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
9 pub use self::suggest::{SelfSource, TraitInfo};
10 pub use self::CandidateSource::*;
11 pub use self::MethodError::*;
13 use crate::check::FnCtxt;
14 use rustc_data_structures::sync::Lrc;
15 use rustc_errors::{Applicability, DiagnosticBuilder};
17 use rustc_hir::def::{CtorOf, DefKind, Namespace};
18 use rustc_hir::def_id::DefId;
19 use rustc_infer::infer::{self, InferOk};
20 use rustc_middle::ty::subst::Subst;
21 use rustc_middle::ty::subst::{InternalSubsts, SubstsRef};
22 use rustc_middle::ty::GenericParamDefKind;
23 use rustc_middle::ty::{self, ToPolyTraitRef, ToPredicate, Ty, TypeFoldable, WithConstness};
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 suggest::provide(providers);
33 probe::provide(providers);
36 #[derive(Clone, Copy, Debug)]
37 pub struct MethodCallee<'tcx> {
38 /// Impl method ID, for inherent methods, or trait method ID, otherwise.
40 pub substs: SubstsRef<'tcx>,
42 /// Instantiated method signature, i.e., it has been
43 /// substituted, normalized, and has had late-bound
44 /// lifetimes replaced with inference variables.
45 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, also the caller may have
60 // forgotten to import a trait.
61 IllegalSizedBound(Vec<DefId>, bool, Span),
63 // Found a match, but the return type is wrong
67 // Contains a list of static methods that may apply, a list of unsatisfied trait predicates which
68 // 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: Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>)>,
72 pub out_of_scope_traits: Vec<DefId>,
73 pub lev_candidate: Option<ty::AssocItem>,
74 pub mode: probe::Mode,
77 impl<'tcx> NoMatchData<'tcx> {
79 static_candidates: Vec<CandidateSource>,
80 unsatisfied_predicates: Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>)>,
81 out_of_scope_traits: Vec<DefId>,
82 lev_candidate: Option<ty::AssocItem>,
87 unsatisfied_predicates,
95 // A pared down enum describing just the places from which a method
96 // candidate can arise. Used for error reporting only.
97 #[derive(Copy, Clone, Debug, Eq, Ord, PartialEq, PartialOrd)]
98 pub enum CandidateSource {
100 TraitSource(DefId /* trait id */),
103 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
104 /// Determines whether the type `self_ty` supports a method name `method_name` or not.
105 pub fn method_exists(
109 call_expr_id: hir::HirId,
112 let mode = probe::Mode::MethodCall;
113 match self.probe_for_name(
120 ProbeScope::TraitsInScope,
123 Err(NoMatch(..)) => false,
124 Err(Ambiguity(..)) => true,
125 Err(PrivateMatch(..)) => allow_private,
126 Err(IllegalSizedBound(..)) => true,
127 Err(BadReturnType) => bug!("no return type expectations but got BadReturnType"),
131 /// Adds a suggestion to call the given method to the provided diagnostic.
132 crate fn suggest_method_call(
134 err: &mut DiagnosticBuilder<'a>,
138 call_expr: &hir::Expr<'_>,
143 probe::Mode::MethodCall,
148 ProbeScope::TraitsInScope,
151 let sig = self.tcx.fn_sig(pick.item.def_id);
152 sig.inputs().skip_binder().len().saturating_sub(1)
156 // Account for `foo.bar<T>`;
157 let sugg_span = call_expr.span.shrink_to_hi();
158 let (suggestion, applicability) = (
159 format!("({})", (0..params).map(|_| "_").collect::<Vec<_>>().join(", ")),
160 if params > 0 { Applicability::HasPlaceholders } else { Applicability::MaybeIncorrect },
163 err.span_suggestion_verbose(sugg_span, msg, suggestion, applicability);
166 /// Performs method lookup. If lookup is successful, it will return the callee
167 /// and store an appropriate adjustment for the self-expr. In some cases it may
168 /// report an error (e.g., invoking the `drop` method).
172 /// Given a method call like `foo.bar::<T1,...Tn>(...)`:
174 /// * `self`: the surrounding `FnCtxt` (!)
175 /// * `self_ty`: the (unadjusted) type of the self expression (`foo`)
176 /// * `segment`: the name and generic arguments of the method (`bar::<T1, ...Tn>`)
177 /// * `span`: the span for the method call
178 /// * `call_expr`: the complete method call: (`foo.bar::<T1,...Tn>(...)`)
179 /// * `self_expr`: the self expression (`foo`)
180 pub fn lookup_method(
183 segment: &hir::PathSegment<'_>,
185 call_expr: &'tcx hir::Expr<'tcx>,
186 self_expr: &'tcx hir::Expr<'tcx>,
187 ) -> Result<MethodCallee<'tcx>, MethodError<'tcx>> {
189 "lookup(method_name={}, self_ty={:?}, call_expr={:?}, self_expr={:?})",
190 segment.ident, self_ty, call_expr, self_expr
194 self.lookup_probe(span, segment.ident, self_ty, call_expr, ProbeScope::TraitsInScope)?;
196 for import_id in &pick.import_ids {
197 debug!("used_trait_import: {:?}", import_id);
198 Lrc::get_mut(&mut self.tables.borrow_mut().used_trait_imports)
203 self.tcx.check_stability(pick.item.def_id, Some(call_expr.hir_id), span);
206 self.confirm_method(span, self_expr, call_expr, self_ty, pick.clone(), segment);
208 if let Some(span) = result.illegal_sized_bound {
209 let mut needs_mut = false;
210 if let ty::Ref(region, t_type, mutability) = self_ty.kind {
211 let trait_type = self
213 .mk_ref(region, ty::TypeAndMut { ty: t_type, mutbl: mutability.invert() });
214 // We probe again to see if there might be a borrow mutability discrepancy.
215 match self.lookup_probe(
220 ProbeScope::TraitsInScope,
222 Ok(ref new_pick) if *new_pick != pick => {
229 // We probe again, taking all traits into account (not only those in scope).
230 let candidates = match self.lookup_probe(
235 ProbeScope::AllTraits,
237 // If we find a different result the caller probably forgot to import a trait.
238 Ok(ref new_pick) if *new_pick != pick => vec![new_pick.item.container.id()],
239 Err(Ambiguity(ref sources)) => sources
241 .filter_map(|source| {
243 // Note: this cannot come from an inherent impl,
244 // because the first probing succeeded.
245 ImplSource(def) => self.tcx.trait_id_of_impl(def),
246 TraitSource(_) => None,
253 return Err(IllegalSizedBound(candidates, needs_mut, span));
264 call_expr: &'tcx hir::Expr<'tcx>,
266 ) -> probe::PickResult<'tcx> {
267 let mode = probe::Mode::MethodCall;
268 let self_ty = self.resolve_vars_if_possible(&self_ty);
280 /// `lookup_method_in_trait` is used for overloaded operators.
281 /// It does a very narrow slice of what the normal probe/confirm path does.
282 /// In particular, it doesn't really do any probing: it simply constructs
283 /// an obligation for a particular trait with the given self type and checks
284 /// whether that trait is implemented.
286 // FIXME(#18741): it seems likely that we can consolidate some of this
287 // code with the other method-lookup code. In particular, the second half
288 // of this method is basically the same as confirmation.
289 pub fn lookup_method_in_trait(
295 opt_input_types: Option<&[Ty<'tcx>]>,
296 ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
298 "lookup_in_trait_adjusted(self_ty={:?}, m_name={}, trait_def_id={:?})",
299 self_ty, m_name, trait_def_id
302 // Construct a trait-reference `self_ty : Trait<input_tys>`
303 let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
305 GenericParamDefKind::Lifetime | GenericParamDefKind::Const => {}
306 GenericParamDefKind::Type { .. } => {
307 if param.index == 0 {
308 return self_ty.into();
309 } else if let Some(ref input_types) = opt_input_types {
310 return input_types[param.index as usize - 1].into();
314 self.var_for_def(span, param)
317 let trait_ref = ty::TraitRef::new(trait_def_id, substs);
319 // Construct an obligation
320 let poly_trait_ref = trait_ref.to_poly_trait_ref();
321 let obligation = traits::Obligation::misc(
325 poly_trait_ref.without_const().to_predicate(self.tcx),
328 // Now we want to know if this can be matched
329 if !self.predicate_may_hold(&obligation) {
330 debug!("--> Cannot match obligation");
331 return None; // Cannot be matched, no such method resolution is possible.
334 // Trait must have a method named `m_name` and it should not have
335 // type parameters or early-bound regions.
337 let method_item = match self.associated_item(trait_def_id, m_name, Namespace::ValueNS) {
338 Some(method_item) => method_item,
340 tcx.sess.delay_span_bug(
342 "operator trait does not have corresponding operator method",
347 let def_id = method_item.def_id;
348 let generics = tcx.generics_of(def_id);
349 assert_eq!(generics.params.len(), 0);
351 debug!("lookup_in_trait_adjusted: method_item={:?}", method_item);
352 let mut obligations = vec![];
354 // Instantiate late-bound regions and substitute the trait
355 // parameters into the method type to get the actual method type.
357 // N.B., instantiate late-bound regions first so that
358 // `instantiate_type_scheme` can normalize associated types that
359 // may reference those regions.
360 let fn_sig = tcx.fn_sig(def_id);
361 let fn_sig = self.replace_bound_vars_with_fresh_vars(span, infer::FnCall, &fn_sig).0;
362 let fn_sig = fn_sig.subst(self.tcx, substs);
364 let InferOk { value, obligations: o } =
365 self.normalize_associated_types_in_as_infer_ok(span, &fn_sig);
367 obligations.extend(o);
371 // Register obligations for the parameters. This will include the
372 // `Self` parameter, which in turn has a bound of the main trait,
373 // so this also effectively registers `obligation` as well. (We
374 // used to register `obligation` explicitly, but that resulted in
375 // double error messages being reported.)
377 // Note that as the method comes from a trait, it should not have
378 // any late-bound regions appearing in its bounds.
379 let bounds = self.tcx.predicates_of(def_id).instantiate(self.tcx, substs);
381 let InferOk { value, obligations: o } =
382 self.normalize_associated_types_in_as_infer_ok(span, &bounds);
384 obligations.extend(o);
388 assert!(!bounds.has_escaping_bound_vars());
390 let cause = traits::ObligationCause::misc(span, self.body_id);
391 obligations.extend(traits::predicates_for_generics(cause.clone(), self.param_env, bounds));
393 // Also add an obligation for the method type being well-formed.
394 let method_ty = tcx.mk_fn_ptr(ty::Binder::bind(fn_sig));
396 "lookup_in_trait_adjusted: matched method method_ty={:?} obligation={:?}",
397 method_ty, obligation
399 obligations.push(traits::Obligation::new(
402 ty::PredicateKind::WellFormed(method_ty.into()).to_predicate(tcx),
405 let callee = MethodCallee { def_id, substs: trait_ref.substs, sig: fn_sig };
407 debug!("callee = {:?}", callee);
409 Some(InferOk { obligations, value: callee })
418 ) -> Result<(DefKind, DefId), MethodError<'tcx>> {
420 "resolve_ufcs: method_name={:?} self_ty={:?} expr_id={:?}",
421 method_name, self_ty, expr_id,
426 // Check if we have an enum variant.
427 if let ty::Adt(adt_def, _) = self_ty.kind {
428 if adt_def.is_enum() {
429 let variant_def = adt_def
432 .find(|vd| tcx.hygienic_eq(method_name, vd.ident, adt_def.did));
433 if let Some(variant_def) = variant_def {
434 // Braced variants generate unusable names in value namespace (reserved for
435 // possible future use), so variants resolved as associated items may refer to
436 // them as well. It's ok to use the variant's id as a ctor id since an
437 // error will be reported on any use of such resolution anyway.
438 let ctor_def_id = variant_def.ctor_def_id.unwrap_or(variant_def.def_id);
439 tcx.check_stability(ctor_def_id, Some(expr_id), span);
441 DefKind::Ctor(CtorOf::Variant, variant_def.ctor_kind),
448 let pick = self.probe_for_name(
455 ProbeScope::TraitsInScope,
457 debug!("resolve_ufcs: pick={:?}", pick);
459 let mut tables = self.tables.borrow_mut();
460 let used_trait_imports = Lrc::get_mut(&mut tables.used_trait_imports).unwrap();
461 for import_id in pick.import_ids {
462 debug!("resolve_ufcs: used_trait_import: {:?}", import_id);
463 used_trait_imports.insert(import_id);
467 let def_kind = pick.item.kind.as_def_kind();
468 debug!("resolve_ufcs: def_kind={:?}, def_id={:?}", def_kind, pick.item.def_id);
469 tcx.check_stability(pick.item.def_id, Some(expr_id), span);
470 Ok((def_kind, pick.item.def_id))
473 /// Finds item with name `item_name` defined in impl/trait `def_id`
474 /// and return it, or `None`, if no such item was defined there.
475 pub fn associated_item(
480 ) -> Option<ty::AssocItem> {
482 .associated_items(def_id)
483 .find_by_name_and_namespace(self.tcx, item_name, ns, def_id)