, MethodError<'tcx>>
335 OP: FnOnce(ProbeContext<'a, 'tcx>) -> Result<R, MethodError<'tcx>>,
337 let mut orig_values = OriginalQueryValues::default();
338 let param_env_and_self_ty = self.canonicalize_query(
339 ParamEnvAnd { param_env: self.param_env, value: self_ty },
343 let steps = if mode == Mode::MethodCall {
344 self.tcx.method_autoderef_steps(param_env_and_self_ty)
347 // Mode::Path - the deref steps is "trivial". This turns
348 // our CanonicalQuery into a "trivial" QueryResponse. This
349 // is a bit inefficient, but I don't think that writing
350 // special handling for this "trivial case" is a good idea.
352 let infcx = &self.infcx;
353 let (ParamEnvAnd { param_env: _, value: self_ty }, canonical_inference_vars) =
354 infcx.instantiate_canonical_with_fresh_inference_vars(
356 ¶m_env_and_self_ty,
359 "probe_op: Mode::Path, param_env_and_self_ty={:?} self_ty={:?}",
360 param_env_and_self_ty, self_ty
362 MethodAutoderefStepsResult {
363 steps: infcx.tcx.arena.alloc_from_iter([CandidateStep {
364 self_ty: self.make_query_response_ignoring_pending_obligations(
365 canonical_inference_vars,
369 from_unsafe_deref: false,
373 reached_recursion_limit: false,
378 // If our autoderef loop had reached the recursion limit,
379 // report an overflow error, but continue going on with
380 // the truncated autoderef list.
381 if steps.reached_recursion_limit {
386 .unwrap_or_else(|| span_bug!(span, "reached the recursion limit in 0 steps?"))
389 .probe_instantiate_query_response(span, &orig_values, ty)
390 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
391 autoderef::report_autoderef_recursion_limit_error(self.tcx, span, ty.value);
395 // If we encountered an `_` type or an error type during autoderef, this is
397 if let Some(bad_ty) = &steps.opt_bad_ty {
399 // Ambiguity was encountered during a suggestion. Just keep going.
400 debug!("ProbeContext: encountered ambiguity in suggestion");
401 } else if bad_ty.reached_raw_pointer && !self.tcx.features().arbitrary_self_types {
402 // this case used to be allowed by the compiler,
403 // so we do a future-compat lint here for the 2015 edition
404 // (see https://github.com/rust-lang/rust/issues/46906)
405 if self.tcx.sess.rust_2018() {
406 self.tcx.sess.emit_err(MethodCallOnUnknownType { span });
408 self.tcx.struct_span_lint_hir(
409 lint::builtin::TYVAR_BEHIND_RAW_POINTER,
412 "type annotations needed",
417 // Encountered a real ambiguity, so abort the lookup. If `ty` is not
418 // an `Err`, report the right "type annotations needed" error pointing
422 .probe_instantiate_query_response(span, &orig_values, ty)
423 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
424 let ty = self.structurally_resolved_type(span, ty.value);
425 assert!(matches!(ty.kind(), ty::Error(_)));
426 return Err(MethodError::NoMatch(NoMatchData {
427 static_candidates: Vec::new(),
428 unsatisfied_predicates: Vec::new(),
429 out_of_scope_traits: Vec::new(),
436 debug!("ProbeContext: steps for self_ty={:?} are {:?}", self_ty, steps);
438 // this creates one big transaction so that all type variables etc
439 // that we create during the probe process are removed later
441 let mut probe_cx = ProbeContext::new(
453 probe_cx.assemble_inherent_candidates();
455 ProbeScope::TraitsInScope => {
456 probe_cx.assemble_extension_candidates_for_traits_in_scope(scope_expr_id)
458 ProbeScope::AllTraits => probe_cx.assemble_extension_candidates_for_all_traits(),
465 pub fn provide(providers: &mut ty::query::Providers) {
466 providers.method_autoderef_steps = method_autoderef_steps;
469 fn method_autoderef_steps<'tcx>(
471 goal: CanonicalTyGoal<'tcx>,
472 ) -> MethodAutoderefStepsResult<'tcx> {
473 debug!("method_autoderef_steps({:?})", goal);
475 let (ref infcx, goal, inference_vars) = tcx.infer_ctxt().build_with_canonical(DUMMY_SP, &goal);
476 let ParamEnvAnd { param_env, value: self_ty } = goal;
479 Autoderef::new(infcx, param_env, hir::CRATE_HIR_ID, DUMMY_SP, self_ty, DUMMY_SP)
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 is_suggestion: IsSuggestion,
546 scope_expr_id: hir::HirId,
547 ) -> ProbeContext<'a, 'tcx> {
554 inherent_candidates: Vec::new(),
555 extension_candidates: Vec::new(),
556 impl_dups: FxHashSet::default(),
557 orig_steps_var_values,
559 static_candidates: Vec::new(),
560 allow_similar_names: false,
561 private_candidate: None,
562 unsatisfied_predicates: Vec::new(),
568 fn reset(&mut self) {
569 self.inherent_candidates.clear();
570 self.extension_candidates.clear();
571 self.impl_dups.clear();
572 self.static_candidates.clear();
573 self.private_candidate = None;
576 ///////////////////////////////////////////////////////////////////////////
577 // CANDIDATE ASSEMBLY
579 fn push_candidate(&mut self, candidate: Candidate<'tcx>, is_inherent: bool) {
580 let is_accessible = if let Some(name) = self.method_name {
581 let item = candidate.item;
584 .adjust_ident_and_get_scope(name, item.container_id(self.tcx), self.body_id)
586 item.visibility(self.tcx).is_accessible_from(def_scope, self.tcx)
592 self.inherent_candidates.push(candidate);
594 self.extension_candidates.push(candidate);
596 } else if self.private_candidate.is_none() {
597 self.private_candidate =
598 Some((candidate.item.kind.as_def_kind(), candidate.item.def_id));
602 fn assemble_inherent_candidates(&mut self) {
603 for step in self.steps.iter() {
604 self.assemble_probe(&step.self_ty);
608 fn assemble_probe(&mut self, self_ty: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>) {
609 debug!("assemble_probe: self_ty={:?}", self_ty);
610 let raw_self_ty = self_ty.value.value;
611 match *raw_self_ty.kind() {
612 ty::Dynamic(data, ..) if let Some(p) = data.principal() => {
613 // Subtle: we can't use `instantiate_query_response` here: using it will
614 // commit to all of the type equalities assumed by inference going through
615 // autoderef (see the `method-probe-no-guessing` test).
617 // However, in this code, it is OK if we end up with an object type that is
618 // "more general" than the object type that we are evaluating. For *every*
619 // object type `MY_OBJECT`, a function call that goes through a trait-ref
620 // of the form `<MY_OBJECT as SuperTraitOf(MY_OBJECT)>::func` is a valid
621 // `ObjectCandidate`, and it should be discoverable "exactly" through one
622 // of the iterations in the autoderef loop, so there is no problem with it
623 // being discoverable in another one of these iterations.
625 // Using `instantiate_canonical_with_fresh_inference_vars` on our
626 // `Canonical<QueryResponse<Ty<'tcx>>>` and then *throwing away* the
627 // `CanonicalVarValues` will exactly give us such a generalization - it
628 // will still match the original object type, but it won't pollute our
629 // type variables in any form, so just do that!
630 let (QueryResponse { value: generalized_self_ty, .. }, _ignored_var_values) =
632 .instantiate_canonical_with_fresh_inference_vars(self.span, self_ty);
634 self.assemble_inherent_candidates_from_object(generalized_self_ty);
635 self.assemble_inherent_impl_candidates_for_type(p.def_id());
636 if self.tcx.has_attr(p.def_id(), sym::rustc_has_incoherent_inherent_impls) {
637 self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
641 let def_id = def.did();
642 self.assemble_inherent_impl_candidates_for_type(def_id);
643 if self.tcx.has_attr(def_id, sym::rustc_has_incoherent_inherent_impls) {
644 self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
647 ty::Foreign(did) => {
648 self.assemble_inherent_impl_candidates_for_type(did);
649 if self.tcx.has_attr(did, sym::rustc_has_incoherent_inherent_impls) {
650 self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
654 self.assemble_inherent_candidates_from_param(p);
667 | ty::Tuple(..) => self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty),
672 fn assemble_inherent_candidates_for_incoherent_ty(&mut self, self_ty: Ty<'tcx>) {
673 let Some(simp) = simplify_type(self.tcx, self_ty, TreatParams::AsInfer) else {
674 bug!("unexpected incoherent type: {:?}", self_ty)
676 for &impl_def_id in self.tcx.incoherent_impls(simp) {
677 self.assemble_inherent_impl_probe(impl_def_id);
681 fn assemble_inherent_impl_candidates_for_type(&mut self, def_id: DefId) {
682 let impl_def_ids = self.tcx.at(self.span).inherent_impls(def_id);
683 for &impl_def_id in impl_def_ids.iter() {
684 self.assemble_inherent_impl_probe(impl_def_id);
688 fn assemble_inherent_impl_probe(&mut self, impl_def_id: DefId) {
689 if !self.impl_dups.insert(impl_def_id) {
690 return; // already visited
693 debug!("assemble_inherent_impl_probe {:?}", impl_def_id);
695 for item in self.impl_or_trait_item(impl_def_id) {
696 if !self.has_applicable_self(&item) {
697 // No receiver declared. Not a candidate.
698 self.record_static_candidate(CandidateSource::Impl(impl_def_id));
702 let (impl_ty, impl_substs) = self.impl_ty_and_substs(impl_def_id);
703 let impl_ty = impl_ty.subst(self.tcx, impl_substs);
705 debug!("impl_ty: {:?}", impl_ty);
707 // Determine the receiver type that the method itself expects.
708 let (xform_self_ty, xform_ret_ty) = self.xform_self_ty(&item, impl_ty, impl_substs);
709 debug!("xform_self_ty: {:?}, xform_ret_ty: {:?}", xform_self_ty, xform_ret_ty);
711 // We can't use normalize_associated_types_in as it will pollute the
712 // fcx's fulfillment context after this probe is over.
713 // Note: we only normalize `xform_self_ty` here since the normalization
714 // of the return type can lead to inference results that prohibit
715 // valid candidates from being found, see issue #85671
716 // FIXME Postponing the normalization of the return type likely only hides a deeper bug,
717 // which might be caused by the `param_env` itself. The clauses of the `param_env`
718 // maybe shouldn't include `Param`s, but rather fresh variables or be canonicalized,
720 let cause = traits::ObligationCause::misc(self.span, self.body_id);
721 let selcx = &mut traits::SelectionContext::new(self.fcx);
722 let traits::Normalized { value: xform_self_ty, obligations } =
723 traits::normalize(selcx, self.param_env, cause, xform_self_ty);
725 "assemble_inherent_impl_probe after normalization: xform_self_ty = {:?}/{:?}",
726 xform_self_ty, xform_ret_ty
734 kind: InherentImplCandidate(impl_substs, obligations),
735 import_ids: smallvec![],
742 fn assemble_inherent_candidates_from_object(&mut self, self_ty: Ty<'tcx>) {
743 debug!("assemble_inherent_candidates_from_object(self_ty={:?})", self_ty);
745 let principal = match self_ty.kind() {
746 ty::Dynamic(ref data, ..) => Some(data),
749 .and_then(|data| data.principal())
753 "non-object {:?} in assemble_inherent_candidates_from_object",
758 // It is illegal to invoke a method on a trait instance that refers to
759 // the `Self` type. An [`ObjectSafetyViolation::SupertraitSelf`] error
760 // will be reported by `object_safety.rs` if the method refers to the
761 // `Self` type anywhere other than the receiver. Here, we use a
762 // substitution that replaces `Self` with the object type itself. Hence,
763 // a `&self` method will wind up with an argument type like `&dyn Trait`.
764 let trait_ref = principal.with_self_ty(self.tcx, self_ty);
765 self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
766 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
768 let (xform_self_ty, xform_ret_ty) =
769 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
775 kind: ObjectCandidate,
776 import_ids: smallvec![],
783 fn assemble_inherent_candidates_from_param(&mut self, param_ty: ty::ParamTy) {
784 // FIXME: do we want to commit to this behavior for param bounds?
785 debug!("assemble_inherent_candidates_from_param(param_ty={:?})", param_ty);
787 let bounds = self.param_env.caller_bounds().iter().filter_map(|predicate| {
788 let bound_predicate = predicate.kind();
789 match bound_predicate.skip_binder() {
790 ty::PredicateKind::Trait(trait_predicate) => {
791 match *trait_predicate.trait_ref.self_ty().kind() {
792 ty::Param(p) if p == param_ty => {
793 Some(bound_predicate.rebind(trait_predicate.trait_ref))
798 ty::PredicateKind::Subtype(..)
799 | ty::PredicateKind::Coerce(..)
800 | ty::PredicateKind::Projection(..)
801 | ty::PredicateKind::RegionOutlives(..)
802 | ty::PredicateKind::WellFormed(..)
803 | ty::PredicateKind::ObjectSafe(..)
804 | ty::PredicateKind::ClosureKind(..)
805 | ty::PredicateKind::TypeOutlives(..)
806 | ty::PredicateKind::ConstEvaluatable(..)
807 | ty::PredicateKind::ConstEquate(..)
808 | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
812 self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
813 let trait_ref = this.erase_late_bound_regions(poly_trait_ref);
815 let (xform_self_ty, xform_ret_ty) =
816 this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs);
818 // Because this trait derives from a where-clause, it
819 // should not contain any inference variables or other
820 // artifacts. This means it is safe to put into the
821 // `WhereClauseCandidate` and (eventually) into the
822 // `WhereClausePick`.
823 assert!(!trait_ref.substs.needs_infer());
830 kind: WhereClauseCandidate(poly_trait_ref),
831 import_ids: smallvec![],
838 // Do a search through a list of bounds, using a callback to actually
839 // create the candidates.
840 fn elaborate_bounds<F>(
842 bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
845 F: for<'b> FnMut(&mut ProbeContext<'b, 'tcx>, ty::PolyTraitRef<'tcx>, ty::AssocItem),
848 for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
849 debug!("elaborate_bounds(bound_trait_ref={:?})", bound_trait_ref);
850 for item in self.impl_or_trait_item(bound_trait_ref.def_id()) {
851 if !self.has_applicable_self(&item) {
852 self.record_static_candidate(CandidateSource::Trait(bound_trait_ref.def_id()));
854 mk_cand(self, bound_trait_ref, item);
860 fn assemble_extension_candidates_for_traits_in_scope(&mut self, expr_hir_id: hir::HirId) {
861 let mut duplicates = FxHashSet::default();
862 let opt_applicable_traits = self.tcx.in_scope_traits(expr_hir_id);
863 if let Some(applicable_traits) = opt_applicable_traits {
864 for trait_candidate in applicable_traits.iter() {
865 let trait_did = trait_candidate.def_id;
866 if duplicates.insert(trait_did) {
867 self.assemble_extension_candidates_for_trait(
868 &trait_candidate.import_ids,
876 fn assemble_extension_candidates_for_all_traits(&mut self) {
877 let mut duplicates = FxHashSet::default();
878 for trait_info in suggest::all_traits(self.tcx) {
879 if duplicates.insert(trait_info.def_id) {
880 self.assemble_extension_candidates_for_trait(&smallvec![], trait_info.def_id);
885 pub fn matches_return_type(
887 method: &ty::AssocItem,
888 self_ty: Option<Ty<'tcx>>,
892 ty::AssocKind::Fn => {
893 let fty = self.tcx.bound_fn_sig(method.def_id);
895 let substs = self.fresh_substs_for_item(self.span, method.def_id);
896 let fty = fty.subst(self.tcx, substs);
898 self.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, fty);
900 if let Some(self_ty) = self_ty {
902 .at(&ObligationCause::dummy(), self.param_env)
903 .sup(fty.inputs()[0], self_ty)
909 self.can_sub(self.param_env, fty.output(), expected).is_ok()
916 fn assemble_extension_candidates_for_trait(
918 import_ids: &SmallVec<[LocalDefId; 1]>,
921 debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})", trait_def_id);
922 let trait_substs = self.fresh_item_substs(trait_def_id);
923 let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
925 if self.tcx.is_trait_alias(trait_def_id) {
926 // For trait aliases, assume all supertraits are relevant.
927 let bounds = iter::once(ty::Binder::dummy(trait_ref));
928 self.elaborate_bounds(bounds, |this, new_trait_ref, item| {
929 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
931 let (xform_self_ty, xform_ret_ty) =
932 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
938 import_ids: import_ids.clone(),
939 kind: TraitCandidate(new_trait_ref),
945 debug_assert!(self.tcx.is_trait(trait_def_id));
946 for item in self.impl_or_trait_item(trait_def_id) {
947 // Check whether `trait_def_id` defines a method with suitable name.
948 if !self.has_applicable_self(&item) {
949 debug!("method has inapplicable self");
950 self.record_static_candidate(CandidateSource::Trait(trait_def_id));
954 let (xform_self_ty, xform_ret_ty) =
955 self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
961 import_ids: import_ids.clone(),
962 kind: TraitCandidate(trait_ref),
970 fn candidate_method_names(&self) -> Vec<Ident> {
971 let mut set = FxHashSet::default();
972 let mut names: Vec<_> = self
975 .chain(&self.extension_candidates)
976 .filter(|candidate| {
977 if let Some(return_ty) = self.return_type {
978 self.matches_return_type(&candidate.item, None, return_ty)
983 .map(|candidate| candidate.item.ident(self.tcx))
984 .filter(|&name| set.insert(name))
987 // Sort them by the name so we have a stable result.
988 names.sort_by(|a, b| a.as_str().partial_cmp(b.as_str()).unwrap());
992 ///////////////////////////////////////////////////////////////////////////
995 fn pick(mut self) -> PickResult<'tcx> {
996 assert!(self.method_name.is_some());
998 if let Some(r) = self.pick_core() {
1002 debug!("pick: actual search failed, assemble diagnostics");
1004 let static_candidates = mem::take(&mut self.static_candidates);
1005 let private_candidate = self.private_candidate.take();
1006 let unsatisfied_predicates = mem::take(&mut self.unsatisfied_predicates);
1008 // things failed, so lets look at all traits, for diagnostic purposes now:
1011 let span = self.span;
1014 self.assemble_extension_candidates_for_all_traits();
1016 let out_of_scope_traits = match self.pick_core() {
1017 Some(Ok(p)) => vec![p.item.container_id(self.tcx)],
1018 //Some(Ok(p)) => p.iter().map(|p| p.item.container().id()).collect(),
1019 Some(Err(MethodError::Ambiguity(v))) => v
1021 .map(|source| match source {
1022 CandidateSource::Trait(id) => id,
1023 CandidateSource::Impl(impl_id) => match tcx.trait_id_of_impl(impl_id) {
1025 None => span_bug!(span, "found inherent method when looking at traits"),
1029 Some(Err(MethodError::NoMatch(NoMatchData {
1030 out_of_scope_traits: others, ..
1032 assert!(others.is_empty());
1038 if let Some((kind, def_id)) = private_candidate {
1039 return Err(MethodError::PrivateMatch(kind, def_id, out_of_scope_traits));
1041 let lev_candidate = self.probe_for_lev_candidate()?;
1043 Err(MethodError::NoMatch(NoMatchData {
1045 unsatisfied_predicates,
1046 out_of_scope_traits,
1052 fn pick_core(&mut self) -> Option<PickResult<'tcx>> {
1053 let mut unstable_candidates = Vec::new();
1054 let pick = self.pick_all_method(Some(&mut unstable_candidates));
1056 // In this case unstable picking is done by `pick_method`.
1057 if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable {
1062 // Emit a lint if there are unstable candidates alongside the stable ones.
1064 // We suppress warning if we're picking the method only because it is a
1066 Some(Ok(ref p)) if !self.is_suggestion.0 && !unstable_candidates.is_empty() => {
1067 self.emit_unstable_name_collision_hint(p, &unstable_candidates);
1071 None => self.pick_all_method(None),
1077 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1078 ) -> Option<PickResult<'tcx>> {
1079 let steps = self.steps.clone();
1083 debug!("pick_all_method: step={:?}", step);
1084 // skip types that are from a type error or that would require dereferencing
1086 !step.self_ty.references_error() && !step.from_unsafe_deref
1089 let InferOk { value: self_ty, obligations: _ } = self
1091 .probe_instantiate_query_response(
1093 &self.orig_steps_var_values,
1096 .unwrap_or_else(|_| {
1097 span_bug!(self.span, "{:?} was applicable but now isn't?", step.self_ty)
1099 self.pick_by_value_method(step, self_ty, unstable_candidates.as_deref_mut())
1101 self.pick_autorefd_method(
1104 hir::Mutability::Not,
1105 unstable_candidates.as_deref_mut(),
1108 self.pick_autorefd_method(
1111 hir::Mutability::Mut,
1112 unstable_candidates.as_deref_mut(),
1116 self.pick_const_ptr_method(
1119 unstable_candidates.as_deref_mut(),
1127 /// For each type `T` in the step list, this attempts to find a method where
1128 /// the (transformed) self type is exactly `T`. We do however do one
1129 /// transformation on the adjustment: if we are passing a region pointer in,
1130 /// we will potentially *reborrow* it to a shorter lifetime. This allows us
1131 /// to transparently pass `&mut` pointers, in particular, without consuming
1132 /// them for their entire lifetime.
1133 fn pick_by_value_method(
1135 step: &CandidateStep<'tcx>,
1137 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1138 ) -> Option<PickResult<'tcx>> {
1143 self.pick_method(self_ty, unstable_candidates).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.map_or(false, |a| a.get_unsize()),
1161 fn pick_autorefd_method(
1163 step: &CandidateStep<'tcx>,
1165 mutbl: hir::Mutability,
1166 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1167 ) -> Option<PickResult<'tcx>> {
1170 // In general, during probing we erase regions.
1171 let region = tcx.lifetimes.re_erased;
1173 let autoref_ty = tcx.mk_ref(region, ty::TypeAndMut { ty: self_ty, mutbl });
1174 self.pick_method(autoref_ty, unstable_candidates).map(|r| {
1176 pick.autoderefs = step.autoderefs;
1177 pick.autoref_or_ptr_adjustment =
1178 Some(AutorefOrPtrAdjustment::Autoref { mutbl, unsize: step.unsize });
1184 /// If `self_ty` is `*mut T` then this picks `*const T` methods. The reason why we have a
1185 /// special case for this is because going from `*mut T` to `*const T` with autoderefs and
1186 /// autorefs would require dereferencing the pointer, which is not safe.
1187 fn pick_const_ptr_method(
1189 step: &CandidateStep<'tcx>,
1191 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1192 ) -> Option<PickResult<'tcx>> {
1193 // Don't convert an unsized reference to ptr
1198 let &ty::RawPtr(ty::TypeAndMut { ty, mutbl: hir::Mutability::Mut }) = self_ty.kind() else {
1202 let const_self_ty = ty::TypeAndMut { ty, mutbl: hir::Mutability::Not };
1203 let const_ptr_ty = self.tcx.mk_ptr(const_self_ty);
1204 self.pick_method(const_ptr_ty, unstable_candidates).map(|r| {
1206 pick.autoderefs = step.autoderefs;
1207 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::ToConstPtr);
1213 fn pick_method_with_unstable(&mut self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
1214 debug!("pick_method_with_unstable(self_ty={})", self.ty_to_string(self_ty));
1216 let mut possibly_unsatisfied_predicates = Vec::new();
1217 let mut unstable_candidates = Vec::new();
1219 for (kind, candidates) in
1220 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1222 debug!("searching {} candidates", kind);
1223 let res = self.consider_candidates(
1226 &mut possibly_unsatisfied_predicates,
1227 Some(&mut unstable_candidates),
1229 if let Some(pick) = res {
1230 if !self.is_suggestion.0 && !unstable_candidates.is_empty() {
1231 if let Ok(p) = &pick {
1232 // Emit a lint if there are unstable candidates alongside the stable ones.
1234 // We suppress warning if we're picking the method only because it is a
1236 self.emit_unstable_name_collision_hint(p, &unstable_candidates);
1243 debug!("searching unstable candidates");
1244 let res = self.consider_candidates(
1246 unstable_candidates.iter().map(|(c, _)| c),
1247 &mut possibly_unsatisfied_predicates,
1251 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1259 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1260 ) -> Option<PickResult<'tcx>> {
1261 if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable {
1262 return self.pick_method_with_unstable(self_ty);
1265 debug!("pick_method(self_ty={})", self.ty_to_string(self_ty));
1267 let mut possibly_unsatisfied_predicates = Vec::new();
1269 for (kind, candidates) in
1270 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1272 debug!("searching {} candidates", kind);
1273 let res = self.consider_candidates(
1276 &mut possibly_unsatisfied_predicates,
1277 unstable_candidates.as_deref_mut(),
1279 if let Some(pick) = res {
1284 // `pick_method` may be called twice for the same self_ty if no stable methods
1285 // match. Only extend once.
1286 if unstable_candidates.is_some() {
1287 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1292 fn consider_candidates<'b, ProbesIter>(
1296 possibly_unsatisfied_predicates: &mut Vec<(
1297 ty::Predicate<'tcx>,
1298 Option<ty::Predicate<'tcx>>,
1299 Option<ObligationCause<'tcx>>,
1301 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1302 ) -> Option<PickResult<'tcx>>
1304 ProbesIter: Iterator<Item = &'b Candidate<'tcx>> + Clone,
1307 let mut applicable_candidates: Vec<_> = probes
1310 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
1312 .filter(|&(_, status)| status != ProbeResult::NoMatch)
1315 debug!("applicable_candidates: {:?}", applicable_candidates);
1317 if applicable_candidates.len() > 1 {
1319 self.collapse_candidates_to_trait_pick(self_ty, &applicable_candidates)
1321 return Some(Ok(pick));
1325 if let Some(uc) = unstable_candidates {
1326 applicable_candidates.retain(|&(p, _)| {
1327 if let stability::EvalResult::Deny { feature, .. } =
1328 self.tcx.eval_stability(p.item.def_id, None, self.span, None)
1330 uc.push((p.clone(), feature));
1337 if applicable_candidates.len() > 1 {
1338 let sources = probes.map(|p| self.candidate_source(p, self_ty)).collect();
1339 return Some(Err(MethodError::Ambiguity(sources)));
1342 applicable_candidates.pop().map(|(probe, status)| {
1343 if status == ProbeResult::Match {
1344 Ok(probe.to_unadjusted_pick(self_ty))
1346 Err(MethodError::BadReturnType)
1351 fn emit_unstable_name_collision_hint(
1353 stable_pick: &Pick<'_>,
1354 unstable_candidates: &[(Candidate<'tcx>, Symbol)],
1356 let def_kind = stable_pick.item.kind.as_def_kind();
1357 self.tcx.struct_span_lint_hir(
1358 lint::builtin::UNSTABLE_NAME_COLLISIONS,
1362 "{} {} with this name may be added to the standard library in the future",
1364 def_kind.descr(stable_pick.item.def_id),
1367 match (stable_pick.item.kind, stable_pick.item.container) {
1368 (ty::AssocKind::Fn, _) => {
1369 // FIXME: This should be a `span_suggestion` instead of `help`
1370 // However `self.span` only
1371 // highlights the method name, so we can't use it. Also consider reusing
1372 // the code from `report_method_error()`.
1374 "call with fully qualified syntax `{}(...)` to keep using the current \
1376 self.tcx.def_path_str(stable_pick.item.def_id),
1379 (ty::AssocKind::Const, ty::AssocItemContainer::TraitContainer) => {
1380 let def_id = stable_pick.item.container_id(self.tcx);
1381 lint.span_suggestion(
1383 "use the fully qualified path to the associated const",
1386 stable_pick.self_ty,
1387 self.tcx.def_path_str(def_id),
1388 stable_pick.item.name
1390 Applicability::MachineApplicable,
1395 if self.tcx.sess.is_nightly_build() {
1396 for (candidate, feature) in unstable_candidates {
1398 "add `#![feature({})]` to the crate attributes to enable `{}`",
1400 self.tcx.def_path_str(candidate.item.def_id),
1410 fn select_trait_candidate(
1412 trait_ref: ty::TraitRef<'tcx>,
1413 ) -> traits::SelectionResult<'tcx, traits::Selection<'tcx>> {
1414 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1415 let predicate = ty::Binder::dummy(trait_ref).to_poly_trait_predicate();
1416 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1417 traits::SelectionContext::new(self).select(&obligation)
1420 fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>) -> CandidateSource {
1421 match candidate.kind {
1422 InherentImplCandidate(..) => {
1423 CandidateSource::Impl(candidate.item.container_id(self.tcx))
1425 ObjectCandidate | WhereClauseCandidate(_) => {
1426 CandidateSource::Trait(candidate.item.container_id(self.tcx))
1428 TraitCandidate(trait_ref) => self.probe(|_| {
1430 .at(&ObligationCause::dummy(), self.param_env)
1431 .define_opaque_types(false)
1432 .sup(candidate.xform_self_ty, self_ty);
1433 match self.select_trait_candidate(trait_ref) {
1434 Ok(Some(traits::ImplSource::UserDefined(ref impl_data))) => {
1435 // If only a single impl matches, make the error message point
1437 CandidateSource::Impl(impl_data.impl_def_id)
1439 _ => CandidateSource::Trait(candidate.item.container_id(self.tcx)),
1448 probe: &Candidate<'tcx>,
1449 possibly_unsatisfied_predicates: &mut Vec<(
1450 ty::Predicate<'tcx>,
1451 Option<ty::Predicate<'tcx>>,
1452 Option<ObligationCause<'tcx>>,
1455 debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe);
1458 // First check that the self type can be related.
1459 let sub_obligations = match self
1460 .at(&ObligationCause::dummy(), self.param_env)
1461 .define_opaque_types(false)
1462 .sup(probe.xform_self_ty, self_ty)
1464 Ok(InferOk { obligations, value: () }) => obligations,
1466 debug!("--> cannot relate self-types {:?}", err);
1467 return ProbeResult::NoMatch;
1471 let mut result = ProbeResult::Match;
1472 let mut xform_ret_ty = probe.xform_ret_ty;
1473 debug!(?xform_ret_ty);
1475 let selcx = &mut traits::SelectionContext::new(self);
1476 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1478 let mut parent_pred = None;
1480 // If so, impls may carry other conditions (e.g., where
1481 // clauses) that must be considered. Make sure that those
1482 // match as well (or at least may match, sometimes we
1483 // don't have enough information to fully evaluate).
1485 InherentImplCandidate(ref substs, ref ref_obligations) => {
1486 // `xform_ret_ty` hasn't been normalized yet, only `xform_self_ty`,
1487 // see the reasons mentioned in the comments in `assemble_inherent_impl_probe`
1488 // for why this is necessary
1489 let traits::Normalized {
1490 value: normalized_xform_ret_ty,
1491 obligations: normalization_obligations,
1492 } = traits::normalize(selcx, self.param_env, cause.clone(), probe.xform_ret_ty);
1493 xform_ret_ty = normalized_xform_ret_ty;
1494 debug!("xform_ret_ty after normalization: {:?}", xform_ret_ty);
1496 // Check whether the impl imposes obligations we have to worry about.
1497 let impl_def_id = probe.item.container_id(self.tcx);
1498 let impl_bounds = self.tcx.predicates_of(impl_def_id);
1499 let impl_bounds = impl_bounds.instantiate(self.tcx, substs);
1500 let traits::Normalized { value: impl_bounds, obligations: norm_obligations } =
1501 traits::normalize(selcx, self.param_env, cause.clone(), impl_bounds);
1503 // Convert the bounds into obligations.
1504 let impl_obligations = traits::predicates_for_generics(
1505 move |_, _| cause.clone(),
1510 let candidate_obligations = impl_obligations
1511 .chain(norm_obligations.into_iter())
1512 .chain(ref_obligations.iter().cloned())
1513 .chain(normalization_obligations.into_iter());
1515 // Evaluate those obligations to see if they might possibly hold.
1516 for o in candidate_obligations {
1517 let o = self.resolve_vars_if_possible(o);
1518 if !self.predicate_may_hold(&o) {
1519 result = ProbeResult::NoMatch;
1520 possibly_unsatisfied_predicates.push((
1529 ObjectCandidate | WhereClauseCandidate(..) => {
1530 // These have no additional conditions to check.
1533 TraitCandidate(trait_ref) => {
1534 if let Some(method_name) = self.method_name {
1535 // Some trait methods are excluded for arrays before 2021.
1536 // (`array.into_iter()` wants a slice iterator for compatibility.)
1537 if self_ty.is_array() && !method_name.span.rust_2021() {
1538 let trait_def = self.tcx.trait_def(trait_ref.def_id);
1539 if trait_def.skip_array_during_method_dispatch {
1540 return ProbeResult::NoMatch;
1545 ty::Binder::dummy(trait_ref).without_const().to_predicate(self.tcx);
1546 parent_pred = Some(predicate);
1547 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1548 if !self.predicate_may_hold(&obligation) {
1549 result = ProbeResult::NoMatch;
1551 match self.select_trait_candidate(trait_ref) {
1552 Err(_) => return true,
1553 Ok(Some(impl_source))
1554 if !impl_source.borrow_nested_obligations().is_empty() =>
1556 for obligation in impl_source.borrow_nested_obligations() {
1557 // Determine exactly which obligation wasn't met, so
1558 // that we can give more context in the error.
1559 if !self.predicate_may_hold(obligation) {
1560 let nested_predicate =
1561 self.resolve_vars_if_possible(obligation.predicate);
1563 self.resolve_vars_if_possible(predicate);
1564 let p = if predicate == nested_predicate {
1565 // Avoid "`MyStruct: Foo` which is required by
1566 // `MyStruct: Foo`" in E0599.
1571 possibly_unsatisfied_predicates.push((
1574 Some(obligation.cause.clone()),
1580 // Some nested subobligation of this predicate
1582 let predicate = self.resolve_vars_if_possible(predicate);
1583 possibly_unsatisfied_predicates.push((predicate, None, None));
1588 // This candidate's primary obligation doesn't even
1589 // select - don't bother registering anything in
1590 // `potentially_unsatisfied_predicates`.
1591 return ProbeResult::NoMatch;
1597 // Evaluate those obligations to see if they might possibly hold.
1598 for o in sub_obligations {
1599 let o = self.resolve_vars_if_possible(o);
1600 if !self.predicate_may_hold(&o) {
1601 result = ProbeResult::NoMatch;
1602 possibly_unsatisfied_predicates.push((o.predicate, parent_pred, Some(o.cause)));
1606 if let ProbeResult::Match = result {
1607 if let (Some(return_ty), Some(xform_ret_ty)) = (self.return_type, xform_ret_ty) {
1608 let xform_ret_ty = self.resolve_vars_if_possible(xform_ret_ty);
1610 "comparing return_ty {:?} with xform ret ty {:?}",
1611 return_ty, probe.xform_ret_ty
1614 .at(&ObligationCause::dummy(), self.param_env)
1615 .define_opaque_types(false)
1616 .sup(return_ty, xform_ret_ty)
1619 return ProbeResult::BadReturnType;
1628 /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1629 /// same trait, but we don't know which impl to use. In this case, since in all cases the
1630 /// external interface of the method can be determined from the trait, it's ok not to decide.
1631 /// We can basically just collapse all of the probes for various impls into one where-clause
1632 /// probe. This will result in a pending obligation so when more type-info is available we can
1633 /// make the final decision.
1635 /// Example (`src/test/ui/method-two-trait-defer-resolution-1.rs`):
1637 /// ```ignore (illustrative)
1638 /// trait Foo { ... }
1639 /// impl Foo for Vec<i32> { ... }
1640 /// impl Foo for Vec<usize> { ... }
1643 /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1644 /// use, so it's ok to just commit to "using the method from the trait Foo".
1645 fn collapse_candidates_to_trait_pick(
1648 probes: &[(&Candidate<'tcx>, ProbeResult)],
1649 ) -> Option<Pick<'tcx>> {
1650 // Do all probes correspond to the same trait?
1651 let container = probes[0].0.item.trait_container(self.tcx)?;
1652 for (p, _) in &probes[1..] {
1653 let p_container = p.item.trait_container(self.tcx)?;
1654 if p_container != container {
1659 // FIXME: check the return type here somehow.
1660 // If so, just use this trait and call it a day.
1662 item: probes[0].0.item,
1664 import_ids: probes[0].0.import_ids.clone(),
1666 autoref_or_ptr_adjustment: None,
1671 /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
1672 /// candidate method where the method name may have been misspelled. Similarly to other
1673 /// Levenshtein based suggestions, we provide at most one such suggestion.
1674 fn probe_for_lev_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
1675 debug!("probing for method names similar to {:?}", self.method_name);
1677 let steps = self.steps.clone();
1679 let mut pcx = ProbeContext::new(
1685 self.orig_steps_var_values.clone(),
1690 pcx.allow_similar_names = true;
1691 pcx.assemble_inherent_candidates();
1693 let method_names = pcx.candidate_method_names();
1694 pcx.allow_similar_names = false;
1695 let applicable_close_candidates: Vec<ty::AssocItem> = method_names
1697 .filter_map(|&method_name| {
1699 pcx.method_name = Some(method_name);
1700 pcx.assemble_inherent_candidates();
1701 pcx.pick_core().and_then(|pick| pick.ok()).map(|pick| pick.item)
1705 if applicable_close_candidates.is_empty() {
1709 let names = applicable_close_candidates
1711 .map(|cand| cand.name)
1712 .collect::<Vec<Symbol>>();
1713 find_best_match_for_name_with_substrings(
1715 self.method_name.unwrap().name,
1720 Ok(applicable_close_candidates.into_iter().find(|method| method.name == best_name))
1725 ///////////////////////////////////////////////////////////////////////////
1727 fn has_applicable_self(&self, item: &ty::AssocItem) -> bool {
1728 // "Fast track" -- check for usage of sugar when in method call
1731 // In Path mode (i.e., resolving a value like `T::next`), consider any
1732 // associated value (i.e., methods, constants) but not types.
1734 Mode::MethodCall => item.fn_has_self_parameter,
1735 Mode::Path => match item.kind {
1736 ty::AssocKind::Type => false,
1737 ty::AssocKind::Fn | ty::AssocKind::Const => true,
1740 // FIXME -- check for types that deref to `Self`,
1741 // like `Rc<Self>` and so on.
1743 // Note also that the current code will break if this type
1744 // includes any of the type parameters defined on the method
1745 // -- but this could be overcome.
1748 fn record_static_candidate(&mut self, source: CandidateSource) {
1749 self.static_candidates.push(source);
1752 #[instrument(level = "debug", skip(self))]
1755 item: &ty::AssocItem,
1757 substs: SubstsRef<'tcx>,
1758 ) -> (Ty<'tcx>, Option<Ty<'tcx>>) {
1759 if item.kind == ty::AssocKind::Fn && self.mode == Mode::MethodCall {
1760 let sig = self.xform_method_sig(item.def_id, substs);
1761 (sig.inputs()[0], Some(sig.output()))
1767 #[instrument(level = "debug", skip(self))]
1768 fn xform_method_sig(&self, method: DefId, substs: SubstsRef<'tcx>) -> ty::FnSig<'tcx> {
1769 let fn_sig = self.tcx.bound_fn_sig(method);
1772 assert!(!substs.has_escaping_bound_vars());
1774 // It is possible for type parameters or early-bound lifetimes
1775 // to appear in the signature of `self`. The substitutions we
1776 // are given do not include type/lifetime parameters for the
1777 // method yet. So create fresh variables here for those too,
1778 // if there are any.
1779 let generics = self.tcx.generics_of(method);
1780 assert_eq!(substs.len(), generics.parent_count as usize);
1782 let xform_fn_sig = if generics.params.is_empty() {
1783 fn_sig.subst(self.tcx, substs)
1785 let substs = InternalSubsts::for_item(self.tcx, method, |param, _| {
1786 let i = param.index as usize;
1787 if i < substs.len() {
1791 GenericParamDefKind::Lifetime => {
1792 // In general, during probe we erase regions.
1793 self.tcx.lifetimes.re_erased.into()
1795 GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
1796 self.var_for_def(self.span, param)
1801 fn_sig.subst(self.tcx, substs)
1804 self.erase_late_bound_regions(xform_fn_sig)
1807 /// Gets the type of an impl and generate substitutions with inference vars.
1808 fn impl_ty_and_substs(
1811 ) -> (ty::EarlyBinder<Ty<'tcx>>, SubstsRef<'tcx>) {
1812 (self.tcx.bound_type_of(impl_def_id), self.fresh_item_substs(impl_def_id))
1815 fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx> {
1816 InternalSubsts::for_item(self.tcx, def_id, |param, _| match param.kind {
1817 GenericParamDefKind::Lifetime => self.tcx.lifetimes.re_erased.into(),
1818 GenericParamDefKind::Type { .. } => self
1819 .next_ty_var(TypeVariableOrigin {
1820 kind: TypeVariableOriginKind::SubstitutionPlaceholder,
1821 span: self.tcx.def_span(def_id),
1824 GenericParamDefKind::Const { .. } => {
1825 let span = self.tcx.def_span(def_id);
1826 let origin = ConstVariableOrigin {
1827 kind: ConstVariableOriginKind::SubstitutionPlaceholder,
1830 self.next_const_var(self.tcx.type_of(param.def_id), origin).into()
1835 /// Replaces late-bound-regions bound by `value` with `'static` using
1836 /// `ty::erase_late_bound_regions`.
1838 /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1839 /// method matching. It is reasonable during the probe phase because we don't consider region
1840 /// relationships at all. Therefore, we can just replace all the region variables with 'static
1841 /// rather than creating fresh region variables. This is nice for two reasons:
1843 /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1844 /// particular method call, it winds up creating fewer types overall, which helps for memory
1845 /// usage. (Admittedly, this is a rather small effect, though measurable.)
1847 /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1848 /// late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1849 /// regions with actual region variables as is proper, we'd have to ensure that the same
1850 /// region got replaced with the same variable, which requires a bit more coordination
1851 /// and/or tracking the substitution and
1853 fn erase_late_bound_regions<T>(&self, value: ty::Binder<'tcx, T>) -> T
1855 T: TypeFoldable<'tcx>,
1857 self.tcx.erase_late_bound_regions(value)
1860 /// Finds the method with the appropriate name (or return type, as the case may be). If
1861 /// `allow_similar_names` is set, find methods with close-matching names.
1862 // The length of the returned iterator is nearly always 0 or 1 and this
1863 // method is fairly hot.
1864 fn impl_or_trait_item(&self, def_id: DefId) -> SmallVec<[ty::AssocItem; 1]> {
1865 if let Some(name) = self.method_name {
1866 if self.allow_similar_names {
1867 let max_dist = max(name.as_str().len(), 3) / 3;
1869 .associated_items(def_id)
1870 .in_definition_order()
1872 if x.kind.namespace() != Namespace::ValueNS {
1875 match lev_distance_with_substrings(name.as_str(), x.name.as_str(), max_dist)
1885 .associated_value(def_id, name)
1886 .map_or_else(SmallVec::new, |x| SmallVec::from_buf([x]))
1889 self.tcx.associated_items(def_id).in_definition_order().copied().collect()
1894 impl<'tcx> Candidate<'tcx> {
1895 fn to_unadjusted_pick(&self, self_ty: Ty<'tcx>) -> Pick<'tcx> {
1898 kind: match self.kind {
1899 InherentImplCandidate(..) => InherentImplPick,
1900 ObjectCandidate => ObjectPick,
1901 TraitCandidate(_) => TraitPick,
1902 WhereClauseCandidate(ref trait_ref) => {
1903 // Only trait derived from where-clauses should
1904 // appear here, so they should not contain any
1905 // inference variables or other artifacts. This
1906 // means they are safe to put into the
1907 // `WhereClausePick`.
1909 !trait_ref.skip_binder().substs.needs_infer()
1910 && !trait_ref.skip_binder().substs.has_placeholders()
1913 WhereClausePick(*trait_ref)
1916 import_ids: self.import_ids.clone(),
1918 autoref_or_ptr_adjustment: None,