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::{self, ParamEnvAnd, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeVisitable};
23 use rustc_middle::ty::{InternalSubsts, SubstsRef};
24 use rustc_session::lint;
25 use rustc_span::def_id::DefId;
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 scope_expr_id: hir::HirId,
90 impl<'a, 'tcx> Deref for ProbeContext<'a, 'tcx> {
91 type Target = FnCtxt<'a, 'tcx>;
92 fn deref(&self) -> &Self::Target {
97 #[derive(Debug, Clone)]
98 struct Candidate<'tcx> {
99 // Candidates are (I'm not quite sure, but they are mostly) basically
100 // some metadata on top of a `ty::AssocItem` (without substs).
102 // However, method probing wants to be able to evaluate the predicates
103 // for a function with the substs applied - for example, if a function
104 // has `where Self: Sized`, we don't want to consider it unless `Self`
105 // is actually `Sized`, and similarly, return-type suggestions want
106 // to consider the "actual" return type.
108 // The way this is handled is through `xform_self_ty`. It contains
109 // the receiver type of this candidate, but `xform_self_ty`,
110 // `xform_ret_ty` and `kind` (which contains the predicates) have the
111 // generic parameters of this candidate substituted with the *same set*
112 // of inference variables, which acts as some weird sort of "query".
114 // When we check out a candidate, we require `xform_self_ty` to be
115 // a subtype of the passed-in self-type, and this equates the type
116 // variables in the rest of the fields.
118 // For example, if we have this candidate:
121 // fn foo(&self) where Self: Sized;
125 // Then `xform_self_ty` will be `&'erased ?X` and `kind` will contain
126 // the predicate `?X: Sized`, so if we are evaluating `Foo` for a
127 // the receiver `&T`, we'll do the subtyping which will make `?X`
128 // get the right value, then when we evaluate the predicate we'll check
130 xform_self_ty: Ty<'tcx>,
131 xform_ret_ty: Option<Ty<'tcx>>,
133 kind: CandidateKind<'tcx>,
134 import_ids: SmallVec<[LocalDefId; 1]>,
137 #[derive(Debug, Clone)]
138 enum CandidateKind<'tcx> {
139 InherentImplCandidate(
141 // Normalize obligations
142 Vec<traits::PredicateObligation<'tcx>>,
145 TraitCandidate(ty::TraitRef<'tcx>),
146 WhereClauseCandidate(
148 ty::PolyTraitRef<'tcx>,
152 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
159 /// When adjusting a receiver we often want to do one of
161 /// - Add a `&` (or `&mut`), converting the receiver from `T` to `&T` (or `&mut T`)
162 /// - If the receiver has type `*mut T`, convert it to `*const T`
164 /// This type tells us which one to do.
166 /// Note that in principle we could do both at the same time. For example, when the receiver has
167 /// type `T`, we could autoref it to `&T`, then convert to `*const T`. Or, when it has type `*mut
168 /// T`, we could convert it to `*const T`, then autoref to `&*const T`. However, currently we do
169 /// (at most) one of these. Either the receiver has type `T` and we convert it to `&T` (or with
170 /// `mut`), or it has type `*mut T` and we convert it to `*const T`.
171 #[derive(Debug, PartialEq, Copy, Clone)]
172 pub enum AutorefOrPtrAdjustment {
173 /// Receiver has type `T`, add `&` or `&mut` (it `T` is `mut`), and maybe also "unsize" it.
174 /// Unsizing is used to convert a `[T; N]` to `[T]`, which only makes sense when autorefing.
176 mutbl: hir::Mutability,
178 /// Indicates that the source expression should be "unsized" to a target type.
179 /// This is special-cased for just arrays unsizing to slices.
182 /// Receiver has type `*mut T`, convert to `*const T`
186 impl AutorefOrPtrAdjustment {
187 fn get_unsize(&self) -> bool {
189 AutorefOrPtrAdjustment::Autoref { mutbl: _, unsize } => *unsize,
190 AutorefOrPtrAdjustment::ToConstPtr => false,
195 #[derive(Debug, Clone)]
196 pub struct Pick<'tcx> {
197 pub item: ty::AssocItem,
198 pub kind: PickKind<'tcx>,
199 pub import_ids: SmallVec<[LocalDefId; 1]>,
201 /// Indicates that the source expression should be autoderef'd N times
202 /// ```ignore (not-rust)
203 /// A = expr | *expr | **expr | ...
205 pub autoderefs: usize,
207 /// Indicates that we want to add an autoref (and maybe also unsize it), or if the receiver is
208 /// `*mut T`, convert it to `*const T`.
209 pub autoref_or_ptr_adjustment: Option<AutorefOrPtrAdjustment>,
210 pub self_ty: Ty<'tcx>,
212 /// Unstable candidates alongside the stable ones.
213 unstable_candidates: Vec<(Candidate<'tcx>, Symbol)>,
216 #[derive(Clone, Debug, PartialEq, Eq)]
217 pub enum PickKind<'tcx> {
223 ty::PolyTraitRef<'tcx>,
227 pub type PickResult<'tcx> = Result<Pick<'tcx>, MethodError<'tcx>>;
229 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
231 // An expression of the form `receiver.method_name(...)`.
232 // Autoderefs are performed on `receiver`, lookup is done based on the
233 // `self` argument of the method, and static methods aren't considered.
235 // An expression of the form `Type::item` or `<T>::item`.
236 // No autoderefs are performed, lookup is done based on the type each
237 // implementation is for, and static methods are included.
241 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
242 pub enum ProbeScope {
243 // Assemble candidates coming only from traits in scope.
246 // Assemble candidates coming from all traits.
250 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
251 /// This is used to offer suggestions to users. It returns methods
252 /// that could have been called which have the desired return
253 /// type. Some effort is made to rule out methods that, if called,
254 /// would result in an error (basically, the same criteria we
255 /// would use to decide if a method is a plausible fit for
256 /// ambiguity purposes).
257 #[instrument(level = "debug", skip(self, candidate_filter))]
258 pub fn probe_for_return_type(
262 return_type: Ty<'tcx>,
264 scope_expr_id: hir::HirId,
265 candidate_filter: impl Fn(&ty::AssocItem) -> bool,
266 ) -> Vec<ty::AssocItem> {
267 let method_names = self
276 ProbeScope::AllTraits,
277 |probe_cx| Ok(probe_cx.candidate_method_names(candidate_filter)),
279 .unwrap_or_default();
282 .flat_map(|&method_name| {
291 ProbeScope::AllTraits,
292 |probe_cx| probe_cx.pick(),
295 .map(|pick| pick.item)
300 #[instrument(level = "debug", skip(self))]
301 pub fn probe_for_name(
305 is_suggestion: IsSuggestion,
307 scope_expr_id: hir::HirId,
309 ) -> PickResult<'tcx> {
319 |probe_cx| probe_cx.pick(),
327 method_name: Option<Ident>,
328 return_type: Option<Ty<'tcx>>,
329 is_suggestion: IsSuggestion,
331 scope_expr_id: hir::HirId,
334 ) -> Result<R, MethodError<'tcx>>
336 OP: FnOnce(ProbeContext<'a, 'tcx>) -> Result<R, MethodError<'tcx>>,
338 let mut orig_values = OriginalQueryValues::default();
339 let param_env_and_self_ty = self.canonicalize_query(
340 ParamEnvAnd { param_env: self.param_env, value: self_ty },
344 let steps = if mode == Mode::MethodCall {
345 self.tcx.method_autoderef_steps(param_env_and_self_ty)
348 // Mode::Path - the deref steps is "trivial". This turns
349 // our CanonicalQuery into a "trivial" QueryResponse. This
350 // is a bit inefficient, but I don't think that writing
351 // special handling for this "trivial case" is a good idea.
353 let infcx = &self.infcx;
354 let (ParamEnvAnd { param_env: _, value: self_ty }, canonical_inference_vars) =
355 infcx.instantiate_canonical_with_fresh_inference_vars(
357 ¶m_env_and_self_ty,
360 "probe_op: Mode::Path, param_env_and_self_ty={:?} self_ty={:?}",
361 param_env_and_self_ty, self_ty
363 MethodAutoderefStepsResult {
364 steps: infcx.tcx.arena.alloc_from_iter([CandidateStep {
365 self_ty: self.make_query_response_ignoring_pending_obligations(
366 canonical_inference_vars,
370 from_unsafe_deref: false,
374 reached_recursion_limit: false,
379 // If our autoderef loop had reached the recursion limit,
380 // report an overflow error, but continue going on with
381 // the truncated autoderef list.
382 if steps.reached_recursion_limit {
387 .unwrap_or_else(|| span_bug!(span, "reached the recursion limit in 0 steps?"))
390 .probe_instantiate_query_response(span, &orig_values, ty)
391 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
392 autoderef::report_autoderef_recursion_limit_error(self.tcx, span, ty.value);
396 // If we encountered an `_` type or an error type during autoderef, this is
398 if let Some(bad_ty) = &steps.opt_bad_ty {
400 // Ambiguity was encountered during a suggestion. Just keep going.
401 debug!("ProbeContext: encountered ambiguity in suggestion");
402 } else if bad_ty.reached_raw_pointer && !self.tcx.features().arbitrary_self_types {
403 // this case used to be allowed by the compiler,
404 // so we do a future-compat lint here for the 2015 edition
405 // (see https://github.com/rust-lang/rust/issues/46906)
406 if self.tcx.sess.rust_2018() {
407 self.tcx.sess.emit_err(MethodCallOnUnknownType { span });
409 self.tcx.struct_span_lint_hir(
410 lint::builtin::TYVAR_BEHIND_RAW_POINTER,
413 "type annotations needed",
418 // Encountered a real ambiguity, so abort the lookup. If `ty` is not
419 // an `Err`, report the right "type annotations needed" error pointing
423 .probe_instantiate_query_response(span, &orig_values, ty)
424 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
425 let ty = self.structurally_resolved_type(span, ty.value);
426 assert!(matches!(ty.kind(), ty::Error(_)));
427 return Err(MethodError::NoMatch(NoMatchData {
428 static_candidates: Vec::new(),
429 unsatisfied_predicates: Vec::new(),
430 out_of_scope_traits: Vec::new(),
437 debug!("ProbeContext: steps for self_ty={:?} are {:?}", self_ty, steps);
439 // this creates one big transaction so that all type variables etc
440 // that we create during the probe process are removed later
442 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;
478 let mut autoderef = Autoderef::new(infcx, param_env, hir::CRATE_HIR_ID, DUMMY_SP, self_ty)
479 .include_raw_pointers()
481 let mut reached_raw_pointer = false;
482 let mut steps: Vec<_> = autoderef
485 let step = CandidateStep {
487 .make_query_response_ignoring_pending_obligations(inference_vars.clone(), ty),
489 from_unsafe_deref: reached_raw_pointer,
492 if let ty::RawPtr(_) = ty.kind() {
493 // all the subsequent steps will be from_unsafe_deref
494 reached_raw_pointer = true;
500 let final_ty = autoderef.final_ty(true);
501 let opt_bad_ty = match final_ty.kind() {
502 ty::Infer(ty::TyVar(_)) | ty::Error(_) => Some(MethodAutoderefBadTy {
504 ty: infcx.make_query_response_ignoring_pending_obligations(inference_vars, final_ty),
506 ty::Array(elem_ty, _) => {
507 let dereferences = steps.len() - 1;
509 steps.push(CandidateStep {
510 self_ty: infcx.make_query_response_ignoring_pending_obligations(
512 infcx.tcx.mk_slice(*elem_ty),
514 autoderefs: dereferences,
515 // this could be from an unsafe deref if we had
516 // a *mut/const [T; N]
517 from_unsafe_deref: reached_raw_pointer,
526 debug!("method_autoderef_steps: steps={:?} opt_bad_ty={:?}", steps, opt_bad_ty);
528 MethodAutoderefStepsResult {
529 steps: tcx.arena.alloc_from_iter(steps),
530 opt_bad_ty: opt_bad_ty.map(|ty| &*tcx.arena.alloc(ty)),
531 reached_recursion_limit: autoderef.reached_recursion_limit(),
535 impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
537 fcx: &'a FnCtxt<'a, 'tcx>,
540 method_name: Option<Ident>,
541 return_type: Option<Ty<'tcx>>,
542 orig_steps_var_values: OriginalQueryValues<'tcx>,
543 steps: &'tcx [CandidateStep<'tcx>],
544 scope_expr_id: hir::HirId,
545 ) -> ProbeContext<'a, 'tcx> {
552 inherent_candidates: Vec::new(),
553 extension_candidates: Vec::new(),
554 impl_dups: FxHashSet::default(),
555 orig_steps_var_values,
557 static_candidates: Vec::new(),
558 allow_similar_names: false,
559 private_candidate: None,
560 unsatisfied_predicates: Vec::new(),
565 fn reset(&mut self) {
566 self.inherent_candidates.clear();
567 self.extension_candidates.clear();
568 self.impl_dups.clear();
569 self.static_candidates.clear();
570 self.private_candidate = None;
573 ///////////////////////////////////////////////////////////////////////////
574 // CANDIDATE ASSEMBLY
576 fn push_candidate(&mut self, candidate: Candidate<'tcx>, is_inherent: bool) {
577 let is_accessible = if let Some(name) = self.method_name {
578 let item = candidate.item;
581 .adjust_ident_and_get_scope(name, item.container_id(self.tcx), self.body_id)
583 item.visibility(self.tcx).is_accessible_from(def_scope, self.tcx)
589 self.inherent_candidates.push(candidate);
591 self.extension_candidates.push(candidate);
593 } else if self.private_candidate.is_none() {
594 self.private_candidate =
595 Some((candidate.item.kind.as_def_kind(), candidate.item.def_id));
599 fn assemble_inherent_candidates(&mut self) {
600 for step in self.steps.iter() {
601 self.assemble_probe(&step.self_ty);
605 fn assemble_probe(&mut self, self_ty: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>) {
606 debug!("assemble_probe: self_ty={:?}", self_ty);
607 let raw_self_ty = self_ty.value.value;
608 match *raw_self_ty.kind() {
609 ty::Dynamic(data, ..) if let Some(p) = data.principal() => {
610 // Subtle: we can't use `instantiate_query_response` here: using it will
611 // commit to all of the type equalities assumed by inference going through
612 // autoderef (see the `method-probe-no-guessing` test).
614 // However, in this code, it is OK if we end up with an object type that is
615 // "more general" than the object type that we are evaluating. For *every*
616 // object type `MY_OBJECT`, a function call that goes through a trait-ref
617 // of the form `<MY_OBJECT as SuperTraitOf(MY_OBJECT)>::func` is a valid
618 // `ObjectCandidate`, and it should be discoverable "exactly" through one
619 // of the iterations in the autoderef loop, so there is no problem with it
620 // being discoverable in another one of these iterations.
622 // Using `instantiate_canonical_with_fresh_inference_vars` on our
623 // `Canonical<QueryResponse<Ty<'tcx>>>` and then *throwing away* the
624 // `CanonicalVarValues` will exactly give us such a generalization - it
625 // will still match the original object type, but it won't pollute our
626 // type variables in any form, so just do that!
627 let (QueryResponse { value: generalized_self_ty, .. }, _ignored_var_values) =
629 .instantiate_canonical_with_fresh_inference_vars(self.span, self_ty);
631 self.assemble_inherent_candidates_from_object(generalized_self_ty);
632 self.assemble_inherent_impl_candidates_for_type(p.def_id());
633 if self.tcx.has_attr(p.def_id(), sym::rustc_has_incoherent_inherent_impls) {
634 self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
638 let def_id = def.did();
639 self.assemble_inherent_impl_candidates_for_type(def_id);
640 if self.tcx.has_attr(def_id, sym::rustc_has_incoherent_inherent_impls) {
641 self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
644 ty::Foreign(did) => {
645 self.assemble_inherent_impl_candidates_for_type(did);
646 if self.tcx.has_attr(did, sym::rustc_has_incoherent_inherent_impls) {
647 self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
651 self.assemble_inherent_candidates_from_param(p);
664 | ty::Tuple(..) => self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty),
669 fn assemble_inherent_candidates_for_incoherent_ty(&mut self, self_ty: Ty<'tcx>) {
670 let Some(simp) = simplify_type(self.tcx, self_ty, TreatParams::AsInfer) else {
671 bug!("unexpected incoherent type: {:?}", self_ty)
673 for &impl_def_id in self.tcx.incoherent_impls(simp) {
674 self.assemble_inherent_impl_probe(impl_def_id);
678 fn assemble_inherent_impl_candidates_for_type(&mut self, def_id: DefId) {
679 let impl_def_ids = self.tcx.at(self.span).inherent_impls(def_id);
680 for &impl_def_id in impl_def_ids.iter() {
681 self.assemble_inherent_impl_probe(impl_def_id);
685 fn assemble_inherent_impl_probe(&mut self, impl_def_id: DefId) {
686 if !self.impl_dups.insert(impl_def_id) {
687 return; // already visited
690 debug!("assemble_inherent_impl_probe {:?}", impl_def_id);
692 for item in self.impl_or_trait_item(impl_def_id) {
693 if !self.has_applicable_self(&item) {
694 // No receiver declared. Not a candidate.
695 self.record_static_candidate(CandidateSource::Impl(impl_def_id));
699 let (impl_ty, impl_substs) = self.impl_ty_and_substs(impl_def_id);
700 let impl_ty = impl_ty.subst(self.tcx, impl_substs);
702 debug!("impl_ty: {:?}", impl_ty);
704 // Determine the receiver type that the method itself expects.
705 let (xform_self_ty, xform_ret_ty) = self.xform_self_ty(&item, impl_ty, impl_substs);
706 debug!("xform_self_ty: {:?}, xform_ret_ty: {:?}", xform_self_ty, xform_ret_ty);
708 // We can't use normalize_associated_types_in as it will pollute the
709 // fcx's fulfillment context after this probe is over.
710 // Note: we only normalize `xform_self_ty` here since the normalization
711 // of the return type can lead to inference results that prohibit
712 // valid candidates from being found, see issue #85671
713 // FIXME Postponing the normalization of the return type likely only hides a deeper bug,
714 // which might be caused by the `param_env` itself. The clauses of the `param_env`
715 // maybe shouldn't include `Param`s, but rather fresh variables or be canonicalized,
717 let cause = traits::ObligationCause::misc(self.span, self.body_id);
718 let selcx = &mut traits::SelectionContext::new(self.fcx);
719 let traits::Normalized { value: xform_self_ty, obligations } =
720 traits::normalize(selcx, self.param_env, cause, xform_self_ty);
722 "assemble_inherent_impl_probe after normalization: xform_self_ty = {:?}/{:?}",
723 xform_self_ty, xform_ret_ty
731 kind: InherentImplCandidate(impl_substs, obligations),
732 import_ids: smallvec![],
739 fn assemble_inherent_candidates_from_object(&mut self, self_ty: Ty<'tcx>) {
740 debug!("assemble_inherent_candidates_from_object(self_ty={:?})", self_ty);
742 let principal = match self_ty.kind() {
743 ty::Dynamic(ref data, ..) => Some(data),
746 .and_then(|data| data.principal())
750 "non-object {:?} in assemble_inherent_candidates_from_object",
755 // It is illegal to invoke a method on a trait instance that refers to
756 // the `Self` type. An [`ObjectSafetyViolation::SupertraitSelf`] error
757 // will be reported by `object_safety.rs` if the method refers to the
758 // `Self` type anywhere other than the receiver. Here, we use a
759 // substitution that replaces `Self` with the object type itself. Hence,
760 // a `&self` method will wind up with an argument type like `&dyn Trait`.
761 let trait_ref = principal.with_self_ty(self.tcx, self_ty);
762 self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
763 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
765 let (xform_self_ty, xform_ret_ty) =
766 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
772 kind: ObjectCandidate,
773 import_ids: smallvec![],
780 fn assemble_inherent_candidates_from_param(&mut self, param_ty: ty::ParamTy) {
781 // FIXME: do we want to commit to this behavior for param bounds?
782 debug!("assemble_inherent_candidates_from_param(param_ty={:?})", param_ty);
784 let bounds = self.param_env.caller_bounds().iter().filter_map(|predicate| {
785 let bound_predicate = predicate.kind();
786 match bound_predicate.skip_binder() {
787 ty::PredicateKind::Trait(trait_predicate) => {
788 match *trait_predicate.trait_ref.self_ty().kind() {
789 ty::Param(p) if p == param_ty => {
790 Some(bound_predicate.rebind(trait_predicate.trait_ref))
795 ty::PredicateKind::Subtype(..)
796 | ty::PredicateKind::Coerce(..)
797 | ty::PredicateKind::Projection(..)
798 | ty::PredicateKind::RegionOutlives(..)
799 | ty::PredicateKind::WellFormed(..)
800 | ty::PredicateKind::ObjectSafe(..)
801 | ty::PredicateKind::ClosureKind(..)
802 | ty::PredicateKind::TypeOutlives(..)
803 | ty::PredicateKind::ConstEvaluatable(..)
804 | ty::PredicateKind::ConstEquate(..)
805 | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
809 self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
810 let trait_ref = this.erase_late_bound_regions(poly_trait_ref);
812 let (xform_self_ty, xform_ret_ty) =
813 this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs);
815 // Because this trait derives from a where-clause, it
816 // should not contain any inference variables or other
817 // artifacts. This means it is safe to put into the
818 // `WhereClauseCandidate` and (eventually) into the
819 // `WhereClausePick`.
820 assert!(!trait_ref.substs.needs_infer());
827 kind: WhereClauseCandidate(poly_trait_ref),
828 import_ids: smallvec![],
835 // Do a search through a list of bounds, using a callback to actually
836 // create the candidates.
837 fn elaborate_bounds<F>(
839 bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
842 F: for<'b> FnMut(&mut ProbeContext<'b, 'tcx>, ty::PolyTraitRef<'tcx>, ty::AssocItem),
845 for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
846 debug!("elaborate_bounds(bound_trait_ref={:?})", bound_trait_ref);
847 for item in self.impl_or_trait_item(bound_trait_ref.def_id()) {
848 if !self.has_applicable_self(&item) {
849 self.record_static_candidate(CandidateSource::Trait(bound_trait_ref.def_id()));
851 mk_cand(self, bound_trait_ref, item);
857 fn assemble_extension_candidates_for_traits_in_scope(&mut self, expr_hir_id: hir::HirId) {
858 let mut duplicates = FxHashSet::default();
859 let opt_applicable_traits = self.tcx.in_scope_traits(expr_hir_id);
860 if let Some(applicable_traits) = opt_applicable_traits {
861 for trait_candidate in applicable_traits.iter() {
862 let trait_did = trait_candidate.def_id;
863 if duplicates.insert(trait_did) {
864 self.assemble_extension_candidates_for_trait(
865 &trait_candidate.import_ids,
873 fn assemble_extension_candidates_for_all_traits(&mut self) {
874 let mut duplicates = FxHashSet::default();
875 for trait_info in suggest::all_traits(self.tcx) {
876 if duplicates.insert(trait_info.def_id) {
877 self.assemble_extension_candidates_for_trait(&smallvec![], trait_info.def_id);
882 fn matches_return_type(
884 method: &ty::AssocItem,
885 self_ty: Option<Ty<'tcx>>,
889 ty::AssocKind::Fn => {
890 let fty = self.tcx.bound_fn_sig(method.def_id);
892 let substs = self.fresh_substs_for_item(self.span, method.def_id);
893 let fty = fty.subst(self.tcx, substs);
895 self.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, fty);
897 if let Some(self_ty) = self_ty {
899 .at(&ObligationCause::dummy(), self.param_env)
900 .sup(fty.inputs()[0], self_ty)
906 self.can_sub(self.param_env, fty.output(), expected).is_ok()
913 fn assemble_extension_candidates_for_trait(
915 import_ids: &SmallVec<[LocalDefId; 1]>,
918 debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})", trait_def_id);
919 let trait_substs = self.fresh_item_substs(trait_def_id);
920 let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
922 if self.tcx.is_trait_alias(trait_def_id) {
923 // For trait aliases, assume all supertraits are relevant.
924 let bounds = iter::once(ty::Binder::dummy(trait_ref));
925 self.elaborate_bounds(bounds, |this, new_trait_ref, item| {
926 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
928 let (xform_self_ty, xform_ret_ty) =
929 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
935 import_ids: import_ids.clone(),
936 kind: TraitCandidate(new_trait_ref),
942 debug_assert!(self.tcx.is_trait(trait_def_id));
943 for item in self.impl_or_trait_item(trait_def_id) {
944 // Check whether `trait_def_id` defines a method with suitable name.
945 if !self.has_applicable_self(&item) {
946 debug!("method has inapplicable self");
947 self.record_static_candidate(CandidateSource::Trait(trait_def_id));
951 let (xform_self_ty, xform_ret_ty) =
952 self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
958 import_ids: import_ids.clone(),
959 kind: TraitCandidate(trait_ref),
967 fn candidate_method_names(
969 candidate_filter: impl Fn(&ty::AssocItem) -> bool,
971 let mut set = FxHashSet::default();
972 let mut names: Vec<_> = self
975 .chain(&self.extension_candidates)
976 .filter(|candidate| candidate_filter(&candidate.item))
977 .filter(|candidate| {
978 if let Some(return_ty) = self.return_type {
979 self.matches_return_type(&candidate.item, None, return_ty)
984 .map(|candidate| candidate.item.ident(self.tcx))
985 .filter(|&name| set.insert(name))
988 // Sort them by the name so we have a stable result.
989 names.sort_by(|a, b| a.as_str().partial_cmp(b.as_str()).unwrap());
993 ///////////////////////////////////////////////////////////////////////////
996 fn pick(mut self) -> PickResult<'tcx> {
997 assert!(self.method_name.is_some());
999 if let Some(r) = self.pick_core() {
1003 debug!("pick: actual search failed, assemble diagnostics");
1005 let static_candidates = mem::take(&mut self.static_candidates);
1006 let private_candidate = self.private_candidate.take();
1007 let unsatisfied_predicates = mem::take(&mut self.unsatisfied_predicates);
1009 // things failed, so lets look at all traits, for diagnostic purposes now:
1012 let span = self.span;
1015 self.assemble_extension_candidates_for_all_traits();
1017 let out_of_scope_traits = match self.pick_core() {
1018 Some(Ok(p)) => vec![p.item.container_id(self.tcx)],
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 pick = self.pick_all_method(Some(&mut vec![]));
1055 // In this case unstable picking is done by `pick_method`.
1056 if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable {
1061 return self.pick_all_method(None);
1068 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1069 ) -> Option<PickResult<'tcx>> {
1070 let steps = self.steps.clone();
1074 debug!("pick_all_method: step={:?}", step);
1075 // skip types that are from a type error or that would require dereferencing
1077 !step.self_ty.references_error() && !step.from_unsafe_deref
1080 let InferOk { value: self_ty, obligations: _ } = self
1082 .probe_instantiate_query_response(
1084 &self.orig_steps_var_values,
1087 .unwrap_or_else(|_| {
1088 span_bug!(self.span, "{:?} was applicable but now isn't?", step.self_ty)
1090 self.pick_by_value_method(step, self_ty, unstable_candidates.as_deref_mut())
1092 self.pick_autorefd_method(
1095 hir::Mutability::Not,
1096 unstable_candidates.as_deref_mut(),
1099 self.pick_autorefd_method(
1102 hir::Mutability::Mut,
1103 unstable_candidates.as_deref_mut(),
1107 self.pick_const_ptr_method(
1110 unstable_candidates.as_deref_mut(),
1118 /// For each type `T` in the step list, this attempts to find a method where
1119 /// the (transformed) self type is exactly `T`. We do however do one
1120 /// transformation on the adjustment: if we are passing a region pointer in,
1121 /// we will potentially *reborrow* it to a shorter lifetime. This allows us
1122 /// to transparently pass `&mut` pointers, in particular, without consuming
1123 /// them for their entire lifetime.
1124 fn pick_by_value_method(
1126 step: &CandidateStep<'tcx>,
1128 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1129 ) -> Option<PickResult<'tcx>> {
1134 self.pick_method(self_ty, unstable_candidates).map(|r| {
1136 pick.autoderefs = step.autoderefs;
1138 // Insert a `&*` or `&mut *` if this is a reference type:
1139 if let ty::Ref(_, _, mutbl) = *step.self_ty.value.value.kind() {
1140 pick.autoderefs += 1;
1141 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::Autoref {
1143 unsize: pick.autoref_or_ptr_adjustment.map_or(false, |a| a.get_unsize()),
1152 fn pick_autorefd_method(
1154 step: &CandidateStep<'tcx>,
1156 mutbl: hir::Mutability,
1157 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1158 ) -> Option<PickResult<'tcx>> {
1161 // In general, during probing we erase regions.
1162 let region = tcx.lifetimes.re_erased;
1164 let autoref_ty = tcx.mk_ref(region, ty::TypeAndMut { ty: self_ty, mutbl });
1165 self.pick_method(autoref_ty, unstable_candidates).map(|r| {
1167 pick.autoderefs = step.autoderefs;
1168 pick.autoref_or_ptr_adjustment =
1169 Some(AutorefOrPtrAdjustment::Autoref { mutbl, unsize: step.unsize });
1175 /// If `self_ty` is `*mut T` then this picks `*const T` methods. The reason why we have a
1176 /// special case for this is because going from `*mut T` to `*const T` with autoderefs and
1177 /// autorefs would require dereferencing the pointer, which is not safe.
1178 fn pick_const_ptr_method(
1180 step: &CandidateStep<'tcx>,
1182 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1183 ) -> Option<PickResult<'tcx>> {
1184 // Don't convert an unsized reference to ptr
1189 let &ty::RawPtr(ty::TypeAndMut { ty, mutbl: hir::Mutability::Mut }) = self_ty.kind() else {
1193 let const_self_ty = ty::TypeAndMut { ty, mutbl: hir::Mutability::Not };
1194 let const_ptr_ty = self.tcx.mk_ptr(const_self_ty);
1195 self.pick_method(const_ptr_ty, unstable_candidates).map(|r| {
1197 pick.autoderefs = step.autoderefs;
1198 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::ToConstPtr);
1204 fn pick_method_with_unstable(&mut self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
1205 debug!("pick_method_with_unstable(self_ty={})", self.ty_to_string(self_ty));
1207 let mut possibly_unsatisfied_predicates = Vec::new();
1209 for (kind, candidates) in
1210 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1212 debug!("searching {} candidates", kind);
1213 let res = self.consider_candidates(
1216 &mut possibly_unsatisfied_predicates,
1224 debug!("searching unstable candidates");
1225 let res = self.consider_candidates(
1227 self.inherent_candidates.iter().chain(&self.extension_candidates),
1228 &mut possibly_unsatisfied_predicates,
1232 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1240 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1241 ) -> Option<PickResult<'tcx>> {
1242 if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable {
1243 return self.pick_method_with_unstable(self_ty);
1246 debug!("pick_method(self_ty={})", self.ty_to_string(self_ty));
1248 let mut possibly_unsatisfied_predicates = Vec::new();
1250 for (kind, candidates) in
1251 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1253 debug!("searching {} candidates", kind);
1254 let res = self.consider_candidates(
1257 &mut possibly_unsatisfied_predicates,
1258 unstable_candidates.as_deref_mut(),
1260 if let Some(pick) = res {
1265 // `pick_method` may be called twice for the same self_ty if no stable methods
1266 // match. Only extend once.
1267 if unstable_candidates.is_some() {
1268 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1273 fn consider_candidates<'b, ProbesIter>(
1277 possibly_unsatisfied_predicates: &mut Vec<(
1278 ty::Predicate<'tcx>,
1279 Option<ty::Predicate<'tcx>>,
1280 Option<ObligationCause<'tcx>>,
1282 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1283 ) -> Option<PickResult<'tcx>>
1285 ProbesIter: Iterator<Item = &'b Candidate<'tcx>> + Clone,
1288 let mut applicable_candidates: Vec<_> = probes
1291 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
1293 .filter(|&(_, status)| status != ProbeResult::NoMatch)
1296 debug!("applicable_candidates: {:?}", applicable_candidates);
1298 if applicable_candidates.len() > 1 {
1300 self.collapse_candidates_to_trait_pick(self_ty, &applicable_candidates)
1302 return Some(Ok(pick));
1306 if let Some(uc) = &mut unstable_candidates {
1307 applicable_candidates.retain(|&(p, _)| {
1308 if let stability::EvalResult::Deny { feature, .. } =
1309 self.tcx.eval_stability(p.item.def_id, None, self.span, None)
1311 uc.push((p.clone(), feature));
1318 if applicable_candidates.len() > 1 {
1319 let sources = probes.map(|p| self.candidate_source(p, self_ty)).collect();
1320 return Some(Err(MethodError::Ambiguity(sources)));
1323 applicable_candidates.pop().map(|(probe, status)| {
1324 if status == ProbeResult::Match {
1326 .to_unadjusted_pick(self_ty, unstable_candidates.cloned().unwrap_or_default()))
1328 Err(MethodError::BadReturnType)
1334 impl<'tcx> Pick<'tcx> {
1335 /// In case there were unstable name collisions, emit them as a lint.
1336 /// Checks whether two picks do not refer to the same trait item for the same `Self` type.
1337 /// Only useful for comparisons of picks in order to improve diagnostics.
1338 /// Do not use for type checking.
1339 pub fn differs_from(&self, other: &Self) -> bool {
1347 trait_item_def_id: _,
1348 fn_has_self_parameter: _,
1353 autoref_or_ptr_adjustment: _,
1355 unstable_candidates: _,
1357 self_ty != other.self_ty || def_id != other.item.def_id
1360 /// In case there were unstable name collisions, emit them as a lint.
1361 pub fn maybe_emit_unstable_name_collision_hint(
1365 scope_expr_id: hir::HirId,
1367 if self.unstable_candidates.is_empty() {
1370 let def_kind = self.item.kind.as_def_kind();
1371 tcx.struct_span_lint_hir(
1372 lint::builtin::UNSTABLE_NAME_COLLISIONS,
1376 "{} {} with this name may be added to the standard library in the future",
1378 def_kind.descr(self.item.def_id),
1381 match (self.item.kind, self.item.container) {
1382 (ty::AssocKind::Fn, _) => {
1383 // FIXME: This should be a `span_suggestion` instead of `help`
1384 // However `self.span` only
1385 // highlights the method name, so we can't use it. Also consider reusing
1386 // the code from `report_method_error()`.
1388 "call with fully qualified syntax `{}(...)` to keep using the current \
1390 tcx.def_path_str(self.item.def_id),
1393 (ty::AssocKind::Const, ty::AssocItemContainer::TraitContainer) => {
1394 let def_id = self.item.container_id(tcx);
1395 lint.span_suggestion(
1397 "use the fully qualified path to the associated const",
1401 tcx.def_path_str(def_id),
1404 Applicability::MachineApplicable,
1409 if tcx.sess.is_nightly_build() {
1410 for (candidate, feature) in &self.unstable_candidates {
1412 "add `#![feature({})]` to the crate attributes to enable `{}`",
1414 tcx.def_path_str(candidate.item.def_id),
1425 impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
1426 fn select_trait_candidate(
1428 trait_ref: ty::TraitRef<'tcx>,
1429 ) -> traits::SelectionResult<'tcx, traits::Selection<'tcx>> {
1430 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1431 let predicate = ty::Binder::dummy(trait_ref).to_poly_trait_predicate();
1432 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1433 traits::SelectionContext::new(self).select(&obligation)
1436 fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>) -> CandidateSource {
1437 match candidate.kind {
1438 InherentImplCandidate(..) => {
1439 CandidateSource::Impl(candidate.item.container_id(self.tcx))
1441 ObjectCandidate | WhereClauseCandidate(_) => {
1442 CandidateSource::Trait(candidate.item.container_id(self.tcx))
1444 TraitCandidate(trait_ref) => self.probe(|_| {
1446 .at(&ObligationCause::dummy(), self.param_env)
1447 .define_opaque_types(false)
1448 .sup(candidate.xform_self_ty, self_ty);
1449 match self.select_trait_candidate(trait_ref) {
1450 Ok(Some(traits::ImplSource::UserDefined(ref impl_data))) => {
1451 // If only a single impl matches, make the error message point
1453 CandidateSource::Impl(impl_data.impl_def_id)
1455 _ => CandidateSource::Trait(candidate.item.container_id(self.tcx)),
1464 probe: &Candidate<'tcx>,
1465 possibly_unsatisfied_predicates: &mut Vec<(
1466 ty::Predicate<'tcx>,
1467 Option<ty::Predicate<'tcx>>,
1468 Option<ObligationCause<'tcx>>,
1471 debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe);
1474 // First check that the self type can be related.
1475 let sub_obligations = match self
1476 .at(&ObligationCause::dummy(), self.param_env)
1477 .define_opaque_types(false)
1478 .sup(probe.xform_self_ty, self_ty)
1480 Ok(InferOk { obligations, value: () }) => obligations,
1482 debug!("--> cannot relate self-types {:?}", err);
1483 return ProbeResult::NoMatch;
1487 let mut result = ProbeResult::Match;
1488 let mut xform_ret_ty = probe.xform_ret_ty;
1489 debug!(?xform_ret_ty);
1491 let selcx = &mut traits::SelectionContext::new(self);
1492 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1494 let mut parent_pred = None;
1496 // If so, impls may carry other conditions (e.g., where
1497 // clauses) that must be considered. Make sure that those
1498 // match as well (or at least may match, sometimes we
1499 // don't have enough information to fully evaluate).
1501 InherentImplCandidate(ref substs, ref ref_obligations) => {
1502 // `xform_ret_ty` hasn't been normalized yet, only `xform_self_ty`,
1503 // see the reasons mentioned in the comments in `assemble_inherent_impl_probe`
1504 // for why this is necessary
1505 let traits::Normalized {
1506 value: normalized_xform_ret_ty,
1507 obligations: normalization_obligations,
1508 } = traits::normalize(selcx, self.param_env, cause.clone(), probe.xform_ret_ty);
1509 xform_ret_ty = normalized_xform_ret_ty;
1510 debug!("xform_ret_ty after normalization: {:?}", xform_ret_ty);
1512 // Check whether the impl imposes obligations we have to worry about.
1513 let impl_def_id = probe.item.container_id(self.tcx);
1514 let impl_bounds = self.tcx.predicates_of(impl_def_id);
1515 let impl_bounds = impl_bounds.instantiate(self.tcx, substs);
1516 let traits::Normalized { value: impl_bounds, obligations: norm_obligations } =
1517 traits::normalize(selcx, self.param_env, cause.clone(), impl_bounds);
1519 // Convert the bounds into obligations.
1520 let impl_obligations = traits::predicates_for_generics(
1521 move |_, _| cause.clone(),
1526 let candidate_obligations = impl_obligations
1527 .chain(norm_obligations.into_iter())
1528 .chain(ref_obligations.iter().cloned())
1529 .chain(normalization_obligations.into_iter());
1531 // Evaluate those obligations to see if they might possibly hold.
1532 for o in candidate_obligations {
1533 let o = self.resolve_vars_if_possible(o);
1534 if !self.predicate_may_hold(&o) {
1535 result = ProbeResult::NoMatch;
1536 possibly_unsatisfied_predicates.push((
1545 ObjectCandidate | WhereClauseCandidate(..) => {
1546 // These have no additional conditions to check.
1549 TraitCandidate(trait_ref) => {
1550 if let Some(method_name) = self.method_name {
1551 // Some trait methods are excluded for arrays before 2021.
1552 // (`array.into_iter()` wants a slice iterator for compatibility.)
1553 if self_ty.is_array() && !method_name.span.rust_2021() {
1554 let trait_def = self.tcx.trait_def(trait_ref.def_id);
1555 if trait_def.skip_array_during_method_dispatch {
1556 return ProbeResult::NoMatch;
1561 ty::Binder::dummy(trait_ref).without_const().to_predicate(self.tcx);
1562 parent_pred = Some(predicate);
1563 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1564 if !self.predicate_may_hold(&obligation) {
1565 result = ProbeResult::NoMatch;
1567 match self.select_trait_candidate(trait_ref) {
1568 Err(_) => return true,
1569 Ok(Some(impl_source))
1570 if !impl_source.borrow_nested_obligations().is_empty() =>
1572 for obligation in impl_source.borrow_nested_obligations() {
1573 // Determine exactly which obligation wasn't met, so
1574 // that we can give more context in the error.
1575 if !self.predicate_may_hold(obligation) {
1576 let nested_predicate =
1577 self.resolve_vars_if_possible(obligation.predicate);
1579 self.resolve_vars_if_possible(predicate);
1580 let p = if predicate == nested_predicate {
1581 // Avoid "`MyStruct: Foo` which is required by
1582 // `MyStruct: Foo`" in E0599.
1587 possibly_unsatisfied_predicates.push((
1590 Some(obligation.cause.clone()),
1596 // Some nested subobligation of this predicate
1598 let predicate = self.resolve_vars_if_possible(predicate);
1599 possibly_unsatisfied_predicates.push((predicate, None, None));
1604 // This candidate's primary obligation doesn't even
1605 // select - don't bother registering anything in
1606 // `potentially_unsatisfied_predicates`.
1607 return ProbeResult::NoMatch;
1613 // Evaluate those obligations to see if they might possibly hold.
1614 for o in sub_obligations {
1615 let o = self.resolve_vars_if_possible(o);
1616 if !self.predicate_may_hold(&o) {
1617 result = ProbeResult::NoMatch;
1618 possibly_unsatisfied_predicates.push((o.predicate, parent_pred, Some(o.cause)));
1622 if let ProbeResult::Match = result {
1623 if let (Some(return_ty), Some(xform_ret_ty)) = (self.return_type, xform_ret_ty) {
1624 let xform_ret_ty = self.resolve_vars_if_possible(xform_ret_ty);
1626 "comparing return_ty {:?} with xform ret ty {:?}",
1627 return_ty, probe.xform_ret_ty
1630 .at(&ObligationCause::dummy(), self.param_env)
1631 .define_opaque_types(false)
1632 .sup(return_ty, xform_ret_ty)
1635 return ProbeResult::BadReturnType;
1644 /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1645 /// same trait, but we don't know which impl to use. In this case, since in all cases the
1646 /// external interface of the method can be determined from the trait, it's ok not to decide.
1647 /// We can basically just collapse all of the probes for various impls into one where-clause
1648 /// probe. This will result in a pending obligation so when more type-info is available we can
1649 /// make the final decision.
1651 /// Example (`src/test/ui/method-two-trait-defer-resolution-1.rs`):
1653 /// ```ignore (illustrative)
1654 /// trait Foo { ... }
1655 /// impl Foo for Vec<i32> { ... }
1656 /// impl Foo for Vec<usize> { ... }
1659 /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1660 /// use, so it's ok to just commit to "using the method from the trait Foo".
1661 fn collapse_candidates_to_trait_pick(
1664 probes: &[(&Candidate<'tcx>, ProbeResult)],
1665 ) -> Option<Pick<'tcx>> {
1666 // Do all probes correspond to the same trait?
1667 let container = probes[0].0.item.trait_container(self.tcx)?;
1668 for (p, _) in &probes[1..] {
1669 let p_container = p.item.trait_container(self.tcx)?;
1670 if p_container != container {
1675 // FIXME: check the return type here somehow.
1676 // If so, just use this trait and call it a day.
1678 item: probes[0].0.item,
1680 import_ids: probes[0].0.import_ids.clone(),
1682 autoref_or_ptr_adjustment: None,
1684 unstable_candidates: vec![],
1688 /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
1689 /// candidate method where the method name may have been misspelled. Similarly to other
1690 /// Levenshtein based suggestions, we provide at most one such suggestion.
1691 fn probe_for_lev_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
1692 debug!("probing for method names similar to {:?}", self.method_name);
1694 let steps = self.steps.clone();
1696 let mut pcx = ProbeContext::new(
1702 self.orig_steps_var_values.clone(),
1706 pcx.allow_similar_names = true;
1707 pcx.assemble_inherent_candidates();
1709 let method_names = pcx.candidate_method_names(|_| true);
1710 pcx.allow_similar_names = false;
1711 let applicable_close_candidates: Vec<ty::AssocItem> = method_names
1713 .filter_map(|&method_name| {
1715 pcx.method_name = Some(method_name);
1716 pcx.assemble_inherent_candidates();
1717 pcx.pick_core().and_then(|pick| pick.ok()).map(|pick| pick.item)
1721 if applicable_close_candidates.is_empty() {
1725 let names = applicable_close_candidates
1727 .map(|cand| cand.name)
1728 .collect::<Vec<Symbol>>();
1729 find_best_match_for_name_with_substrings(
1731 self.method_name.unwrap().name,
1736 Ok(applicable_close_candidates.into_iter().find(|method| method.name == best_name))
1741 ///////////////////////////////////////////////////////////////////////////
1743 fn has_applicable_self(&self, item: &ty::AssocItem) -> bool {
1744 // "Fast track" -- check for usage of sugar when in method call
1747 // In Path mode (i.e., resolving a value like `T::next`), consider any
1748 // associated value (i.e., methods, constants) but not types.
1750 Mode::MethodCall => item.fn_has_self_parameter,
1751 Mode::Path => match item.kind {
1752 ty::AssocKind::Type => false,
1753 ty::AssocKind::Fn | ty::AssocKind::Const => true,
1756 // FIXME -- check for types that deref to `Self`,
1757 // like `Rc<Self>` and so on.
1759 // Note also that the current code will break if this type
1760 // includes any of the type parameters defined on the method
1761 // -- but this could be overcome.
1764 fn record_static_candidate(&mut self, source: CandidateSource) {
1765 self.static_candidates.push(source);
1768 #[instrument(level = "debug", skip(self))]
1771 item: &ty::AssocItem,
1773 substs: SubstsRef<'tcx>,
1774 ) -> (Ty<'tcx>, Option<Ty<'tcx>>) {
1775 if item.kind == ty::AssocKind::Fn && self.mode == Mode::MethodCall {
1776 let sig = self.xform_method_sig(item.def_id, substs);
1777 (sig.inputs()[0], Some(sig.output()))
1783 #[instrument(level = "debug", skip(self))]
1784 fn xform_method_sig(&self, method: DefId, substs: SubstsRef<'tcx>) -> ty::FnSig<'tcx> {
1785 let fn_sig = self.tcx.bound_fn_sig(method);
1788 assert!(!substs.has_escaping_bound_vars());
1790 // It is possible for type parameters or early-bound lifetimes
1791 // to appear in the signature of `self`. The substitutions we
1792 // are given do not include type/lifetime parameters for the
1793 // method yet. So create fresh variables here for those too,
1794 // if there are any.
1795 let generics = self.tcx.generics_of(method);
1796 assert_eq!(substs.len(), generics.parent_count as usize);
1798 let xform_fn_sig = if generics.params.is_empty() {
1799 fn_sig.subst(self.tcx, substs)
1801 let substs = InternalSubsts::for_item(self.tcx, method, |param, _| {
1802 let i = param.index as usize;
1803 if i < substs.len() {
1807 GenericParamDefKind::Lifetime => {
1808 // In general, during probe we erase regions.
1809 self.tcx.lifetimes.re_erased.into()
1811 GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
1812 self.var_for_def(self.span, param)
1817 fn_sig.subst(self.tcx, substs)
1820 self.erase_late_bound_regions(xform_fn_sig)
1823 /// Gets the type of an impl and generate substitutions with inference vars.
1824 fn impl_ty_and_substs(
1827 ) -> (ty::EarlyBinder<Ty<'tcx>>, SubstsRef<'tcx>) {
1828 (self.tcx.bound_type_of(impl_def_id), self.fresh_item_substs(impl_def_id))
1831 fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx> {
1832 InternalSubsts::for_item(self.tcx, def_id, |param, _| match param.kind {
1833 GenericParamDefKind::Lifetime => self.tcx.lifetimes.re_erased.into(),
1834 GenericParamDefKind::Type { .. } => self
1835 .next_ty_var(TypeVariableOrigin {
1836 kind: TypeVariableOriginKind::SubstitutionPlaceholder,
1837 span: self.tcx.def_span(def_id),
1840 GenericParamDefKind::Const { .. } => {
1841 let span = self.tcx.def_span(def_id);
1842 let origin = ConstVariableOrigin {
1843 kind: ConstVariableOriginKind::SubstitutionPlaceholder,
1846 self.next_const_var(self.tcx.type_of(param.def_id), origin).into()
1851 /// Replaces late-bound-regions bound by `value` with `'static` using
1852 /// `ty::erase_late_bound_regions`.
1854 /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1855 /// method matching. It is reasonable during the probe phase because we don't consider region
1856 /// relationships at all. Therefore, we can just replace all the region variables with 'static
1857 /// rather than creating fresh region variables. This is nice for two reasons:
1859 /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1860 /// particular method call, it winds up creating fewer types overall, which helps for memory
1861 /// usage. (Admittedly, this is a rather small effect, though measurable.)
1863 /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1864 /// late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1865 /// regions with actual region variables as is proper, we'd have to ensure that the same
1866 /// region got replaced with the same variable, which requires a bit more coordination
1867 /// and/or tracking the substitution and
1869 fn erase_late_bound_regions<T>(&self, value: ty::Binder<'tcx, T>) -> T
1871 T: TypeFoldable<'tcx>,
1873 self.tcx.erase_late_bound_regions(value)
1876 /// Finds the method with the appropriate name (or return type, as the case may be). If
1877 /// `allow_similar_names` is set, find methods with close-matching names.
1878 // The length of the returned iterator is nearly always 0 or 1 and this
1879 // method is fairly hot.
1880 fn impl_or_trait_item(&self, def_id: DefId) -> SmallVec<[ty::AssocItem; 1]> {
1881 if let Some(name) = self.method_name {
1882 if self.allow_similar_names {
1883 let max_dist = max(name.as_str().len(), 3) / 3;
1885 .associated_items(def_id)
1886 .in_definition_order()
1888 if x.kind.namespace() != Namespace::ValueNS {
1891 match lev_distance_with_substrings(name.as_str(), x.name.as_str(), max_dist)
1901 .associated_value(def_id, name)
1902 .map_or_else(SmallVec::new, |x| SmallVec::from_buf([x]))
1905 self.tcx.associated_items(def_id).in_definition_order().copied().collect()
1910 impl<'tcx> Candidate<'tcx> {
1911 fn to_unadjusted_pick(
1914 unstable_candidates: Vec<(Candidate<'tcx>, Symbol)>,
1918 kind: match self.kind {
1919 InherentImplCandidate(..) => InherentImplPick,
1920 ObjectCandidate => ObjectPick,
1921 TraitCandidate(_) => TraitPick,
1922 WhereClauseCandidate(ref trait_ref) => {
1923 // Only trait derived from where-clauses should
1924 // appear here, so they should not contain any
1925 // inference variables or other artifacts. This
1926 // means they are safe to put into the
1927 // `WhereClausePick`.
1929 !trait_ref.skip_binder().substs.needs_infer()
1930 && !trait_ref.skip_binder().substs.has_placeholders()
1933 WhereClausePick(*trait_ref)
1936 import_ids: self.import_ids.clone(),
1938 autoref_or_ptr_adjustment: None,
1940 unstable_candidates,