1 //! Method lookup: the secret sauce of Rust. See the [rustc dev guide] for more information.
3 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/method-lookup.html
10 pub use self::suggest::SelfSource;
11 pub use self::MethodError::*;
13 use crate::errors::OpMethodGenericParams;
14 use crate::{Expectation, FnCtxt};
15 use rustc_data_structures::sync::Lrc;
16 use rustc_errors::{Applicability, Diagnostic};
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, DefIdTree, GenericParamDefKind, Ty, TypeVisitable};
24 use rustc_span::symbol::Ident;
26 use rustc_trait_selection::traits;
27 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
29 use self::probe::{IsSuggestion, ProbeScope};
31 pub fn provide(providers: &mut ty::query::Providers) {
32 probe::provide(providers);
35 #[derive(Clone, Copy, Debug)]
36 pub struct MethodCallee<'tcx> {
37 /// Impl method ID, for inherent methods, or trait method ID, otherwise.
39 pub substs: SubstsRef<'tcx>,
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>,
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>),
52 // Multiple methods might apply.
53 Ambiguity(Vec<CandidateSource>),
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>),
59 // Found a `Self: Sized` bound where `Self` is a trait object.
60 IllegalSizedBound(Vec<DefId>, bool, Span),
62 // Found a match, but the return type is wrong
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.
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,
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 {
83 Trait(DefId /* trait id */),
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))]
93 call_expr_id: hir::HirId,
96 match self.probe_for_name(
97 probe::Mode::MethodCall,
102 ProbeScope::TraitsInScope,
105 pick.maybe_emit_unstable_name_collision_hint(
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"),
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(
124 err: &mut Diagnostic,
128 call_expr: &hir::Expr<'_>,
133 probe::Mode::MethodCall,
138 ProbeScope::TraitsInScope,
141 let sig = self.tcx.fn_sig(pick.item.def_id);
142 sig.inputs().skip_binder().len().saturating_sub(1)
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 },
153 err.span_suggestion_verbose(sugg_span, msg, suggestion, applicability);
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).
162 /// Given a method call like `foo.bar::<T1,...Tn>(a, b + 1, ...)`:
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(
175 segment: &hir::PathSegment<'_>,
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>> {
182 self.lookup_probe(segment.ident, self_ty, call_expr, ProbeScope::TraitsInScope)?;
184 self.lint_dot_call_from_2018(self_ty, segment, span, call_expr, self_expr, &pick, args);
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)
193 self.tcx.check_stability(pick.item.def_id, Some(call_expr.hir_id), span, None);
196 self.confirm_method(span, self_expr, call_expr, self_ty, pick.clone(), segment);
197 debug!("result = {:?}", result);
199 if let Some(span) = result.illegal_sized_bound {
200 let mut needs_mut = false;
201 if let ty::Ref(region, t_type, mutability) = self_ty.kind() {
202 let trait_type = self
204 .mk_ref(*region, ty::TypeAndMut { ty: *t_type, mutbl: mutability.invert() });
205 // We probe again to see if there might be a borrow mutability discrepancy.
206 match self.lookup_probe(
210 ProbeScope::TraitsInScope,
212 Ok(ref new_pick) if pick.differs_from(new_pick) => {
219 // We probe again, taking all traits into account (not only those in scope).
221 match self.lookup_probe(segment.ident, self_ty, call_expr, ProbeScope::AllTraits) {
222 // If we find a different result the caller probably forgot to import a trait.
223 Ok(ref new_pick) if pick.differs_from(new_pick) => {
224 vec![new_pick.item.container_id(self.tcx)]
226 Err(Ambiguity(ref sources)) => sources
228 .filter_map(|source| {
230 // Note: this cannot come from an inherent impl,
231 // because the first probing succeeded.
232 CandidateSource::Impl(def) => self.tcx.trait_id_of_impl(def),
233 CandidateSource::Trait(_) => None,
239 candidates.retain(|candidate| *candidate != self.tcx.parent(result.callee.def_id));
241 return Err(IllegalSizedBound(candidates, needs_mut, span));
247 #[instrument(level = "debug", skip(self, call_expr))]
252 call_expr: &'tcx hir::Expr<'tcx>,
254 ) -> probe::PickResult<'tcx> {
255 let pick = self.probe_for_name(
256 probe::Mode::MethodCall,
263 pick.maybe_emit_unstable_name_collision_hint(self.tcx, method_name.span, call_expr.hir_id);
267 pub(super) fn obligation_for_method(
272 opt_input_types: Option<&[Ty<'tcx>]>,
273 ) -> (traits::Obligation<'tcx, ty::Predicate<'tcx>>, &'tcx ty::List<ty::subst::GenericArg<'tcx>>)
275 // Construct a trait-reference `self_ty : Trait<input_tys>`
276 let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
278 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => {}
279 GenericParamDefKind::Type { .. } => {
280 if param.index == 0 {
281 return self_ty.into();
282 } else if let Some(input_types) = opt_input_types {
283 return input_types[param.index as usize - 1].into();
287 self.var_for_def(span, param)
290 let trait_ref = ty::TraitRef::new(trait_def_id, substs);
292 // Construct an obligation
293 let poly_trait_ref = ty::Binder::dummy(trait_ref);
295 traits::Obligation::misc(
300 poly_trait_ref.without_const(),
306 pub(super) fn obligation_for_op_method(
311 opt_input_type: Option<Ty<'tcx>>,
312 opt_input_expr: Option<&'tcx hir::Expr<'tcx>>,
313 expected: Expectation<'tcx>,
314 ) -> (traits::Obligation<'tcx, ty::Predicate<'tcx>>, &'tcx ty::List<ty::subst::GenericArg<'tcx>>)
316 // Construct a trait-reference `self_ty : Trait<input_tys>`
317 let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
319 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => {}
320 GenericParamDefKind::Type { .. } => {
321 if param.index == 0 {
322 return self_ty.into();
323 } else if let Some(input_type) = opt_input_type {
324 return input_type.into();
328 self.var_for_def(span, param)
331 let trait_ref = ty::TraitRef::new(trait_def_id, substs);
333 // Construct an obligation
334 let poly_trait_ref = ty::Binder::dummy(trait_ref);
335 let output_ty = expected.only_has_type(self).and_then(|ty| (!ty.needs_infer()).then(|| ty));
338 traits::Obligation::new(
340 traits::ObligationCause::new(
344 rhs_span: opt_input_expr.map(|expr| expr.span),
345 is_lit: opt_input_expr
346 .map_or(false, |expr| matches!(expr.kind, hir::ExprKind::Lit(_))),
351 poly_trait_ref.without_const(),
357 /// `lookup_method_in_trait` is used for overloaded operators.
358 /// It does a very narrow slice of what the normal probe/confirm path does.
359 /// In particular, it doesn't really do any probing: it simply constructs
360 /// an obligation for a particular trait with the given self type and checks
361 /// whether that trait is implemented.
362 #[instrument(level = "debug", skip(self, span))]
363 pub(super) fn lookup_method_in_trait(
369 opt_input_types: Option<&[Ty<'tcx>]>,
370 ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
371 let (obligation, substs) =
372 self.obligation_for_method(span, trait_def_id, self_ty, opt_input_types);
373 self.construct_obligation_for_trait(
384 pub(super) fn lookup_op_method_in_trait(
390 opt_input_type: Option<Ty<'tcx>>,
391 opt_input_expr: Option<&'tcx hir::Expr<'tcx>>,
392 expected: Expectation<'tcx>,
393 ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
394 let (obligation, substs) = self.obligation_for_op_method(
402 self.construct_obligation_for_trait(
413 // FIXME(#18741): it seems likely that we can consolidate some of this
414 // code with the other method-lookup code. In particular, the second half
415 // of this method is basically the same as confirmation.
416 fn construct_obligation_for_trait(
421 obligation: traits::PredicateObligation<'tcx>,
422 substs: &'tcx ty::List<ty::subst::GenericArg<'tcx>>,
423 opt_input_expr: Option<&'tcx hir::Expr<'tcx>>,
425 ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
428 // Now we want to know if this can be matched
429 if !self.predicate_may_hold(&obligation) {
430 debug!("--> Cannot match obligation");
431 // Cannot be matched, no such method resolution is possible.
435 // Trait must have a method named `m_name` and it should not have
436 // type parameters or early-bound regions.
438 let Some(method_item) = self.associated_value(trait_def_id, m_name) else {
439 tcx.sess.delay_span_bug(
441 "operator trait does not have corresponding operator method",
445 let def_id = method_item.def_id;
446 let generics = tcx.generics_of(def_id);
448 if generics.params.len() != 0 {
449 tcx.sess.emit_fatal(OpMethodGenericParams {
450 span: tcx.def_span(method_item.def_id),
451 method_name: m_name.to_string(),
455 debug!("lookup_in_trait_adjusted: method_item={:?}", method_item);
456 let mut obligations = vec![];
458 // Instantiate late-bound regions and substitute the trait
459 // parameters into the method type to get the actual method type.
461 // N.B., instantiate late-bound regions first so that
462 // `instantiate_type_scheme` can normalize associated types that
463 // may reference those regions.
464 let fn_sig = tcx.bound_fn_sig(def_id);
465 let fn_sig = fn_sig.subst(self.tcx, substs);
466 let fn_sig = self.replace_bound_vars_with_fresh_vars(span, infer::FnCall, fn_sig);
468 let InferOk { value, obligations: o } = if is_op {
469 self.normalize_op_associated_types_in_as_infer_ok(span, fn_sig, opt_input_expr)
471 self.normalize_associated_types_in_as_infer_ok(span, fn_sig)
474 obligations.extend(o);
478 // Register obligations for the parameters. This will include the
479 // `Self` parameter, which in turn has a bound of the main trait,
480 // so this also effectively registers `obligation` as well. (We
481 // used to register `obligation` explicitly, but that resulted in
482 // double error messages being reported.)
484 // Note that as the method comes from a trait, it should not have
485 // any late-bound regions appearing in its bounds.
486 let bounds = self.tcx.predicates_of(def_id).instantiate(self.tcx, substs);
488 let InferOk { value, obligations: o } = if is_op {
489 self.normalize_op_associated_types_in_as_infer_ok(span, bounds, opt_input_expr)
491 self.normalize_associated_types_in_as_infer_ok(span, bounds)
494 obligations.extend(o);
498 assert!(!bounds.has_escaping_bound_vars());
500 let cause = if is_op {
501 ObligationCause::new(
505 rhs_span: opt_input_expr.map(|expr| expr.span),
506 is_lit: opt_input_expr
507 .map_or(false, |expr| matches!(expr.kind, hir::ExprKind::Lit(_))),
512 traits::ObligationCause::misc(span, self.body_id)
514 let predicates_cause = cause.clone();
515 obligations.extend(traits::predicates_for_generics(
516 move |_, _| predicates_cause.clone(),
521 // Also add an obligation for the method type being well-formed.
522 let method_ty = tcx.mk_fn_ptr(ty::Binder::dummy(fn_sig));
524 "lookup_in_trait_adjusted: matched method method_ty={:?} obligation={:?}",
525 method_ty, obligation
527 obligations.push(traits::Obligation::new(
531 ty::Binder::dummy(ty::PredicateKind::WellFormed(method_ty.into())),
534 let callee = MethodCallee { def_id, substs, sig: fn_sig };
536 debug!("callee = {:?}", callee);
538 Some(InferOk { obligations, value: callee })
541 /// Performs a [full-qualified function call] (formerly "universal function call") lookup. If
542 /// lookup is successful, it will return the type of definition and the [`DefId`] of the found
543 /// function definition.
545 /// [full-qualified function call]: https://doc.rust-lang.org/reference/expressions/call-expr.html#disambiguating-function-calls
549 /// Given a function call like `Foo::bar::<T1,...Tn>(...)`:
551 /// * `self`: the surrounding `FnCtxt` (!)
552 /// * `span`: the span of the call, excluding arguments (`Foo::bar::<T1, ...Tn>`)
553 /// * `method_name`: the identifier of the function within the container type (`bar`)
554 /// * `self_ty`: the type to search within (`Foo`)
555 /// * `self_ty_span` the span for the type being searched within (span of `Foo`)
556 /// * `expr_id`: the [`hir::HirId`] of the expression composing the entire call
557 #[instrument(level = "debug", skip(self), ret)]
558 pub fn resolve_fully_qualified_call(
565 ) -> Result<(DefKind, DefId), MethodError<'tcx>> {
568 // Check if we have an enum variant.
569 let mut struct_variant = None;
570 if let ty::Adt(adt_def, _) = self_ty.kind() {
571 if adt_def.is_enum() {
572 let variant_def = adt_def
575 .find(|vd| tcx.hygienic_eq(method_name, vd.ident(tcx), adt_def.did()));
576 if let Some(variant_def) = variant_def {
577 if let Some((ctor_kind, ctor_def_id)) = variant_def.ctor {
582 Some(method_name.span),
584 return Ok((DefKind::Ctor(CtorOf::Variant, ctor_kind), ctor_def_id));
586 struct_variant = Some((DefKind::Variant, variant_def.def_id));
592 let pick = self.probe_for_name(
598 ProbeScope::TraitsInScope,
600 let pick = match (pick, struct_variant) {
601 // Fall back to a resolution that will produce an error later.
602 (Err(_), Some(res)) => return Ok(res),
606 pick.maybe_emit_unstable_name_collision_hint(self.tcx, span, expr_id);
608 self.lint_fully_qualified_call_from_2018(
619 let mut typeck_results = self.typeck_results.borrow_mut();
620 let used_trait_imports = Lrc::get_mut(&mut typeck_results.used_trait_imports).unwrap();
621 for import_id in pick.import_ids {
622 debug!(used_trait_import=?import_id);
623 used_trait_imports.insert(import_id);
627 let def_kind = pick.item.kind.as_def_kind();
628 tcx.check_stability(pick.item.def_id, Some(expr_id), span, Some(method_name.span));
629 Ok((def_kind, pick.item.def_id))
632 /// Finds item with name `item_name` defined in impl/trait `def_id`
633 /// and return it, or `None`, if no such item was defined there.
634 pub fn associated_value(&self, def_id: DefId, item_name: Ident) -> Option<ty::AssocItem> {
636 .associated_items(def_id)
637 .find_by_name_and_namespace(self.tcx, item_name, Namespace::ValueNS, def_id)