62 lines
2.2 KiB
Rust
62 lines
2.2 KiB
Rust
use crate::{LateContext, LateLintPass, LintContext};
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use rustc_hir as hir;
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use rustc_span::sym;
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declare_lint! {
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/// The `multiple_supertrait_upcastable` lint detects when an object-safe trait has multiple
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/// supertraits.
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///
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/// ### Example
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///
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/// ```rust
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/// #![feature(multiple_supertrait_upcastable)]
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/// trait A {}
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/// trait B {}
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///
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/// #[warn(multiple_supertrait_upcastable)]
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/// trait C: A + B {}
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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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/// To support upcasting with multiple supertraits, we need to store multiple vtables and this
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/// can result in extra space overhead, even if no code actually uses upcasting.
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/// This lint allows users to identify when such scenarios occur and to decide whether the
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/// additional overhead is justified.
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pub MULTIPLE_SUPERTRAIT_UPCASTABLE,
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Allow,
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"detect when an object-safe trait has multiple supertraits",
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@feature_gate = sym::multiple_supertrait_upcastable;
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}
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declare_lint_pass!(MultipleSupertraitUpcastable => [MULTIPLE_SUPERTRAIT_UPCASTABLE]);
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impl<'tcx> LateLintPass<'tcx> for MultipleSupertraitUpcastable {
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fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
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let def_id = item.owner_id.to_def_id();
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// NOTE(nbdd0121): use `object_safety_violations` instead of `check_is_object_safe` because
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// the latter will report `where_clause_object_safety` lint.
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if let hir::ItemKind::Trait(_, _, _, _, _) = item.kind
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&& cx.tcx.object_safety_violations(def_id).is_empty()
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{
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let direct_super_traits_iter = cx.tcx
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.super_predicates_of(def_id)
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.predicates
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.into_iter()
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.filter_map(|(pred, _)| pred.as_trait_clause());
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if direct_super_traits_iter.count() > 1 {
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cx.emit_spanned_lint(
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MULTIPLE_SUPERTRAIT_UPCASTABLE,
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cx.tcx.def_span(def_id),
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crate::lints::MultipleSupertraitUpcastable {
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ident: item.ident
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},
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);
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}
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}
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}
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}
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