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::traits::{ObligationCauseCode, UnifyReceiverContext};
10 use rustc_middle::ty::adjustment::{Adjust, Adjustment, PointerCast};
11 use rustc_middle::ty::adjustment::{AllowTwoPhase, AutoBorrow, AutoBorrowMutability};
12 use rustc_middle::ty::fold::TypeFoldable;
13 use rustc_middle::ty::subst::{Subst, SubstsRef};
14 use rustc_middle::ty::{self, GenericParamDefKind, Ty};
16 use rustc_trait_selection::traits;
20 struct ConfirmContext<'a, 'tcx> {
21 fcx: &'a FnCtxt<'a, 'tcx>,
23 self_expr: &'tcx hir::Expr<'tcx>,
24 call_expr: &'tcx hir::Expr<'tcx>,
27 impl<'a, 'tcx> Deref for ConfirmContext<'a, 'tcx> {
28 type Target = FnCtxt<'a, 'tcx>;
29 fn deref(&self) -> &Self::Target {
34 pub struct ConfirmResult<'tcx> {
35 pub callee: MethodCallee<'tcx>,
36 pub illegal_sized_bound: Option<Span>,
39 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
40 pub fn confirm_method(
43 self_expr: &'tcx hir::Expr<'tcx>,
44 call_expr: &'tcx hir::Expr<'tcx>,
45 unadjusted_self_ty: Ty<'tcx>,
46 pick: probe::Pick<'tcx>,
47 segment: &hir::PathSegment<'_>,
48 ) -> ConfirmResult<'tcx> {
50 "confirm(unadjusted_self_ty={:?}, pick={:?}, generic_args={:?})",
51 unadjusted_self_ty, pick, segment.args,
54 let mut confirm_cx = ConfirmContext::new(self, span, self_expr, call_expr);
55 confirm_cx.confirm(unadjusted_self_ty, pick, segment)
59 impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
61 fcx: &'a FnCtxt<'a, 'tcx>,
63 self_expr: &'tcx hir::Expr<'tcx>,
64 call_expr: &'tcx hir::Expr<'tcx>,
65 ) -> ConfirmContext<'a, 'tcx> {
66 ConfirmContext { fcx, span, self_expr, call_expr }
71 unadjusted_self_ty: Ty<'tcx>,
72 pick: probe::Pick<'tcx>,
73 segment: &hir::PathSegment<'_>,
74 ) -> ConfirmResult<'tcx> {
75 // Adjust the self expression the user provided and obtain the adjusted type.
76 let self_ty = self.adjust_self_ty(unadjusted_self_ty, &pick);
78 // Create substitutions for the method's type parameters.
79 let rcvr_substs = self.fresh_receiver_substs(self_ty, &pick);
80 let all_substs = self.instantiate_method_substs(&pick, segment, rcvr_substs);
82 debug!("all_substs={:?}", all_substs);
84 // Create the final signature for the method, replacing late-bound regions.
85 let (method_sig, method_predicates) = self.instantiate_method_sig(&pick, all_substs);
87 // Unify the (adjusted) self type with what the method expects.
89 // SUBTLE: if we want good error messages, because of "guessing" while matching
90 // traits, no trait system method can be called before this point because they
91 // could alter our Self-type, except for normalizing the receiver from the
92 // signature (which is also done during probing).
94 self.normalize_associated_types_in(self.span, &method_sig.inputs()[0]);
96 "confirm: self_ty={:?} method_sig_rcvr={:?} method_sig={:?} method_predicates={:?}",
97 self_ty, method_sig_rcvr, method_sig, method_predicates
99 self.unify_receivers(self_ty, method_sig_rcvr, &pick, all_substs);
101 let (method_sig, method_predicates) =
102 self.normalize_associated_types_in(self.span, &(method_sig, method_predicates));
104 // Make sure nobody calls `drop()` explicitly.
105 self.enforce_illegal_method_limitations(&pick);
107 // If there is a `Self: Sized` bound and `Self` is a trait object, it is possible that
108 // something which derefs to `Self` actually implements the trait and the caller
109 // wanted to make a static dispatch on it but forgot to import the trait.
110 // See test `src/test/ui/issue-35976.rs`.
112 // In that case, we'll error anyway, but we'll also re-run the search with all traits
113 // in scope, and if we find another method which can be used, we'll output an
114 // appropriate hint suggesting to import the trait.
115 let illegal_sized_bound = self.predicates_require_illegal_sized_bound(&method_predicates);
117 // Add any trait/regions obligations specified on the method's type parameters.
118 // We won't add these if we encountered an illegal sized bound, so that we can use
119 // a custom error in that case.
120 if illegal_sized_bound.is_none() {
121 let method_ty = self.tcx.mk_fn_ptr(ty::Binder::bind(method_sig));
122 self.add_obligations(method_ty, all_substs, method_predicates);
125 // Create the final `MethodCallee`.
126 let callee = MethodCallee { def_id: pick.item.def_id, substs: all_substs, sig: method_sig };
127 ConfirmResult { callee, illegal_sized_bound }
130 ///////////////////////////////////////////////////////////////////////////
135 unadjusted_self_ty: Ty<'tcx>,
136 pick: &probe::Pick<'tcx>,
138 // Commit the autoderefs by calling `autoderef` again, but this
139 // time writing the results into the various typeck results.
140 let mut autoderef = self.autoderef(self.span, unadjusted_self_ty);
141 let (_, n) = match autoderef.nth(pick.autoderefs) {
144 return self.tcx.ty_error_with_message(
145 rustc_span::DUMMY_SP,
146 &format!("failed autoderef {}", pick.autoderefs),
150 assert_eq!(n, pick.autoderefs);
152 let mut adjustments = self.adjust_steps(&autoderef);
155 self.structurally_resolved_type(autoderef.span(), autoderef.final_ty(false));
157 if let Some(mutbl) = pick.autoref {
158 let region = self.next_region_var(infer::Autoref(self.span, pick.item));
159 target = self.tcx.mk_ref(region, ty::TypeAndMut { mutbl, ty: target });
160 let mutbl = match mutbl {
161 hir::Mutability::Not => AutoBorrowMutability::Not,
162 hir::Mutability::Mut => AutoBorrowMutability::Mut {
163 // Method call receivers are the primary use case
164 // for two-phase borrows.
165 allow_two_phase_borrow: AllowTwoPhase::Yes,
169 .push(Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)), target });
171 if let Some(unsize_target) = pick.unsize {
174 .mk_ref(region, ty::TypeAndMut { mutbl: mutbl.into(), ty: unsize_target });
175 adjustments.push(Adjustment { kind: Adjust::Pointer(PointerCast::Unsize), target });
178 // No unsizing should be performed without autoref (at
179 // least during method dispach). This is because we
180 // currently only unsize `[T;N]` to `[T]`, and naturally
181 // that must occur being a reference.
182 assert!(pick.unsize.is_none());
185 self.register_predicates(autoderef.into_obligations());
187 // Write out the final adjustments.
188 self.apply_adjustments(self.self_expr, adjustments);
193 /// Returns a set of substitutions for the method *receiver* where all type and region
194 /// parameters are instantiated with fresh variables. This substitution does not include any
195 /// parameters declared on the method itself.
197 /// Note that this substitution may include late-bound regions from the impl level. If so,
198 /// these are instantiated later in the `instantiate_method_sig` routine.
199 fn fresh_receiver_substs(
202 pick: &probe::Pick<'tcx>,
203 ) -> SubstsRef<'tcx> {
205 probe::InherentImplPick => {
206 let impl_def_id = pick.item.container.id();
208 self.tcx.impl_trait_ref(impl_def_id).is_none(),
209 "impl {:?} is not an inherent impl",
212 self.fresh_substs_for_item(self.span, impl_def_id)
215 probe::ObjectPick => {
216 let trait_def_id = pick.item.container.id();
217 self.extract_existential_trait_ref(self_ty, |this, object_ty, principal| {
218 // The object data has no entry for the Self
219 // Type. For the purposes of this method call, we
220 // substitute the object type itself. This
221 // wouldn't be a sound substitution in all cases,
222 // since each instance of the object type is a
223 // different existential and hence could match
224 // distinct types (e.g., if `Self` appeared as an
225 // argument type), but those cases have already
226 // been ruled out when we deemed the trait to be
228 let original_poly_trait_ref = principal.with_self_ty(this.tcx, object_ty);
229 let upcast_poly_trait_ref = this.upcast(original_poly_trait_ref, trait_def_id);
230 let upcast_trait_ref =
231 this.replace_bound_vars_with_fresh_vars(&upcast_poly_trait_ref);
233 "original_poly_trait_ref={:?} upcast_trait_ref={:?} target_trait={:?}",
234 original_poly_trait_ref, upcast_trait_ref, trait_def_id
236 upcast_trait_ref.substs
240 probe::TraitPick => {
241 let trait_def_id = pick.item.container.id();
243 // Make a trait reference `$0 : Trait<$1...$n>`
244 // consisting entirely of type variables. Later on in
245 // the process we will unify the transformed-self-type
246 // of the method with the actual type in order to
247 // unify some of these variables.
248 self.fresh_substs_for_item(self.span, trait_def_id)
251 probe::WhereClausePick(ref poly_trait_ref) => {
252 // Where clauses can have bound regions in them. We need to instantiate
253 // those to convert from a poly-trait-ref to a trait-ref.
254 self.replace_bound_vars_with_fresh_vars(&poly_trait_ref).substs
259 fn extract_existential_trait_ref<R, F>(&mut self, self_ty: Ty<'tcx>, mut closure: F) -> R
261 F: FnMut(&mut ConfirmContext<'a, 'tcx>, Ty<'tcx>, ty::PolyExistentialTraitRef<'tcx>) -> R,
263 // If we specified that this is an object method, then the
264 // self-type ought to be something that can be dereferenced to
265 // yield an object-type (e.g., `&Object` or `Box<Object>`
268 // FIXME: this feels, like, super dubious
270 .autoderef(self.span, self_ty)
271 .include_raw_pointers()
272 .find_map(|(ty, _)| match ty.kind {
273 ty::Dynamic(ref data, ..) => Some(closure(
276 data.principal().unwrap_or_else(|| {
277 span_bug!(self.span, "calling trait method on empty object?")
285 "self-type `{}` for ObjectPick never dereferenced to an object",
291 fn instantiate_method_substs(
293 pick: &probe::Pick<'tcx>,
294 seg: &hir::PathSegment<'_>,
295 parent_substs: SubstsRef<'tcx>,
296 ) -> SubstsRef<'tcx> {
297 // Determine the values for the generic parameters of the method.
298 // If they were not explicitly supplied, just construct fresh
300 let generics = self.tcx.generics_of(pick.item.def_id);
301 let arg_count_correct = AstConv::check_generic_arg_count_for_call(
302 self.tcx, self.span, &generics, &seg, true, // `is_method_call`
305 // Create subst for early-bound lifetime parameters, combining
306 // parameters from the type and those from the method.
307 assert_eq!(generics.parent_count, parent_substs.len());
309 AstConv::create_substs_for_generic_args(
316 // Provide the generic args, and whether types should be inferred.
318 // The last component of the returned tuple here is unimportant.
319 if def_id == pick.item.def_id {
320 if let Some(ref data) = seg.args {
321 return (Some(data), false);
326 // Provide substitutions for parameters for which (valid) arguments have been provided.
327 |param, arg| match (¶m.kind, arg) {
328 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
329 AstConv::ast_region_to_region(self.fcx, lt, Some(param)).into()
331 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => self.to_ty(ty).into(),
332 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
333 self.const_arg_to_const(&ct.value, param.def_id).into()
337 // Provide substitutions for parameters for which arguments are inferred.
338 |_, param, _| self.var_for_def(self.span, param),
345 method_self_ty: Ty<'tcx>,
346 pick: &probe::Pick<'tcx>,
347 substs: SubstsRef<'tcx>,
350 "unify_receivers: self_ty={:?} method_self_ty={:?} span={:?} pick={:?}",
351 self_ty, method_self_ty, self.span, pick
353 let cause = self.cause(
355 ObligationCauseCode::UnifyReceiver(Box::new(UnifyReceiverContext {
356 assoc_item: pick.item,
357 param_env: self.param_env,
361 match self.at(&cause, self.param_env).sup(method_self_ty, self_ty) {
362 Ok(InferOk { obligations, value: () }) => {
363 self.register_predicates(obligations);
368 "{} was a subtype of {} but now is not?",
376 // NOTE: this returns the *unnormalized* predicates and method sig. Because of
377 // inference guessing, the predicates and method signature can't be normalized
378 // until we unify the `Self` type.
379 fn instantiate_method_sig(
381 pick: &probe::Pick<'tcx>,
382 all_substs: SubstsRef<'tcx>,
383 ) -> (ty::FnSig<'tcx>, ty::InstantiatedPredicates<'tcx>) {
384 debug!("instantiate_method_sig(pick={:?}, all_substs={:?})", pick, all_substs);
386 // Instantiate the bounds on the method with the
387 // type/early-bound-regions substitutions performed. There can
388 // be no late-bound regions appearing here.
389 let def_id = pick.item.def_id;
390 let method_predicates = self.tcx.predicates_of(def_id).instantiate(self.tcx, all_substs);
392 debug!("method_predicates after subst = {:?}", method_predicates);
394 let sig = self.tcx.fn_sig(def_id);
396 // Instantiate late-bound regions and substitute the trait
397 // parameters into the method type to get the actual method type.
399 // N.B., instantiate late-bound regions first so that
400 // `instantiate_type_scheme` can normalize associated types that
401 // may reference those regions.
402 let method_sig = self.replace_bound_vars_with_fresh_vars(&sig);
403 debug!("late-bound lifetimes from method instantiated, method_sig={:?}", method_sig);
405 let method_sig = method_sig.subst(self.tcx, all_substs);
406 debug!("type scheme substituted, method_sig={:?}", method_sig);
408 (method_sig, method_predicates)
414 all_substs: SubstsRef<'tcx>,
415 method_predicates: ty::InstantiatedPredicates<'tcx>,
418 "add_obligations: fty={:?} all_substs={:?} method_predicates={:?}",
419 fty, all_substs, method_predicates
422 self.add_obligations_for_parameters(
423 traits::ObligationCause::misc(self.span, self.body_id),
427 // this is a projection from a trait reference, so we have to
428 // make sure that the trait reference inputs are well-formed.
429 self.add_wf_bounds(all_substs, self.call_expr);
431 // the function type must also be well-formed (this is not
432 // implied by the substs being well-formed because of inherent
433 // impls and late-bound regions - see issue #28609).
434 self.register_wf_obligation(fty.into(), self.span, traits::MiscObligation);
437 ///////////////////////////////////////////////////////////////////////////
440 fn predicates_require_illegal_sized_bound(
442 predicates: &ty::InstantiatedPredicates<'tcx>,
444 let sized_def_id = match self.tcx.lang_items().sized_trait() {
445 Some(def_id) => def_id,
449 traits::elaborate_predicates(self.tcx, predicates.predicates.iter().copied())
450 .filter_map(|obligation| match obligation.predicate.kind() {
451 ty::PredicateKind::Trait(trait_pred, _) if trait_pred.def_id() == sized_def_id => {
452 let span = predicates
455 .zip(predicates.spans.iter())
457 |(p, span)| if *p == obligation.predicate { Some(*span) } else { None },
459 .unwrap_or(rustc_span::DUMMY_SP);
460 Some((trait_pred, span))
464 .find_map(|(trait_pred, span)| match trait_pred.skip_binder().self_ty().kind {
465 ty::Dynamic(..) => Some(span),
470 fn enforce_illegal_method_limitations(&self, pick: &probe::Pick<'_>) {
471 // Disallow calls to the method `drop` defined in the `Drop` trait.
472 match pick.item.container {
473 ty::TraitContainer(trait_def_id) => callee::check_legal_trait_for_method_call(
476 Some(self.self_expr.span),
479 ty::ImplContainer(..) => {}
485 source_trait_ref: ty::PolyTraitRef<'tcx>,
486 target_trait_def_id: DefId,
487 ) -> ty::PolyTraitRef<'tcx> {
488 let upcast_trait_refs =
489 traits::upcast_choices(self.tcx, source_trait_ref, target_trait_def_id);
491 // must be exactly one trait ref or we'd get an ambig error etc
492 if upcast_trait_refs.len() != 1 {
495 "cannot uniquely upcast `{:?}` to `{:?}`: `{:?}`",
502 upcast_trait_refs.into_iter().next().unwrap()
505 fn replace_bound_vars_with_fresh_vars<T>(&self, value: &ty::Binder<T>) -> T
507 T: TypeFoldable<'tcx>,
509 self.fcx.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, value).0