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Autotrait bounds on dyn-safe trait methods

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David Tolnay 2023-01-19 01:24:45 -08:00
parent 9e1c600f74
commit 4501d3abe1
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4 changed files with 110 additions and 10 deletions
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60
compiler/rustc_trait_selection/src/traits/object_safety.rs
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@ -547,16 +547,56 @@ fn virtual_call_violation_for_method<'tcx>(
// NOTE: This check happens last, because it results in a lint, and not a
// hard error.
if tcx
.predicates_of(method.def_id)
.predicates
.iter()
// A trait object can't claim to live more than the concrete type,
// so outlives predicates will always hold.
.cloned()
.filter(|(p, _)| p.to_opt_type_outlives().is_none())
.any(|pred| contains_illegal_self_type_reference(tcx, trait_def_id, pred))
{
if tcx.predicates_of(method.def_id).predicates.iter().any(|&(pred, span)| {
// dyn Trait is okay:
//
// trait Trait {
// fn f(&self) where Self: 'static;
// }
//
// because a trait object can't claim to live longer than the concrete
// type. If the lifetime bound holds on dyn Trait then it's guaranteed
// to hold as well on the concrete type.
if pred.to_opt_type_outlives().is_some() {
return false;
}
// dyn Trait is okay:
//
// auto trait AutoTrait {}
//
// trait Trait {
// fn f(&self) where Self: AutoTrait;
// }
//
// because `impl AutoTrait for dyn Trait` is disallowed by coherence.
// Traits with a default impl are implemented for a trait object if and
// only if the autotrait is one of the trait object's trait bounds, like
// in `dyn Trait + AutoTrait`. This guarantees that trait objects only
// implement auto traits if the underlying type does as well.
if let ty::PredicateKind::Clause(ty::Clause::Trait(ty::TraitPredicate {
trait_ref: pred_trait_ref,
constness: ty::BoundConstness::NotConst,
polarity: ty::ImplPolarity::Positive,
})) = pred.kind().skip_binder()
&& pred_trait_ref.self_ty() == tcx.types.self_param
&& tcx.trait_is_auto(pred_trait_ref.def_id)
{
// Consider bounds like `Self: Bound<Self>`. Auto traits are not
// allowed to have generic parameters so `auto trait Bound<T> {}`
// would already have reported an error at the definition of the
// auto trait.
if pred_trait_ref.substs.len() != 1 {
tcx.sess.diagnostic().delay_span_bug(
span,
"auto traits cannot have generic parameters",
);
}
return false;
}
contains_illegal_self_type_reference(tcx, trait_def_id, pred.clone())
}) {
return Some(MethodViolationCode::WhereClauseReferencesSelf);
}