1 use super::{probe, MethodCallee};
3 use crate::astconv::AstConv;
4 use crate::check::{callee, FnCtxt};
5 use crate::hir::def_id::DefId;
6 use crate::hir::GenericArg;
8 use rustc_infer::infer::{self, InferOk};
9 use rustc_middle::ty::adjustment::{Adjust, Adjustment, PointerCast};
10 use rustc_middle::ty::adjustment::{AllowTwoPhase, AutoBorrow, AutoBorrowMutability};
11 use rustc_middle::ty::fold::TypeFoldable;
12 use rustc_middle::ty::subst::{Subst, SubstsRef};
13 use rustc_middle::ty::{self, GenericParamDefKind, Ty};
15 use rustc_trait_selection::traits;
19 struct ConfirmContext<'a, 'tcx> {
20 fcx: &'a FnCtxt<'a, 'tcx>,
22 self_expr: &'tcx hir::Expr<'tcx>,
23 call_expr: &'tcx hir::Expr<'tcx>,
26 impl<'a, 'tcx> Deref for ConfirmContext<'a, 'tcx> {
27 type Target = FnCtxt<'a, 'tcx>;
28 fn deref(&self) -> &Self::Target {
33 pub struct ConfirmResult<'tcx> {
34 pub callee: MethodCallee<'tcx>,
35 pub illegal_sized_bound: Option<Span>,
38 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
39 pub fn confirm_method(
42 self_expr: &'tcx hir::Expr<'tcx>,
43 call_expr: &'tcx hir::Expr<'tcx>,
44 unadjusted_self_ty: Ty<'tcx>,
45 pick: probe::Pick<'tcx>,
46 segment: &hir::PathSegment<'_>,
47 ) -> ConfirmResult<'tcx> {
49 "confirm(unadjusted_self_ty={:?}, pick={:?}, generic_args={:?})",
50 unadjusted_self_ty, pick, segment.args,
53 let mut confirm_cx = ConfirmContext::new(self, span, self_expr, call_expr);
54 confirm_cx.confirm(unadjusted_self_ty, pick, segment)
58 impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
60 fcx: &'a FnCtxt<'a, 'tcx>,
62 self_expr: &'tcx hir::Expr<'tcx>,
63 call_expr: &'tcx hir::Expr<'tcx>,
64 ) -> ConfirmContext<'a, 'tcx> {
65 ConfirmContext { fcx, span, self_expr, call_expr }
70 unadjusted_self_ty: Ty<'tcx>,
71 pick: probe::Pick<'tcx>,
72 segment: &hir::PathSegment<'_>,
73 ) -> ConfirmResult<'tcx> {
74 // Adjust the self expression the user provided and obtain the adjusted type.
75 let self_ty = self.adjust_self_ty(unadjusted_self_ty, &pick);
77 // Create substitutions for the method's type parameters.
78 let rcvr_substs = self.fresh_receiver_substs(self_ty, &pick);
79 let all_substs = self.instantiate_method_substs(&pick, segment, rcvr_substs);
81 debug!("all_substs={:?}", all_substs);
83 // Create the final signature for the method, replacing late-bound regions.
84 let (method_sig, method_predicates) = self.instantiate_method_sig(&pick, all_substs);
86 // Unify the (adjusted) self type with what the method expects.
88 // SUBTLE: if we want good error messages, because of "guessing" while matching
89 // traits, no trait system method can be called before this point because they
90 // could alter our Self-type, except for normalizing the receiver from the
91 // signature (which is also done during probing).
93 self.normalize_associated_types_in(self.span, &method_sig.inputs()[0]);
94 self.unify_receivers(self_ty, method_sig_rcvr);
96 let (method_sig, method_predicates) =
97 self.normalize_associated_types_in(self.span, &(method_sig, method_predicates));
99 // Make sure nobody calls `drop()` explicitly.
100 self.enforce_illegal_method_limitations(&pick);
102 // If there is a `Self: Sized` bound and `Self` is a trait object, it is possible that
103 // something which derefs to `Self` actually implements the trait and the caller
104 // wanted to make a static dispatch on it but forgot to import the trait.
105 // See test `src/test/ui/issue-35976.rs`.
107 // In that case, we'll error anyway, but we'll also re-run the search with all traits
108 // in scope, and if we find another method which can be used, we'll output an
109 // appropriate hint suggesting to import the trait.
110 let illegal_sized_bound = self.predicates_require_illegal_sized_bound(&method_predicates);
112 // Add any trait/regions obligations specified on the method's type parameters.
113 // We won't add these if we encountered an illegal sized bound, so that we can use
114 // a custom error in that case.
115 if illegal_sized_bound.is_none() {
116 let method_ty = self.tcx.mk_fn_ptr(ty::Binder::bind(method_sig));
117 self.add_obligations(method_ty, all_substs, method_predicates);
120 // Create the final `MethodCallee`.
121 let callee = MethodCallee { def_id: pick.item.def_id, substs: all_substs, sig: method_sig };
122 ConfirmResult { callee, illegal_sized_bound }
125 ///////////////////////////////////////////////////////////////////////////
130 unadjusted_self_ty: Ty<'tcx>,
131 pick: &probe::Pick<'tcx>,
133 // Commit the autoderefs by calling `autoderef` again, but this
134 // time writing the results into the various typeck results.
135 let mut autoderef = self.autoderef(self.span, unadjusted_self_ty);
136 let (_, n) = match autoderef.nth(pick.autoderefs) {
139 return self.tcx.ty_error_with_message(
140 rustc_span::DUMMY_SP,
141 &format!("failed autoderef {}", pick.autoderefs),
145 assert_eq!(n, pick.autoderefs);
147 let mut adjustments = self.adjust_steps(&autoderef);
150 self.structurally_resolved_type(autoderef.span(), autoderef.final_ty(false));
152 if let Some(mutbl) = pick.autoref {
153 let region = self.next_region_var(infer::Autoref(self.span));
154 target = self.tcx.mk_ref(region, ty::TypeAndMut { mutbl, ty: target });
155 let mutbl = match mutbl {
156 hir::Mutability::Not => AutoBorrowMutability::Not,
157 hir::Mutability::Mut => AutoBorrowMutability::Mut {
158 // Method call receivers are the primary use case
159 // for two-phase borrows.
160 allow_two_phase_borrow: AllowTwoPhase::Yes,
164 .push(Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)), target });
166 if let Some(unsize_target) = pick.unsize {
169 .mk_ref(region, ty::TypeAndMut { mutbl: mutbl.into(), ty: unsize_target });
170 adjustments.push(Adjustment { kind: Adjust::Pointer(PointerCast::Unsize), target });
173 // No unsizing should be performed without autoref (at
174 // least during method dispach). This is because we
175 // currently only unsize `[T;N]` to `[T]`, and naturally
176 // that must occur being a reference.
177 assert!(pick.unsize.is_none());
180 self.register_predicates(autoderef.into_obligations());
182 // Write out the final adjustments.
183 self.apply_adjustments(self.self_expr, adjustments);
188 /// Returns a set of substitutions for the method *receiver* where all type and region
189 /// parameters are instantiated with fresh variables. This substitution does not include any
190 /// parameters declared on the method itself.
192 /// Note that this substitution may include late-bound regions from the impl level. If so,
193 /// these are instantiated later in the `instantiate_method_sig` routine.
194 fn fresh_receiver_substs(
197 pick: &probe::Pick<'tcx>,
198 ) -> SubstsRef<'tcx> {
200 probe::InherentImplPick => {
201 let impl_def_id = pick.item.container.id();
203 self.tcx.impl_trait_ref(impl_def_id).is_none(),
204 "impl {:?} is not an inherent impl",
207 self.fresh_substs_for_item(self.span, impl_def_id)
210 probe::ObjectPick => {
211 let trait_def_id = pick.item.container.id();
212 self.extract_existential_trait_ref(self_ty, |this, object_ty, principal| {
213 // The object data has no entry for the Self
214 // Type. For the purposes of this method call, we
215 // substitute the object type itself. This
216 // wouldn't be a sound substitution in all cases,
217 // since each instance of the object type is a
218 // different existential and hence could match
219 // distinct types (e.g., if `Self` appeared as an
220 // argument type), but those cases have already
221 // been ruled out when we deemed the trait to be
223 let original_poly_trait_ref = principal.with_self_ty(this.tcx, object_ty);
224 let upcast_poly_trait_ref = this.upcast(original_poly_trait_ref, trait_def_id);
225 let upcast_trait_ref =
226 this.replace_bound_vars_with_fresh_vars(&upcast_poly_trait_ref);
228 "original_poly_trait_ref={:?} upcast_trait_ref={:?} target_trait={:?}",
229 original_poly_trait_ref, upcast_trait_ref, trait_def_id
231 upcast_trait_ref.substs
235 probe::TraitPick => {
236 let trait_def_id = pick.item.container.id();
238 // Make a trait reference `$0 : Trait<$1...$n>`
239 // consisting entirely of type variables. Later on in
240 // the process we will unify the transformed-self-type
241 // of the method with the actual type in order to
242 // unify some of these variables.
243 self.fresh_substs_for_item(self.span, trait_def_id)
246 probe::WhereClausePick(ref poly_trait_ref) => {
247 // Where clauses can have bound regions in them. We need to instantiate
248 // those to convert from a poly-trait-ref to a trait-ref.
249 self.replace_bound_vars_with_fresh_vars(&poly_trait_ref).substs
254 fn extract_existential_trait_ref<R, F>(&mut self, self_ty: Ty<'tcx>, mut closure: F) -> R
256 F: FnMut(&mut ConfirmContext<'a, 'tcx>, Ty<'tcx>, ty::PolyExistentialTraitRef<'tcx>) -> R,
258 // If we specified that this is an object method, then the
259 // self-type ought to be something that can be dereferenced to
260 // yield an object-type (e.g., `&Object` or `Box<Object>`
263 // FIXME: this feels, like, super dubious
265 .autoderef(self.span, self_ty)
266 .include_raw_pointers()
267 .find_map(|(ty, _)| match ty.kind {
268 ty::Dynamic(ref data, ..) => Some(closure(
271 data.principal().unwrap_or_else(|| {
272 span_bug!(self.span, "calling trait method on empty object?")
280 "self-type `{}` for ObjectPick never dereferenced to an object",
286 fn instantiate_method_substs(
288 pick: &probe::Pick<'tcx>,
289 seg: &hir::PathSegment<'_>,
290 parent_substs: SubstsRef<'tcx>,
291 ) -> SubstsRef<'tcx> {
292 // Determine the values for the generic parameters of the method.
293 // If they were not explicitly supplied, just construct fresh
295 let generics = self.tcx.generics_of(pick.item.def_id);
296 let arg_count_correct = AstConv::check_generic_arg_count_for_call(
297 self.tcx, self.span, &generics, &seg, true, // `is_method_call`
300 // Create subst for early-bound lifetime parameters, combining
301 // parameters from the type and those from the method.
302 assert_eq!(generics.parent_count, parent_substs.len());
304 AstConv::create_substs_for_generic_args(
311 // Provide the generic args, and whether types should be inferred.
313 // The last component of the returned tuple here is unimportant.
314 if def_id == pick.item.def_id {
315 if let Some(ref data) = seg.args {
316 return (Some(data), false);
321 // Provide substitutions for parameters for which (valid) arguments have been provided.
322 |param, arg| match (¶m.kind, arg) {
323 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
324 AstConv::ast_region_to_region(self.fcx, lt, Some(param)).into()
326 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => self.to_ty(ty).into(),
327 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
328 self.const_arg_to_const(&ct.value, param.def_id).into()
332 // Provide substitutions for parameters for which arguments are inferred.
333 |_, param, _| self.var_for_def(self.span, param),
337 fn unify_receivers(&mut self, self_ty: Ty<'tcx>, method_self_ty: Ty<'tcx>) {
338 match self.at(&self.misc(self.span), self.param_env).sup(method_self_ty, self_ty) {
339 Ok(InferOk { obligations, value: () }) => {
340 self.register_predicates(obligations);
345 "{} was a subtype of {} but now is not?",
353 // NOTE: this returns the *unnormalized* predicates and method sig. Because of
354 // inference guessing, the predicates and method signature can't be normalized
355 // until we unify the `Self` type.
356 fn instantiate_method_sig(
358 pick: &probe::Pick<'tcx>,
359 all_substs: SubstsRef<'tcx>,
360 ) -> (ty::FnSig<'tcx>, ty::InstantiatedPredicates<'tcx>) {
361 debug!("instantiate_method_sig(pick={:?}, all_substs={:?})", pick, all_substs);
363 // Instantiate the bounds on the method with the
364 // type/early-bound-regions substitutions performed. There can
365 // be no late-bound regions appearing here.
366 let def_id = pick.item.def_id;
367 let method_predicates = self.tcx.predicates_of(def_id).instantiate(self.tcx, all_substs);
369 debug!("method_predicates after subst = {:?}", method_predicates);
371 let sig = self.tcx.fn_sig(def_id);
373 // Instantiate late-bound regions and substitute the trait
374 // parameters into the method type to get the actual method type.
376 // N.B., instantiate late-bound regions first so that
377 // `instantiate_type_scheme` can normalize associated types that
378 // may reference those regions.
379 let method_sig = self.replace_bound_vars_with_fresh_vars(&sig);
380 debug!("late-bound lifetimes from method instantiated, method_sig={:?}", method_sig);
382 let method_sig = method_sig.subst(self.tcx, all_substs);
383 debug!("type scheme substituted, method_sig={:?}", method_sig);
385 (method_sig, method_predicates)
391 all_substs: SubstsRef<'tcx>,
392 method_predicates: ty::InstantiatedPredicates<'tcx>,
395 "add_obligations: fty={:?} all_substs={:?} method_predicates={:?}",
396 fty, all_substs, method_predicates
399 self.add_obligations_for_parameters(
400 traits::ObligationCause::misc(self.span, self.body_id),
404 // this is a projection from a trait reference, so we have to
405 // make sure that the trait reference inputs are well-formed.
406 self.add_wf_bounds(all_substs, self.call_expr);
408 // the function type must also be well-formed (this is not
409 // implied by the substs being well-formed because of inherent
410 // impls and late-bound regions - see issue #28609).
411 self.register_wf_obligation(fty.into(), self.span, traits::MiscObligation);
414 ///////////////////////////////////////////////////////////////////////////
417 fn predicates_require_illegal_sized_bound(
419 predicates: &ty::InstantiatedPredicates<'tcx>,
421 let sized_def_id = match self.tcx.lang_items().sized_trait() {
422 Some(def_id) => def_id,
426 traits::elaborate_predicates(self.tcx, predicates.predicates.iter().copied())
427 .filter_map(|obligation| match obligation.predicate.kind() {
428 ty::PredicateKind::Trait(trait_pred, _) if trait_pred.def_id() == sized_def_id => {
429 let span = predicates
432 .zip(predicates.spans.iter())
434 |(p, span)| if *p == obligation.predicate { Some(*span) } else { None },
436 .unwrap_or(rustc_span::DUMMY_SP);
437 Some((trait_pred, span))
441 .find_map(|(trait_pred, span)| match trait_pred.skip_binder().self_ty().kind {
442 ty::Dynamic(..) => Some(span),
447 fn enforce_illegal_method_limitations(&self, pick: &probe::Pick<'_>) {
448 // Disallow calls to the method `drop` defined in the `Drop` trait.
449 match pick.item.container {
450 ty::TraitContainer(trait_def_id) => callee::check_legal_trait_for_method_call(
453 Some(self.self_expr.span),
456 ty::ImplContainer(..) => {}
462 source_trait_ref: ty::PolyTraitRef<'tcx>,
463 target_trait_def_id: DefId,
464 ) -> ty::PolyTraitRef<'tcx> {
465 let upcast_trait_refs =
466 traits::upcast_choices(self.tcx, source_trait_ref, target_trait_def_id);
468 // must be exactly one trait ref or we'd get an ambig error etc
469 if upcast_trait_refs.len() != 1 {
472 "cannot uniquely upcast `{:?}` to `{:?}`: `{:?}`",
479 upcast_trait_refs.into_iter().next().unwrap()
482 fn replace_bound_vars_with_fresh_vars<T>(&self, value: &ty::Binder<T>) -> T
484 T: TypeFoldable<'tcx>,
486 self.fcx.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, value).0