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|
use crate::{
lints::{SupertraitAsDerefTarget, SupertraitAsDerefTargetLabel},
LateContext, LateLintPass, LintContext,
};
use rustc_hir as hir;
use rustc_middle::{traits::util::supertraits, ty};
use rustc_span::sym;
declare_lint! {
/// The `deref_into_dyn_supertrait` lint is output whenever there is a use of the
/// `Deref` implementation with a `dyn SuperTrait` type as `Output`.
///
/// These implementations will become shadowed when the `trait_upcasting` feature is stabilized.
/// The `deref` functions will no longer be called implicitly, so there might be behavior change.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(deref_into_dyn_supertrait)]
/// #![allow(dead_code)]
///
/// use core::ops::Deref;
///
/// trait A {}
/// trait B: A {}
/// impl<'a> Deref for dyn 'a + B {
/// type Target = dyn A;
/// fn deref(&self) -> &Self::Target {
/// todo!()
/// }
/// }
///
/// fn take_a(_: &dyn A) { }
///
/// fn take_b(b: &dyn B) {
/// take_a(b);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The dyn upcasting coercion feature adds new coercion rules, taking priority
/// over certain other coercion rules, which will cause some behavior change.
pub DEREF_INTO_DYN_SUPERTRAIT,
Warn,
"`Deref` implementation usage with a supertrait trait object for output might be shadowed in the future",
@future_incompatible = FutureIncompatibleInfo {
reference: "issue #89460 <https://github.com/rust-lang/rust/issues/89460>",
};
}
declare_lint_pass!(DerefIntoDynSupertrait => [DEREF_INTO_DYN_SUPERTRAIT]);
impl<'tcx> LateLintPass<'tcx> for DerefIntoDynSupertrait {
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
// `Deref` is being implemented for `t`
if let hir::ItemKind::Impl(impl_) = item.kind
&& let Some(trait_) = &impl_.of_trait
&& let t = cx.tcx.type_of(item.owner_id).subst_identity()
&& let opt_did @ Some(did) = trait_.trait_def_id()
&& opt_did == cx.tcx.lang_items().deref_trait()
// `t` is `dyn t_principal`
&& let ty::Dynamic(data, _, ty::Dyn) = t.kind()
&& let Some(t_principal) = data.principal()
// `<T as Deref>::Target` is `dyn target_principal`
&& let Some(target) = cx.get_associated_type(t, did, "Target")
&& let ty::Dynamic(data, _, ty::Dyn) = target.kind()
&& let Some(target_principal) = data.principal()
// `target_principal` is a supertrait of `t_principal`
&& supertraits(cx.tcx, t_principal.with_self_ty(cx.tcx, cx.tcx.types.trait_object_dummy_self))
.any(|sup| sup.map_bound(|x| ty::ExistentialTraitRef::erase_self_ty(cx.tcx, x)) == target_principal)
{
let label = impl_.items.iter().find_map(|i| (i.ident.name == sym::Target).then_some(i.span)).map(|label| SupertraitAsDerefTargetLabel {
label,
});
cx.emit_spanned_lint(DEREF_INTO_DYN_SUPERTRAIT, cx.tcx.def_span(item.owner_id.def_id), SupertraitAsDerefTarget {
t,
target_principal,
label,
});
}
}
}
|
