]> git.lizzy.rs Git - rust.git/blob - compiler/rustc_hir_typeck/src/method/mod.rs
Replacing bound vars is actually instantiating a binder
[rust.git] / compiler / rustc_hir_typeck / src / method / mod.rs
1 //! Method lookup: the secret sauce of Rust. See the [rustc dev guide] for more information.
2 //!
3 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/method-lookup.html
4
5 mod confirm;
6 mod prelude2021;
7 pub mod probe;
8 mod suggest;
9
10 pub use self::suggest::SelfSource;
11 pub use self::MethodError::*;
12
13 use crate::errors::OpMethodGenericParams;
14 use crate::FnCtxt;
15 use rustc_data_structures::sync::Lrc;
16 use rustc_errors::{Applicability, Diagnostic};
17 use rustc_hir as hir;
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, GenericParamDefKind, Ty, TypeVisitable};
24 use rustc_span::symbol::Ident;
25 use rustc_span::Span;
26 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
27 use rustc_trait_selection::traits::{self, NormalizeExt};
28
29 use self::probe::{IsSuggestion, ProbeScope};
30
31 pub fn provide(providers: &mut ty::query::Providers) {
32     probe::provide(providers);
33 }
34
35 #[derive(Clone, Copy, Debug)]
36 pub struct MethodCallee<'tcx> {
37     /// Impl method ID, for inherent methods, or trait method ID, otherwise.
38     pub def_id: DefId,
39     pub substs: SubstsRef<'tcx>,
40
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>,
45 }
46
47 #[derive(Debug)]
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>),
51
52     // Multiple methods might apply.
53     Ambiguity(Vec<CandidateSource>),
54
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>),
58
59     // Found a `Self: Sized` bound where `Self` is a trait object.
60     IllegalSizedBound {
61         candidates: Vec<DefId>,
62         needs_mut: bool,
63         bound_span: Span,
64         self_expr: &'tcx hir::Expr<'tcx>,
65     },
66
67     // Found a match, but the return type is wrong
68     BadReturnType,
69 }
70
71 // Contains a list of static methods that may apply, a list of unsatisfied trait predicates which
72 // could lead to matches if satisfied, and a list of not-in-scope traits which may work.
73 #[derive(Debug)]
74 pub struct NoMatchData<'tcx> {
75     pub static_candidates: Vec<CandidateSource>,
76     pub unsatisfied_predicates:
77         Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>, Option<ObligationCause<'tcx>>)>,
78     pub out_of_scope_traits: Vec<DefId>,
79     pub similar_candidate: Option<ty::AssocItem>,
80     pub mode: probe::Mode,
81 }
82
83 // A pared down enum describing just the places from which a method
84 // candidate can arise. Used for error reporting only.
85 #[derive(Copy, Clone, Debug, Eq, Ord, PartialEq, PartialOrd)]
86 pub enum CandidateSource {
87     Impl(DefId),
88     Trait(DefId /* trait id */),
89 }
90
91 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
92     /// Determines whether the type `self_ty` supports a method name `method_name` or not.
93     #[instrument(level = "debug", skip(self))]
94     pub fn method_exists(
95         &self,
96         method_name: Ident,
97         self_ty: Ty<'tcx>,
98         call_expr_id: hir::HirId,
99         allow_private: bool,
100         return_type: Option<Ty<'tcx>>,
101     ) -> bool {
102         match self.probe_for_name(
103             probe::Mode::MethodCall,
104             method_name,
105             return_type,
106             IsSuggestion(false),
107             self_ty,
108             call_expr_id,
109             ProbeScope::TraitsInScope,
110         ) {
111             Ok(pick) => {
112                 pick.maybe_emit_unstable_name_collision_hint(
113                     self.tcx,
114                     method_name.span,
115                     call_expr_id,
116                 );
117                 true
118             }
119             Err(NoMatch(..)) => false,
120             Err(Ambiguity(..)) => true,
121             Err(PrivateMatch(..)) => allow_private,
122             Err(IllegalSizedBound { .. }) => true,
123             Err(BadReturnType) => false,
124         }
125     }
126
127     /// Adds a suggestion to call the given method to the provided diagnostic.
128     #[instrument(level = "debug", skip(self, err, call_expr))]
129     pub(crate) fn suggest_method_call(
130         &self,
131         err: &mut Diagnostic,
132         msg: &str,
133         method_name: Ident,
134         self_ty: Ty<'tcx>,
135         call_expr: &hir::Expr<'tcx>,
136         span: Option<Span>,
137     ) {
138         let params = self
139             .lookup_probe_for_diagnostic(
140                 method_name,
141                 self_ty,
142                 call_expr,
143                 ProbeScope::TraitsInScope,
144                 None,
145             )
146             .map(|pick| {
147                 let sig = self.tcx.fn_sig(pick.item.def_id);
148                 sig.skip_binder().inputs().skip_binder().len().saturating_sub(1)
149             })
150             .unwrap_or(0);
151
152         // Account for `foo.bar<T>`;
153         let sugg_span = span.unwrap_or(call_expr.span).shrink_to_hi();
154         let (suggestion, applicability) = (
155             format!("({})", (0..params).map(|_| "_").collect::<Vec<_>>().join(", ")),
156             if params > 0 { Applicability::HasPlaceholders } else { Applicability::MaybeIncorrect },
157         );
158
159         err.span_suggestion_verbose(sugg_span, msg, suggestion, applicability);
160     }
161
162     /// Performs method lookup. If lookup is successful, it will return the callee
163     /// and store an appropriate adjustment for the self-expr. In some cases it may
164     /// report an error (e.g., invoking the `drop` method).
165     ///
166     /// # Arguments
167     ///
168     /// Given a method call like `foo.bar::<T1,...Tn>(a, b + 1, ...)`:
169     ///
170     /// * `self`:                  the surrounding `FnCtxt` (!)
171     /// * `self_ty`:               the (unadjusted) type of the self expression (`foo`)
172     /// * `segment`:               the name and generic arguments of the method (`bar::<T1, ...Tn>`)
173     /// * `span`:                  the span for the method call
174     /// * `call_expr`:             the complete method call: (`foo.bar::<T1,...Tn>(...)`)
175     /// * `self_expr`:             the self expression (`foo`)
176     /// * `args`:                  the expressions of the arguments (`a, b + 1, ...`)
177     #[instrument(level = "debug", skip(self))]
178     pub fn lookup_method(
179         &self,
180         self_ty: Ty<'tcx>,
181         segment: &hir::PathSegment<'_>,
182         span: Span,
183         call_expr: &'tcx hir::Expr<'tcx>,
184         self_expr: &'tcx hir::Expr<'tcx>,
185         args: &'tcx [hir::Expr<'tcx>],
186     ) -> Result<MethodCallee<'tcx>, MethodError<'tcx>> {
187         let pick =
188             self.lookup_probe(segment.ident, self_ty, call_expr, ProbeScope::TraitsInScope)?;
189
190         self.lint_dot_call_from_2018(self_ty, segment, span, call_expr, self_expr, &pick, args);
191
192         for import_id in &pick.import_ids {
193             debug!("used_trait_import: {:?}", import_id);
194             Lrc::get_mut(&mut self.typeck_results.borrow_mut().used_trait_imports)
195                 .unwrap()
196                 .insert(*import_id);
197         }
198
199         self.tcx.check_stability(pick.item.def_id, Some(call_expr.hir_id), span, None);
200
201         let result = self.confirm_method(span, self_expr, call_expr, self_ty, &pick, segment);
202         debug!("result = {:?}", result);
203
204         if let Some(span) = result.illegal_sized_bound {
205             let mut needs_mut = false;
206             if let ty::Ref(region, t_type, mutability) = self_ty.kind() {
207                 let trait_type = self
208                     .tcx
209                     .mk_ref(*region, ty::TypeAndMut { ty: *t_type, mutbl: mutability.invert() });
210                 // We probe again to see if there might be a borrow mutability discrepancy.
211                 match self.lookup_probe(
212                     segment.ident,
213                     trait_type,
214                     call_expr,
215                     ProbeScope::TraitsInScope,
216                 ) {
217                     Ok(ref new_pick) if pick.differs_from(new_pick) => {
218                         needs_mut = new_pick.self_ty.ref_mutability() != self_ty.ref_mutability();
219                     }
220                     _ => {}
221                 }
222             }
223
224             // We probe again, taking all traits into account (not only those in scope).
225             let candidates = match self.lookup_probe_for_diagnostic(
226                 segment.ident,
227                 self_ty,
228                 call_expr,
229                 ProbeScope::AllTraits,
230                 None,
231             ) {
232                 // If we find a different result the caller probably forgot to import a trait.
233                 Ok(ref new_pick) if pick.differs_from(new_pick) => {
234                     vec![new_pick.item.container_id(self.tcx)]
235                 }
236                 Err(Ambiguity(ref sources)) => sources
237                     .iter()
238                     .filter_map(|source| {
239                         match *source {
240                             // Note: this cannot come from an inherent impl,
241                             // because the first probing succeeded.
242                             CandidateSource::Impl(def) => self.tcx.trait_id_of_impl(def),
243                             CandidateSource::Trait(_) => None,
244                         }
245                     })
246                     .collect(),
247                 _ => Vec::new(),
248             };
249
250             return Err(IllegalSizedBound { candidates, needs_mut, bound_span: span, self_expr });
251         }
252
253         Ok(result.callee)
254     }
255
256     #[instrument(level = "debug", skip(self, call_expr))]
257     pub fn lookup_probe(
258         &self,
259         method_name: Ident,
260         self_ty: Ty<'tcx>,
261         call_expr: &hir::Expr<'_>,
262         scope: ProbeScope,
263     ) -> probe::PickResult<'tcx> {
264         let pick = self.probe_for_name(
265             probe::Mode::MethodCall,
266             method_name,
267             None,
268             IsSuggestion(false),
269             self_ty,
270             call_expr.hir_id,
271             scope,
272         )?;
273         pick.maybe_emit_unstable_name_collision_hint(self.tcx, method_name.span, call_expr.hir_id);
274         Ok(pick)
275     }
276
277     pub fn lookup_probe_for_diagnostic(
278         &self,
279         method_name: Ident,
280         self_ty: Ty<'tcx>,
281         call_expr: &hir::Expr<'_>,
282         scope: ProbeScope,
283         return_type: Option<Ty<'tcx>>,
284     ) -> probe::PickResult<'tcx> {
285         let pick = self.probe_for_name(
286             probe::Mode::MethodCall,
287             method_name,
288             return_type,
289             IsSuggestion(true),
290             self_ty,
291             call_expr.hir_id,
292             scope,
293         )?;
294         Ok(pick)
295     }
296
297     pub(super) fn obligation_for_method(
298         &self,
299         cause: ObligationCause<'tcx>,
300         trait_def_id: DefId,
301         self_ty: Ty<'tcx>,
302         opt_input_types: Option<&[Ty<'tcx>]>,
303     ) -> (traits::Obligation<'tcx, ty::Predicate<'tcx>>, &'tcx ty::List<ty::subst::GenericArg<'tcx>>)
304     {
305         // Construct a trait-reference `self_ty : Trait<input_tys>`
306         let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
307             match param.kind {
308                 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => {}
309                 GenericParamDefKind::Type { .. } => {
310                     if param.index == 0 {
311                         return self_ty.into();
312                     } else if let Some(input_types) = opt_input_types {
313                         return input_types[param.index as usize - 1].into();
314                     }
315                 }
316             }
317             self.var_for_def(cause.span, param)
318         });
319
320         let trait_ref = self.tcx.mk_trait_ref(trait_def_id, substs);
321
322         // Construct an obligation
323         let poly_trait_ref = ty::Binder::dummy(trait_ref);
324         (
325             traits::Obligation::new(
326                 self.tcx,
327                 cause,
328                 self.param_env,
329                 poly_trait_ref.without_const(),
330             ),
331             substs,
332         )
333     }
334
335     /// `lookup_method_in_trait` is used for overloaded operators.
336     /// It does a very narrow slice of what the normal probe/confirm path does.
337     /// In particular, it doesn't really do any probing: it simply constructs
338     /// an obligation for a particular trait with the given self type and checks
339     /// whether that trait is implemented.
340     #[instrument(level = "debug", skip(self))]
341     pub(super) fn lookup_method_in_trait(
342         &self,
343         cause: ObligationCause<'tcx>,
344         m_name: Ident,
345         trait_def_id: DefId,
346         self_ty: Ty<'tcx>,
347         opt_input_types: Option<&[Ty<'tcx>]>,
348     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
349         let (obligation, substs) =
350             self.obligation_for_method(cause, trait_def_id, self_ty, opt_input_types);
351         self.construct_obligation_for_trait(m_name, trait_def_id, obligation, substs)
352     }
353
354     // FIXME(#18741): it seems likely that we can consolidate some of this
355     // code with the other method-lookup code. In particular, the second half
356     // of this method is basically the same as confirmation.
357     fn construct_obligation_for_trait(
358         &self,
359         m_name: Ident,
360         trait_def_id: DefId,
361         obligation: traits::PredicateObligation<'tcx>,
362         substs: &'tcx ty::List<ty::subst::GenericArg<'tcx>>,
363     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
364         debug!(?obligation);
365
366         // Now we want to know if this can be matched
367         if !self.predicate_may_hold(&obligation) {
368             debug!("--> Cannot match obligation");
369             // Cannot be matched, no such method resolution is possible.
370             return None;
371         }
372
373         // Trait must have a method named `m_name` and it should not have
374         // type parameters or early-bound regions.
375         let tcx = self.tcx;
376         let Some(method_item) = self.associated_value(trait_def_id, m_name) else {
377             tcx.sess.delay_span_bug(
378                 obligation.cause.span,
379                 "operator trait does not have corresponding operator method",
380             );
381             return None;
382         };
383         let def_id = method_item.def_id;
384         let generics = tcx.generics_of(def_id);
385
386         if generics.params.len() != 0 {
387             tcx.sess.emit_fatal(OpMethodGenericParams {
388                 span: tcx.def_span(method_item.def_id),
389                 method_name: m_name.to_string(),
390             });
391         }
392
393         debug!("lookup_in_trait_adjusted: method_item={:?}", method_item);
394         let mut obligations = vec![];
395
396         // Instantiate late-bound regions and substitute the trait
397         // parameters into the method type to get the actual method type.
398         //
399         // N.B., instantiate late-bound regions before normalizing the
400         // function signature so that normalization does not need to deal
401         // with bound regions.
402         let fn_sig = tcx.fn_sig(def_id).subst(self.tcx, substs);
403         let fn_sig =
404             self.instantiate_binder_with_fresh_vars(obligation.cause.span, infer::FnCall, fn_sig);
405
406         let InferOk { value, obligations: o } =
407             self.at(&obligation.cause, self.param_env).normalize(fn_sig);
408         let fn_sig = {
409             obligations.extend(o);
410             value
411         };
412
413         // Register obligations for the parameters. This will include the
414         // `Self` parameter, which in turn has a bound of the main trait,
415         // so this also effectively registers `obligation` as well. (We
416         // used to register `obligation` explicitly, but that resulted in
417         // double error messages being reported.)
418         //
419         // Note that as the method comes from a trait, it should not have
420         // any late-bound regions appearing in its bounds.
421         let bounds = self.tcx.predicates_of(def_id).instantiate(self.tcx, substs);
422
423         let InferOk { value, obligations: o } =
424             self.at(&obligation.cause, self.param_env).normalize(bounds);
425         let bounds = {
426             obligations.extend(o);
427             value
428         };
429
430         assert!(!bounds.has_escaping_bound_vars());
431
432         let predicates_cause = obligation.cause.clone();
433         obligations.extend(traits::predicates_for_generics(
434             move |_, _| predicates_cause.clone(),
435             self.param_env,
436             bounds,
437         ));
438
439         // Also add an obligation for the method type being well-formed.
440         let method_ty = tcx.mk_fn_ptr(ty::Binder::dummy(fn_sig));
441         debug!(
442             "lookup_in_trait_adjusted: matched method method_ty={:?} obligation={:?}",
443             method_ty, obligation
444         );
445         obligations.push(traits::Obligation::new(
446             tcx,
447             obligation.cause,
448             self.param_env,
449             ty::Binder::dummy(ty::PredicateKind::WellFormed(method_ty.into())),
450         ));
451
452         let callee = MethodCallee { def_id, substs, sig: fn_sig };
453
454         debug!("callee = {:?}", callee);
455
456         Some(InferOk { obligations, value: callee })
457     }
458
459     /// Performs a [full-qualified function call] (formerly "universal function call") lookup. If
460     /// lookup is successful, it will return the type of definition and the [`DefId`] of the found
461     /// function definition.
462     ///
463     /// [full-qualified function call]: https://doc.rust-lang.org/reference/expressions/call-expr.html#disambiguating-function-calls
464     ///
465     /// # Arguments
466     ///
467     /// Given a function call like `Foo::bar::<T1,...Tn>(...)`:
468     ///
469     /// * `self`:                  the surrounding `FnCtxt` (!)
470     /// * `span`:                  the span of the call, excluding arguments (`Foo::bar::<T1, ...Tn>`)
471     /// * `method_name`:           the identifier of the function within the container type (`bar`)
472     /// * `self_ty`:               the type to search within (`Foo`)
473     /// * `self_ty_span`           the span for the type being searched within (span of `Foo`)
474     /// * `expr_id`:               the [`hir::HirId`] of the expression composing the entire call
475     #[instrument(level = "debug", skip(self), ret)]
476     pub fn resolve_fully_qualified_call(
477         &self,
478         span: Span,
479         method_name: Ident,
480         self_ty: Ty<'tcx>,
481         self_ty_span: Span,
482         expr_id: hir::HirId,
483     ) -> Result<(DefKind, DefId), MethodError<'tcx>> {
484         let tcx = self.tcx;
485
486         // Check if we have an enum variant.
487         let mut struct_variant = None;
488         if let ty::Adt(adt_def, _) = self_ty.kind() {
489             if adt_def.is_enum() {
490                 let variant_def = adt_def
491                     .variants()
492                     .iter()
493                     .find(|vd| tcx.hygienic_eq(method_name, vd.ident(tcx), adt_def.did()));
494                 if let Some(variant_def) = variant_def {
495                     if let Some((ctor_kind, ctor_def_id)) = variant_def.ctor {
496                         tcx.check_stability(
497                             ctor_def_id,
498                             Some(expr_id),
499                             span,
500                             Some(method_name.span),
501                         );
502                         return Ok((DefKind::Ctor(CtorOf::Variant, ctor_kind), ctor_def_id));
503                     } else {
504                         struct_variant = Some((DefKind::Variant, variant_def.def_id));
505                     }
506                 }
507             }
508         }
509
510         let pick = self.probe_for_name(
511             probe::Mode::Path,
512             method_name,
513             None,
514             IsSuggestion(false),
515             self_ty,
516             expr_id,
517             ProbeScope::TraitsInScope,
518         );
519         let pick = match (pick, struct_variant) {
520             // Fall back to a resolution that will produce an error later.
521             (Err(_), Some(res)) => return Ok(res),
522             (pick, _) => pick?,
523         };
524
525         pick.maybe_emit_unstable_name_collision_hint(self.tcx, span, expr_id);
526
527         self.lint_fully_qualified_call_from_2018(
528             span,
529             method_name,
530             self_ty,
531             self_ty_span,
532             expr_id,
533             &pick,
534         );
535
536         debug!(?pick);
537         {
538             let mut typeck_results = self.typeck_results.borrow_mut();
539             let used_trait_imports = Lrc::get_mut(&mut typeck_results.used_trait_imports).unwrap();
540             for import_id in pick.import_ids {
541                 debug!(used_trait_import=?import_id);
542                 used_trait_imports.insert(import_id);
543             }
544         }
545
546         let def_kind = pick.item.kind.as_def_kind();
547         tcx.check_stability(pick.item.def_id, Some(expr_id), span, Some(method_name.span));
548         Ok((def_kind, pick.item.def_id))
549     }
550
551     /// Finds item with name `item_name` defined in impl/trait `def_id`
552     /// and return it, or `None`, if no such item was defined there.
553     pub fn associated_value(&self, def_id: DefId, item_name: Ident) -> Option<ty::AssocItem> {
554         self.tcx
555             .associated_items(def_id)
556             .find_by_name_and_namespace(self.tcx, item_name, Namespace::ValueNS, def_id)
557             .copied()
558     }
559 }