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::NormalizeExt;
40 use rustc_trait_selection::traits::{self, ObligationCause};
41 use std::cell::RefCell;
46 use smallvec::{smallvec, SmallVec};
48 use self::CandidateKind::*;
49 pub use self::PickKind::*;
51 /// Boolean flag used to indicate if this search is for a suggestion
52 /// or not. If true, we can allow ambiguity and so forth.
53 #[derive(Clone, Copy, Debug)]
54 pub struct IsSuggestion(pub bool);
56 struct ProbeContext<'a, 'tcx> {
57 fcx: &'a FnCtxt<'a, 'tcx>,
60 method_name: Option<Ident>,
61 return_type: Option<Ty<'tcx>>,
63 /// This is the OriginalQueryValues for the steps queries
64 /// that are answered in steps.
65 orig_steps_var_values: &'a OriginalQueryValues<'tcx>,
66 steps: &'tcx [CandidateStep<'tcx>],
68 inherent_candidates: Vec<Candidate<'tcx>>,
69 extension_candidates: Vec<Candidate<'tcx>>,
70 impl_dups: FxHashSet<DefId>,
72 /// When probing for names, include names that are close to the
73 /// requested name (by Levenshtein distance)
74 allow_similar_names: bool,
76 /// Some(candidate) if there is a private candidate
77 private_candidate: Option<(DefKind, DefId)>,
79 /// Collects near misses when the candidate functions are missing a `self` keyword and is only
80 /// used for error reporting
81 static_candidates: RefCell<Vec<CandidateSource>>,
83 /// Collects near misses when trait bounds for type parameters are unsatisfied and is only used
84 /// for error reporting
85 unsatisfied_predicates: RefCell<
86 Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>, Option<ObligationCause<'tcx>>)>,
89 scope_expr_id: hir::HirId,
92 impl<'a, 'tcx> Deref for ProbeContext<'a, 'tcx> {
93 type Target = FnCtxt<'a, 'tcx>;
94 fn deref(&self) -> &Self::Target {
99 #[derive(Debug, Clone)]
100 struct Candidate<'tcx> {
101 // Candidates are (I'm not quite sure, but they are mostly) basically
102 // some metadata on top of a `ty::AssocItem` (without substs).
104 // However, method probing wants to be able to evaluate the predicates
105 // for a function with the substs applied - for example, if a function
106 // has `where Self: Sized`, we don't want to consider it unless `Self`
107 // is actually `Sized`, and similarly, return-type suggestions want
108 // to consider the "actual" return type.
110 // The way this is handled is through `xform_self_ty`. It contains
111 // the receiver type of this candidate, but `xform_self_ty`,
112 // `xform_ret_ty` and `kind` (which contains the predicates) have the
113 // generic parameters of this candidate substituted with the *same set*
114 // of inference variables, which acts as some weird sort of "query".
116 // When we check out a candidate, we require `xform_self_ty` to be
117 // a subtype of the passed-in self-type, and this equates the type
118 // variables in the rest of the fields.
120 // For example, if we have this candidate:
123 // fn foo(&self) where Self: Sized;
127 // Then `xform_self_ty` will be `&'erased ?X` and `kind` will contain
128 // the predicate `?X: Sized`, so if we are evaluating `Foo` for a
129 // the receiver `&T`, we'll do the subtyping which will make `?X`
130 // get the right value, then when we evaluate the predicate we'll check
132 xform_self_ty: Ty<'tcx>,
133 xform_ret_ty: Option<Ty<'tcx>>,
135 kind: CandidateKind<'tcx>,
136 import_ids: SmallVec<[LocalDefId; 1]>,
139 #[derive(Debug, Clone)]
140 enum CandidateKind<'tcx> {
141 InherentImplCandidate(
143 // Normalize obligations
144 Vec<traits::PredicateObligation<'tcx>>,
147 TraitCandidate(ty::TraitRef<'tcx>),
148 WhereClauseCandidate(
150 ty::PolyTraitRef<'tcx>,
154 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
161 /// When adjusting a receiver we often want to do one of
163 /// - Add a `&` (or `&mut`), converting the receiver from `T` to `&T` (or `&mut T`)
164 /// - If the receiver has type `*mut T`, convert it to `*const T`
166 /// This type tells us which one to do.
168 /// Note that in principle we could do both at the same time. For example, when the receiver has
169 /// type `T`, we could autoref it to `&T`, then convert to `*const T`. Or, when it has type `*mut
170 /// T`, we could convert it to `*const T`, then autoref to `&*const T`. However, currently we do
171 /// (at most) one of these. Either the receiver has type `T` and we convert it to `&T` (or with
172 /// `mut`), or it has type `*mut T` and we convert it to `*const T`.
173 #[derive(Debug, PartialEq, Copy, Clone)]
174 pub enum AutorefOrPtrAdjustment {
175 /// Receiver has type `T`, add `&` or `&mut` (it `T` is `mut`), and maybe also "unsize" it.
176 /// Unsizing is used to convert a `[T; N]` to `[T]`, which only makes sense when autorefing.
178 mutbl: hir::Mutability,
180 /// Indicates that the source expression should be "unsized" to a target type.
181 /// This is special-cased for just arrays unsizing to slices.
184 /// Receiver has type `*mut T`, convert to `*const T`
188 impl AutorefOrPtrAdjustment {
189 fn get_unsize(&self) -> bool {
191 AutorefOrPtrAdjustment::Autoref { mutbl: _, unsize } => *unsize,
192 AutorefOrPtrAdjustment::ToConstPtr => false,
197 #[derive(Debug, Clone)]
198 pub struct Pick<'tcx> {
199 pub item: ty::AssocItem,
200 pub kind: PickKind<'tcx>,
201 pub import_ids: SmallVec<[LocalDefId; 1]>,
203 /// Indicates that the source expression should be autoderef'd N times
204 /// ```ignore (not-rust)
205 /// A = expr | *expr | **expr | ...
207 pub autoderefs: usize,
209 /// Indicates that we want to add an autoref (and maybe also unsize it), or if the receiver is
210 /// `*mut T`, convert it to `*const T`.
211 pub autoref_or_ptr_adjustment: Option<AutorefOrPtrAdjustment>,
212 pub self_ty: Ty<'tcx>,
214 /// Unstable candidates alongside the stable ones.
215 unstable_candidates: Vec<(Candidate<'tcx>, Symbol)>,
218 #[derive(Clone, Debug, PartialEq, Eq)]
219 pub enum PickKind<'tcx> {
225 ty::PolyTraitRef<'tcx>,
229 pub type PickResult<'tcx> = Result<Pick<'tcx>, MethodError<'tcx>>;
231 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
233 // An expression of the form `receiver.method_name(...)`.
234 // Autoderefs are performed on `receiver`, lookup is done based on the
235 // `self` argument of the method, and static methods aren't considered.
237 // An expression of the form `Type::item` or `<T>::item`.
238 // No autoderefs are performed, lookup is done based on the type each
239 // implementation is for, and static methods are included.
243 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
244 pub enum ProbeScope {
245 // Assemble candidates coming only from traits in scope.
248 // Assemble candidates coming from all traits.
252 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
253 /// This is used to offer suggestions to users. It returns methods
254 /// that could have been called which have the desired return
255 /// type. Some effort is made to rule out methods that, if called,
256 /// would result in an error (basically, the same criteria we
257 /// would use to decide if a method is a plausible fit for
258 /// ambiguity purposes).
259 #[instrument(level = "debug", skip(self, candidate_filter))]
260 pub fn probe_for_return_type(
264 return_type: Ty<'tcx>,
266 scope_expr_id: hir::HirId,
267 candidate_filter: impl Fn(&ty::AssocItem) -> bool,
268 ) -> Vec<ty::AssocItem> {
269 let method_names = self
278 ProbeScope::AllTraits,
279 |probe_cx| Ok(probe_cx.candidate_method_names(candidate_filter)),
281 .unwrap_or_default();
284 .flat_map(|&method_name| {
293 ProbeScope::AllTraits,
294 |probe_cx| probe_cx.pick(),
297 .map(|pick| pick.item)
302 #[instrument(level = "debug", skip(self))]
303 pub fn probe_for_name(
307 is_suggestion: IsSuggestion,
309 scope_expr_id: hir::HirId,
311 ) -> PickResult<'tcx> {
321 |probe_cx| probe_cx.pick(),
329 method_name: Option<Ident>,
330 return_type: Option<Ty<'tcx>>,
331 is_suggestion: IsSuggestion,
333 scope_expr_id: hir::HirId,
336 ) -> Result<R, MethodError<'tcx>>
338 OP: FnOnce(ProbeContext<'_, 'tcx>) -> Result<R, MethodError<'tcx>>,
340 let mut orig_values = OriginalQueryValues::default();
341 let param_env_and_self_ty = self.canonicalize_query(
342 ParamEnvAnd { param_env: self.param_env, value: self_ty },
346 let steps = match mode {
347 Mode::MethodCall => self.tcx.method_autoderef_steps(param_env_and_self_ty),
348 Mode::Path => self.probe(|_| {
349 // Mode::Path - the deref steps is "trivial". This turns
350 // our CanonicalQuery into a "trivial" QueryResponse. This
351 // is a bit inefficient, but I don't think that writing
352 // special handling for this "trivial case" is a good idea.
354 let infcx = &self.infcx;
355 let (ParamEnvAnd { param_env: _, value: self_ty }, canonical_inference_vars) =
356 infcx.instantiate_canonical_with_fresh_inference_vars(
358 ¶m_env_and_self_ty,
361 "probe_op: Mode::Path, param_env_and_self_ty={:?} self_ty={:?}",
362 param_env_and_self_ty, self_ty
364 MethodAutoderefStepsResult {
365 steps: infcx.tcx.arena.alloc_from_iter([CandidateStep {
366 self_ty: self.make_query_response_ignoring_pending_obligations(
367 canonical_inference_vars,
371 from_unsafe_deref: false,
375 reached_recursion_limit: false,
380 // If our autoderef loop had reached the recursion limit,
381 // report an overflow error, but continue going on with
382 // the truncated autoderef list.
383 if steps.reached_recursion_limit {
388 .unwrap_or_else(|| span_bug!(span, "reached the recursion limit in 0 steps?"))
391 .probe_instantiate_query_response(span, &orig_values, ty)
392 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
393 autoderef::report_autoderef_recursion_limit_error(self.tcx, span, ty.value);
397 // If we encountered an `_` type or an error type during autoderef, this is
399 if let Some(bad_ty) = &steps.opt_bad_ty {
401 // Ambiguity was encountered during a suggestion. Just keep going.
402 debug!("ProbeContext: encountered ambiguity in suggestion");
403 } else if bad_ty.reached_raw_pointer && !self.tcx.features().arbitrary_self_types {
404 // this case used to be allowed by the compiler,
405 // so we do a future-compat lint here for the 2015 edition
406 // (see https://github.com/rust-lang/rust/issues/46906)
407 if self.tcx.sess.rust_2018() {
408 self.tcx.sess.emit_err(MethodCallOnUnknownType { span });
410 self.tcx.struct_span_lint_hir(
411 lint::builtin::TYVAR_BEHIND_RAW_POINTER,
414 "type annotations needed",
419 // Encountered a real ambiguity, so abort the lookup. If `ty` is not
420 // an `Err`, report the right "type annotations needed" error pointing
424 .probe_instantiate_query_response(span, &orig_values, ty)
425 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
426 let ty = self.structurally_resolved_type(span, ty.value);
427 assert!(matches!(ty.kind(), ty::Error(_)));
428 return Err(MethodError::NoMatch(NoMatchData {
429 static_candidates: Vec::new(),
430 unsatisfied_predicates: Vec::new(),
431 out_of_scope_traits: Vec::new(),
438 debug!("ProbeContext: steps for self_ty={:?} are {:?}", self_ty, steps);
440 // this creates one big transaction so that all type variables etc
441 // that we create during the probe process are removed later
443 let mut probe_cx = ProbeContext::new(
454 probe_cx.assemble_inherent_candidates();
456 ProbeScope::TraitsInScope => {
457 probe_cx.assemble_extension_candidates_for_traits_in_scope(scope_expr_id)
459 ProbeScope::AllTraits => probe_cx.assemble_extension_candidates_for_all_traits(),
466 pub fn provide(providers: &mut ty::query::Providers) {
467 providers.method_autoderef_steps = method_autoderef_steps;
470 fn method_autoderef_steps<'tcx>(
472 goal: CanonicalTyGoal<'tcx>,
473 ) -> MethodAutoderefStepsResult<'tcx> {
474 debug!("method_autoderef_steps({:?})", goal);
476 let (ref infcx, goal, inference_vars) = tcx.infer_ctxt().build_with_canonical(DUMMY_SP, &goal);
477 let ParamEnvAnd { param_env, value: self_ty } = goal;
479 let mut autoderef = Autoderef::new(infcx, param_env, hir::CRATE_HIR_ID, DUMMY_SP, self_ty)
480 .include_raw_pointers()
482 let mut reached_raw_pointer = false;
483 let mut steps: Vec<_> = autoderef
486 let step = CandidateStep {
488 .make_query_response_ignoring_pending_obligations(inference_vars.clone(), ty),
490 from_unsafe_deref: reached_raw_pointer,
493 if let ty::RawPtr(_) = ty.kind() {
494 // all the subsequent steps will be from_unsafe_deref
495 reached_raw_pointer = true;
501 let final_ty = autoderef.final_ty(true);
502 let opt_bad_ty = match final_ty.kind() {
503 ty::Infer(ty::TyVar(_)) | ty::Error(_) => Some(MethodAutoderefBadTy {
505 ty: infcx.make_query_response_ignoring_pending_obligations(inference_vars, final_ty),
507 ty::Array(elem_ty, _) => {
508 let dereferences = steps.len() - 1;
510 steps.push(CandidateStep {
511 self_ty: infcx.make_query_response_ignoring_pending_obligations(
513 infcx.tcx.mk_slice(*elem_ty),
515 autoderefs: dereferences,
516 // this could be from an unsafe deref if we had
517 // a *mut/const [T; N]
518 from_unsafe_deref: reached_raw_pointer,
527 debug!("method_autoderef_steps: steps={:?} opt_bad_ty={:?}", steps, opt_bad_ty);
529 MethodAutoderefStepsResult {
530 steps: tcx.arena.alloc_from_iter(steps),
531 opt_bad_ty: opt_bad_ty.map(|ty| &*tcx.arena.alloc(ty)),
532 reached_recursion_limit: autoderef.reached_recursion_limit(),
536 impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
538 fcx: &'a FnCtxt<'a, 'tcx>,
541 method_name: Option<Ident>,
542 return_type: Option<Ty<'tcx>>,
543 orig_steps_var_values: &'a OriginalQueryValues<'tcx>,
544 steps: &'tcx [CandidateStep<'tcx>],
545 scope_expr_id: hir::HirId,
546 ) -> ProbeContext<'a, 'tcx> {
553 inherent_candidates: Vec::new(),
554 extension_candidates: Vec::new(),
555 impl_dups: FxHashSet::default(),
556 orig_steps_var_values,
558 allow_similar_names: false,
559 private_candidate: None,
560 static_candidates: RefCell::new(Vec::new()),
561 unsatisfied_predicates: RefCell::new(Vec::new()),
566 fn reset(&mut self) {
567 self.inherent_candidates.clear();
568 self.extension_candidates.clear();
569 self.impl_dups.clear();
570 self.private_candidate = None;
571 self.static_candidates.borrow_mut().clear();
572 self.unsatisfied_predicates.borrow_mut().clear();
575 ///////////////////////////////////////////////////////////////////////////
576 // CANDIDATE ASSEMBLY
578 fn push_candidate(&mut self, candidate: Candidate<'tcx>, is_inherent: bool) {
579 let is_accessible = if let Some(name) = self.method_name {
580 let item = candidate.item;
583 .adjust_ident_and_get_scope(name, item.container_id(self.tcx), self.body_id)
585 item.visibility(self.tcx).is_accessible_from(def_scope, self.tcx)
591 self.inherent_candidates.push(candidate);
593 self.extension_candidates.push(candidate);
595 } else if self.private_candidate.is_none() {
596 self.private_candidate =
597 Some((candidate.item.kind.as_def_kind(), candidate.item.def_id));
601 fn assemble_inherent_candidates(&mut self) {
602 for step in self.steps.iter() {
603 self.assemble_probe(&step.self_ty);
607 fn assemble_probe(&mut self, self_ty: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>) {
608 debug!("assemble_probe: self_ty={:?}", self_ty);
609 let raw_self_ty = self_ty.value.value;
610 match *raw_self_ty.kind() {
611 ty::Dynamic(data, ..) if let Some(p) = data.principal() => {
612 // Subtle: we can't use `instantiate_query_response` here: using it will
613 // commit to all of the type equalities assumed by inference going through
614 // autoderef (see the `method-probe-no-guessing` test).
616 // However, in this code, it is OK if we end up with an object type that is
617 // "more general" than the object type that we are evaluating. For *every*
618 // object type `MY_OBJECT`, a function call that goes through a trait-ref
619 // of the form `<MY_OBJECT as SuperTraitOf(MY_OBJECT)>::func` is a valid
620 // `ObjectCandidate`, and it should be discoverable "exactly" through one
621 // of the iterations in the autoderef loop, so there is no problem with it
622 // being discoverable in another one of these iterations.
624 // Using `instantiate_canonical_with_fresh_inference_vars` on our
625 // `Canonical<QueryResponse<Ty<'tcx>>>` and then *throwing away* the
626 // `CanonicalVarValues` will exactly give us such a generalization - it
627 // will still match the original object type, but it won't pollute our
628 // type variables in any form, so just do that!
629 let (QueryResponse { value: generalized_self_ty, .. }, _ignored_var_values) =
631 .instantiate_canonical_with_fresh_inference_vars(self.span, self_ty);
633 self.assemble_inherent_candidates_from_object(generalized_self_ty);
634 self.assemble_inherent_impl_candidates_for_type(p.def_id());
635 if self.tcx.has_attr(p.def_id(), sym::rustc_has_incoherent_inherent_impls) {
636 self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
640 let def_id = def.did();
641 self.assemble_inherent_impl_candidates_for_type(def_id);
642 if self.tcx.has_attr(def_id, sym::rustc_has_incoherent_inherent_impls) {
643 self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
646 ty::Foreign(did) => {
647 self.assemble_inherent_impl_candidates_for_type(did);
648 if self.tcx.has_attr(did, sym::rustc_has_incoherent_inherent_impls) {
649 self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
653 self.assemble_inherent_candidates_from_param(p);
666 | ty::Tuple(..) => self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty),
671 fn assemble_inherent_candidates_for_incoherent_ty(&mut self, self_ty: Ty<'tcx>) {
672 let Some(simp) = simplify_type(self.tcx, self_ty, TreatParams::AsInfer) else {
673 bug!("unexpected incoherent type: {:?}", self_ty)
675 for &impl_def_id in self.tcx.incoherent_impls(simp) {
676 self.assemble_inherent_impl_probe(impl_def_id);
680 fn assemble_inherent_impl_candidates_for_type(&mut self, def_id: DefId) {
681 let impl_def_ids = self.tcx.at(self.span).inherent_impls(def_id);
682 for &impl_def_id in impl_def_ids.iter() {
683 self.assemble_inherent_impl_probe(impl_def_id);
687 fn assemble_inherent_impl_probe(&mut self, impl_def_id: DefId) {
688 if !self.impl_dups.insert(impl_def_id) {
689 return; // already visited
692 debug!("assemble_inherent_impl_probe {:?}", impl_def_id);
694 for item in self.impl_or_trait_item(impl_def_id) {
695 if !self.has_applicable_self(&item) {
696 // No receiver declared. Not a candidate.
697 self.record_static_candidate(CandidateSource::Impl(impl_def_id));
701 let (impl_ty, impl_substs) = self.impl_ty_and_substs(impl_def_id);
702 let impl_ty = impl_ty.subst(self.tcx, impl_substs);
704 debug!("impl_ty: {:?}", impl_ty);
706 // Determine the receiver type that the method itself expects.
707 let (xform_self_ty, xform_ret_ty) = self.xform_self_ty(&item, impl_ty, impl_substs);
708 debug!("xform_self_ty: {:?}, xform_ret_ty: {:?}", xform_self_ty, xform_ret_ty);
710 // We can't use normalize_associated_types_in as it will pollute the
711 // fcx's fulfillment context after this probe is over.
712 // Note: we only normalize `xform_self_ty` here since the normalization
713 // of the return type can lead to inference results that prohibit
714 // valid candidates from being found, see issue #85671
715 // FIXME Postponing the normalization of the return type likely only hides a deeper bug,
716 // which might be caused by the `param_env` itself. The clauses of the `param_env`
717 // maybe shouldn't include `Param`s, but rather fresh variables or be canonicalized,
719 let cause = traits::ObligationCause::misc(self.span, self.body_id);
720 let InferOk { value: xform_self_ty, obligations } =
721 self.fcx.at(&cause, self.param_env).normalize(xform_self_ty);
724 "assemble_inherent_impl_probe after normalization: xform_self_ty = {:?}/{:?}",
725 xform_self_ty, xform_ret_ty
733 kind: InherentImplCandidate(impl_substs, obligations),
734 import_ids: smallvec![],
741 fn assemble_inherent_candidates_from_object(&mut self, self_ty: Ty<'tcx>) {
742 debug!("assemble_inherent_candidates_from_object(self_ty={:?})", self_ty);
744 let principal = match self_ty.kind() {
745 ty::Dynamic(ref data, ..) => Some(data),
748 .and_then(|data| data.principal())
752 "non-object {:?} in assemble_inherent_candidates_from_object",
757 // It is illegal to invoke a method on a trait instance that refers to
758 // the `Self` type. An [`ObjectSafetyViolation::SupertraitSelf`] error
759 // will be reported by `object_safety.rs` if the method refers to the
760 // `Self` type anywhere other than the receiver. Here, we use a
761 // substitution that replaces `Self` with the object type itself. Hence,
762 // a `&self` method will wind up with an argument type like `&dyn Trait`.
763 let trait_ref = principal.with_self_ty(self.tcx, self_ty);
764 self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
765 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
767 let (xform_self_ty, xform_ret_ty) =
768 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
774 kind: ObjectCandidate,
775 import_ids: smallvec![],
782 fn assemble_inherent_candidates_from_param(&mut self, param_ty: ty::ParamTy) {
783 // FIXME: do we want to commit to this behavior for param bounds?
784 debug!("assemble_inherent_candidates_from_param(param_ty={:?})", param_ty);
786 let bounds = self.param_env.caller_bounds().iter().filter_map(|predicate| {
787 let bound_predicate = predicate.kind();
788 match bound_predicate.skip_binder() {
789 ty::PredicateKind::Clause(ty::Clause::Trait(trait_predicate)) => {
790 match *trait_predicate.trait_ref.self_ty().kind() {
791 ty::Param(p) if p == param_ty => {
792 Some(bound_predicate.rebind(trait_predicate.trait_ref))
797 ty::PredicateKind::Subtype(..)
798 | ty::PredicateKind::Coerce(..)
799 | ty::PredicateKind::Clause(ty::Clause::Projection(..))
800 | ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..))
801 | ty::PredicateKind::WellFormed(..)
802 | ty::PredicateKind::ObjectSafe(..)
803 | ty::PredicateKind::ClosureKind(..)
804 | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..))
805 | ty::PredicateKind::ConstEvaluatable(..)
806 | ty::PredicateKind::ConstEquate(..)
807 | ty::PredicateKind::Ambiguous
808 | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
812 self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
813 let trait_ref = this.erase_late_bound_regions(poly_trait_ref);
815 let (xform_self_ty, xform_ret_ty) =
816 this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs);
818 // Because this trait derives from a where-clause, it
819 // should not contain any inference variables or other
820 // artifacts. This means it is safe to put into the
821 // `WhereClauseCandidate` and (eventually) into the
822 // `WhereClausePick`.
823 assert!(!trait_ref.substs.needs_infer());
830 kind: WhereClauseCandidate(poly_trait_ref),
831 import_ids: smallvec![],
838 // Do a search through a list of bounds, using a callback to actually
839 // create the candidates.
840 fn elaborate_bounds<F>(
842 bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
845 F: for<'b> FnMut(&mut ProbeContext<'b, 'tcx>, ty::PolyTraitRef<'tcx>, ty::AssocItem),
848 for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
849 debug!("elaborate_bounds(bound_trait_ref={:?})", bound_trait_ref);
850 for item in self.impl_or_trait_item(bound_trait_ref.def_id()) {
851 if !self.has_applicable_self(&item) {
852 self.record_static_candidate(CandidateSource::Trait(bound_trait_ref.def_id()));
854 mk_cand(self, bound_trait_ref, item);
860 fn assemble_extension_candidates_for_traits_in_scope(&mut self, expr_hir_id: hir::HirId) {
861 let mut duplicates = FxHashSet::default();
862 let opt_applicable_traits = self.tcx.in_scope_traits(expr_hir_id);
863 if let Some(applicable_traits) = opt_applicable_traits {
864 for trait_candidate in applicable_traits.iter() {
865 let trait_did = trait_candidate.def_id;
866 if duplicates.insert(trait_did) {
867 self.assemble_extension_candidates_for_trait(
868 &trait_candidate.import_ids,
876 fn assemble_extension_candidates_for_all_traits(&mut self) {
877 let mut duplicates = FxHashSet::default();
878 for trait_info in suggest::all_traits(self.tcx) {
879 if duplicates.insert(trait_info.def_id) {
880 self.assemble_extension_candidates_for_trait(&smallvec![], trait_info.def_id);
885 fn matches_return_type(
887 method: &ty::AssocItem,
888 self_ty: Option<Ty<'tcx>>,
892 ty::AssocKind::Fn => {
893 let fty = self.tcx.bound_fn_sig(method.def_id);
895 let substs = self.fresh_substs_for_item(self.span, method.def_id);
896 let fty = fty.subst(self.tcx, substs);
898 self.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, fty);
900 if let Some(self_ty) = self_ty {
902 .at(&ObligationCause::dummy(), self.param_env)
903 .sup(fty.inputs()[0], self_ty)
909 self.can_sub(self.param_env, fty.output(), expected).is_ok()
916 fn assemble_extension_candidates_for_trait(
918 import_ids: &SmallVec<[LocalDefId; 1]>,
921 debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})", trait_def_id);
922 let trait_substs = self.fresh_item_substs(trait_def_id);
923 let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
925 if self.tcx.is_trait_alias(trait_def_id) {
926 // For trait aliases, assume all supertraits are relevant.
927 let bounds = iter::once(ty::Binder::dummy(trait_ref));
928 self.elaborate_bounds(bounds, |this, new_trait_ref, item| {
929 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
931 let (xform_self_ty, xform_ret_ty) =
932 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
938 import_ids: import_ids.clone(),
939 kind: TraitCandidate(new_trait_ref),
945 debug_assert!(self.tcx.is_trait(trait_def_id));
946 for item in self.impl_or_trait_item(trait_def_id) {
947 // Check whether `trait_def_id` defines a method with suitable name.
948 if !self.has_applicable_self(&item) {
949 debug!("method has inapplicable self");
950 self.record_static_candidate(CandidateSource::Trait(trait_def_id));
954 let (xform_self_ty, xform_ret_ty) =
955 self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
961 import_ids: import_ids.clone(),
962 kind: TraitCandidate(trait_ref),
970 fn candidate_method_names(
972 candidate_filter: impl Fn(&ty::AssocItem) -> bool,
974 let mut set = FxHashSet::default();
975 let mut names: Vec<_> = self
978 .chain(&self.extension_candidates)
979 .filter(|candidate| candidate_filter(&candidate.item))
980 .filter(|candidate| {
981 if let Some(return_ty) = self.return_type {
982 self.matches_return_type(&candidate.item, None, return_ty)
987 .map(|candidate| candidate.item.ident(self.tcx))
988 .filter(|&name| set.insert(name))
991 // Sort them by the name so we have a stable result.
992 names.sort_by(|a, b| a.as_str().partial_cmp(b.as_str()).unwrap());
996 ///////////////////////////////////////////////////////////////////////////
999 fn pick(mut self) -> PickResult<'tcx> {
1000 assert!(self.method_name.is_some());
1002 if let Some(r) = self.pick_core() {
1006 debug!("pick: actual search failed, assemble diagnostics");
1008 let static_candidates = std::mem::take(self.static_candidates.get_mut());
1009 let private_candidate = self.private_candidate.take();
1010 let unsatisfied_predicates = std::mem::take(self.unsatisfied_predicates.get_mut());
1012 // things failed, so lets look at all traits, for diagnostic purposes now:
1015 let span = self.span;
1018 self.assemble_extension_candidates_for_all_traits();
1020 let out_of_scope_traits = match self.pick_core() {
1021 Some(Ok(p)) => vec![p.item.container_id(self.tcx)],
1022 Some(Err(MethodError::Ambiguity(v))) => v
1024 .map(|source| match source {
1025 CandidateSource::Trait(id) => id,
1026 CandidateSource::Impl(impl_id) => match tcx.trait_id_of_impl(impl_id) {
1028 None => span_bug!(span, "found inherent method when looking at traits"),
1032 Some(Err(MethodError::NoMatch(NoMatchData {
1033 out_of_scope_traits: others, ..
1035 assert!(others.is_empty());
1041 if let Some((kind, def_id)) = private_candidate {
1042 return Err(MethodError::PrivateMatch(kind, def_id, out_of_scope_traits));
1044 let lev_candidate = self.probe_for_lev_candidate()?;
1046 Err(MethodError::NoMatch(NoMatchData {
1048 unsatisfied_predicates,
1049 out_of_scope_traits,
1055 fn pick_core(&self) -> Option<PickResult<'tcx>> {
1056 let pick = self.pick_all_method(Some(&mut vec![]));
1058 // In this case unstable picking is done by `pick_method`.
1059 if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable {
1064 return self.pick_all_method(None);
1071 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1072 ) -> Option<PickResult<'tcx>> {
1076 debug!("pick_all_method: step={:?}", step);
1077 // skip types that are from a type error or that would require dereferencing
1079 !step.self_ty.references_error() && !step.from_unsafe_deref
1082 let InferOk { value: self_ty, obligations: _ } = self
1084 .probe_instantiate_query_response(
1086 &self.orig_steps_var_values,
1089 .unwrap_or_else(|_| {
1090 span_bug!(self.span, "{:?} was applicable but now isn't?", step.self_ty)
1092 self.pick_by_value_method(step, self_ty, unstable_candidates.as_deref_mut())
1094 self.pick_autorefd_method(
1097 hir::Mutability::Not,
1098 unstable_candidates.as_deref_mut(),
1101 self.pick_autorefd_method(
1104 hir::Mutability::Mut,
1105 unstable_candidates.as_deref_mut(),
1109 self.pick_const_ptr_method(
1112 unstable_candidates.as_deref_mut(),
1120 /// For each type `T` in the step list, this attempts to find a method where
1121 /// the (transformed) self type is exactly `T`. We do however do one
1122 /// transformation on the adjustment: if we are passing a region pointer in,
1123 /// we will potentially *reborrow* it to a shorter lifetime. This allows us
1124 /// to transparently pass `&mut` pointers, in particular, without consuming
1125 /// them for their entire lifetime.
1126 fn pick_by_value_method(
1128 step: &CandidateStep<'tcx>,
1130 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1131 ) -> Option<PickResult<'tcx>> {
1136 self.pick_method(self_ty, unstable_candidates).map(|r| {
1138 pick.autoderefs = step.autoderefs;
1140 // Insert a `&*` or `&mut *` if this is a reference type:
1141 if let ty::Ref(_, _, mutbl) = *step.self_ty.value.value.kind() {
1142 pick.autoderefs += 1;
1143 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::Autoref {
1145 unsize: pick.autoref_or_ptr_adjustment.map_or(false, |a| a.get_unsize()),
1154 fn pick_autorefd_method(
1156 step: &CandidateStep<'tcx>,
1158 mutbl: hir::Mutability,
1159 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1160 ) -> Option<PickResult<'tcx>> {
1163 // In general, during probing we erase regions.
1164 let region = tcx.lifetimes.re_erased;
1166 let autoref_ty = tcx.mk_ref(region, ty::TypeAndMut { ty: self_ty, mutbl });
1167 self.pick_method(autoref_ty, unstable_candidates).map(|r| {
1169 pick.autoderefs = step.autoderefs;
1170 pick.autoref_or_ptr_adjustment =
1171 Some(AutorefOrPtrAdjustment::Autoref { mutbl, unsize: step.unsize });
1177 /// If `self_ty` is `*mut T` then this picks `*const T` methods. The reason why we have a
1178 /// special case for this is because going from `*mut T` to `*const T` with autoderefs and
1179 /// autorefs would require dereferencing the pointer, which is not safe.
1180 fn pick_const_ptr_method(
1182 step: &CandidateStep<'tcx>,
1184 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1185 ) -> Option<PickResult<'tcx>> {
1186 // Don't convert an unsized reference to ptr
1191 let &ty::RawPtr(ty::TypeAndMut { ty, mutbl: hir::Mutability::Mut }) = self_ty.kind() else {
1195 let const_self_ty = ty::TypeAndMut { ty, mutbl: hir::Mutability::Not };
1196 let const_ptr_ty = self.tcx.mk_ptr(const_self_ty);
1197 self.pick_method(const_ptr_ty, unstable_candidates).map(|r| {
1199 pick.autoderefs = step.autoderefs;
1200 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::ToConstPtr);
1206 fn pick_method_with_unstable(&self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
1207 debug!("pick_method_with_unstable(self_ty={})", self.ty_to_string(self_ty));
1209 let mut possibly_unsatisfied_predicates = Vec::new();
1211 for (kind, candidates) in
1212 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1214 debug!("searching {} candidates", kind);
1215 let res = self.consider_candidates(
1218 &mut possibly_unsatisfied_predicates,
1226 for (kind, candidates) in
1227 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1229 debug!("searching unstable {kind} candidates");
1230 let res = self.consider_candidates(
1233 &mut possibly_unsatisfied_predicates,
1241 self.unsatisfied_predicates.borrow_mut().extend(possibly_unsatisfied_predicates);
1248 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1249 ) -> Option<PickResult<'tcx>> {
1250 if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable {
1251 return self.pick_method_with_unstable(self_ty);
1254 debug!("pick_method(self_ty={})", self.ty_to_string(self_ty));
1256 let mut possibly_unsatisfied_predicates = Vec::new();
1258 for (kind, candidates) in
1259 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1261 debug!("searching {} candidates", kind);
1262 let res = self.consider_candidates(
1265 &mut possibly_unsatisfied_predicates,
1266 unstable_candidates.as_deref_mut(),
1268 if let Some(pick) = res {
1273 // `pick_method` may be called twice for the same self_ty if no stable methods
1274 // match. Only extend once.
1275 if unstable_candidates.is_some() {
1276 self.unsatisfied_predicates.borrow_mut().extend(possibly_unsatisfied_predicates);
1281 fn consider_candidates(
1284 candidates: &[Candidate<'tcx>],
1285 possibly_unsatisfied_predicates: &mut Vec<(
1286 ty::Predicate<'tcx>,
1287 Option<ty::Predicate<'tcx>>,
1288 Option<ObligationCause<'tcx>>,
1290 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1291 ) -> Option<PickResult<'tcx>> {
1292 let mut applicable_candidates: Vec<_> = candidates
1295 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
1297 .filter(|&(_, status)| status != ProbeResult::NoMatch)
1300 debug!("applicable_candidates: {:?}", applicable_candidates);
1302 if applicable_candidates.len() > 1 {
1304 self.collapse_candidates_to_trait_pick(self_ty, &applicable_candidates)
1306 return Some(Ok(pick));
1310 if let Some(uc) = &mut unstable_candidates {
1311 applicable_candidates.retain(|&(candidate, _)| {
1312 if let stability::EvalResult::Deny { feature, .. } =
1313 self.tcx.eval_stability(candidate.item.def_id, None, self.span, None)
1315 uc.push((candidate.clone(), feature));
1322 if applicable_candidates.len() > 1 {
1323 let sources = candidates.iter().map(|p| self.candidate_source(p, self_ty)).collect();
1324 return Some(Err(MethodError::Ambiguity(sources)));
1327 applicable_candidates.pop().map(|(probe, status)| {
1328 if status == ProbeResult::Match {
1330 .to_unadjusted_pick(self_ty, unstable_candidates.cloned().unwrap_or_default()))
1332 Err(MethodError::BadReturnType)
1338 impl<'tcx> Pick<'tcx> {
1339 /// In case there were unstable name collisions, emit them as a lint.
1340 /// Checks whether two picks do not refer to the same trait item for the same `Self` type.
1341 /// Only useful for comparisons of picks in order to improve diagnostics.
1342 /// Do not use for type checking.
1343 pub fn differs_from(&self, other: &Self) -> bool {
1351 trait_item_def_id: _,
1352 fn_has_self_parameter: _,
1357 autoref_or_ptr_adjustment: _,
1359 unstable_candidates: _,
1361 self_ty != other.self_ty || def_id != other.item.def_id
1364 /// In case there were unstable name collisions, emit them as a lint.
1365 pub fn maybe_emit_unstable_name_collision_hint(
1369 scope_expr_id: hir::HirId,
1371 if self.unstable_candidates.is_empty() {
1374 let def_kind = self.item.kind.as_def_kind();
1375 tcx.struct_span_lint_hir(
1376 lint::builtin::UNSTABLE_NAME_COLLISIONS,
1380 "{} {} with this name may be added to the standard library in the future",
1382 def_kind.descr(self.item.def_id),
1385 match (self.item.kind, self.item.container) {
1386 (ty::AssocKind::Fn, _) => {
1387 // FIXME: This should be a `span_suggestion` instead of `help`
1388 // However `self.span` only
1389 // highlights the method name, so we can't use it. Also consider reusing
1390 // the code from `report_method_error()`.
1392 "call with fully qualified syntax `{}(...)` to keep using the current \
1394 tcx.def_path_str(self.item.def_id),
1397 (ty::AssocKind::Const, ty::AssocItemContainer::TraitContainer) => {
1398 let def_id = self.item.container_id(tcx);
1399 lint.span_suggestion(
1401 "use the fully qualified path to the associated const",
1405 tcx.def_path_str(def_id),
1408 Applicability::MachineApplicable,
1413 if tcx.sess.is_nightly_build() {
1414 for (candidate, feature) in &self.unstable_candidates {
1416 "add `#![feature({})]` to the crate attributes to enable `{}`",
1418 tcx.def_path_str(candidate.item.def_id),
1429 impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
1430 fn select_trait_candidate(
1432 trait_ref: ty::TraitRef<'tcx>,
1433 ) -> traits::SelectionResult<'tcx, traits::Selection<'tcx>> {
1434 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1435 let predicate = ty::Binder::dummy(trait_ref);
1436 let obligation = traits::Obligation::new(self.tcx, cause, self.param_env, predicate);
1437 traits::SelectionContext::new(self).select(&obligation)
1440 fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>) -> CandidateSource {
1441 match candidate.kind {
1442 InherentImplCandidate(..) => {
1443 CandidateSource::Impl(candidate.item.container_id(self.tcx))
1445 ObjectCandidate | WhereClauseCandidate(_) => {
1446 CandidateSource::Trait(candidate.item.container_id(self.tcx))
1448 TraitCandidate(trait_ref) => self.probe(|_| {
1450 .at(&ObligationCause::dummy(), self.param_env)
1451 .define_opaque_types(false)
1452 .sup(candidate.xform_self_ty, self_ty);
1453 match self.select_trait_candidate(trait_ref) {
1454 Ok(Some(traits::ImplSource::UserDefined(ref impl_data))) => {
1455 // If only a single impl matches, make the error message point
1457 CandidateSource::Impl(impl_data.impl_def_id)
1459 _ => CandidateSource::Trait(candidate.item.container_id(self.tcx)),
1468 probe: &Candidate<'tcx>,
1469 possibly_unsatisfied_predicates: &mut Vec<(
1470 ty::Predicate<'tcx>,
1471 Option<ty::Predicate<'tcx>>,
1472 Option<ObligationCause<'tcx>>,
1475 debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe);
1478 // First check that the self type can be related.
1479 let sub_obligations = match self
1480 .at(&ObligationCause::dummy(), self.param_env)
1481 .define_opaque_types(false)
1482 .sup(probe.xform_self_ty, self_ty)
1484 Ok(InferOk { obligations, value: () }) => obligations,
1486 debug!("--> cannot relate self-types {:?}", err);
1487 return ProbeResult::NoMatch;
1491 let mut result = ProbeResult::Match;
1492 let mut xform_ret_ty = probe.xform_ret_ty;
1493 debug!(?xform_ret_ty);
1495 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1497 let mut parent_pred = None;
1499 // If so, impls may carry other conditions (e.g., where
1500 // clauses) that must be considered. Make sure that those
1501 // match as well (or at least may match, sometimes we
1502 // don't have enough information to fully evaluate).
1504 InherentImplCandidate(ref substs, ref ref_obligations) => {
1505 // `xform_ret_ty` hasn't been normalized yet, only `xform_self_ty`,
1506 // see the reasons mentioned in the comments in `assemble_inherent_impl_probe`
1507 // for why this is necessary
1509 value: normalized_xform_ret_ty,
1510 obligations: normalization_obligations,
1511 } = self.fcx.at(&cause, self.param_env).normalize(probe.xform_ret_ty);
1512 xform_ret_ty = normalized_xform_ret_ty;
1513 debug!("xform_ret_ty after normalization: {:?}", xform_ret_ty);
1515 // Check whether the impl imposes obligations we have to worry about.
1516 let impl_def_id = probe.item.container_id(self.tcx);
1517 let impl_bounds = self.tcx.predicates_of(impl_def_id);
1518 let impl_bounds = impl_bounds.instantiate(self.tcx, substs);
1520 let InferOk { value: impl_bounds, obligations: norm_obligations } =
1521 self.fcx.at(&cause, self.param_env).normalize(impl_bounds);
1523 // Convert the bounds into obligations.
1524 let impl_obligations = traits::predicates_for_generics(
1525 move |_, _| cause.clone(),
1530 let candidate_obligations = impl_obligations
1531 .chain(norm_obligations.into_iter())
1532 .chain(ref_obligations.iter().cloned())
1533 .chain(normalization_obligations.into_iter());
1535 // Evaluate those obligations to see if they might possibly hold.
1536 for o in candidate_obligations {
1537 let o = self.resolve_vars_if_possible(o);
1538 if !self.predicate_may_hold(&o) {
1539 result = ProbeResult::NoMatch;
1540 possibly_unsatisfied_predicates.push((
1549 ObjectCandidate | WhereClauseCandidate(..) => {
1550 // These have no additional conditions to check.
1553 TraitCandidate(trait_ref) => {
1554 if let Some(method_name) = self.method_name {
1555 // Some trait methods are excluded for arrays before 2021.
1556 // (`array.into_iter()` wants a slice iterator for compatibility.)
1557 if self_ty.is_array() && !method_name.span.rust_2021() {
1558 let trait_def = self.tcx.trait_def(trait_ref.def_id);
1559 if trait_def.skip_array_during_method_dispatch {
1560 return ProbeResult::NoMatch;
1565 ty::Binder::dummy(trait_ref).without_const().to_predicate(self.tcx);
1566 parent_pred = Some(predicate);
1568 traits::Obligation::new(self.tcx, cause, self.param_env, predicate);
1569 if !self.predicate_may_hold(&obligation) {
1570 result = ProbeResult::NoMatch;
1572 match self.select_trait_candidate(trait_ref) {
1573 Err(_) => return true,
1574 Ok(Some(impl_source))
1575 if !impl_source.borrow_nested_obligations().is_empty() =>
1577 for obligation in impl_source.borrow_nested_obligations() {
1578 // Determine exactly which obligation wasn't met, so
1579 // that we can give more context in the error.
1580 if !self.predicate_may_hold(obligation) {
1581 let nested_predicate =
1582 self.resolve_vars_if_possible(obligation.predicate);
1584 self.resolve_vars_if_possible(predicate);
1585 let p = if predicate == nested_predicate {
1586 // Avoid "`MyStruct: Foo` which is required by
1587 // `MyStruct: Foo`" in E0599.
1592 possibly_unsatisfied_predicates.push((
1595 Some(obligation.cause.clone()),
1601 // Some nested subobligation of this predicate
1603 let predicate = self.resolve_vars_if_possible(predicate);
1604 possibly_unsatisfied_predicates.push((predicate, None, None));
1609 // This candidate's primary obligation doesn't even
1610 // select - don't bother registering anything in
1611 // `potentially_unsatisfied_predicates`.
1612 return ProbeResult::NoMatch;
1618 // Evaluate those obligations to see if they might possibly hold.
1619 for o in sub_obligations {
1620 let o = self.resolve_vars_if_possible(o);
1621 if !self.predicate_may_hold(&o) {
1622 result = ProbeResult::NoMatch;
1623 possibly_unsatisfied_predicates.push((o.predicate, parent_pred, Some(o.cause)));
1627 if let ProbeResult::Match = result {
1628 if let (Some(return_ty), Some(xform_ret_ty)) = (self.return_type, xform_ret_ty) {
1629 let xform_ret_ty = self.resolve_vars_if_possible(xform_ret_ty);
1631 "comparing return_ty {:?} with xform ret ty {:?}",
1632 return_ty, probe.xform_ret_ty
1635 .at(&ObligationCause::dummy(), self.param_env)
1636 .define_opaque_types(false)
1637 .sup(return_ty, xform_ret_ty)
1640 return ProbeResult::BadReturnType;
1649 /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1650 /// same trait, but we don't know which impl to use. In this case, since in all cases the
1651 /// external interface of the method can be determined from the trait, it's ok not to decide.
1652 /// We can basically just collapse all of the probes for various impls into one where-clause
1653 /// probe. This will result in a pending obligation so when more type-info is available we can
1654 /// make the final decision.
1656 /// Example (`src/test/ui/method-two-trait-defer-resolution-1.rs`):
1658 /// ```ignore (illustrative)
1659 /// trait Foo { ... }
1660 /// impl Foo for Vec<i32> { ... }
1661 /// impl Foo for Vec<usize> { ... }
1664 /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1665 /// use, so it's ok to just commit to "using the method from the trait Foo".
1666 fn collapse_candidates_to_trait_pick(
1669 probes: &[(&Candidate<'tcx>, ProbeResult)],
1670 ) -> Option<Pick<'tcx>> {
1671 // Do all probes correspond to the same trait?
1672 let container = probes[0].0.item.trait_container(self.tcx)?;
1673 for (p, _) in &probes[1..] {
1674 let p_container = p.item.trait_container(self.tcx)?;
1675 if p_container != container {
1680 // FIXME: check the return type here somehow.
1681 // If so, just use this trait and call it a day.
1683 item: probes[0].0.item,
1685 import_ids: probes[0].0.import_ids.clone(),
1687 autoref_or_ptr_adjustment: None,
1689 unstable_candidates: vec![],
1693 /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
1694 /// candidate method where the method name may have been misspelled. Similarly to other
1695 /// Levenshtein based suggestions, we provide at most one such suggestion.
1696 fn probe_for_lev_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
1697 debug!("probing for method names similar to {:?}", self.method_name);
1699 let steps = self.steps.clone();
1701 let mut pcx = ProbeContext::new(
1707 &self.orig_steps_var_values,
1711 pcx.allow_similar_names = true;
1712 pcx.assemble_inherent_candidates();
1714 let method_names = pcx.candidate_method_names(|_| true);
1715 pcx.allow_similar_names = false;
1716 let applicable_close_candidates: Vec<ty::AssocItem> = method_names
1718 .filter_map(|&method_name| {
1720 pcx.method_name = Some(method_name);
1721 pcx.assemble_inherent_candidates();
1722 pcx.pick_core().and_then(|pick| pick.ok()).map(|pick| pick.item)
1726 if applicable_close_candidates.is_empty() {
1730 let names = applicable_close_candidates
1732 .map(|cand| cand.name)
1733 .collect::<Vec<Symbol>>();
1734 find_best_match_for_name_with_substrings(
1736 self.method_name.unwrap().name,
1741 Ok(applicable_close_candidates.into_iter().find(|method| method.name == best_name))
1746 ///////////////////////////////////////////////////////////////////////////
1748 fn has_applicable_self(&self, item: &ty::AssocItem) -> bool {
1749 // "Fast track" -- check for usage of sugar when in method call
1752 // In Path mode (i.e., resolving a value like `T::next`), consider any
1753 // associated value (i.e., methods, constants) but not types.
1755 Mode::MethodCall => item.fn_has_self_parameter,
1756 Mode::Path => match item.kind {
1757 ty::AssocKind::Type => false,
1758 ty::AssocKind::Fn | ty::AssocKind::Const => true,
1761 // FIXME -- check for types that deref to `Self`,
1762 // like `Rc<Self>` and so on.
1764 // Note also that the current code will break if this type
1765 // includes any of the type parameters defined on the method
1766 // -- but this could be overcome.
1769 fn record_static_candidate(&self, source: CandidateSource) {
1770 self.static_candidates.borrow_mut().push(source);
1773 #[instrument(level = "debug", skip(self))]
1776 item: &ty::AssocItem,
1778 substs: SubstsRef<'tcx>,
1779 ) -> (Ty<'tcx>, Option<Ty<'tcx>>) {
1780 if item.kind == ty::AssocKind::Fn && self.mode == Mode::MethodCall {
1781 let sig = self.xform_method_sig(item.def_id, substs);
1782 (sig.inputs()[0], Some(sig.output()))
1788 #[instrument(level = "debug", skip(self))]
1789 fn xform_method_sig(&self, method: DefId, substs: SubstsRef<'tcx>) -> ty::FnSig<'tcx> {
1790 let fn_sig = self.tcx.bound_fn_sig(method);
1793 assert!(!substs.has_escaping_bound_vars());
1795 // It is possible for type parameters or early-bound lifetimes
1796 // to appear in the signature of `self`. The substitutions we
1797 // are given do not include type/lifetime parameters for the
1798 // method yet. So create fresh variables here for those too,
1799 // if there are any.
1800 let generics = self.tcx.generics_of(method);
1801 assert_eq!(substs.len(), generics.parent_count as usize);
1803 let xform_fn_sig = if generics.params.is_empty() {
1804 fn_sig.subst(self.tcx, substs)
1806 let substs = InternalSubsts::for_item(self.tcx, method, |param, _| {
1807 let i = param.index as usize;
1808 if i < substs.len() {
1812 GenericParamDefKind::Lifetime => {
1813 // In general, during probe we erase regions.
1814 self.tcx.lifetimes.re_erased.into()
1816 GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
1817 self.var_for_def(self.span, param)
1822 fn_sig.subst(self.tcx, substs)
1825 self.erase_late_bound_regions(xform_fn_sig)
1828 /// Gets the type of an impl and generate substitutions with inference vars.
1829 fn impl_ty_and_substs(
1832 ) -> (ty::EarlyBinder<Ty<'tcx>>, SubstsRef<'tcx>) {
1833 (self.tcx.bound_type_of(impl_def_id), self.fresh_item_substs(impl_def_id))
1836 fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx> {
1837 InternalSubsts::for_item(self.tcx, def_id, |param, _| match param.kind {
1838 GenericParamDefKind::Lifetime => self.tcx.lifetimes.re_erased.into(),
1839 GenericParamDefKind::Type { .. } => self
1840 .next_ty_var(TypeVariableOrigin {
1841 kind: TypeVariableOriginKind::SubstitutionPlaceholder,
1842 span: self.tcx.def_span(def_id),
1845 GenericParamDefKind::Const { .. } => {
1846 let span = self.tcx.def_span(def_id);
1847 let origin = ConstVariableOrigin {
1848 kind: ConstVariableOriginKind::SubstitutionPlaceholder,
1851 self.next_const_var(self.tcx.type_of(param.def_id), origin).into()
1856 /// Replaces late-bound-regions bound by `value` with `'static` using
1857 /// `ty::erase_late_bound_regions`.
1859 /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1860 /// method matching. It is reasonable during the probe phase because we don't consider region
1861 /// relationships at all. Therefore, we can just replace all the region variables with 'static
1862 /// rather than creating fresh region variables. This is nice for two reasons:
1864 /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1865 /// particular method call, it winds up creating fewer types overall, which helps for memory
1866 /// usage. (Admittedly, this is a rather small effect, though measurable.)
1868 /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1869 /// late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1870 /// regions with actual region variables as is proper, we'd have to ensure that the same
1871 /// region got replaced with the same variable, which requires a bit more coordination
1872 /// and/or tracking the substitution and
1874 fn erase_late_bound_regions<T>(&self, value: ty::Binder<'tcx, T>) -> T
1876 T: TypeFoldable<'tcx>,
1878 self.tcx.erase_late_bound_regions(value)
1881 /// Determine if the given associated item type is relevant in the current context.
1882 fn is_relevant_kind_for_mode(&self, kind: ty::AssocKind) -> bool {
1883 match (self.mode, kind) {
1884 (Mode::MethodCall, ty::AssocKind::Fn) => true,
1885 (Mode::Path, ty::AssocKind::Const | ty::AssocKind::Fn) => true,
1890 /// Finds the method with the appropriate name (or return type, as the case may be). If
1891 /// `allow_similar_names` is set, find methods with close-matching names.
1892 // The length of the returned iterator is nearly always 0 or 1 and this
1893 // method is fairly hot.
1894 fn impl_or_trait_item(&self, def_id: DefId) -> SmallVec<[ty::AssocItem; 1]> {
1895 if let Some(name) = self.method_name {
1896 if self.allow_similar_names {
1897 let max_dist = max(name.as_str().len(), 3) / 3;
1899 .associated_items(def_id)
1900 .in_definition_order()
1902 if !self.is_relevant_kind_for_mode(x.kind) {
1905 match lev_distance_with_substrings(name.as_str(), x.name.as_str(), max_dist)
1915 .associated_value(def_id, name)
1916 .filter(|x| self.is_relevant_kind_for_mode(x.kind))
1917 .map_or_else(SmallVec::new, |x| SmallVec::from_buf([x]))
1921 .associated_items(def_id)
1922 .in_definition_order()
1923 .filter(|x| self.is_relevant_kind_for_mode(x.kind))
1930 impl<'tcx> Candidate<'tcx> {
1931 fn to_unadjusted_pick(
1934 unstable_candidates: Vec<(Candidate<'tcx>, Symbol)>,
1938 kind: match self.kind {
1939 InherentImplCandidate(..) => InherentImplPick,
1940 ObjectCandidate => ObjectPick,
1941 TraitCandidate(_) => TraitPick,
1942 WhereClauseCandidate(ref trait_ref) => {
1943 // Only trait derived from where-clauses should
1944 // appear here, so they should not contain any
1945 // inference variables or other artifacts. This
1946 // means they are safe to put into the
1947 // `WhereClausePick`.
1949 !trait_ref.skip_binder().substs.needs_infer()
1950 && !trait_ref.skip_binder().substs.has_placeholders()
1953 WhereClausePick(*trait_ref)
1956 import_ids: self.import_ids.clone(),
1958 autoref_or_ptr_adjustment: None,
1960 unstable_candidates,