diff options
Diffstat (limited to 'compiler/rustc_lint/src/deref_into_dyn_supertrait.rs')
-rw-r--r-- | compiler/rustc_lint/src/deref_into_dyn_supertrait.rs | 92 |
1 files changed, 92 insertions, 0 deletions
diff --git a/compiler/rustc_lint/src/deref_into_dyn_supertrait.rs b/compiler/rustc_lint/src/deref_into_dyn_supertrait.rs new file mode 100644 index 000000000..1d29a234a --- /dev/null +++ b/compiler/rustc_lint/src/deref_into_dyn_supertrait.rs @@ -0,0 +1,92 @@ +use crate::{LateContext, LateLintPass, LintContext}; + +use rustc_errors::DelayDm; +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) + && 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) + { + cx.struct_span_lint( + DEREF_INTO_DYN_SUPERTRAIT, + cx.tcx.def_span(item.owner_id.def_id), + DelayDm(|| { + format!( + "`{t}` implements `Deref` with supertrait `{target_principal}` as target" + ) + }), + |lint| { + if let Some(target_span) = impl_.items.iter().find_map(|i| (i.ident.name == sym::Target).then_some(i.span)) { + lint.span_label(target_span, "target type is set here"); + } + + lint + }, + ) + } + } +} |