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 lev_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     ) -> bool {
 101         match self.probe_for_name(
 102             probe::Mode::MethodCall,
 103             method_name,
 104             IsSuggestion(false),
 105             self_ty,
 106             call_expr_id,
 107             ProbeScope::TraitsInScope,
 108         ) {
 109             Ok(pick) => {
 110                 pick.maybe_emit_unstable_name_collision_hint(
 111                     self.tcx,
 112                     method_name.span,
 113                     call_expr_id,
 114                 );
 115                 true
 116             }
 117             Err(NoMatch(..)) => false,
 118             Err(Ambiguity(..)) => true,
 119             Err(PrivateMatch(..)) => allow_private,
 120             Err(IllegalSizedBound { .. }) => true,
 121             Err(BadReturnType) => bug!("no return type expectations but got BadReturnType"),
 122         }
 123     }
 124
 125     /// Adds a suggestion to call the given method to the provided diagnostic.
 126     #[instrument(level = "debug", skip(self, err, call_expr))]
 127     pub(crate) fn suggest_method_call(
 128         &self,
 129         err: &mut Diagnostic,
 130         msg: &str,
 131         method_name: Ident,
 132         self_ty: Ty<'tcx>,
 133         call_expr: &hir::Expr<'_>,
 134         span: Option<Span>,
 135     ) {
 136         let params = self
 137             .probe_for_name(
 138                 probe::Mode::MethodCall,
 139                 method_name,
 140                 IsSuggestion(true),
 141                 self_ty,
 142                 call_expr.hir_id,
 143                 ProbeScope::TraitsInScope,
 144             )
 145             .map(|pick| {
 146                 let sig = self.tcx.fn_sig(pick.item.def_id);
 147                 sig.inputs().skip_binder().len().saturating_sub(1)
 148             })
 149             .unwrap_or(0);
 150
 151         // Account for `foo.bar<T>`;
 152         let sugg_span = span.unwrap_or(call_expr.span).shrink_to_hi();
 153         let (suggestion, applicability) = (
 154             format!("({})", (0..params).map(|_| "_").collect::<Vec<_>>().join(", ")),
 155             if params > 0 { Applicability::HasPlaceholders } else { Applicability::MaybeIncorrect },
 156         );
 157
 158         err.span_suggestion_verbose(sugg_span, msg, suggestion, applicability);
 159     }
 160
 161     /// Performs method lookup. If lookup is successful, it will return the callee
 162     /// and store an appropriate adjustment for the self-expr. In some cases it may
 163     /// report an error (e.g., invoking the `drop` method).
 164     ///
 165     /// # Arguments
 166     ///
 167     /// Given a method call like `foo.bar::<T1,...Tn>(a, b + 1, ...)`:
 168     ///
 169     /// * `self`:                  the surrounding `FnCtxt` (!)
 170     /// * `self_ty`:               the (unadjusted) type of the self expression (`foo`)
 171     /// * `segment`:               the name and generic arguments of the method (`bar::<T1, ...Tn>`)
 172     /// * `span`:                  the span for the method call
 173     /// * `call_expr`:             the complete method call: (`foo.bar::<T1,...Tn>(...)`)
 174     /// * `self_expr`:             the self expression (`foo`)
 175     /// * `args`:                  the expressions of the arguments (`a, b + 1, ...`)
 176     #[instrument(level = "debug", skip(self))]
 177     pub fn lookup_method(
 178         &self,
 179         self_ty: Ty<'tcx>,
 180         segment: &hir::PathSegment<'_>,
 181         span: Span,
 182         call_expr: &'tcx hir::Expr<'tcx>,
 183         self_expr: &'tcx hir::Expr<'tcx>,
 184         args: &'tcx [hir::Expr<'tcx>],
 185     ) -> Result<MethodCallee<'tcx>, MethodError<'tcx>> {
 186         let pick =
 187             self.lookup_probe(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 = self.confirm_method(span, self_expr, call_expr, self_ty, &pick, segment);
 201         debug!("result = {:?}", result);
 202
 203         if let Some(span) = result.illegal_sized_bound {
 204             let mut needs_mut = false;
 205             if let ty::Ref(region, t_type, mutability) = self_ty.kind() {
 206                 let trait_type = self
 207                     .tcx
 208                     .mk_ref(*region, ty::TypeAndMut { ty: *t_type, mutbl: mutability.invert() });
 209                 // We probe again to see if there might be a borrow mutability discrepancy.
 210                 match self.lookup_probe(
 211                     segment.ident,
 212                     trait_type,
 213                     call_expr,
 214                     ProbeScope::TraitsInScope,
 215                 ) {
 216                     Ok(ref new_pick) if pick.differs_from(new_pick) => {
 217                         needs_mut = new_pick.self_ty.ref_mutability() != self_ty.ref_mutability();
 218                     }
 219                     _ => {}
 220                 }
 221             }
 222
 223             // We probe again, taking all traits into account (not only those in scope).
 224             let candidates =
 225                 match self.lookup_probe(segment.ident, self_ty, call_expr, ProbeScope::AllTraits) {
 226                     // If we find a different result the caller probably forgot to import a trait.
 227                     Ok(ref new_pick) if pick.differs_from(new_pick) => {
 228                         vec![new_pick.item.container_id(self.tcx)]
 229                     }
 230                     Err(Ambiguity(ref sources)) => sources
 231                         .iter()
 232                         .filter_map(|source| {
 233                             match *source {
 234                                 // Note: this cannot come from an inherent impl,
 235                                 // because the first probing succeeded.
 236                                 CandidateSource::Impl(def) => self.tcx.trait_id_of_impl(def),
 237                                 CandidateSource::Trait(_) => None,
 238                             }
 239                         })
 240                         .collect(),
 241                     _ => Vec::new(),
 242                 };
 243
 244             return Err(IllegalSizedBound { candidates, needs_mut, bound_span: span, self_expr });
 245         }
 246
 247         Ok(result.callee)
 248     }
 249
 250     #[instrument(level = "debug", skip(self, call_expr))]
 251     pub fn lookup_probe(
 252         &self,
 253         method_name: Ident,
 254         self_ty: Ty<'tcx>,
 255         call_expr: &'tcx hir::Expr<'tcx>,
 256         scope: ProbeScope,
 257     ) -> probe::PickResult<'tcx> {
 258         let pick = self.probe_for_name(
 259             probe::Mode::MethodCall,
 260             method_name,
 261             IsSuggestion(false),
 262             self_ty,
 263             call_expr.hir_id,
 264             scope,
 265         )?;
 266         pick.maybe_emit_unstable_name_collision_hint(self.tcx, method_name.span, call_expr.hir_id);
 267         Ok(pick)
 268     }
 269
 270     pub(super) fn obligation_for_method(
 271         &self,
 272         cause: ObligationCause<'tcx>,
 273         trait_def_id: DefId,
 274         self_ty: Ty<'tcx>,
 275         opt_input_types: Option<&[Ty<'tcx>]>,
 276     ) -> (traits::Obligation<'tcx, ty::Predicate<'tcx>>, &'tcx ty::List<ty::subst::GenericArg<'tcx>>)
 277     {
 278         // Construct a trait-reference `self_ty : Trait<input_tys>`
 279         let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
 280             match param.kind {
 281                 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => {}
 282                 GenericParamDefKind::Type { .. } => {
 283                     if param.index == 0 {
 284                         return self_ty.into();
 285                     } else if let Some(input_types) = opt_input_types {
 286                         return input_types[param.index as usize - 1].into();
 287                     }
 288                 }
 289             }
 290             self.var_for_def(cause.span, param)
 291         });
 292
 293         let trait_ref = self.tcx.mk_trait_ref(trait_def_id, substs);
 294
 295         // Construct an obligation
 296         let poly_trait_ref = ty::Binder::dummy(trait_ref);
 297         (
 298             traits::Obligation::new(
 299                 self.tcx,
 300                 cause,
 301                 self.param_env,
 302                 poly_trait_ref.without_const(),
 303             ),
 304             substs,
 305         )
 306     }
 307
 308     /// `lookup_method_in_trait` is used for overloaded operators.
 309     /// It does a very narrow slice of what the normal probe/confirm path does.
 310     /// In particular, it doesn't really do any probing: it simply constructs
 311     /// an obligation for a particular trait with the given self type and checks
 312     /// whether that trait is implemented.
 313     #[instrument(level = "debug", skip(self))]
 314     pub(super) fn lookup_method_in_trait(
 315         &self,
 316         cause: ObligationCause<'tcx>,
 317         m_name: Ident,
 318         trait_def_id: DefId,
 319         self_ty: Ty<'tcx>,
 320         opt_input_types: Option<&[Ty<'tcx>]>,
 321     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 322         let (obligation, substs) =
 323             self.obligation_for_method(cause, trait_def_id, self_ty, opt_input_types);
 324         self.construct_obligation_for_trait(m_name, trait_def_id, obligation, substs)
 325     }
 326
 327     // FIXME(#18741): it seems likely that we can consolidate some of this
 328     // code with the other method-lookup code. In particular, the second half
 329     // of this method is basically the same as confirmation.
 330     fn construct_obligation_for_trait(
 331         &self,
 332         m_name: Ident,
 333         trait_def_id: DefId,
 334         obligation: traits::PredicateObligation<'tcx>,
 335         substs: &'tcx ty::List<ty::subst::GenericArg<'tcx>>,
 336     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 337         debug!(?obligation);
 338
 339         // Now we want to know if this can be matched
 340         if !self.predicate_may_hold(&obligation) {
 341             debug!("--> Cannot match obligation");
 342             // Cannot be matched, no such method resolution is possible.
 343             return None;
 344         }
 345
 346         // Trait must have a method named `m_name` and it should not have
 347         // type parameters or early-bound regions.
 348         let tcx = self.tcx;
 349         let Some(method_item) = self.associated_value(trait_def_id, m_name) else {
 350             tcx.sess.delay_span_bug(
 351                 obligation.cause.span,
 352                 "operator trait does not have corresponding operator method",
 353             );
 354             return None;
 355         };
 356         let def_id = method_item.def_id;
 357         let generics = tcx.generics_of(def_id);
 358
 359         if generics.params.len() != 0 {
 360             tcx.sess.emit_fatal(OpMethodGenericParams {
 361                 span: tcx.def_span(method_item.def_id),
 362                 method_name: m_name.to_string(),
 363             });
 364         }
 365
 366         debug!("lookup_in_trait_adjusted: method_item={:?}", method_item);
 367         let mut obligations = vec![];
 368
 369         // Instantiate late-bound regions and substitute the trait
 370         // parameters into the method type to get the actual method type.
 371         //
 372         // N.B., instantiate late-bound regions before normalizing the
 373         // function signature so that normalization does not need to deal
 374         // with bound regions.
 375         let fn_sig = tcx.bound_fn_sig(def_id);
 376         let fn_sig = fn_sig.subst(self.tcx, substs);
 377         let fn_sig =
 378             self.replace_bound_vars_with_fresh_vars(obligation.cause.span, infer::FnCall, fn_sig);
 379
 380         let InferOk { value, obligations: o } =
 381             self.at(&obligation.cause, self.param_env).normalize(fn_sig);
 382         let fn_sig = {
 383             obligations.extend(o);
 384             value
 385         };
 386
 387         // Register obligations for the parameters. This will include the
 388         // `Self` parameter, which in turn has a bound of the main trait,
 389         // so this also effectively registers `obligation` as well.  (We
 390         // used to register `obligation` explicitly, but that resulted in
 391         // double error messages being reported.)
 392         //
 393         // Note that as the method comes from a trait, it should not have
 394         // any late-bound regions appearing in its bounds.
 395         let bounds = self.tcx.predicates_of(def_id).instantiate(self.tcx, substs);
 396
 397         let InferOk { value, obligations: o } =
 398             self.at(&obligation.cause, self.param_env).normalize(bounds);
 399         let bounds = {
 400             obligations.extend(o);
 401             value
 402         };
 403
 404         assert!(!bounds.has_escaping_bound_vars());
 405
 406         let predicates_cause = obligation.cause.clone();
 407         obligations.extend(traits::predicates_for_generics(
 408             move |_, _| predicates_cause.clone(),
 409             self.param_env,
 410             bounds,
 411         ));
 412
 413         // Also add an obligation for the method type being well-formed.
 414         let method_ty = tcx.mk_fn_ptr(ty::Binder::dummy(fn_sig));
 415         debug!(
 416             "lookup_in_trait_adjusted: matched method method_ty={:?} obligation={:?}",
 417             method_ty, obligation
 418         );
 419         obligations.push(traits::Obligation::new(
 420             tcx,
 421             obligation.cause,
 422             self.param_env,
 423             ty::Binder::dummy(ty::PredicateKind::WellFormed(method_ty.into())),
 424         ));
 425
 426         let callee = MethodCallee { def_id, substs, sig: fn_sig };
 427
 428         debug!("callee = {:?}", callee);
 429
 430         Some(InferOk { obligations, value: callee })
 431     }
 432
 433     /// Performs a [full-qualified function call] (formerly "universal function call") lookup. If
 434     /// lookup is successful, it will return the type of definition and the [`DefId`] of the found
 435     /// function definition.
 436     ///
 437     /// [full-qualified function call]: https://doc.rust-lang.org/reference/expressions/call-expr.html#disambiguating-function-calls
 438     ///
 439     /// # Arguments
 440     ///
 441     /// Given a function call like `Foo::bar::<T1,...Tn>(...)`:
 442     ///
 443     /// * `self`:                  the surrounding `FnCtxt` (!)
 444     /// * `span`:                  the span of the call, excluding arguments (`Foo::bar::<T1, ...Tn>`)
 445     /// * `method_name`:           the identifier of the function within the container type (`bar`)
 446     /// * `self_ty`:               the type to search within (`Foo`)
 447     /// * `self_ty_span`           the span for the type being searched within (span of `Foo`)
 448     /// * `expr_id`:               the [`hir::HirId`] of the expression composing the entire call
 449     #[instrument(level = "debug", skip(self), ret)]
 450     pub fn resolve_fully_qualified_call(
 451         &self,
 452         span: Span,
 453         method_name: Ident,
 454         self_ty: Ty<'tcx>,
 455         self_ty_span: Span,
 456         expr_id: hir::HirId,
 457     ) -> Result<(DefKind, DefId), MethodError<'tcx>> {
 458         let tcx = self.tcx;
 459
 460         // Check if we have an enum variant.
 461         let mut struct_variant = None;
 462         if let ty::Adt(adt_def, _) = self_ty.kind() {
 463             if adt_def.is_enum() {
 464                 let variant_def = adt_def
 465                     .variants()
 466                     .iter()
 467                     .find(|vd| tcx.hygienic_eq(method_name, vd.ident(tcx), adt_def.did()));
 468                 if let Some(variant_def) = variant_def {
 469                     if let Some((ctor_kind, ctor_def_id)) = variant_def.ctor {
 470                         tcx.check_stability(
 471                             ctor_def_id,
 472                             Some(expr_id),
 473                             span,
 474                             Some(method_name.span),
 475                         );
 476                         return Ok((DefKind::Ctor(CtorOf::Variant, ctor_kind), ctor_def_id));
 477                     } else {
 478                         struct_variant = Some((DefKind::Variant, variant_def.def_id));
 479                     }
 480                 }
 481             }
 482         }
 483
 484         let pick = self.probe_for_name(
 485             probe::Mode::Path,
 486             method_name,
 487             IsSuggestion(false),
 488             self_ty,
 489             expr_id,
 490             ProbeScope::TraitsInScope,
 491         );
 492         let pick = match (pick, struct_variant) {
 493             // Fall back to a resolution that will produce an error later.
 494             (Err(_), Some(res)) => return Ok(res),
 495             (pick, _) => pick?,
 496         };
 497
 498         pick.maybe_emit_unstable_name_collision_hint(self.tcx, span, expr_id);
 499
 500         self.lint_fully_qualified_call_from_2018(
 501             span,
 502             method_name,
 503             self_ty,
 504             self_ty_span,
 505             expr_id,
 506             &pick,
 507         );
 508
 509         debug!(?pick);
 510         {
 511             let mut typeck_results = self.typeck_results.borrow_mut();
 512             let used_trait_imports = Lrc::get_mut(&mut typeck_results.used_trait_imports).unwrap();
 513             for import_id in pick.import_ids {
 514                 debug!(used_trait_import=?import_id);
 515                 used_trait_imports.insert(import_id);
 516             }
 517         }
 518
 519         let def_kind = pick.item.kind.as_def_kind();
 520         tcx.check_stability(pick.item.def_id, Some(expr_id), span, Some(method_name.span));
 521         Ok((def_kind, pick.item.def_id))
 522     }
 523
 524     /// Finds item with name `item_name` defined in impl/trait `def_id`
 525     /// and return it, or `None`, if no such item was defined there.
 526     pub fn associated_value(&self, def_id: DefId, item_name: Ident) -> Option<ty::AssocItem> {
 527         self.tcx
 528             .associated_items(def_id)
 529             .find_by_name_and_namespace(self.tcx, item_name, Namespace::ValueNS, def_id)
 530             .copied()
 531     }
 532 }