diff options
Diffstat (limited to 'compiler/rustc_hir_analysis/src/coherence/orphan.rs')
| -rw-r--r-- | compiler/rustc_hir_analysis/src/coherence/orphan.rs | 271 |
1 files changed, 211 insertions, 60 deletions
diff --git a/compiler/rustc_hir_analysis/src/coherence/orphan.rs b/compiler/rustc_hir_analysis/src/coherence/orphan.rs index 95b03eb82..1f2de3f21 100644 --- a/compiler/rustc_hir_analysis/src/coherence/orphan.rs +++ b/compiler/rustc_hir_analysis/src/coherence/orphan.rs @@ -8,7 +8,8 @@ use rustc_hir as hir; use rustc_middle::ty::subst::InternalSubsts; use rustc_middle::ty::util::IgnoreRegions; use rustc_middle::ty::{ - self, ImplPolarity, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor, + self, AliasKind, ImplPolarity, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitableExt, + TypeVisitor, }; use rustc_session::lint; use rustc_span::def_id::{DefId, LocalDefId}; @@ -39,25 +40,27 @@ fn do_orphan_check_impl<'tcx>( ) -> Result<(), ErrorGuaranteed> { let trait_def_id = trait_ref.def_id; - let item = tcx.hir().expect_item(def_id); - let hir::ItemKind::Impl(impl_) = item.kind else { - bug!("{:?} is not an impl: {:?}", def_id, item); - }; - let sp = tcx.def_span(def_id); - let tr = impl_.of_trait.as_ref().unwrap(); - - match traits::orphan_check(tcx, item.owner_id.to_def_id()) { + match traits::orphan_check(tcx, def_id.to_def_id()) { Ok(()) => {} - Err(err) => emit_orphan_check_error( - tcx, - sp, - item.span, - tr.path.span, - trait_ref, - impl_.self_ty.span, - &impl_.generics, - err, - )?, + Err(err) => { + let item = tcx.hir().expect_item(def_id); + let hir::ItemKind::Impl(impl_) = item.kind else { + bug!("{:?} is not an impl: {:?}", def_id, item); + }; + let tr = impl_.of_trait.as_ref().unwrap(); + let sp = tcx.def_span(def_id); + + emit_orphan_check_error( + tcx, + sp, + item.span, + tr.path.span, + trait_ref, + impl_.self_ty.span, + &impl_.generics, + err, + )? + } } // In addition to the above rules, we restrict impls of auto traits @@ -86,7 +89,7 @@ fn do_orphan_check_impl<'tcx>( // struct B { } // impl Foo for A { } // impl Foo for B { } - // impl !Send for (A, B) { } + // impl !Foo for (A, B) { } // ``` // // This final impl is legal according to the orphan @@ -99,50 +102,198 @@ fn do_orphan_check_impl<'tcx>( tcx.trait_is_auto(trait_def_id) ); - if tcx.trait_is_auto(trait_def_id) && !trait_def_id.is_local() { + if tcx.trait_is_auto(trait_def_id) { let self_ty = trait_ref.self_ty(); - let opt_self_def_id = match *self_ty.kind() { - ty::Adt(self_def, _) => Some(self_def.did()), - ty::Foreign(did) => Some(did), - _ => None, - }; - let msg = match opt_self_def_id { - // We only want to permit nominal types, but not *all* nominal types. - // They must be local to the current crate, so that people - // can't do `unsafe impl Send for Rc<SomethingLocal>` or - // `impl !Send for Box<SomethingLocalAndSend>`. - Some(self_def_id) => { - if self_def_id.is_local() { - None + // If the impl is in the same crate as the auto-trait, almost anything + // goes. + // + // impl MyAuto for Rc<Something> {} // okay + // impl<T> !MyAuto for *const T {} // okay + // impl<T> MyAuto for T {} // okay + // + // But there is one important exception: implementing for a trait object + // is not allowed. + // + // impl MyAuto for dyn Trait {} // NOT OKAY + // impl<T: ?Sized> MyAuto for T {} // NOT OKAY + // + // With this restriction, it's guaranteed that an auto-trait is + // implemented for a trait object if and only if the auto-trait is one + // of the trait object's trait bounds (or a supertrait of a bound). In + // other words `dyn Trait + AutoTrait` always implements AutoTrait, + // while `dyn Trait` never implements AutoTrait. + // + // This is necessary in order for autotrait bounds on methods of trait + // objects to be sound. + // + // auto trait AutoTrait {} + // + // trait ObjectSafeTrait { + // fn f(&self) where Self: AutoTrait; + // } + // + // We can allow f to be called on `dyn ObjectSafeTrait + AutoTrait`. + // + // If we didn't deny `impl AutoTrait for dyn Trait`, it would be unsound + // for the ObjectSafeTrait shown above to be object safe because someone + // could take some type implementing ObjectSafeTrait but not AutoTrait, + // unsize it to `dyn ObjectSafeTrait`, and call .f() which has no + // concrete implementation (issue #50781). + enum LocalImpl { + Allow, + Disallow { problematic_kind: &'static str }, + } + + // If the auto-trait is from a dependency, it must only be getting + // implemented for a nominal type, and specifically one local to the + // current crate. + // + // impl<T> Sync for MyStruct<T> {} // okay + // + // impl Sync for Rc<MyStruct> {} // NOT OKAY + enum NonlocalImpl { + Allow, + DisallowBecauseNonlocal, + DisallowOther, + } + + // Exhaustive match considering that this logic is essential for + // soundness. + let (local_impl, nonlocal_impl) = match self_ty.kind() { + // struct Struct<T>; + // impl AutoTrait for Struct<Foo> {} + ty::Adt(self_def, _) => ( + LocalImpl::Allow, + if self_def.did().is_local() { + NonlocalImpl::Allow } else { - Some(( - format!( - "cross-crate traits with a default impl, like `{}`, \ - can only be implemented for a struct/enum type \ - defined in the current crate", - tcx.def_path_str(trait_def_id) - ), - "can't implement cross-crate trait for type in another crate", - )) - } + NonlocalImpl::DisallowBecauseNonlocal + }, + ), + + // extern { type OpaqueType; } + // impl AutoTrait for OpaqueType {} + ty::Foreign(did) => ( + LocalImpl::Allow, + if did.is_local() { + NonlocalImpl::Allow + } else { + NonlocalImpl::DisallowBecauseNonlocal + }, + ), + + // impl AutoTrait for dyn Trait {} + ty::Dynamic(..) => ( + LocalImpl::Disallow { problematic_kind: "trait object" }, + NonlocalImpl::DisallowOther, + ), + + // impl<T> AutoTrait for T {} + // impl<T: ?Sized> AutoTrait for T {} + ty::Param(..) => ( + if self_ty.is_sized(tcx, tcx.param_env(def_id)) { + LocalImpl::Allow + } else { + LocalImpl::Disallow { problematic_kind: "generic type" } + }, + NonlocalImpl::DisallowOther, + ), + + // trait Id { type This: ?Sized; } + // impl<T: ?Sized> Id for T { + // type This = T; + // } + // impl<T: ?Sized> AutoTrait for <T as Id>::This {} + ty::Alias(AliasKind::Projection, _) => ( + LocalImpl::Disallow { problematic_kind: "associated type" }, + NonlocalImpl::DisallowOther, + ), + + // type Opaque = impl Trait; + // impl AutoTrait for Opaque {} + ty::Alias(AliasKind::Opaque, _) => ( + LocalImpl::Disallow { problematic_kind: "opaque type" }, + NonlocalImpl::DisallowOther, + ), + + ty::Bool + | ty::Char + | ty::Int(..) + | ty::Uint(..) + | ty::Float(..) + | ty::Str + | ty::Array(..) + | ty::Slice(..) + | ty::RawPtr(..) + | ty::Ref(..) + | ty::FnDef(..) + | ty::FnPtr(..) + | ty::Never + | ty::Tuple(..) => (LocalImpl::Allow, NonlocalImpl::DisallowOther), + + ty::Closure(..) + | ty::Generator(..) + | ty::GeneratorWitness(..) + | ty::GeneratorWitnessMIR(..) + | ty::Bound(..) + | ty::Placeholder(..) + | ty::Infer(..) => { + let sp = tcx.def_span(def_id); + span_bug!(sp, "weird self type for autotrait impl") } - _ => Some(( - format!( - "cross-crate traits with a default impl, like `{}`, can \ - only be implemented for a struct/enum type, not `{}`", - tcx.def_path_str(trait_def_id), - self_ty - ), - "can't implement cross-crate trait with a default impl for \ - non-struct/enum type", - )), + + ty::Error(..) => (LocalImpl::Allow, NonlocalImpl::Allow), }; - if let Some((msg, label)) = msg { - let reported = - struct_span_err!(tcx.sess, sp, E0321, "{}", msg).span_label(sp, label).emit(); - return Err(reported); + if trait_def_id.is_local() { + match local_impl { + LocalImpl::Allow => {} + LocalImpl::Disallow { problematic_kind } => { + let msg = format!( + "traits with a default impl, like `{trait}`, \ + cannot be implemented for {problematic_kind} `{self_ty}`", + trait = tcx.def_path_str(trait_def_id), + ); + let label = format!( + "a trait object implements `{trait}` if and only if `{trait}` \ + is one of the trait object's trait bounds", + trait = tcx.def_path_str(trait_def_id), + ); + let sp = tcx.def_span(def_id); + let reported = + struct_span_err!(tcx.sess, sp, E0321, "{}", msg).note(label).emit(); + return Err(reported); + } + } + } else { + if let Some((msg, label)) = match nonlocal_impl { + NonlocalImpl::Allow => None, + NonlocalImpl::DisallowBecauseNonlocal => Some(( + format!( + "cross-crate traits with a default impl, like `{}`, \ + can only be implemented for a struct/enum type \ + defined in the current crate", + tcx.def_path_str(trait_def_id) + ), + "can't implement cross-crate trait for type in another crate", + )), + NonlocalImpl::DisallowOther => Some(( + format!( + "cross-crate traits with a default impl, like `{}`, can \ + only be implemented for a struct/enum type, not `{}`", + tcx.def_path_str(trait_def_id), + self_ty + ), + "can't implement cross-crate trait with a default impl for \ + non-struct/enum type", + )), + } { + let sp = tcx.def_span(def_id); + let reported = + struct_span_err!(tcx.sess, sp, E0321, "{}", msg).span_label(sp, label).emit(); + return Err(reported); + } } } @@ -381,7 +532,7 @@ fn lint_auto_trait_impl<'tcx>( }), |lint| { let item_span = tcx.def_span(self_type_did); - let self_descr = tcx.def_kind(self_type_did).descr(self_type_did); + let self_descr = tcx.def_descr(self_type_did); match arg { ty::util::NotUniqueParam::DuplicateParam(arg) => { lint.note(&format!("`{}` is mentioned multiple times", arg)); @@ -409,7 +560,7 @@ fn fast_reject_auto_impl<'tcx>(tcx: TyCtxt<'tcx>, trait_def_id: DefId, self_ty: seen: FxHashSet<DefId>, } - impl<'tcx> TypeVisitor<'tcx> for DisableAutoTraitVisitor<'tcx> { + impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for DisableAutoTraitVisitor<'tcx> { type BreakTy = (); fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> { let tcx = self.tcx; |