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Diffstat (limited to 'compiler/rustc_typeck/src/check/method/mod.rs')
| -rw-r--r-- | compiler/rustc_typeck/src/check/method/mod.rs | 658 |
1 files changed, 658 insertions, 0 deletions
diff --git a/compiler/rustc_typeck/src/check/method/mod.rs b/compiler/rustc_typeck/src/check/method/mod.rs new file mode 100644 index 000000000..0e678c41f --- /dev/null +++ b/compiler/rustc_typeck/src/check/method/mod.rs @@ -0,0 +1,658 @@ +//! Method lookup: the secret sauce of Rust. See the [rustc dev guide] for more information. +//! +//! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/method-lookup.html + +mod confirm; +mod prelude2021; +pub mod probe; +mod suggest; + +pub use self::suggest::SelfSource; +pub use self::MethodError::*; + +use crate::check::{Expectation, FnCtxt}; +use crate::ObligationCause; +use rustc_data_structures::sync::Lrc; +use rustc_errors::{Applicability, Diagnostic}; +use rustc_hir as hir; +use rustc_hir::def::{CtorOf, DefKind, Namespace}; +use rustc_hir::def_id::DefId; +use rustc_infer::infer::{self, InferOk}; +use rustc_middle::ty::subst::Subst; +use rustc_middle::ty::subst::{InternalSubsts, SubstsRef}; +use rustc_middle::ty::{ + self, AssocKind, DefIdTree, GenericParamDefKind, ProjectionPredicate, ProjectionTy, Term, + ToPredicate, Ty, TypeVisitable, +}; +use rustc_span::symbol::Ident; +use rustc_span::Span; +use rustc_trait_selection::traits; +use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt; + +use self::probe::{IsSuggestion, ProbeScope}; + +pub fn provide(providers: &mut ty::query::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>, +} + +#[derive(Debug)] +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>, bool, Span), + + // 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. +#[derive(Debug)] +pub struct NoMatchData<'tcx> { + pub static_candidates: Vec<CandidateSource>, + pub unsatisfied_predicates: + Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>, Option<ObligationCause<'tcx>>)>, + pub out_of_scope_traits: Vec<DefId>, + pub lev_candidate: Option<ty::AssocItem>, + pub mode: probe::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 { + Impl(DefId), + Trait(DefId /* trait id */), +} + +impl<'a, 'tcx> FnCtxt<'a, 'tcx> { + /// Determines whether the type `self_ty` supports a method name `method_name` or not. + #[instrument(level = "debug", skip(self))] + pub fn method_exists( + &self, + method_name: 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. + #[instrument(level = "debug", skip(self, err, call_expr))] + pub(crate) fn suggest_method_call( + &self, + err: &mut Diagnostic, + msg: &str, + method_name: Ident, + self_ty: Ty<'tcx>, + call_expr: &hir::Expr<'_>, + span: Option<Span>, + ) { + let params = self + .probe_for_name( + method_name.span, + probe::Mode::MethodCall, + method_name, + IsSuggestion(false), + self_ty, + call_expr.hir_id, + ProbeScope::TraitsInScope, + ) + .map(|pick| { + let sig = self.tcx.fn_sig(pick.item.def_id); + sig.inputs().skip_binder().len().saturating_sub(1) + }) + .unwrap_or(0); + + // Account for `foo.bar<T>`; + let sugg_span = span.unwrap_or(call_expr.span).shrink_to_hi(); + let (suggestion, applicability) = ( + format!("({})", (0..params).map(|_| "_").collect::<Vec<_>>().join(", ")), + if params > 0 { Applicability::HasPlaceholders } else { Applicability::MaybeIncorrect }, + ); + + err.span_suggestion_verbose(sugg_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>(a, b + 1, ...)`: + /// + /// * `self`: the surrounding `FnCtxt` (!) + /// * `self_ty`: the (unadjusted) type of the self expression (`foo`) + /// * `segment`: the name and generic arguments of the method (`bar::<T1, ...Tn>`) + /// * `span`: the span for the method call + /// * `call_expr`: the complete method call: (`foo.bar::<T1,...Tn>(...)`) + /// * `self_expr`: the self expression (`foo`) + /// * `args`: the expressions of the arguments (`a, b + 1, ...`) + #[instrument(level = "debug", skip(self, call_expr, self_expr))] + pub fn lookup_method( + &self, + self_ty: Ty<'tcx>, + segment: &hir::PathSegment<'_>, + span: Span, + call_expr: &'tcx hir::Expr<'tcx>, + self_expr: &'tcx hir::Expr<'tcx>, + args: &'tcx [hir::Expr<'tcx>], + ) -> 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)?; + + self.lint_dot_call_from_2018(self_ty, segment, span, call_expr, self_expr, &pick, args); + + for import_id in &pick.import_ids { + debug!("used_trait_import: {:?}", import_id); + Lrc::get_mut(&mut self.typeck_results.borrow_mut().used_trait_imports) + .unwrap() + .insert(*import_id); + } + + self.tcx.check_stability(pick.item.def_id, Some(call_expr.hir_id), span, None); + + let result = + self.confirm_method(span, self_expr, call_expr, self_ty, pick.clone(), segment); + debug!("result = {:?}", result); + + if let Some(span) = result.illegal_sized_bound { + let mut needs_mut = false; + if let ty::Ref(region, t_type, mutability) = self_ty.kind() { + let trait_type = self + .tcx + .mk_ref(*region, ty::TypeAndMut { ty: *t_type, mutbl: mutability.invert() }); + // We probe again to see if there might be a borrow mutability discrepancy. + match self.lookup_probe( + span, + segment.ident, + trait_type, + call_expr, + ProbeScope::TraitsInScope, + ) { + Ok(ref new_pick) if *new_pick != pick => { + needs_mut = true; + } + _ => {} + } + } + + // We probe again, taking all traits into account (not only those in scope). + let mut 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(self.tcx)], + Err(Ambiguity(ref sources)) => sources + .iter() + .filter_map(|source| { + match *source { + // Note: this cannot come from an inherent impl, + // because the first probing succeeded. + CandidateSource::Impl(def) => self.tcx.trait_id_of_impl(def), + CandidateSource::Trait(_) => None, + } + }) + .collect(), + _ => Vec::new(), + }; + candidates.retain(|candidate| *candidate != self.tcx.parent(result.callee.def_id)); + + return Err(IllegalSizedBound(candidates, needs_mut, span)); + } + + Ok(result.callee) + } + + #[instrument(level = "debug", skip(self, call_expr))] + pub fn lookup_probe( + &self, + span: Span, + method_name: Ident, + self_ty: Ty<'tcx>, + call_expr: &'tcx hir::Expr<'tcx>, + 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, + ) + } + + pub(super) fn obligation_for_method( + &self, + span: Span, + trait_def_id: DefId, + self_ty: Ty<'tcx>, + opt_input_types: Option<&[Ty<'tcx>]>, + ) -> (traits::Obligation<'tcx, ty::Predicate<'tcx>>, &'tcx ty::List<ty::subst::GenericArg<'tcx>>) + { + // 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(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 = ty::Binder::dummy(trait_ref); + ( + traits::Obligation::misc( + span, + self.body_id, + self.param_env, + poly_trait_ref.without_const().to_predicate(self.tcx), + ), + substs, + ) + } + + pub(super) fn obligation_for_op_method( + &self, + span: Span, + trait_def_id: DefId, + self_ty: Ty<'tcx>, + opt_input_type: Option<Ty<'tcx>>, + opt_input_expr: Option<&'tcx hir::Expr<'tcx>>, + expected: Expectation<'tcx>, + ) -> (traits::Obligation<'tcx, ty::Predicate<'tcx>>, &'tcx ty::List<ty::subst::GenericArg<'tcx>>) + { + // 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(input_type) = opt_input_type { + return input_type.into(); + } + } + } + self.var_for_def(span, param) + }); + + let trait_ref = ty::TraitRef::new(trait_def_id, substs); + + // Construct an obligation + let poly_trait_ref = ty::Binder::dummy(trait_ref); + let opt_output_ty = + expected.only_has_type(self).and_then(|ty| (!ty.needs_infer()).then(|| ty)); + let opt_output_assoc_item = self.tcx.associated_items(trait_def_id).find_by_name_and_kind( + self.tcx, + Ident::from_str("Output"), + AssocKind::Type, + trait_def_id, + ); + let output_pred = + opt_output_ty.zip(opt_output_assoc_item).map(|(output_ty, output_assoc_item)| { + ty::Binder::dummy(ty::PredicateKind::Projection(ProjectionPredicate { + projection_ty: ProjectionTy { substs, item_def_id: output_assoc_item.def_id }, + term: Term::Ty(output_ty), + })) + .to_predicate(self.tcx) + }); + + ( + traits::Obligation::new( + traits::ObligationCause::new( + span, + self.body_id, + traits::BinOp { + rhs_span: opt_input_expr.map(|expr| expr.span), + is_lit: opt_input_expr + .map_or(false, |expr| matches!(expr.kind, hir::ExprKind::Lit(_))), + output_pred, + }, + ), + self.param_env, + poly_trait_ref.without_const().to_predicate(self.tcx), + ), + substs, + ) + } + + /// `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. + #[instrument(level = "debug", skip(self, span, opt_input_types))] + pub(super) fn lookup_method_in_trait( + &self, + span: Span, + m_name: 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={:?}, opt_input_types={:?})", + self_ty, m_name, trait_def_id, opt_input_types + ); + + let (obligation, substs) = + self.obligation_for_method(span, trait_def_id, self_ty, opt_input_types); + self.construct_obligation_for_trait( + span, + m_name, + trait_def_id, + obligation, + substs, + None, + false, + ) + } + + pub(super) fn lookup_op_method_in_trait( + &self, + span: Span, + m_name: Ident, + trait_def_id: DefId, + self_ty: Ty<'tcx>, + opt_input_type: Option<Ty<'tcx>>, + opt_input_expr: Option<&'tcx hir::Expr<'tcx>>, + expected: Expectation<'tcx>, + ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> { + let (obligation, substs) = self.obligation_for_op_method( + span, + trait_def_id, + self_ty, + opt_input_type, + opt_input_expr, + expected, + ); + self.construct_obligation_for_trait( + span, + m_name, + trait_def_id, + obligation, + substs, + opt_input_expr, + true, + ) + } + + // 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. + fn construct_obligation_for_trait( + &self, + span: Span, + m_name: Ident, + trait_def_id: DefId, + obligation: traits::PredicateObligation<'tcx>, + substs: &'tcx ty::List<ty::subst::GenericArg<'tcx>>, + opt_input_expr: Option<&'tcx hir::Expr<'tcx>>, + is_op: bool, + ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> { + debug!(?obligation); + + // Now we want to know if this can be matched + if !self.predicate_may_hold(&obligation) { + debug!("--> Cannot match obligation"); + // Cannot be matched, no such method resolution is possible. + return None; + } + + // Trait must have a method named `m_name` and it should not have + // type parameters or early-bound regions. + let tcx = self.tcx; + let Some(method_item) = self.associated_value(trait_def_id, m_name) else { + 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.bound_fn_sig(def_id); + let fn_sig = fn_sig.subst(self.tcx, substs); + let fn_sig = self.replace_bound_vars_with_fresh_vars(span, infer::FnCall, fn_sig); + + let InferOk { value, obligations: o } = if is_op { + self.normalize_op_associated_types_in_as_infer_ok(span, fn_sig, opt_input_expr) + } else { + self.normalize_associated_types_in_as_infer_ok(span, fn_sig) + }; + let fn_sig = { + 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 InferOk { value, obligations: o } = if is_op { + self.normalize_op_associated_types_in_as_infer_ok(span, bounds, opt_input_expr) + } else { + self.normalize_associated_types_in_as_infer_ok(span, bounds) + }; + let bounds = { + obligations.extend(o); + value + }; + + assert!(!bounds.has_escaping_bound_vars()); + + let cause = if is_op { + ObligationCause::new( + span, + self.body_id, + traits::BinOp { + rhs_span: opt_input_expr.map(|expr| expr.span), + is_lit: opt_input_expr + .map_or(false, |expr| matches!(expr.kind, hir::ExprKind::Lit(_))), + output_pred: None, + }, + ) + } else { + 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::dummy(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::Binder::dummy(ty::PredicateKind::WellFormed(method_ty.into())).to_predicate(tcx), + )); + + let callee = MethodCallee { def_id, substs, sig: fn_sig }; + + debug!("callee = {:?}", callee); + + Some(InferOk { obligations, value: callee }) + } + + /// Performs a [full-qualified function call] (formerly "universal function call") lookup. If + /// lookup is successful, it will return the type of definition and the [`DefId`] of the found + /// function definition. + /// + /// [full-qualified function call]: https://doc.rust-lang.org/reference/expressions/call-expr.html#disambiguating-function-calls + /// + /// # Arguments + /// + /// Given a function call like `Foo::bar::<T1,...Tn>(...)`: + /// + /// * `self`: the surrounding `FnCtxt` (!) + /// * `span`: the span of the call, excluding arguments (`Foo::bar::<T1, ...Tn>`) + /// * `method_name`: the identifier of the function within the container type (`bar`) + /// * `self_ty`: the type to search within (`Foo`) + /// * `self_ty_span` the span for the type being searched within (span of `Foo`) + /// * `expr_id`: the [`hir::HirId`] of the expression composing the entire call + #[instrument(level = "debug", skip(self))] + pub fn resolve_fully_qualified_call( + &self, + span: Span, + method_name: Ident, + self_ty: Ty<'tcx>, + self_ty_span: Span, + expr_id: hir::HirId, + ) -> Result<(DefKind, DefId), MethodError<'tcx>> { + debug!( + "resolve_fully_qualified_call: 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.kind() { + if adt_def.is_enum() { + let variant_def = adt_def + .variants() + .iter() + .find(|vd| tcx.hygienic_eq(method_name, vd.ident(tcx), 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, Some(method_name.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, + )?; + + self.lint_fully_qualified_call_from_2018( + span, + method_name, + self_ty, + self_ty_span, + expr_id, + &pick, + ); + + debug!("resolve_fully_qualified_call: pick={:?}", pick); + { + let mut typeck_results = self.typeck_results.borrow_mut(); + let used_trait_imports = Lrc::get_mut(&mut typeck_results.used_trait_imports).unwrap(); + for import_id in pick.import_ids { + debug!("resolve_fully_qualified_call: used_trait_import: {:?}", import_id); + used_trait_imports.insert(import_id); + } + } + + let def_kind = pick.item.kind.as_def_kind(); + debug!( + "resolve_fully_qualified_call: def_kind={:?}, def_id={:?}", + def_kind, pick.item.def_id + ); + tcx.check_stability(pick.item.def_id, Some(expr_id), span, Some(method_name.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_value(&self, def_id: DefId, item_name: Ident) -> Option<ty::AssocItem> { + self.tcx + .associated_items(def_id) + .find_by_name_and_namespace(self.tcx, item_name, Namespace::ValueNS, def_id) + .copied() + } +} |