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_infer::infer::canonical::OriginalQueryValues;
13 use rustc_infer::infer::canonical::{Canonical, QueryResponse};
14 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
15 use rustc_infer::infer::{self, InferOk, TyCtxtInferExt};
16 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
17 use rustc_middle::middle::stability;
18 use rustc_middle::ty::fast_reject::{simplify_type, TreatParams};
19 use rustc_middle::ty::AssocItem;
20 use rustc_middle::ty::GenericParamDefKind;
21 use rustc_middle::ty::ToPredicate;
22 use rustc_middle::ty::{self, ParamEnvAnd, 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::Ambiguous
806 | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
810 self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
811 let trait_ref = this.erase_late_bound_regions(poly_trait_ref);
813 let (xform_self_ty, xform_ret_ty) =
814 this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs);
816 // Because this trait derives from a where-clause, it
817 // should not contain any inference variables or other
818 // artifacts. This means it is safe to put into the
819 // `WhereClauseCandidate` and (eventually) into the
820 // `WhereClausePick`.
821 assert!(!trait_ref.substs.needs_infer());
828 kind: WhereClauseCandidate(poly_trait_ref),
829 import_ids: smallvec![],
836 // Do a search through a list of bounds, using a callback to actually
837 // create the candidates.
838 fn elaborate_bounds<F>(
840 bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
843 F: for<'b> FnMut(&mut ProbeContext<'b, 'tcx>, ty::PolyTraitRef<'tcx>, ty::AssocItem),
846 for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
847 debug!("elaborate_bounds(bound_trait_ref={:?})", bound_trait_ref);
848 for item in self.impl_or_trait_item(bound_trait_ref.def_id()) {
849 if !self.has_applicable_self(&item) {
850 self.record_static_candidate(CandidateSource::Trait(bound_trait_ref.def_id()));
852 mk_cand(self, bound_trait_ref, item);
858 fn assemble_extension_candidates_for_traits_in_scope(&mut self, expr_hir_id: hir::HirId) {
859 let mut duplicates = FxHashSet::default();
860 let opt_applicable_traits = self.tcx.in_scope_traits(expr_hir_id);
861 if let Some(applicable_traits) = opt_applicable_traits {
862 for trait_candidate in applicable_traits.iter() {
863 let trait_did = trait_candidate.def_id;
864 if duplicates.insert(trait_did) {
865 self.assemble_extension_candidates_for_trait(
866 &trait_candidate.import_ids,
874 fn assemble_extension_candidates_for_all_traits(&mut self) {
875 let mut duplicates = FxHashSet::default();
876 for trait_info in suggest::all_traits(self.tcx) {
877 if duplicates.insert(trait_info.def_id) {
878 self.assemble_extension_candidates_for_trait(&smallvec![], trait_info.def_id);
883 fn matches_return_type(
885 method: &ty::AssocItem,
886 self_ty: Option<Ty<'tcx>>,
890 ty::AssocKind::Fn => {
891 let fty = self.tcx.bound_fn_sig(method.def_id);
893 let substs = self.fresh_substs_for_item(self.span, method.def_id);
894 let fty = fty.subst(self.tcx, substs);
896 self.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, fty);
898 if let Some(self_ty) = self_ty {
900 .at(&ObligationCause::dummy(), self.param_env)
901 .sup(fty.inputs()[0], self_ty)
907 self.can_sub(self.param_env, fty.output(), expected).is_ok()
914 fn assemble_extension_candidates_for_trait(
916 import_ids: &SmallVec<[LocalDefId; 1]>,
919 debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})", trait_def_id);
920 let trait_substs = self.fresh_item_substs(trait_def_id);
921 let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
923 if self.tcx.is_trait_alias(trait_def_id) {
924 // For trait aliases, assume all supertraits are relevant.
925 let bounds = iter::once(ty::Binder::dummy(trait_ref));
926 self.elaborate_bounds(bounds, |this, new_trait_ref, item| {
927 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
929 let (xform_self_ty, xform_ret_ty) =
930 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
936 import_ids: import_ids.clone(),
937 kind: TraitCandidate(new_trait_ref),
943 debug_assert!(self.tcx.is_trait(trait_def_id));
944 for item in self.impl_or_trait_item(trait_def_id) {
945 // Check whether `trait_def_id` defines a method with suitable name.
946 if !self.has_applicable_self(&item) {
947 debug!("method has inapplicable self");
948 self.record_static_candidate(CandidateSource::Trait(trait_def_id));
952 let (xform_self_ty, xform_ret_ty) =
953 self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
959 import_ids: import_ids.clone(),
960 kind: TraitCandidate(trait_ref),
968 fn candidate_method_names(
970 candidate_filter: impl Fn(&ty::AssocItem) -> bool,
972 let mut set = FxHashSet::default();
973 let mut names: Vec<_> = self
976 .chain(&self.extension_candidates)
977 .filter(|candidate| candidate_filter(&candidate.item))
978 .filter(|candidate| {
979 if let Some(return_ty) = self.return_type {
980 self.matches_return_type(&candidate.item, None, return_ty)
985 .map(|candidate| candidate.item.ident(self.tcx))
986 .filter(|&name| set.insert(name))
989 // Sort them by the name so we have a stable result.
990 names.sort_by(|a, b| a.as_str().partial_cmp(b.as_str()).unwrap());
994 ///////////////////////////////////////////////////////////////////////////
997 fn pick(mut self) -> PickResult<'tcx> {
998 assert!(self.method_name.is_some());
1000 if let Some(r) = self.pick_core() {
1004 debug!("pick: actual search failed, assemble diagnostics");
1006 let static_candidates = mem::take(&mut self.static_candidates);
1007 let private_candidate = self.private_candidate.take();
1008 let unsatisfied_predicates = mem::take(&mut self.unsatisfied_predicates);
1010 // things failed, so lets look at all traits, for diagnostic purposes now:
1013 let span = self.span;
1016 self.assemble_extension_candidates_for_all_traits();
1018 let out_of_scope_traits = match self.pick_core() {
1019 Some(Ok(p)) => vec![p.item.container_id(self.tcx)],
1020 Some(Err(MethodError::Ambiguity(v))) => v
1022 .map(|source| match source {
1023 CandidateSource::Trait(id) => id,
1024 CandidateSource::Impl(impl_id) => match tcx.trait_id_of_impl(impl_id) {
1026 None => span_bug!(span, "found inherent method when looking at traits"),
1030 Some(Err(MethodError::NoMatch(NoMatchData {
1031 out_of_scope_traits: others, ..
1033 assert!(others.is_empty());
1039 if let Some((kind, def_id)) = private_candidate {
1040 return Err(MethodError::PrivateMatch(kind, def_id, out_of_scope_traits));
1042 let lev_candidate = self.probe_for_lev_candidate()?;
1044 Err(MethodError::NoMatch(NoMatchData {
1046 unsatisfied_predicates,
1047 out_of_scope_traits,
1053 fn pick_core(&mut self) -> Option<PickResult<'tcx>> {
1054 let pick = self.pick_all_method(Some(&mut vec![]));
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 return self.pick_all_method(None);
1069 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1070 ) -> Option<PickResult<'tcx>> {
1071 let steps = self.steps.clone();
1075 debug!("pick_all_method: step={:?}", step);
1076 // skip types that are from a type error or that would require dereferencing
1078 !step.self_ty.references_error() && !step.from_unsafe_deref
1081 let InferOk { value: self_ty, obligations: _ } = self
1083 .probe_instantiate_query_response(
1085 &self.orig_steps_var_values,
1088 .unwrap_or_else(|_| {
1089 span_bug!(self.span, "{:?} was applicable but now isn't?", step.self_ty)
1091 self.pick_by_value_method(step, self_ty, unstable_candidates.as_deref_mut())
1093 self.pick_autorefd_method(
1096 hir::Mutability::Not,
1097 unstable_candidates.as_deref_mut(),
1100 self.pick_autorefd_method(
1103 hir::Mutability::Mut,
1104 unstable_candidates.as_deref_mut(),
1108 self.pick_const_ptr_method(
1111 unstable_candidates.as_deref_mut(),
1119 /// For each type `T` in the step list, this attempts to find a method where
1120 /// the (transformed) self type is exactly `T`. We do however do one
1121 /// transformation on the adjustment: if we are passing a region pointer in,
1122 /// we will potentially *reborrow* it to a shorter lifetime. This allows us
1123 /// to transparently pass `&mut` pointers, in particular, without consuming
1124 /// them for their entire lifetime.
1125 fn pick_by_value_method(
1127 step: &CandidateStep<'tcx>,
1129 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1130 ) -> Option<PickResult<'tcx>> {
1135 self.pick_method(self_ty, unstable_candidates).map(|r| {
1137 pick.autoderefs = step.autoderefs;
1139 // Insert a `&*` or `&mut *` if this is a reference type:
1140 if let ty::Ref(_, _, mutbl) = *step.self_ty.value.value.kind() {
1141 pick.autoderefs += 1;
1142 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::Autoref {
1144 unsize: pick.autoref_or_ptr_adjustment.map_or(false, |a| a.get_unsize()),
1153 fn pick_autorefd_method(
1155 step: &CandidateStep<'tcx>,
1157 mutbl: hir::Mutability,
1158 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1159 ) -> Option<PickResult<'tcx>> {
1162 // In general, during probing we erase regions.
1163 let region = tcx.lifetimes.re_erased;
1165 let autoref_ty = tcx.mk_ref(region, ty::TypeAndMut { ty: self_ty, mutbl });
1166 self.pick_method(autoref_ty, unstable_candidates).map(|r| {
1168 pick.autoderefs = step.autoderefs;
1169 pick.autoref_or_ptr_adjustment =
1170 Some(AutorefOrPtrAdjustment::Autoref { mutbl, unsize: step.unsize });
1176 /// If `self_ty` is `*mut T` then this picks `*const T` methods. The reason why we have a
1177 /// special case for this is because going from `*mut T` to `*const T` with autoderefs and
1178 /// autorefs would require dereferencing the pointer, which is not safe.
1179 fn pick_const_ptr_method(
1181 step: &CandidateStep<'tcx>,
1183 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1184 ) -> Option<PickResult<'tcx>> {
1185 // Don't convert an unsized reference to ptr
1190 let &ty::RawPtr(ty::TypeAndMut { ty, mutbl: hir::Mutability::Mut }) = self_ty.kind() else {
1194 let const_self_ty = ty::TypeAndMut { ty, mutbl: hir::Mutability::Not };
1195 let const_ptr_ty = self.tcx.mk_ptr(const_self_ty);
1196 self.pick_method(const_ptr_ty, unstable_candidates).map(|r| {
1198 pick.autoderefs = step.autoderefs;
1199 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::ToConstPtr);
1205 fn pick_method_with_unstable(&mut self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
1206 debug!("pick_method_with_unstable(self_ty={})", self.ty_to_string(self_ty));
1208 let mut possibly_unsatisfied_predicates = Vec::new();
1210 for (kind, candidates) in
1211 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1213 debug!("searching {} candidates", kind);
1214 let res = self.consider_candidates(
1217 &mut possibly_unsatisfied_predicates,
1225 debug!("searching unstable candidates");
1226 let res = self.consider_candidates(
1228 self.inherent_candidates.iter().chain(&self.extension_candidates),
1229 &mut possibly_unsatisfied_predicates,
1233 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1241 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1242 ) -> Option<PickResult<'tcx>> {
1243 if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable {
1244 return self.pick_method_with_unstable(self_ty);
1247 debug!("pick_method(self_ty={})", self.ty_to_string(self_ty));
1249 let mut possibly_unsatisfied_predicates = Vec::new();
1251 for (kind, candidates) in
1252 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1254 debug!("searching {} candidates", kind);
1255 let res = self.consider_candidates(
1258 &mut possibly_unsatisfied_predicates,
1259 unstable_candidates.as_deref_mut(),
1261 if let Some(pick) = res {
1266 // `pick_method` may be called twice for the same self_ty if no stable methods
1267 // match. Only extend once.
1268 if unstable_candidates.is_some() {
1269 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1274 fn consider_candidates<'b, ProbesIter>(
1278 possibly_unsatisfied_predicates: &mut Vec<(
1279 ty::Predicate<'tcx>,
1280 Option<ty::Predicate<'tcx>>,
1281 Option<ObligationCause<'tcx>>,
1283 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1284 ) -> Option<PickResult<'tcx>>
1286 ProbesIter: Iterator<Item = &'b Candidate<'tcx>> + Clone,
1289 let mut applicable_candidates: Vec<_> = probes
1292 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
1294 .filter(|&(_, status)| status != ProbeResult::NoMatch)
1297 debug!("applicable_candidates: {:?}", applicable_candidates);
1299 if applicable_candidates.len() > 1 {
1301 self.collapse_candidates_to_trait_pick(self_ty, &applicable_candidates)
1303 return Some(Ok(pick));
1307 if let Some(uc) = &mut unstable_candidates {
1308 applicable_candidates.retain(|&(p, _)| {
1309 if let stability::EvalResult::Deny { feature, .. } =
1310 self.tcx.eval_stability(p.item.def_id, None, self.span, None)
1312 uc.push((p.clone(), feature));
1319 if applicable_candidates.len() > 1 {
1320 let sources = probes.map(|p| self.candidate_source(p, self_ty)).collect();
1321 return Some(Err(MethodError::Ambiguity(sources)));
1324 applicable_candidates.pop().map(|(probe, status)| {
1325 if status == ProbeResult::Match {
1327 .to_unadjusted_pick(self_ty, unstable_candidates.cloned().unwrap_or_default()))
1329 Err(MethodError::BadReturnType)
1335 impl<'tcx> Pick<'tcx> {
1336 /// In case there were unstable name collisions, emit them as a lint.
1337 /// Checks whether two picks do not refer to the same trait item for the same `Self` type.
1338 /// Only useful for comparisons of picks in order to improve diagnostics.
1339 /// Do not use for type checking.
1340 pub fn differs_from(&self, other: &Self) -> bool {
1348 trait_item_def_id: _,
1349 fn_has_self_parameter: _,
1354 autoref_or_ptr_adjustment: _,
1356 unstable_candidates: _,
1358 self_ty != other.self_ty || def_id != other.item.def_id
1361 /// In case there were unstable name collisions, emit them as a lint.
1362 pub fn maybe_emit_unstable_name_collision_hint(
1366 scope_expr_id: hir::HirId,
1368 if self.unstable_candidates.is_empty() {
1371 let def_kind = self.item.kind.as_def_kind();
1372 tcx.struct_span_lint_hir(
1373 lint::builtin::UNSTABLE_NAME_COLLISIONS,
1377 "{} {} with this name may be added to the standard library in the future",
1379 def_kind.descr(self.item.def_id),
1382 match (self.item.kind, self.item.container) {
1383 (ty::AssocKind::Fn, _) => {
1384 // FIXME: This should be a `span_suggestion` instead of `help`
1385 // However `self.span` only
1386 // highlights the method name, so we can't use it. Also consider reusing
1387 // the code from `report_method_error()`.
1389 "call with fully qualified syntax `{}(...)` to keep using the current \
1391 tcx.def_path_str(self.item.def_id),
1394 (ty::AssocKind::Const, ty::AssocItemContainer::TraitContainer) => {
1395 let def_id = self.item.container_id(tcx);
1396 lint.span_suggestion(
1398 "use the fully qualified path to the associated const",
1402 tcx.def_path_str(def_id),
1405 Applicability::MachineApplicable,
1410 if tcx.sess.is_nightly_build() {
1411 for (candidate, feature) in &self.unstable_candidates {
1413 "add `#![feature({})]` to the crate attributes to enable `{}`",
1415 tcx.def_path_str(candidate.item.def_id),
1426 impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
1427 fn select_trait_candidate(
1429 trait_ref: ty::TraitRef<'tcx>,
1430 ) -> traits::SelectionResult<'tcx, traits::Selection<'tcx>> {
1431 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1432 let predicate = ty::Binder::dummy(trait_ref).to_poly_trait_predicate();
1433 let obligation = traits::Obligation::new(self.tcx, cause, self.param_env, predicate);
1434 traits::SelectionContext::new(self).select(&obligation)
1437 fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>) -> CandidateSource {
1438 match candidate.kind {
1439 InherentImplCandidate(..) => {
1440 CandidateSource::Impl(candidate.item.container_id(self.tcx))
1442 ObjectCandidate | WhereClauseCandidate(_) => {
1443 CandidateSource::Trait(candidate.item.container_id(self.tcx))
1445 TraitCandidate(trait_ref) => self.probe(|_| {
1447 .at(&ObligationCause::dummy(), self.param_env)
1448 .define_opaque_types(false)
1449 .sup(candidate.xform_self_ty, self_ty);
1450 match self.select_trait_candidate(trait_ref) {
1451 Ok(Some(traits::ImplSource::UserDefined(ref impl_data))) => {
1452 // If only a single impl matches, make the error message point
1454 CandidateSource::Impl(impl_data.impl_def_id)
1456 _ => CandidateSource::Trait(candidate.item.container_id(self.tcx)),
1465 probe: &Candidate<'tcx>,
1466 possibly_unsatisfied_predicates: &mut Vec<(
1467 ty::Predicate<'tcx>,
1468 Option<ty::Predicate<'tcx>>,
1469 Option<ObligationCause<'tcx>>,
1472 debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe);
1475 // First check that the self type can be related.
1476 let sub_obligations = match self
1477 .at(&ObligationCause::dummy(), self.param_env)
1478 .define_opaque_types(false)
1479 .sup(probe.xform_self_ty, self_ty)
1481 Ok(InferOk { obligations, value: () }) => obligations,
1483 debug!("--> cannot relate self-types {:?}", err);
1484 return ProbeResult::NoMatch;
1488 let mut result = ProbeResult::Match;
1489 let mut xform_ret_ty = probe.xform_ret_ty;
1490 debug!(?xform_ret_ty);
1492 let selcx = &mut traits::SelectionContext::new(self);
1493 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1495 let mut parent_pred = None;
1497 // If so, impls may carry other conditions (e.g., where
1498 // clauses) that must be considered. Make sure that those
1499 // match as well (or at least may match, sometimes we
1500 // don't have enough information to fully evaluate).
1502 InherentImplCandidate(ref substs, ref ref_obligations) => {
1503 // `xform_ret_ty` hasn't been normalized yet, only `xform_self_ty`,
1504 // see the reasons mentioned in the comments in `assemble_inherent_impl_probe`
1505 // for why this is necessary
1506 let traits::Normalized {
1507 value: normalized_xform_ret_ty,
1508 obligations: normalization_obligations,
1509 } = traits::normalize(selcx, self.param_env, cause.clone(), probe.xform_ret_ty);
1510 xform_ret_ty = normalized_xform_ret_ty;
1511 debug!("xform_ret_ty after normalization: {:?}", xform_ret_ty);
1513 // Check whether the impl imposes obligations we have to worry about.
1514 let impl_def_id = probe.item.container_id(self.tcx);
1515 let impl_bounds = self.tcx.predicates_of(impl_def_id);
1516 let impl_bounds = impl_bounds.instantiate(self.tcx, substs);
1517 let traits::Normalized { value: impl_bounds, obligations: norm_obligations } =
1518 traits::normalize(selcx, self.param_env, cause.clone(), impl_bounds);
1520 // Convert the bounds into obligations.
1521 let impl_obligations = traits::predicates_for_generics(
1522 move |_, _| cause.clone(),
1527 let candidate_obligations = impl_obligations
1528 .chain(norm_obligations.into_iter())
1529 .chain(ref_obligations.iter().cloned())
1530 .chain(normalization_obligations.into_iter());
1532 // Evaluate those obligations to see if they might possibly hold.
1533 for o in candidate_obligations {
1534 let o = self.resolve_vars_if_possible(o);
1535 if !self.predicate_may_hold(&o) {
1536 result = ProbeResult::NoMatch;
1537 possibly_unsatisfied_predicates.push((
1546 ObjectCandidate | WhereClauseCandidate(..) => {
1547 // These have no additional conditions to check.
1550 TraitCandidate(trait_ref) => {
1551 if let Some(method_name) = self.method_name {
1552 // Some trait methods are excluded for arrays before 2021.
1553 // (`array.into_iter()` wants a slice iterator for compatibility.)
1554 if self_ty.is_array() && !method_name.span.rust_2021() {
1555 let trait_def = self.tcx.trait_def(trait_ref.def_id);
1556 if trait_def.skip_array_during_method_dispatch {
1557 return ProbeResult::NoMatch;
1562 ty::Binder::dummy(trait_ref).without_const().to_predicate(self.tcx);
1563 parent_pred = Some(predicate);
1565 traits::Obligation::new(self.tcx, cause, self.param_env, predicate);
1566 if !self.predicate_may_hold(&obligation) {
1567 result = ProbeResult::NoMatch;
1569 match self.select_trait_candidate(trait_ref) {
1570 Err(_) => return true,
1571 Ok(Some(impl_source))
1572 if !impl_source.borrow_nested_obligations().is_empty() =>
1574 for obligation in impl_source.borrow_nested_obligations() {
1575 // Determine exactly which obligation wasn't met, so
1576 // that we can give more context in the error.
1577 if !self.predicate_may_hold(obligation) {
1578 let nested_predicate =
1579 self.resolve_vars_if_possible(obligation.predicate);
1581 self.resolve_vars_if_possible(predicate);
1582 let p = if predicate == nested_predicate {
1583 // Avoid "`MyStruct: Foo` which is required by
1584 // `MyStruct: Foo`" in E0599.
1589 possibly_unsatisfied_predicates.push((
1592 Some(obligation.cause.clone()),
1598 // Some nested subobligation of this predicate
1600 let predicate = self.resolve_vars_if_possible(predicate);
1601 possibly_unsatisfied_predicates.push((predicate, None, None));
1606 // This candidate's primary obligation doesn't even
1607 // select - don't bother registering anything in
1608 // `potentially_unsatisfied_predicates`.
1609 return ProbeResult::NoMatch;
1615 // Evaluate those obligations to see if they might possibly hold.
1616 for o in sub_obligations {
1617 let o = self.resolve_vars_if_possible(o);
1618 if !self.predicate_may_hold(&o) {
1619 result = ProbeResult::NoMatch;
1620 possibly_unsatisfied_predicates.push((o.predicate, parent_pred, Some(o.cause)));
1624 if let ProbeResult::Match = result {
1625 if let (Some(return_ty), Some(xform_ret_ty)) = (self.return_type, xform_ret_ty) {
1626 let xform_ret_ty = self.resolve_vars_if_possible(xform_ret_ty);
1628 "comparing return_ty {:?} with xform ret ty {:?}",
1629 return_ty, probe.xform_ret_ty
1632 .at(&ObligationCause::dummy(), self.param_env)
1633 .define_opaque_types(false)
1634 .sup(return_ty, xform_ret_ty)
1637 return ProbeResult::BadReturnType;
1646 /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1647 /// same trait, but we don't know which impl to use. In this case, since in all cases the
1648 /// external interface of the method can be determined from the trait, it's ok not to decide.
1649 /// We can basically just collapse all of the probes for various impls into one where-clause
1650 /// probe. This will result in a pending obligation so when more type-info is available we can
1651 /// make the final decision.
1653 /// Example (`src/test/ui/method-two-trait-defer-resolution-1.rs`):
1655 /// ```ignore (illustrative)
1656 /// trait Foo { ... }
1657 /// impl Foo for Vec<i32> { ... }
1658 /// impl Foo for Vec<usize> { ... }
1661 /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1662 /// use, so it's ok to just commit to "using the method from the trait Foo".
1663 fn collapse_candidates_to_trait_pick(
1666 probes: &[(&Candidate<'tcx>, ProbeResult)],
1667 ) -> Option<Pick<'tcx>> {
1668 // Do all probes correspond to the same trait?
1669 let container = probes[0].0.item.trait_container(self.tcx)?;
1670 for (p, _) in &probes[1..] {
1671 let p_container = p.item.trait_container(self.tcx)?;
1672 if p_container != container {
1677 // FIXME: check the return type here somehow.
1678 // If so, just use this trait and call it a day.
1680 item: probes[0].0.item,
1682 import_ids: probes[0].0.import_ids.clone(),
1684 autoref_or_ptr_adjustment: None,
1686 unstable_candidates: vec![],
1690 /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
1691 /// candidate method where the method name may have been misspelled. Similarly to other
1692 /// Levenshtein based suggestions, we provide at most one such suggestion.
1693 fn probe_for_lev_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
1694 debug!("probing for method names similar to {:?}", self.method_name);
1696 let steps = self.steps.clone();
1698 let mut pcx = ProbeContext::new(
1704 self.orig_steps_var_values.clone(),
1708 pcx.allow_similar_names = true;
1709 pcx.assemble_inherent_candidates();
1711 let method_names = pcx.candidate_method_names(|_| true);
1712 pcx.allow_similar_names = false;
1713 let applicable_close_candidates: Vec<ty::AssocItem> = method_names
1715 .filter_map(|&method_name| {
1717 pcx.method_name = Some(method_name);
1718 pcx.assemble_inherent_candidates();
1719 pcx.pick_core().and_then(|pick| pick.ok()).map(|pick| pick.item)
1723 if applicable_close_candidates.is_empty() {
1727 let names = applicable_close_candidates
1729 .map(|cand| cand.name)
1730 .collect::<Vec<Symbol>>();
1731 find_best_match_for_name_with_substrings(
1733 self.method_name.unwrap().name,
1738 Ok(applicable_close_candidates.into_iter().find(|method| method.name == best_name))
1743 ///////////////////////////////////////////////////////////////////////////
1745 fn has_applicable_self(&self, item: &ty::AssocItem) -> bool {
1746 // "Fast track" -- check for usage of sugar when in method call
1749 // In Path mode (i.e., resolving a value like `T::next`), consider any
1750 // associated value (i.e., methods, constants) but not types.
1752 Mode::MethodCall => item.fn_has_self_parameter,
1753 Mode::Path => match item.kind {
1754 ty::AssocKind::Type => false,
1755 ty::AssocKind::Fn | ty::AssocKind::Const => true,
1758 // FIXME -- check for types that deref to `Self`,
1759 // like `Rc<Self>` and so on.
1761 // Note also that the current code will break if this type
1762 // includes any of the type parameters defined on the method
1763 // -- but this could be overcome.
1766 fn record_static_candidate(&mut self, source: CandidateSource) {
1767 self.static_candidates.push(source);
1770 #[instrument(level = "debug", skip(self))]
1773 item: &ty::AssocItem,
1775 substs: SubstsRef<'tcx>,
1776 ) -> (Ty<'tcx>, Option<Ty<'tcx>>) {
1777 if item.kind == ty::AssocKind::Fn && self.mode == Mode::MethodCall {
1778 let sig = self.xform_method_sig(item.def_id, substs);
1779 (sig.inputs()[0], Some(sig.output()))
1785 #[instrument(level = "debug", skip(self))]
1786 fn xform_method_sig(&self, method: DefId, substs: SubstsRef<'tcx>) -> ty::FnSig<'tcx> {
1787 let fn_sig = self.tcx.bound_fn_sig(method);
1790 assert!(!substs.has_escaping_bound_vars());
1792 // It is possible for type parameters or early-bound lifetimes
1793 // to appear in the signature of `self`. The substitutions we
1794 // are given do not include type/lifetime parameters for the
1795 // method yet. So create fresh variables here for those too,
1796 // if there are any.
1797 let generics = self.tcx.generics_of(method);
1798 assert_eq!(substs.len(), generics.parent_count as usize);
1800 let xform_fn_sig = if generics.params.is_empty() {
1801 fn_sig.subst(self.tcx, substs)
1803 let substs = InternalSubsts::for_item(self.tcx, method, |param, _| {
1804 let i = param.index as usize;
1805 if i < substs.len() {
1809 GenericParamDefKind::Lifetime => {
1810 // In general, during probe we erase regions.
1811 self.tcx.lifetimes.re_erased.into()
1813 GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
1814 self.var_for_def(self.span, param)
1819 fn_sig.subst(self.tcx, substs)
1822 self.erase_late_bound_regions(xform_fn_sig)
1825 /// Gets the type of an impl and generate substitutions with inference vars.
1826 fn impl_ty_and_substs(
1829 ) -> (ty::EarlyBinder<Ty<'tcx>>, SubstsRef<'tcx>) {
1830 (self.tcx.bound_type_of(impl_def_id), self.fresh_item_substs(impl_def_id))
1833 fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx> {
1834 InternalSubsts::for_item(self.tcx, def_id, |param, _| match param.kind {
1835 GenericParamDefKind::Lifetime => self.tcx.lifetimes.re_erased.into(),
1836 GenericParamDefKind::Type { .. } => self
1837 .next_ty_var(TypeVariableOrigin {
1838 kind: TypeVariableOriginKind::SubstitutionPlaceholder,
1839 span: self.tcx.def_span(def_id),
1842 GenericParamDefKind::Const { .. } => {
1843 let span = self.tcx.def_span(def_id);
1844 let origin = ConstVariableOrigin {
1845 kind: ConstVariableOriginKind::SubstitutionPlaceholder,
1848 self.next_const_var(self.tcx.type_of(param.def_id), origin).into()
1853 /// Replaces late-bound-regions bound by `value` with `'static` using
1854 /// `ty::erase_late_bound_regions`.
1856 /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1857 /// method matching. It is reasonable during the probe phase because we don't consider region
1858 /// relationships at all. Therefore, we can just replace all the region variables with 'static
1859 /// rather than creating fresh region variables. This is nice for two reasons:
1861 /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1862 /// particular method call, it winds up creating fewer types overall, which helps for memory
1863 /// usage. (Admittedly, this is a rather small effect, though measurable.)
1865 /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1866 /// late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1867 /// regions with actual region variables as is proper, we'd have to ensure that the same
1868 /// region got replaced with the same variable, which requires a bit more coordination
1869 /// and/or tracking the substitution and
1871 fn erase_late_bound_regions<T>(&self, value: ty::Binder<'tcx, T>) -> T
1873 T: TypeFoldable<'tcx>,
1875 self.tcx.erase_late_bound_regions(value)
1878 /// Determine if the given associated item type is relevant in the current context.
1879 fn is_relevant_kind_for_mode(&self, kind: ty::AssocKind) -> bool {
1880 match (self.mode, kind) {
1881 (Mode::MethodCall, ty::AssocKind::Fn) => true,
1882 (Mode::Path, ty::AssocKind::Const | ty::AssocKind::Fn) => true,
1887 /// Finds the method with the appropriate name (or return type, as the case may be). If
1888 /// `allow_similar_names` is set, find methods with close-matching names.
1889 // The length of the returned iterator is nearly always 0 or 1 and this
1890 // method is fairly hot.
1891 fn impl_or_trait_item(&self, def_id: DefId) -> SmallVec<[ty::AssocItem; 1]> {
1892 if let Some(name) = self.method_name {
1893 if self.allow_similar_names {
1894 let max_dist = max(name.as_str().len(), 3) / 3;
1896 .associated_items(def_id)
1897 .in_definition_order()
1899 if !self.is_relevant_kind_for_mode(x.kind) {
1902 match lev_distance_with_substrings(name.as_str(), x.name.as_str(), max_dist)
1912 .associated_value(def_id, name)
1913 .filter(|x| self.is_relevant_kind_for_mode(x.kind))
1914 .map_or_else(SmallVec::new, |x| SmallVec::from_buf([x]))
1918 .associated_items(def_id)
1919 .in_definition_order()
1920 .filter(|x| self.is_relevant_kind_for_mode(x.kind))
1927 impl<'tcx> Candidate<'tcx> {
1928 fn to_unadjusted_pick(
1931 unstable_candidates: Vec<(Candidate<'tcx>, Symbol)>,
1935 kind: match self.kind {
1936 InherentImplCandidate(..) => InherentImplPick,
1937 ObjectCandidate => ObjectPick,
1938 TraitCandidate(_) => TraitPick,
1939 WhereClauseCandidate(ref trait_ref) => {
1940 // Only trait derived from where-clauses should
1941 // appear here, so they should not contain any
1942 // inference variables or other artifacts. This
1943 // means they are safe to put into the
1944 // `WhereClausePick`.
1946 !trait_ref.skip_binder().substs.needs_infer()
1947 && !trait_ref.skip_binder().substs.has_placeholders()
1950 WhereClausePick(*trait_ref)
1953 import_ids: self.import_ids.clone(),
1955 autoref_or_ptr_adjustment: None,
1957 unstable_candidates,