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::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, GenericParamDefKind, Ty, TypeVisitable};
  24 use rustc_span::symbol::Ident;
  25 use rustc_span::Span;
  26 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
  27 use rustc_trait_selection::traits::{self, NormalizeExt};
  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 {
  61         candidates: Vec<DefId>,
  62         needs_mut: bool,
  63         bound_span: Span,
  64         self_expr: &'tcx hir::Expr<'tcx>,
  65     },
  66
  67     // Found a match, but the return type is wrong
  68     BadReturnType,
  69 }
  70
  71 // Contains a list of static methods that may apply, a list of unsatisfied trait predicates which
  72 // could lead to matches if satisfied, and a list of not-in-scope traits which may work.
  73 #[derive(Debug)]
  74 pub struct NoMatchData<'tcx> {
  75     pub static_candidates: Vec<CandidateSource>,
  76     pub unsatisfied_predicates:
  77         Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>, Option<ObligationCause<'tcx>>)>,
  78     pub out_of_scope_traits: Vec<DefId>,
  79     pub similar_candidate: Option<ty::AssocItem>,
  80     pub mode: probe::Mode,
  81 }
  82
  83 // A pared down enum describing just the places from which a method
  84 // candidate can arise. Used for error reporting only.
  85 #[derive(Copy, Clone, Debug, Eq, Ord, PartialEq, PartialOrd)]
  86 pub enum CandidateSource {
  87     Impl(DefId),
  88     Trait(DefId /* trait id */),
  89 }
  90
  91 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  92     /// Determines whether the type `self_ty` supports a method name `method_name` or not.
  93     #[instrument(level = "debug", skip(self))]
  94     pub fn method_exists(
  95         &self,
  96         method_name: Ident,
  97         self_ty: Ty<'tcx>,
  98         call_expr_id: hir::HirId,
  99         allow_private: bool,
 100         return_type: Option<Ty<'tcx>>,
 101     ) -> bool {
 102         match self.probe_for_name(
 103             probe::Mode::MethodCall,
 104             method_name,
 105             return_type,
 106             IsSuggestion(false),
 107             self_ty,
 108             call_expr_id,
 109             ProbeScope::TraitsInScope,
 110         ) {
 111             Ok(pick) => {
 112                 pick.maybe_emit_unstable_name_collision_hint(
 113                     self.tcx,
 114                     method_name.span,
 115                     call_expr_id,
 116                 );
 117                 true
 118             }
 119             Err(NoMatch(..)) => false,
 120             Err(Ambiguity(..)) => true,
 121             Err(PrivateMatch(..)) => allow_private,
 122             Err(IllegalSizedBound { .. }) => true,
 123             Err(BadReturnType) => false,
 124         }
 125     }
 126
 127     /// Adds a suggestion to call the given method to the provided diagnostic.
 128     #[instrument(level = "debug", skip(self, err, call_expr))]
 129     pub(crate) fn suggest_method_call(
 130         &self,
 131         err: &mut Diagnostic,
 132         msg: &str,
 133         method_name: Ident,
 134         self_ty: Ty<'tcx>,
 135         call_expr: &hir::Expr<'tcx>,
 136         span: Option<Span>,
 137     ) {
 138         let params = self
 139             .lookup_probe_for_diagnostic(
 140                 method_name,
 141                 self_ty,
 142                 call_expr,
 143                 ProbeScope::TraitsInScope,
 144                 None,
 145             )
 146             .map(|pick| {
 147                 let sig = self.tcx.fn_sig(pick.item.def_id);
 148                 sig.skip_binder().inputs().skip_binder().len().saturating_sub(1)
 149             })
 150             .unwrap_or(0);
 151
 152         // Account for `foo.bar<T>`;
 153         let sugg_span = span.unwrap_or(call_expr.span).shrink_to_hi();
 154         let (suggestion, applicability) = (
 155             format!("({})", (0..params).map(|_| "_").collect::<Vec<_>>().join(", ")),
 156             if params > 0 { Applicability::HasPlaceholders } else { Applicability::MaybeIncorrect },
 157         );
 158
 159         err.span_suggestion_verbose(sugg_span, msg, suggestion, applicability);
 160     }
 161
 162     /// Performs method lookup. If lookup is successful, it will return the callee
 163     /// and store an appropriate adjustment for the self-expr. In some cases it may
 164     /// report an error (e.g., invoking the `drop` method).
 165     ///
 166     /// # Arguments
 167     ///
 168     /// Given a method call like `foo.bar::<T1,...Tn>(a, b + 1, ...)`:
 169     ///
 170     /// * `self`:                  the surrounding `FnCtxt` (!)
 171     /// * `self_ty`:               the (unadjusted) type of the self expression (`foo`)
 172     /// * `segment`:               the name and generic arguments of the method (`bar::<T1, ...Tn>`)
 173     /// * `span`:                  the span for the method call
 174     /// * `call_expr`:             the complete method call: (`foo.bar::<T1,...Tn>(...)`)
 175     /// * `self_expr`:             the self expression (`foo`)
 176     /// * `args`:                  the expressions of the arguments (`a, b + 1, ...`)
 177     #[instrument(level = "debug", skip(self))]
 178     pub fn lookup_method(
 179         &self,
 180         self_ty: Ty<'tcx>,
 181         segment: &hir::PathSegment<'_>,
 182         span: Span,
 183         call_expr: &'tcx hir::Expr<'tcx>,
 184         self_expr: &'tcx hir::Expr<'tcx>,
 185         args: &'tcx [hir::Expr<'tcx>],
 186     ) -> Result<MethodCallee<'tcx>, MethodError<'tcx>> {
 187         let pick =
 188             self.lookup_probe(segment.ident, self_ty, call_expr, ProbeScope::TraitsInScope)?;
 189
 190         self.lint_dot_call_from_2018(self_ty, segment, span, call_expr, self_expr, &pick, args);
 191
 192         for import_id in &pick.import_ids {
 193             debug!("used_trait_import: {:?}", import_id);
 194             Lrc::get_mut(&mut self.typeck_results.borrow_mut().used_trait_imports)
 195                 .unwrap()
 196                 .insert(*import_id);
 197         }
 198
 199         self.tcx.check_stability(pick.item.def_id, Some(call_expr.hir_id), span, None);
 200
 201         let result = self.confirm_method(span, self_expr, call_expr, self_ty, &pick, 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                     segment.ident,
 213                     trait_type,
 214                     call_expr,
 215                     ProbeScope::TraitsInScope,
 216                 ) {
 217                     Ok(ref new_pick) if pick.differs_from(new_pick) => {
 218                         needs_mut = new_pick.self_ty.ref_mutability() != self_ty.ref_mutability();
 219                     }
 220                     _ => {}
 221                 }
 222             }
 223
 224             // We probe again, taking all traits into account (not only those in scope).
 225             let candidates = match self.lookup_probe_for_diagnostic(
 226                 segment.ident,
 227                 self_ty,
 228                 call_expr,
 229                 ProbeScope::AllTraits,
 230                 None,
 231             ) {
 232                 // If we find a different result the caller probably forgot to import a trait.
 233                 Ok(ref new_pick) if pick.differs_from(new_pick) => {
 234                     vec![new_pick.item.container_id(self.tcx)]
 235                 }
 236                 Err(Ambiguity(ref sources)) => sources
 237                     .iter()
 238                     .filter_map(|source| {
 239                         match *source {
 240                             // Note: this cannot come from an inherent impl,
 241                             // because the first probing succeeded.
 242                             CandidateSource::Impl(def) => self.tcx.trait_id_of_impl(def),
 243                             CandidateSource::Trait(_) => None,
 244                         }
 245                     })
 246                     .collect(),
 247                 _ => Vec::new(),
 248             };
 249
 250             return Err(IllegalSizedBound { candidates, needs_mut, bound_span: span, self_expr });
 251         }
 252
 253         Ok(result.callee)
 254     }
 255
 256     #[instrument(level = "debug", skip(self, call_expr))]
 257     pub fn lookup_probe(
 258         &self,
 259         method_name: Ident,
 260         self_ty: Ty<'tcx>,
 261         call_expr: &hir::Expr<'_>,
 262         scope: ProbeScope,
 263     ) -> probe::PickResult<'tcx> {
 264         let pick = self.probe_for_name(
 265             probe::Mode::MethodCall,
 266             method_name,
 267             None,
 268             IsSuggestion(false),
 269             self_ty,
 270             call_expr.hir_id,
 271             scope,
 272         )?;
 273         pick.maybe_emit_unstable_name_collision_hint(self.tcx, method_name.span, call_expr.hir_id);
 274         Ok(pick)
 275     }
 276
 277     pub fn lookup_probe_for_diagnostic(
 278         &self,
 279         method_name: Ident,
 280         self_ty: Ty<'tcx>,
 281         call_expr: &hir::Expr<'_>,
 282         scope: ProbeScope,
 283         return_type: Option<Ty<'tcx>>,
 284     ) -> probe::PickResult<'tcx> {
 285         let pick = self.probe_for_name(
 286             probe::Mode::MethodCall,
 287             method_name,
 288             return_type,
 289             IsSuggestion(true),
 290             self_ty,
 291             call_expr.hir_id,
 292             scope,
 293         )?;
 294         Ok(pick)
 295     }
 296
 297     pub(super) fn obligation_for_method(
 298         &self,
 299         cause: ObligationCause<'tcx>,
 300         trait_def_id: DefId,
 301         self_ty: Ty<'tcx>,
 302         opt_input_types: Option<&[Ty<'tcx>]>,
 303     ) -> (traits::Obligation<'tcx, ty::Predicate<'tcx>>, &'tcx ty::List<ty::subst::GenericArg<'tcx>>)
 304     {
 305         // Construct a trait-reference `self_ty : Trait<input_tys>`
 306         let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
 307             match param.kind {
 308                 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => {}
 309                 GenericParamDefKind::Type { .. } => {
 310                     if param.index == 0 {
 311                         return self_ty.into();
 312                     } else if let Some(input_types) = opt_input_types {
 313                         return input_types[param.index as usize - 1].into();
 314                     }
 315                 }
 316             }
 317             self.var_for_def(cause.span, param)
 318         });
 319
 320         let trait_ref = self.tcx.mk_trait_ref(trait_def_id, substs);
 321
 322         // Construct an obligation
 323         let poly_trait_ref = ty::Binder::dummy(trait_ref);
 324         (
 325             traits::Obligation::new(
 326                 self.tcx,
 327                 cause,
 328                 self.param_env,
 329                 poly_trait_ref.without_const(),
 330             ),
 331             substs,
 332         )
 333     }
 334
 335     /// `lookup_method_in_trait` is used for overloaded operators.
 336     /// It does a very narrow slice of what the normal probe/confirm path does.
 337     /// In particular, it doesn't really do any probing: it simply constructs
 338     /// an obligation for a particular trait with the given self type and checks
 339     /// whether that trait is implemented.
 340     #[instrument(level = "debug", skip(self))]
 341     pub(super) fn lookup_method_in_trait(
 342         &self,
 343         cause: ObligationCause<'tcx>,
 344         m_name: Ident,
 345         trait_def_id: DefId,
 346         self_ty: Ty<'tcx>,
 347         opt_input_types: Option<&[Ty<'tcx>]>,
 348     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 349         let (obligation, substs) =
 350             self.obligation_for_method(cause, trait_def_id, self_ty, opt_input_types);
 351         self.construct_obligation_for_trait(m_name, trait_def_id, obligation, substs)
 352     }
 353
 354     // FIXME(#18741): it seems likely that we can consolidate some of this
 355     // code with the other method-lookup code. In particular, the second half
 356     // of this method is basically the same as confirmation.
 357     fn construct_obligation_for_trait(
 358         &self,
 359         m_name: Ident,
 360         trait_def_id: DefId,
 361         obligation: traits::PredicateObligation<'tcx>,
 362         substs: &'tcx ty::List<ty::subst::GenericArg<'tcx>>,
 363     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 364         debug!(?obligation);
 365
 366         // Now we want to know if this can be matched
 367         if !self.predicate_may_hold(&obligation) {
 368             debug!("--> Cannot match obligation");
 369             // Cannot be matched, no such method resolution is possible.
 370             return None;
 371         }
 372
 373         // Trait must have a method named `m_name` and it should not have
 374         // type parameters or early-bound regions.
 375         let tcx = self.tcx;
 376         let Some(method_item) = self.associated_value(trait_def_id, m_name) else {
 377             tcx.sess.delay_span_bug(
 378                 obligation.cause.span,
 379                 "operator trait does not have corresponding operator method",
 380             );
 381             return None;
 382         };
 383         let def_id = method_item.def_id;
 384         let generics = tcx.generics_of(def_id);
 385
 386         if generics.params.len() != 0 {
 387             tcx.sess.emit_fatal(OpMethodGenericParams {
 388                 span: tcx.def_span(method_item.def_id),
 389                 method_name: m_name.to_string(),
 390             });
 391         }
 392
 393         debug!("lookup_in_trait_adjusted: method_item={:?}", method_item);
 394         let mut obligations = vec![];
 395
 396         // Instantiate late-bound regions and substitute the trait
 397         // parameters into the method type to get the actual method type.
 398         //
 399         // N.B., instantiate late-bound regions before normalizing the
 400         // function signature so that normalization does not need to deal
 401         // with bound regions.
 402         let fn_sig = tcx.fn_sig(def_id).subst(self.tcx, substs);
 403         let fn_sig =
 404             self.instantiate_binder_with_fresh_vars(obligation.cause.span, infer::FnCall, fn_sig);
 405
 406         let InferOk { value, obligations: o } =
 407             self.at(&obligation.cause, self.param_env).normalize(fn_sig);
 408         let fn_sig = {
 409             obligations.extend(o);
 410             value
 411         };
 412
 413         // Register obligations for the parameters. This will include the
 414         // `Self` parameter, which in turn has a bound of the main trait,
 415         // so this also effectively registers `obligation` as well. (We
 416         // used to register `obligation` explicitly, but that resulted in
 417         // double error messages being reported.)
 418         //
 419         // Note that as the method comes from a trait, it should not have
 420         // any late-bound regions appearing in its bounds.
 421         let bounds = self.tcx.predicates_of(def_id).instantiate(self.tcx, substs);
 422
 423         let InferOk { value, obligations: o } =
 424             self.at(&obligation.cause, self.param_env).normalize(bounds);
 425         let bounds = {
 426             obligations.extend(o);
 427             value
 428         };
 429
 430         assert!(!bounds.has_escaping_bound_vars());
 431
 432         let predicates_cause = obligation.cause.clone();
 433         obligations.extend(traits::predicates_for_generics(
 434             move |_, _| predicates_cause.clone(),
 435             self.param_env,
 436             bounds,
 437         ));
 438
 439         // Also add an obligation for the method type being well-formed.
 440         let method_ty = tcx.mk_fn_ptr(ty::Binder::dummy(fn_sig));
 441         debug!(
 442             "lookup_in_trait_adjusted: matched method method_ty={:?} obligation={:?}",
 443             method_ty, obligation
 444         );
 445         obligations.push(traits::Obligation::new(
 446             tcx,
 447             obligation.cause,
 448             self.param_env,
 449             ty::Binder::dummy(ty::PredicateKind::WellFormed(method_ty.into())),
 450         ));
 451
 452         let callee = MethodCallee { def_id, substs, sig: fn_sig };
 453
 454         debug!("callee = {:?}", callee);
 455
 456         Some(InferOk { obligations, value: callee })
 457     }
 458
 459     /// Performs a [full-qualified function call] (formerly "universal function call") lookup. If
 460     /// lookup is successful, it will return the type of definition and the [`DefId`] of the found
 461     /// function definition.
 462     ///
 463     /// [full-qualified function call]: https://doc.rust-lang.org/reference/expressions/call-expr.html#disambiguating-function-calls
 464     ///
 465     /// # Arguments
 466     ///
 467     /// Given a function call like `Foo::bar::<T1,...Tn>(...)`:
 468     ///
 469     /// * `self`:                  the surrounding `FnCtxt` (!)
 470     /// * `span`:                  the span of the call, excluding arguments (`Foo::bar::<T1, ...Tn>`)
 471     /// * `method_name`:           the identifier of the function within the container type (`bar`)
 472     /// * `self_ty`:               the type to search within (`Foo`)
 473     /// * `self_ty_span`           the span for the type being searched within (span of `Foo`)
 474     /// * `expr_id`:               the [`hir::HirId`] of the expression composing the entire call
 475     #[instrument(level = "debug", skip(self), ret)]
 476     pub fn resolve_fully_qualified_call(
 477         &self,
 478         span: Span,
 479         method_name: Ident,
 480         self_ty: Ty<'tcx>,
 481         self_ty_span: Span,
 482         expr_id: hir::HirId,
 483     ) -> Result<(DefKind, DefId), MethodError<'tcx>> {
 484         let tcx = self.tcx;
 485
 486         // Check if we have an enum variant.
 487         let mut struct_variant = None;
 488         if let ty::Adt(adt_def, _) = self_ty.kind() {
 489             if adt_def.is_enum() {
 490                 let variant_def = adt_def
 491                     .variants()
 492                     .iter()
 493                     .find(|vd| tcx.hygienic_eq(method_name, vd.ident(tcx), adt_def.did()));
 494                 if let Some(variant_def) = variant_def {
 495                     if let Some((ctor_kind, ctor_def_id)) = variant_def.ctor {
 496                         tcx.check_stability(
 497                             ctor_def_id,
 498                             Some(expr_id),
 499                             span,
 500                             Some(method_name.span),
 501                         );
 502                         return Ok((DefKind::Ctor(CtorOf::Variant, ctor_kind), ctor_def_id));
 503                     } else {
 504                         struct_variant = Some((DefKind::Variant, variant_def.def_id));
 505                     }
 506                 }
 507             }
 508         }
 509
 510         let pick = self.probe_for_name(
 511             probe::Mode::Path,
 512             method_name,
 513             None,
 514             IsSuggestion(false),
 515             self_ty,
 516             expr_id,
 517             ProbeScope::TraitsInScope,
 518         );
 519         let pick = match (pick, struct_variant) {
 520             // Fall back to a resolution that will produce an error later.
 521             (Err(_), Some(res)) => return Ok(res),
 522             (pick, _) => pick?,
 523         };
 524
 525         pick.maybe_emit_unstable_name_collision_hint(self.tcx, span, expr_id);
 526
 527         self.lint_fully_qualified_call_from_2018(
 528             span,
 529             method_name,
 530             self_ty,
 531             self_ty_span,
 532             expr_id,
 533             &pick,
 534         );
 535
 536         debug!(?pick);
 537         {
 538             let mut typeck_results = self.typeck_results.borrow_mut();
 539             let used_trait_imports = Lrc::get_mut(&mut typeck_results.used_trait_imports).unwrap();
 540             for import_id in pick.import_ids {
 541                 debug!(used_trait_import=?import_id);
 542                 used_trait_imports.insert(import_id);
 543             }
 544         }
 545
 546         let def_kind = pick.item.kind.as_def_kind();
 547         tcx.check_stability(pick.item.def_id, Some(expr_id), span, Some(method_name.span));
 548         Ok((def_kind, pick.item.def_id))
 549     }
 550
 551     /// Finds item with name `item_name` defined in impl/trait `def_id`
 552     /// and return it, or `None`, if no such item was defined there.
 553     pub fn associated_value(&self, def_id: DefId, item_name: Ident) -> Option<ty::AssocItem> {
 554         self.tcx
 555             .associated_items(def_id)
 556             .find_by_name_and_namespace(self.tcx, item_name, Namespace::ValueNS, def_id)
 557             .copied()
 558     }
 559 }