compiler/rustc_typeck/src/check/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::check::{Expectation, FnCtxt};
  14 use crate::ObligationCause;
  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::ty::subst::Subst;
  22 use rustc_middle::ty::subst::{InternalSubsts, SubstsRef};
  23 use rustc_middle::ty::{
  24     self, AssocKind, DefIdTree, GenericParamDefKind, ProjectionPredicate, ProjectionTy, Term,
  25     ToPredicate, Ty, TypeVisitable,
  26 };
  27 use rustc_span::symbol::Ident;
  28 use rustc_span::Span;
  29 use rustc_trait_selection::traits;
  30 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
  31
  32 use self::probe::{IsSuggestion, ProbeScope};
  33
  34 pub fn provide(providers: &mut ty::query::Providers) {
  35     probe::provide(providers);
  36 }
  37
  38 #[derive(Clone, Copy, Debug)]
  39 pub struct MethodCallee<'tcx> {
  40     /// Impl method ID, for inherent methods, or trait method ID, otherwise.
  41     pub def_id: DefId,
  42     pub substs: SubstsRef<'tcx>,
  43
  44     /// Instantiated method signature, i.e., it has been
  45     /// substituted, normalized, and has had late-bound
  46     /// lifetimes replaced with inference variables.
  47     pub sig: ty::FnSig<'tcx>,
  48 }
  49
  50 #[derive(Debug)]
  51 pub enum MethodError<'tcx> {
  52     // Did not find an applicable method, but we did find various near-misses that may work.
  53     NoMatch(NoMatchData<'tcx>),
  54
  55     // Multiple methods might apply.
  56     Ambiguity(Vec<CandidateSource>),
  57
  58     // Found an applicable method, but it is not visible. The third argument contains a list of
  59     // not-in-scope traits which may work.
  60     PrivateMatch(DefKind, DefId, Vec<DefId>),
  61
  62     // Found a `Self: Sized` bound where `Self` is a trait object, also the caller may have
  63     // forgotten to import a trait.
  64     IllegalSizedBound(Vec<DefId>, bool, Span),
  65
  66     // Found a match, but the return type is wrong
  67     BadReturnType,
  68 }
  69
  70 // Contains a list of static methods that may apply, a list of unsatisfied trait predicates which
  71 // could lead to matches if satisfied, and a list of not-in-scope traits which may work.
  72 #[derive(Debug)]
  73 pub struct NoMatchData<'tcx> {
  74     pub static_candidates: Vec<CandidateSource>,
  75     pub unsatisfied_predicates:
  76         Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>, Option<ObligationCause<'tcx>>)>,
  77     pub out_of_scope_traits: Vec<DefId>,
  78     pub lev_candidate: Option<ty::AssocItem>,
  79     pub mode: probe::Mode,
  80 }
  81
  82 // A pared down enum describing just the places from which a method
  83 // candidate can arise. Used for error reporting only.
  84 #[derive(Copy, Clone, Debug, Eq, Ord, PartialEq, PartialOrd)]
  85 pub enum CandidateSource {
  86     Impl(DefId),
  87     Trait(DefId /* trait id */),
  88 }
  89
  90 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  91     /// Determines whether the type `self_ty` supports a method name `method_name` or not.
  92     #[instrument(level = "debug", skip(self))]
  93     pub fn method_exists(
  94         &self,
  95         method_name: Ident,
  96         self_ty: Ty<'tcx>,
  97         call_expr_id: hir::HirId,
  98         allow_private: bool,
  99     ) -> bool {
 100         let mode = probe::Mode::MethodCall;
 101         match self.probe_for_name(
 102             method_name.span,
 103             mode,
 104             method_name,
 105             IsSuggestion(false),
 106             self_ty,
 107             call_expr_id,
 108             ProbeScope::TraitsInScope,
 109         ) {
 110             Ok(..) => true,
 111             Err(NoMatch(..)) => false,
 112             Err(Ambiguity(..)) => true,
 113             Err(PrivateMatch(..)) => allow_private,
 114             Err(IllegalSizedBound(..)) => true,
 115             Err(BadReturnType) => bug!("no return type expectations but got BadReturnType"),
 116         }
 117     }
 118
 119     /// Adds a suggestion to call the given method to the provided diagnostic.
 120     #[instrument(level = "debug", skip(self, err, call_expr))]
 121     pub(crate) fn suggest_method_call(
 122         &self,
 123         err: &mut Diagnostic,
 124         msg: &str,
 125         method_name: Ident,
 126         self_ty: Ty<'tcx>,
 127         call_expr: &hir::Expr<'_>,
 128         span: Option<Span>,
 129     ) {
 130         let params = self
 131             .probe_for_name(
 132                 method_name.span,
 133                 probe::Mode::MethodCall,
 134                 method_name,
 135                 IsSuggestion(false),
 136                 self_ty,
 137                 call_expr.hir_id,
 138                 ProbeScope::TraitsInScope,
 139             )
 140             .map(|pick| {
 141                 let sig = self.tcx.fn_sig(pick.item.def_id);
 142                 sig.inputs().skip_binder().len().saturating_sub(1)
 143             })
 144             .unwrap_or(0);
 145
 146         // Account for `foo.bar<T>`;
 147         let sugg_span = span.unwrap_or(call_expr.span).shrink_to_hi();
 148         let (suggestion, applicability) = (
 149             format!("({})", (0..params).map(|_| "_").collect::<Vec<_>>().join(", ")),
 150             if params > 0 { Applicability::HasPlaceholders } else { Applicability::MaybeIncorrect },
 151         );
 152
 153         err.span_suggestion_verbose(sugg_span, msg, suggestion, applicability);
 154     }
 155
 156     /// Performs method lookup. If lookup is successful, it will return the callee
 157     /// and store an appropriate adjustment for the self-expr. In some cases it may
 158     /// report an error (e.g., invoking the `drop` method).
 159     ///
 160     /// # Arguments
 161     ///
 162     /// Given a method call like `foo.bar::<T1,...Tn>(a, b + 1, ...)`:
 163     ///
 164     /// * `self`:                  the surrounding `FnCtxt` (!)
 165     /// * `self_ty`:               the (unadjusted) type of the self expression (`foo`)
 166     /// * `segment`:               the name and generic arguments of the method (`bar::<T1, ...Tn>`)
 167     /// * `span`:                  the span for the method call
 168     /// * `call_expr`:             the complete method call: (`foo.bar::<T1,...Tn>(...)`)
 169     /// * `self_expr`:             the self expression (`foo`)
 170     /// * `args`:                  the expressions of the arguments (`a, b + 1, ...`)
 171     #[instrument(level = "debug", skip(self, call_expr, self_expr))]
 172     pub fn lookup_method(
 173         &self,
 174         self_ty: Ty<'tcx>,
 175         segment: &hir::PathSegment<'_>,
 176         span: Span,
 177         call_expr: &'tcx hir::Expr<'tcx>,
 178         self_expr: &'tcx hir::Expr<'tcx>,
 179         args: &'tcx [hir::Expr<'tcx>],
 180     ) -> Result<MethodCallee<'tcx>, MethodError<'tcx>> {
 181         debug!(
 182             "lookup(method_name={}, self_ty={:?}, call_expr={:?}, self_expr={:?})",
 183             segment.ident, self_ty, call_expr, self_expr
 184         );
 185
 186         let pick =
 187             self.lookup_probe(span, segment.ident, self_ty, call_expr, ProbeScope::TraitsInScope)?;
 188
 189         self.lint_dot_call_from_2018(self_ty, segment, span, call_expr, self_expr, &pick, args);
 190
 191         for import_id in &pick.import_ids {
 192             debug!("used_trait_import: {:?}", import_id);
 193             Lrc::get_mut(&mut self.typeck_results.borrow_mut().used_trait_imports)
 194                 .unwrap()
 195                 .insert(*import_id);
 196         }
 197
 198         self.tcx.check_stability(pick.item.def_id, Some(call_expr.hir_id), span, None);
 199
 200         let result =
 201             self.confirm_method(span, self_expr, call_expr, self_ty, pick.clone(), segment);
 202         debug!("result = {:?}", result);
 203
 204         if let Some(span) = result.illegal_sized_bound {
 205             let mut needs_mut = false;
 206             if let ty::Ref(region, t_type, mutability) = self_ty.kind() {
 207                 let trait_type = self
 208                     .tcx
 209                     .mk_ref(*region, ty::TypeAndMut { ty: *t_type, mutbl: mutability.invert() });
 210                 // We probe again to see if there might be a borrow mutability discrepancy.
 211                 match self.lookup_probe(
 212                     span,
 213                     segment.ident,
 214                     trait_type,
 215                     call_expr,
 216                     ProbeScope::TraitsInScope,
 217                 ) {
 218                     Ok(ref new_pick) if *new_pick != pick => {
 219                         needs_mut = true;
 220                     }
 221                     _ => {}
 222                 }
 223             }
 224
 225             // We probe again, taking all traits into account (not only those in scope).
 226             let mut candidates = match self.lookup_probe(
 227                 span,
 228                 segment.ident,
 229                 self_ty,
 230                 call_expr,
 231                 ProbeScope::AllTraits,
 232             ) {
 233                 // If we find a different result the caller probably forgot to import a trait.
 234                 Ok(ref new_pick) if *new_pick != pick => vec![new_pick.item.container.id()],
 235                 Err(Ambiguity(ref sources)) => sources
 236                     .iter()
 237                     .filter_map(|source| {
 238                         match *source {
 239                             // Note: this cannot come from an inherent impl,
 240                             // because the first probing succeeded.
 241                             CandidateSource::Impl(def) => self.tcx.trait_id_of_impl(def),
 242                             CandidateSource::Trait(_) => None,
 243                         }
 244                     })
 245                     .collect(),
 246                 _ => Vec::new(),
 247             };
 248             candidates.retain(|candidate| *candidate != self.tcx.parent(result.callee.def_id));
 249
 250             return Err(IllegalSizedBound(candidates, needs_mut, span));
 251         }
 252
 253         Ok(result.callee)
 254     }
 255
 256     #[instrument(level = "debug", skip(self, call_expr))]
 257     pub fn lookup_probe(
 258         &self,
 259         span: Span,
 260         method_name: Ident,
 261         self_ty: Ty<'tcx>,
 262         call_expr: &'tcx hir::Expr<'tcx>,
 263         scope: ProbeScope,
 264     ) -> probe::PickResult<'tcx> {
 265         let mode = probe::Mode::MethodCall;
 266         let self_ty = self.resolve_vars_if_possible(self_ty);
 267         self.probe_for_name(
 268             span,
 269             mode,
 270             method_name,
 271             IsSuggestion(false),
 272             self_ty,
 273             call_expr.hir_id,
 274             scope,
 275         )
 276     }
 277
 278     pub(super) fn obligation_for_method(
 279         &self,
 280         span: Span,
 281         trait_def_id: DefId,
 282         self_ty: Ty<'tcx>,
 283         opt_input_types: Option<&[Ty<'tcx>]>,
 284     ) -> (traits::Obligation<'tcx, ty::Predicate<'tcx>>, &'tcx ty::List<ty::subst::GenericArg<'tcx>>)
 285     {
 286         // Construct a trait-reference `self_ty : Trait<input_tys>`
 287         let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
 288             match param.kind {
 289                 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => {}
 290                 GenericParamDefKind::Type { .. } => {
 291                     if param.index == 0 {
 292                         return self_ty.into();
 293                     } else if let Some(input_types) = opt_input_types {
 294                         return input_types[param.index as usize - 1].into();
 295                     }
 296                 }
 297             }
 298             self.var_for_def(span, param)
 299         });
 300
 301         let trait_ref = ty::TraitRef::new(trait_def_id, substs);
 302
 303         // Construct an obligation
 304         let poly_trait_ref = ty::Binder::dummy(trait_ref);
 305         (
 306             traits::Obligation::misc(
 307                 span,
 308                 self.body_id,
 309                 self.param_env,
 310                 poly_trait_ref.without_const().to_predicate(self.tcx),
 311             ),
 312             substs,
 313         )
 314     }
 315
 316     pub(super) fn obligation_for_op_method(
 317         &self,
 318         span: Span,
 319         trait_def_id: DefId,
 320         self_ty: Ty<'tcx>,
 321         opt_input_type: Option<Ty<'tcx>>,
 322         opt_input_expr: Option<&'tcx hir::Expr<'tcx>>,
 323         expected: Expectation<'tcx>,
 324     ) -> (traits::Obligation<'tcx, ty::Predicate<'tcx>>, &'tcx ty::List<ty::subst::GenericArg<'tcx>>)
 325     {
 326         // Construct a trait-reference `self_ty : Trait<input_tys>`
 327         let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
 328             match param.kind {
 329                 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => {}
 330                 GenericParamDefKind::Type { .. } => {
 331                     if param.index == 0 {
 332                         return self_ty.into();
 333                     } else if let Some(input_type) = opt_input_type {
 334                         return input_type.into();
 335                     }
 336                 }
 337             }
 338             self.var_for_def(span, param)
 339         });
 340
 341         let trait_ref = ty::TraitRef::new(trait_def_id, substs);
 342
 343         // Construct an obligation
 344         let poly_trait_ref = ty::Binder::dummy(trait_ref);
 345         let opt_output_ty =
 346             expected.only_has_type(self).and_then(|ty| (!ty.needs_infer()).then(|| ty));
 347         let opt_output_assoc_item = self.tcx.associated_items(trait_def_id).find_by_name_and_kind(
 348             self.tcx,
 349             Ident::from_str("Output"),
 350             AssocKind::Type,
 351             trait_def_id,
 352         );
 353         let output_pred =
 354             opt_output_ty.zip(opt_output_assoc_item).map(|(output_ty, output_assoc_item)| {
 355                 ty::Binder::dummy(ty::PredicateKind::Projection(ProjectionPredicate {
 356                     projection_ty: ProjectionTy { substs, item_def_id: output_assoc_item.def_id },
 357                     term: Term::Ty(output_ty),
 358                 }))
 359                 .to_predicate(self.tcx)
 360             });
 361
 362         (
 363             traits::Obligation::new(
 364                 traits::ObligationCause::new(
 365                     span,
 366                     self.body_id,
 367                     traits::BinOp {
 368                         rhs_span: opt_input_expr.map(|expr| expr.span),
 369                         is_lit: opt_input_expr
 370                             .map_or(false, |expr| matches!(expr.kind, hir::ExprKind::Lit(_))),
 371                         output_pred,
 372                     },
 373                 ),
 374                 self.param_env,
 375                 poly_trait_ref.without_const().to_predicate(self.tcx),
 376             ),
 377             substs,
 378         )
 379     }
 380
 381     /// `lookup_method_in_trait` is used for overloaded operators.
 382     /// It does a very narrow slice of what the normal probe/confirm path does.
 383     /// In particular, it doesn't really do any probing: it simply constructs
 384     /// an obligation for a particular trait with the given self type and checks
 385     /// whether that trait is implemented.
 386     #[instrument(level = "debug", skip(self, span, opt_input_types))]
 387     pub(super) fn lookup_method_in_trait(
 388         &self,
 389         span: Span,
 390         m_name: Ident,
 391         trait_def_id: DefId,
 392         self_ty: Ty<'tcx>,
 393         opt_input_types: Option<&[Ty<'tcx>]>,
 394     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 395         debug!(
 396             "lookup_in_trait_adjusted(self_ty={:?}, m_name={}, trait_def_id={:?}, opt_input_types={:?})",
 397             self_ty, m_name, trait_def_id, opt_input_types
 398         );
 399
 400         let (obligation, substs) =
 401             self.obligation_for_method(span, trait_def_id, self_ty, opt_input_types);
 402         self.construct_obligation_for_trait(
 403             span,
 404             m_name,
 405             trait_def_id,
 406             obligation,
 407             substs,
 408             None,
 409             false,
 410         )
 411     }
 412
 413     pub(super) fn lookup_op_method_in_trait(
 414         &self,
 415         span: Span,
 416         m_name: Ident,
 417         trait_def_id: DefId,
 418         self_ty: Ty<'tcx>,
 419         opt_input_type: Option<Ty<'tcx>>,
 420         opt_input_expr: Option<&'tcx hir::Expr<'tcx>>,
 421         expected: Expectation<'tcx>,
 422     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 423         let (obligation, substs) = self.obligation_for_op_method(
 424             span,
 425             trait_def_id,
 426             self_ty,
 427             opt_input_type,
 428             opt_input_expr,
 429             expected,
 430         );
 431         self.construct_obligation_for_trait(
 432             span,
 433             m_name,
 434             trait_def_id,
 435             obligation,
 436             substs,
 437             opt_input_expr,
 438             true,
 439         )
 440     }
 441
 442     // FIXME(#18741): it seems likely that we can consolidate some of this
 443     // code with the other method-lookup code. In particular, the second half
 444     // of this method is basically the same as confirmation.
 445     fn construct_obligation_for_trait(
 446         &self,
 447         span: Span,
 448         m_name: Ident,
 449         trait_def_id: DefId,
 450         obligation: traits::PredicateObligation<'tcx>,
 451         substs: &'tcx ty::List<ty::subst::GenericArg<'tcx>>,
 452         opt_input_expr: Option<&'tcx hir::Expr<'tcx>>,
 453         is_op: bool,
 454     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 455         debug!(?obligation);
 456
 457         // Now we want to know if this can be matched
 458         if !self.predicate_may_hold(&obligation) {
 459             debug!("--> Cannot match obligation");
 460             // Cannot be matched, no such method resolution is possible.
 461             return None;
 462         }
 463
 464         // Trait must have a method named `m_name` and it should not have
 465         // type parameters or early-bound regions.
 466         let tcx = self.tcx;
 467         let Some(method_item) = self.associated_value(trait_def_id, m_name) else {
 468             tcx.sess.delay_span_bug(
 469                 span,
 470                 "operator trait does not have corresponding operator method",
 471             );
 472             return None;
 473         };
 474         let def_id = method_item.def_id;
 475         let generics = tcx.generics_of(def_id);
 476         assert_eq!(generics.params.len(), 0);
 477
 478         debug!("lookup_in_trait_adjusted: method_item={:?}", method_item);
 479         let mut obligations = vec![];
 480
 481         // Instantiate late-bound regions and substitute the trait
 482         // parameters into the method type to get the actual method type.
 483         //
 484         // N.B., instantiate late-bound regions first so that
 485         // `instantiate_type_scheme` can normalize associated types that
 486         // may reference those regions.
 487         let fn_sig = tcx.bound_fn_sig(def_id);
 488         let fn_sig = fn_sig.subst(self.tcx, substs);
 489         let fn_sig = self.replace_bound_vars_with_fresh_vars(span, infer::FnCall, fn_sig);
 490
 491         let InferOk { value, obligations: o } = if is_op {
 492             self.normalize_op_associated_types_in_as_infer_ok(span, fn_sig, opt_input_expr)
 493         } else {
 494             self.normalize_associated_types_in_as_infer_ok(span, fn_sig)
 495         };
 496         let fn_sig = {
 497             obligations.extend(o);
 498             value
 499         };
 500
 501         // Register obligations for the parameters. This will include the
 502         // `Self` parameter, which in turn has a bound of the main trait,
 503         // so this also effectively registers `obligation` as well.  (We
 504         // used to register `obligation` explicitly, but that resulted in
 505         // double error messages being reported.)
 506         //
 507         // Note that as the method comes from a trait, it should not have
 508         // any late-bound regions appearing in its bounds.
 509         let bounds = self.tcx.predicates_of(def_id).instantiate(self.tcx, substs);
 510
 511         let InferOk { value, obligations: o } = if is_op {
 512             self.normalize_op_associated_types_in_as_infer_ok(span, bounds, opt_input_expr)
 513         } else {
 514             self.normalize_associated_types_in_as_infer_ok(span, bounds)
 515         };
 516         let bounds = {
 517             obligations.extend(o);
 518             value
 519         };
 520
 521         assert!(!bounds.has_escaping_bound_vars());
 522
 523         let cause = if is_op {
 524             ObligationCause::new(
 525                 span,
 526                 self.body_id,
 527                 traits::BinOp {
 528                     rhs_span: opt_input_expr.map(|expr| expr.span),
 529                     is_lit: opt_input_expr
 530                         .map_or(false, |expr| matches!(expr.kind, hir::ExprKind::Lit(_))),
 531                     output_pred: None,
 532                 },
 533             )
 534         } else {
 535             traits::ObligationCause::misc(span, self.body_id)
 536         };
 537         obligations.extend(traits::predicates_for_generics(cause.clone(), self.param_env, bounds));
 538
 539         // Also add an obligation for the method type being well-formed.
 540         let method_ty = tcx.mk_fn_ptr(ty::Binder::dummy(fn_sig));
 541         debug!(
 542             "lookup_in_trait_adjusted: matched method method_ty={:?} obligation={:?}",
 543             method_ty, obligation
 544         );
 545         obligations.push(traits::Obligation::new(
 546             cause,
 547             self.param_env,
 548             ty::Binder::dummy(ty::PredicateKind::WellFormed(method_ty.into())).to_predicate(tcx),
 549         ));
 550
 551         let callee = MethodCallee { def_id, substs, sig: fn_sig };
 552
 553         debug!("callee = {:?}", callee);
 554
 555         Some(InferOk { obligations, value: callee })
 556     }
 557
 558     /// Performs a [full-qualified function call] (formerly "universal function call") lookup. If
 559     /// lookup is successful, it will return the type of definition and the [`DefId`] of the found
 560     /// function definition.
 561     ///
 562     /// [full-qualified function call]: https://doc.rust-lang.org/reference/expressions/call-expr.html#disambiguating-function-calls
 563     ///
 564     /// # Arguments
 565     ///
 566     /// Given a function call like `Foo::bar::<T1,...Tn>(...)`:
 567     ///
 568     /// * `self`:                  the surrounding `FnCtxt` (!)
 569     /// * `span`:                  the span of the call, excluding arguments (`Foo::bar::<T1, ...Tn>`)
 570     /// * `method_name`:           the identifier of the function within the container type (`bar`)
 571     /// * `self_ty`:               the type to search within (`Foo`)
 572     /// * `self_ty_span`           the span for the type being searched within (span of `Foo`)
 573     /// * `expr_id`:               the [`hir::HirId`] of the expression composing the entire call
 574     #[instrument(level = "debug", skip(self))]
 575     pub fn resolve_fully_qualified_call(
 576         &self,
 577         span: Span,
 578         method_name: Ident,
 579         self_ty: Ty<'tcx>,
 580         self_ty_span: Span,
 581         expr_id: hir::HirId,
 582     ) -> Result<(DefKind, DefId), MethodError<'tcx>> {
 583         debug!(
 584             "resolve_fully_qualified_call: method_name={:?} self_ty={:?} expr_id={:?}",
 585             method_name, self_ty, expr_id,
 586         );
 587
 588         let tcx = self.tcx;
 589
 590         // Check if we have an enum variant.
 591         if let ty::Adt(adt_def, _) = self_ty.kind() {
 592             if adt_def.is_enum() {
 593                 let variant_def = adt_def
 594                     .variants()
 595                     .iter()
 596                     .find(|vd| tcx.hygienic_eq(method_name, vd.ident(tcx), adt_def.did()));
 597                 if let Some(variant_def) = variant_def {
 598                     // Braced variants generate unusable names in value namespace (reserved for
 599                     // possible future use), so variants resolved as associated items may refer to
 600                     // them as well. It's ok to use the variant's id as a ctor id since an
 601                     // error will be reported on any use of such resolution anyway.
 602                     let ctor_def_id = variant_def.ctor_def_id.unwrap_or(variant_def.def_id);
 603                     tcx.check_stability(ctor_def_id, Some(expr_id), span, Some(method_name.span));
 604                     return Ok((
 605                         DefKind::Ctor(CtorOf::Variant, variant_def.ctor_kind),
 606                         ctor_def_id,
 607                     ));
 608                 }
 609             }
 610         }
 611
 612         let pick = self.probe_for_name(
 613             span,
 614             probe::Mode::Path,
 615             method_name,
 616             IsSuggestion(false),
 617             self_ty,
 618             expr_id,
 619             ProbeScope::TraitsInScope,
 620         )?;
 621
 622         self.lint_fully_qualified_call_from_2018(
 623             span,
 624             method_name,
 625             self_ty,
 626             self_ty_span,
 627             expr_id,
 628             &pick,
 629         );
 630
 631         debug!("resolve_fully_qualified_call: pick={:?}", pick);
 632         {
 633             let mut typeck_results = self.typeck_results.borrow_mut();
 634             let used_trait_imports = Lrc::get_mut(&mut typeck_results.used_trait_imports).unwrap();
 635             for import_id in pick.import_ids {
 636                 debug!("resolve_fully_qualified_call: used_trait_import: {:?}", import_id);
 637                 used_trait_imports.insert(import_id);
 638             }
 639         }
 640
 641         let def_kind = pick.item.kind.as_def_kind();
 642         debug!(
 643             "resolve_fully_qualified_call: def_kind={:?}, def_id={:?}",
 644             def_kind, pick.item.def_id
 645         );
 646         tcx.check_stability(pick.item.def_id, Some(expr_id), span, Some(method_name.span));
 647         Ok((def_kind, pick.item.def_id))
 648     }
 649
 650     /// Finds item with name `item_name` defined in impl/trait `def_id`
 651     /// and return it, or `None`, if no such item was defined there.
 652     pub fn associated_value(&self, def_id: DefId, item_name: Ident) -> Option<ty::AssocItem> {
 653         self.tcx
 654             .associated_items(def_id)
 655             .find_by_name_and_namespace(self.tcx, item_name, Namespace::ValueNS, def_id)
 656             .copied()
 657     }
 658 }