| //! Method lookup: the secret sauce of Rust. See the [rustc guide] for more information. |
| //! |
| //! [rustc guide]: https://rust-lang.github.io/rustc-guide/method-lookup.html |
| |
| mod confirm; |
| pub mod probe; |
| mod suggest; |
| |
| pub use self::MethodError::*; |
| pub use self::CandidateSource::*; |
| pub use self::suggest::{SelfSource, TraitInfo}; |
| |
| use crate::check::FnCtxt; |
| use crate::namespace::Namespace; |
| use errors::{Applicability, DiagnosticBuilder}; |
| use rustc_data_structures::sync::Lrc; |
| use rustc::hir; |
| use rustc::hir::def::{CtorOf, DefKind}; |
| use rustc::hir::def_id::DefId; |
| use rustc::traits; |
| use rustc::ty::subst::{InternalSubsts, SubstsRef}; |
| use rustc::ty::{self, Ty, ToPredicate, ToPolyTraitRef, TraitRef, TypeFoldable}; |
| use rustc::ty::GenericParamDefKind; |
| use rustc::ty::subst::Subst; |
| use rustc::infer::{self, InferOk}; |
| use syntax::ast; |
| use syntax_pos::Span; |
| |
| use self::probe::{IsSuggestion, ProbeScope}; |
| |
| pub fn provide(providers: &mut ty::query::Providers<'_>) { |
| suggest::provide(providers); |
| probe::provide(providers); |
| } |
| |
| #[derive(Clone, Copy, Debug)] |
| pub struct MethodCallee<'tcx> { |
| /// Impl method ID, for inherent methods, or trait method ID, otherwise. |
| pub def_id: DefId, |
| pub substs: SubstsRef<'tcx>, |
| |
| /// Instantiated method signature, i.e., it has been |
| /// substituted, normalized, and has had late-bound |
| /// lifetimes replaced with inference variables. |
| pub sig: ty::FnSig<'tcx>, |
| } |
| |
| pub enum MethodError<'tcx> { |
| // Did not find an applicable method, but we did find various near-misses that may work. |
| NoMatch(NoMatchData<'tcx>), |
| |
| // Multiple methods might apply. |
| Ambiguity(Vec<CandidateSource>), |
| |
| // Found an applicable method, but it is not visible. The third argument contains a list of |
| // not-in-scope traits which may work. |
| PrivateMatch(DefKind, DefId, Vec<DefId>), |
| |
| // Found a `Self: Sized` bound where `Self` is a trait object, also the caller may have |
| // forgotten to import a trait. |
| IllegalSizedBound(Vec<DefId>), |
| |
| // Found a match, but the return type is wrong |
| BadReturnType, |
| } |
| |
| // Contains a list of static methods that may apply, a list of unsatisfied trait predicates which |
| // could lead to matches if satisfied, and a list of not-in-scope traits which may work. |
| pub struct NoMatchData<'tcx> { |
| pub static_candidates: Vec<CandidateSource>, |
| pub unsatisfied_predicates: Vec<TraitRef<'tcx>>, |
| pub out_of_scope_traits: Vec<DefId>, |
| pub lev_candidate: Option<ty::AssocItem>, |
| pub mode: probe::Mode, |
| } |
| |
| impl<'tcx> NoMatchData<'tcx> { |
| pub fn new(static_candidates: Vec<CandidateSource>, |
| unsatisfied_predicates: Vec<TraitRef<'tcx>>, |
| out_of_scope_traits: Vec<DefId>, |
| lev_candidate: Option<ty::AssocItem>, |
| mode: probe::Mode) |
| -> Self { |
| NoMatchData { |
| static_candidates, |
| unsatisfied_predicates, |
| out_of_scope_traits, |
| lev_candidate, |
| mode, |
| } |
| } |
| } |
| |
| // A pared down enum describing just the places from which a method |
| // candidate can arise. Used for error reporting only. |
| #[derive(Copy, Clone, Debug, Eq, Ord, PartialEq, PartialOrd)] |
| pub enum CandidateSource { |
| ImplSource(DefId), |
| TraitSource(DefId /* trait id */), |
| } |
| |
| impl<'a, 'tcx> FnCtxt<'a, 'tcx> { |
| /// Determines whether the type `self_ty` supports a method name `method_name` or not. |
| pub fn method_exists(&self, |
| method_name: ast::Ident, |
| self_ty: Ty<'tcx>, |
| call_expr_id: hir::HirId, |
| allow_private: bool) |
| -> bool { |
| let mode = probe::Mode::MethodCall; |
| match self.probe_for_name(method_name.span, mode, method_name, |
| IsSuggestion(false), self_ty, call_expr_id, |
| ProbeScope::TraitsInScope) { |
| Ok(..) => true, |
| Err(NoMatch(..)) => false, |
| Err(Ambiguity(..)) => true, |
| Err(PrivateMatch(..)) => allow_private, |
| Err(IllegalSizedBound(..)) => true, |
| Err(BadReturnType) => { |
| bug!("no return type expectations but got BadReturnType") |
| } |
| |
| } |
| } |
| |
| /// Adds a suggestion to call the given method to the provided diagnostic. |
| crate fn suggest_method_call( |
| &self, |
| err: &mut DiagnosticBuilder<'a>, |
| msg: &str, |
| method_name: ast::Ident, |
| self_ty: Ty<'tcx>, |
| call_expr_id: hir::HirId, |
| ) { |
| let has_params = self |
| .probe_for_name( |
| method_name.span, |
| probe::Mode::MethodCall, |
| method_name, |
| IsSuggestion(false), |
| self_ty, |
| call_expr_id, |
| ProbeScope::TraitsInScope, |
| ) |
| .and_then(|pick| { |
| let sig = self.tcx.fn_sig(pick.item.def_id); |
| Ok(sig.inputs().skip_binder().len() > 1) |
| }); |
| |
| let (suggestion, applicability) = if has_params.unwrap_or_default() { |
| ( |
| format!("{}(...)", method_name), |
| Applicability::HasPlaceholders, |
| ) |
| } else { |
| (format!("{}()", method_name), Applicability::MaybeIncorrect) |
| }; |
| |
| err.span_suggestion(method_name.span, msg, suggestion, applicability); |
| } |
| |
| /// Performs method lookup. If lookup is successful, it will return the callee |
| /// and store an appropriate adjustment for the self-expr. In some cases it may |
| /// report an error (e.g., invoking the `drop` method). |
| /// |
| /// # Arguments |
| /// |
| /// Given a method call like `foo.bar::<T1,...Tn>(...)`: |
| /// |
| /// * `fcx`: the surrounding `FnCtxt` (!) |
| /// * `span`: the span for the method call |
| /// * `method_name`: the name of the method being called (`bar`) |
| /// * `self_ty`: the (unadjusted) type of the self expression (`foo`) |
| /// * `supplied_method_types`: the explicit method type parameters, if any (`T1..Tn`) |
| /// * `self_expr`: the self expression (`foo`) |
| pub fn lookup_method( |
| &self, |
| self_ty: Ty<'tcx>, |
| segment: &hir::PathSegment, |
| span: Span, |
| call_expr: &'tcx hir::Expr, |
| self_expr: &'tcx hir::Expr, |
| ) -> Result<MethodCallee<'tcx>, MethodError<'tcx>> { |
| debug!("lookup(method_name={}, self_ty={:?}, call_expr={:?}, self_expr={:?})", |
| segment.ident, |
| self_ty, |
| call_expr, |
| self_expr); |
| |
| let pick = self.lookup_probe( |
| span, |
| segment.ident, |
| self_ty, |
| call_expr, |
| ProbeScope::TraitsInScope |
| )?; |
| |
| for import_id in &pick.import_ids { |
| let import_def_id = self.tcx.hir().local_def_id(*import_id); |
| debug!("used_trait_import: {:?}", import_def_id); |
| Lrc::get_mut(&mut self.tables.borrow_mut().used_trait_imports) |
| .unwrap().insert(import_def_id); |
| } |
| |
| self.tcx.check_stability(pick.item.def_id, Some(call_expr.hir_id), span); |
| |
| let result = self.confirm_method( |
| span, |
| self_expr, |
| call_expr, |
| self_ty, |
| pick.clone(), |
| segment, |
| ); |
| |
| if result.illegal_sized_bound { |
| // We probe again, taking all traits into account (not only those in scope). |
| let candidates = |
| match self.lookup_probe(span, |
| segment.ident, |
| self_ty, |
| call_expr, |
| ProbeScope::AllTraits) { |
| |
| // If we find a different result the caller probably forgot to import a trait. |
| Ok(ref new_pick) if *new_pick != pick => vec![new_pick.item.container.id()], |
| Err(Ambiguity(ref sources)) => { |
| sources.iter() |
| .filter_map(|source| { |
| match *source { |
| // Note: this cannot come from an inherent impl, |
| // because the first probing succeeded. |
| ImplSource(def) => self.tcx.trait_id_of_impl(def), |
| TraitSource(_) => None, |
| } |
| }) |
| .collect() |
| } |
| _ => Vec::new(), |
| }; |
| |
| return Err(IllegalSizedBound(candidates)); |
| } |
| |
| Ok(result.callee) |
| } |
| |
| pub fn lookup_probe( |
| &self, |
| span: Span, |
| method_name: ast::Ident, |
| self_ty: Ty<'tcx>, |
| call_expr: &'tcx hir::Expr, |
| scope: ProbeScope, |
| ) -> probe::PickResult<'tcx> { |
| let mode = probe::Mode::MethodCall; |
| let self_ty = self.resolve_vars_if_possible(&self_ty); |
| self.probe_for_name(span, mode, method_name, IsSuggestion(false), |
| self_ty, call_expr.hir_id, scope) |
| } |
| |
| /// `lookup_method_in_trait` is used for overloaded operators. |
| /// It does a very narrow slice of what the normal probe/confirm path does. |
| /// In particular, it doesn't really do any probing: it simply constructs |
| /// an obligation for a particular trait with the given self type and checks |
| /// whether that trait is implemented. |
| // |
| // FIXME(#18741): it seems likely that we can consolidate some of this |
| // code with the other method-lookup code. In particular, the second half |
| // of this method is basically the same as confirmation. |
| pub fn lookup_method_in_trait(&self, |
| span: Span, |
| m_name: ast::Ident, |
| trait_def_id: DefId, |
| self_ty: Ty<'tcx>, |
| opt_input_types: Option<&[Ty<'tcx>]>) |
| -> Option<InferOk<'tcx, MethodCallee<'tcx>>> { |
| debug!("lookup_in_trait_adjusted(self_ty={:?}, \ |
| m_name={}, trait_def_id={:?})", |
| self_ty, |
| m_name, |
| trait_def_id); |
| |
| // Construct a trait-reference `self_ty : Trait<input_tys>` |
| let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| { |
| match param.kind { |
| GenericParamDefKind::Lifetime | GenericParamDefKind::Const => {} |
| GenericParamDefKind::Type { .. } => { |
| if param.index == 0 { |
| return self_ty.into(); |
| } else if let Some(ref input_types) = opt_input_types { |
| return input_types[param.index as usize - 1].into(); |
| } |
| } |
| } |
| self.var_for_def(span, param) |
| }); |
| |
| let trait_ref = ty::TraitRef::new(trait_def_id, substs); |
| |
| // Construct an obligation |
| let poly_trait_ref = trait_ref.to_poly_trait_ref(); |
| let obligation = |
| traits::Obligation::misc(span, |
| self.body_id, |
| self.param_env, |
| poly_trait_ref.to_predicate()); |
| |
| // Now we want to know if this can be matched |
| if !self.predicate_may_hold(&obligation) { |
| debug!("--> Cannot match obligation"); |
| return None; // Cannot be matched, no such method resolution is possible. |
| } |
| |
| // Trait must have a method named `m_name` and it should not have |
| // type parameters or early-bound regions. |
| let tcx = self.tcx; |
| let method_item = match self.associated_item(trait_def_id, m_name, Namespace::Value) { |
| Some(method_item) => method_item, |
| None => { |
| tcx.sess.delay_span_bug(span, |
| "operator trait does not have corresponding operator method"); |
| return None; |
| } |
| }; |
| let def_id = method_item.def_id; |
| let generics = tcx.generics_of(def_id); |
| assert_eq!(generics.params.len(), 0); |
| |
| debug!("lookup_in_trait_adjusted: method_item={:?}", method_item); |
| let mut obligations = vec![]; |
| |
| // Instantiate late-bound regions and substitute the trait |
| // parameters into the method type to get the actual method type. |
| // |
| // N.B., instantiate late-bound regions first so that |
| // `instantiate_type_scheme` can normalize associated types that |
| // may reference those regions. |
| let fn_sig = tcx.fn_sig(def_id); |
| let fn_sig = self.replace_bound_vars_with_fresh_vars( |
| span, |
| infer::FnCall, |
| &fn_sig |
| ).0; |
| let fn_sig = fn_sig.subst(self.tcx, substs); |
| let fn_sig = match self.normalize_associated_types_in_as_infer_ok(span, &fn_sig) { |
| InferOk { value, obligations: o } => { |
| obligations.extend(o); |
| value |
| } |
| }; |
| |
| // Register obligations for the parameters. This will include the |
| // `Self` parameter, which in turn has a bound of the main trait, |
| // so this also effectively registers `obligation` as well. (We |
| // used to register `obligation` explicitly, but that resulted in |
| // double error messages being reported.) |
| // |
| // Note that as the method comes from a trait, it should not have |
| // any late-bound regions appearing in its bounds. |
| let bounds = self.tcx.predicates_of(def_id).instantiate(self.tcx, substs); |
| let bounds = match self.normalize_associated_types_in_as_infer_ok(span, &bounds) { |
| InferOk { value, obligations: o } => { |
| obligations.extend(o); |
| value |
| } |
| }; |
| assert!(!bounds.has_escaping_bound_vars()); |
| |
| let cause = traits::ObligationCause::misc(span, self.body_id); |
| obligations.extend(traits::predicates_for_generics(cause.clone(), |
| self.param_env, |
| &bounds)); |
| |
| // Also add an obligation for the method type being well-formed. |
| let method_ty = tcx.mk_fn_ptr(ty::Binder::bind(fn_sig)); |
| debug!("lookup_in_trait_adjusted: matched method method_ty={:?} obligation={:?}", |
| method_ty, |
| obligation); |
| obligations.push(traits::Obligation::new(cause, |
| self.param_env, |
| ty::Predicate::WellFormed(method_ty))); |
| |
| let callee = MethodCallee { |
| def_id, |
| substs: trait_ref.substs, |
| sig: fn_sig, |
| }; |
| |
| debug!("callee = {:?}", callee); |
| |
| Some(InferOk { |
| obligations, |
| value: callee |
| }) |
| } |
| |
| pub fn resolve_ufcs( |
| &self, |
| span: Span, |
| method_name: ast::Ident, |
| self_ty: Ty<'tcx>, |
| expr_id: hir::HirId |
| ) -> Result<(DefKind, DefId), MethodError<'tcx>> { |
| debug!( |
| "resolve_ufcs: method_name={:?} self_ty={:?} expr_id={:?}", |
| method_name, self_ty, expr_id, |
| ); |
| |
| let tcx = self.tcx; |
| |
| // Check if we have an enum variant. |
| if let ty::Adt(adt_def, _) = self_ty.sty { |
| if adt_def.is_enum() { |
| let variant_def = adt_def.variants.iter().find(|vd| { |
| tcx.hygienic_eq(method_name, vd.ident, adt_def.did) |
| }); |
| if let Some(variant_def) = variant_def { |
| // Braced variants generate unusable names in value namespace (reserved for |
| // possible future use), so variants resolved as associated items may refer to |
| // them as well. It's ok to use the variant's id as a ctor id since an |
| // error will be reported on any use of such resolution anyway. |
| let ctor_def_id = variant_def.ctor_def_id.unwrap_or(variant_def.def_id); |
| tcx.check_stability(ctor_def_id, Some(expr_id), span); |
| return Ok(( |
| DefKind::Ctor(CtorOf::Variant, variant_def.ctor_kind), |
| ctor_def_id, |
| )); |
| } |
| } |
| } |
| |
| let pick = self.probe_for_name(span, probe::Mode::Path, method_name, IsSuggestion(false), |
| self_ty, expr_id, ProbeScope::TraitsInScope)?; |
| debug!("resolve_ufcs: pick={:?}", pick); |
| for import_id in pick.import_ids { |
| let import_def_id = tcx.hir().local_def_id(import_id); |
| debug!("resolve_ufcs: used_trait_import: {:?}", import_def_id); |
| Lrc::get_mut(&mut self.tables.borrow_mut().used_trait_imports) |
| .unwrap().insert(import_def_id); |
| } |
| |
| let def_kind = pick.item.def_kind(); |
| debug!("resolve_ufcs: def_kind={:?}, def_id={:?}", def_kind, pick.item.def_id); |
| tcx.check_stability(pick.item.def_id, Some(expr_id), span); |
| Ok((def_kind, pick.item.def_id)) |
| } |
| |
| /// Finds item with name `item_name` defined in impl/trait `def_id` |
| /// and return it, or `None`, if no such item was defined there. |
| pub fn associated_item(&self, def_id: DefId, item_name: ast::Ident, ns: Namespace) |
| -> Option<ty::AssocItem> { |
| self.tcx.associated_items(def_id).find(|item| { |
| Namespace::from(item.kind) == ns && |
| self.tcx.hygienic_eq(item_name, item.ident, def_id) |
| }) |
| } |
| } |