2 use super::CandidateSource;
3 use super::MethodError;
4 use super::NoMatchData;
6 use crate::check::FnCtxt;
7 use crate::errors::MethodCallOnUnknownType;
8 use crate::hir::def::DefKind;
9 use crate::hir::def_id::DefId;
11 use rustc_data_structures::fx::FxHashSet;
12 use rustc_errors::Applicability;
14 use rustc_hir::def::Namespace;
15 use rustc_infer::infer::canonical::OriginalQueryValues;
16 use rustc_infer::infer::canonical::{Canonical, QueryResponse};
17 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
18 use rustc_infer::infer::{self, InferOk, TyCtxtInferExt};
19 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
20 use rustc_middle::middle::stability;
21 use rustc_middle::ty::fast_reject::{simplify_type, TreatParams};
22 use rustc_middle::ty::subst::{InternalSubsts, Subst, SubstsRef};
23 use rustc_middle::ty::GenericParamDefKind;
24 use rustc_middle::ty::{self, ParamEnvAnd, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeVisitable};
25 use rustc_session::lint;
26 use rustc_span::def_id::LocalDefId;
27 use rustc_span::lev_distance::{
28 find_best_match_for_name_with_substrings, lev_distance_with_substrings,
30 use rustc_span::symbol::sym;
31 use rustc_span::{symbol::Ident, Span, Symbol, DUMMY_SP};
32 use rustc_trait_selection::autoderef::{self, Autoderef};
33 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
34 use rustc_trait_selection::traits::query::method_autoderef::MethodAutoderefBadTy;
35 use rustc_trait_selection::traits::query::method_autoderef::{
36 CandidateStep, MethodAutoderefStepsResult,
38 use rustc_trait_selection::traits::query::CanonicalTyGoal;
39 use rustc_trait_selection::traits::{self, ObligationCause};
45 use smallvec::{smallvec, SmallVec};
47 use self::CandidateKind::*;
48 pub use self::PickKind::*;
50 /// Boolean flag used to indicate if this search is for a suggestion
51 /// or not. If true, we can allow ambiguity and so forth.
52 #[derive(Clone, Copy, Debug)]
53 pub struct IsSuggestion(pub bool);
55 struct ProbeContext<'a, 'tcx> {
56 fcx: &'a FnCtxt<'a, 'tcx>,
59 method_name: Option<Ident>,
60 return_type: Option<Ty<'tcx>>,
62 /// This is the OriginalQueryValues for the steps queries
63 /// that are answered in steps.
64 orig_steps_var_values: OriginalQueryValues<'tcx>,
65 steps: &'tcx [CandidateStep<'tcx>],
67 inherent_candidates: Vec<Candidate<'tcx>>,
68 extension_candidates: Vec<Candidate<'tcx>>,
69 impl_dups: FxHashSet<DefId>,
71 /// Collects near misses when the candidate functions are missing a `self` keyword and is only
72 /// used for error reporting
73 static_candidates: Vec<CandidateSource>,
75 /// When probing for names, include names that are close to the
76 /// requested name (by Levensthein distance)
77 allow_similar_names: bool,
79 /// Some(candidate) if there is a private candidate
80 private_candidate: Option<(DefKind, DefId)>,
82 /// Collects near misses when trait bounds for type parameters are unsatisfied and is only used
83 /// for error reporting
84 unsatisfied_predicates:
85 Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>, Option<ObligationCause<'tcx>>)>,
87 is_suggestion: IsSuggestion,
89 scope_expr_id: hir::HirId,
92 impl<'a, 'tcx> Deref for ProbeContext<'a, 'tcx> {
93 type Target = FnCtxt<'a, 'tcx>;
94 fn deref(&self) -> &Self::Target {
99 #[derive(Debug, Clone)]
100 struct Candidate<'tcx> {
101 // Candidates are (I'm not quite sure, but they are mostly) basically
102 // some metadata on top of a `ty::AssocItem` (without substs).
104 // However, method probing wants to be able to evaluate the predicates
105 // for a function with the substs applied - for example, if a function
106 // has `where Self: Sized`, we don't want to consider it unless `Self`
107 // is actually `Sized`, and similarly, return-type suggestions want
108 // to consider the "actual" return type.
110 // The way this is handled is through `xform_self_ty`. It contains
111 // the receiver type of this candidate, but `xform_self_ty`,
112 // `xform_ret_ty` and `kind` (which contains the predicates) have the
113 // generic parameters of this candidate substituted with the *same set*
114 // of inference variables, which acts as some weird sort of "query".
116 // When we check out a candidate, we require `xform_self_ty` to be
117 // a subtype of the passed-in self-type, and this equates the type
118 // variables in the rest of the fields.
120 // For example, if we have this candidate:
123 // fn foo(&self) where Self: Sized;
127 // Then `xform_self_ty` will be `&'erased ?X` and `kind` will contain
128 // the predicate `?X: Sized`, so if we are evaluating `Foo` for a
129 // the receiver `&T`, we'll do the subtyping which will make `?X`
130 // get the right value, then when we evaluate the predicate we'll check
132 xform_self_ty: Ty<'tcx>,
133 xform_ret_ty: Option<Ty<'tcx>>,
135 kind: CandidateKind<'tcx>,
136 import_ids: SmallVec<[LocalDefId; 1]>,
139 #[derive(Debug, Clone)]
140 enum CandidateKind<'tcx> {
141 InherentImplCandidate(
143 // Normalize obligations
144 Vec<traits::PredicateObligation<'tcx>>,
147 TraitCandidate(ty::TraitRef<'tcx>),
148 WhereClauseCandidate(
150 ty::PolyTraitRef<'tcx>,
154 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
161 /// When adjusting a receiver we often want to do one of
163 /// - Add a `&` (or `&mut`), converting the receiver from `T` to `&T` (or `&mut T`)
164 /// - If the receiver has type `*mut T`, convert it to `*const T`
166 /// This type tells us which one to do.
168 /// Note that in principle we could do both at the same time. For example, when the receiver has
169 /// type `T`, we could autoref it to `&T`, then convert to `*const T`. Or, when it has type `*mut
170 /// T`, we could convert it to `*const T`, then autoref to `&*const T`. However, currently we do
171 /// (at most) one of these. Either the receiver has type `T` and we convert it to `&T` (or with
172 /// `mut`), or it has type `*mut T` and we convert it to `*const T`.
173 #[derive(Debug, PartialEq, Copy, Clone)]
174 pub enum AutorefOrPtrAdjustment {
175 /// Receiver has type `T`, add `&` or `&mut` (it `T` is `mut`), and maybe also "unsize" it.
176 /// Unsizing is used to convert a `[T; N]` to `[T]`, which only makes sense when autorefing.
178 mutbl: hir::Mutability,
180 /// Indicates that the source expression should be "unsized" to a target type.
181 /// This is special-cased for just arrays unsizing to slices.
184 /// Receiver has type `*mut T`, convert to `*const T`
188 impl AutorefOrPtrAdjustment {
189 fn get_unsize(&self) -> bool {
191 AutorefOrPtrAdjustment::Autoref { mutbl: _, unsize } => *unsize,
192 AutorefOrPtrAdjustment::ToConstPtr => false,
197 #[derive(Debug, PartialEq, Clone)]
198 pub struct Pick<'tcx> {
199 pub item: ty::AssocItem,
200 pub kind: PickKind<'tcx>,
201 pub import_ids: SmallVec<[LocalDefId; 1]>,
203 /// Indicates that the source expression should be autoderef'd N times
204 /// ```ignore (not-rust)
205 /// A = expr | *expr | **expr | ...
207 pub autoderefs: usize,
209 /// Indicates that we want to add an autoref (and maybe also unsize it), or if the receiver is
210 /// `*mut T`, convert it to `*const T`.
211 pub autoref_or_ptr_adjustment: Option<AutorefOrPtrAdjustment>,
212 pub self_ty: Ty<'tcx>,
215 #[derive(Clone, Debug, PartialEq, Eq)]
216 pub enum PickKind<'tcx> {
222 ty::PolyTraitRef<'tcx>,
226 pub type PickResult<'tcx> = Result<Pick<'tcx>, MethodError<'tcx>>;
228 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
230 // An expression of the form `receiver.method_name(...)`.
231 // Autoderefs are performed on `receiver`, lookup is done based on the
232 // `self` argument of the method, and static methods aren't considered.
234 // An expression of the form `Type::item` or `<T>::item`.
235 // No autoderefs are performed, lookup is done based on the type each
236 // implementation is for, and static methods are included.
240 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
241 pub enum ProbeScope {
242 // Assemble candidates coming only from traits in scope.
245 // Assemble candidates coming from all traits.
249 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
250 /// This is used to offer suggestions to users. It returns methods
251 /// that could have been called which have the desired return
252 /// type. Some effort is made to rule out methods that, if called,
253 /// would result in an error (basically, the same criteria we
254 /// would use to decide if a method is a plausible fit for
255 /// ambiguity purposes).
256 #[instrument(level = "debug", skip(self, scope_expr_id))]
257 pub fn probe_for_return_type(
261 return_type: Ty<'tcx>,
263 scope_expr_id: hir::HirId,
264 ) -> Vec<ty::AssocItem> {
266 "probe(self_ty={:?}, return_type={}, scope_expr_id={})",
267 self_ty, return_type, scope_expr_id
269 let method_names = self
278 ProbeScope::AllTraits,
279 |probe_cx| Ok(probe_cx.candidate_method_names()),
281 .unwrap_or_default();
284 .flat_map(|&method_name| {
293 ProbeScope::AllTraits,
294 |probe_cx| probe_cx.pick(),
297 .map(|pick| pick.item)
302 #[instrument(level = "debug", skip(self, scope_expr_id))]
303 pub fn probe_for_name(
308 is_suggestion: IsSuggestion,
310 scope_expr_id: hir::HirId,
312 ) -> PickResult<'tcx> {
314 "probe(self_ty={:?}, item_name={}, scope_expr_id={})",
315 self_ty, item_name, scope_expr_id
326 |probe_cx| probe_cx.pick(),
334 method_name: Option<Ident>,
335 return_type: Option<Ty<'tcx>>,
336 is_suggestion: IsSuggestion,
338 scope_expr_id: hir::HirId,
341 ) -> Result<R, MethodError<'tcx>>
343 OP: FnOnce(ProbeContext<'a, 'tcx>) -> Result<R, MethodError<'tcx>>,
345 let mut orig_values = OriginalQueryValues::default();
346 let param_env_and_self_ty = self.canonicalize_query(
347 ParamEnvAnd { param_env: self.param_env, value: self_ty },
351 let steps = if mode == Mode::MethodCall {
352 self.tcx.method_autoderef_steps(param_env_and_self_ty)
355 // Mode::Path - the deref steps is "trivial". This turns
356 // our CanonicalQuery into a "trivial" QueryResponse. This
357 // is a bit inefficient, but I don't think that writing
358 // special handling for this "trivial case" is a good idea.
360 let infcx = &self.infcx;
361 let (ParamEnvAnd { param_env: _, value: self_ty }, canonical_inference_vars) =
362 infcx.instantiate_canonical_with_fresh_inference_vars(
364 ¶m_env_and_self_ty,
367 "probe_op: Mode::Path, param_env_and_self_ty={:?} self_ty={:?}",
368 param_env_and_self_ty, self_ty
370 MethodAutoderefStepsResult {
371 steps: infcx.tcx.arena.alloc_from_iter([CandidateStep {
372 self_ty: self.make_query_response_ignoring_pending_obligations(
373 canonical_inference_vars,
377 from_unsafe_deref: false,
381 reached_recursion_limit: false,
386 // If our autoderef loop had reached the recursion limit,
387 // report an overflow error, but continue going on with
388 // the truncated autoderef list.
389 if steps.reached_recursion_limit {
394 .unwrap_or_else(|| span_bug!(span, "reached the recursion limit in 0 steps?"))
397 .probe_instantiate_query_response(span, &orig_values, ty)
398 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
399 autoderef::report_autoderef_recursion_limit_error(self.tcx, span, ty.value);
403 // If we encountered an `_` type or an error type during autoderef, this is
405 if let Some(bad_ty) = &steps.opt_bad_ty {
407 // Ambiguity was encountered during a suggestion. Just keep going.
408 debug!("ProbeContext: encountered ambiguity in suggestion");
409 } else if bad_ty.reached_raw_pointer && !self.tcx.features().arbitrary_self_types {
410 // this case used to be allowed by the compiler,
411 // so we do a future-compat lint here for the 2015 edition
412 // (see https://github.com/rust-lang/rust/issues/46906)
413 if self.tcx.sess.rust_2018() {
414 self.tcx.sess.emit_err(MethodCallOnUnknownType { span });
416 self.tcx.struct_span_lint_hir(
417 lint::builtin::TYVAR_BEHIND_RAW_POINTER,
421 lint.build("type annotations needed").emit();
426 // Encountered a real ambiguity, so abort the lookup. If `ty` is not
427 // an `Err`, report the right "type annotations needed" error pointing
431 .probe_instantiate_query_response(span, &orig_values, ty)
432 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
433 let ty = self.structurally_resolved_type(span, ty.value);
434 assert!(matches!(ty.kind(), ty::Error(_)));
435 return Err(MethodError::NoMatch(NoMatchData {
436 static_candidates: Vec::new(),
437 unsatisfied_predicates: Vec::new(),
438 out_of_scope_traits: Vec::new(),
445 debug!("ProbeContext: steps for self_ty={:?} are {:?}", self_ty, steps);
447 // this creates one big transaction so that all type variables etc
448 // that we create during the probe process are removed later
450 let mut probe_cx = ProbeContext::new(
462 probe_cx.assemble_inherent_candidates();
464 ProbeScope::TraitsInScope => {
465 probe_cx.assemble_extension_candidates_for_traits_in_scope(scope_expr_id)
467 ProbeScope::AllTraits => probe_cx.assemble_extension_candidates_for_all_traits(),
474 pub fn provide(providers: &mut ty::query::Providers) {
475 providers.method_autoderef_steps = method_autoderef_steps;
478 fn method_autoderef_steps<'tcx>(
480 goal: CanonicalTyGoal<'tcx>,
481 ) -> MethodAutoderefStepsResult<'tcx> {
482 debug!("method_autoderef_steps({:?})", goal);
484 tcx.infer_ctxt().enter_with_canonical(DUMMY_SP, &goal, |ref infcx, goal, inference_vars| {
485 let ParamEnvAnd { param_env, value: self_ty } = goal;
488 Autoderef::new(infcx, param_env, hir::CRATE_HIR_ID, DUMMY_SP, self_ty, DUMMY_SP)
489 .include_raw_pointers()
491 let mut reached_raw_pointer = false;
492 let mut steps: Vec<_> = autoderef
495 let step = CandidateStep {
496 self_ty: infcx.make_query_response_ignoring_pending_obligations(
497 inference_vars.clone(),
501 from_unsafe_deref: reached_raw_pointer,
504 if let ty::RawPtr(_) = ty.kind() {
505 // all the subsequent steps will be from_unsafe_deref
506 reached_raw_pointer = true;
512 let final_ty = autoderef.final_ty(true);
513 let opt_bad_ty = match final_ty.kind() {
514 ty::Infer(ty::TyVar(_)) | ty::Error(_) => Some(MethodAutoderefBadTy {
517 .make_query_response_ignoring_pending_obligations(inference_vars, final_ty),
519 ty::Array(elem_ty, _) => {
520 let dereferences = steps.len() - 1;
522 steps.push(CandidateStep {
523 self_ty: infcx.make_query_response_ignoring_pending_obligations(
525 infcx.tcx.mk_slice(*elem_ty),
527 autoderefs: dereferences,
528 // this could be from an unsafe deref if we had
529 // a *mut/const [T; N]
530 from_unsafe_deref: reached_raw_pointer,
539 debug!("method_autoderef_steps: steps={:?} opt_bad_ty={:?}", steps, opt_bad_ty);
541 MethodAutoderefStepsResult {
542 steps: tcx.arena.alloc_from_iter(steps),
543 opt_bad_ty: opt_bad_ty.map(|ty| &*tcx.arena.alloc(ty)),
544 reached_recursion_limit: autoderef.reached_recursion_limit(),
549 impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
551 fcx: &'a FnCtxt<'a, 'tcx>,
554 method_name: Option<Ident>,
555 return_type: Option<Ty<'tcx>>,
556 orig_steps_var_values: OriginalQueryValues<'tcx>,
557 steps: &'tcx [CandidateStep<'tcx>],
558 is_suggestion: IsSuggestion,
559 scope_expr_id: hir::HirId,
560 ) -> ProbeContext<'a, 'tcx> {
567 inherent_candidates: Vec::new(),
568 extension_candidates: Vec::new(),
569 impl_dups: FxHashSet::default(),
570 orig_steps_var_values,
572 static_candidates: Vec::new(),
573 allow_similar_names: false,
574 private_candidate: None,
575 unsatisfied_predicates: Vec::new(),
581 fn reset(&mut self) {
582 self.inherent_candidates.clear();
583 self.extension_candidates.clear();
584 self.impl_dups.clear();
585 self.static_candidates.clear();
586 self.private_candidate = None;
589 ///////////////////////////////////////////////////////////////////////////
590 // CANDIDATE ASSEMBLY
592 fn push_candidate(&mut self, candidate: Candidate<'tcx>, is_inherent: bool) {
593 let is_accessible = if let Some(name) = self.method_name {
594 let item = candidate.item;
596 self.tcx.adjust_ident_and_get_scope(name, item.container.id(), self.body_id).1;
597 item.vis.is_accessible_from(def_scope, self.tcx)
603 self.inherent_candidates.push(candidate);
605 self.extension_candidates.push(candidate);
607 } else if self.private_candidate.is_none() {
608 self.private_candidate =
609 Some((candidate.item.kind.as_def_kind(), candidate.item.def_id));
613 fn assemble_inherent_candidates(&mut self) {
614 for step in self.steps.iter() {
615 self.assemble_probe(&step.self_ty);
619 fn assemble_probe(&mut self, self_ty: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>) {
620 debug!("assemble_probe: self_ty={:?}", self_ty);
621 let raw_self_ty = self_ty.value.value;
622 match *raw_self_ty.kind() {
623 ty::Dynamic(data, ..) if let Some(p) = data.principal() => {
624 // Subtle: we can't use `instantiate_query_response` here: using it will
625 // commit to all of the type equalities assumed by inference going through
626 // autoderef (see the `method-probe-no-guessing` test).
628 // However, in this code, it is OK if we end up with an object type that is
629 // "more general" than the object type that we are evaluating. For *every*
630 // object type `MY_OBJECT`, a function call that goes through a trait-ref
631 // of the form `<MY_OBJECT as SuperTraitOf(MY_OBJECT)>::func` is a valid
632 // `ObjectCandidate`, and it should be discoverable "exactly" through one
633 // of the iterations in the autoderef loop, so there is no problem with it
634 // being discoverable in another one of these iterations.
636 // Using `instantiate_canonical_with_fresh_inference_vars` on our
637 // `Canonical<QueryResponse<Ty<'tcx>>>` and then *throwing away* the
638 // `CanonicalVarValues` will exactly give us such a generalization - it
639 // will still match the original object type, but it won't pollute our
640 // type variables in any form, so just do that!
641 let (QueryResponse { value: generalized_self_ty, .. }, _ignored_var_values) =
643 .instantiate_canonical_with_fresh_inference_vars(self.span, self_ty);
645 self.assemble_inherent_candidates_from_object(generalized_self_ty);
646 self.assemble_inherent_impl_candidates_for_type(p.def_id());
647 if self.tcx.has_attr(p.def_id(), sym::rustc_has_incoherent_inherent_impls) {
648 self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
652 let def_id = def.did();
653 self.assemble_inherent_impl_candidates_for_type(def_id);
654 if self.tcx.has_attr(def_id, sym::rustc_has_incoherent_inherent_impls) {
655 self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
658 ty::Foreign(did) => {
659 self.assemble_inherent_impl_candidates_for_type(did);
660 if self.tcx.has_attr(did, sym::rustc_has_incoherent_inherent_impls) {
661 self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
665 self.assemble_inherent_candidates_from_param(p);
678 | ty::Tuple(..) => self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty),
683 fn assemble_inherent_candidates_for_incoherent_ty(&mut self, self_ty: Ty<'tcx>) {
684 let Some(simp) = simplify_type(self.tcx, self_ty, TreatParams::AsInfer) else {
685 bug!("unexpected incoherent type: {:?}", self_ty)
687 for &impl_def_id in self.tcx.incoherent_impls(simp) {
688 self.assemble_inherent_impl_probe(impl_def_id);
692 fn assemble_inherent_impl_candidates_for_type(&mut self, def_id: DefId) {
693 let impl_def_ids = self.tcx.at(self.span).inherent_impls(def_id);
694 for &impl_def_id in impl_def_ids.iter() {
695 self.assemble_inherent_impl_probe(impl_def_id);
699 fn assemble_inherent_impl_probe(&mut self, impl_def_id: DefId) {
700 if !self.impl_dups.insert(impl_def_id) {
701 return; // already visited
704 debug!("assemble_inherent_impl_probe {:?}", impl_def_id);
706 for item in self.impl_or_trait_item(impl_def_id) {
707 if !self.has_applicable_self(&item) {
708 // No receiver declared. Not a candidate.
709 self.record_static_candidate(CandidateSource::Impl(impl_def_id));
713 let (impl_ty, impl_substs) = self.impl_ty_and_substs(impl_def_id);
714 let impl_ty = impl_ty.subst(self.tcx, impl_substs);
716 debug!("impl_ty: {:?}", impl_ty);
718 // Determine the receiver type that the method itself expects.
719 let (xform_self_ty, xform_ret_ty) = self.xform_self_ty(&item, impl_ty, impl_substs);
720 debug!("xform_self_ty: {:?}, xform_ret_ty: {:?}", xform_self_ty, xform_ret_ty);
722 // We can't use normalize_associated_types_in as it will pollute the
723 // fcx's fulfillment context after this probe is over.
724 // Note: we only normalize `xform_self_ty` here since the normalization
725 // of the return type can lead to inference results that prohibit
726 // valid candidates from being found, see issue #85671
727 // FIXME Postponing the normalization of the return type likely only hides a deeper bug,
728 // which might be caused by the `param_env` itself. The clauses of the `param_env`
729 // maybe shouldn't include `Param`s, but rather fresh variables or be canonicalized,
731 let cause = traits::ObligationCause::misc(self.span, self.body_id);
732 let selcx = &mut traits::SelectionContext::new(self.fcx);
733 let traits::Normalized { value: xform_self_ty, obligations } =
734 traits::normalize(selcx, self.param_env, cause, xform_self_ty);
736 "assemble_inherent_impl_probe after normalization: xform_self_ty = {:?}/{:?}",
737 xform_self_ty, xform_ret_ty
745 kind: InherentImplCandidate(impl_substs, obligations),
746 import_ids: smallvec![],
753 fn assemble_inherent_candidates_from_object(&mut self, self_ty: Ty<'tcx>) {
754 debug!("assemble_inherent_candidates_from_object(self_ty={:?})", self_ty);
756 let principal = match self_ty.kind() {
757 ty::Dynamic(ref data, ..) => Some(data),
760 .and_then(|data| data.principal())
764 "non-object {:?} in assemble_inherent_candidates_from_object",
769 // It is illegal to invoke a method on a trait instance that refers to
770 // the `Self` type. An [`ObjectSafetyViolation::SupertraitSelf`] error
771 // will be reported by `object_safety.rs` if the method refers to the
772 // `Self` type anywhere other than the receiver. Here, we use a
773 // substitution that replaces `Self` with the object type itself. Hence,
774 // a `&self` method will wind up with an argument type like `&dyn Trait`.
775 let trait_ref = principal.with_self_ty(self.tcx, self_ty);
776 self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
777 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
779 let (xform_self_ty, xform_ret_ty) =
780 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
786 kind: ObjectCandidate,
787 import_ids: smallvec![],
794 fn assemble_inherent_candidates_from_param(&mut self, param_ty: ty::ParamTy) {
795 // FIXME: do we want to commit to this behavior for param bounds?
796 debug!("assemble_inherent_candidates_from_param(param_ty={:?})", param_ty);
798 let bounds = self.param_env.caller_bounds().iter().filter_map(|predicate| {
799 let bound_predicate = predicate.kind();
800 match bound_predicate.skip_binder() {
801 ty::PredicateKind::Trait(trait_predicate) => {
802 match *trait_predicate.trait_ref.self_ty().kind() {
803 ty::Param(p) if p == param_ty => {
804 Some(bound_predicate.rebind(trait_predicate.trait_ref))
809 ty::PredicateKind::Subtype(..)
810 | ty::PredicateKind::Coerce(..)
811 | ty::PredicateKind::Projection(..)
812 | ty::PredicateKind::RegionOutlives(..)
813 | ty::PredicateKind::WellFormed(..)
814 | ty::PredicateKind::ObjectSafe(..)
815 | ty::PredicateKind::ClosureKind(..)
816 | ty::PredicateKind::TypeOutlives(..)
817 | ty::PredicateKind::ConstEvaluatable(..)
818 | ty::PredicateKind::ConstEquate(..)
819 | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
823 self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
824 let trait_ref = this.erase_late_bound_regions(poly_trait_ref);
826 let (xform_self_ty, xform_ret_ty) =
827 this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs);
829 // Because this trait derives from a where-clause, it
830 // should not contain any inference variables or other
831 // artifacts. This means it is safe to put into the
832 // `WhereClauseCandidate` and (eventually) into the
833 // `WhereClausePick`.
834 assert!(!trait_ref.substs.needs_infer());
841 kind: WhereClauseCandidate(poly_trait_ref),
842 import_ids: smallvec![],
849 // Do a search through a list of bounds, using a callback to actually
850 // create the candidates.
851 fn elaborate_bounds<F>(
853 bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
856 F: for<'b> FnMut(&mut ProbeContext<'b, 'tcx>, ty::PolyTraitRef<'tcx>, ty::AssocItem),
859 for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
860 debug!("elaborate_bounds(bound_trait_ref={:?})", bound_trait_ref);
861 for item in self.impl_or_trait_item(bound_trait_ref.def_id()) {
862 if !self.has_applicable_self(&item) {
863 self.record_static_candidate(CandidateSource::Trait(bound_trait_ref.def_id()));
865 mk_cand(self, bound_trait_ref, item);
871 fn assemble_extension_candidates_for_traits_in_scope(&mut self, expr_hir_id: hir::HirId) {
872 let mut duplicates = FxHashSet::default();
873 let opt_applicable_traits = self.tcx.in_scope_traits(expr_hir_id);
874 if let Some(applicable_traits) = opt_applicable_traits {
875 for trait_candidate in applicable_traits.iter() {
876 let trait_did = trait_candidate.def_id;
877 if duplicates.insert(trait_did) {
878 self.assemble_extension_candidates_for_trait(
879 &trait_candidate.import_ids,
887 fn assemble_extension_candidates_for_all_traits(&mut self) {
888 let mut duplicates = FxHashSet::default();
889 for trait_info in suggest::all_traits(self.tcx) {
890 if duplicates.insert(trait_info.def_id) {
891 self.assemble_extension_candidates_for_trait(&smallvec![], trait_info.def_id);
896 pub fn matches_return_type(
898 method: &ty::AssocItem,
899 self_ty: Option<Ty<'tcx>>,
903 ty::AssocKind::Fn => {
904 let fty = self.tcx.bound_fn_sig(method.def_id);
906 let substs = self.fresh_substs_for_item(self.span, method.def_id);
907 let fty = fty.subst(self.tcx, substs);
909 self.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, fty);
911 if let Some(self_ty) = self_ty {
913 .at(&ObligationCause::dummy(), self.param_env)
914 .sup(fty.inputs()[0], self_ty)
920 self.can_sub(self.param_env, fty.output(), expected).is_ok()
927 fn assemble_extension_candidates_for_trait(
929 import_ids: &SmallVec<[LocalDefId; 1]>,
932 debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})", trait_def_id);
933 let trait_substs = self.fresh_item_substs(trait_def_id);
934 let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
936 if self.tcx.is_trait_alias(trait_def_id) {
937 // For trait aliases, assume all supertraits are relevant.
938 let bounds = iter::once(ty::Binder::dummy(trait_ref));
939 self.elaborate_bounds(bounds, |this, new_trait_ref, item| {
940 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
942 let (xform_self_ty, xform_ret_ty) =
943 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
949 import_ids: import_ids.clone(),
950 kind: TraitCandidate(new_trait_ref),
956 debug_assert!(self.tcx.is_trait(trait_def_id));
957 for item in self.impl_or_trait_item(trait_def_id) {
958 // Check whether `trait_def_id` defines a method with suitable name.
959 if !self.has_applicable_self(&item) {
960 debug!("method has inapplicable self");
961 self.record_static_candidate(CandidateSource::Trait(trait_def_id));
965 let (xform_self_ty, xform_ret_ty) =
966 self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
972 import_ids: import_ids.clone(),
973 kind: TraitCandidate(trait_ref),
981 fn candidate_method_names(&self) -> Vec<Ident> {
982 let mut set = FxHashSet::default();
983 let mut names: Vec<_> = self
986 .chain(&self.extension_candidates)
987 .filter(|candidate| {
988 if let Some(return_ty) = self.return_type {
989 self.matches_return_type(&candidate.item, None, return_ty)
994 .map(|candidate| candidate.item.ident(self.tcx))
995 .filter(|&name| set.insert(name))
998 // Sort them by the name so we have a stable result.
999 names.sort_by(|a, b| a.as_str().partial_cmp(b.as_str()).unwrap());
1003 ///////////////////////////////////////////////////////////////////////////
1004 // THE ACTUAL SEARCH
1006 fn pick(mut self) -> PickResult<'tcx> {
1007 assert!(self.method_name.is_some());
1009 if let Some(r) = self.pick_core() {
1013 debug!("pick: actual search failed, assemble diagnostics");
1015 let static_candidates = mem::take(&mut self.static_candidates);
1016 let private_candidate = self.private_candidate.take();
1017 let unsatisfied_predicates = mem::take(&mut self.unsatisfied_predicates);
1019 // things failed, so lets look at all traits, for diagnostic purposes now:
1022 let span = self.span;
1025 self.assemble_extension_candidates_for_all_traits();
1027 let out_of_scope_traits = match self.pick_core() {
1028 Some(Ok(p)) => vec![p.item.container.id()],
1029 //Some(Ok(p)) => p.iter().map(|p| p.item.container().id()).collect(),
1030 Some(Err(MethodError::Ambiguity(v))) => v
1032 .map(|source| match source {
1033 CandidateSource::Trait(id) => id,
1034 CandidateSource::Impl(impl_id) => match tcx.trait_id_of_impl(impl_id) {
1036 None => span_bug!(span, "found inherent method when looking at traits"),
1040 Some(Err(MethodError::NoMatch(NoMatchData {
1041 out_of_scope_traits: others, ..
1043 assert!(others.is_empty());
1049 if let Some((kind, def_id)) = private_candidate {
1050 return Err(MethodError::PrivateMatch(kind, def_id, out_of_scope_traits));
1052 let lev_candidate = self.probe_for_lev_candidate()?;
1054 Err(MethodError::NoMatch(NoMatchData {
1056 unsatisfied_predicates,
1057 out_of_scope_traits,
1063 fn pick_core(&mut self) -> Option<PickResult<'tcx>> {
1064 let mut unstable_candidates = Vec::new();
1065 let pick = self.pick_all_method(Some(&mut unstable_candidates));
1067 // In this case unstable picking is done by `pick_method`.
1068 if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable {
1073 // Emit a lint if there are unstable candidates alongside the stable ones.
1075 // We suppress warning if we're picking the method only because it is a
1077 Some(Ok(ref p)) if !self.is_suggestion.0 && !unstable_candidates.is_empty() => {
1078 self.emit_unstable_name_collision_hint(p, &unstable_candidates);
1082 None => self.pick_all_method(None),
1088 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1089 ) -> Option<PickResult<'tcx>> {
1090 let steps = self.steps.clone();
1094 debug!("pick_all_method: step={:?}", step);
1095 // skip types that are from a type error or that would require dereferencing
1097 !step.self_ty.references_error() && !step.from_unsafe_deref
1100 let InferOk { value: self_ty, obligations: _ } = self
1102 .probe_instantiate_query_response(
1104 &self.orig_steps_var_values,
1107 .unwrap_or_else(|_| {
1108 span_bug!(self.span, "{:?} was applicable but now isn't?", step.self_ty)
1110 self.pick_by_value_method(step, self_ty, unstable_candidates.as_deref_mut())
1112 self.pick_autorefd_method(
1115 hir::Mutability::Not,
1116 unstable_candidates.as_deref_mut(),
1119 self.pick_autorefd_method(
1122 hir::Mutability::Mut,
1123 unstable_candidates.as_deref_mut(),
1127 self.pick_const_ptr_method(
1130 unstable_candidates.as_deref_mut(),
1138 /// For each type `T` in the step list, this attempts to find a method where
1139 /// the (transformed) self type is exactly `T`. We do however do one
1140 /// transformation on the adjustment: if we are passing a region pointer in,
1141 /// we will potentially *reborrow* it to a shorter lifetime. This allows us
1142 /// to transparently pass `&mut` pointers, in particular, without consuming
1143 /// them for their entire lifetime.
1144 fn pick_by_value_method(
1146 step: &CandidateStep<'tcx>,
1148 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1149 ) -> Option<PickResult<'tcx>> {
1154 self.pick_method(self_ty, unstable_candidates).map(|r| {
1156 pick.autoderefs = step.autoderefs;
1158 // Insert a `&*` or `&mut *` if this is a reference type:
1159 if let ty::Ref(_, _, mutbl) = *step.self_ty.value.value.kind() {
1160 pick.autoderefs += 1;
1161 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::Autoref {
1163 unsize: pick.autoref_or_ptr_adjustment.map_or(false, |a| a.get_unsize()),
1172 fn pick_autorefd_method(
1174 step: &CandidateStep<'tcx>,
1176 mutbl: hir::Mutability,
1177 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1178 ) -> Option<PickResult<'tcx>> {
1181 // In general, during probing we erase regions.
1182 let region = tcx.lifetimes.re_erased;
1184 let autoref_ty = tcx.mk_ref(region, ty::TypeAndMut { ty: self_ty, mutbl });
1185 self.pick_method(autoref_ty, unstable_candidates).map(|r| {
1187 pick.autoderefs = step.autoderefs;
1188 pick.autoref_or_ptr_adjustment =
1189 Some(AutorefOrPtrAdjustment::Autoref { mutbl, unsize: step.unsize });
1195 /// If `self_ty` is `*mut T` then this picks `*const T` methods. The reason why we have a
1196 /// special case for this is because going from `*mut T` to `*const T` with autoderefs and
1197 /// autorefs would require dereferencing the pointer, which is not safe.
1198 fn pick_const_ptr_method(
1200 step: &CandidateStep<'tcx>,
1202 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1203 ) -> Option<PickResult<'tcx>> {
1204 // Don't convert an unsized reference to ptr
1209 let &ty::RawPtr(ty::TypeAndMut { ty, mutbl: hir::Mutability::Mut }) = self_ty.kind() else {
1213 let const_self_ty = ty::TypeAndMut { ty, mutbl: hir::Mutability::Not };
1214 let const_ptr_ty = self.tcx.mk_ptr(const_self_ty);
1215 self.pick_method(const_ptr_ty, unstable_candidates).map(|r| {
1217 pick.autoderefs = step.autoderefs;
1218 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::ToConstPtr);
1224 fn pick_method_with_unstable(&mut self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
1225 debug!("pick_method_with_unstable(self_ty={})", self.ty_to_string(self_ty));
1227 let mut possibly_unsatisfied_predicates = Vec::new();
1228 let mut unstable_candidates = Vec::new();
1230 for (kind, candidates) in
1231 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1233 debug!("searching {} candidates", kind);
1234 let res = self.consider_candidates(
1237 &mut possibly_unsatisfied_predicates,
1238 Some(&mut unstable_candidates),
1240 if let Some(pick) = res {
1241 if !self.is_suggestion.0 && !unstable_candidates.is_empty() {
1242 if let Ok(p) = &pick {
1243 // Emit a lint if there are unstable candidates alongside the stable ones.
1245 // We suppress warning if we're picking the method only because it is a
1247 self.emit_unstable_name_collision_hint(p, &unstable_candidates);
1254 debug!("searching unstable candidates");
1255 let res = self.consider_candidates(
1257 unstable_candidates.iter().map(|(c, _)| c),
1258 &mut possibly_unsatisfied_predicates,
1262 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1270 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1271 ) -> Option<PickResult<'tcx>> {
1272 if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable {
1273 return self.pick_method_with_unstable(self_ty);
1276 debug!("pick_method(self_ty={})", self.ty_to_string(self_ty));
1278 let mut possibly_unsatisfied_predicates = Vec::new();
1280 for (kind, candidates) in
1281 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1283 debug!("searching {} candidates", kind);
1284 let res = self.consider_candidates(
1287 &mut possibly_unsatisfied_predicates,
1288 unstable_candidates.as_deref_mut(),
1290 if let Some(pick) = res {
1295 // `pick_method` may be called twice for the same self_ty if no stable methods
1296 // match. Only extend once.
1297 if unstable_candidates.is_some() {
1298 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1303 fn consider_candidates<'b, ProbesIter>(
1307 possibly_unsatisfied_predicates: &mut Vec<(
1308 ty::Predicate<'tcx>,
1309 Option<ty::Predicate<'tcx>>,
1310 Option<ObligationCause<'tcx>>,
1312 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1313 ) -> Option<PickResult<'tcx>>
1315 ProbesIter: Iterator<Item = &'b Candidate<'tcx>> + Clone,
1318 let mut applicable_candidates: Vec<_> = probes
1321 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
1323 .filter(|&(_, status)| status != ProbeResult::NoMatch)
1326 debug!("applicable_candidates: {:?}", applicable_candidates);
1328 if applicable_candidates.len() > 1 {
1330 self.collapse_candidates_to_trait_pick(self_ty, &applicable_candidates)
1332 return Some(Ok(pick));
1336 if let Some(uc) = unstable_candidates {
1337 applicable_candidates.retain(|&(p, _)| {
1338 if let stability::EvalResult::Deny { feature, .. } =
1339 self.tcx.eval_stability(p.item.def_id, None, self.span, None)
1341 uc.push((p.clone(), feature));
1348 if applicable_candidates.len() > 1 {
1349 let sources = probes.map(|p| self.candidate_source(p, self_ty)).collect();
1350 return Some(Err(MethodError::Ambiguity(sources)));
1353 applicable_candidates.pop().map(|(probe, status)| {
1354 if status == ProbeResult::Match {
1355 Ok(probe.to_unadjusted_pick(self_ty))
1357 Err(MethodError::BadReturnType)
1362 fn emit_unstable_name_collision_hint(
1364 stable_pick: &Pick<'_>,
1365 unstable_candidates: &[(Candidate<'tcx>, Symbol)],
1367 self.tcx.struct_span_lint_hir(
1368 lint::builtin::UNSTABLE_NAME_COLLISIONS,
1372 let def_kind = stable_pick.item.kind.as_def_kind();
1373 let mut diag = lint.build(&format!(
1374 "{} {} with this name may be added to the standard library in the future",
1376 def_kind.descr(stable_pick.item.def_id),
1378 match (stable_pick.item.kind, stable_pick.item.container) {
1379 (ty::AssocKind::Fn, _) => {
1380 // FIXME: This should be a `span_suggestion` instead of `help`
1381 // However `self.span` only
1382 // highlights the method name, so we can't use it. Also consider reusing
1383 // the code from `report_method_error()`.
1385 "call with fully qualified syntax `{}(...)` to keep using the current \
1387 self.tcx.def_path_str(stable_pick.item.def_id),
1390 (ty::AssocKind::Const, ty::AssocItemContainer::TraitContainer(def_id)) => {
1391 diag.span_suggestion(
1393 "use the fully qualified path to the associated const",
1396 stable_pick.self_ty,
1397 self.tcx.def_path_str(def_id),
1398 stable_pick.item.name
1400 Applicability::MachineApplicable,
1405 if self.tcx.sess.is_nightly_build() {
1406 for (candidate, feature) in unstable_candidates {
1408 "add `#![feature({})]` to the crate attributes to enable `{}`",
1410 self.tcx.def_path_str(candidate.item.def_id),
1420 fn select_trait_candidate(
1422 trait_ref: ty::TraitRef<'tcx>,
1423 ) -> traits::SelectionResult<'tcx, traits::Selection<'tcx>> {
1424 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1425 let predicate = ty::Binder::dummy(trait_ref).to_poly_trait_predicate();
1426 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1427 traits::SelectionContext::new(self).select(&obligation)
1430 fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>) -> CandidateSource {
1431 match candidate.kind {
1432 InherentImplCandidate(..) => CandidateSource::Impl(candidate.item.container.id()),
1433 ObjectCandidate | WhereClauseCandidate(_) => {
1434 CandidateSource::Trait(candidate.item.container.id())
1436 TraitCandidate(trait_ref) => self.probe(|_| {
1438 .at(&ObligationCause::dummy(), self.param_env)
1439 .define_opaque_types(false)
1440 .sup(candidate.xform_self_ty, self_ty);
1441 match self.select_trait_candidate(trait_ref) {
1442 Ok(Some(traits::ImplSource::UserDefined(ref impl_data))) => {
1443 // If only a single impl matches, make the error message point
1445 CandidateSource::Impl(impl_data.impl_def_id)
1447 _ => CandidateSource::Trait(candidate.item.container.id()),
1456 probe: &Candidate<'tcx>,
1457 possibly_unsatisfied_predicates: &mut Vec<(
1458 ty::Predicate<'tcx>,
1459 Option<ty::Predicate<'tcx>>,
1460 Option<ObligationCause<'tcx>>,
1463 debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe);
1466 // First check that the self type can be related.
1467 let sub_obligations = match self
1468 .at(&ObligationCause::dummy(), self.param_env)
1469 .define_opaque_types(false)
1470 .sup(probe.xform_self_ty, self_ty)
1472 Ok(InferOk { obligations, value: () }) => obligations,
1474 debug!("--> cannot relate self-types {:?}", err);
1475 return ProbeResult::NoMatch;
1479 let mut result = ProbeResult::Match;
1480 let mut xform_ret_ty = probe.xform_ret_ty;
1481 debug!(?xform_ret_ty);
1483 let selcx = &mut traits::SelectionContext::new(self);
1484 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1486 let mut parent_pred = None;
1488 // If so, impls may carry other conditions (e.g., where
1489 // clauses) that must be considered. Make sure that those
1490 // match as well (or at least may match, sometimes we
1491 // don't have enough information to fully evaluate).
1493 InherentImplCandidate(ref substs, ref ref_obligations) => {
1494 // `xform_ret_ty` hasn't been normalized yet, only `xform_self_ty`,
1495 // see the reasons mentioned in the comments in `assemble_inherent_impl_probe`
1496 // for why this is necessary
1497 let traits::Normalized {
1498 value: normalized_xform_ret_ty,
1499 obligations: normalization_obligations,
1500 } = traits::normalize(selcx, self.param_env, cause.clone(), probe.xform_ret_ty);
1501 xform_ret_ty = normalized_xform_ret_ty;
1502 debug!("xform_ret_ty after normalization: {:?}", xform_ret_ty);
1504 // Check whether the impl imposes obligations we have to worry about.
1505 let impl_def_id = probe.item.container.id();
1506 let impl_bounds = self.tcx.predicates_of(impl_def_id);
1507 let impl_bounds = impl_bounds.instantiate(self.tcx, substs);
1508 let traits::Normalized { value: impl_bounds, obligations: norm_obligations } =
1509 traits::normalize(selcx, self.param_env, cause.clone(), impl_bounds);
1511 // Convert the bounds into obligations.
1512 let impl_obligations =
1513 traits::predicates_for_generics(cause, self.param_env, impl_bounds);
1515 let candidate_obligations = impl_obligations
1516 .chain(norm_obligations.into_iter())
1517 .chain(ref_obligations.iter().cloned())
1518 .chain(normalization_obligations.into_iter());
1520 // Evaluate those obligations to see if they might possibly hold.
1521 for o in candidate_obligations {
1522 let o = self.resolve_vars_if_possible(o);
1523 if !self.predicate_may_hold(&o) {
1524 result = ProbeResult::NoMatch;
1525 possibly_unsatisfied_predicates.push((
1534 ObjectCandidate | WhereClauseCandidate(..) => {
1535 // These have no additional conditions to check.
1538 TraitCandidate(trait_ref) => {
1539 if let Some(method_name) = self.method_name {
1540 // Some trait methods are excluded for arrays before 2021.
1541 // (`array.into_iter()` wants a slice iterator for compatibility.)
1542 if self_ty.is_array() && !method_name.span.rust_2021() {
1543 let trait_def = self.tcx.trait_def(trait_ref.def_id);
1544 if trait_def.skip_array_during_method_dispatch {
1545 return ProbeResult::NoMatch;
1550 ty::Binder::dummy(trait_ref).without_const().to_predicate(self.tcx);
1551 parent_pred = Some(predicate);
1552 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1553 if !self.predicate_may_hold(&obligation) {
1554 result = ProbeResult::NoMatch;
1556 match self.select_trait_candidate(trait_ref) {
1557 Err(_) => return true,
1558 Ok(Some(impl_source))
1559 if !impl_source.borrow_nested_obligations().is_empty() =>
1561 for obligation in impl_source.borrow_nested_obligations() {
1562 // Determine exactly which obligation wasn't met, so
1563 // that we can give more context in the error.
1564 if !self.predicate_may_hold(obligation) {
1565 let nested_predicate =
1566 self.resolve_vars_if_possible(obligation.predicate);
1568 self.resolve_vars_if_possible(predicate);
1569 let p = if predicate == nested_predicate {
1570 // Avoid "`MyStruct: Foo` which is required by
1571 // `MyStruct: Foo`" in E0599.
1576 possibly_unsatisfied_predicates.push((
1579 Some(obligation.cause.clone()),
1585 // Some nested subobligation of this predicate
1587 let predicate = self.resolve_vars_if_possible(predicate);
1588 possibly_unsatisfied_predicates.push((predicate, None, None));
1593 // This candidate's primary obligation doesn't even
1594 // select - don't bother registering anything in
1595 // `potentially_unsatisfied_predicates`.
1596 return ProbeResult::NoMatch;
1602 // Evaluate those obligations to see if they might possibly hold.
1603 for o in sub_obligations {
1604 let o = self.resolve_vars_if_possible(o);
1605 if !self.predicate_may_hold(&o) {
1606 result = ProbeResult::NoMatch;
1607 possibly_unsatisfied_predicates.push((o.predicate, parent_pred, Some(o.cause)));
1611 if let ProbeResult::Match = result {
1612 if let (Some(return_ty), Some(xform_ret_ty)) = (self.return_type, xform_ret_ty) {
1613 let xform_ret_ty = self.resolve_vars_if_possible(xform_ret_ty);
1615 "comparing return_ty {:?} with xform ret ty {:?}",
1616 return_ty, probe.xform_ret_ty
1619 .at(&ObligationCause::dummy(), self.param_env)
1620 .define_opaque_types(false)
1621 .sup(return_ty, xform_ret_ty)
1624 return ProbeResult::BadReturnType;
1633 /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1634 /// same trait, but we don't know which impl to use. In this case, since in all cases the
1635 /// external interface of the method can be determined from the trait, it's ok not to decide.
1636 /// We can basically just collapse all of the probes for various impls into one where-clause
1637 /// probe. This will result in a pending obligation so when more type-info is available we can
1638 /// make the final decision.
1640 /// Example (`src/test/ui/method-two-trait-defer-resolution-1.rs`):
1642 /// ```ignore (illustrative)
1643 /// trait Foo { ... }
1644 /// impl Foo for Vec<i32> { ... }
1645 /// impl Foo for Vec<usize> { ... }
1648 /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1649 /// use, so it's ok to just commit to "using the method from the trait Foo".
1650 fn collapse_candidates_to_trait_pick(
1653 probes: &[(&Candidate<'tcx>, ProbeResult)],
1654 ) -> Option<Pick<'tcx>> {
1655 // Do all probes correspond to the same trait?
1656 let container = probes[0].0.item.container;
1657 if let ty::ImplContainer(_) = container {
1660 if probes[1..].iter().any(|&(p, _)| p.item.container != container) {
1664 // FIXME: check the return type here somehow.
1665 // If so, just use this trait and call it a day.
1667 item: probes[0].0.item,
1669 import_ids: probes[0].0.import_ids.clone(),
1671 autoref_or_ptr_adjustment: None,
1676 /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
1677 /// candidate method where the method name may have been misspelled. Similarly to other
1678 /// Levenshtein based suggestions, we provide at most one such suggestion.
1679 fn probe_for_lev_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
1680 debug!("probing for method names similar to {:?}", self.method_name);
1682 let steps = self.steps.clone();
1684 let mut pcx = ProbeContext::new(
1690 self.orig_steps_var_values.clone(),
1695 pcx.allow_similar_names = true;
1696 pcx.assemble_inherent_candidates();
1698 let method_names = pcx.candidate_method_names();
1699 pcx.allow_similar_names = false;
1700 let applicable_close_candidates: Vec<ty::AssocItem> = method_names
1702 .filter_map(|&method_name| {
1704 pcx.method_name = Some(method_name);
1705 pcx.assemble_inherent_candidates();
1706 pcx.pick_core().and_then(|pick| pick.ok()).map(|pick| pick.item)
1710 if applicable_close_candidates.is_empty() {
1714 let names = applicable_close_candidates
1716 .map(|cand| cand.name)
1717 .collect::<Vec<Symbol>>();
1718 find_best_match_for_name_with_substrings(
1720 self.method_name.unwrap().name,
1725 Ok(applicable_close_candidates.into_iter().find(|method| method.name == best_name))
1730 ///////////////////////////////////////////////////////////////////////////
1732 fn has_applicable_self(&self, item: &ty::AssocItem) -> bool {
1733 // "Fast track" -- check for usage of sugar when in method call
1736 // In Path mode (i.e., resolving a value like `T::next`), consider any
1737 // associated value (i.e., methods, constants) but not types.
1739 Mode::MethodCall => item.fn_has_self_parameter,
1740 Mode::Path => match item.kind {
1741 ty::AssocKind::Type => false,
1742 ty::AssocKind::Fn | ty::AssocKind::Const => true,
1745 // FIXME -- check for types that deref to `Self`,
1746 // like `Rc<Self>` and so on.
1748 // Note also that the current code will break if this type
1749 // includes any of the type parameters defined on the method
1750 // -- but this could be overcome.
1753 fn record_static_candidate(&mut self, source: CandidateSource) {
1754 self.static_candidates.push(source);
1757 #[instrument(level = "debug", skip(self))]
1760 item: &ty::AssocItem,
1762 substs: SubstsRef<'tcx>,
1763 ) -> (Ty<'tcx>, Option<Ty<'tcx>>) {
1764 if item.kind == ty::AssocKind::Fn && self.mode == Mode::MethodCall {
1765 let sig = self.xform_method_sig(item.def_id, substs);
1766 (sig.inputs()[0], Some(sig.output()))
1772 #[instrument(level = "debug", skip(self))]
1773 fn xform_method_sig(&self, method: DefId, substs: SubstsRef<'tcx>) -> ty::FnSig<'tcx> {
1774 let fn_sig = self.tcx.bound_fn_sig(method);
1777 assert!(!substs.has_escaping_bound_vars());
1779 // It is possible for type parameters or early-bound lifetimes
1780 // to appear in the signature of `self`. The substitutions we
1781 // are given do not include type/lifetime parameters for the
1782 // method yet. So create fresh variables here for those too,
1783 // if there are any.
1784 let generics = self.tcx.generics_of(method);
1785 assert_eq!(substs.len(), generics.parent_count as usize);
1787 let xform_fn_sig = if generics.params.is_empty() {
1788 fn_sig.subst(self.tcx, substs)
1790 let substs = InternalSubsts::for_item(self.tcx, method, |param, _| {
1791 let i = param.index as usize;
1792 if i < substs.len() {
1796 GenericParamDefKind::Lifetime => {
1797 // In general, during probe we erase regions.
1798 self.tcx.lifetimes.re_erased.into()
1800 GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
1801 self.var_for_def(self.span, param)
1806 fn_sig.subst(self.tcx, substs)
1809 self.erase_late_bound_regions(xform_fn_sig)
1812 /// Gets the type of an impl and generate substitutions with inference vars.
1813 fn impl_ty_and_substs(
1816 ) -> (ty::EarlyBinder<Ty<'tcx>>, SubstsRef<'tcx>) {
1817 (self.tcx.bound_type_of(impl_def_id), self.fresh_item_substs(impl_def_id))
1820 fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx> {
1821 InternalSubsts::for_item(self.tcx, def_id, |param, _| match param.kind {
1822 GenericParamDefKind::Lifetime => self.tcx.lifetimes.re_erased.into(),
1823 GenericParamDefKind::Type { .. } => self
1824 .next_ty_var(TypeVariableOrigin {
1825 kind: TypeVariableOriginKind::SubstitutionPlaceholder,
1826 span: self.tcx.def_span(def_id),
1829 GenericParamDefKind::Const { .. } => {
1830 let span = self.tcx.def_span(def_id);
1831 let origin = ConstVariableOrigin {
1832 kind: ConstVariableOriginKind::SubstitutionPlaceholder,
1835 self.next_const_var(self.tcx.type_of(param.def_id), origin).into()
1840 /// Replaces late-bound-regions bound by `value` with `'static` using
1841 /// `ty::erase_late_bound_regions`.
1843 /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1844 /// method matching. It is reasonable during the probe phase because we don't consider region
1845 /// relationships at all. Therefore, we can just replace all the region variables with 'static
1846 /// rather than creating fresh region variables. This is nice for two reasons:
1848 /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1849 /// particular method call, it winds up creating fewer types overall, which helps for memory
1850 /// usage. (Admittedly, this is a rather small effect, though measurable.)
1852 /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1853 /// late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1854 /// regions with actual region variables as is proper, we'd have to ensure that the same
1855 /// region got replaced with the same variable, which requires a bit more coordination
1856 /// and/or tracking the substitution and
1858 fn erase_late_bound_regions<T>(&self, value: ty::Binder<'tcx, T>) -> T
1860 T: TypeFoldable<'tcx>,
1862 self.tcx.erase_late_bound_regions(value)
1865 /// Finds the method with the appropriate name (or return type, as the case may be). If
1866 /// `allow_similar_names` is set, find methods with close-matching names.
1867 // The length of the returned iterator is nearly always 0 or 1 and this
1868 // method is fairly hot.
1869 fn impl_or_trait_item(&self, def_id: DefId) -> SmallVec<[ty::AssocItem; 1]> {
1870 if let Some(name) = self.method_name {
1871 if self.allow_similar_names {
1872 let max_dist = max(name.as_str().len(), 3) / 3;
1874 .associated_items(def_id)
1875 .in_definition_order()
1877 if x.kind.namespace() != Namespace::ValueNS {
1880 match lev_distance_with_substrings(name.as_str(), x.name.as_str(), max_dist)
1890 .associated_value(def_id, name)
1891 .map_or_else(SmallVec::new, |x| SmallVec::from_buf([x]))
1894 self.tcx.associated_items(def_id).in_definition_order().copied().collect()
1899 impl<'tcx> Candidate<'tcx> {
1900 fn to_unadjusted_pick(&self, self_ty: Ty<'tcx>) -> Pick<'tcx> {
1903 kind: match self.kind {
1904 InherentImplCandidate(..) => InherentImplPick,
1905 ObjectCandidate => ObjectPick,
1906 TraitCandidate(_) => TraitPick,
1907 WhereClauseCandidate(ref trait_ref) => {
1908 // Only trait derived from where-clauses should
1909 // appear here, so they should not contain any
1910 // inference variables or other artifacts. This
1911 // means they are safe to put into the
1912 // `WhereClausePick`.
1914 !trait_ref.skip_binder().substs.needs_infer()
1915 && !trait_ref.skip_binder().substs.has_placeholders()
1918 WhereClausePick(*trait_ref)
1921 import_ids: self.import_ids.clone(),
1923 autoref_or_ptr_adjustment: None,