1 //! Method lookup: the secret sauce of Rust. See the [rustc guide] for more information.
3 //! [rustc guide]: https://rust-lang.github.io/rustc-guide/method-lookup.html
9 pub use self::MethodError::*;
10 pub use self::CandidateSource::*;
11 pub use self::suggest::{SelfSource, TraitInfo};
13 use crate::check::FnCtxt;
14 use crate::namespace::Namespace;
15 use errors::{Applicability, DiagnosticBuilder};
16 use rustc_data_structures::sync::Lrc;
18 use rustc::hir::def::{CtorOf, DefKind};
19 use rustc::hir::def_id::DefId;
21 use rustc::ty::subst::{InternalSubsts, SubstsRef};
22 use rustc::ty::{self, Ty, ToPredicate, ToPolyTraitRef, TraitRef, TypeFoldable};
23 use rustc::ty::GenericParamDefKind;
24 use rustc::ty::subst::Subst;
25 use rustc::infer::{self, InferOk};
29 use crate::{check_type_alias_enum_variants_enabled};
30 use self::probe::{IsSuggestion, ProbeScope};
32 pub fn provide(providers: &mut ty::query::Providers<'_>) {
33 suggest::provide(providers);
34 probe::provide(providers);
37 #[derive(Clone, Copy, Debug)]
38 pub struct MethodCallee<'tcx> {
39 /// Impl method ID, for inherent methods, or trait method ID, otherwise.
41 pub substs: SubstsRef<'tcx>,
43 /// Instantiated method signature, i.e., it has been
44 /// substituted, normalized, and has had late-bound
45 /// lifetimes replaced with inference variables.
46 pub sig: ty::FnSig<'tcx>,
49 pub enum MethodError<'tcx> {
50 // Did not find an applicable method, but we did find various near-misses that may work.
51 NoMatch(NoMatchData<'tcx>),
53 // Multiple methods might apply.
54 Ambiguity(Vec<CandidateSource>),
56 // Found an applicable method, but it is not visible. The third argument contains a list of
57 // not-in-scope traits which may work.
58 PrivateMatch(DefKind, DefId, Vec<DefId>),
60 // Found a `Self: Sized` bound where `Self` is a trait object, also the caller may have
61 // forgotten to import a trait.
62 IllegalSizedBound(Vec<DefId>),
64 // Found a match, but the return type is wrong
68 // Contains a list of static methods that may apply, a list of unsatisfied trait predicates which
69 // could lead to matches if satisfied, and a list of not-in-scope traits which may work.
70 pub struct NoMatchData<'tcx> {
71 pub static_candidates: Vec<CandidateSource>,
72 pub unsatisfied_predicates: Vec<TraitRef<'tcx>>,
73 pub out_of_scope_traits: Vec<DefId>,
74 pub lev_candidate: Option<ty::AssociatedItem>,
75 pub mode: probe::Mode,
78 impl<'tcx> NoMatchData<'tcx> {
79 pub fn new(static_candidates: Vec<CandidateSource>,
80 unsatisfied_predicates: Vec<TraitRef<'tcx>>,
81 out_of_scope_traits: Vec<DefId>,
82 lev_candidate: Option<ty::AssociatedItem>,
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, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
104 /// Determines whether the type `self_ty` supports a method name `method_name` or not.
105 pub fn method_exists(&self,
106 method_name: ast::Ident,
108 call_expr_id: hir::HirId,
111 let mode = probe::Mode::MethodCall;
112 match self.probe_for_name(method_name.span, mode, method_name,
113 IsSuggestion(false), self_ty, call_expr_id,
114 ProbeScope::TraitsInScope) {
116 Err(NoMatch(..)) => false,
117 Err(Ambiguity(..)) => true,
118 Err(PrivateMatch(..)) => allow_private,
119 Err(IllegalSizedBound(..)) => true,
120 Err(BadReturnType) => {
121 bug!("no return type expectations but got BadReturnType")
127 /// Adds a suggestion to call the given method to the provided diagnostic.
128 crate fn suggest_method_call(
130 err: &mut DiagnosticBuilder<'a>,
132 method_name: ast::Ident,
134 call_expr_id: hir::HirId,
136 let has_params = self
139 probe::Mode::MethodCall,
144 ProbeScope::TraitsInScope,
147 let sig = self.tcx.fn_sig(pick.item.def_id);
148 Ok(sig.inputs().skip_binder().len() > 1)
151 let (suggestion, applicability) = if has_params.unwrap_or_default() {
153 format!("{}(...)", method_name),
154 Applicability::HasPlaceholders,
157 (format!("{}()", method_name), Applicability::MaybeIncorrect)
160 err.span_suggestion(method_name.span, msg, suggestion, applicability);
163 /// Performs method lookup. If lookup is successful, it will return the callee
164 /// and store an appropriate adjustment for the self-expr. In some cases it may
165 /// report an error (e.g., invoking the `drop` method).
169 /// Given a method call like `foo.bar::<T1,...Tn>(...)`:
171 /// * `fcx`: the surrounding `FnCtxt` (!)
172 /// * `span`: the span for the method call
173 /// * `method_name`: the name of the method being called (`bar`)
174 /// * `self_ty`: the (unadjusted) type of the self expression (`foo`)
175 /// * `supplied_method_types`: the explicit method type parameters, if any (`T1..Tn`)
176 /// * `self_expr`: the self expression (`foo`)
177 pub fn lookup_method(&self,
179 segment: &hir::PathSegment,
181 call_expr: &'gcx hir::Expr,
182 self_expr: &'gcx hir::Expr)
183 -> Result<MethodCallee<'tcx>, MethodError<'tcx>> {
184 debug!("lookup(method_name={}, self_ty={:?}, call_expr={:?}, self_expr={:?})",
190 let pick = self.lookup_probe(
195 ProbeScope::TraitsInScope
198 if let Some(import_id) = pick.import_id {
199 let import_def_id = self.tcx.hir().local_def_id_from_hir_id(import_id);
200 debug!("used_trait_import: {:?}", import_def_id);
201 Lrc::get_mut(&mut self.tables.borrow_mut().used_trait_imports)
202 .unwrap().insert(import_def_id);
205 self.tcx.check_stability(pick.item.def_id, Some(call_expr.hir_id), span);
207 let result = self.confirm_method(
216 if result.illegal_sized_bound {
217 // We probe again, taking all traits into account (not only those in scope).
219 match self.lookup_probe(span,
223 ProbeScope::AllTraits) {
225 // If we find a different result the caller probably forgot to import a trait.
226 Ok(ref new_pick) if *new_pick != pick => vec![new_pick.item.container.id()],
227 Err(Ambiguity(ref sources)) => {
229 .filter_map(|source| {
231 // Note: this cannot come from an inherent impl,
232 // because the first probing succeeded.
233 ImplSource(def) => self.tcx.trait_id_of_impl(def),
234 TraitSource(_) => None,
242 return Err(IllegalSizedBound(candidates));
248 fn lookup_probe(&self,
250 method_name: ast::Ident,
252 call_expr: &'gcx hir::Expr,
254 -> probe::PickResult<'tcx> {
255 let mode = probe::Mode::MethodCall;
256 let self_ty = self.resolve_type_vars_if_possible(&self_ty);
257 self.probe_for_name(span, mode, method_name, IsSuggestion(false),
258 self_ty, call_expr.hir_id, scope)
261 /// `lookup_method_in_trait` is used for overloaded operators.
262 /// It does a very narrow slice of what the normal probe/confirm path does.
263 /// In particular, it doesn't really do any probing: it simply constructs
264 /// an obligation for a particular trait with the given self type and checks
265 /// whether that trait is implemented.
267 // FIXME(#18741): it seems likely that we can consolidate some of this
268 // code with the other method-lookup code. In particular, the second half
269 // of this method is basically the same as confirmation.
270 pub fn lookup_method_in_trait(&self,
275 opt_input_types: Option<&[Ty<'tcx>]>)
276 -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
277 debug!("lookup_in_trait_adjusted(self_ty={:?}, \
278 m_name={}, trait_def_id={:?})",
283 // Construct a trait-reference `self_ty : Trait<input_tys>`
284 let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
286 GenericParamDefKind::Lifetime | GenericParamDefKind::Const => {}
287 GenericParamDefKind::Type { .. } => {
288 if param.index == 0 {
289 return self_ty.into();
290 } else if let Some(ref input_types) = opt_input_types {
291 return input_types[param.index as usize - 1].into();
295 self.var_for_def(span, param)
298 let trait_ref = ty::TraitRef::new(trait_def_id, substs);
300 // Construct an obligation
301 let poly_trait_ref = trait_ref.to_poly_trait_ref();
303 traits::Obligation::misc(span,
306 poly_trait_ref.to_predicate());
308 // Now we want to know if this can be matched
309 if !self.predicate_may_hold(&obligation) {
310 debug!("--> Cannot match obligation");
311 return None; // Cannot be matched, no such method resolution is possible.
314 // Trait must have a method named `m_name` and it should not have
315 // type parameters or early-bound regions.
317 let method_item = match self.associated_item(trait_def_id, m_name, Namespace::Value) {
318 Some(method_item) => method_item,
320 tcx.sess.delay_span_bug(span,
321 "operator trait does not have corresponding operator method");
325 let def_id = method_item.def_id;
326 let generics = tcx.generics_of(def_id);
327 assert_eq!(generics.params.len(), 0);
329 debug!("lookup_in_trait_adjusted: method_item={:?}", method_item);
330 let mut obligations = vec![];
332 // Instantiate late-bound regions and substitute the trait
333 // parameters into the method type to get the actual method type.
335 // N.B., instantiate late-bound regions first so that
336 // `instantiate_type_scheme` can normalize associated types that
337 // may reference those regions.
338 let fn_sig = tcx.fn_sig(def_id);
339 let fn_sig = self.replace_bound_vars_with_fresh_vars(
344 let fn_sig = fn_sig.subst(self.tcx, substs);
345 let fn_sig = match self.normalize_associated_types_in_as_infer_ok(span, &fn_sig) {
346 InferOk { value, obligations: o } => {
347 obligations.extend(o);
352 // Register obligations for the parameters. This will include the
353 // `Self` parameter, which in turn has a bound of the main trait,
354 // so this also effectively registers `obligation` as well. (We
355 // used to register `obligation` explicitly, but that resulted in
356 // double error messages being reported.)
358 // Note that as the method comes from a trait, it should not have
359 // any late-bound regions appearing in its bounds.
360 let bounds = self.tcx.predicates_of(def_id).instantiate(self.tcx, substs);
361 let bounds = match self.normalize_associated_types_in_as_infer_ok(span, &bounds) {
362 InferOk { value, obligations: o } => {
363 obligations.extend(o);
367 assert!(!bounds.has_escaping_bound_vars());
369 let cause = traits::ObligationCause::misc(span, self.body_id);
370 obligations.extend(traits::predicates_for_generics(cause.clone(),
374 // Also add an obligation for the method type being well-formed.
375 let method_ty = tcx.mk_fn_ptr(ty::Binder::bind(fn_sig));
376 debug!("lookup_in_trait_adjusted: matched method method_ty={:?} obligation={:?}",
379 obligations.push(traits::Obligation::new(cause,
381 ty::Predicate::WellFormed(method_ty)));
383 let callee = MethodCallee {
385 substs: trait_ref.substs,
389 debug!("callee = {:?}", callee);
400 method_name: ast::Ident,
403 ) -> Result<(DefKind, DefId), MethodError<'tcx>> {
405 "resolve_ufcs: method_name={:?} self_ty={:?} expr_id={:?}",
406 method_name, self_ty, expr_id,
411 // Check if we have an enum variant.
412 if let ty::Adt(adt_def, _) = self_ty.sty {
413 if adt_def.is_enum() {
414 let variant_def = adt_def.variants.iter().find(|vd| {
415 tcx.hygienic_eq(method_name, vd.ident, adt_def.did)
417 if let Some(variant_def) = variant_def {
418 check_type_alias_enum_variants_enabled(tcx, span);
420 // Braced variants generate unusable names in value namespace (reserved for
421 // possible future use), so variants resolved as associated items may refer to
422 // them as well. It's ok to use the variant's id as a ctor id since an
423 // error will be reported on any use of such resolution anyway.
424 let ctor_def_id = variant_def.ctor_def_id.unwrap_or(variant_def.def_id);
425 tcx.check_stability(ctor_def_id, Some(expr_id), span);
427 DefKind::Ctor(CtorOf::Variant, variant_def.ctor_kind),
434 let pick = self.probe_for_name(span, probe::Mode::Path, method_name, IsSuggestion(false),
435 self_ty, expr_id, ProbeScope::TraitsInScope)?;
436 debug!("resolve_ufcs: pick={:?}", pick);
437 if let Some(import_id) = pick.import_id {
438 let import_def_id = tcx.hir().local_def_id_from_hir_id(import_id);
439 debug!("resolve_ufcs: used_trait_import: {:?}", import_def_id);
440 Lrc::get_mut(&mut self.tables.borrow_mut().used_trait_imports)
441 .unwrap().insert(import_def_id);
444 let def_kind = pick.item.def_kind();
445 debug!("resolve_ufcs: def_kind={:?}, def_id={:?}", def_kind, pick.item.def_id);
446 tcx.check_stability(pick.item.def_id, Some(expr_id), span);
447 Ok((def_kind, pick.item.def_id))
450 /// Finds item with name `item_name` defined in impl/trait `def_id`
451 /// and return it, or `None`, if no such item was defined there.
452 pub fn associated_item(&self, def_id: DefId, item_name: ast::Ident, ns: Namespace)
453 -> Option<ty::AssociatedItem> {
454 self.tcx.associated_items(def_id).find(|item| {
455 Namespace::from(item.kind) == ns &&
456 self.tcx.hygienic_eq(item_name, item.ident, def_id)