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, TypeVariableOriginKind};
24 use rustc::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
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 rustc_error_codes::*;
40 use smallvec::{smallvec, SmallVec};
42 use self::CandidateKind::*;
43 pub use self::PickKind::*;
45 /// Boolean flag used to indicate if this search is for a suggestion
46 /// or not. If true, we can allow ambiguity and so forth.
47 #[derive(Clone, Copy)]
48 pub struct IsSuggestion(pub bool);
50 struct ProbeContext<'a, 'tcx> {
51 fcx: &'a FnCtxt<'a, 'tcx>,
54 method_name: Option<ast::Ident>,
55 return_type: Option<Ty<'tcx>>,
57 /// This is the OriginalQueryValues for the steps queries
58 /// that are answered in steps.
59 orig_steps_var_values: OriginalQueryValues<'tcx>,
60 steps: Lrc<Vec<CandidateStep<'tcx>>>,
62 inherent_candidates: Vec<Candidate<'tcx>>,
63 extension_candidates: Vec<Candidate<'tcx>>,
64 impl_dups: FxHashSet<DefId>,
66 /// Collects near misses when the candidate functions are missing a `self` keyword and is only
67 /// used for error reporting
68 static_candidates: Vec<CandidateSource>,
70 /// When probing for names, include names that are close to the
71 /// requested name (by Levensthein distance)
72 allow_similar_names: bool,
74 /// Some(candidate) if there is a private candidate
75 private_candidate: Option<(DefKind, DefId)>,
77 /// Collects near misses when trait bounds for type parameters are unsatisfied and is only used
78 /// for error reporting
79 unsatisfied_predicates: Vec<TraitRef<'tcx>>,
81 is_suggestion: IsSuggestion,
84 impl<'a, 'tcx> Deref for ProbeContext<'a, 'tcx> {
85 type Target = FnCtxt<'a, 'tcx>;
86 fn deref(&self) -> &Self::Target {
92 struct Candidate<'tcx> {
93 // Candidates are (I'm not quite sure, but they are mostly) basically
94 // some metadata on top of a `ty::AssocItem` (without substs).
96 // However, method probing wants to be able to evaluate the predicates
97 // for a function with the substs applied - for example, if a function
98 // has `where Self: Sized`, we don't want to consider it unless `Self`
99 // is actually `Sized`, and similarly, return-type suggestions want
100 // to consider the "actual" return type.
102 // The way this is handled is through `xform_self_ty`. It contains
103 // the receiver type of this candidate, but `xform_self_ty`,
104 // `xform_ret_ty` and `kind` (which contains the predicates) have the
105 // generic parameters of this candidate substituted with the *same set*
106 // of inference variables, which acts as some weird sort of "query".
108 // When we check out a candidate, we require `xform_self_ty` to be
109 // a subtype of the passed-in self-type, and this equates the type
110 // variables in the rest of the fields.
112 // For example, if we have this candidate:
115 // fn foo(&self) where Self: Sized;
119 // Then `xform_self_ty` will be `&'erased ?X` and `kind` will contain
120 // the predicate `?X: Sized`, so if we are evaluating `Foo` for a
121 // the receiver `&T`, we'll do the subtyping which will make `?X`
122 // get the right value, then when we evaluate the predicate we'll check
124 xform_self_ty: Ty<'tcx>,
125 xform_ret_ty: Option<Ty<'tcx>>,
127 kind: CandidateKind<'tcx>,
128 import_ids: SmallVec<[hir::HirId; 1]>,
132 enum CandidateKind<'tcx> {
133 InherentImplCandidate(SubstsRef<'tcx>,
134 // Normalize obligations
135 Vec<traits::PredicateObligation<'tcx>>),
137 TraitCandidate(ty::TraitRef<'tcx>),
138 WhereClauseCandidate(// Trait
139 ty::PolyTraitRef<'tcx>),
142 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
149 #[derive(Debug, PartialEq, Clone)]
150 pub struct Pick<'tcx> {
151 pub item: ty::AssocItem,
152 pub kind: PickKind<'tcx>,
153 pub import_ids: SmallVec<[hir::HirId; 1]>,
155 // Indicates that the source expression should be autoderef'd N times
157 // A = expr | *expr | **expr | ...
158 pub autoderefs: usize,
160 // Indicates that an autoref is applied after the optional autoderefs
162 // B = A | &A | &mut A
163 pub autoref: Option<hir::Mutability>,
165 // Indicates that the source expression should be "unsized" to a
166 // target type. This should probably eventually go away in favor
167 // of just coercing method receivers.
170 pub unsize: Option<Ty<'tcx>>,
173 #[derive(Clone, Debug, PartialEq, Eq)]
174 pub enum PickKind<'tcx> {
178 WhereClausePick(// Trait
179 ty::PolyTraitRef<'tcx>),
182 pub type PickResult<'tcx> = Result<Pick<'tcx>, MethodError<'tcx>>;
184 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
186 // An expression of the form `receiver.method_name(...)`.
187 // Autoderefs are performed on `receiver`, lookup is done based on the
188 // `self` argument of the method, and static methods aren't considered.
190 // An expression of the form `Type::item` or `<T>::item`.
191 // No autoderefs are performed, lookup is done based on the type each
192 // implementation is for, and static methods are included.
196 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
197 pub enum ProbeScope {
198 // Assemble candidates coming only from traits in scope.
201 // Assemble candidates coming from all traits.
205 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
206 /// This is used to offer suggestions to users. It returns methods
207 /// that could have been called which have the desired return
208 /// type. Some effort is made to rule out methods that, if called,
209 /// would result in an error (basically, the same criteria we
210 /// would use to decide if a method is a plausible fit for
211 /// ambiguity purposes).
212 pub fn probe_for_return_type(&self,
215 return_type: Ty<'tcx>,
217 scope_expr_id: hir::HirId)
218 -> Vec<ty::AssocItem> {
219 debug!("probe(self_ty={:?}, return_type={}, scope_expr_id={})",
224 self.probe_op(span, mode, None, Some(return_type), IsSuggestion(true),
225 self_ty, scope_expr_id, ProbeScope::AllTraits,
226 |probe_cx| Ok(probe_cx.candidate_method_names()))
230 .flat_map(|&method_name| {
232 span, mode, Some(method_name), Some(return_type),
233 IsSuggestion(true), self_ty, scope_expr_id,
234 ProbeScope::AllTraits, |probe_cx| probe_cx.pick()
235 ).ok().map(|pick| pick.item)
240 pub fn probe_for_name(&self,
243 item_name: ast::Ident,
244 is_suggestion: IsSuggestion,
246 scope_expr_id: hir::HirId,
248 -> PickResult<'tcx> {
249 debug!("probe(self_ty={:?}, item_name={}, scope_expr_id={})",
261 |probe_cx| probe_cx.pick())
268 method_name: Option<ast::Ident>,
269 return_type: Option<Ty<'tcx>>,
270 is_suggestion: IsSuggestion,
272 scope_expr_id: hir::HirId,
275 ) -> Result<R, MethodError<'tcx>>
277 OP: FnOnce(ProbeContext<'a, 'tcx>) -> Result<R, MethodError<'tcx>>,
279 let mut orig_values = OriginalQueryValues::default();
280 let param_env_and_self_ty =
281 self.infcx.canonicalize_query(
283 param_env: self.param_env,
285 }, &mut orig_values);
287 let steps = if mode == Mode::MethodCall {
288 self.tcx.method_autoderef_steps(param_env_and_self_ty)
290 self.infcx.probe(|_| {
291 // Mode::Path - the deref steps is "trivial". This turns
292 // our CanonicalQuery into a "trivial" QueryResponse. This
293 // is a bit inefficient, but I don't think that writing
294 // special handling for this "trivial case" is a good idea.
296 let infcx = &self.infcx;
300 }, canonical_inference_vars) =
301 infcx.instantiate_canonical_with_fresh_inference_vars(
302 span, ¶m_env_and_self_ty);
303 debug!("probe_op: Mode::Path, param_env_and_self_ty={:?} self_ty={:?}",
304 param_env_and_self_ty, self_ty);
305 MethodAutoderefStepsResult {
306 steps: Lrc::new(vec![CandidateStep {
307 self_ty: self.make_query_response_ignoring_pending_obligations(
308 canonical_inference_vars, self_ty),
310 from_unsafe_deref: false,
314 reached_recursion_limit: false
319 // If our autoderef loop had reached the recursion limit,
320 // report an overflow error, but continue going on with
321 // the truncated autoderef list.
322 if steps.reached_recursion_limit {
324 let ty = &steps.steps.last().unwrap_or_else(|| {
325 span_bug!(span, "reached the recursion limit in 0 steps?")
327 let ty = self.probe_instantiate_query_response(span, &orig_values, ty)
328 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
329 autoderef::report_autoderef_recursion_limit_error(self.tcx, span,
335 // If we encountered an `_` type or an error type during autoderef, this is
337 if let Some(bad_ty) = &steps.opt_bad_ty {
339 // Ambiguity was encountered during a suggestion. Just keep going.
340 debug!("ProbeContext: encountered ambiguity in suggestion");
341 } else if bad_ty.reached_raw_pointer && !self.tcx.features().arbitrary_self_types {
342 // this case used to be allowed by the compiler,
343 // so we do a future-compat lint here for the 2015 edition
344 // (see https://github.com/rust-lang/rust/issues/46906)
345 if self.tcx.sess.rust_2018() {
346 span_err!(self.tcx.sess, span, E0699,
347 "the type of this value must be known \
348 to call a method on a raw pointer on it");
351 lint::builtin::TYVAR_BEHIND_RAW_POINTER,
354 "type annotations needed");
357 // Encountered a real ambiguity, so abort the lookup. If `ty` is not
358 // an `Err`, report the right "type annotations needed" error pointing
361 let ty = self.probe_instantiate_query_response(span, &orig_values, ty)
362 .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty));
363 let ty = self.structurally_resolved_type(span, ty.value);
364 assert_eq!(ty, self.tcx.types.err);
365 return Err(MethodError::NoMatch(NoMatchData::new(Vec::new(),
373 debug!("ProbeContext: steps for self_ty={:?} are {:?}",
378 // this creates one big transaction so that all type variables etc
379 // that we create during the probe process are removed later
381 let mut probe_cx = ProbeContext::new(
382 self, span, mode, method_name, return_type, orig_values,
383 steps.steps, is_suggestion,
386 probe_cx.assemble_inherent_candidates();
388 ProbeScope::TraitsInScope =>
389 probe_cx.assemble_extension_candidates_for_traits_in_scope(scope_expr_id)?,
390 ProbeScope::AllTraits =>
391 probe_cx.assemble_extension_candidates_for_all_traits()?,
398 pub fn provide(providers: &mut ty::query::Providers<'_>) {
399 providers.method_autoderef_steps = method_autoderef_steps;
402 fn method_autoderef_steps<'tcx>(
404 goal: CanonicalTyGoal<'tcx>,
405 ) -> MethodAutoderefStepsResult<'tcx> {
406 debug!("method_autoderef_steps({:?})", goal);
408 tcx.infer_ctxt().enter_with_canonical(DUMMY_SP, &goal, |ref infcx, goal, inference_vars| {
409 let ParamEnvAnd { param_env, value: self_ty } = goal;
411 let mut autoderef = Autoderef::new(infcx, param_env, hir::DUMMY_HIR_ID, DUMMY_SP, self_ty)
412 .include_raw_pointers()
414 let mut reached_raw_pointer = false;
415 let mut steps: Vec<_> = autoderef.by_ref()
417 let step = CandidateStep {
418 self_ty: infcx.make_query_response_ignoring_pending_obligations(
419 inference_vars.clone(), ty),
421 from_unsafe_deref: reached_raw_pointer,
424 if let ty::RawPtr(_) = ty.kind {
425 // all the subsequent steps will be from_unsafe_deref
426 reached_raw_pointer = true;
432 let final_ty = autoderef.maybe_ambiguous_final_ty();
433 let opt_bad_ty = match final_ty.kind {
434 ty::Infer(ty::TyVar(_)) |
436 Some(MethodAutoderefBadTy {
438 ty: infcx.make_query_response_ignoring_pending_obligations(
439 inference_vars, final_ty)
442 ty::Array(elem_ty, _) => {
443 let dereferences = steps.len() - 1;
445 steps.push(CandidateStep {
446 self_ty: infcx.make_query_response_ignoring_pending_obligations(
447 inference_vars, infcx.tcx.mk_slice(elem_ty)),
448 autoderefs: dereferences,
449 // this could be from an unsafe deref if we had
450 // a *mut/const [T; N]
451 from_unsafe_deref: reached_raw_pointer,
460 debug!("method_autoderef_steps: steps={:?} opt_bad_ty={:?}", steps, opt_bad_ty);
462 MethodAutoderefStepsResult {
463 steps: Lrc::new(steps),
464 opt_bad_ty: opt_bad_ty.map(Lrc::new),
465 reached_recursion_limit: autoderef.reached_recursion_limit()
470 impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
472 fcx: &'a FnCtxt<'a, 'tcx>,
475 method_name: Option<ast::Ident>,
476 return_type: Option<Ty<'tcx>>,
477 orig_steps_var_values: OriginalQueryValues<'tcx>,
478 steps: Lrc<Vec<CandidateStep<'tcx>>>,
479 is_suggestion: IsSuggestion,
480 ) -> ProbeContext<'a, 'tcx> {
487 inherent_candidates: Vec::new(),
488 extension_candidates: Vec::new(),
489 impl_dups: FxHashSet::default(),
490 orig_steps_var_values,
492 static_candidates: Vec::new(),
493 allow_similar_names: false,
494 private_candidate: None,
495 unsatisfied_predicates: Vec::new(),
500 fn reset(&mut self) {
501 self.inherent_candidates.clear();
502 self.extension_candidates.clear();
503 self.impl_dups.clear();
504 self.static_candidates.clear();
505 self.private_candidate = None;
508 ///////////////////////////////////////////////////////////////////////////
509 // CANDIDATE ASSEMBLY
511 fn push_candidate(&mut self,
512 candidate: Candidate<'tcx>,
515 let is_accessible = if let Some(name) = self.method_name {
516 let item = candidate.item;
518 self.tcx.adjust_ident_and_get_scope(name, item.container.id(), self.body_id).1;
519 item.vis.is_accessible_from(def_scope, self.tcx)
525 self.inherent_candidates.push(candidate);
527 self.extension_candidates.push(candidate);
529 } else if self.private_candidate.is_none() {
530 self.private_candidate =
531 Some((candidate.item.def_kind(), candidate.item.def_id));
535 fn assemble_inherent_candidates(&mut self) {
536 let steps = self.steps.clone();
537 for step in steps.iter() {
538 self.assemble_probe(&step.self_ty);
542 fn assemble_probe(&mut self, self_ty: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>) {
543 debug!("assemble_probe: self_ty={:?}", self_ty);
544 let lang_items = self.tcx.lang_items();
546 match self_ty.value.value.kind {
547 ty::Dynamic(ref data, ..) => {
548 if let Some(p) = data.principal() {
549 // Subtle: we can't use `instantiate_query_response` here: using it will
550 // commit to all of the type equalities assumed by inference going through
551 // autoderef (see the `method-probe-no-guessing` test).
553 // However, in this code, it is OK if we end up with an object type that is
554 // "more general" than the object type that we are evaluating. For *every*
555 // object type `MY_OBJECT`, a function call that goes through a trait-ref
556 // of the form `<MY_OBJECT as SuperTraitOf(MY_OBJECT)>::func` is a valid
557 // `ObjectCandidate`, and it should be discoverable "exactly" through one
558 // of the iterations in the autoderef loop, so there is no problem with it
559 // being discoverable in another one of these iterations.
561 // Using `instantiate_canonical_with_fresh_inference_vars` on our
562 // `Canonical<QueryResponse<Ty<'tcx>>>` and then *throwing away* the
563 // `CanonicalVarValues` will exactly give us such a generalization - it
564 // will still match the original object type, but it won't pollute our
565 // type variables in any form, so just do that!
566 let (QueryResponse { value: generalized_self_ty, .. }, _ignored_var_values) =
567 self.fcx.instantiate_canonical_with_fresh_inference_vars(
568 self.span, &self_ty);
570 self.assemble_inherent_candidates_from_object(generalized_self_ty);
571 self.assemble_inherent_impl_candidates_for_type(p.def_id());
575 self.assemble_inherent_impl_candidates_for_type(def.did);
577 ty::Foreign(did) => {
578 self.assemble_inherent_impl_candidates_for_type(did);
581 self.assemble_inherent_candidates_from_param(p);
584 let lang_def_id = lang_items.bool_impl();
585 self.assemble_inherent_impl_for_primitive(lang_def_id);
588 let lang_def_id = lang_items.char_impl();
589 self.assemble_inherent_impl_for_primitive(lang_def_id);
592 let lang_def_id = lang_items.str_impl();
593 self.assemble_inherent_impl_for_primitive(lang_def_id);
595 let lang_def_id = lang_items.str_alloc_impl();
596 self.assemble_inherent_impl_for_primitive(lang_def_id);
599 let lang_def_id = lang_items.slice_impl();
600 self.assemble_inherent_impl_for_primitive(lang_def_id);
602 let lang_def_id = lang_items.slice_u8_impl();
603 self.assemble_inherent_impl_for_primitive(lang_def_id);
605 let lang_def_id = lang_items.slice_alloc_impl();
606 self.assemble_inherent_impl_for_primitive(lang_def_id);
608 let lang_def_id = lang_items.slice_u8_alloc_impl();
609 self.assemble_inherent_impl_for_primitive(lang_def_id);
611 ty::RawPtr(ty::TypeAndMut { ty: _, mutbl: hir::Mutability::Immutable }) => {
612 let lang_def_id = lang_items.const_ptr_impl();
613 self.assemble_inherent_impl_for_primitive(lang_def_id);
615 ty::RawPtr(ty::TypeAndMut { ty: _, mutbl: hir::Mutability::Mutable }) => {
616 let lang_def_id = lang_items.mut_ptr_impl();
617 self.assemble_inherent_impl_for_primitive(lang_def_id);
619 ty::Int(ast::IntTy::I8) => {
620 let lang_def_id = lang_items.i8_impl();
621 self.assemble_inherent_impl_for_primitive(lang_def_id);
623 ty::Int(ast::IntTy::I16) => {
624 let lang_def_id = lang_items.i16_impl();
625 self.assemble_inherent_impl_for_primitive(lang_def_id);
627 ty::Int(ast::IntTy::I32) => {
628 let lang_def_id = lang_items.i32_impl();
629 self.assemble_inherent_impl_for_primitive(lang_def_id);
631 ty::Int(ast::IntTy::I64) => {
632 let lang_def_id = lang_items.i64_impl();
633 self.assemble_inherent_impl_for_primitive(lang_def_id);
635 ty::Int(ast::IntTy::I128) => {
636 let lang_def_id = lang_items.i128_impl();
637 self.assemble_inherent_impl_for_primitive(lang_def_id);
639 ty::Int(ast::IntTy::Isize) => {
640 let lang_def_id = lang_items.isize_impl();
641 self.assemble_inherent_impl_for_primitive(lang_def_id);
643 ty::Uint(ast::UintTy::U8) => {
644 let lang_def_id = lang_items.u8_impl();
645 self.assemble_inherent_impl_for_primitive(lang_def_id);
647 ty::Uint(ast::UintTy::U16) => {
648 let lang_def_id = lang_items.u16_impl();
649 self.assemble_inherent_impl_for_primitive(lang_def_id);
651 ty::Uint(ast::UintTy::U32) => {
652 let lang_def_id = lang_items.u32_impl();
653 self.assemble_inherent_impl_for_primitive(lang_def_id);
655 ty::Uint(ast::UintTy::U64) => {
656 let lang_def_id = lang_items.u64_impl();
657 self.assemble_inherent_impl_for_primitive(lang_def_id);
659 ty::Uint(ast::UintTy::U128) => {
660 let lang_def_id = lang_items.u128_impl();
661 self.assemble_inherent_impl_for_primitive(lang_def_id);
663 ty::Uint(ast::UintTy::Usize) => {
664 let lang_def_id = lang_items.usize_impl();
665 self.assemble_inherent_impl_for_primitive(lang_def_id);
667 ty::Float(ast::FloatTy::F32) => {
668 let lang_def_id = lang_items.f32_impl();
669 self.assemble_inherent_impl_for_primitive(lang_def_id);
671 let lang_def_id = lang_items.f32_runtime_impl();
672 self.assemble_inherent_impl_for_primitive(lang_def_id);
674 ty::Float(ast::FloatTy::F64) => {
675 let lang_def_id = lang_items.f64_impl();
676 self.assemble_inherent_impl_for_primitive(lang_def_id);
678 let lang_def_id = lang_items.f64_runtime_impl();
679 self.assemble_inherent_impl_for_primitive(lang_def_id);
685 fn assemble_inherent_impl_for_primitive(&mut self, lang_def_id: Option<DefId>) {
686 if let Some(impl_def_id) = lang_def_id {
687 self.assemble_inherent_impl_probe(impl_def_id);
691 fn assemble_inherent_impl_candidates_for_type(&mut self, def_id: DefId) {
692 let impl_def_ids = self.tcx.at(self.span).inherent_impls(def_id);
693 for &impl_def_id in impl_def_ids.iter() {
694 self.assemble_inherent_impl_probe(impl_def_id);
698 fn assemble_inherent_impl_probe(&mut self, impl_def_id: DefId) {
699 if !self.impl_dups.insert(impl_def_id) {
700 return; // already visited
703 debug!("assemble_inherent_impl_probe {:?}", impl_def_id);
705 for item in self.impl_or_trait_item(impl_def_id) {
706 if !self.has_applicable_self(&item) {
707 // No receiver declared. Not a candidate.
708 self.record_static_candidate(ImplSource(impl_def_id));
712 let (impl_ty, impl_substs) = self.impl_ty_and_substs(impl_def_id);
713 let impl_ty = impl_ty.subst(self.tcx, impl_substs);
715 // Determine the receiver type that the method itself expects.
716 let xform_tys = self.xform_self_ty(&item, impl_ty, impl_substs);
718 // We can't use normalize_associated_types_in as it will pollute the
719 // fcx's fulfillment context after this probe is over.
720 let cause = traits::ObligationCause::misc(self.span, self.body_id);
721 let selcx = &mut traits::SelectionContext::new(self.fcx);
722 let traits::Normalized { value: (xform_self_ty, xform_ret_ty), obligations } =
723 traits::normalize(selcx, self.param_env, cause, &xform_tys);
724 debug!("assemble_inherent_impl_probe: xform_self_ty = {:?}/{:?}",
725 xform_self_ty, xform_ret_ty);
727 self.push_candidate(Candidate {
728 xform_self_ty, xform_ret_ty, item,
729 kind: InherentImplCandidate(impl_substs, obligations),
730 import_ids: smallvec![]
735 fn assemble_inherent_candidates_from_object(&mut self,
737 debug!("assemble_inherent_candidates_from_object(self_ty={:?})",
740 let principal = match self_ty.kind {
741 ty::Dynamic(ref data, ..) => Some(data),
743 }.and_then(|data| data.principal()).unwrap_or_else(|| {
744 span_bug!(self.span, "non-object {:?} in assemble_inherent_candidates_from_object",
748 // It is illegal to invoke a method on a trait instance that
749 // refers to the `Self` type. An error will be reported by
750 // `enforce_object_limitations()` if the method refers to the
751 // `Self` type anywhere other than the receiver. Here, we use
752 // a substitution that replaces `Self` with the object type
753 // itself. Hence, a `&self` method will wind up with an
754 // argument type like `&Trait`.
755 let trait_ref = principal.with_self_ty(self.tcx, self_ty);
756 self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
757 let new_trait_ref = this.erase_late_bound_regions(&new_trait_ref);
759 let (xform_self_ty, xform_ret_ty) =
760 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
761 this.push_candidate(Candidate {
762 xform_self_ty, xform_ret_ty, item,
763 kind: ObjectCandidate,
764 import_ids: smallvec![]
769 fn assemble_inherent_candidates_from_param(&mut self, param_ty: ty::ParamTy) {
770 // FIXME: do we want to commit to this behavior for param bounds?
772 let bounds = self.param_env
775 .filter_map(|predicate| {
777 ty::Predicate::Trait(ref trait_predicate) => {
778 match trait_predicate.skip_binder().trait_ref.self_ty().kind {
779 ty::Param(ref p) if *p == param_ty => {
780 Some(trait_predicate.to_poly_trait_ref())
785 ty::Predicate::Subtype(..) |
786 ty::Predicate::Projection(..) |
787 ty::Predicate::RegionOutlives(..) |
788 ty::Predicate::WellFormed(..) |
789 ty::Predicate::ObjectSafe(..) |
790 ty::Predicate::ClosureKind(..) |
791 ty::Predicate::TypeOutlives(..) |
792 ty::Predicate::ConstEvaluatable(..) => None,
796 self.elaborate_bounds(bounds, |this, poly_trait_ref, item| {
797 let trait_ref = this.erase_late_bound_regions(&poly_trait_ref);
799 let (xform_self_ty, xform_ret_ty) =
800 this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs);
802 // Because this trait derives from a where-clause, it
803 // should not contain any inference variables or other
804 // artifacts. This means it is safe to put into the
805 // `WhereClauseCandidate` and (eventually) into the
806 // `WhereClausePick`.
807 assert!(!trait_ref.substs.needs_infer());
809 this.push_candidate(Candidate {
810 xform_self_ty, xform_ret_ty, item,
811 kind: WhereClauseCandidate(poly_trait_ref),
812 import_ids: smallvec![]
817 // Do a search through a list of bounds, using a callback to actually
818 // create the candidates.
819 fn elaborate_bounds<F>(
821 bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
824 F: for<'b> FnMut(&mut ProbeContext<'b, 'tcx>, ty::PolyTraitRef<'tcx>, ty::AssocItem),
827 for bound_trait_ref in traits::transitive_bounds(tcx, bounds) {
828 debug!("elaborate_bounds(bound_trait_ref={:?})", bound_trait_ref);
829 for item in self.impl_or_trait_item(bound_trait_ref.def_id()) {
830 if !self.has_applicable_self(&item) {
831 self.record_static_candidate(TraitSource(bound_trait_ref.def_id()));
833 mk_cand(self, bound_trait_ref, item);
839 fn assemble_extension_candidates_for_traits_in_scope(&mut self,
840 expr_hir_id: hir::HirId)
841 -> Result<(), MethodError<'tcx>> {
842 if expr_hir_id == hir::DUMMY_HIR_ID {
845 let mut duplicates = FxHashSet::default();
846 let opt_applicable_traits = self.tcx.in_scope_traits(expr_hir_id);
847 if let Some(applicable_traits) = opt_applicable_traits {
848 for trait_candidate in applicable_traits.iter() {
849 let trait_did = trait_candidate.def_id;
850 if duplicates.insert(trait_did) {
851 let import_ids = trait_candidate.import_ids.iter().map(|node_id|
852 self.fcx.tcx.hir().node_to_hir_id(*node_id)).collect();
853 let result = self.assemble_extension_candidates_for_trait(import_ids,
862 fn assemble_extension_candidates_for_all_traits(&mut self) -> Result<(), MethodError<'tcx>> {
863 let mut duplicates = FxHashSet::default();
864 for trait_info in suggest::all_traits(self.tcx) {
865 if duplicates.insert(trait_info.def_id) {
866 self.assemble_extension_candidates_for_trait(smallvec![], trait_info.def_id)?;
872 pub fn matches_return_type(&self,
873 method: &ty::AssocItem,
874 self_ty: Option<Ty<'tcx>>,
875 expected: Ty<'tcx>) -> bool {
877 ty::AssocKind::Method => {
878 let fty = self.tcx.fn_sig(method.def_id);
880 let substs = self.fresh_substs_for_item(self.span, method.def_id);
881 let fty = fty.subst(self.tcx, substs);
882 let (fty, _) = self.replace_bound_vars_with_fresh_vars(
888 if let Some(self_ty) = self_ty {
889 if self.at(&ObligationCause::dummy(), self.param_env)
890 .sup(fty.inputs()[0], self_ty)
896 self.can_sub(self.param_env, fty.output(), expected).is_ok()
903 fn assemble_extension_candidates_for_trait(&mut self,
904 import_ids: SmallVec<[hir::HirId; 1]>,
906 -> Result<(), MethodError<'tcx>> {
907 debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})",
909 let trait_substs = self.fresh_item_substs(trait_def_id);
910 let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
912 if self.tcx.is_trait_alias(trait_def_id) {
913 // For trait aliases, assume all super-traits are relevant.
914 let bounds = iter::once(trait_ref.to_poly_trait_ref());
915 self.elaborate_bounds(bounds, |this, new_trait_ref, item| {
916 let new_trait_ref = this.erase_late_bound_regions(&new_trait_ref);
918 let (xform_self_ty, xform_ret_ty) =
919 this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
920 this.push_candidate(Candidate {
921 xform_self_ty, xform_ret_ty, item, import_ids: import_ids.clone(),
922 kind: TraitCandidate(new_trait_ref),
926 debug_assert!(self.tcx.is_trait(trait_def_id));
927 for item in self.impl_or_trait_item(trait_def_id) {
928 // Check whether `trait_def_id` defines a method with suitable name.
929 if !self.has_applicable_self(&item) {
930 debug!("method has inapplicable self");
931 self.record_static_candidate(TraitSource(trait_def_id));
935 let (xform_self_ty, xform_ret_ty) =
936 self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
937 self.push_candidate(Candidate {
938 xform_self_ty, xform_ret_ty, item, import_ids: import_ids.clone(),
939 kind: TraitCandidate(trait_ref),
946 fn candidate_method_names(&self) -> Vec<ast::Ident> {
947 let mut set = FxHashSet::default();
948 let mut names: Vec<_> = self.inherent_candidates
950 .chain(&self.extension_candidates)
951 .filter(|candidate| {
952 if let Some(return_ty) = self.return_type {
953 self.matches_return_type(&candidate.item, None, return_ty)
958 .map(|candidate| candidate.item.ident)
959 .filter(|&name| set.insert(name))
962 // Sort them by the name so we have a stable result.
963 names.sort_by_cached_key(|n| n.as_str());
967 ///////////////////////////////////////////////////////////////////////////
970 fn pick(mut self) -> PickResult<'tcx> {
971 assert!(self.method_name.is_some());
973 if let Some(r) = self.pick_core() {
977 debug!("pick: actual search failed, assemble diagnotics");
979 let static_candidates = mem::take(&mut self.static_candidates);
980 let private_candidate = self.private_candidate.take();
981 let unsatisfied_predicates = mem::take(&mut self.unsatisfied_predicates);
983 // things failed, so lets look at all traits, for diagnostic purposes now:
986 let span = self.span;
989 self.assemble_extension_candidates_for_all_traits()?;
991 let out_of_scope_traits = match self.pick_core() {
992 Some(Ok(p)) => vec![p.item.container.id()],
993 //Some(Ok(p)) => p.iter().map(|p| p.item.container().id()).collect(),
994 Some(Err(MethodError::Ambiguity(v))) => {
998 TraitSource(id) => id,
999 ImplSource(impl_id) => {
1000 match tcx.trait_id_of_impl(impl_id) {
1004 "found inherent method when looking at traits")
1012 Some(Err(MethodError::NoMatch(NoMatchData { out_of_scope_traits: others, .. }))) => {
1013 assert!(others.is_empty());
1019 if let Some((kind, def_id)) = private_candidate {
1020 return Err(MethodError::PrivateMatch(kind, def_id, out_of_scope_traits));
1022 let lev_candidate = self.probe_for_lev_candidate()?;
1024 Err(MethodError::NoMatch(NoMatchData::new(static_candidates,
1025 unsatisfied_predicates,
1026 out_of_scope_traits,
1031 fn pick_core(&mut self) -> Option<PickResult<'tcx>> {
1032 let steps = self.steps.clone();
1034 // find the first step that works
1038 debug!("pick_core: step={:?}", step);
1039 // skip types that are from a type error or that would require dereferencing
1041 !step.self_ty.references_error() && !step.from_unsafe_deref
1042 }).flat_map(|step| {
1043 let InferOk { value: self_ty, obligations: _ } =
1044 self.fcx.probe_instantiate_query_response(
1045 self.span, &self.orig_steps_var_values, &step.self_ty
1046 ).unwrap_or_else(|_| {
1047 span_bug!(self.span, "{:?} was applicable but now isn't?", step.self_ty)
1049 self.pick_by_value_method(step, self_ty).or_else(|| {
1050 self.pick_autorefd_method(step, self_ty, hir::Mutability::Immutable).or_else(|| {
1051 self.pick_autorefd_method(step, self_ty, hir::Mutability::Mutable)
1056 fn pick_by_value_method(
1058 step: &CandidateStep<'tcx>,
1060 ) -> Option<PickResult<'tcx>> {
1061 //! For each type `T` in the step list, this attempts to find a
1062 //! method where the (transformed) self type is exactly `T`. We
1063 //! do however do one transformation on the adjustment: if we
1064 //! are passing a region pointer in, we will potentially
1065 //! *reborrow* it to a shorter lifetime. This allows us to
1066 //! transparently pass `&mut` pointers, in particular, without
1067 //! consuming them for their entire lifetime.
1073 self.pick_method(self_ty).map(|r| {
1075 pick.autoderefs = step.autoderefs;
1077 // Insert a `&*` or `&mut *` if this is a reference type:
1078 if let ty::Ref(_, _, mutbl) = step.self_ty.value.value.kind {
1079 pick.autoderefs += 1;
1080 pick.autoref = Some(mutbl);
1088 fn pick_autorefd_method(
1090 step: &CandidateStep<'tcx>,
1092 mutbl: hir::Mutability,
1093 ) -> Option<PickResult<'tcx>> {
1096 // In general, during probing we erase regions. See
1097 // `impl_self_ty()` for an explanation.
1098 let region = tcx.lifetimes.re_erased;
1100 let autoref_ty = tcx.mk_ref(region,
1104 self.pick_method(autoref_ty).map(|r| {
1106 pick.autoderefs = step.autoderefs;
1107 pick.autoref = Some(mutbl);
1108 pick.unsize = if step.unsize {
1118 fn pick_method(&mut self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> {
1119 debug!("pick_method(self_ty={})", self.ty_to_string(self_ty));
1121 let mut possibly_unsatisfied_predicates = Vec::new();
1122 let mut unstable_candidates = Vec::new();
1124 for (kind, candidates) in &[
1125 ("inherent", &self.inherent_candidates),
1126 ("extension", &self.extension_candidates),
1128 debug!("searching {} candidates", kind);
1129 let res = self.consider_candidates(
1132 &mut possibly_unsatisfied_predicates,
1133 Some(&mut unstable_candidates),
1135 if let Some(pick) = res {
1136 if !self.is_suggestion.0 && !unstable_candidates.is_empty() {
1137 if let Ok(p) = &pick {
1138 // Emit a lint if there are unstable candidates alongside the stable ones.
1140 // We suppress warning if we're picking the method only because it is a
1142 self.emit_unstable_name_collision_hint(p, &unstable_candidates);
1149 debug!("searching unstable candidates");
1150 let res = self.consider_candidates(
1152 unstable_candidates.into_iter().map(|(c, _)| c),
1153 &mut possibly_unsatisfied_predicates,
1157 self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates);
1162 fn consider_candidates<'b, ProbesIter>(
1166 possibly_unsatisfied_predicates: &mut Vec<TraitRef<'tcx>>,
1167 unstable_candidates: Option<&mut Vec<(&'b Candidate<'tcx>, Symbol)>>,
1168 ) -> Option<PickResult<'tcx>>
1170 ProbesIter: Iterator<Item = &'b Candidate<'tcx>> + Clone,
1172 let mut applicable_candidates: Vec<_> = probes.clone()
1174 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
1176 .filter(|&(_, status)| status != ProbeResult::NoMatch)
1179 debug!("applicable_candidates: {:?}", applicable_candidates);
1181 if applicable_candidates.len() > 1 {
1182 if let Some(pick) = self.collapse_candidates_to_trait_pick(&applicable_candidates[..]) {
1183 return Some(Ok(pick));
1187 if let Some(uc) = unstable_candidates {
1188 applicable_candidates.retain(|&(p, _)| {
1189 if let stability::EvalResult::Deny { feature, .. } =
1190 self.tcx.eval_stability(p.item.def_id, None, self.span)
1192 uc.push((p, feature));
1199 if applicable_candidates.len() > 1 {
1200 let sources = probes
1201 .map(|p| self.candidate_source(p, self_ty))
1203 return Some(Err(MethodError::Ambiguity(sources)));
1206 applicable_candidates.pop().map(|(probe, status)| {
1207 if status == ProbeResult::Match {
1208 Ok(probe.to_unadjusted_pick())
1210 Err(MethodError::BadReturnType)
1215 fn emit_unstable_name_collision_hint(
1217 stable_pick: &Pick<'_>,
1218 unstable_candidates: &[(&Candidate<'tcx>, Symbol)],
1220 let mut diag = self.tcx.struct_span_lint_hir(
1221 lint::builtin::UNSTABLE_NAME_COLLISIONS,
1224 "a method with this name may be added to the standard library in the future",
1227 // FIXME: This should be a `span_suggestion` instead of `help`
1228 // However `self.span` only
1229 // highlights the method name, so we can't use it. Also consider reusing the code from
1230 // `report_method_error()`.
1232 "call with fully qualified syntax `{}(...)` to keep using the current method",
1233 self.tcx.def_path_str(stable_pick.item.def_id),
1236 if nightly_options::is_nightly_build() {
1237 for (candidate, feature) in unstable_candidates {
1239 "add `#![feature({})]` to the crate attributes to enable `{}`",
1241 self.tcx.def_path_str(candidate.item.def_id),
1249 fn select_trait_candidate(&self, trait_ref: ty::TraitRef<'tcx>)
1250 -> traits::SelectionResult<'tcx, traits::Selection<'tcx>>
1252 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1254 trait_ref.to_poly_trait_ref().to_poly_trait_predicate();
1255 let obligation = traits::Obligation::new(cause, self.param_env, predicate);
1256 traits::SelectionContext::new(self).select(&obligation)
1259 fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>)
1262 match candidate.kind {
1263 InherentImplCandidate(..) => ImplSource(candidate.item.container.id()),
1265 WhereClauseCandidate(_) => TraitSource(candidate.item.container.id()),
1266 TraitCandidate(trait_ref) => self.probe(|_| {
1267 let _ = self.at(&ObligationCause::dummy(), self.param_env)
1268 .sup(candidate.xform_self_ty, self_ty);
1269 match self.select_trait_candidate(trait_ref) {
1270 Ok(Some(traits::Vtable::VtableImpl(ref impl_data))) => {
1271 // If only a single impl matches, make the error message point
1273 ImplSource(impl_data.impl_def_id)
1276 TraitSource(candidate.item.container.id())
1283 fn consider_probe(&self,
1285 probe: &Candidate<'tcx>,
1286 possibly_unsatisfied_predicates: &mut Vec<TraitRef<'tcx>>)
1288 debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe);
1291 // First check that the self type can be related.
1292 let sub_obligations = match self.at(&ObligationCause::dummy(), self.param_env)
1293 .sup(probe.xform_self_ty, self_ty) {
1294 Ok(InferOk { obligations, value: () }) => obligations,
1296 debug!("--> cannot relate self-types");
1297 return ProbeResult::NoMatch;
1301 let mut result = ProbeResult::Match;
1302 let selcx = &mut traits::SelectionContext::new(self);
1303 let cause = traits::ObligationCause::misc(self.span, self.body_id);
1305 // If so, impls may carry other conditions (e.g., where
1306 // clauses) that must be considered. Make sure that those
1307 // match as well (or at least may match, sometimes we
1308 // don't have enough information to fully evaluate).
1309 let candidate_obligations : Vec<_> = match probe.kind {
1310 InherentImplCandidate(ref substs, ref ref_obligations) => {
1311 // Check whether the impl imposes obligations we have to worry about.
1312 let impl_def_id = probe.item.container.id();
1313 let impl_bounds = self.tcx.predicates_of(impl_def_id);
1314 let impl_bounds = impl_bounds.instantiate(self.tcx, substs);
1315 let traits::Normalized { value: impl_bounds, obligations: norm_obligations } =
1316 traits::normalize(selcx, self.param_env, cause.clone(), &impl_bounds);
1318 // Convert the bounds into obligations.
1319 let impl_obligations = traits::predicates_for_generics(
1320 cause, self.param_env, &impl_bounds);
1322 debug!("impl_obligations={:?}", impl_obligations);
1323 impl_obligations.into_iter()
1324 .chain(norm_obligations.into_iter())
1325 .chain(ref_obligations.iter().cloned())
1330 WhereClauseCandidate(..) => {
1331 // These have no additional conditions to check.
1335 TraitCandidate(trait_ref) => {
1336 let predicate = trait_ref.to_predicate();
1338 traits::Obligation::new(cause, self.param_env, predicate);
1339 if !self.predicate_may_hold(&obligation) {
1340 if self.probe(|_| self.select_trait_candidate(trait_ref).is_err()) {
1341 // This candidate's primary obligation doesn't even
1342 // select - don't bother registering anything in
1343 // `potentially_unsatisfied_predicates`.
1344 return ProbeResult::NoMatch;
1346 // Some nested subobligation of this predicate
1349 // FIXME: try to find the exact nested subobligation
1350 // and point at it rather than reporting the entire
1352 result = ProbeResult::NoMatch;
1353 let trait_ref = self.resolve_vars_if_possible(&trait_ref);
1354 possibly_unsatisfied_predicates.push(trait_ref);
1361 debug!("consider_probe - candidate_obligations={:?} sub_obligations={:?}",
1362 candidate_obligations, sub_obligations);
1364 // Evaluate those obligations to see if they might possibly hold.
1365 for o in candidate_obligations.into_iter().chain(sub_obligations) {
1366 let o = self.resolve_vars_if_possible(&o);
1367 if !self.predicate_may_hold(&o) {
1368 result = ProbeResult::NoMatch;
1369 if let &ty::Predicate::Trait(ref pred) = &o.predicate {
1370 possibly_unsatisfied_predicates.push(pred.skip_binder().trait_ref);
1375 if let ProbeResult::Match = result {
1376 if let (Some(return_ty), Some(xform_ret_ty)) =
1377 (self.return_type, probe.xform_ret_ty)
1379 let xform_ret_ty = self.resolve_vars_if_possible(&xform_ret_ty);
1380 debug!("comparing return_ty {:?} with xform ret ty {:?}",
1382 probe.xform_ret_ty);
1383 if self.at(&ObligationCause::dummy(), self.param_env)
1384 .sup(return_ty, xform_ret_ty)
1387 return ProbeResult::BadReturnType;
1396 /// Sometimes we get in a situation where we have multiple probes that are all impls of the
1397 /// same trait, but we don't know which impl to use. In this case, since in all cases the
1398 /// external interface of the method can be determined from the trait, it's ok not to decide.
1399 /// We can basically just collapse all of the probes for various impls into one where-clause
1400 /// probe. This will result in a pending obligation so when more type-info is available we can
1401 /// make the final decision.
1403 /// Example (`src/test/ui/method-two-trait-defer-resolution-1.rs`):
1406 /// trait Foo { ... }
1407 /// impl Foo for Vec<int> { ... }
1408 /// impl Foo for Vec<usize> { ... }
1411 /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we
1412 /// use, so it's ok to just commit to "using the method from the trait Foo".
1413 fn collapse_candidates_to_trait_pick(&self, probes: &[(&Candidate<'tcx>, ProbeResult)])
1414 -> Option<Pick<'tcx>>
1416 // Do all probes correspond to the same trait?
1417 let container = probes[0].0.item.container;
1418 if let ty::ImplContainer(_) = container {
1421 if probes[1..].iter().any(|&(p, _)| p.item.container != container) {
1425 // FIXME: check the return type here somehow.
1426 // If so, just use this trait and call it a day.
1428 item: probes[0].0.item.clone(),
1430 import_ids: probes[0].0.import_ids.clone(),
1437 /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
1438 /// candidate method where the method name may have been misspelt. Similarly to other
1439 /// Levenshtein based suggestions, we provide at most one such suggestion.
1440 fn probe_for_lev_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
1441 debug!("probing for method names similar to {:?}",
1444 let steps = self.steps.clone();
1446 let mut pcx = ProbeContext::new(self.fcx, self.span, self.mode, self.method_name,
1448 self.orig_steps_var_values.clone(),
1449 steps, IsSuggestion(true));
1450 pcx.allow_similar_names = true;
1451 pcx.assemble_inherent_candidates();
1452 pcx.assemble_extension_candidates_for_traits_in_scope(hir::DUMMY_HIR_ID)?;
1454 let method_names = pcx.candidate_method_names();
1455 pcx.allow_similar_names = false;
1456 let applicable_close_candidates: Vec<ty::AssocItem> = method_names
1458 .filter_map(|&method_name| {
1460 pcx.method_name = Some(method_name);
1461 pcx.assemble_inherent_candidates();
1462 pcx.assemble_extension_candidates_for_traits_in_scope(hir::DUMMY_HIR_ID)
1463 .ok().map_or(None, |_| {
1465 .and_then(|pick| pick.ok())
1466 .and_then(|pick| Some(pick.item))
1471 if applicable_close_candidates.is_empty() {
1475 let names = applicable_close_candidates.iter().map(|cand| &cand.ident.name);
1476 find_best_match_for_name(names,
1477 &self.method_name.unwrap().as_str(),
1480 Ok(applicable_close_candidates
1482 .find(|method| method.ident.name == best_name))
1487 ///////////////////////////////////////////////////////////////////////////
1489 fn has_applicable_self(&self, item: &ty::AssocItem) -> bool {
1490 // "Fast track" -- check for usage of sugar when in method call
1493 // In Path mode (i.e., resolving a value like `T::next`), consider any
1494 // associated value (i.e., methods, constants) but not types.
1496 Mode::MethodCall => item.method_has_self_argument,
1497 Mode::Path => match item.kind {
1498 ty::AssocKind::OpaqueTy |
1499 ty::AssocKind::Type => false,
1500 ty::AssocKind::Method | ty::AssocKind::Const => true
1503 // FIXME -- check for types that deref to `Self`,
1504 // like `Rc<Self>` and so on.
1506 // Note also that the current code will break if this type
1507 // includes any of the type parameters defined on the method
1508 // -- but this could be overcome.
1511 fn record_static_candidate(&mut self, source: CandidateSource) {
1512 self.static_candidates.push(source);
1515 fn xform_self_ty(&self,
1516 item: &ty::AssocItem,
1518 substs: SubstsRef<'tcx>)
1519 -> (Ty<'tcx>, Option<Ty<'tcx>>) {
1520 if item.kind == ty::AssocKind::Method && self.mode == Mode::MethodCall {
1521 let sig = self.xform_method_sig(item.def_id, substs);
1522 (sig.inputs()[0], Some(sig.output()))
1528 fn xform_method_sig(&self,
1530 substs: SubstsRef<'tcx>)
1533 let fn_sig = self.tcx.fn_sig(method);
1534 debug!("xform_self_ty(fn_sig={:?}, substs={:?})",
1538 assert!(!substs.has_escaping_bound_vars());
1540 // It is possible for type parameters or early-bound lifetimes
1541 // to appear in the signature of `self`. The substitutions we
1542 // are given do not include type/lifetime parameters for the
1543 // method yet. So create fresh variables here for those too,
1544 // if there are any.
1545 let generics = self.tcx.generics_of(method);
1546 assert_eq!(substs.len(), generics.parent_count as usize);
1548 // Erase any late-bound regions from the method and substitute
1549 // in the values from the substitution.
1550 let xform_fn_sig = self.erase_late_bound_regions(&fn_sig);
1552 if generics.params.is_empty() {
1553 xform_fn_sig.subst(self.tcx, substs)
1555 let substs = InternalSubsts::for_item(self.tcx, method, |param, _| {
1556 let i = param.index as usize;
1557 if i < substs.len() {
1561 GenericParamDefKind::Lifetime => {
1562 // In general, during probe we erase regions. See
1563 // `impl_self_ty()` for an explanation.
1564 self.tcx.lifetimes.re_erased.into()
1566 GenericParamDefKind::Type { .. }
1567 | GenericParamDefKind::Const => {
1568 self.var_for_def(self.span, param)
1573 xform_fn_sig.subst(self.tcx, substs)
1577 /// Gets the type of an impl and generate substitutions with placeholders.
1578 fn impl_ty_and_substs(&self, impl_def_id: DefId) -> (Ty<'tcx>, SubstsRef<'tcx>) {
1579 (self.tcx.type_of(impl_def_id), self.fresh_item_substs(impl_def_id))
1582 fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx> {
1583 InternalSubsts::for_item(self.tcx, def_id, |param, _| {
1585 GenericParamDefKind::Lifetime => self.tcx.lifetimes.re_erased.into(),
1586 GenericParamDefKind::Type { .. } => {
1587 self.next_ty_var(TypeVariableOrigin {
1588 kind: TypeVariableOriginKind::SubstitutionPlaceholder,
1589 span: self.tcx.def_span(def_id),
1592 GenericParamDefKind::Const { .. } => {
1593 let span = self.tcx.def_span(def_id);
1594 let origin = ConstVariableOrigin {
1595 kind: ConstVariableOriginKind::SubstitutionPlaceholder,
1598 self.next_const_var(self.tcx.type_of(param.def_id), origin).into()
1604 /// Replaces late-bound-regions bound by `value` with `'static` using
1605 /// `ty::erase_late_bound_regions`.
1607 /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of
1608 /// method matching. It is reasonable during the probe phase because we don't consider region
1609 /// relationships at all. Therefore, we can just replace all the region variables with 'static
1610 /// rather than creating fresh region variables. This is nice for two reasons:
1612 /// 1. Because the numbers of the region variables would otherwise be fairly unique to this
1613 /// particular method call, it winds up creating fewer types overall, which helps for memory
1614 /// usage. (Admittedly, this is a rather small effect, though measurable.)
1616 /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any
1617 /// late-bound regions with 'static. Otherwise, if we were going to replace late-bound
1618 /// regions with actual region variables as is proper, we'd have to ensure that the same
1619 /// region got replaced with the same variable, which requires a bit more coordination
1620 /// and/or tracking the substitution and
1622 fn erase_late_bound_regions<T>(&self, value: &ty::Binder<T>) -> T
1623 where T: TypeFoldable<'tcx>
1625 self.tcx.erase_late_bound_regions(value)
1628 /// Finds the method with the appropriate name (or return type, as the case may be). If
1629 /// `allow_similar_names` is set, find methods with close-matching names.
1630 fn impl_or_trait_item(&self, def_id: DefId) -> Vec<ty::AssocItem> {
1631 if let Some(name) = self.method_name {
1632 if self.allow_similar_names {
1633 let max_dist = max(name.as_str().len(), 3) / 3;
1634 self.tcx.associated_items(def_id)
1636 let dist = lev_distance(&*name.as_str(), &x.ident.as_str());
1637 Namespace::from(x.kind) == Namespace::Value && dist > 0
1643 .associated_item(def_id, name, Namespace::Value)
1644 .map_or(Vec::new(), |x| vec![x])
1647 self.tcx.associated_items(def_id).collect()
1652 impl<'tcx> Candidate<'tcx> {
1653 fn to_unadjusted_pick(&self) -> Pick<'tcx> {
1655 item: self.item.clone(),
1656 kind: match self.kind {
1657 InherentImplCandidate(..) => InherentImplPick,
1658 ObjectCandidate => ObjectPick,
1659 TraitCandidate(_) => TraitPick,
1660 WhereClauseCandidate(ref trait_ref) => {
1661 // Only trait derived from where-clauses should
1662 // appear here, so they should not contain any
1663 // inference variables or other artifacts. This
1664 // means they are safe to put into the
1665 // `WhereClausePick`.
1667 !trait_ref.skip_binder().substs.needs_infer()
1668 && !trait_ref.skip_binder().substs.has_placeholders()
1671 WhereClausePick(trait_ref.clone())
1674 import_ids: self.import_ids.clone(),