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};
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::Ident, Span, Symbol, DUMMY_SP};
31 use rustc_trait_selection::autoderef::{self, Autoderef};
32 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
33 use rustc_trait_selection::traits::query::method_autoderef::MethodAutoderefBadTy;
34 use rustc_trait_selection::traits::query::method_autoderef::{
35 CandidateStep, MethodAutoderefStepsResult,
37 use rustc_trait_selection::traits::query::CanonicalTyGoal;
38 use rustc_trait_selection::traits::{self, ObligationCause};
44 use smallvec::{smallvec, SmallVec};
46 use self::CandidateKind::*;
47 pub use self::PickKind::*;
49 /// Boolean flag used to indicate if this search is for a suggestion
50 /// or not. If true, we can allow ambiguity and so forth.
51 #[derive(Clone, Copy, Debug)]
52 pub struct IsSuggestion(pub bool);
54 struct ProbeContext<'a, 'tcx> {
55 fcx: &'a FnCtxt<'a, 'tcx>,
58 method_name: Option<Ident>,
59 return_type: Option<Ty<'tcx>>,
61 /// This is the OriginalQueryValues for the steps queries
62 /// that are answered in steps.
63 orig_steps_var_values: OriginalQueryValues<'tcx>,
64 steps: &'tcx [CandidateStep<'tcx>],
66 inherent_candidates: Vec<Candidate<'tcx>>,
67 extension_candidates: Vec<Candidate<'tcx>>,
68 impl_dups: FxHashSet<DefId>,
70 /// Collects near misses when the candidate functions are missing a `self` keyword and is only
71 /// used for error reporting
72 static_candidates: Vec<CandidateSource>,
74 /// When probing for names, include names that are close to the
75 /// requested name (by Levensthein distance)
76 allow_similar_names: bool,
78 /// Some(candidate) if there is a private candidate
79 private_candidate: Option<(DefKind, DefId)>,
81 /// Collects near misses when trait bounds for type parameters are unsatisfied and is only used
82 /// for error reporting
83 unsatisfied_predicates:
84 Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>, Option<ObligationCause<'tcx>>)>,
86 is_suggestion: IsSuggestion,
88 scope_expr_id: hir::HirId,
91 impl<'a, 'tcx> Deref for ProbeContext<'a, 'tcx> {
92 type Target = FnCtxt<'a, 'tcx>;
93 fn deref(&self) -> &Self::Target {
98 #[derive(Debug, Clone)]
99 struct Candidate<'tcx> {
100 // Candidates are (I'm not quite sure, but they are mostly) basically
101 // some metadata on top of a `ty::AssocItem` (without substs).
103 // However, method probing wants to be able to evaluate the predicates
104 // for a function with the substs applied - for example, if a function
105 // has `where Self: Sized`, we don't want to consider it unless `Self`
106 // is actually `Sized`, and similarly, return-type suggestions want
107 // to consider the "actual" return type.
109 // The way this is handled is through `xform_self_ty`. It contains
110 // the receiver type of this candidate, but `xform_self_ty`,
111 // `xform_ret_ty` and `kind` (which contains the predicates) have the
112 // generic parameters of this candidate substituted with the *same set*
113 // of inference variables, which acts as some weird sort of "query".
115 // When we check out a candidate, we require `xform_self_ty` to be
116 // a subtype of the passed-in self-type, and this equates the type
117 // variables in the rest of the fields.
119 // For example, if we have this candidate:
122 // fn foo(&self) where Self: Sized;
126 // Then `xform_self_ty` will be `&'erased ?X` and `kind` will contain
127 // the predicate `?X: Sized`, so if we are evaluating `Foo` for a
128 // the receiver `&T`, we'll do the subtyping which will make `?X`
129 // get the right value, then when we evaluate the predicate we'll check
131 xform_self_ty: Ty<'tcx>,
132 xform_ret_ty: Option<Ty<'tcx>>,
134 kind: CandidateKind<'tcx>,
135 import_ids: SmallVec<[LocalDefId; 1]>,
138 #[derive(Debug, Clone)]
139 enum CandidateKind<'tcx> {
140 InherentImplCandidate(
142 // Normalize obligations
143 Vec<traits::PredicateObligation<'tcx>>,
146 TraitCandidate(ty::TraitRef<'tcx>),
147 WhereClauseCandidate(
149 ty::PolyTraitRef<'tcx>,
153 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
160 /// When adjusting a receiver we often want to do one of
162 /// - Add a `&` (or `&mut`), converting the receiver from `T` to `&T` (or `&mut T`)
163 /// - If the receiver has type `*mut T`, convert it to `*const T`
165 /// This type tells us which one to do.
167 /// Note that in principle we could do both at the same time. For example, when the receiver has
168 /// type `T`, we could autoref it to `&T`, then convert to `*const T`. Or, when it has type `*mut
169 /// T`, we could convert it to `*const T`, then autoref to `&*const T`. However, currently we do
170 /// (at most) one of these. Either the receiver has type `T` and we convert it to `&T` (or with
171 /// `mut`), or it has type `*mut T` and we convert it to `*const T`.
172 #[derive(Debug, PartialEq, Copy, Clone)]
173 pub enum AutorefOrPtrAdjustment {
174 /// Receiver has type `T`, add `&` or `&mut` (it `T` is `mut`), and maybe also "unsize" it.
175 /// Unsizing is used to convert a `[T; N]` to `[T]`, which only makes sense when autorefing.
177 mutbl: hir::Mutability,
179 /// Indicates that the source expression should be "unsized" to a target type.
180 /// This is special-cased for just arrays unsizing to slices.
183 /// Receiver has type `*mut T`, convert to `*const T`
187 impl AutorefOrPtrAdjustment {
188 fn get_unsize(&self) -> bool {
190 AutorefOrPtrAdjustment::Autoref { mutbl: _, unsize } => *unsize,
191 AutorefOrPtrAdjustment::ToConstPtr => false,
196 #[derive(Debug, PartialEq, Clone)]
197 pub struct Pick<'tcx> {
198 pub item: ty::AssocItem,
199 pub kind: PickKind<'tcx>,
200 pub import_ids: SmallVec<[LocalDefId; 1]>,
202 /// Indicates that the source expression should be autoderef'd N times
203 /// ```ignore (not-rust)
204 /// A = expr | *expr | **expr | ...
206 pub autoderefs: usize,
208 /// Indicates that we want to add an autoref (and maybe also unsize it), or if the receiver is
209 /// `*mut T`, convert it to `*const T`.
210 pub autoref_or_ptr_adjustment: Option<AutorefOrPtrAdjustment>,
211 pub self_ty: Ty<'tcx>,
214 #[derive(Clone, Debug, PartialEq, Eq)]
215 pub enum PickKind<'tcx> {
221 ty::PolyTraitRef<'tcx>,
225 pub type PickResult<'tcx> = Result<Pick<'tcx>, MethodError<'tcx>>;
227 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
229 // An expression of the form `receiver.method_name(...)`.
230 // Autoderefs are performed on `receiver`, lookup is done based on the
231 // `self` argument of the method, and static methods aren't considered.
233 // An expression of the form `Type::item` or `<T>::item`.
234 // No autoderefs are performed, lookup is done based on the type each
235 // implementation is for, and static methods are included.
239 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
240 pub enum ProbeScope {
241 // Assemble candidates coming only from traits in scope.
244 // Assemble candidates coming from all traits.
248 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
249 /// This is used to offer suggestions to users. It returns methods
250 /// that could have been called which have the desired return
251 /// type. Some effort is made to rule out methods that, if called,
252 /// would result in an error (basically, the same criteria we
253 /// would use to decide if a method is a plausible fit for
254 /// ambiguity purposes).
255 #[instrument(level = "debug", skip(self, scope_expr_id))]
256 pub fn probe_for_return_type(
260 return_type: Ty<'tcx>,
262 scope_expr_id: hir::HirId,
263 ) -> Vec<ty::AssocItem> {
265 "probe(self_ty={:?}, return_type={}, scope_expr_id={})",
266 self_ty, return_type, scope_expr_id
268 let method_names = self
277 ProbeScope::AllTraits,
278 |probe_cx| Ok(probe_cx.candidate_method_names()),
280 .unwrap_or_default();
283 .flat_map(|&method_name| {
292 ProbeScope::AllTraits,
293 |probe_cx| probe_cx.pick(),
296 .map(|pick| pick.item)
301 #[instrument(level = "debug", skip(self, scope_expr_id))]
302 pub fn probe_for_name(
307 is_suggestion: IsSuggestion,
309 scope_expr_id: hir::HirId,
311 ) -> PickResult<'tcx> {
313 "probe(self_ty={:?}, item_name={}, scope_expr_id={})",
314 self_ty, item_name, scope_expr_id
325 |probe_cx| probe_cx.pick(),
333 method_name: Option<Ident>,
334 return_type: Option<Ty<'tcx>>,
335 is_suggestion: IsSuggestion,
337 scope_expr_id: hir::HirId,
340 ) -> Result<R, MethodError<'tcx>>
342 OP: FnOnce(ProbeContext<'a, 'tcx>) -> Result<R, MethodError<'tcx>>,
344 let mut orig_values = OriginalQueryValues::default();
345 let param_env_and_self_ty = self.infcx.canonicalize_query(
346 ParamEnvAnd { param_env: self.param_env, value: self_ty },
350 let steps = if mode == Mode::MethodCall {
351 self.tcx.method_autoderef_steps(param_env_and_self_ty)
353 self.infcx.probe(|_| {
354 // Mode::Path - the deref steps is "trivial". This turns
355 // our CanonicalQuery into a "trivial" QueryResponse. This
356 // is a bit inefficient, but I don't think that writing
357 // special handling for this "trivial case" is a good idea.
359 let infcx = &self.infcx;
360 let (ParamEnvAnd { param_env: _, value: self_ty }, canonical_inference_vars) =
361 infcx.instantiate_canonical_with_fresh_inference_vars(
363 ¶m_env_and_self_ty,
366 "probe_op: Mode::Path, param_env_and_self_ty={:?} self_ty={:?}",
367 param_env_and_self_ty, self_ty
369 MethodAutoderefStepsResult {
370 steps: infcx.tcx.arena.alloc_from_iter([CandidateStep {
371 self_ty: self.make_query_response_ignoring_pending_obligations(
372 canonical_inference_vars,
376 from_unsafe_deref: false,
380 reached_recursion_limit: false,
385 // If our autoderef loop had reached the recursion limit,
386 // report an overflow error, but continue going on with
387 // the truncated autoderef list.
388 if steps.reached_recursion_limit {
393 .unwrap_or_else(|| span_bug!(span, "reached the recursion limit in 0 steps?"))
396 .probe_instantiate_query_response(span, &orig_values, ty)
397 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
398 autoderef::report_autoderef_recursion_limit_error(self.tcx, span, ty.value);
402 // If we encountered an `_` type or an error type during autoderef, this is
404 if let Some(bad_ty) = &steps.opt_bad_ty {
406 // Ambiguity was encountered during a suggestion. Just keep going.
407 debug!("ProbeContext: encountered ambiguity in suggestion");
408 } else if bad_ty.reached_raw_pointer && !self.tcx.features().arbitrary_self_types {
409 // this case used to be allowed by the compiler,
410 // so we do a future-compat lint here for the 2015 edition
411 // (see https://github.com/rust-lang/rust/issues/46906)
412 if self.tcx.sess.rust_2018() {
413 self.tcx.sess.emit_err(MethodCallOnUnknownType { span });
415 self.tcx.struct_span_lint_hir(
416 lint::builtin::TYVAR_BEHIND_RAW_POINTER,
420 lint.build("type annotations needed").emit();
425 // Encountered a real ambiguity, so abort the lookup. If `ty` is not
426 // an `Err`, report the right "type annotations needed" error pointing
430 .probe_instantiate_query_response(span, &orig_values, ty)
431 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
432 let ty = self.structurally_resolved_type(span, ty.value);
433 assert!(matches!(ty.kind(), ty::Error(_)));
434 return Err(MethodError::NoMatch(NoMatchData {
435 static_candidates: Vec::new(),
436 unsatisfied_predicates: Vec::new(),
437 out_of_scope_traits: Vec::new(),
444 debug!("ProbeContext: steps for self_ty={:?} are {:?}", self_ty, steps);
446 // this creates one big transaction so that all type variables etc
447 // that we create during the probe process are removed later
449 let mut probe_cx = ProbeContext::new(
461 probe_cx.assemble_inherent_candidates();
463 ProbeScope::TraitsInScope => {
464 probe_cx.assemble_extension_candidates_for_traits_in_scope(scope_expr_id)
466 ProbeScope::AllTraits => probe_cx.assemble_extension_candidates_for_all_traits(),
473 pub fn provide(providers: &mut ty::query::Providers) {
474 providers.method_autoderef_steps = method_autoderef_steps;
477 fn method_autoderef_steps<'tcx>(
479 goal: CanonicalTyGoal<'tcx>,
480 ) -> MethodAutoderefStepsResult<'tcx> {
481 debug!("method_autoderef_steps({:?})", goal);
483 tcx.infer_ctxt().enter_with_canonical(DUMMY_SP, &goal, |ref infcx, goal, inference_vars| {
484 let ParamEnvAnd { param_env, value: self_ty } = goal;
487 Autoderef::new(infcx, param_env, hir::CRATE_HIR_ID, DUMMY_SP, self_ty, DUMMY_SP)
488 .include_raw_pointers()
490 let mut reached_raw_pointer = false;
491 let mut steps: Vec<_> = autoderef
494 let step = CandidateStep {
495 self_ty: infcx.make_query_response_ignoring_pending_obligations(
496 inference_vars.clone(),
500 from_unsafe_deref: reached_raw_pointer,
503 if let ty::RawPtr(_) = ty.kind() {
504 // all the subsequent steps will be from_unsafe_deref
505 reached_raw_pointer = true;
511 let final_ty = autoderef.final_ty(true);
512 let opt_bad_ty = match final_ty.kind() {
513 ty::Infer(ty::TyVar(_)) | ty::Error(_) => Some(MethodAutoderefBadTy {
516 .make_query_response_ignoring_pending_obligations(inference_vars, final_ty),
518 ty::Array(elem_ty, _) => {
519 let dereferences = steps.len() - 1;
521 steps.push(CandidateStep {
522 self_ty: infcx.make_query_response_ignoring_pending_obligations(
524 infcx.tcx.mk_slice(*elem_ty),
526 autoderefs: dereferences,
527 // this could be from an unsafe deref if we had
528 // a *mut/const [T; N]
529 from_unsafe_deref: reached_raw_pointer,
538 debug!("method_autoderef_steps: steps={:?} opt_bad_ty={:?}", steps, opt_bad_ty);
540 MethodAutoderefStepsResult {
541 steps: tcx.arena.alloc_from_iter(steps),
542 opt_bad_ty: opt_bad_ty.map(|ty| &*tcx.arena.alloc(ty)),
543 reached_recursion_limit: autoderef.reached_recursion_limit(),
548 impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
550 fcx: &'a FnCtxt<'a, 'tcx>,
553 method_name: Option<Ident>,
554 return_type: Option<Ty<'tcx>>,
555 orig_steps_var_values: OriginalQueryValues<'tcx>,
556 steps: &'tcx [CandidateStep<'tcx>],
557 is_suggestion: IsSuggestion,
558 scope_expr_id: hir::HirId,
559 ) -> ProbeContext<'a, 'tcx> {
566 inherent_candidates: Vec::new(),
567 extension_candidates: Vec::new(),
568 impl_dups: FxHashSet::default(),
569 orig_steps_var_values,
571 static_candidates: Vec::new(),
572 allow_similar_names: false,
573 private_candidate: None,
574 unsatisfied_predicates: Vec::new(),
580 fn reset(&mut self) {
581 self.inherent_candidates.clear();
582 self.extension_candidates.clear();
583 self.impl_dups.clear();
584 self.static_candidates.clear();
585 self.private_candidate = None;
588 ///////////////////////////////////////////////////////////////////////////
589 // CANDIDATE ASSEMBLY
591 fn push_candidate(&mut self, candidate: Candidate<'tcx>, is_inherent: bool) {
592 let is_accessible = if let Some(name) = self.method_name {
593 let item = candidate.item;
595 self.tcx.adjust_ident_and_get_scope(name, item.container.id(), self.body_id).1;
596 item.vis.is_accessible_from(def_scope, self.tcx)
602 self.inherent_candidates.push(candidate);
604 self.extension_candidates.push(candidate);
606 } else if self.private_candidate.is_none() {
607 self.private_candidate =
608 Some((candidate.item.kind.as_def_kind(), candidate.item.def_id));
612 fn assemble_inherent_candidates(&mut self) {
613 for step in self.steps.iter() {
614 self.assemble_probe(&step.self_ty);
618 fn assemble_probe(&mut self, self_ty: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>) {
619 debug!("assemble_probe: self_ty={:?}", self_ty);
620 let raw_self_ty = self_ty.value.value;
621 match *raw_self_ty.kind() {
622 ty::Dynamic(data, ..) if let Some(p) = data.principal() => {
623 // Subtle: we can't use `instantiate_query_response` here: using it will
624 // commit to all of the type equalities assumed by inference going through
625 // autoderef (see the `method-probe-no-guessing` test).
627 // However, in this code, it is OK if we end up with an object type that is
628 // "more general" than the object type that we are evaluating. For *every*
629 // object type `MY_OBJECT`, a function call that goes through a trait-ref
630 // of the form `<MY_OBJECT as SuperTraitOf(MY_OBJECT)>::func` is a valid
631 // `ObjectCandidate`, and it should be discoverable "exactly" through one
632 // of the iterations in the autoderef loop, so there is no problem with it
633 // being discoverable in another one of these iterations.
635 // Using `instantiate_canonical_with_fresh_inference_vars` on our
636 // `Canonical<QueryResponse<Ty<'tcx>>>` and then *throwing away* the
637 // `CanonicalVarValues` will exactly give us such a generalization - it
638 // will still match the original object type, but it won't pollute our
639 // type variables in any form, so just do that!
640 let (QueryResponse { value: generalized_self_ty, .. }, _ignored_var_values) =
642 .instantiate_canonical_with_fresh_inference_vars(self.span, self_ty);
644 self.assemble_inherent_candidates_from_object(generalized_self_ty);
645 self.assemble_inherent_impl_candidates_for_type(p.def_id());
648 let def_id = def.did();
649 self.assemble_inherent_impl_candidates_for_type(def_id);
650 if Some(def_id) == self.tcx.lang_items().c_str() {
651 self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
654 ty::Foreign(did) => {
655 self.assemble_inherent_impl_candidates_for_type(did);
658 self.assemble_inherent_candidates_from_param(p);
671 | ty::Tuple(..) => self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty),
676 fn assemble_inherent_candidates_for_incoherent_ty(&mut self, self_ty: Ty<'tcx>) {
677 let Some(simp) = simplify_type(self.tcx, self_ty, TreatParams::AsPlaceholders) else {
678 bug!("unexpected incoherent type: {:?}", self_ty)
680 for &impl_def_id in self.tcx.incoherent_impls(simp) {
681 self.assemble_inherent_impl_probe(impl_def_id);
685 fn assemble_inherent_impl_candidates_for_type(&mut self, def_id: DefId) {
686 let impl_def_ids = self.tcx.at(self.span).inherent_impls(def_id);
687 for &impl_def_id in impl_def_ids.iter() {
688 self.assemble_inherent_impl_probe(impl_def_id);
692 fn assemble_inherent_impl_probe(&mut self, impl_def_id: DefId) {
693 if !self.impl_dups.insert(impl_def_id) {
694 return; // already visited
697 debug!("assemble_inherent_impl_probe {:?}", impl_def_id);
699 for item in self.impl_or_trait_item(impl_def_id) {
700 if !self.has_applicable_self(&item) {
701 // No receiver declared. Not a candidate.
702 self.record_static_candidate(CandidateSource::Impl(impl_def_id));
706 let (impl_ty, impl_substs) = self.impl_ty_and_substs(impl_def_id);
707 let impl_ty = impl_ty.subst(self.tcx, impl_substs);
709 debug!("impl_ty: {:?}", impl_ty);
711 // Determine the receiver type that the method itself expects.
712 let (xform_self_ty, xform_ret_ty) = self.xform_self_ty(&item, impl_ty, impl_substs);
713 debug!("xform_self_ty: {:?}, xform_ret_ty: {:?}", xform_self_ty, xform_ret_ty);
715 // We can't use normalize_associated_types_in as it will pollute the
716 // fcx's fulfillment context after this probe is over.
717 // Note: we only normalize `xform_self_ty` here since the normalization
718 // of the return type can lead to inference results that prohibit
719 // valid candidates from being found, see issue #85671
720 // FIXME Postponing the normalization of the return type likely only hides a deeper bug,
721 // which might be caused by the `param_env` itself. The clauses of the `param_env`
722 // maybe shouldn't include `Param`s, but rather fresh variables or be canonicalized,
724 let cause = traits::ObligationCause::misc(self.span, self.body_id);
725 let selcx = &mut traits::SelectionContext::new(self.fcx);
726 let traits::Normalized { value: xform_self_ty, obligations } =
727 traits::normalize(selcx, self.param_env, cause, xform_self_ty);
729 "assemble_inherent_impl_probe after normalization: xform_self_ty = {:?}/{:?}",
730 xform_self_ty, xform_ret_ty
738 kind: InherentImplCandidate(impl_substs, obligations),
739 import_ids: smallvec![],
746 fn assemble_inherent_candidates_from_object(&mut self, self_ty: Ty<'tcx>) {
747 debug!("assemble_inherent_candidates_from_object(self_ty={:?})", self_ty);
749 let principal = match self_ty.kind() {
750 ty::Dynamic(ref data, ..) => Some(data),
753 .and_then(|data| data.principal())
757 "non-object {:?} in assemble_inherent_candidates_from_object",
762 // It is illegal to invoke a method on a trait instance that refers to
763 // the `Self` type. An [`ObjectSafetyViolation::SupertraitSelf`] error
764 // will be reported by `object_safety.rs` if the method refers to the
765 // `Self` type anywhere other than the receiver. Here, we use a
766 // substitution that replaces `Self` with the object type itself. Hence,
767 // a `&self` method will wind up with an argument type like `&dyn Trait`.
768 let trait_ref = principal.with_self_ty(self.tcx, self_ty);
769 self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
770 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
772 let (xform_self_ty, xform_ret_ty) =
773 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
779 kind: ObjectCandidate,
780 import_ids: smallvec![],
787 fn assemble_inherent_candidates_from_param(&mut self, param_ty: ty::ParamTy) {
788 // FIXME: do we want to commit to this behavior for param bounds?
789 debug!("assemble_inherent_candidates_from_param(param_ty={:?})", param_ty);
791 let bounds = self.param_env.caller_bounds().iter().filter_map(|predicate| {
792 let bound_predicate = predicate.kind();
793 match bound_predicate.skip_binder() {
794 ty::PredicateKind::Trait(trait_predicate) => {
795 match *trait_predicate.trait_ref.self_ty().kind() {
796 ty::Param(p) if p == param_ty => {
797 Some(bound_predicate.rebind(trait_predicate.trait_ref))
802 ty::PredicateKind::Subtype(..)
803 | ty::PredicateKind::Coerce(..)
804 | ty::PredicateKind::Projection(..)
805 | ty::PredicateKind::RegionOutlives(..)
806 | ty::PredicateKind::WellFormed(..)
807 | ty::PredicateKind::ObjectSafe(..)
808 | ty::PredicateKind::ClosureKind(..)
809 | ty::PredicateKind::TypeOutlives(..)
810 | ty::PredicateKind::ConstEvaluatable(..)
811 | ty::PredicateKind::ConstEquate(..)
812 | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
816 self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
817 let trait_ref = this.erase_late_bound_regions(poly_trait_ref);
819 let (xform_self_ty, xform_ret_ty) =
820 this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs);
822 // Because this trait derives from a where-clause, it
823 // should not contain any inference variables or other
824 // artifacts. This means it is safe to put into the
825 // `WhereClauseCandidate` and (eventually) into the
826 // `WhereClausePick`.
827 assert!(!trait_ref.substs.needs_infer());
834 kind: WhereClauseCandidate(poly_trait_ref),
835 import_ids: smallvec![],
842 // Do a search through a list of bounds, using a callback to actually
843 // create the candidates.
844 fn elaborate_bounds<F>(
846 bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
849 F: for<'b> FnMut(&mut ProbeContext<'b, 'tcx>, ty::PolyTraitRef<'tcx>, ty::AssocItem),
852 for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
853 debug!("elaborate_bounds(bound_trait_ref={:?})", bound_trait_ref);
854 for item in self.impl_or_trait_item(bound_trait_ref.def_id()) {
855 if !self.has_applicable_self(&item) {
856 self.record_static_candidate(CandidateSource::Trait(bound_trait_ref.def_id()));
858 mk_cand(self, bound_trait_ref, item);
864 fn assemble_extension_candidates_for_traits_in_scope(&mut self, expr_hir_id: hir::HirId) {
865 let mut duplicates = FxHashSet::default();
866 let opt_applicable_traits = self.tcx.in_scope_traits(expr_hir_id);
867 if let Some(applicable_traits) = opt_applicable_traits {
868 for trait_candidate in applicable_traits.iter() {
869 let trait_did = trait_candidate.def_id;
870 if duplicates.insert(trait_did) {
871 self.assemble_extension_candidates_for_trait(
872 &trait_candidate.import_ids,
880 fn assemble_extension_candidates_for_all_traits(&mut self) {
881 let mut duplicates = FxHashSet::default();
882 for trait_info in suggest::all_traits(self.tcx) {
883 if duplicates.insert(trait_info.def_id) {
884 self.assemble_extension_candidates_for_trait(&smallvec![], trait_info.def_id);
889 pub fn matches_return_type(
891 method: &ty::AssocItem,
892 self_ty: Option<Ty<'tcx>>,
896 ty::AssocKind::Fn => {
897 let fty = self.tcx.fn_sig(method.def_id);
899 let substs = self.fresh_substs_for_item(self.span, method.def_id);
900 let fty = fty.subst(self.tcx, substs);
902 self.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, fty);
904 if let Some(self_ty) = self_ty {
906 .at(&ObligationCause::dummy(), self.param_env)
907 .sup(fty.inputs()[0], self_ty)
913 self.can_sub(self.param_env, fty.output(), expected).is_ok()
920 fn assemble_extension_candidates_for_trait(
922 import_ids: &SmallVec<[LocalDefId; 1]>,
925 debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})", trait_def_id);
926 let trait_substs = self.fresh_item_substs(trait_def_id);
927 let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
929 if self.tcx.is_trait_alias(trait_def_id) {
930 // For trait aliases, assume all supertraits are relevant.
931 let bounds = iter::once(ty::Binder::dummy(trait_ref));
932 self.elaborate_bounds(bounds, |this, new_trait_ref, item| {
933 let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
935 let (xform_self_ty, xform_ret_ty) =
936 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
942 import_ids: import_ids.clone(),
943 kind: TraitCandidate(new_trait_ref),
949 debug_assert!(self.tcx.is_trait(trait_def_id));
950 for item in self.impl_or_trait_item(trait_def_id) {
951 // Check whether `trait_def_id` defines a method with suitable name.
952 if !self.has_applicable_self(&item) {
953 debug!("method has inapplicable self");
954 self.record_static_candidate(CandidateSource::Trait(trait_def_id));
958 let (xform_self_ty, xform_ret_ty) =
959 self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
965 import_ids: import_ids.clone(),
966 kind: TraitCandidate(trait_ref),
974 fn candidate_method_names(&self) -> Vec<Ident> {
975 let mut set = FxHashSet::default();
976 let mut names: Vec<_> = self
979 .chain(&self.extension_candidates)
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 = mem::take(&mut self.static_candidates);
1009 let private_candidate = self.private_candidate.take();
1010 let unsatisfied_predicates = mem::take(&mut self.unsatisfied_predicates);
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()],
1022 //Some(Ok(p)) => p.iter().map(|p| p.item.container().id()).collect(),
1023 Some(Err(MethodError::Ambiguity(v))) => v
1025 .map(|source| match source {
1026 CandidateSource::Trait(id) => id,
1027 CandidateSource::Impl(impl_id) => match tcx.trait_id_of_impl(impl_id) {
1029 None => span_bug!(span, "found inherent method when looking at traits"),
1033 Some(Err(MethodError::NoMatch(NoMatchData {
1034 out_of_scope_traits: others, ..
1036 assert!(others.is_empty());
1042 if let Some((kind, def_id)) = private_candidate {
1043 return Err(MethodError::PrivateMatch(kind, def_id, out_of_scope_traits));
1045 let lev_candidate = self.probe_for_lev_candidate()?;
1047 Err(MethodError::NoMatch(NoMatchData {
1049 unsatisfied_predicates,
1050 out_of_scope_traits,
1056 fn pick_core(&mut self) -> Option<PickResult<'tcx>> {
1057 let mut unstable_candidates = Vec::new();
1058 let pick = self.pick_all_method(Some(&mut unstable_candidates));
1060 // In this case unstable picking is done by `pick_method`.
1061 if !self.tcx.sess.opts.debugging_opts.pick_stable_methods_before_any_unstable {
1066 // Emit a lint if there are unstable candidates alongside the stable ones.
1068 // We suppress warning if we're picking the method only because it is a
1070 Some(Ok(ref p)) if !self.is_suggestion.0 && !unstable_candidates.is_empty() => {
1071 self.emit_unstable_name_collision_hint(p, &unstable_candidates);
1075 None => self.pick_all_method(None),
1081 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1082 ) -> Option<PickResult<'tcx>> {
1083 let steps = self.steps.clone();
1087 debug!("pick_all_method: step={:?}", step);
1088 // skip types that are from a type error or that would require dereferencing
1090 !step.self_ty.references_error() && !step.from_unsafe_deref
1093 let InferOk { value: self_ty, obligations: _ } = self
1095 .probe_instantiate_query_response(
1097 &self.orig_steps_var_values,
1100 .unwrap_or_else(|_| {
1101 span_bug!(self.span, "{:?} was applicable but now isn't?", step.self_ty)
1103 self.pick_by_value_method(step, self_ty, unstable_candidates.as_deref_mut())
1105 self.pick_autorefd_method(
1108 hir::Mutability::Not,
1109 unstable_candidates.as_deref_mut(),
1112 self.pick_autorefd_method(
1115 hir::Mutability::Mut,
1116 unstable_candidates.as_deref_mut(),
1120 self.pick_const_ptr_method(
1123 unstable_candidates.as_deref_mut(),
1131 /// For each type `T` in the step list, this attempts to find a method where
1132 /// the (transformed) self type is exactly `T`. We do however do one
1133 /// transformation on the adjustment: if we are passing a region pointer in,
1134 /// we will potentially *reborrow* it to a shorter lifetime. This allows us
1135 /// to transparently pass `&mut` pointers, in particular, without consuming
1136 /// them for their entire lifetime.
1137 fn pick_by_value_method(
1139 step: &CandidateStep<'tcx>,
1141 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1142 ) -> Option<PickResult<'tcx>> {
1147 self.pick_method(self_ty, unstable_candidates).map(|r| {
1149 pick.autoderefs = step.autoderefs;
1151 // Insert a `&*` or `&mut *` if this is a reference type:
1152 if let ty::Ref(_, _, mutbl) = *step.self_ty.value.value.kind() {
1153 pick.autoderefs += 1;
1154 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::Autoref {
1156 unsize: pick.autoref_or_ptr_adjustment.map_or(false, |a| a.get_unsize()),
1165 fn pick_autorefd_method(
1167 step: &CandidateStep<'tcx>,
1169 mutbl: hir::Mutability,
1170 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1171 ) -> Option<PickResult<'tcx>> {
1174 // In general, during probing we erase regions.
1175 let region = tcx.lifetimes.re_erased;
1177 let autoref_ty = tcx.mk_ref(region, ty::TypeAndMut { ty: self_ty, mutbl });
1178 self.pick_method(autoref_ty, unstable_candidates).map(|r| {
1180 pick.autoderefs = step.autoderefs;
1181 pick.autoref_or_ptr_adjustment =
1182 Some(AutorefOrPtrAdjustment::Autoref { mutbl, unsize: step.unsize });
1188 /// If `self_ty` is `*mut T` then this picks `*const T` methods. The reason why we have a
1189 /// special case for this is because going from `*mut T` to `*const T` with autoderefs and
1190 /// autorefs would require dereferencing the pointer, which is not safe.
1191 fn pick_const_ptr_method(
1193 step: &CandidateStep<'tcx>,
1195 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1196 ) -> Option<PickResult<'tcx>> {
1197 // Don't convert an unsized reference to ptr
1202 let &ty::RawPtr(ty::TypeAndMut { ty, mutbl: hir::Mutability::Mut }) = self_ty.kind() else {
1206 let const_self_ty = ty::TypeAndMut { ty, mutbl: hir::Mutability::Not };
1207 let const_ptr_ty = self.tcx.mk_ptr(const_self_ty);
1208 self.pick_method(const_ptr_ty, unstable_candidates).map(|r| {
1210 pick.autoderefs = step.autoderefs;
1211 pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::ToConstPtr);
1217 fn pick_method_with_unstable(&mut self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
1218 debug!("pick_method_with_unstable(self_ty={})", self.ty_to_string(self_ty));
1220 let mut possibly_unsatisfied_predicates = Vec::new();
1221 let mut unstable_candidates = Vec::new();
1223 for (kind, candidates) in
1224 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1226 debug!("searching {} candidates", kind);
1227 let res = self.consider_candidates(
1230 &mut possibly_unsatisfied_predicates,
1231 Some(&mut unstable_candidates),
1233 if let Some(pick) = res {
1234 if !self.is_suggestion.0 && !unstable_candidates.is_empty() {
1235 if let Ok(p) = &pick {
1236 // Emit a lint if there are unstable candidates alongside the stable ones.
1238 // We suppress warning if we're picking the method only because it is a
1240 self.emit_unstable_name_collision_hint(p, &unstable_candidates);
1247 debug!("searching unstable candidates");
1248 let res = self.consider_candidates(
1250 unstable_candidates.iter().map(|(c, _)| c),
1251 &mut possibly_unsatisfied_predicates,
1255 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1263 mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1264 ) -> Option<PickResult<'tcx>> {
1265 if !self.tcx.sess.opts.debugging_opts.pick_stable_methods_before_any_unstable {
1266 return self.pick_method_with_unstable(self_ty);
1269 debug!("pick_method(self_ty={})", self.ty_to_string(self_ty));
1271 let mut possibly_unsatisfied_predicates = Vec::new();
1273 for (kind, candidates) in
1274 &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)]
1276 debug!("searching {} candidates", kind);
1277 let res = self.consider_candidates(
1280 &mut possibly_unsatisfied_predicates,
1281 unstable_candidates.as_deref_mut(),
1283 if let Some(pick) = res {
1288 // `pick_method` may be called twice for the same self_ty if no stable methods
1289 // match. Only extend once.
1290 if unstable_candidates.is_some() {
1291 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1296 fn consider_candidates<'b, ProbesIter>(
1300 possibly_unsatisfied_predicates: &mut Vec<(
1301 ty::Predicate<'tcx>,
1302 Option<ty::Predicate<'tcx>>,
1303 Option<ObligationCause<'tcx>>,
1305 unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
1306 ) -> Option<PickResult<'tcx>>
1308 ProbesIter: Iterator<Item = &'b Candidate<'tcx>> + Clone,
1311 let mut applicable_candidates: Vec<_> = probes
1314 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
1316 .filter(|&(_, status)| status != ProbeResult::NoMatch)
1319 debug!("applicable_candidates: {:?}", applicable_candidates);
1321 if applicable_candidates.len() > 1 {
1323 self.collapse_candidates_to_trait_pick(self_ty, &applicable_candidates)
1325 return Some(Ok(pick));
1329 if let Some(uc) = unstable_candidates {
1330 applicable_candidates.retain(|&(p, _)| {
1331 if let stability::EvalResult::Deny { feature, .. } =
1332 self.tcx.eval_stability(p.item.def_id, None, self.span, None)
1334 uc.push((p.clone(), feature));
1341 if applicable_candidates.len() > 1 {
1342 let sources = probes.map(|p| self.candidate_source(p, self_ty)).collect();
1343 return Some(Err(MethodError::Ambiguity(sources)));
1346 applicable_candidates.pop().map(|(probe, status)| {
1347 if status == ProbeResult::Match {
1348 Ok(probe.to_unadjusted_pick(self_ty))
1350 Err(MethodError::BadReturnType)
1355 fn emit_unstable_name_collision_hint(
1357 stable_pick: &Pick<'_>,
1358 unstable_candidates: &[(Candidate<'tcx>, Symbol)],
1360 self.tcx.struct_span_lint_hir(
1361 lint::builtin::UNSTABLE_NAME_COLLISIONS,
1365 let def_kind = stable_pick.item.kind.as_def_kind();
1366 let mut diag = lint.build(&format!(
1367 "{} {} with this name may be added to the standard library in the future",
1369 def_kind.descr(stable_pick.item.def_id),
1371 match (stable_pick.item.kind, stable_pick.item.container) {
1372 (ty::AssocKind::Fn, _) => {
1373 // FIXME: This should be a `span_suggestion` instead of `help`
1374 // However `self.span` only
1375 // highlights the method name, so we can't use it. Also consider reusing
1376 // the code from `report_method_error()`.
1378 "call with fully qualified syntax `{}(...)` to keep using the current \
1380 self.tcx.def_path_str(stable_pick.item.def_id),
1383 (ty::AssocKind::Const, ty::AssocItemContainer::TraitContainer(def_id)) => {
1384 diag.span_suggestion(
1386 "use the fully qualified path to the associated const",
1389 stable_pick.self_ty,
1390 self.tcx.def_path_str(def_id),
1391 stable_pick.item.name
1393 Applicability::MachineApplicable,
1398 if self.tcx.sess.is_nightly_build() {
1399 for (candidate, feature) in unstable_candidates {
1401 "add `#![feature({})]` to the crate attributes to enable `{}`",
1403 self.tcx.def_path_str(candidate.item.def_id),
1413 fn select_trait_candidate(
1415 trait_ref: ty::TraitRef<'tcx>,
1416 ) -> traits::SelectionResult<'tcx, traits::Selection<'tcx>> {
1417 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1418 let predicate = ty::Binder::dummy(trait_ref).to_poly_trait_predicate();
1419 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1420 traits::SelectionContext::new(self).select(&obligation)
1423 fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>) -> CandidateSource {
1424 match candidate.kind {
1425 InherentImplCandidate(..) => CandidateSource::Impl(candidate.item.container.id()),
1426 ObjectCandidate | WhereClauseCandidate(_) => {
1427 CandidateSource::Trait(candidate.item.container.id())
1429 TraitCandidate(trait_ref) => self.probe(|_| {
1431 .at(&ObligationCause::dummy(), self.param_env)
1432 .define_opaque_types(false)
1433 .sup(candidate.xform_self_ty, self_ty);
1434 match self.select_trait_candidate(trait_ref) {
1435 Ok(Some(traits::ImplSource::UserDefined(ref impl_data))) => {
1436 // If only a single impl matches, make the error message point
1438 CandidateSource::Impl(impl_data.impl_def_id)
1440 _ => CandidateSource::Trait(candidate.item.container.id()),
1449 probe: &Candidate<'tcx>,
1450 possibly_unsatisfied_predicates: &mut Vec<(
1451 ty::Predicate<'tcx>,
1452 Option<ty::Predicate<'tcx>>,
1453 Option<ObligationCause<'tcx>>,
1456 debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe);
1459 // First check that the self type can be related.
1460 let sub_obligations = match self
1461 .at(&ObligationCause::dummy(), self.param_env)
1462 .define_opaque_types(false)
1463 .sup(probe.xform_self_ty, self_ty)
1465 Ok(InferOk { obligations, value: () }) => obligations,
1467 debug!("--> cannot relate self-types {:?}", err);
1468 return ProbeResult::NoMatch;
1472 let mut result = ProbeResult::Match;
1473 let mut xform_ret_ty = probe.xform_ret_ty;
1474 debug!(?xform_ret_ty);
1476 let selcx = &mut traits::SelectionContext::new(self);
1477 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1479 let mut parent_pred = None;
1481 // If so, impls may carry other conditions (e.g., where
1482 // clauses) that must be considered. Make sure that those
1483 // match as well (or at least may match, sometimes we
1484 // don't have enough information to fully evaluate).
1486 InherentImplCandidate(ref substs, ref ref_obligations) => {
1487 // `xform_ret_ty` hasn't been normalized yet, only `xform_self_ty`,
1488 // see the reasons mentioned in the comments in `assemble_inherent_impl_probe`
1489 // for why this is necessary
1490 let traits::Normalized {
1491 value: normalized_xform_ret_ty,
1492 obligations: normalization_obligations,
1493 } = traits::normalize(selcx, self.param_env, cause.clone(), probe.xform_ret_ty);
1494 xform_ret_ty = normalized_xform_ret_ty;
1495 debug!("xform_ret_ty after normalization: {:?}", xform_ret_ty);
1497 // Check whether the impl imposes obligations we have to worry about.
1498 let impl_def_id = probe.item.container.id();
1499 let impl_bounds = self.tcx.predicates_of(impl_def_id);
1500 let impl_bounds = impl_bounds.instantiate(self.tcx, substs);
1501 let traits::Normalized { value: impl_bounds, obligations: norm_obligations } =
1502 traits::normalize(selcx, self.param_env, cause.clone(), impl_bounds);
1504 // Convert the bounds into obligations.
1505 let impl_obligations =
1506 traits::predicates_for_generics(cause, self.param_env, impl_bounds);
1508 let candidate_obligations = impl_obligations
1509 .chain(norm_obligations.into_iter())
1510 .chain(ref_obligations.iter().cloned())
1511 .chain(normalization_obligations.into_iter());
1513 // Evaluate those obligations to see if they might possibly hold.
1514 for o in candidate_obligations {
1515 let o = self.resolve_vars_if_possible(o);
1516 if !self.predicate_may_hold(&o) {
1517 result = ProbeResult::NoMatch;
1518 possibly_unsatisfied_predicates.push((
1527 ObjectCandidate | WhereClauseCandidate(..) => {
1528 // These have no additional conditions to check.
1531 TraitCandidate(trait_ref) => {
1532 if let Some(method_name) = self.method_name {
1533 // Some trait methods are excluded for arrays before 2021.
1534 // (`array.into_iter()` wants a slice iterator for compatibility.)
1535 if self_ty.is_array() && !method_name.span.rust_2021() {
1536 let trait_def = self.tcx.trait_def(trait_ref.def_id);
1537 if trait_def.skip_array_during_method_dispatch {
1538 return ProbeResult::NoMatch;
1543 ty::Binder::dummy(trait_ref).without_const().to_predicate(self.tcx);
1544 parent_pred = Some(predicate);
1545 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1546 if !self.predicate_may_hold(&obligation) {
1547 result = ProbeResult::NoMatch;
1549 match self.select_trait_candidate(trait_ref) {
1550 Err(_) => return true,
1551 Ok(Some(impl_source))
1552 if !impl_source.borrow_nested_obligations().is_empty() =>
1554 for obligation in impl_source.borrow_nested_obligations() {
1555 // Determine exactly which obligation wasn't met, so
1556 // that we can give more context in the error.
1557 if !self.predicate_may_hold(obligation) {
1558 let nested_predicate =
1559 self.resolve_vars_if_possible(obligation.predicate);
1561 self.resolve_vars_if_possible(predicate);
1562 let p = if predicate == nested_predicate {
1563 // Avoid "`MyStruct: Foo` which is required by
1564 // `MyStruct: Foo`" in E0599.
1569 possibly_unsatisfied_predicates.push((
1572 Some(obligation.cause.clone()),
1578 // Some nested subobligation of this predicate
1580 let predicate = self.resolve_vars_if_possible(predicate);
1581 possibly_unsatisfied_predicates.push((predicate, None, None));
1586 // This candidate's primary obligation doesn't even
1587 // select - don't bother registering anything in
1588 // `potentially_unsatisfied_predicates`.
1589 return ProbeResult::NoMatch;
1595 // Evaluate those obligations to see if they might possibly hold.
1596 for o in sub_obligations {
1597 let o = self.resolve_vars_if_possible(o);
1598 if !self.predicate_may_hold(&o) {
1599 result = ProbeResult::NoMatch;
1600 possibly_unsatisfied_predicates.push((o.predicate, parent_pred, Some(o.cause)));
1604 if let ProbeResult::Match = result {
1605 if let (Some(return_ty), Some(xform_ret_ty)) = (self.return_type, xform_ret_ty) {
1606 let xform_ret_ty = self.resolve_vars_if_possible(xform_ret_ty);
1608 "comparing return_ty {:?} with xform ret ty {:?}",
1609 return_ty, probe.xform_ret_ty
1612 .at(&ObligationCause::dummy(), self.param_env)
1613 .define_opaque_types(false)
1614 .sup(return_ty, xform_ret_ty)
1617 return ProbeResult::BadReturnType;
1626 /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1627 /// same trait, but we don't know which impl to use. In this case, since in all cases the
1628 /// external interface of the method can be determined from the trait, it's ok not to decide.
1629 /// We can basically just collapse all of the probes for various impls into one where-clause
1630 /// probe. This will result in a pending obligation so when more type-info is available we can
1631 /// make the final decision.
1633 /// Example (`src/test/ui/method-two-trait-defer-resolution-1.rs`):
1635 /// ```ignore (illustrative)
1636 /// trait Foo { ... }
1637 /// impl Foo for Vec<i32> { ... }
1638 /// impl Foo for Vec<usize> { ... }
1641 /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1642 /// use, so it's ok to just commit to "using the method from the trait Foo".
1643 fn collapse_candidates_to_trait_pick(
1646 probes: &[(&Candidate<'tcx>, ProbeResult)],
1647 ) -> Option<Pick<'tcx>> {
1648 // Do all probes correspond to the same trait?
1649 let container = probes[0].0.item.container;
1650 if let ty::ImplContainer(_) = container {
1653 if probes[1..].iter().any(|&(p, _)| p.item.container != container) {
1657 // FIXME: check the return type here somehow.
1658 // If so, just use this trait and call it a day.
1660 item: probes[0].0.item,
1662 import_ids: probes[0].0.import_ids.clone(),
1664 autoref_or_ptr_adjustment: None,
1669 /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
1670 /// candidate method where the method name may have been misspelled. Similarly to other
1671 /// Levenshtein based suggestions, we provide at most one such suggestion.
1672 fn probe_for_lev_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
1673 debug!("probing for method names similar to {:?}", self.method_name);
1675 let steps = self.steps.clone();
1677 let mut pcx = ProbeContext::new(
1683 self.orig_steps_var_values.clone(),
1688 pcx.allow_similar_names = true;
1689 pcx.assemble_inherent_candidates();
1691 let method_names = pcx.candidate_method_names();
1692 pcx.allow_similar_names = false;
1693 let applicable_close_candidates: Vec<ty::AssocItem> = method_names
1695 .filter_map(|&method_name| {
1697 pcx.method_name = Some(method_name);
1698 pcx.assemble_inherent_candidates();
1699 pcx.pick_core().and_then(|pick| pick.ok()).map(|pick| pick.item)
1703 if applicable_close_candidates.is_empty() {
1707 let names = applicable_close_candidates
1709 .map(|cand| cand.name)
1710 .collect::<Vec<Symbol>>();
1711 find_best_match_for_name_with_substrings(
1713 self.method_name.unwrap().name,
1718 Ok(applicable_close_candidates.into_iter().find(|method| method.name == best_name))
1723 ///////////////////////////////////////////////////////////////////////////
1725 fn has_applicable_self(&self, item: &ty::AssocItem) -> bool {
1726 // "Fast track" -- check for usage of sugar when in method call
1729 // In Path mode (i.e., resolving a value like `T::next`), consider any
1730 // associated value (i.e., methods, constants) but not types.
1732 Mode::MethodCall => item.fn_has_self_parameter,
1733 Mode::Path => match item.kind {
1734 ty::AssocKind::Type => false,
1735 ty::AssocKind::Fn | ty::AssocKind::Const => true,
1738 // FIXME -- check for types that deref to `Self`,
1739 // like `Rc<Self>` and so on.
1741 // Note also that the current code will break if this type
1742 // includes any of the type parameters defined on the method
1743 // -- but this could be overcome.
1746 fn record_static_candidate(&mut self, source: CandidateSource) {
1747 self.static_candidates.push(source);
1750 #[instrument(level = "debug", skip(self))]
1753 item: &ty::AssocItem,
1755 substs: SubstsRef<'tcx>,
1756 ) -> (Ty<'tcx>, Option<Ty<'tcx>>) {
1757 if item.kind == ty::AssocKind::Fn && self.mode == Mode::MethodCall {
1758 let sig = self.xform_method_sig(item.def_id, substs);
1759 (sig.inputs()[0], Some(sig.output()))
1765 #[instrument(level = "debug", skip(self))]
1766 fn xform_method_sig(&self, method: DefId, substs: SubstsRef<'tcx>) -> ty::FnSig<'tcx> {
1767 let fn_sig = self.tcx.fn_sig(method);
1770 assert!(!substs.has_escaping_bound_vars());
1772 // It is possible for type parameters or early-bound lifetimes
1773 // to appear in the signature of `self`. The substitutions we
1774 // are given do not include type/lifetime parameters for the
1775 // method yet. So create fresh variables here for those too,
1776 // if there are any.
1777 let generics = self.tcx.generics_of(method);
1778 assert_eq!(substs.len(), generics.parent_count as usize);
1780 // Erase any late-bound regions from the method and substitute
1781 // in the values from the substitution.
1782 let xform_fn_sig = self.erase_late_bound_regions(fn_sig);
1784 if generics.params.is_empty() {
1785 xform_fn_sig.subst(self.tcx, substs)
1787 let substs = InternalSubsts::for_item(self.tcx, method, |param, _| {
1788 let i = param.index as usize;
1789 if i < substs.len() {
1793 GenericParamDefKind::Lifetime => {
1794 // In general, during probe we erase regions.
1795 self.tcx.lifetimes.re_erased.into()
1797 GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
1798 self.var_for_def(self.span, param)
1803 xform_fn_sig.subst(self.tcx, substs)
1807 /// Gets the type of an impl and generate substitutions with placeholders.
1808 fn impl_ty_and_substs(&self, impl_def_id: DefId) -> (Ty<'tcx>, SubstsRef<'tcx>) {
1809 (self.tcx.type_of(impl_def_id), self.fresh_item_substs(impl_def_id))
1812 fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx> {
1813 InternalSubsts::for_item(self.tcx, def_id, |param, _| match param.kind {
1814 GenericParamDefKind::Lifetime => self.tcx.lifetimes.re_erased.into(),
1815 GenericParamDefKind::Type { .. } => self
1816 .next_ty_var(TypeVariableOrigin {
1817 kind: TypeVariableOriginKind::SubstitutionPlaceholder,
1818 span: self.tcx.def_span(def_id),
1821 GenericParamDefKind::Const { .. } => {
1822 let span = self.tcx.def_span(def_id);
1823 let origin = ConstVariableOrigin {
1824 kind: ConstVariableOriginKind::SubstitutionPlaceholder,
1827 self.next_const_var(self.tcx.type_of(param.def_id), origin).into()
1832 /// Replaces late-bound-regions bound by `value` with `'static` using
1833 /// `ty::erase_late_bound_regions`.
1835 /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1836 /// method matching. It is reasonable during the probe phase because we don't consider region
1837 /// relationships at all. Therefore, we can just replace all the region variables with 'static
1838 /// rather than creating fresh region variables. This is nice for two reasons:
1840 /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1841 /// particular method call, it winds up creating fewer types overall, which helps for memory
1842 /// usage. (Admittedly, this is a rather small effect, though measurable.)
1844 /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1845 /// late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1846 /// regions with actual region variables as is proper, we'd have to ensure that the same
1847 /// region got replaced with the same variable, which requires a bit more coordination
1848 /// and/or tracking the substitution and
1850 fn erase_late_bound_regions<T>(&self, value: ty::Binder<'tcx, T>) -> T
1852 T: TypeFoldable<'tcx>,
1854 self.tcx.erase_late_bound_regions(value)
1857 /// Finds the method with the appropriate name (or return type, as the case may be). If
1858 /// `allow_similar_names` is set, find methods with close-matching names.
1859 // The length of the returned iterator is nearly always 0 or 1 and this
1860 // method is fairly hot.
1861 fn impl_or_trait_item(&self, def_id: DefId) -> SmallVec<[ty::AssocItem; 1]> {
1862 if let Some(name) = self.method_name {
1863 if self.allow_similar_names {
1864 let max_dist = max(name.as_str().len(), 3) / 3;
1866 .associated_items(def_id)
1867 .in_definition_order()
1869 if x.kind.namespace() != Namespace::ValueNS {
1872 match lev_distance_with_substrings(name.as_str(), x.name.as_str(), max_dist)
1882 .associated_value(def_id, name)
1883 .map_or_else(SmallVec::new, |x| SmallVec::from_buf([x]))
1886 self.tcx.associated_items(def_id).in_definition_order().copied().collect()
1891 impl<'tcx> Candidate<'tcx> {
1892 fn to_unadjusted_pick(&self, self_ty: Ty<'tcx>) -> Pick<'tcx> {
1895 kind: match self.kind {
1896 InherentImplCandidate(..) => InherentImplPick,
1897 ObjectCandidate => ObjectPick,
1898 TraitCandidate(_) => TraitPick,
1899 WhereClauseCandidate(ref trait_ref) => {
1900 // Only trait derived from where-clauses should
1901 // appear here, so they should not contain any
1902 // inference variables or other artifacts. This
1903 // means they are safe to put into the
1904 // `WhereClausePick`.
1906 !trait_ref.skip_binder().substs.needs_infer()
1907 && !trait_ref.skip_binder().substs.has_placeholders()
1910 WhereClausePick(*trait_ref)
1913 import_ids: self.import_ids.clone(),
1915 autoref_or_ptr_adjustment: None,