1 use super::MethodError;
2 use super::NoMatchData;
3 use super::{CandidateSource, ImplSource, TraitSource};
6 use crate::check::autoderef::{self, Autoderef};
7 use crate::check::FnCtxt;
8 use crate::hir::def_id::DefId;
9 use crate::hir::def::DefKind;
10 use crate::namespace::Namespace;
12 use rustc_data_structures::sync::Lrc;
15 use rustc::session::config::nightly_options;
16 use rustc::ty::subst::{Subst, InternalSubsts, SubstsRef};
17 use rustc::traits::{self, ObligationCause};
18 use rustc::traits::query::{CanonicalTyGoal};
19 use rustc::traits::query::method_autoderef::{CandidateStep, MethodAutoderefStepsResult};
20 use rustc::traits::query::method_autoderef::{MethodAutoderefBadTy};
21 use rustc::ty::{self, ParamEnvAnd, Ty, TyCtxt, ToPolyTraitRef, ToPredicate, TraitRef, TypeFoldable};
22 use rustc::ty::GenericParamDefKind;
23 use rustc::infer::type_variable::TypeVariableOrigin;
24 use rustc::infer::unify_key::ConstVariableOrigin;
25 use rustc::util::nodemap::FxHashSet;
26 use rustc::infer::{self, InferOk};
27 use rustc::infer::canonical::{Canonical, QueryResponse};
28 use rustc::infer::canonical::{OriginalQueryValues};
29 use rustc::middle::stability;
31 use syntax::util::lev_distance::{lev_distance, find_best_match_for_name};
32 use syntax_pos::{DUMMY_SP, Span, symbol::Symbol};
38 use self::CandidateKind::*;
39 pub use self::PickKind::*;
41 /// Boolean flag used to indicate if this search is for a suggestion
42 /// or not. If true, we can allow ambiguity and so forth.
43 #[derive(Clone, Copy)]
44 pub struct IsSuggestion(pub bool);
46 struct ProbeContext<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
47 fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
50 method_name: Option<ast::Ident>,
51 return_type: Option<Ty<'tcx>>,
53 /// This is the OriginalQueryValues for the steps queries
54 /// that are answered in steps.
55 orig_steps_var_values: OriginalQueryValues<'tcx>,
56 steps: Lrc<Vec<CandidateStep<'gcx>>>,
58 inherent_candidates: Vec<Candidate<'tcx>>,
59 extension_candidates: Vec<Candidate<'tcx>>,
60 impl_dups: FxHashSet<DefId>,
62 /// Collects near misses when the candidate functions are missing a `self` keyword and is only
63 /// used for error reporting
64 static_candidates: Vec<CandidateSource>,
66 /// When probing for names, include names that are close to the
67 /// requested name (by Levensthein distance)
68 allow_similar_names: bool,
70 /// Some(candidate) if there is a private candidate
71 private_candidate: Option<(DefKind, DefId)>,
73 /// Collects near misses when trait bounds for type parameters are unsatisfied and is only used
74 /// for error reporting
75 unsatisfied_predicates: Vec<TraitRef<'tcx>>,
77 is_suggestion: IsSuggestion,
80 impl<'a, 'gcx, 'tcx> Deref for ProbeContext<'a, 'gcx, 'tcx> {
81 type Target = FnCtxt<'a, 'gcx, 'tcx>;
82 fn deref(&self) -> &Self::Target {
88 struct Candidate<'tcx> {
89 // Candidates are (I'm not quite sure, but they are mostly) basically
90 // some metadata on top of a `ty::AssociatedItem` (without substs).
92 // However, method probing wants to be able to evaluate the predicates
93 // for a function with the substs applied - for example, if a function
94 // has `where Self: Sized`, we don't want to consider it unless `Self`
95 // is actually `Sized`, and similarly, return-type suggestions want
96 // to consider the "actual" return type.
98 // The way this is handled is through `xform_self_ty`. It contains
99 // the receiver type of this candidate, but `xform_self_ty`,
100 // `xform_ret_ty` and `kind` (which contains the predicates) have the
101 // generic parameters of this candidate substituted with the *same set*
102 // of inference variables, which acts as some weird sort of "query".
104 // When we check out a candidate, we require `xform_self_ty` to be
105 // a subtype of the passed-in self-type, and this equates the type
106 // variables in the rest of the fields.
108 // For example, if we have this candidate:
111 // fn foo(&self) where Self: Sized;
115 // Then `xform_self_ty` will be `&'erased ?X` and `kind` will contain
116 // the predicate `?X: Sized`, so if we are evaluating `Foo` for a
117 // the receiver `&T`, we'll do the subtyping which will make `?X`
118 // get the right value, then when we evaluate the predicate we'll check
120 xform_self_ty: Ty<'tcx>,
121 xform_ret_ty: Option<Ty<'tcx>>,
122 item: ty::AssociatedItem,
123 kind: CandidateKind<'tcx>,
124 import_id: Option<hir::HirId>,
128 enum CandidateKind<'tcx> {
129 InherentImplCandidate(SubstsRef<'tcx>,
130 // Normalize obligations
131 Vec<traits::PredicateObligation<'tcx>>),
133 TraitCandidate(ty::TraitRef<'tcx>),
134 WhereClauseCandidate(// Trait
135 ty::PolyTraitRef<'tcx>),
138 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
145 #[derive(Debug, PartialEq, Clone)]
146 pub struct Pick<'tcx> {
147 pub item: ty::AssociatedItem,
148 pub kind: PickKind<'tcx>,
149 pub import_id: Option<hir::HirId>,
151 // Indicates that the source expression should be autoderef'd N times
153 // A = expr | *expr | **expr | ...
154 pub autoderefs: usize,
156 // Indicates that an autoref is applied after the optional autoderefs
158 // B = A | &A | &mut A
159 pub autoref: Option<hir::Mutability>,
161 // Indicates that the source expression should be "unsized" to a
162 // target type. This should probably eventually go away in favor
163 // of just coercing method receivers.
166 pub unsize: Option<Ty<'tcx>>,
169 #[derive(Clone, Debug, PartialEq, Eq)]
170 pub enum PickKind<'tcx> {
174 WhereClausePick(// Trait
175 ty::PolyTraitRef<'tcx>),
178 pub type PickResult<'tcx> = Result<Pick<'tcx>, MethodError<'tcx>>;
180 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
182 // An expression of the form `receiver.method_name(...)`.
183 // Autoderefs are performed on `receiver`, lookup is done based on the
184 // `self` argument of the method, and static methods aren't considered.
186 // An expression of the form `Type::item` or `<T>::item`.
187 // No autoderefs are performed, lookup is done based on the type each
188 // implementation is for, and static methods are included.
192 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
193 pub enum ProbeScope {
194 // Assemble candidates coming only from traits in scope.
197 // Assemble candidates coming from all traits.
201 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
202 /// This is used to offer suggestions to users. It returns methods
203 /// that could have been called which have the desired return
204 /// type. Some effort is made to rule out methods that, if called,
205 /// would result in an error (basically, the same criteria we
206 /// would use to decide if a method is a plausible fit for
207 /// ambiguity purposes).
208 pub fn probe_for_return_type(&self,
211 return_type: Ty<'tcx>,
213 scope_expr_id: hir::HirId)
214 -> Vec<ty::AssociatedItem> {
215 debug!("probe(self_ty={:?}, return_type={}, scope_expr_id={})",
220 self.probe_op(span, mode, None, Some(return_type), IsSuggestion(true),
221 self_ty, scope_expr_id, ProbeScope::AllTraits,
222 |probe_cx| Ok(probe_cx.candidate_method_names()))
226 .flat_map(|&method_name| {
228 span, mode, Some(method_name), Some(return_type),
229 IsSuggestion(true), self_ty, scope_expr_id,
230 ProbeScope::AllTraits, |probe_cx| probe_cx.pick()
231 ).ok().map(|pick| pick.item)
236 pub fn probe_for_name(&self,
239 item_name: ast::Ident,
240 is_suggestion: IsSuggestion,
242 scope_expr_id: hir::HirId,
244 -> PickResult<'tcx> {
245 debug!("probe(self_ty={:?}, item_name={}, scope_expr_id={})",
257 |probe_cx| probe_cx.pick())
260 fn probe_op<OP,R>(&'a self,
263 method_name: Option<ast::Ident>,
264 return_type: Option<Ty<'tcx>>,
265 is_suggestion: IsSuggestion,
267 scope_expr_id: hir::HirId,
270 -> Result<R, MethodError<'tcx>>
271 where OP: FnOnce(ProbeContext<'a, 'gcx, 'tcx>) -> Result<R, MethodError<'tcx>>
273 let mut orig_values = OriginalQueryValues::default();
274 let param_env_and_self_ty =
275 self.infcx.canonicalize_query(
277 param_env: self.param_env,
279 }, &mut orig_values);
281 let steps = if mode == Mode::MethodCall {
282 self.tcx.method_autoderef_steps(param_env_and_self_ty)
284 self.infcx.probe(|_| {
285 // Mode::Path - the deref steps is "trivial". This turns
286 // our CanonicalQuery into a "trivial" QueryResponse. This
287 // is a bit inefficient, but I don't think that writing
288 // special handling for this "trivial case" is a good idea.
290 let infcx = &self.infcx;
294 }, canonical_inference_vars) =
295 infcx.instantiate_canonical_with_fresh_inference_vars(
296 span, ¶m_env_and_self_ty);
297 debug!("probe_op: Mode::Path, param_env_and_self_ty={:?} self_ty={:?}",
298 param_env_and_self_ty, self_ty);
299 MethodAutoderefStepsResult {
300 steps: Lrc::new(vec![CandidateStep {
301 self_ty: self.make_query_response_ignoring_pending_obligations(
302 canonical_inference_vars, self_ty),
304 from_unsafe_deref: false,
308 reached_recursion_limit: false
313 // If our autoderef loop had reached the recursion limit,
314 // report an overflow error, but continue going on with
315 // the truncated autoderef list.
316 if steps.reached_recursion_limit {
318 let ty = &steps.steps.last().unwrap_or_else(|| {
319 span_bug!(span, "reached the recursion limit in 0 steps?")
321 let ty = self.probe_instantiate_query_response(span, &orig_values, ty)
322 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
323 autoderef::report_autoderef_recursion_limit_error(self.tcx, span,
329 // If we encountered an `_` type or an error type during autoderef, this is
331 if let Some(bad_ty) = &steps.opt_bad_ty {
333 // Ambiguity was encountered during a suggestion. Just keep going.
334 debug!("ProbeContext: encountered ambiguity in suggestion");
335 } else if bad_ty.reached_raw_pointer && !self.tcx.features().arbitrary_self_types {
336 // this case used to be allowed by the compiler,
337 // so we do a future-compat lint here for the 2015 edition
338 // (see https://github.com/rust-lang/rust/issues/46906)
339 if self.tcx.sess.rust_2018() {
340 span_err!(self.tcx.sess, span, E0699,
341 "the type of this value must be known \
342 to call a method on a raw pointer on it");
345 lint::builtin::TYVAR_BEHIND_RAW_POINTER,
348 "type annotations needed");
351 // Encountered a real ambiguity, so abort the lookup. If `ty` is not
352 // an `Err`, report the right "type annotations needed" error pointing
355 let ty = self.probe_instantiate_query_response(span, &orig_values, ty)
356 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
357 let ty = self.structurally_resolved_type(span, ty.value);
358 assert_eq!(ty, self.tcx.types.err);
359 return Err(MethodError::NoMatch(NoMatchData::new(Vec::new(),
367 debug!("ProbeContext: steps for self_ty={:?} are {:?}",
372 // this creates one big transaction so that all type variables etc
373 // that we create during the probe process are removed later
375 let mut probe_cx = ProbeContext::new(
376 self, span, mode, method_name, return_type, orig_values,
377 steps.steps, is_suggestion,
380 probe_cx.assemble_inherent_candidates();
382 ProbeScope::TraitsInScope =>
383 probe_cx.assemble_extension_candidates_for_traits_in_scope(scope_expr_id)?,
384 ProbeScope::AllTraits =>
385 probe_cx.assemble_extension_candidates_for_all_traits()?,
392 pub fn provide(providers: &mut ty::query::Providers<'_>) {
393 providers.method_autoderef_steps = method_autoderef_steps;
396 fn method_autoderef_steps<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>,
397 goal: CanonicalTyGoal<'tcx>)
398 -> MethodAutoderefStepsResult<'gcx>
400 debug!("method_autoderef_steps({:?})", goal);
402 tcx.infer_ctxt().enter_with_canonical(DUMMY_SP, &goal, |ref infcx, goal, inference_vars| {
403 let ParamEnvAnd { param_env, value: self_ty } = goal;
405 let mut autoderef = Autoderef::new(infcx, param_env, hir::DUMMY_HIR_ID, DUMMY_SP, self_ty)
406 .include_raw_pointers()
408 let mut reached_raw_pointer = false;
409 let mut steps: Vec<_> = autoderef.by_ref()
411 let step = CandidateStep {
412 self_ty: infcx.make_query_response_ignoring_pending_obligations(
413 inference_vars.clone(), ty),
415 from_unsafe_deref: reached_raw_pointer,
418 if let ty::RawPtr(_) = ty.sty {
419 // all the subsequent steps will be from_unsafe_deref
420 reached_raw_pointer = true;
426 let final_ty = autoderef.maybe_ambiguous_final_ty();
427 let opt_bad_ty = match final_ty.sty {
428 ty::Infer(ty::TyVar(_)) |
430 Some(MethodAutoderefBadTy {
432 ty: infcx.make_query_response_ignoring_pending_obligations(
433 inference_vars, final_ty)
436 ty::Array(elem_ty, _) => {
437 let dereferences = steps.len() - 1;
439 steps.push(CandidateStep {
440 self_ty: infcx.make_query_response_ignoring_pending_obligations(
441 inference_vars, infcx.tcx.mk_slice(elem_ty)),
442 autoderefs: dereferences,
443 // this could be from an unsafe deref if we had
444 // a *mut/const [T; N]
445 from_unsafe_deref: reached_raw_pointer,
454 debug!("method_autoderef_steps: steps={:?} opt_bad_ty={:?}", steps, opt_bad_ty);
456 MethodAutoderefStepsResult {
457 steps: Lrc::new(steps),
458 opt_bad_ty: opt_bad_ty.map(Lrc::new),
459 reached_recursion_limit: autoderef.reached_recursion_limit()
465 impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
466 fn new(fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
469 method_name: Option<ast::Ident>,
470 return_type: Option<Ty<'tcx>>,
471 orig_steps_var_values: OriginalQueryValues<'tcx>,
472 steps: Lrc<Vec<CandidateStep<'gcx>>>,
473 is_suggestion: IsSuggestion)
474 -> ProbeContext<'a, 'gcx, 'tcx> {
481 inherent_candidates: Vec::new(),
482 extension_candidates: Vec::new(),
483 impl_dups: FxHashSet::default(),
484 orig_steps_var_values,
486 static_candidates: Vec::new(),
487 allow_similar_names: false,
488 private_candidate: None,
489 unsatisfied_predicates: Vec::new(),
494 fn reset(&mut self) {
495 self.inherent_candidates.clear();
496 self.extension_candidates.clear();
497 self.impl_dups.clear();
498 self.static_candidates.clear();
499 self.private_candidate = None;
502 ///////////////////////////////////////////////////////////////////////////
503 // CANDIDATE ASSEMBLY
505 fn push_candidate(&mut self,
506 candidate: Candidate<'tcx>,
509 let is_accessible = if let Some(name) = self.method_name {
510 let item = candidate.item;
511 let def_scope = self.tcx.adjust_ident(name, item.container.id(), self.body_id).1;
512 item.vis.is_accessible_from(def_scope, self.tcx)
518 self.inherent_candidates.push(candidate);
520 self.extension_candidates.push(candidate);
522 } else if self.private_candidate.is_none() {
523 self.private_candidate =
524 Some((candidate.item.def_kind(), candidate.item.def_id));
528 fn assemble_inherent_candidates(&mut self) {
529 let steps = self.steps.clone();
530 for step in steps.iter() {
531 self.assemble_probe(&step.self_ty);
535 fn assemble_probe(&mut self, self_ty: &Canonical<'gcx, QueryResponse<'gcx, Ty<'gcx>>>) {
536 debug!("assemble_probe: self_ty={:?}", self_ty);
537 let lang_items = self.tcx.lang_items();
539 match self_ty.value.value.sty {
540 ty::Dynamic(ref data, ..) => {
541 if let Some(p) = data.principal() {
542 // Subtle: we can't use `instantiate_query_response` here: using it will
543 // commit to all of the type equalities assumed by inference going through
544 // autoderef (see the `method-probe-no-guessing` test).
546 // However, in this code, it is OK if we end up with an object type that is
547 // "more general" than the object type that we are evaluating. For *every*
548 // object type `MY_OBJECT`, a function call that goes through a trait-ref
549 // of the form `<MY_OBJECT as SuperTraitOf(MY_OBJECT)>::func` is a valid
550 // `ObjectCandidate`, and it should be discoverable "exactly" through one
551 // of the iterations in the autoderef loop, so there is no problem with it
552 // being discoverable in another one of these iterations.
554 // Using `instantiate_canonical_with_fresh_inference_vars` on our
555 // `Canonical<QueryResponse<Ty<'tcx>>>` and then *throwing away* the
556 // `CanonicalVarValues` will exactly give us such a generalization - it
557 // will still match the original object type, but it won't pollute our
558 // type variables in any form, so just do that!
559 let (QueryResponse { value: generalized_self_ty, .. }, _ignored_var_values) =
560 self.fcx.instantiate_canonical_with_fresh_inference_vars(
561 self.span, &self_ty);
563 self.assemble_inherent_candidates_from_object(generalized_self_ty);
564 self.assemble_inherent_impl_candidates_for_type(p.def_id());
568 self.assemble_inherent_impl_candidates_for_type(def.did);
570 ty::Foreign(did) => {
571 self.assemble_inherent_impl_candidates_for_type(did);
574 self.assemble_inherent_candidates_from_param(p);
577 let lang_def_id = lang_items.char_impl();
578 self.assemble_inherent_impl_for_primitive(lang_def_id);
581 let lang_def_id = lang_items.str_impl();
582 self.assemble_inherent_impl_for_primitive(lang_def_id);
584 let lang_def_id = lang_items.str_alloc_impl();
585 self.assemble_inherent_impl_for_primitive(lang_def_id);
588 let lang_def_id = lang_items.slice_impl();
589 self.assemble_inherent_impl_for_primitive(lang_def_id);
591 let lang_def_id = lang_items.slice_u8_impl();
592 self.assemble_inherent_impl_for_primitive(lang_def_id);
594 let lang_def_id = lang_items.slice_alloc_impl();
595 self.assemble_inherent_impl_for_primitive(lang_def_id);
597 let lang_def_id = lang_items.slice_u8_alloc_impl();
598 self.assemble_inherent_impl_for_primitive(lang_def_id);
600 ty::RawPtr(ty::TypeAndMut { ty: _, mutbl: hir::MutImmutable }) => {
601 let lang_def_id = lang_items.const_ptr_impl();
602 self.assemble_inherent_impl_for_primitive(lang_def_id);
604 ty::RawPtr(ty::TypeAndMut { ty: _, mutbl: hir::MutMutable }) => {
605 let lang_def_id = lang_items.mut_ptr_impl();
606 self.assemble_inherent_impl_for_primitive(lang_def_id);
608 ty::Int(ast::IntTy::I8) => {
609 let lang_def_id = lang_items.i8_impl();
610 self.assemble_inherent_impl_for_primitive(lang_def_id);
612 ty::Int(ast::IntTy::I16) => {
613 let lang_def_id = lang_items.i16_impl();
614 self.assemble_inherent_impl_for_primitive(lang_def_id);
616 ty::Int(ast::IntTy::I32) => {
617 let lang_def_id = lang_items.i32_impl();
618 self.assemble_inherent_impl_for_primitive(lang_def_id);
620 ty::Int(ast::IntTy::I64) => {
621 let lang_def_id = lang_items.i64_impl();
622 self.assemble_inherent_impl_for_primitive(lang_def_id);
624 ty::Int(ast::IntTy::I128) => {
625 let lang_def_id = lang_items.i128_impl();
626 self.assemble_inherent_impl_for_primitive(lang_def_id);
628 ty::Int(ast::IntTy::Isize) => {
629 let lang_def_id = lang_items.isize_impl();
630 self.assemble_inherent_impl_for_primitive(lang_def_id);
632 ty::Uint(ast::UintTy::U8) => {
633 let lang_def_id = lang_items.u8_impl();
634 self.assemble_inherent_impl_for_primitive(lang_def_id);
636 ty::Uint(ast::UintTy::U16) => {
637 let lang_def_id = lang_items.u16_impl();
638 self.assemble_inherent_impl_for_primitive(lang_def_id);
640 ty::Uint(ast::UintTy::U32) => {
641 let lang_def_id = lang_items.u32_impl();
642 self.assemble_inherent_impl_for_primitive(lang_def_id);
644 ty::Uint(ast::UintTy::U64) => {
645 let lang_def_id = lang_items.u64_impl();
646 self.assemble_inherent_impl_for_primitive(lang_def_id);
648 ty::Uint(ast::UintTy::U128) => {
649 let lang_def_id = lang_items.u128_impl();
650 self.assemble_inherent_impl_for_primitive(lang_def_id);
652 ty::Uint(ast::UintTy::Usize) => {
653 let lang_def_id = lang_items.usize_impl();
654 self.assemble_inherent_impl_for_primitive(lang_def_id);
656 ty::Float(ast::FloatTy::F32) => {
657 let lang_def_id = lang_items.f32_impl();
658 self.assemble_inherent_impl_for_primitive(lang_def_id);
660 let lang_def_id = lang_items.f32_runtime_impl();
661 self.assemble_inherent_impl_for_primitive(lang_def_id);
663 ty::Float(ast::FloatTy::F64) => {
664 let lang_def_id = lang_items.f64_impl();
665 self.assemble_inherent_impl_for_primitive(lang_def_id);
667 let lang_def_id = lang_items.f64_runtime_impl();
668 self.assemble_inherent_impl_for_primitive(lang_def_id);
674 fn assemble_inherent_impl_for_primitive(&mut self, lang_def_id: Option<DefId>) {
675 if let Some(impl_def_id) = lang_def_id {
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(ImplSource(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 // Determine the receiver type that the method itself expects.
705 let xform_tys = self.xform_self_ty(&item, impl_ty, impl_substs);
707 // We can't use normalize_associated_types_in as it will pollute the
708 // fcx's fulfillment context after this probe is over.
709 let cause = traits::ObligationCause::misc(self.span, self.body_id);
710 let selcx = &mut traits::SelectionContext::new(self.fcx);
711 let traits::Normalized { value: (xform_self_ty, xform_ret_ty), obligations } =
712 traits::normalize(selcx, self.param_env, cause, &xform_tys);
713 debug!("assemble_inherent_impl_probe: xform_self_ty = {:?}/{:?}",
714 xform_self_ty, xform_ret_ty);
716 self.push_candidate(Candidate {
717 xform_self_ty, xform_ret_ty, item,
718 kind: InherentImplCandidate(impl_substs, obligations),
724 fn assemble_inherent_candidates_from_object(&mut self,
726 debug!("assemble_inherent_candidates_from_object(self_ty={:?})",
729 let principal = match self_ty.sty {
730 ty::Dynamic(ref data, ..) => Some(data),
732 }.and_then(|data| data.principal()).unwrap_or_else(|| {
733 span_bug!(self.span, "non-object {:?} in assemble_inherent_candidates_from_object",
737 // It is illegal to invoke a method on a trait instance that
738 // refers to the `Self` type. An error will be reported by
739 // `enforce_object_limitations()` if the method refers to the
740 // `Self` type anywhere other than the receiver. Here, we use
741 // a substitution that replaces `Self` with the object type
742 // itself. Hence, a `&self` method will wind up with an
743 // argument type like `&Trait`.
744 let trait_ref = principal.with_self_ty(self.tcx, self_ty);
745 self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
746 let new_trait_ref = this.erase_late_bound_regions(&new_trait_ref);
748 let (xform_self_ty, xform_ret_ty) =
749 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
750 this.push_candidate(Candidate {
751 xform_self_ty, xform_ret_ty, item,
752 kind: ObjectCandidate,
758 fn assemble_inherent_candidates_from_param(&mut self,
759 param_ty: ty::ParamTy) {
760 // FIXME -- Do we want to commit to this behavior for param bounds?
762 let bounds = self.param_env
765 .filter_map(|predicate| {
767 ty::Predicate::Trait(ref trait_predicate) => {
768 match trait_predicate.skip_binder().trait_ref.self_ty().sty {
769 ty::Param(ref p) if *p == param_ty => {
770 Some(trait_predicate.to_poly_trait_ref())
775 ty::Predicate::Subtype(..) |
776 ty::Predicate::Projection(..) |
777 ty::Predicate::RegionOutlives(..) |
778 ty::Predicate::WellFormed(..) |
779 ty::Predicate::ObjectSafe(..) |
780 ty::Predicate::ClosureKind(..) |
781 ty::Predicate::TypeOutlives(..) |
782 ty::Predicate::ConstEvaluatable(..) => None,
786 self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
787 let trait_ref = this.erase_late_bound_regions(&poly_trait_ref);
789 let (xform_self_ty, xform_ret_ty) =
790 this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs);
792 // Because this trait derives from a where-clause, it
793 // should not contain any inference variables or other
794 // artifacts. This means it is safe to put into the
795 // `WhereClauseCandidate` and (eventually) into the
796 // `WhereClausePick`.
797 assert!(!trait_ref.substs.needs_infer());
799 this.push_candidate(Candidate {
800 xform_self_ty, xform_ret_ty, item,
801 kind: WhereClauseCandidate(poly_trait_ref),
807 // Do a search through a list of bounds, using a callback to actually
808 // create the candidates.
809 fn elaborate_bounds<F>(&mut self,
810 bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
812 where F: for<'b> FnMut(&mut ProbeContext<'b, 'gcx, 'tcx>,
813 ty::PolyTraitRef<'tcx>,
817 for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
818 debug!("elaborate_bounds(bound_trait_ref={:?})", bound_trait_ref);
819 for item in self.impl_or_trait_item(bound_trait_ref.def_id()) {
820 if !self.has_applicable_self(&item) {
821 self.record_static_candidate(TraitSource(bound_trait_ref.def_id()));
823 mk_cand(self, bound_trait_ref, item);
829 fn assemble_extension_candidates_for_traits_in_scope(&mut self,
830 expr_hir_id: hir::HirId)
831 -> Result<(), MethodError<'tcx>> {
832 if expr_hir_id == hir::DUMMY_HIR_ID {
835 let mut duplicates = FxHashSet::default();
836 let opt_applicable_traits = self.tcx.in_scope_traits(expr_hir_id);
837 if let Some(applicable_traits) = opt_applicable_traits {
838 for trait_candidate in applicable_traits.iter() {
839 let trait_did = trait_candidate.def_id;
840 if duplicates.insert(trait_did) {
841 let import_id = trait_candidate.import_id.map(|node_id|
842 self.fcx.tcx.hir().node_to_hir_id(node_id));
843 let result = self.assemble_extension_candidates_for_trait(import_id, trait_did);
851 fn assemble_extension_candidates_for_all_traits(&mut self) -> Result<(), MethodError<'tcx>> {
852 let mut duplicates = FxHashSet::default();
853 for trait_info in suggest::all_traits(self.tcx) {
854 if duplicates.insert(trait_info.def_id) {
855 self.assemble_extension_candidates_for_trait(None, trait_info.def_id)?;
861 pub fn matches_return_type(&self,
862 method: &ty::AssociatedItem,
863 self_ty: Option<Ty<'tcx>>,
864 expected: Ty<'tcx>) -> bool {
866 ty::AssociatedKind::Method => {
867 let fty = self.tcx.fn_sig(method.def_id);
869 let substs = self.fresh_substs_for_item(self.span, method.def_id);
870 let fty = fty.subst(self.tcx, substs);
871 let (fty, _) = self.replace_bound_vars_with_fresh_vars(
877 if let Some(self_ty) = self_ty {
878 if self.at(&ObligationCause::dummy(), self.param_env)
879 .sup(fty.inputs()[0], self_ty)
885 self.can_sub(self.param_env, fty.output(), expected).is_ok()
892 fn assemble_extension_candidates_for_trait(&mut self,
893 import_id: Option<hir::HirId>,
895 -> Result<(), MethodError<'tcx>> {
896 debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})",
898 let trait_substs = self.fresh_item_substs(trait_def_id);
899 let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
901 if self.tcx.is_trait_alias(trait_def_id) {
902 // For trait aliases, assume all super-traits are relevant.
903 let bounds = iter::once(trait_ref.to_poly_trait_ref());
904 self.elaborate_bounds(bounds, |this, new_trait_ref, item| {
905 let new_trait_ref = this.erase_late_bound_regions(&new_trait_ref);
907 let (xform_self_ty, xform_ret_ty) =
908 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
909 this.push_candidate(Candidate {
910 xform_self_ty, xform_ret_ty, item, import_id,
911 kind: TraitCandidate(new_trait_ref),
915 debug_assert!(self.tcx.is_trait(trait_def_id));
916 for item in self.impl_or_trait_item(trait_def_id) {
917 // Check whether `trait_def_id` defines a method with suitable name.
918 if !self.has_applicable_self(&item) {
919 debug!("method has inapplicable self");
920 self.record_static_candidate(TraitSource(trait_def_id));
924 let (xform_self_ty, xform_ret_ty) =
925 self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
926 self.push_candidate(Candidate {
927 xform_self_ty, xform_ret_ty, item, import_id,
928 kind: TraitCandidate(trait_ref),
935 fn candidate_method_names(&self) -> Vec<ast::Ident> {
936 let mut set = FxHashSet::default();
937 let mut names: Vec<_> = self.inherent_candidates
939 .chain(&self.extension_candidates)
940 .filter(|candidate| {
941 if let Some(return_ty) = self.return_type {
942 self.matches_return_type(&candidate.item, None, return_ty)
947 .map(|candidate| candidate.item.ident)
948 .filter(|&name| set.insert(name))
951 // Sort them by the name so we have a stable result.
952 names.sort_by_cached_key(|n| n.as_str());
956 ///////////////////////////////////////////////////////////////////////////
959 fn pick(mut self) -> PickResult<'tcx> {
960 assert!(self.method_name.is_some());
962 if let Some(r) = self.pick_core() {
966 debug!("pick: actual search failed, assemble diagnotics");
968 let static_candidates = mem::replace(&mut self.static_candidates, vec![]);
969 let private_candidate = self.private_candidate.take();
970 let unsatisfied_predicates = mem::replace(&mut self.unsatisfied_predicates, vec![]);
972 // things failed, so lets look at all traits, for diagnostic purposes now:
975 let span = self.span;
978 self.assemble_extension_candidates_for_all_traits()?;
980 let out_of_scope_traits = match self.pick_core() {
981 Some(Ok(p)) => vec![p.item.container.id()],
982 //Some(Ok(p)) => p.iter().map(|p| p.item.container().id()).collect(),
983 Some(Err(MethodError::Ambiguity(v))) => {
987 TraitSource(id) => id,
988 ImplSource(impl_id) => {
989 match tcx.trait_id_of_impl(impl_id) {
993 "found inherent method when looking at traits")
1001 Some(Err(MethodError::NoMatch(NoMatchData { out_of_scope_traits: others, .. }))) => {
1002 assert!(others.is_empty());
1008 if let Some((kind, def_id)) = private_candidate {
1009 return Err(MethodError::PrivateMatch(kind, def_id, out_of_scope_traits));
1011 let lev_candidate = self.probe_for_lev_candidate()?;
1013 Err(MethodError::NoMatch(NoMatchData::new(static_candidates,
1014 unsatisfied_predicates,
1015 out_of_scope_traits,
1020 fn pick_core(&mut self) -> Option<PickResult<'tcx>> {
1021 let steps = self.steps.clone();
1023 // find the first step that works
1027 debug!("pick_core: step={:?}", step);
1028 // skip types that are from a type error or that would require dereferencing
1030 !step.self_ty.references_error() && !step.from_unsafe_deref
1031 }).flat_map(|step| {
1032 let InferOk { value: self_ty, obligations: _ } =
1033 self.fcx.probe_instantiate_query_response(
1034 self.span, &self.orig_steps_var_values, &step.self_ty
1035 ).unwrap_or_else(|_| {
1036 span_bug!(self.span, "{:?} was applicable but now isn't?", step.self_ty)
1038 self.pick_by_value_method(step, self_ty).or_else(|| {
1039 self.pick_autorefd_method(step, self_ty, hir::MutImmutable).or_else(|| {
1040 self.pick_autorefd_method(step, self_ty, hir::MutMutable)
1045 fn pick_by_value_method(&mut self, step: &CandidateStep<'gcx>, self_ty: Ty<'tcx>)
1046 -> Option<PickResult<'tcx>>
1048 //! For each type `T` in the step list, this attempts to find a
1049 //! method where the (transformed) self type is exactly `T`. We
1050 //! do however do one transformation on the adjustment: if we
1051 //! are passing a region pointer in, we will potentially
1052 //! *reborrow* it to a shorter lifetime. This allows us to
1053 //! transparently pass `&mut` pointers, in particular, without
1054 //! consuming them for their entire lifetime.
1060 self.pick_method(self_ty).map(|r| {
1062 pick.autoderefs = step.autoderefs;
1064 // Insert a `&*` or `&mut *` if this is a reference type:
1065 if let ty::Ref(_, _, mutbl) = step.self_ty.value.value.sty {
1066 pick.autoderefs += 1;
1067 pick.autoref = Some(mutbl);
1075 fn pick_autorefd_method(&mut self,
1076 step: &CandidateStep<'gcx>,
1078 mutbl: hir::Mutability)
1079 -> Option<PickResult<'tcx>> {
1082 // In general, during probing we erase regions. See
1083 // `impl_self_ty()` for an explanation.
1084 let region = tcx.lifetimes.re_erased;
1086 let autoref_ty = tcx.mk_ref(region,
1090 self.pick_method(autoref_ty).map(|r| {
1092 pick.autoderefs = step.autoderefs;
1093 pick.autoref = Some(mutbl);
1094 pick.unsize = if step.unsize {
1104 fn pick_method(&mut self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
1105 debug!("pick_method(self_ty={})", self.ty_to_string(self_ty));
1107 let mut possibly_unsatisfied_predicates = Vec::new();
1108 let mut unstable_candidates = Vec::new();
1110 for (kind, candidates) in &[
1111 ("inherent", &self.inherent_candidates),
1112 ("extension", &self.extension_candidates),
1114 debug!("searching {} candidates", kind);
1115 let res = self.consider_candidates(
1118 &mut possibly_unsatisfied_predicates,
1119 Some(&mut unstable_candidates),
1121 if let Some(pick) = res {
1122 if !self.is_suggestion.0 && !unstable_candidates.is_empty() {
1123 if let Ok(p) = &pick {
1124 // Emit a lint if there are unstable candidates alongside the stable ones.
1126 // We suppress warning if we're picking the method only because it is a
1128 self.emit_unstable_name_collision_hint(p, &unstable_candidates);
1135 debug!("searching unstable candidates");
1136 let res = self.consider_candidates(
1138 unstable_candidates.into_iter().map(|(c, _)| c),
1139 &mut possibly_unsatisfied_predicates,
1143 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1148 fn consider_candidates<'b, ProbesIter>(
1152 possibly_unsatisfied_predicates: &mut Vec<TraitRef<'tcx>>,
1153 unstable_candidates: Option<&mut Vec<(&'b Candidate<'tcx>, Symbol)>>,
1154 ) -> Option<PickResult<'tcx>>
1156 ProbesIter: Iterator<Item = &'b Candidate<'tcx>> + Clone,
1158 let mut applicable_candidates: Vec<_> = probes.clone()
1160 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
1162 .filter(|&(_, status)| status != ProbeResult::NoMatch)
1165 debug!("applicable_candidates: {:?}", applicable_candidates);
1167 if applicable_candidates.len() > 1 {
1168 if let Some(pick) = self.collapse_candidates_to_trait_pick(&applicable_candidates[..]) {
1169 return Some(Ok(pick));
1173 if let Some(uc) = unstable_candidates {
1174 applicable_candidates.retain(|&(p, _)| {
1175 if let stability::EvalResult::Deny { feature, .. } =
1176 self.tcx.eval_stability(p.item.def_id, None, self.span)
1178 uc.push((p, feature));
1185 if applicable_candidates.len() > 1 {
1186 let sources = probes
1187 .map(|p| self.candidate_source(p, self_ty))
1189 return Some(Err(MethodError::Ambiguity(sources)));
1192 applicable_candidates.pop().map(|(probe, status)| {
1193 if status == ProbeResult::Match {
1194 Ok(probe.to_unadjusted_pick())
1196 Err(MethodError::BadReturnType)
1201 fn emit_unstable_name_collision_hint(
1203 stable_pick: &Pick<'_>,
1204 unstable_candidates: &[(&Candidate<'tcx>, Symbol)],
1206 let mut diag = self.tcx.struct_span_lint_hir(
1207 lint::builtin::UNSTABLE_NAME_COLLISIONS,
1210 "a method with this name may be added to the standard library in the future",
1213 // FIXME: This should be a `span_suggestion` instead of `help`
1214 // However `self.span` only
1215 // highlights the method name, so we can't use it. Also consider reusing the code from
1216 // `report_method_error()`.
1218 "call with fully qualified syntax `{}(...)` to keep using the current method",
1219 self.tcx.def_path_str(stable_pick.item.def_id),
1222 if nightly_options::is_nightly_build() {
1223 for (candidate, feature) in unstable_candidates {
1225 "add #![feature({})] to the crate attributes to enable `{}`",
1227 self.tcx.def_path_str(candidate.item.def_id),
1235 fn select_trait_candidate(&self, trait_ref: ty::TraitRef<'tcx>)
1236 -> traits::SelectionResult<'tcx, traits::Selection<'tcx>>
1238 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1240 trait_ref.to_poly_trait_ref().to_poly_trait_predicate();
1241 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1242 traits::SelectionContext::new(self).select(&obligation)
1245 fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>)
1248 match candidate.kind {
1249 InherentImplCandidate(..) => ImplSource(candidate.item.container.id()),
1251 WhereClauseCandidate(_) => TraitSource(candidate.item.container.id()),
1252 TraitCandidate(trait_ref) => self.probe(|_| {
1253 let _ = self.at(&ObligationCause::dummy(), self.param_env)
1254 .sup(candidate.xform_self_ty, self_ty);
1255 match self.select_trait_candidate(trait_ref) {
1256 Ok(Some(traits::Vtable::VtableImpl(ref impl_data))) => {
1257 // If only a single impl matches, make the error message point
1259 ImplSource(impl_data.impl_def_id)
1262 TraitSource(candidate.item.container.id())
1269 fn consider_probe(&self,
1271 probe: &Candidate<'tcx>,
1272 possibly_unsatisfied_predicates: &mut Vec<TraitRef<'tcx>>)
1274 debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe);
1277 // First check that the self type can be related.
1278 let sub_obligations = match self.at(&ObligationCause::dummy(), self.param_env)
1279 .sup(probe.xform_self_ty, self_ty) {
1280 Ok(InferOk { obligations, value: () }) => obligations,
1282 debug!("--> cannot relate self-types");
1283 return ProbeResult::NoMatch;
1287 let mut result = ProbeResult::Match;
1288 let selcx = &mut traits::SelectionContext::new(self);
1289 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1291 // If so, impls may carry other conditions (e.g., where
1292 // clauses) that must be considered. Make sure that those
1293 // match as well (or at least may match, sometimes we
1294 // don't have enough information to fully evaluate).
1295 let candidate_obligations : Vec<_> = match probe.kind {
1296 InherentImplCandidate(ref substs, ref ref_obligations) => {
1297 // Check whether the impl imposes obligations we have to worry about.
1298 let impl_def_id = probe.item.container.id();
1299 let impl_bounds = self.tcx.predicates_of(impl_def_id);
1300 let impl_bounds = impl_bounds.instantiate(self.tcx, substs);
1301 let traits::Normalized { value: impl_bounds, obligations: norm_obligations } =
1302 traits::normalize(selcx, self.param_env, cause.clone(), &impl_bounds);
1304 // Convert the bounds into obligations.
1305 let impl_obligations = traits::predicates_for_generics(
1306 cause, self.param_env, &impl_bounds);
1308 debug!("impl_obligations={:?}", impl_obligations);
1309 impl_obligations.into_iter()
1310 .chain(norm_obligations.into_iter())
1311 .chain(ref_obligations.iter().cloned())
1316 WhereClauseCandidate(..) => {
1317 // These have no additional conditions to check.
1321 TraitCandidate(trait_ref) => {
1322 let predicate = trait_ref.to_predicate();
1324 traits::Obligation::new(cause, self.param_env, predicate);
1325 if !self.predicate_may_hold(&obligation) {
1326 if self.probe(|_| self.select_trait_candidate(trait_ref).is_err()) {
1327 // This candidate's primary obligation doesn't even
1328 // select - don't bother registering anything in
1329 // `potentially_unsatisfied_predicates`.
1330 return ProbeResult::NoMatch;
1332 // Some nested subobligation of this predicate
1335 // FIXME: try to find the exact nested subobligation
1336 // and point at it rather than reporting the entire
1338 result = ProbeResult::NoMatch;
1339 let trait_ref = self.resolve_type_vars_if_possible(&trait_ref);
1340 possibly_unsatisfied_predicates.push(trait_ref);
1347 debug!("consider_probe - candidate_obligations={:?} sub_obligations={:?}",
1348 candidate_obligations, sub_obligations);
1350 // Evaluate those obligations to see if they might possibly hold.
1351 for o in candidate_obligations.into_iter().chain(sub_obligations) {
1352 let o = self.resolve_type_vars_if_possible(&o);
1353 if !self.predicate_may_hold(&o) {
1354 result = ProbeResult::NoMatch;
1355 if let &ty::Predicate::Trait(ref pred) = &o.predicate {
1356 possibly_unsatisfied_predicates.push(pred.skip_binder().trait_ref);
1361 if let ProbeResult::Match = result {
1362 if let (Some(return_ty), Some(xform_ret_ty)) =
1363 (self.return_type, probe.xform_ret_ty)
1365 let xform_ret_ty = self.resolve_type_vars_if_possible(&xform_ret_ty);
1366 debug!("comparing return_ty {:?} with xform ret ty {:?}",
1368 probe.xform_ret_ty);
1369 if self.at(&ObligationCause::dummy(), self.param_env)
1370 .sup(return_ty, xform_ret_ty)
1373 return ProbeResult::BadReturnType;
1382 /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1383 /// same trait, but we don't know which impl to use. In this case, since in all cases the
1384 /// external interface of the method can be determined from the trait, it's ok not to decide.
1385 /// We can basically just collapse all of the probes for various impls into one where-clause
1386 /// probe. This will result in a pending obligation so when more type-info is available we can
1387 /// make the final decision.
1389 /// Example (`src/test/run-pass/method-two-trait-defer-resolution-1.rs`):
1392 /// trait Foo { ... }
1393 /// impl Foo for Vec<int> { ... }
1394 /// impl Foo for Vec<usize> { ... }
1397 /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1398 /// use, so it's ok to just commit to "using the method from the trait Foo".
1399 fn collapse_candidates_to_trait_pick(&self, probes: &[(&Candidate<'tcx>, ProbeResult)])
1400 -> Option<Pick<'tcx>>
1402 // Do all probes correspond to the same trait?
1403 let container = probes[0].0.item.container;
1404 if let ty::ImplContainer(_) = container {
1407 if probes[1..].iter().any(|&(p, _)| p.item.container != container) {
1411 // FIXME: check the return type here somehow.
1412 // If so, just use this trait and call it a day.
1414 item: probes[0].0.item.clone(),
1416 import_id: probes[0].0.import_id,
1423 /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
1424 /// candidate method where the method name may have been misspelt. Similarly to other
1425 /// Levenshtein based suggestions, we provide at most one such suggestion.
1426 fn probe_for_lev_candidate(&mut self) -> Result<Option<ty::AssociatedItem>, MethodError<'tcx>> {
1427 debug!("Probing for method names similar to {:?}",
1430 let steps = self.steps.clone();
1432 let mut pcx = ProbeContext::new(self.fcx, self.span, self.mode, self.method_name,
1434 self.orig_steps_var_values.clone(),
1435 steps, IsSuggestion(true));
1436 pcx.allow_similar_names = true;
1437 pcx.assemble_inherent_candidates();
1438 pcx.assemble_extension_candidates_for_traits_in_scope(hir::DUMMY_HIR_ID)?;
1440 let method_names = pcx.candidate_method_names();
1441 pcx.allow_similar_names = false;
1442 let applicable_close_candidates: Vec<ty::AssociatedItem> = method_names
1444 .filter_map(|&method_name| {
1446 pcx.method_name = Some(method_name);
1447 pcx.assemble_inherent_candidates();
1448 pcx.assemble_extension_candidates_for_traits_in_scope(hir::DUMMY_HIR_ID)
1449 .ok().map_or(None, |_| {
1451 .and_then(|pick| pick.ok())
1452 .and_then(|pick| Some(pick.item))
1457 if applicable_close_candidates.is_empty() {
1461 let names = applicable_close_candidates.iter().map(|cand| &cand.ident.name);
1462 find_best_match_for_name(names,
1463 &self.method_name.unwrap().as_str(),
1466 Ok(applicable_close_candidates
1468 .find(|method| method.ident.name == best_name))
1473 ///////////////////////////////////////////////////////////////////////////
1475 fn has_applicable_self(&self, item: &ty::AssociatedItem) -> bool {
1476 // "Fast track" -- check for usage of sugar when in method call
1479 // In Path mode (i.e., resolving a value like `T::next`), consider any
1480 // associated value (i.e., methods, constants) but not types.
1482 Mode::MethodCall => item.method_has_self_argument,
1483 Mode::Path => match item.kind {
1484 ty::AssociatedKind::Existential |
1485 ty::AssociatedKind::Type => false,
1486 ty::AssociatedKind::Method | ty::AssociatedKind::Const => true
1489 // FIXME -- check for types that deref to `Self`,
1490 // like `Rc<Self>` and so on.
1492 // Note also that the current code will break if this type
1493 // includes any of the type parameters defined on the method
1494 // -- but this could be overcome.
1497 fn record_static_candidate(&mut self, source: CandidateSource) {
1498 self.static_candidates.push(source);
1501 fn xform_self_ty(&self,
1502 item: &ty::AssociatedItem,
1504 substs: SubstsRef<'tcx>)
1505 -> (Ty<'tcx>, Option<Ty<'tcx>>) {
1506 if item.kind == ty::AssociatedKind::Method && self.mode == Mode::MethodCall {
1507 let sig = self.xform_method_sig(item.def_id, substs);
1508 (sig.inputs()[0], Some(sig.output()))
1514 fn xform_method_sig(&self,
1516 substs: SubstsRef<'tcx>)
1519 let fn_sig = self.tcx.fn_sig(method);
1520 debug!("xform_self_ty(fn_sig={:?}, substs={:?})",
1524 assert!(!substs.has_escaping_bound_vars());
1526 // It is possible for type parameters or early-bound lifetimes
1527 // to appear in the signature of `self`. The substitutions we
1528 // are given do not include type/lifetime parameters for the
1529 // method yet. So create fresh variables here for those too,
1530 // if there are any.
1531 let generics = self.tcx.generics_of(method);
1532 assert_eq!(substs.len(), generics.parent_count as usize);
1534 // Erase any late-bound regions from the method and substitute
1535 // in the values from the substitution.
1536 let xform_fn_sig = self.erase_late_bound_regions(&fn_sig);
1538 if generics.params.is_empty() {
1539 xform_fn_sig.subst(self.tcx, substs)
1541 let substs = InternalSubsts::for_item(self.tcx, method, |param, _| {
1542 let i = param.index as usize;
1543 if i < substs.len() {
1547 GenericParamDefKind::Lifetime => {
1548 // In general, during probe we erase regions. See
1549 // `impl_self_ty()` for an explanation.
1550 self.tcx.lifetimes.re_erased.into()
1552 GenericParamDefKind::Type { .. }
1553 | GenericParamDefKind::Const => {
1554 self.var_for_def(self.span, param)
1559 xform_fn_sig.subst(self.tcx, substs)
1563 /// Gets the type of an impl and generate substitutions with placeholders.
1564 fn impl_ty_and_substs(&self, impl_def_id: DefId) -> (Ty<'tcx>, SubstsRef<'tcx>) {
1565 (self.tcx.type_of(impl_def_id), self.fresh_item_substs(impl_def_id))
1568 fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx> {
1569 InternalSubsts::for_item(self.tcx, def_id, |param, _| {
1571 GenericParamDefKind::Lifetime => self.tcx.lifetimes.re_erased.into(),
1572 GenericParamDefKind::Type { .. } => {
1573 self.next_ty_var(TypeVariableOrigin::SubstitutionPlaceholder(
1574 self.tcx.def_span(def_id))).into()
1576 GenericParamDefKind::Const { .. } => {
1577 let span = self.tcx.def_span(def_id);
1578 let origin = ConstVariableOrigin::SubstitutionPlaceholder(span);
1579 self.next_const_var(self.tcx.type_of(param.def_id), origin).into()
1585 /// Replaces late-bound-regions bound by `value` with `'static` using
1586 /// `ty::erase_late_bound_regions`.
1588 /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1589 /// method matching. It is reasonable during the probe phase because we don't consider region
1590 /// relationships at all. Therefore, we can just replace all the region variables with 'static
1591 /// rather than creating fresh region variables. This is nice for two reasons:
1593 /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1594 /// particular method call, it winds up creating fewer types overall, which helps for memory
1595 /// usage. (Admittedly, this is a rather small effect, though measurable.)
1597 /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1598 /// late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1599 /// regions with actual region variables as is proper, we'd have to ensure that the same
1600 /// region got replaced with the same variable, which requires a bit more coordination
1601 /// and/or tracking the substitution and
1603 fn erase_late_bound_regions<T>(&self, value: &ty::Binder<T>) -> T
1604 where T: TypeFoldable<'tcx>
1606 self.tcx.erase_late_bound_regions(value)
1609 /// Finds the method with the appropriate name (or return type, as the case may be). If
1610 /// `allow_similar_names` is set, find methods with close-matching names.
1611 fn impl_or_trait_item(&self, def_id: DefId) -> Vec<ty::AssociatedItem> {
1612 if let Some(name) = self.method_name {
1613 if self.allow_similar_names {
1614 let max_dist = max(name.as_str().len(), 3) / 3;
1615 self.tcx.associated_items(def_id)
1617 let dist = lev_distance(&*name.as_str(), &x.ident.as_str());
1618 Namespace::from(x.kind) == Namespace::Value && dist > 0
1624 .associated_item(def_id, name, Namespace::Value)
1625 .map_or(Vec::new(), |x| vec![x])
1628 self.tcx.associated_items(def_id).collect()
1633 impl<'tcx> Candidate<'tcx> {
1634 fn to_unadjusted_pick(&self) -> Pick<'tcx> {
1636 item: self.item.clone(),
1637 kind: match self.kind {
1638 InherentImplCandidate(..) => InherentImplPick,
1639 ObjectCandidate => ObjectPick,
1640 TraitCandidate(_) => TraitPick,
1641 WhereClauseCandidate(ref trait_ref) => {
1642 // Only trait derived from where-clauses should
1643 // appear here, so they should not contain any
1644 // inference variables or other artifacts. This
1645 // means they are safe to put into the
1646 // `WhereClausePick`.
1648 !trait_ref.skip_binder().substs.needs_infer()
1649 && !trait_ref.skip_binder().substs.has_placeholders()
1652 WhereClausePick(trait_ref.clone())
1655 import_id: self.import_id,