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108 lines
4.3 KiB
Rust
108 lines
4.3 KiB
Rust
use rustc_hir::{self as hir, LangItem};
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use rustc_middle::ty;
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use rustc_session::{declare_lint, declare_lint_pass};
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use rustc_span::{Ident, sym};
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use rustc_trait_selection::traits::supertraits;
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use crate::lints::{SupertraitAsDerefTarget, SupertraitAsDerefTargetLabel};
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use crate::{LateContext, LateLintPass, LintContext};
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declare_lint! {
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/// The `deref_into_dyn_supertrait` lint is emitted whenever there is a `Deref` implementation
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/// for `dyn SubTrait` with a `dyn SuperTrait` type as the `Output` type.
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///
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/// These implementations are "shadowed" by trait upcasting (stabilized since
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/// 1.86.0). The `deref` functions is no longer called implicitly, which might
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/// change behavior compared to previous rustc versions.
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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 trait upcasting coercion added a new coercion rule, taking priority over certain other
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/// coercion rules, which causes some behavior change compared to older `rustc` versions.
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///
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/// `deref` can be still called explicitly, it just isn't called as part of a deref coercion
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/// (since trait upcasting coercion takes priority).
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pub DEREF_INTO_DYN_SUPERTRAIT,
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Allow,
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"`Deref` implementation with a supertrait trait object for output is shadowed by trait upcasting",
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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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let tcx = cx.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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// the trait is a `Deref` implementation
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&& let Some(trait_) = &impl_.of_trait
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&& let Some(did) = trait_.trait_def_id()
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&& tcx.is_lang_item(did, LangItem::Deref)
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// the self type is `dyn t_principal`
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&& let self_ty = tcx.type_of(item.owner_id).instantiate_identity()
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&& let ty::Dynamic(data, _, ty::Dyn) = self_ty.kind()
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&& let Some(self_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(self_ty, did, sym::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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&& let Some(supertrait_principal) = supertraits(tcx, self_principal.with_self_ty(tcx, self_ty))
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.find(|supertrait| supertrait.def_id() == target_principal.def_id())
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{
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// erase regions in self type for better diagnostic presentation
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let (self_ty, target_principal, supertrait_principal) =
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tcx.erase_regions((self_ty, target_principal, supertrait_principal));
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let label2 = tcx
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.associated_items(item.owner_id)
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.find_by_ident_and_kind(
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tcx,
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Ident::with_dummy_span(sym::Target),
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ty::AssocTag::Type,
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item.owner_id.to_def_id(),
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)
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.map(|label| SupertraitAsDerefTargetLabel { label: tcx.def_span(label.def_id) });
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let span = tcx.def_span(item.owner_id.def_id);
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cx.emit_span_lint(
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DEREF_INTO_DYN_SUPERTRAIT,
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span,
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SupertraitAsDerefTarget {
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self_ty,
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supertrait_principal: supertrait_principal.map_bound(|trait_ref| {
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ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
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}),
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target_principal,
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label: span,
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label2,
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},
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);
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}
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}
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}
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