diff options
Diffstat (limited to 'compiler/rustc_typeck/src/check/method/confirm.rs')
| -rw-r--r-- | compiler/rustc_typeck/src/check/method/confirm.rs | 582 |
1 files changed, 582 insertions, 0 deletions
diff --git a/compiler/rustc_typeck/src/check/method/confirm.rs b/compiler/rustc_typeck/src/check/method/confirm.rs new file mode 100644 index 000000000..2c89b63ae --- /dev/null +++ b/compiler/rustc_typeck/src/check/method/confirm.rs @@ -0,0 +1,582 @@ +use super::{probe, MethodCallee}; + +use crate::astconv::{AstConv, CreateSubstsForGenericArgsCtxt, IsMethodCall}; +use crate::check::{callee, FnCtxt}; +use rustc_hir as hir; +use rustc_hir::def_id::DefId; +use rustc_hir::GenericArg; +use rustc_infer::infer::{self, InferOk}; +use rustc_middle::traits::{ObligationCauseCode, UnifyReceiverContext}; +use rustc_middle::ty::adjustment::{Adjust, Adjustment, PointerCast}; +use rustc_middle::ty::adjustment::{AllowTwoPhase, AutoBorrow, AutoBorrowMutability}; +use rustc_middle::ty::fold::TypeFoldable; +use rustc_middle::ty::subst::{self, Subst, SubstsRef}; +use rustc_middle::ty::{self, GenericParamDefKind, Ty}; +use rustc_span::Span; +use rustc_trait_selection::traits; + +use std::iter; +use std::ops::Deref; + +struct ConfirmContext<'a, 'tcx> { + fcx: &'a FnCtxt<'a, 'tcx>, + span: Span, + self_expr: &'tcx hir::Expr<'tcx>, + call_expr: &'tcx hir::Expr<'tcx>, +} + +impl<'a, 'tcx> Deref for ConfirmContext<'a, 'tcx> { + type Target = FnCtxt<'a, 'tcx>; + fn deref(&self) -> &Self::Target { + self.fcx + } +} + +#[derive(Debug)] +pub struct ConfirmResult<'tcx> { + pub callee: MethodCallee<'tcx>, + pub illegal_sized_bound: Option<Span>, +} + +impl<'a, 'tcx> FnCtxt<'a, 'tcx> { + pub fn confirm_method( + &self, + span: Span, + self_expr: &'tcx hir::Expr<'tcx>, + call_expr: &'tcx hir::Expr<'tcx>, + unadjusted_self_ty: Ty<'tcx>, + pick: probe::Pick<'tcx>, + segment: &hir::PathSegment<'_>, + ) -> ConfirmResult<'tcx> { + debug!( + "confirm(unadjusted_self_ty={:?}, pick={:?}, generic_args={:?})", + unadjusted_self_ty, pick, segment.args, + ); + + let mut confirm_cx = ConfirmContext::new(self, span, self_expr, call_expr); + confirm_cx.confirm(unadjusted_self_ty, pick, segment) + } +} + +impl<'a, 'tcx> ConfirmContext<'a, 'tcx> { + fn new( + fcx: &'a FnCtxt<'a, 'tcx>, + span: Span, + self_expr: &'tcx hir::Expr<'tcx>, + call_expr: &'tcx hir::Expr<'tcx>, + ) -> ConfirmContext<'a, 'tcx> { + ConfirmContext { fcx, span, self_expr, call_expr } + } + + fn confirm( + &mut self, + unadjusted_self_ty: Ty<'tcx>, + pick: probe::Pick<'tcx>, + segment: &hir::PathSegment<'_>, + ) -> ConfirmResult<'tcx> { + // Adjust the self expression the user provided and obtain the adjusted type. + let self_ty = self.adjust_self_ty(unadjusted_self_ty, &pick); + + // Create substitutions for the method's type parameters. + let rcvr_substs = self.fresh_receiver_substs(self_ty, &pick); + let all_substs = self.instantiate_method_substs(&pick, segment, rcvr_substs); + + debug!("rcvr_substs={rcvr_substs:?}, all_substs={all_substs:?}"); + + // Create the final signature for the method, replacing late-bound regions. + let (method_sig, method_predicates) = self.instantiate_method_sig(&pick, all_substs); + + // If there is a `Self: Sized` bound and `Self` is a trait object, it is possible that + // something which derefs to `Self` actually implements the trait and the caller + // wanted to make a static dispatch on it but forgot to import the trait. + // See test `src/test/ui/issue-35976.rs`. + // + // In that case, we'll error anyway, but we'll also re-run the search with all traits + // in scope, and if we find another method which can be used, we'll output an + // appropriate hint suggesting to import the trait. + let filler_substs = rcvr_substs + .extend_to(self.tcx, pick.item.def_id, |def, _| self.tcx.mk_param_from_def(def)); + let illegal_sized_bound = self.predicates_require_illegal_sized_bound( + &self.tcx.predicates_of(pick.item.def_id).instantiate(self.tcx, filler_substs), + ); + + // Unify the (adjusted) self type with what the method expects. + // + // SUBTLE: if we want good error messages, because of "guessing" while matching + // traits, no trait system method can be called before this point because they + // could alter our Self-type, except for normalizing the receiver from the + // signature (which is also done during probing). + let method_sig_rcvr = self.normalize_associated_types_in(self.span, method_sig.inputs()[0]); + debug!( + "confirm: self_ty={:?} method_sig_rcvr={:?} method_sig={:?} method_predicates={:?}", + self_ty, method_sig_rcvr, method_sig, method_predicates + ); + self.unify_receivers(self_ty, method_sig_rcvr, &pick, all_substs); + + let (method_sig, method_predicates) = + self.normalize_associated_types_in(self.span, (method_sig, method_predicates)); + let method_sig = ty::Binder::dummy(method_sig); + + // Make sure nobody calls `drop()` explicitly. + self.enforce_illegal_method_limitations(&pick); + + // Add any trait/regions obligations specified on the method's type parameters. + // We won't add these if we encountered an illegal sized bound, so that we can use + // a custom error in that case. + if illegal_sized_bound.is_none() { + self.add_obligations( + self.tcx.mk_fn_ptr(method_sig), + all_substs, + method_predicates, + pick.item.def_id, + ); + } + + // Create the final `MethodCallee`. + let callee = MethodCallee { + def_id: pick.item.def_id, + substs: all_substs, + sig: method_sig.skip_binder(), + }; + ConfirmResult { callee, illegal_sized_bound } + } + + /////////////////////////////////////////////////////////////////////////// + // ADJUSTMENTS + + fn adjust_self_ty( + &mut self, + unadjusted_self_ty: Ty<'tcx>, + pick: &probe::Pick<'tcx>, + ) -> Ty<'tcx> { + // Commit the autoderefs by calling `autoderef` again, but this + // time writing the results into the various typeck results. + let mut autoderef = + self.autoderef_overloaded_span(self.span, unadjusted_self_ty, self.call_expr.span); + let Some((ty, n)) = autoderef.nth(pick.autoderefs) else { + return self.tcx.ty_error_with_message( + rustc_span::DUMMY_SP, + &format!("failed autoderef {}", pick.autoderefs), + ); + }; + assert_eq!(n, pick.autoderefs); + + let mut adjustments = self.adjust_steps(&autoderef); + let mut target = self.structurally_resolved_type(autoderef.span(), ty); + + match pick.autoref_or_ptr_adjustment { + Some(probe::AutorefOrPtrAdjustment::Autoref { mutbl, unsize }) => { + let region = self.next_region_var(infer::Autoref(self.span)); + // Type we're wrapping in a reference, used later for unsizing + let base_ty = target; + + target = self.tcx.mk_ref(region, ty::TypeAndMut { mutbl, ty: target }); + let mutbl = match mutbl { + hir::Mutability::Not => AutoBorrowMutability::Not, + hir::Mutability::Mut => AutoBorrowMutability::Mut { + // Method call receivers are the primary use case + // for two-phase borrows. + allow_two_phase_borrow: AllowTwoPhase::Yes, + }, + }; + adjustments.push(Adjustment { + kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)), + target, + }); + + if unsize { + let unsized_ty = if let ty::Array(elem_ty, _) = base_ty.kind() { + self.tcx.mk_slice(*elem_ty) + } else { + bug!( + "AutorefOrPtrAdjustment's unsize flag should only be set for array ty, found {}", + base_ty + ) + }; + target = self + .tcx + .mk_ref(region, ty::TypeAndMut { mutbl: mutbl.into(), ty: unsized_ty }); + adjustments + .push(Adjustment { kind: Adjust::Pointer(PointerCast::Unsize), target }); + } + } + Some(probe::AutorefOrPtrAdjustment::ToConstPtr) => { + target = match target.kind() { + &ty::RawPtr(ty::TypeAndMut { ty, mutbl }) => { + assert_eq!(mutbl, hir::Mutability::Mut); + self.tcx.mk_ptr(ty::TypeAndMut { mutbl: hir::Mutability::Not, ty }) + } + other => panic!("Cannot adjust receiver type {:?} to const ptr", other), + }; + + adjustments.push(Adjustment { + kind: Adjust::Pointer(PointerCast::MutToConstPointer), + target, + }); + } + None => {} + } + + self.register_predicates(autoderef.into_obligations()); + + // Write out the final adjustments. + self.apply_adjustments(self.self_expr, adjustments); + + target + } + + /// Returns a set of substitutions for the method *receiver* where all type and region + /// parameters are instantiated with fresh variables. This substitution does not include any + /// parameters declared on the method itself. + /// + /// Note that this substitution may include late-bound regions from the impl level. If so, + /// these are instantiated later in the `instantiate_method_sig` routine. + fn fresh_receiver_substs( + &mut self, + self_ty: Ty<'tcx>, + pick: &probe::Pick<'tcx>, + ) -> SubstsRef<'tcx> { + match pick.kind { + probe::InherentImplPick => { + let impl_def_id = pick.item.container_id(self.tcx); + assert!( + self.tcx.impl_trait_ref(impl_def_id).is_none(), + "impl {:?} is not an inherent impl", + impl_def_id + ); + self.fresh_substs_for_item(self.span, impl_def_id) + } + + probe::ObjectPick => { + let trait_def_id = pick.item.container_id(self.tcx); + self.extract_existential_trait_ref(self_ty, |this, object_ty, principal| { + // The object data has no entry for the Self + // Type. For the purposes of this method call, we + // substitute the object type itself. This + // wouldn't be a sound substitution in all cases, + // since each instance of the object type is a + // different existential and hence could match + // distinct types (e.g., if `Self` appeared as an + // argument type), but those cases have already + // been ruled out when we deemed the trait to be + // "object safe". + let original_poly_trait_ref = principal.with_self_ty(this.tcx, object_ty); + let upcast_poly_trait_ref = this.upcast(original_poly_trait_ref, trait_def_id); + let upcast_trait_ref = + this.replace_bound_vars_with_fresh_vars(upcast_poly_trait_ref); + debug!( + "original_poly_trait_ref={:?} upcast_trait_ref={:?} target_trait={:?}", + original_poly_trait_ref, upcast_trait_ref, trait_def_id + ); + upcast_trait_ref.substs + }) + } + + probe::TraitPick => { + let trait_def_id = pick.item.container_id(self.tcx); + + // Make a trait reference `$0 : Trait<$1...$n>` + // consisting entirely of type variables. Later on in + // the process we will unify the transformed-self-type + // of the method with the actual type in order to + // unify some of these variables. + self.fresh_substs_for_item(self.span, trait_def_id) + } + + probe::WhereClausePick(poly_trait_ref) => { + // Where clauses can have bound regions in them. We need to instantiate + // those to convert from a poly-trait-ref to a trait-ref. + self.replace_bound_vars_with_fresh_vars(poly_trait_ref).substs + } + } + } + + fn extract_existential_trait_ref<R, F>(&mut self, self_ty: Ty<'tcx>, mut closure: F) -> R + where + F: FnMut(&mut ConfirmContext<'a, 'tcx>, Ty<'tcx>, ty::PolyExistentialTraitRef<'tcx>) -> R, + { + // If we specified that this is an object method, then the + // self-type ought to be something that can be dereferenced to + // yield an object-type (e.g., `&Object` or `Box<Object>` + // etc). + + // FIXME: this feels, like, super dubious + self.fcx + .autoderef(self.span, self_ty) + .include_raw_pointers() + .find_map(|(ty, _)| match ty.kind() { + ty::Dynamic(data, ..) => Some(closure( + self, + ty, + data.principal().unwrap_or_else(|| { + span_bug!(self.span, "calling trait method on empty object?") + }), + )), + _ => None, + }) + .unwrap_or_else(|| { + span_bug!( + self.span, + "self-type `{}` for ObjectPick never dereferenced to an object", + self_ty + ) + }) + } + + fn instantiate_method_substs( + &mut self, + pick: &probe::Pick<'tcx>, + seg: &hir::PathSegment<'_>, + parent_substs: SubstsRef<'tcx>, + ) -> SubstsRef<'tcx> { + // Determine the values for the generic parameters of the method. + // If they were not explicitly supplied, just construct fresh + // variables. + let generics = self.tcx.generics_of(pick.item.def_id); + + let arg_count_correct = <dyn AstConv<'_>>::check_generic_arg_count_for_call( + self.tcx, + self.span, + pick.item.def_id, + generics, + seg, + IsMethodCall::Yes, + ); + + // Create subst for early-bound lifetime parameters, combining + // parameters from the type and those from the method. + assert_eq!(generics.parent_count, parent_substs.len()); + + struct MethodSubstsCtxt<'a, 'tcx> { + cfcx: &'a ConfirmContext<'a, 'tcx>, + pick: &'a probe::Pick<'tcx>, + seg: &'a hir::PathSegment<'a>, + } + impl<'a, 'tcx> CreateSubstsForGenericArgsCtxt<'a, 'tcx> for MethodSubstsCtxt<'a, 'tcx> { + fn args_for_def_id( + &mut self, + def_id: DefId, + ) -> (Option<&'a hir::GenericArgs<'a>>, bool) { + if def_id == self.pick.item.def_id { + if let Some(data) = self.seg.args { + return (Some(data), false); + } + } + (None, false) + } + + fn provided_kind( + &mut self, + param: &ty::GenericParamDef, + arg: &GenericArg<'_>, + ) -> subst::GenericArg<'tcx> { + match (¶m.kind, arg) { + (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => { + <dyn AstConv<'_>>::ast_region_to_region(self.cfcx.fcx, lt, Some(param)) + .into() + } + (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => { + self.cfcx.to_ty(ty).into() + } + (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => { + self.cfcx.const_arg_to_const(&ct.value, param.def_id).into() + } + (GenericParamDefKind::Type { .. }, GenericArg::Infer(inf)) => { + self.cfcx.ty_infer(Some(param), inf.span).into() + } + (GenericParamDefKind::Const { .. }, GenericArg::Infer(inf)) => { + let tcx = self.cfcx.tcx(); + self.cfcx.ct_infer(tcx.type_of(param.def_id), Some(param), inf.span).into() + } + _ => unreachable!(), + } + } + + fn inferred_kind( + &mut self, + _substs: Option<&[subst::GenericArg<'tcx>]>, + param: &ty::GenericParamDef, + _infer_args: bool, + ) -> subst::GenericArg<'tcx> { + self.cfcx.var_for_def(self.cfcx.span, param) + } + } + <dyn AstConv<'_>>::create_substs_for_generic_args( + self.tcx, + pick.item.def_id, + parent_substs, + false, + None, + &arg_count_correct, + &mut MethodSubstsCtxt { cfcx: self, pick, seg }, + ) + } + + fn unify_receivers( + &mut self, + self_ty: Ty<'tcx>, + method_self_ty: Ty<'tcx>, + pick: &probe::Pick<'tcx>, + substs: SubstsRef<'tcx>, + ) { + debug!( + "unify_receivers: self_ty={:?} method_self_ty={:?} span={:?} pick={:?}", + self_ty, method_self_ty, self.span, pick + ); + let cause = self.cause( + self.span, + ObligationCauseCode::UnifyReceiver(Box::new(UnifyReceiverContext { + assoc_item: pick.item, + param_env: self.param_env, + substs, + })), + ); + match self.at(&cause, self.param_env).sup(method_self_ty, self_ty) { + Ok(InferOk { obligations, value: () }) => { + self.register_predicates(obligations); + } + Err(_) => { + span_bug!( + self.span, + "{} was a subtype of {} but now is not?", + self_ty, + method_self_ty + ); + } + } + } + + // NOTE: this returns the *unnormalized* predicates and method sig. Because of + // inference guessing, the predicates and method signature can't be normalized + // until we unify the `Self` type. + fn instantiate_method_sig( + &mut self, + pick: &probe::Pick<'tcx>, + all_substs: SubstsRef<'tcx>, + ) -> (ty::FnSig<'tcx>, ty::InstantiatedPredicates<'tcx>) { + debug!("instantiate_method_sig(pick={:?}, all_substs={:?})", pick, all_substs); + + // Instantiate the bounds on the method with the + // type/early-bound-regions substitutions performed. There can + // be no late-bound regions appearing here. + let def_id = pick.item.def_id; + let method_predicates = self.tcx.predicates_of(def_id).instantiate(self.tcx, all_substs); + + debug!("method_predicates after subst = {:?}", method_predicates); + + let sig = self.tcx.bound_fn_sig(def_id); + + let sig = sig.subst(self.tcx, all_substs); + debug!("type scheme substituted, sig={:?}", sig); + + let sig = self.replace_bound_vars_with_fresh_vars(sig); + debug!("late-bound lifetimes from method instantiated, sig={:?}", sig); + + (sig, method_predicates) + } + + fn add_obligations( + &mut self, + fty: Ty<'tcx>, + all_substs: SubstsRef<'tcx>, + method_predicates: ty::InstantiatedPredicates<'tcx>, + def_id: DefId, + ) { + debug!( + "add_obligations: fty={:?} all_substs={:?} method_predicates={:?} def_id={:?}", + fty, all_substs, method_predicates, def_id + ); + + // FIXME: could replace with the following, but we already calculated `method_predicates`, + // so we just call `predicates_for_generics` directly to avoid redoing work. + // `self.add_required_obligations(self.span, def_id, &all_substs);` + for obligation in traits::predicates_for_generics( + traits::ObligationCause::new(self.span, self.body_id, traits::ItemObligation(def_id)), + self.param_env, + method_predicates, + ) { + self.register_predicate(obligation); + } + + // this is a projection from a trait reference, so we have to + // make sure that the trait reference inputs are well-formed. + self.add_wf_bounds(all_substs, self.call_expr); + + // the function type must also be well-formed (this is not + // implied by the substs being well-formed because of inherent + // impls and late-bound regions - see issue #28609). + self.register_wf_obligation(fty.into(), self.span, traits::WellFormed(None)); + } + + /////////////////////////////////////////////////////////////////////////// + // MISCELLANY + + fn predicates_require_illegal_sized_bound( + &self, + predicates: &ty::InstantiatedPredicates<'tcx>, + ) -> Option<Span> { + let sized_def_id = self.tcx.lang_items().sized_trait()?; + + traits::elaborate_predicates(self.tcx, predicates.predicates.iter().copied()) + // We don't care about regions here. + .filter_map(|obligation| match obligation.predicate.kind().skip_binder() { + ty::PredicateKind::Trait(trait_pred) if trait_pred.def_id() == sized_def_id => { + let span = iter::zip(&predicates.predicates, &predicates.spans) + .find_map( + |(p, span)| { + if *p == obligation.predicate { Some(*span) } else { None } + }, + ) + .unwrap_or(rustc_span::DUMMY_SP); + Some((trait_pred, span)) + } + _ => None, + }) + .find_map(|(trait_pred, span)| match trait_pred.self_ty().kind() { + ty::Dynamic(..) => Some(span), + _ => None, + }) + } + + fn enforce_illegal_method_limitations(&self, pick: &probe::Pick<'_>) { + // Disallow calls to the method `drop` defined in the `Drop` trait. + if let Some(trait_def_id) = pick.item.trait_container(self.tcx) { + callee::check_legal_trait_for_method_call( + self.tcx, + self.span, + Some(self.self_expr.span), + self.call_expr.span, + trait_def_id, + ) + } + } + + fn upcast( + &mut self, + source_trait_ref: ty::PolyTraitRef<'tcx>, + target_trait_def_id: DefId, + ) -> ty::PolyTraitRef<'tcx> { + let upcast_trait_refs = + traits::upcast_choices(self.tcx, source_trait_ref, target_trait_def_id); + + // must be exactly one trait ref or we'd get an ambig error etc + if upcast_trait_refs.len() != 1 { + span_bug!( + self.span, + "cannot uniquely upcast `{:?}` to `{:?}`: `{:?}`", + source_trait_ref, + target_trait_def_id, + upcast_trait_refs + ); + } + + upcast_trait_refs.into_iter().next().unwrap() + } + + fn replace_bound_vars_with_fresh_vars<T>(&self, value: ty::Binder<'tcx, T>) -> T + where + T: TypeFoldable<'tcx> + Copy, + { + self.fcx.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, value) + } +} |