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.typeck_results
.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
::PredicateAtom
::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 typeck_results
= self.typeck_results
.borrow_mut();
460 let used_trait_imports
= Lrc
::get_mut(&mut typeck_results
.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
)