| //! Orphan checker: every impl either implements a trait defined in this |
| //! crate or pertains to a type defined in this crate. |
| |
| use rustc_data_structures::fx::FxHashSet; |
| use rustc_errors::{struct_span_err, DelayDm}; |
| use rustc_errors::{Diagnostic, ErrorGuaranteed}; |
| 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, |
| }; |
| use rustc_session::lint; |
| use rustc_span::def_id::{DefId, LocalDefId}; |
| use rustc_span::Span; |
| use rustc_trait_selection::traits; |
| use std::ops::ControlFlow; |
| |
| #[instrument(skip(tcx), level = "debug")] |
| pub(crate) fn orphan_check_impl( |
| tcx: TyCtxt<'_>, |
| impl_def_id: LocalDefId, |
| ) -> Result<(), ErrorGuaranteed> { |
| let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap(); |
| trait_ref.error_reported()?; |
| |
| let ret = do_orphan_check_impl(tcx, trait_ref, impl_def_id); |
| if tcx.trait_is_auto(trait_ref.def_id) { |
| lint_auto_trait_impl(tcx, trait_ref, impl_def_id); |
| } |
| |
| ret |
| } |
| |
| fn do_orphan_check_impl<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| trait_ref: ty::TraitRef<'tcx>, |
| def_id: LocalDefId, |
| ) -> Result<(), ErrorGuaranteed> { |
| let trait_def_id = trait_ref.def_id; |
| |
| let item = tcx.hir().expect_item(def_id); |
| let hir::ItemKind::Impl(ref 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()) { |
| Ok(()) => {} |
| Err(err) => emit_orphan_check_error( |
| tcx, |
| sp, |
| item.span, |
| tr.path.span, |
| trait_ref.self_ty(), |
| impl_.self_ty.span, |
| &impl_.generics, |
| err, |
| )?, |
| } |
| |
| // In addition to the above rules, we restrict impls of auto traits |
| // so that they can only be implemented on nominal types, such as structs, |
| // enums or foreign types. To see why this restriction exists, consider the |
| // following example (#22978). Imagine that crate A defines an auto trait |
| // `Foo` and a fn that operates on pairs of types: |
| // |
| // ``` |
| // // Crate A |
| // auto trait Foo { } |
| // fn two_foos<A:Foo,B:Foo>(..) { |
| // one_foo::<(A,B)>(..) |
| // } |
| // fn one_foo<T:Foo>(..) { .. } |
| // ``` |
| // |
| // This type-checks fine; in particular the fn |
| // `two_foos` is able to conclude that `(A,B):Foo` |
| // because `A:Foo` and `B:Foo`. |
| // |
| // Now imagine that crate B comes along and does the following: |
| // |
| // ``` |
| // struct A { } |
| // struct B { } |
| // impl Foo for A { } |
| // impl Foo for B { } |
| // impl !Send for (A, B) { } |
| // ``` |
| // |
| // This final impl is legal according to the orphan |
| // rules, but it invalidates the reasoning from |
| // `two_foos` above. |
| debug!( |
| "trait_ref={:?} trait_def_id={:?} trait_is_auto={}", |
| trait_ref, |
| trait_def_id, |
| tcx.trait_is_auto(trait_def_id) |
| ); |
| |
| if tcx.trait_is_auto(trait_def_id) && !trait_def_id.is_local() { |
| 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 |
| } 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", |
| )) |
| } |
| } |
| _ => 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", |
| )), |
| }; |
| |
| if let Some((msg, label)) = msg { |
| let reported = |
| struct_span_err!(tcx.sess, sp, E0321, "{}", msg).span_label(sp, label).emit(); |
| return Err(reported); |
| } |
| } |
| |
| Ok(()) |
| } |
| |
| fn emit_orphan_check_error<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| sp: Span, |
| full_impl_span: Span, |
| trait_span: Span, |
| self_ty: Ty<'tcx>, |
| self_ty_span: Span, |
| generics: &hir::Generics<'tcx>, |
| err: traits::OrphanCheckErr<'tcx>, |
| ) -> Result<!, ErrorGuaranteed> { |
| Err(match err { |
| traits::OrphanCheckErr::NonLocalInputType(tys) => { |
| let msg = match self_ty.kind() { |
| ty::Adt(..) => "can be implemented for types defined outside of the crate", |
| _ if self_ty.is_primitive() => "can be implemented for primitive types", |
| _ => "can be implemented for arbitrary types", |
| }; |
| let mut err = struct_span_err!( |
| tcx.sess, |
| sp, |
| E0117, |
| "only traits defined in the current crate {msg}" |
| ); |
| err.span_label(sp, "impl doesn't use only types from inside the current crate"); |
| for &(mut ty, is_target_ty) in &tys { |
| ty = tcx.erase_regions(ty); |
| ty = match ty.kind() { |
| // Remove the type arguments from the output, as they are not relevant. |
| // You can think of this as the reverse of `resolve_vars_if_possible`. |
| // That way if we had `Vec<MyType>`, we will properly attribute the |
| // problem to `Vec<T>` and avoid confusing the user if they were to see |
| // `MyType` in the error. |
| ty::Adt(def, _) => tcx.mk_adt(*def, ty::List::empty()), |
| _ => ty, |
| }; |
| let this = "this".to_string(); |
| let (ty, postfix) = match &ty.kind() { |
| ty::Slice(_) => (this, " because slices are always foreign"), |
| ty::Array(..) => (this, " because arrays are always foreign"), |
| ty::Tuple(..) => (this, " because tuples are always foreign"), |
| ty::RawPtr(ptr_ty) => { |
| emit_newtype_suggestion_for_raw_ptr( |
| full_impl_span, |
| self_ty, |
| self_ty_span, |
| ptr_ty, |
| &mut err, |
| ); |
| |
| (format!("`{}`", ty), " because raw pointers are always foreign") |
| } |
| _ => (format!("`{}`", ty), ""), |
| }; |
| |
| let msg = format!("{} is not defined in the current crate{}", ty, postfix); |
| if is_target_ty { |
| // Point at `D<A>` in `impl<A, B> for C<B> in D<A>` |
| err.span_label(self_ty_span, &msg); |
| } else { |
| // Point at `C<B>` in `impl<A, B> for C<B> in D<A>` |
| err.span_label(trait_span, &msg); |
| } |
| } |
| err.note("define and implement a trait or new type instead"); |
| err.emit() |
| } |
| traits::OrphanCheckErr::UncoveredTy(param_ty, local_type) => { |
| let mut sp = sp; |
| for param in generics.params { |
| if param.name.ident().to_string() == param_ty.to_string() { |
| sp = param.span; |
| } |
| } |
| |
| match local_type { |
| Some(local_type) => struct_span_err!( |
| tcx.sess, |
| sp, |
| E0210, |
| "type parameter `{}` must be covered by another type \ |
| when it appears before the first local type (`{}`)", |
| param_ty, |
| local_type |
| ) |
| .span_label( |
| sp, |
| format!( |
| "type parameter `{}` must be covered by another type \ |
| when it appears before the first local type (`{}`)", |
| param_ty, local_type |
| ), |
| ) |
| .note( |
| "implementing a foreign trait is only possible if at \ |
| least one of the types for which it is implemented is local, \ |
| and no uncovered type parameters appear before that first \ |
| local type", |
| ) |
| .note( |
| "in this case, 'before' refers to the following order: \ |
| `impl<..> ForeignTrait<T1, ..., Tn> for T0`, \ |
| where `T0` is the first and `Tn` is the last", |
| ) |
| .emit(), |
| None => struct_span_err!( |
| tcx.sess, |
| sp, |
| E0210, |
| "type parameter `{}` must be used as the type parameter for some \ |
| local type (e.g., `MyStruct<{}>`)", |
| param_ty, |
| param_ty |
| ) |
| .span_label( |
| sp, |
| format!( |
| "type parameter `{}` must be used as the type parameter for some \ |
| local type", |
| param_ty, |
| ), |
| ) |
| .note( |
| "implementing a foreign trait is only possible if at \ |
| least one of the types for which it is implemented is local", |
| ) |
| .note( |
| "only traits defined in the current crate can be \ |
| implemented for a type parameter", |
| ) |
| .emit(), |
| } |
| } |
| }) |
| } |
| |
| fn emit_newtype_suggestion_for_raw_ptr( |
| full_impl_span: Span, |
| self_ty: Ty<'_>, |
| self_ty_span: Span, |
| ptr_ty: &ty::TypeAndMut<'_>, |
| diag: &mut Diagnostic, |
| ) { |
| if !self_ty.needs_subst() { |
| let mut_key = ptr_ty.mutbl.prefix_str(); |
| let msg_sugg = "consider introducing a new wrapper type".to_owned(); |
| let sugg = vec![ |
| ( |
| full_impl_span.shrink_to_lo(), |
| format!("struct WrapperType(*{}{});\n\n", mut_key, ptr_ty.ty), |
| ), |
| (self_ty_span, "WrapperType".to_owned()), |
| ]; |
| diag.multipart_suggestion(msg_sugg, sugg, rustc_errors::Applicability::MaybeIncorrect); |
| } |
| } |
| |
| /// Lint impls of auto traits if they are likely to have |
| /// unsound or surprising effects on auto impls. |
| fn lint_auto_trait_impl<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| trait_ref: ty::TraitRef<'tcx>, |
| impl_def_id: LocalDefId, |
| ) { |
| if tcx.impl_polarity(impl_def_id) != ImplPolarity::Positive { |
| return; |
| } |
| |
| assert_eq!(trait_ref.substs.len(), 1); |
| let self_ty = trait_ref.self_ty(); |
| let (self_type_did, substs) = match self_ty.kind() { |
| ty::Adt(def, substs) => (def.did(), substs), |
| _ => { |
| // FIXME: should also lint for stuff like `&i32` but |
| // considering that auto traits are unstable, that |
| // isn't too important for now as this only affects |
| // crates using `nightly`, and std. |
| return; |
| } |
| }; |
| |
| // Impls which completely cover a given root type are fine as they |
| // disable auto impls entirely. So only lint if the substs |
| // are not a permutation of the identity substs. |
| let Err(arg) = tcx.uses_unique_generic_params(substs, IgnoreRegions::Yes) else { |
| // ok |
| return; |
| }; |
| |
| // Ideally: |
| // |
| // - compute the requirements for the auto impl candidate |
| // - check whether these are implied by the non covering impls |
| // - if not, emit the lint |
| // |
| // What we do here is a bit simpler: |
| // |
| // - badly check if an auto impl candidate definitely does not apply |
| // for the given simplified type |
| // - if so, do not lint |
| if fast_reject_auto_impl(tcx, trait_ref.def_id, self_ty) { |
| // ok |
| return; |
| } |
| |
| tcx.struct_span_lint_hir( |
| lint::builtin::SUSPICIOUS_AUTO_TRAIT_IMPLS, |
| tcx.hir().local_def_id_to_hir_id(impl_def_id), |
| tcx.def_span(impl_def_id), |
| DelayDm(|| { |
| format!( |
| "cross-crate traits with a default impl, like `{}`, \ |
| should not be specialized", |
| tcx.def_path_str(trait_ref.def_id), |
| ) |
| }), |
| |lint| { |
| let item_span = tcx.def_span(self_type_did); |
| let self_descr = tcx.def_kind(self_type_did).descr(self_type_did); |
| match arg { |
| ty::util::NotUniqueParam::DuplicateParam(arg) => { |
| lint.note(&format!("`{}` is mentioned multiple times", arg)); |
| } |
| ty::util::NotUniqueParam::NotParam(arg) => { |
| lint.note(&format!("`{}` is not a generic parameter", arg)); |
| } |
| } |
| lint.span_note( |
| item_span, |
| &format!( |
| "try using the same sequence of generic parameters as the {} definition", |
| self_descr, |
| ), |
| ) |
| }, |
| ); |
| } |
| |
| fn fast_reject_auto_impl<'tcx>(tcx: TyCtxt<'tcx>, trait_def_id: DefId, self_ty: Ty<'tcx>) -> bool { |
| struct DisableAutoTraitVisitor<'tcx> { |
| tcx: TyCtxt<'tcx>, |
| trait_def_id: DefId, |
| self_ty_root: Ty<'tcx>, |
| seen: FxHashSet<DefId>, |
| } |
| |
| impl<'tcx> TypeVisitor<'tcx> for DisableAutoTraitVisitor<'tcx> { |
| type BreakTy = (); |
| fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> { |
| let tcx = self.tcx; |
| if t != self.self_ty_root { |
| for impl_def_id in tcx.non_blanket_impls_for_ty(self.trait_def_id, t) { |
| match tcx.impl_polarity(impl_def_id) { |
| ImplPolarity::Negative => return ControlFlow::BREAK, |
| ImplPolarity::Reservation => {} |
| // FIXME(@lcnr): That's probably not good enough, idk |
| // |
| // We might just want to take the rustdoc code and somehow avoid |
| // explicit impls for `Self`. |
| ImplPolarity::Positive => return ControlFlow::CONTINUE, |
| } |
| } |
| } |
| |
| match t.kind() { |
| ty::Adt(def, substs) if def.is_phantom_data() => substs.visit_with(self), |
| ty::Adt(def, substs) => { |
| // @lcnr: This is the only place where cycles can happen. We avoid this |
| // by only visiting each `DefId` once. |
| // |
| // This will be is incorrect in subtle cases, but I don't care :) |
| if self.seen.insert(def.did()) { |
| for ty in def.all_fields().map(|field| field.ty(tcx, substs)) { |
| ty.visit_with(self)?; |
| } |
| } |
| |
| ControlFlow::CONTINUE |
| } |
| _ => t.super_visit_with(self), |
| } |
| } |
| } |
| |
| let self_ty_root = match self_ty.kind() { |
| ty::Adt(def, _) => tcx.mk_adt(*def, InternalSubsts::identity_for_item(tcx, def.did())), |
| _ => unimplemented!("unexpected self ty {:?}", self_ty), |
| }; |
| |
| self_ty_root |
| .visit_with(&mut DisableAutoTraitVisitor { |
| tcx, |
| self_ty_root, |
| trait_def_id, |
| seen: FxHashSet::default(), |
| }) |
| .is_break() |
| } |
