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