compiler/rustc_hir_typeck/src/method/mod.rs

   1 //! Method lookup: the secret sauce of Rust. See the [rustc dev guide] for more information.
   2 //!
   3 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/method-lookup.html
   4
   5 mod confirm;
   6 mod prelude2021;
   7 pub mod probe;
   8 mod suggest;
   9
  10 pub use self::suggest::SelfSource;
  11 pub use self::MethodError::*;
  12
  13 use crate::errors::OpMethodGenericParams;
  14 use crate::{Expectation, FnCtxt};
  15 use rustc_data_structures::sync::Lrc;
  16 use rustc_errors::{Applicability, Diagnostic};
  17 use rustc_hir as hir;
  18 use rustc_hir::def::{CtorOf, DefKind, Namespace};
  19 use rustc_hir::def_id::DefId;
  20 use rustc_infer::infer::{self, InferOk};
  21 use rustc_middle::traits::ObligationCause;
  22 use rustc_middle::ty::subst::{InternalSubsts, SubstsRef};
  23 use rustc_middle::ty::{self, DefIdTree, GenericParamDefKind, ToPredicate, Ty, TypeVisitable};
  24 use rustc_span::symbol::Ident;
  25 use rustc_span::Span;
  26 use rustc_trait_selection::traits;
  27 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
  28
  29 use self::probe::{IsSuggestion, ProbeScope};
  30
  31 pub fn provide(providers: &mut ty::query::Providers) {
  32     probe::provide(providers);
  33 }
  34
  35 #[derive(Clone, Copy, Debug)]
  36 pub struct MethodCallee<'tcx> {
  37     /// Impl method ID, for inherent methods, or trait method ID, otherwise.
  38     pub def_id: DefId,
  39     pub substs: SubstsRef<'tcx>,
  40
  41     /// Instantiated method signature, i.e., it has been
  42     /// substituted, normalized, and has had late-bound
  43     /// lifetimes replaced with inference variables.
  44     pub sig: ty::FnSig<'tcx>,
  45 }
  46
  47 #[derive(Debug)]
  48 pub enum MethodError<'tcx> {
  49     // Did not find an applicable method, but we did find various near-misses that may work.
  50     NoMatch(NoMatchData<'tcx>),
  51
  52     // Multiple methods might apply.
  53     Ambiguity(Vec<CandidateSource>),
  54
  55     // Found an applicable method, but it is not visible. The third argument contains a list of
  56     // not-in-scope traits which may work.
  57     PrivateMatch(DefKind, DefId, Vec<DefId>),
  58
  59     // Found a `Self: Sized` bound where `Self` is a trait object.
  60     IllegalSizedBound(Vec<DefId>, bool, Span),
  61
  62     // Found a match, but the return type is wrong
  63     BadReturnType,
  64 }
  65
  66 // Contains a list of static methods that may apply, a list of unsatisfied trait predicates which
  67 // could lead to matches if satisfied, and a list of not-in-scope traits which may work.
  68 #[derive(Debug)]
  69 pub struct NoMatchData<'tcx> {
  70     pub static_candidates: Vec<CandidateSource>,
  71     pub unsatisfied_predicates:
  72         Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>, Option<ObligationCause<'tcx>>)>,
  73     pub out_of_scope_traits: Vec<DefId>,
  74     pub lev_candidate: Option<ty::AssocItem>,
  75     pub mode: probe::Mode,
  76 }
  77
  78 // A pared down enum describing just the places from which a method
  79 // candidate can arise. Used for error reporting only.
  80 #[derive(Copy, Clone, Debug, Eq, Ord, PartialEq, PartialOrd)]
  81 pub enum CandidateSource {
  82     Impl(DefId),
  83     Trait(DefId /* trait id */),
  84 }
  85
  86 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  87     /// Determines whether the type `self_ty` supports a method name `method_name` or not.
  88     #[instrument(level = "debug", skip(self))]
  89     pub fn method_exists(
  90         &self,
  91         method_name: Ident,
  92         self_ty: Ty<'tcx>,
  93         call_expr_id: hir::HirId,
  94         allow_private: bool,
  95     ) -> bool {
  96         match self.probe_for_name(
  97             probe::Mode::MethodCall,
  98             method_name,
  99             IsSuggestion(false),
 100             self_ty,
 101             call_expr_id,
 102             ProbeScope::TraitsInScope,
 103         ) {
 104             Ok(..) => true,
 105             Err(NoMatch(..)) => false,
 106             Err(Ambiguity(..)) => true,
 107             Err(PrivateMatch(..)) => allow_private,
 108             Err(IllegalSizedBound(..)) => true,
 109             Err(BadReturnType) => bug!("no return type expectations but got BadReturnType"),
 110         }
 111     }
 112
 113     /// Adds a suggestion to call the given method to the provided diagnostic.
 114     #[instrument(level = "debug", skip(self, err, call_expr))]
 115     pub(crate) fn suggest_method_call(
 116         &self,
 117         err: &mut Diagnostic,
 118         msg: &str,
 119         method_name: Ident,
 120         self_ty: Ty<'tcx>,
 121         call_expr: &hir::Expr<'_>,
 122         span: Option<Span>,
 123     ) {
 124         let params = self
 125             .probe_for_name(
 126                 probe::Mode::MethodCall,
 127                 method_name,
 128                 IsSuggestion(true),
 129                 self_ty,
 130                 call_expr.hir_id,
 131                 ProbeScope::TraitsInScope,
 132             )
 133             .map(|pick| {
 134                 let sig = self.tcx.fn_sig(pick.item.def_id);
 135                 sig.inputs().skip_binder().len().saturating_sub(1)
 136             })
 137             .unwrap_or(0);
 138
 139         // Account for `foo.bar<T>`;
 140         let sugg_span = span.unwrap_or(call_expr.span).shrink_to_hi();
 141         let (suggestion, applicability) = (
 142             format!("({})", (0..params).map(|_| "_").collect::<Vec<_>>().join(", ")),
 143             if params > 0 { Applicability::HasPlaceholders } else { Applicability::MaybeIncorrect },
 144         );
 145
 146         err.span_suggestion_verbose(sugg_span, msg, suggestion, applicability);
 147     }
 148
 149     /// Performs method lookup. If lookup is successful, it will return the callee
 150     /// and store an appropriate adjustment for the self-expr. In some cases it may
 151     /// report an error (e.g., invoking the `drop` method).
 152     ///
 153     /// # Arguments
 154     ///
 155     /// Given a method call like `foo.bar::<T1,...Tn>(a, b + 1, ...)`:
 156     ///
 157     /// * `self`:                  the surrounding `FnCtxt` (!)
 158     /// * `self_ty`:               the (unadjusted) type of the self expression (`foo`)
 159     /// * `segment`:               the name and generic arguments of the method (`bar::<T1, ...Tn>`)
 160     /// * `span`:                  the span for the method call
 161     /// * `call_expr`:             the complete method call: (`foo.bar::<T1,...Tn>(...)`)
 162     /// * `self_expr`:             the self expression (`foo`)
 163     /// * `args`:                  the expressions of the arguments (`a, b + 1, ...`)
 164     #[instrument(level = "debug", skip(self))]
 165     pub fn lookup_method(
 166         &self,
 167         self_ty: Ty<'tcx>,
 168         segment: &hir::PathSegment<'_>,
 169         span: Span,
 170         call_expr: &'tcx hir::Expr<'tcx>,
 171         self_expr: &'tcx hir::Expr<'tcx>,
 172         args: &'tcx [hir::Expr<'tcx>],
 173     ) -> Result<MethodCallee<'tcx>, MethodError<'tcx>> {
 174         let pick =
 175             self.lookup_probe(segment.ident, self_ty, call_expr, ProbeScope::TraitsInScope)?;
 176
 177         self.lint_dot_call_from_2018(self_ty, segment, span, call_expr, self_expr, &pick, args);
 178
 179         for import_id in &pick.import_ids {
 180             debug!("used_trait_import: {:?}", import_id);
 181             Lrc::get_mut(&mut self.typeck_results.borrow_mut().used_trait_imports)
 182                 .unwrap()
 183                 .insert(*import_id);
 184         }
 185
 186         self.tcx.check_stability(pick.item.def_id, Some(call_expr.hir_id), span, None);
 187
 188         let result =
 189             self.confirm_method(span, self_expr, call_expr, self_ty, pick.clone(), segment);
 190         debug!("result = {:?}", result);
 191
 192         if let Some(span) = result.illegal_sized_bound {
 193             let mut needs_mut = false;
 194             if let ty::Ref(region, t_type, mutability) = self_ty.kind() {
 195                 let trait_type = self
 196                     .tcx
 197                     .mk_ref(*region, ty::TypeAndMut { ty: *t_type, mutbl: mutability.invert() });
 198                 // We probe again to see if there might be a borrow mutability discrepancy.
 199                 match self.lookup_probe(
 200                     segment.ident,
 201                     trait_type,
 202                     call_expr,
 203                     ProbeScope::TraitsInScope,
 204                 ) {
 205                     Ok(ref new_pick) if *new_pick != pick => {
 206                         needs_mut = true;
 207                     }
 208                     _ => {}
 209                 }
 210             }
 211
 212             // We probe again, taking all traits into account (not only those in scope).
 213             let mut candidates =
 214                 match self.lookup_probe(segment.ident, self_ty, call_expr, ProbeScope::AllTraits) {
 215                     // If we find a different result the caller probably forgot to import a trait.
 216                     Ok(ref new_pick) if *new_pick != pick => {
 217                         vec![new_pick.item.container_id(self.tcx)]
 218                     }
 219                     Err(Ambiguity(ref sources)) => sources
 220                         .iter()
 221                         .filter_map(|source| {
 222                             match *source {
 223                                 // Note: this cannot come from an inherent impl,
 224                                 // because the first probing succeeded.
 225                                 CandidateSource::Impl(def) => self.tcx.trait_id_of_impl(def),
 226                                 CandidateSource::Trait(_) => None,
 227                             }
 228                         })
 229                         .collect(),
 230                     _ => Vec::new(),
 231                 };
 232             candidates.retain(|candidate| *candidate != self.tcx.parent(result.callee.def_id));
 233
 234             return Err(IllegalSizedBound(candidates, needs_mut, span));
 235         }
 236
 237         Ok(result.callee)
 238     }
 239
 240     #[instrument(level = "debug", skip(self, call_expr))]
 241     pub fn lookup_probe(
 242         &self,
 243         method_name: Ident,
 244         self_ty: Ty<'tcx>,
 245         call_expr: &'tcx hir::Expr<'tcx>,
 246         scope: ProbeScope,
 247     ) -> probe::PickResult<'tcx> {
 248         self.probe_for_name(
 249             probe::Mode::MethodCall,
 250             method_name,
 251             IsSuggestion(false),
 252             self_ty,
 253             call_expr.hir_id,
 254             scope,
 255         )
 256     }
 257
 258     pub(super) fn obligation_for_method(
 259         &self,
 260         span: Span,
 261         trait_def_id: DefId,
 262         self_ty: Ty<'tcx>,
 263         opt_input_types: Option<&[Ty<'tcx>]>,
 264     ) -> (traits::Obligation<'tcx, ty::Predicate<'tcx>>, &'tcx ty::List<ty::subst::GenericArg<'tcx>>)
 265     {
 266         // Construct a trait-reference `self_ty : Trait<input_tys>`
 267         let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
 268             match param.kind {
 269                 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => {}
 270                 GenericParamDefKind::Type { .. } => {
 271                     if param.index == 0 {
 272                         return self_ty.into();
 273                     } else if let Some(input_types) = opt_input_types {
 274                         return input_types[param.index as usize - 1].into();
 275                     }
 276                 }
 277             }
 278             self.var_for_def(span, param)
 279         });
 280
 281         let trait_ref = ty::TraitRef::new(trait_def_id, substs);
 282
 283         // Construct an obligation
 284         let poly_trait_ref = ty::Binder::dummy(trait_ref);
 285         (
 286             traits::Obligation::misc(
 287                 span,
 288                 self.body_id,
 289                 self.param_env,
 290                 poly_trait_ref.without_const().to_predicate(self.tcx),
 291             ),
 292             substs,
 293         )
 294     }
 295
 296     pub(super) fn obligation_for_op_method(
 297         &self,
 298         span: Span,
 299         trait_def_id: DefId,
 300         self_ty: Ty<'tcx>,
 301         opt_input_type: Option<Ty<'tcx>>,
 302         opt_input_expr: Option<&'tcx hir::Expr<'tcx>>,
 303         expected: Expectation<'tcx>,
 304     ) -> (traits::Obligation<'tcx, ty::Predicate<'tcx>>, &'tcx ty::List<ty::subst::GenericArg<'tcx>>)
 305     {
 306         // Construct a trait-reference `self_ty : Trait<input_tys>`
 307         let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
 308             match param.kind {
 309                 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => {}
 310                 GenericParamDefKind::Type { .. } => {
 311                     if param.index == 0 {
 312                         return self_ty.into();
 313                     } else if let Some(input_type) = opt_input_type {
 314                         return input_type.into();
 315                     }
 316                 }
 317             }
 318             self.var_for_def(span, param)
 319         });
 320
 321         let trait_ref = ty::TraitRef::new(trait_def_id, substs);
 322
 323         // Construct an obligation
 324         let poly_trait_ref = ty::Binder::dummy(trait_ref);
 325         let output_ty = expected.only_has_type(self).and_then(|ty| (!ty.needs_infer()).then(|| ty));
 326
 327         (
 328             traits::Obligation::new(
 329                 traits::ObligationCause::new(
 330                     span,
 331                     self.body_id,
 332                     traits::BinOp {
 333                         rhs_span: opt_input_expr.map(|expr| expr.span),
 334                         is_lit: opt_input_expr
 335                             .map_or(false, |expr| matches!(expr.kind, hir::ExprKind::Lit(_))),
 336                         output_ty,
 337                     },
 338                 ),
 339                 self.param_env,
 340                 poly_trait_ref.without_const().to_predicate(self.tcx),
 341             ),
 342             substs,
 343         )
 344     }
 345
 346     /// `lookup_method_in_trait` is used for overloaded operators.
 347     /// It does a very narrow slice of what the normal probe/confirm path does.
 348     /// In particular, it doesn't really do any probing: it simply constructs
 349     /// an obligation for a particular trait with the given self type and checks
 350     /// whether that trait is implemented.
 351     #[instrument(level = "debug", skip(self, span))]
 352     pub(super) fn lookup_method_in_trait(
 353         &self,
 354         span: Span,
 355         m_name: Ident,
 356         trait_def_id: DefId,
 357         self_ty: Ty<'tcx>,
 358         opt_input_types: Option<&[Ty<'tcx>]>,
 359     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 360         let (obligation, substs) =
 361             self.obligation_for_method(span, trait_def_id, self_ty, opt_input_types);
 362         self.construct_obligation_for_trait(
 363             span,
 364             m_name,
 365             trait_def_id,
 366             obligation,
 367             substs,
 368             None,
 369             false,
 370         )
 371     }
 372
 373     pub(super) fn lookup_op_method_in_trait(
 374         &self,
 375         span: Span,
 376         m_name: Ident,
 377         trait_def_id: DefId,
 378         self_ty: Ty<'tcx>,
 379         opt_input_type: Option<Ty<'tcx>>,
 380         opt_input_expr: Option<&'tcx hir::Expr<'tcx>>,
 381         expected: Expectation<'tcx>,
 382     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 383         let (obligation, substs) = self.obligation_for_op_method(
 384             span,
 385             trait_def_id,
 386             self_ty,
 387             opt_input_type,
 388             opt_input_expr,
 389             expected,
 390         );
 391         self.construct_obligation_for_trait(
 392             span,
 393             m_name,
 394             trait_def_id,
 395             obligation,
 396             substs,
 397             opt_input_expr,
 398             true,
 399         )
 400     }
 401
 402     // FIXME(#18741): it seems likely that we can consolidate some of this
 403     // code with the other method-lookup code. In particular, the second half
 404     // of this method is basically the same as confirmation.
 405     fn construct_obligation_for_trait(
 406         &self,
 407         span: Span,
 408         m_name: Ident,
 409         trait_def_id: DefId,
 410         obligation: traits::PredicateObligation<'tcx>,
 411         substs: &'tcx ty::List<ty::subst::GenericArg<'tcx>>,
 412         opt_input_expr: Option<&'tcx hir::Expr<'tcx>>,
 413         is_op: bool,
 414     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 415         debug!(?obligation);
 416
 417         // Now we want to know if this can be matched
 418         if !self.predicate_may_hold(&obligation) {
 419             debug!("--> Cannot match obligation");
 420             // Cannot be matched, no such method resolution is possible.
 421             return None;
 422         }
 423
 424         // Trait must have a method named `m_name` and it should not have
 425         // type parameters or early-bound regions.
 426         let tcx = self.tcx;
 427         let Some(method_item) = self.associated_value(trait_def_id, m_name) else {
 428             tcx.sess.delay_span_bug(
 429                 span,
 430                 "operator trait does not have corresponding operator method",
 431             );
 432             return None;
 433         };
 434         let def_id = method_item.def_id;
 435         let generics = tcx.generics_of(def_id);
 436
 437         if generics.params.len() != 0 {
 438             tcx.sess.emit_fatal(OpMethodGenericParams {
 439                 span: tcx.def_span(method_item.def_id),
 440                 method_name: m_name.to_string(),
 441             });
 442         }
 443
 444         debug!("lookup_in_trait_adjusted: method_item={:?}", method_item);
 445         let mut obligations = vec![];
 446
 447         // Instantiate late-bound regions and substitute the trait
 448         // parameters into the method type to get the actual method type.
 449         //
 450         // N.B., instantiate late-bound regions first so that
 451         // `instantiate_type_scheme` can normalize associated types that
 452         // may reference those regions.
 453         let fn_sig = tcx.bound_fn_sig(def_id);
 454         let fn_sig = fn_sig.subst(self.tcx, substs);
 455         let fn_sig = self.replace_bound_vars_with_fresh_vars(span, infer::FnCall, fn_sig);
 456
 457         let InferOk { value, obligations: o } = if is_op {
 458             self.normalize_op_associated_types_in_as_infer_ok(span, fn_sig, opt_input_expr)
 459         } else {
 460             self.normalize_associated_types_in_as_infer_ok(span, fn_sig)
 461         };
 462         let fn_sig = {
 463             obligations.extend(o);
 464             value
 465         };
 466
 467         // Register obligations for the parameters. This will include the
 468         // `Self` parameter, which in turn has a bound of the main trait,
 469         // so this also effectively registers `obligation` as well.  (We
 470         // used to register `obligation` explicitly, but that resulted in
 471         // double error messages being reported.)
 472         //
 473         // Note that as the method comes from a trait, it should not have
 474         // any late-bound regions appearing in its bounds.
 475         let bounds = self.tcx.predicates_of(def_id).instantiate(self.tcx, substs);
 476
 477         let InferOk { value, obligations: o } = if is_op {
 478             self.normalize_op_associated_types_in_as_infer_ok(span, bounds, opt_input_expr)
 479         } else {
 480             self.normalize_associated_types_in_as_infer_ok(span, bounds)
 481         };
 482         let bounds = {
 483             obligations.extend(o);
 484             value
 485         };
 486
 487         assert!(!bounds.has_escaping_bound_vars());
 488
 489         let cause = if is_op {
 490             ObligationCause::new(
 491                 span,
 492                 self.body_id,
 493                 traits::BinOp {
 494                     rhs_span: opt_input_expr.map(|expr| expr.span),
 495                     is_lit: opt_input_expr
 496                         .map_or(false, |expr| matches!(expr.kind, hir::ExprKind::Lit(_))),
 497                     output_ty: None,
 498                 },
 499             )
 500         } else {
 501             traits::ObligationCause::misc(span, self.body_id)
 502         };
 503         let predicates_cause = cause.clone();
 504         obligations.extend(traits::predicates_for_generics(
 505             move |_, _| predicates_cause.clone(),
 506             self.param_env,
 507             bounds,
 508         ));
 509
 510         // Also add an obligation for the method type being well-formed.
 511         let method_ty = tcx.mk_fn_ptr(ty::Binder::dummy(fn_sig));
 512         debug!(
 513             "lookup_in_trait_adjusted: matched method method_ty={:?} obligation={:?}",
 514             method_ty, obligation
 515         );
 516         obligations.push(traits::Obligation::new(
 517             cause,
 518             self.param_env,
 519             ty::Binder::dummy(ty::PredicateKind::WellFormed(method_ty.into())).to_predicate(tcx),
 520         ));
 521
 522         let callee = MethodCallee { def_id, substs, sig: fn_sig };
 523
 524         debug!("callee = {:?}", callee);
 525
 526         Some(InferOk { obligations, value: callee })
 527     }
 528
 529     /// Performs a [full-qualified function call] (formerly "universal function call") lookup. If
 530     /// lookup is successful, it will return the type of definition and the [`DefId`] of the found
 531     /// function definition.
 532     ///
 533     /// [full-qualified function call]: https://doc.rust-lang.org/reference/expressions/call-expr.html#disambiguating-function-calls
 534     ///
 535     /// # Arguments
 536     ///
 537     /// Given a function call like `Foo::bar::<T1,...Tn>(...)`:
 538     ///
 539     /// * `self`:                  the surrounding `FnCtxt` (!)
 540     /// * `span`:                  the span of the call, excluding arguments (`Foo::bar::<T1, ...Tn>`)
 541     /// * `method_name`:           the identifier of the function within the container type (`bar`)
 542     /// * `self_ty`:               the type to search within (`Foo`)
 543     /// * `self_ty_span`           the span for the type being searched within (span of `Foo`)
 544     /// * `expr_id`:               the [`hir::HirId`] of the expression composing the entire call
 545     #[instrument(level = "debug", skip(self), ret)]
 546     pub fn resolve_fully_qualified_call(
 547         &self,
 548         span: Span,
 549         method_name: Ident,
 550         self_ty: Ty<'tcx>,
 551         self_ty_span: Span,
 552         expr_id: hir::HirId,
 553     ) -> Result<(DefKind, DefId), MethodError<'tcx>> {
 554         let tcx = self.tcx;
 555
 556         // Check if we have an enum variant.
 557         if let ty::Adt(adt_def, _) = self_ty.kind() {
 558             if adt_def.is_enum() {
 559                 let variant_def = adt_def
 560                     .variants()
 561                     .iter()
 562                     .find(|vd| tcx.hygienic_eq(method_name, vd.ident(tcx), adt_def.did()));
 563                 if let Some(variant_def) = variant_def {
 564                     // Braced variants generate unusable names in value namespace (reserved for
 565                     // possible future use), so variants resolved as associated items may refer to
 566                     // them as well. It's ok to use the variant's id as a ctor id since an
 567                     // error will be reported on any use of such resolution anyway.
 568                     let ctor_def_id = variant_def.ctor_def_id.unwrap_or(variant_def.def_id);
 569                     tcx.check_stability(ctor_def_id, Some(expr_id), span, Some(method_name.span));
 570                     return Ok((
 571                         DefKind::Ctor(CtorOf::Variant, variant_def.ctor_kind),
 572                         ctor_def_id,
 573                     ));
 574                 }
 575             }
 576         }
 577
 578         let pick = self.probe_for_name(
 579             probe::Mode::Path,
 580             method_name.with_span_pos(span),
 581             IsSuggestion(false),
 582             self_ty,
 583             expr_id,
 584             ProbeScope::TraitsInScope,
 585         )?;
 586
 587         self.lint_fully_qualified_call_from_2018(
 588             span,
 589             method_name,
 590             self_ty,
 591             self_ty_span,
 592             expr_id,
 593             &pick,
 594         );
 595
 596         debug!(?pick);
 597         {
 598             let mut typeck_results = self.typeck_results.borrow_mut();
 599             let used_trait_imports = Lrc::get_mut(&mut typeck_results.used_trait_imports).unwrap();
 600             for import_id in pick.import_ids {
 601                 debug!(used_trait_import=?import_id);
 602                 used_trait_imports.insert(import_id);
 603             }
 604         }
 605
 606         let def_kind = pick.item.kind.as_def_kind();
 607         tcx.check_stability(pick.item.def_id, Some(expr_id), span, Some(method_name.span));
 608         Ok((def_kind, pick.item.def_id))
 609     }
 610
 611     /// Finds item with name `item_name` defined in impl/trait `def_id`
 612     /// and return it, or `None`, if no such item was defined there.
 613     pub fn associated_value(&self, def_id: DefId, item_name: Ident) -> Option<ty::AssocItem> {
 614         self.tcx
 615             .associated_items(def_id)
 616             .find_by_name_and_namespace(self.tcx, item_name, Namespace::ValueNS, def_id)
 617             .copied()
 618     }
 619 }