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::ty::subst::Subst;
15 use rustc::ty::subst::{InternalSubsts, SubstsRef};
16 use rustc::ty::GenericParamDefKind;
17 use rustc::ty::{self, ToPolyTraitRef, ToPredicate, Ty, TypeFoldable, WithConstness};
19 use rustc_data_structures::sync::Lrc;
20 use rustc_errors::{Applicability, DiagnosticBuilder};
22 use rustc_hir::def::{CtorOf, DefKind, Namespace};
23 use rustc_hir::def_id::DefId;
24 use rustc_infer::infer::{self, InferOk};
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(
107 method_name: ast::Ident,
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>,
136 method_name: ast::Ident,
138 call_expr: &hir::Expr<'_>,
140 let has_params = self
143 probe::Mode::MethodCall,
148 ProbeScope::TraitsInScope,
151 let sig = self.tcx.fn_sig(pick.item.def_id);
152 Ok(sig.inputs().skip_binder().len() > 1)
155 // Account for `foo.bar<T>`;
156 let sugg_span = method_name.span.with_hi(call_expr.span.hi());
161 .span_to_snippet(sugg_span)
162 .unwrap_or_else(|_| method_name.to_string());
163 let (suggestion, applicability) = if has_params.unwrap_or_default() {
164 (format!("{}(...)", snippet), Applicability::HasPlaceholders)
166 (format!("{}()", snippet), Applicability::MaybeIncorrect)
169 err.span_suggestion(sugg_span, msg, suggestion, applicability);
172 /// Performs method lookup. If lookup is successful, it will return the callee
173 /// and store an appropriate adjustment for the self-expr. In some cases it may
174 /// report an error (e.g., invoking the `drop` method).
178 /// Given a method call like `foo.bar::<T1,...Tn>(...)`:
180 /// * `fcx`: the surrounding `FnCtxt` (!)
181 /// * `span`: the span for the method call
182 /// * `method_name`: the name of the method being called (`bar`)
183 /// * `self_ty`: the (unadjusted) type of the self expression (`foo`)
184 /// * `supplied_method_types`: the explicit method type parameters, if any (`T1..Tn`)
185 /// * `self_expr`: the self expression (`foo`)
186 pub fn lookup_method(
189 segment: &hir::PathSegment<'_>,
191 call_expr: &'tcx hir::Expr<'tcx>,
192 self_expr: &'tcx hir::Expr<'tcx>,
193 ) -> Result<MethodCallee<'tcx>, MethodError<'tcx>> {
195 "lookup(method_name={}, self_ty={:?}, call_expr={:?}, self_expr={:?})",
196 segment.ident, self_ty, call_expr, self_expr
200 self.lookup_probe(span, segment.ident, self_ty, call_expr, ProbeScope::TraitsInScope)?;
202 for import_id in &pick.import_ids {
203 let import_def_id = self.tcx.hir().local_def_id(*import_id);
204 debug!("used_trait_import: {:?}", import_def_id);
205 Lrc::get_mut(&mut self.tables.borrow_mut().used_trait_imports)
207 .insert(import_def_id);
210 self.tcx.check_stability(pick.item.def_id, Some(call_expr.hir_id), span);
213 self.confirm_method(span, self_expr, call_expr, self_ty, pick.clone(), segment);
215 if let Some(span) = result.illegal_sized_bound {
216 let mut needs_mut = false;
217 if let ty::Ref(region, t_type, mutability) = self_ty.kind {
218 let trait_type = self
220 .mk_ref(region, ty::TypeAndMut { ty: t_type, mutbl: mutability.invert() });
221 // We probe again to see if there might be a borrow mutability discrepancy.
222 match self.lookup_probe(
227 ProbeScope::TraitsInScope,
229 Ok(ref new_pick) if *new_pick != pick => {
236 // We probe again, taking all traits into account (not only those in scope).
237 let candidates = match self.lookup_probe(
242 ProbeScope::AllTraits,
244 // If we find a different result the caller probably forgot to import a trait.
245 Ok(ref new_pick) if *new_pick != pick => vec![new_pick.item.container.id()],
246 Err(Ambiguity(ref sources)) => sources
248 .filter_map(|source| {
250 // Note: this cannot come from an inherent impl,
251 // because the first probing succeeded.
252 ImplSource(def) => self.tcx.trait_id_of_impl(def),
253 TraitSource(_) => None,
260 return Err(IllegalSizedBound(candidates, needs_mut, span));
269 method_name: ast::Ident,
271 call_expr: &'tcx hir::Expr<'tcx>,
273 ) -> probe::PickResult<'tcx> {
274 let mode = probe::Mode::MethodCall;
275 let self_ty = self.resolve_vars_if_possible(&self_ty);
287 /// `lookup_method_in_trait` is used for overloaded operators.
288 /// It does a very narrow slice of what the normal probe/confirm path does.
289 /// In particular, it doesn't really do any probing: it simply constructs
290 /// an obligation for a particular trait with the given self type and checks
291 /// whether that trait is implemented.
293 // FIXME(#18741): it seems likely that we can consolidate some of this
294 // code with the other method-lookup code. In particular, the second half
295 // of this method is basically the same as confirmation.
296 pub fn lookup_method_in_trait(
302 opt_input_types: Option<&[Ty<'tcx>]>,
303 ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
305 "lookup_in_trait_adjusted(self_ty={:?}, \
306 m_name={}, trait_def_id={:?})",
307 self_ty, m_name, trait_def_id
310 // Construct a trait-reference `self_ty : Trait<input_tys>`
311 let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
313 GenericParamDefKind::Lifetime | GenericParamDefKind::Const => {}
314 GenericParamDefKind::Type { .. } => {
315 if param.index == 0 {
316 return self_ty.into();
317 } else if let Some(ref input_types) = opt_input_types {
318 return input_types[param.index as usize - 1].into();
322 self.var_for_def(span, param)
325 let trait_ref = ty::TraitRef::new(trait_def_id, substs);
327 // Construct an obligation
328 let poly_trait_ref = trait_ref.to_poly_trait_ref();
329 let obligation = traits::Obligation::misc(
333 poly_trait_ref.without_const().to_predicate(),
336 // Now we want to know if this can be matched
337 if !self.predicate_may_hold(&obligation) {
338 debug!("--> Cannot match obligation");
339 return None; // Cannot be matched, no such method resolution is possible.
342 // Trait must have a method named `m_name` and it should not have
343 // type parameters or early-bound regions.
345 let method_item = match self.associated_item(trait_def_id, m_name, Namespace::ValueNS) {
346 Some(method_item) => method_item,
348 tcx.sess.delay_span_bug(
350 "operator trait does not have corresponding operator method",
355 let def_id = method_item.def_id;
356 let generics = tcx.generics_of(def_id);
357 assert_eq!(generics.params.len(), 0);
359 debug!("lookup_in_trait_adjusted: method_item={:?}", method_item);
360 let mut obligations = vec![];
362 // Instantiate late-bound regions and substitute the trait
363 // parameters into the method type to get the actual method type.
365 // N.B., instantiate late-bound regions first so that
366 // `instantiate_type_scheme` can normalize associated types that
367 // may reference those regions.
368 let fn_sig = tcx.fn_sig(def_id);
369 let fn_sig = self.replace_bound_vars_with_fresh_vars(span, infer::FnCall, &fn_sig).0;
370 let fn_sig = fn_sig.subst(self.tcx, substs);
371 let fn_sig = match self.normalize_associated_types_in_as_infer_ok(span, &fn_sig) {
372 InferOk { value, obligations: o } => {
373 obligations.extend(o);
378 // Register obligations for the parameters. This will include the
379 // `Self` parameter, which in turn has a bound of the main trait,
380 // so this also effectively registers `obligation` as well. (We
381 // used to register `obligation` explicitly, but that resulted in
382 // double error messages being reported.)
384 // Note that as the method comes from a trait, it should not have
385 // any late-bound regions appearing in its bounds.
386 let bounds = self.tcx.predicates_of(def_id).instantiate(self.tcx, substs);
387 let bounds = match self.normalize_associated_types_in_as_infer_ok(span, &bounds) {
388 InferOk { value, obligations: o } => {
389 obligations.extend(o);
393 assert!(!bounds.has_escaping_bound_vars());
395 let cause = traits::ObligationCause::misc(span, self.body_id);
396 obligations.extend(traits::predicates_for_generics(cause.clone(), self.param_env, &bounds));
398 // Also add an obligation for the method type being well-formed.
399 let method_ty = tcx.mk_fn_ptr(ty::Binder::bind(fn_sig));
401 "lookup_in_trait_adjusted: matched method method_ty={:?} obligation={:?}",
402 method_ty, obligation
404 obligations.push(traits::Obligation::new(
407 ty::Predicate::WellFormed(method_ty),
410 let callee = MethodCallee { def_id, substs: trait_ref.substs, sig: fn_sig };
412 debug!("callee = {:?}", callee);
414 Some(InferOk { obligations, value: callee })
420 method_name: ast::Ident,
423 ) -> Result<(DefKind, DefId), MethodError<'tcx>> {
425 "resolve_ufcs: method_name={:?} self_ty={:?} expr_id={:?}",
426 method_name, self_ty, expr_id,
431 // Check if we have an enum variant.
432 if let ty::Adt(adt_def, _) = self_ty.kind {
433 if adt_def.is_enum() {
434 let variant_def = adt_def
437 .find(|vd| tcx.hygienic_eq(method_name, vd.ident, adt_def.did));
438 if let Some(variant_def) = variant_def {
439 // Braced variants generate unusable names in value namespace (reserved for
440 // possible future use), so variants resolved as associated items may refer to
441 // them as well. It's ok to use the variant's id as a ctor id since an
442 // error will be reported on any use of such resolution anyway.
443 let ctor_def_id = variant_def.ctor_def_id.unwrap_or(variant_def.def_id);
444 tcx.check_stability(ctor_def_id, Some(expr_id), span);
446 DefKind::Ctor(CtorOf::Variant, variant_def.ctor_kind),
453 let pick = self.probe_for_name(
460 ProbeScope::TraitsInScope,
462 debug!("resolve_ufcs: pick={:?}", pick);
464 let mut tables = self.tables.borrow_mut();
465 let used_trait_imports = Lrc::get_mut(&mut tables.used_trait_imports).unwrap();
466 for import_id in pick.import_ids {
467 let import_def_id = tcx.hir().local_def_id(import_id);
468 debug!("resolve_ufcs: used_trait_import: {:?}", import_def_id);
469 used_trait_imports.insert(import_def_id);
473 let def_kind = pick.item.def_kind();
474 debug!("resolve_ufcs: def_kind={:?}, def_id={:?}", def_kind, pick.item.def_id);
475 tcx.check_stability(pick.item.def_id, Some(expr_id), span);
476 Ok((def_kind, pick.item.def_id))
479 /// Finds item with name `item_name` defined in impl/trait `def_id`
480 /// and return it, or `None`, if no such item was defined there.
481 pub fn associated_item(
484 item_name: ast::Ident,
486 ) -> Option<ty::AssocItem> {
488 .associated_items(def_id)
489 .find_by_name_and_namespace(self.tcx, item_name, ns, def_id)