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(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(pick) => {
 105                 pick.maybe_emit_unstable_name_collision_hint(
 106                     self.tcx,
 107                     method_name.span,
 108                     call_expr_id,
 109                 );
 110                 true
 111             }
 112             Err(NoMatch(..)) => false,
 113             Err(Ambiguity(..)) => true,
 114             Err(PrivateMatch(..)) => allow_private,
 115             Err(IllegalSizedBound(..)) => true,
 116             Err(BadReturnType) => bug!("no return type expectations but got BadReturnType"),
 117         }
 118     }
 119
 120     /// Adds a suggestion to call the given method to the provided diagnostic.
 121     #[instrument(level = "debug", skip(self, err, call_expr))]
 122     pub(crate) fn suggest_method_call(
 123         &self,
 124         err: &mut Diagnostic,
 125         msg: &str,
 126         method_name: Ident,
 127         self_ty: Ty<'tcx>,
 128         call_expr: &hir::Expr<'_>,
 129         span: Option<Span>,
 130     ) {
 131         let params = self
 132             .probe_for_name(
 133                 probe::Mode::MethodCall,
 134                 method_name,
 135                 IsSuggestion(true),
 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))]
 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         let pick =
 182             self.lookup_probe(segment.ident, self_ty, call_expr, ProbeScope::TraitsInScope)?;
 183
 184         self.lint_dot_call_from_2018(self_ty, segment, span, call_expr, self_expr, &pick, args);
 185
 186         for import_id in &pick.import_ids {
 187             debug!("used_trait_import: {:?}", import_id);
 188             Lrc::get_mut(&mut self.typeck_results.borrow_mut().used_trait_imports)
 189                 .unwrap()
 190                 .insert(*import_id);
 191         }
 192
 193         self.tcx.check_stability(pick.item.def_id, Some(call_expr.hir_id), span, None);
 194
 195         let result = self.confirm_method(span, self_expr, call_expr, self_ty, &pick, segment);
 196         debug!("result = {:?}", result);
 197
 198         if let Some(span) = result.illegal_sized_bound {
 199             let mut needs_mut = false;
 200             if let ty::Ref(region, t_type, mutability) = self_ty.kind() {
 201                 let trait_type = self
 202                     .tcx
 203                     .mk_ref(*region, ty::TypeAndMut { ty: *t_type, mutbl: mutability.invert() });
 204                 // We probe again to see if there might be a borrow mutability discrepancy.
 205                 match self.lookup_probe(
 206                     segment.ident,
 207                     trait_type,
 208                     call_expr,
 209                     ProbeScope::TraitsInScope,
 210                 ) {
 211                     Ok(ref new_pick) if pick.differs_from(new_pick) => {
 212                         needs_mut = new_pick.self_ty.ref_mutability() != self_ty.ref_mutability();
 213                     }
 214                     _ => {}
 215                 }
 216             }
 217
 218             // We probe again, taking all traits into account (not only those in scope).
 219             let candidates =
 220                 match self.lookup_probe(segment.ident, self_ty, call_expr, ProbeScope::AllTraits) {
 221                     // If we find a different result the caller probably forgot to import a trait.
 222                     Ok(ref new_pick) if pick.differs_from(new_pick) => {
 223                         vec![new_pick.item.container_id(self.tcx)]
 224                     }
 225                     Err(Ambiguity(ref sources)) => sources
 226                         .iter()
 227                         .filter_map(|source| {
 228                             match *source {
 229                                 // Note: this cannot come from an inherent impl,
 230                                 // because the first probing succeeded.
 231                                 CandidateSource::Impl(def) => self.tcx.trait_id_of_impl(def),
 232                                 CandidateSource::Trait(_) => None,
 233                             }
 234                         })
 235                         .collect(),
 236                     _ => Vec::new(),
 237                 };
 238
 239             return Err(IllegalSizedBound(candidates, needs_mut, span));
 240         }
 241
 242         Ok(result.callee)
 243     }
 244
 245     #[instrument(level = "debug", skip(self, call_expr))]
 246     pub fn lookup_probe(
 247         &self,
 248         method_name: Ident,
 249         self_ty: Ty<'tcx>,
 250         call_expr: &'tcx hir::Expr<'tcx>,
 251         scope: ProbeScope,
 252     ) -> probe::PickResult<'tcx> {
 253         let pick = self.probe_for_name(
 254             probe::Mode::MethodCall,
 255             method_name,
 256             IsSuggestion(false),
 257             self_ty,
 258             call_expr.hir_id,
 259             scope,
 260         )?;
 261         pick.maybe_emit_unstable_name_collision_hint(self.tcx, method_name.span, call_expr.hir_id);
 262         Ok(pick)
 263     }
 264
 265     pub(super) fn obligation_for_method(
 266         &self,
 267         cause: ObligationCause<'tcx>,
 268         trait_def_id: DefId,
 269         self_ty: Ty<'tcx>,
 270         opt_input_types: Option<&[Ty<'tcx>]>,
 271     ) -> (traits::Obligation<'tcx, ty::Predicate<'tcx>>, &'tcx ty::List<ty::subst::GenericArg<'tcx>>)
 272     {
 273         // Construct a trait-reference `self_ty : Trait<input_tys>`
 274         let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
 275             match param.kind {
 276                 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => {}
 277                 GenericParamDefKind::Type { .. } => {
 278                     if param.index == 0 {
 279                         return self_ty.into();
 280                     } else if let Some(input_types) = opt_input_types {
 281                         return input_types[param.index as usize - 1].into();
 282                     }
 283                 }
 284             }
 285             self.var_for_def(cause.span, param)
 286         });
 287
 288         let trait_ref = self.tcx.mk_trait_ref(trait_def_id, substs);
 289
 290         // Construct an obligation
 291         let poly_trait_ref = ty::Binder::dummy(trait_ref);
 292         (
 293             traits::Obligation::new(
 294                 self.tcx,
 295                 cause,
 296                 self.param_env,
 297                 poly_trait_ref.without_const(),
 298             ),
 299             substs,
 300         )
 301     }
 302
 303     /// `lookup_method_in_trait` is used for overloaded operators.
 304     /// It does a very narrow slice of what the normal probe/confirm path does.
 305     /// In particular, it doesn't really do any probing: it simply constructs
 306     /// an obligation for a particular trait with the given self type and checks
 307     /// whether that trait is implemented.
 308     #[instrument(level = "debug", skip(self))]
 309     pub(super) fn lookup_method_in_trait(
 310         &self,
 311         cause: ObligationCause<'tcx>,
 312         m_name: Ident,
 313         trait_def_id: DefId,
 314         self_ty: Ty<'tcx>,
 315         opt_input_types: Option<&[Ty<'tcx>]>,
 316     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 317         let (obligation, substs) =
 318             self.obligation_for_method(cause, trait_def_id, self_ty, opt_input_types);
 319         self.construct_obligation_for_trait(m_name, trait_def_id, obligation, substs)
 320     }
 321
 322     // FIXME(#18741): it seems likely that we can consolidate some of this
 323     // code with the other method-lookup code. In particular, the second half
 324     // of this method is basically the same as confirmation.
 325     fn construct_obligation_for_trait(
 326         &self,
 327         m_name: Ident,
 328         trait_def_id: DefId,
 329         obligation: traits::PredicateObligation<'tcx>,
 330         substs: &'tcx ty::List<ty::subst::GenericArg<'tcx>>,
 331     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 332         debug!(?obligation);
 333
 334         // Now we want to know if this can be matched
 335         if !self.predicate_may_hold(&obligation) {
 336             debug!("--> Cannot match obligation");
 337             // Cannot be matched, no such method resolution is possible.
 338             return None;
 339         }
 340
 341         // Trait must have a method named `m_name` and it should not have
 342         // type parameters or early-bound regions.
 343         let tcx = self.tcx;
 344         let Some(method_item) = self.associated_value(trait_def_id, m_name) else {
 345             tcx.sess.delay_span_bug(
 346                 obligation.cause.span,
 347                 "operator trait does not have corresponding operator method",
 348             );
 349             return None;
 350         };
 351         let def_id = method_item.def_id;
 352         let generics = tcx.generics_of(def_id);
 353
 354         if generics.params.len() != 0 {
 355             tcx.sess.emit_fatal(OpMethodGenericParams {
 356                 span: tcx.def_span(method_item.def_id),
 357                 method_name: m_name.to_string(),
 358             });
 359         }
 360
 361         debug!("lookup_in_trait_adjusted: method_item={:?}", method_item);
 362         let mut obligations = vec![];
 363
 364         // Instantiate late-bound regions and substitute the trait
 365         // parameters into the method type to get the actual method type.
 366         //
 367         // N.B., instantiate late-bound regions before normalizing the
 368         // function signature so that normalization does not need to deal
 369         // with bound regions.
 370         let fn_sig = tcx.bound_fn_sig(def_id);
 371         let fn_sig = fn_sig.subst(self.tcx, substs);
 372         let fn_sig =
 373             self.replace_bound_vars_with_fresh_vars(obligation.cause.span, infer::FnCall, fn_sig);
 374
 375         let InferOk { value, obligations: o } =
 376             self.at(&obligation.cause, self.param_env).normalize(fn_sig);
 377         let fn_sig = {
 378             obligations.extend(o);
 379             value
 380         };
 381
 382         // Register obligations for the parameters. This will include the
 383         // `Self` parameter, which in turn has a bound of the main trait,
 384         // so this also effectively registers `obligation` as well.  (We
 385         // used to register `obligation` explicitly, but that resulted in
 386         // double error messages being reported.)
 387         //
 388         // Note that as the method comes from a trait, it should not have
 389         // any late-bound regions appearing in its bounds.
 390         let bounds = self.tcx.predicates_of(def_id).instantiate(self.tcx, substs);
 391
 392         let InferOk { value, obligations: o } =
 393             self.at(&obligation.cause, self.param_env).normalize(bounds);
 394         let bounds = {
 395             obligations.extend(o);
 396             value
 397         };
 398
 399         assert!(!bounds.has_escaping_bound_vars());
 400
 401         let predicates_cause = obligation.cause.clone();
 402         obligations.extend(traits::predicates_for_generics(
 403             move |_, _| predicates_cause.clone(),
 404             self.param_env,
 405             bounds,
 406         ));
 407
 408         // Also add an obligation for the method type being well-formed.
 409         let method_ty = tcx.mk_fn_ptr(ty::Binder::dummy(fn_sig));
 410         debug!(
 411             "lookup_in_trait_adjusted: matched method method_ty={:?} obligation={:?}",
 412             method_ty, obligation
 413         );
 414         obligations.push(traits::Obligation::new(
 415             tcx,
 416             obligation.cause,
 417             self.param_env,
 418             ty::Binder::dummy(ty::PredicateKind::WellFormed(method_ty.into())),
 419         ));
 420
 421         let callee = MethodCallee { def_id, substs, sig: fn_sig };
 422
 423         debug!("callee = {:?}", callee);
 424
 425         Some(InferOk { obligations, value: callee })
 426     }
 427
 428     /// Performs a [full-qualified function call] (formerly "universal function call") lookup. If
 429     /// lookup is successful, it will return the type of definition and the [`DefId`] of the found
 430     /// function definition.
 431     ///
 432     /// [full-qualified function call]: https://doc.rust-lang.org/reference/expressions/call-expr.html#disambiguating-function-calls
 433     ///
 434     /// # Arguments
 435     ///
 436     /// Given a function call like `Foo::bar::<T1,...Tn>(...)`:
 437     ///
 438     /// * `self`:                  the surrounding `FnCtxt` (!)
 439     /// * `span`:                  the span of the call, excluding arguments (`Foo::bar::<T1, ...Tn>`)
 440     /// * `method_name`:           the identifier of the function within the container type (`bar`)
 441     /// * `self_ty`:               the type to search within (`Foo`)
 442     /// * `self_ty_span`           the span for the type being searched within (span of `Foo`)
 443     /// * `expr_id`:               the [`hir::HirId`] of the expression composing the entire call
 444     #[instrument(level = "debug", skip(self), ret)]
 445     pub fn resolve_fully_qualified_call(
 446         &self,
 447         span: Span,
 448         method_name: Ident,
 449         self_ty: Ty<'tcx>,
 450         self_ty_span: Span,
 451         expr_id: hir::HirId,
 452     ) -> Result<(DefKind, DefId), MethodError<'tcx>> {
 453         let tcx = self.tcx;
 454
 455         // Check if we have an enum variant.
 456         let mut struct_variant = None;
 457         if let ty::Adt(adt_def, _) = self_ty.kind() {
 458             if adt_def.is_enum() {
 459                 let variant_def = adt_def
 460                     .variants()
 461                     .iter()
 462                     .find(|vd| tcx.hygienic_eq(method_name, vd.ident(tcx), adt_def.did()));
 463                 if let Some(variant_def) = variant_def {
 464                     if let Some((ctor_kind, ctor_def_id)) = variant_def.ctor {
 465                         tcx.check_stability(
 466                             ctor_def_id,
 467                             Some(expr_id),
 468                             span,
 469                             Some(method_name.span),
 470                         );
 471                         return Ok((DefKind::Ctor(CtorOf::Variant, ctor_kind), ctor_def_id));
 472                     } else {
 473                         struct_variant = Some((DefKind::Variant, variant_def.def_id));
 474                     }
 475                 }
 476             }
 477         }
 478
 479         let pick = self.probe_for_name(
 480             probe::Mode::Path,
 481             method_name,
 482             IsSuggestion(false),
 483             self_ty,
 484             expr_id,
 485             ProbeScope::TraitsInScope,
 486         );
 487         let pick = match (pick, struct_variant) {
 488             // Fall back to a resolution that will produce an error later.
 489             (Err(_), Some(res)) => return Ok(res),
 490             (pick, _) => pick?,
 491         };
 492
 493         pick.maybe_emit_unstable_name_collision_hint(self.tcx, span, expr_id);
 494
 495         self.lint_fully_qualified_call_from_2018(
 496             span,
 497             method_name,
 498             self_ty,
 499             self_ty_span,
 500             expr_id,
 501             &pick,
 502         );
 503
 504         debug!(?pick);
 505         {
 506             let mut typeck_results = self.typeck_results.borrow_mut();
 507             let used_trait_imports = Lrc::get_mut(&mut typeck_results.used_trait_imports).unwrap();
 508             for import_id in pick.import_ids {
 509                 debug!(used_trait_import=?import_id);
 510                 used_trait_imports.insert(import_id);
 511             }
 512         }
 513
 514         let def_kind = pick.item.kind.as_def_kind();
 515         tcx.check_stability(pick.item.def_id, Some(expr_id), span, Some(method_name.span));
 516         Ok((def_kind, pick.item.def_id))
 517     }
 518
 519     /// Finds item with name `item_name` defined in impl/trait `def_id`
 520     /// and return it, or `None`, if no such item was defined there.
 521     pub fn associated_value(&self, def_id: DefId, item_name: Ident) -> Option<ty::AssocItem> {
 522         self.tcx
 523             .associated_items(def_id)
 524             .find_by_name_and_namespace(self.tcx, item_name, Namespace::ValueNS, def_id)
 525             .copied()
 526     }
 527 }