Disallow impl autotrait for trait object
This commit is contained in:
David Tolnay
parent
a94b9fd0ac
commit
9e1c600f74
6 changed files with 269 additions and 70 deletions
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@ -8,7 +8,7 @@ use rustc_hir as hir;
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use rustc_middle::ty::subst::InternalSubsts;
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use rustc_middle::ty::util::IgnoreRegions;
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use rustc_middle::ty::{
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self, ImplPolarity, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor,
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self, AliasKind, ImplPolarity, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor,
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};
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use rustc_session::lint;
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use rustc_span::def_id::{DefId, LocalDefId};
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@ -86,7 +86,7 @@ fn do_orphan_check_impl<'tcx>(
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// struct B { }
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// impl Foo for A { }
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// impl Foo for B { }
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// impl !Send for (A, B) { }
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// impl !Foo for (A, B) { }
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// ```
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//
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// This final impl is legal according to the orphan
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@ -99,50 +99,171 @@ fn do_orphan_check_impl<'tcx>(
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tcx.trait_is_auto(trait_def_id)
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);
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if tcx.trait_is_auto(trait_def_id) && !trait_def_id.is_local() {
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if tcx.trait_is_auto(trait_def_id) {
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let self_ty = trait_ref.self_ty();
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let opt_self_def_id = match *self_ty.kind() {
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ty::Adt(self_def, _) => Some(self_def.did()),
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ty::Foreign(did) => Some(did),
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_ => None,
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// If the impl is in the same crate as the auto-trait, almost anything
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// goes.
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//
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// impl MyAuto for Rc<Something> {} // okay
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// impl<T> !MyAuto for *const T {} // okay
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// impl<T> MyAuto for T {} // okay
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//
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// But there is one important exception: implementing for a trait object
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// is not allowed.
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//
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// impl MyAuto for dyn Trait {} // NOT OKAY
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// impl<T: ?Sized> MyAuto for T {} // NOT OKAY
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//
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enum LocalImpl {
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Allow,
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Disallow { problematic_kind: &'static str },
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}
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// If the auto-trait is from a dependency, it must only be getting
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// implemented for a nominal type, and specifically one local to the
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// current crate.
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//
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// impl<T> Sync for MyStruct<T> {} // okay
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//
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// impl Sync for Rc<MyStruct> {} // NOT OKAY
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enum NonlocalImpl {
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Allow,
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DisallowBecauseNonlocal,
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DisallowOther,
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}
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// Exhaustive match considering that this logic is essential for
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// soundness.
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let (local_impl, nonlocal_impl) = match self_ty.kind() {
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// struct Struct<T>;
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// impl AutoTrait for Struct<Foo> {}
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ty::Adt(self_def, _) => (
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LocalImpl::Allow,
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if self_def.did().is_local() {
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NonlocalImpl::Allow
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} else {
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NonlocalImpl::DisallowBecauseNonlocal
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},
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),
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// extern { type OpaqueType; }
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// impl AutoTrait for OpaqueType {}
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ty::Foreign(did) => (
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LocalImpl::Allow,
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if did.is_local() {
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NonlocalImpl::Allow
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} else {
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NonlocalImpl::DisallowBecauseNonlocal
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},
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),
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// impl AutoTrait for dyn Trait {}
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ty::Dynamic(..) => (
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LocalImpl::Disallow { problematic_kind: "trait object" },
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NonlocalImpl::DisallowOther,
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),
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// impl<T> AutoTrait for T {}
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// impl<T: ?Sized> AutoTrait for T {}
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ty::Param(..) => (
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if self_ty.is_sized(tcx, tcx.param_env(def_id)) {
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LocalImpl::Allow
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} else {
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LocalImpl::Disallow { problematic_kind: "generic type" }
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},
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NonlocalImpl::DisallowOther,
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),
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// trait Id { type This: ?Sized; }
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// impl<T: ?Sized> Id for T {
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// type This = T;
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// }
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// impl<T: ?Sized> AutoTrait for <T as Id>::This {}
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ty::Alias(AliasKind::Projection, _) => (
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LocalImpl::Disallow { problematic_kind: "associated type" },
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NonlocalImpl::DisallowOther,
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),
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// type Opaque = impl Trait;
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// impl AutoTrait for Opaque {}
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ty::Alias(AliasKind::Opaque, _) => (
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LocalImpl::Disallow { problematic_kind: "opaque type" },
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NonlocalImpl::DisallowOther,
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),
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ty::Bool
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| ty::Char
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| ty::Int(..)
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| ty::Uint(..)
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| ty::Float(..)
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| ty::Str
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| ty::Array(..)
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| ty::Slice(..)
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| ty::RawPtr(..)
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| ty::Ref(..)
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| ty::FnDef(..)
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| ty::FnPtr(..)
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| ty::Never
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| ty::Tuple(..) => (LocalImpl::Allow, NonlocalImpl::DisallowOther),
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ty::Closure(..)
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| ty::Generator(..)
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| ty::GeneratorWitness(..)
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| ty::GeneratorWitnessMIR(..)
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| ty::Bound(..)
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| ty::Placeholder(..)
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| ty::Infer(..) => span_bug!(sp, "weird self type for autotrait impl"),
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ty::Error(..) => (LocalImpl::Allow, NonlocalImpl::Allow),
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};
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let msg = match opt_self_def_id {
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// We only want to permit nominal types, but not *all* nominal types.
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// They must be local to the current crate, so that people
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// can't do `unsafe impl Send for Rc<SomethingLocal>` or
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// `impl !Send for Box<SomethingLocalAndSend>`.
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Some(self_def_id) => {
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if self_def_id.is_local() {
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None
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} else {
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Some((
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format!(
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"cross-crate traits with a default impl, like `{}`, \
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can only be implemented for a struct/enum type \
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defined in the current crate",
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tcx.def_path_str(trait_def_id)
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),
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"can't implement cross-crate trait for type in another crate",
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))
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if trait_def_id.is_local() {
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match local_impl {
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LocalImpl::Allow => {}
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LocalImpl::Disallow { problematic_kind } => {
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let msg = format!(
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"traits with a default impl, like `{trait}`, \
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cannot be implemented for {problematic_kind} `{self_ty}`",
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trait = tcx.def_path_str(trait_def_id),
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);
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let label = format!(
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"a trait object implements `{trait}` if and only if `{trait}` \
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is one of the trait object's trait bounds",
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trait = tcx.def_path_str(trait_def_id),
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);
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let reported =
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struct_span_err!(tcx.sess, sp, E0321, "{}", msg).note(label).emit();
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return Err(reported);
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}
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}
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_ => Some((
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format!(
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"cross-crate traits with a default impl, like `{}`, can \
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} else {
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if let Some((msg, label)) = match nonlocal_impl {
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NonlocalImpl::Allow => None,
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NonlocalImpl::DisallowBecauseNonlocal => Some((
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format!(
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"cross-crate traits with a default impl, like `{}`, \
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can only be implemented for a struct/enum type \
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defined in the current crate",
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tcx.def_path_str(trait_def_id)
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),
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"can't implement cross-crate trait for type in another crate",
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)),
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NonlocalImpl::DisallowOther => Some((
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format!(
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"cross-crate traits with a default impl, like `{}`, can \
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only be implemented for a struct/enum type, not `{}`",
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tcx.def_path_str(trait_def_id),
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self_ty
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),
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"can't implement cross-crate trait with a default impl for \
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non-struct/enum type",
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)),
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};
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if let Some((msg, label)) = msg {
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let reported =
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struct_span_err!(tcx.sess, sp, E0321, "{}", msg).span_label(sp, label).emit();
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return Err(reported);
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tcx.def_path_str(trait_def_id),
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self_ty
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),
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"can't implement cross-crate trait with a default impl for \
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non-struct/enum type",
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)),
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} {
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let reported =
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struct_span_err!(tcx.sess, sp, E0321, "{}", msg).span_label(sp, label).emit();
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return Err(reported);
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}
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}
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}
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