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Revert "Implement allow-by-default multiple_supertrait_upcastable lint"

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This reverts commit 5e44a65517.
This commit is contained in:
David Tolnay 2022-12-29 00:47:23 -08:00
parent c5f66726f0
commit 06ec0bf8b0
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7 changed files with 0 additions and 74 deletions
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63
compiler/rustc_lint/src/multiple_supertrait_upcastable.rs
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@ -1,63 +0,0 @@
use crate::{LateContext, LateLintPass, LintContext};
use rustc_errors::DelayDm;
use rustc_hir as hir;
use rustc_span::sym;
declare_lint! {
/// The `multiple_supertrait_upcastable` lint detects when an object-safe trait has multiple
/// supertraits.
///
/// ### Example
///
/// ```rust
/// trait A {}
/// trait B {}
///
/// #[warn(multiple_supertrait_upcastable)]
/// trait C: A + B {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// To support upcasting with multiple supertraits, we need to store multiple vtables and this
/// can result in extra space overhead, even if no code actually uses upcasting.
/// This lint allows users to identify when such scenarios occur and to decide whether the
/// additional overhead is justified.
pub MULTIPLE_SUPERTRAIT_UPCASTABLE,
Allow,
"detect when an object-safe trait has multiple supertraits",
@feature_gate = sym::multiple_supertrait_upcastable;
}
declare_lint_pass!(MultipleSupertraitUpcastable => [MULTIPLE_SUPERTRAIT_UPCASTABLE]);
impl<'tcx> LateLintPass<'tcx> for MultipleSupertraitUpcastable {
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
let def_id = item.owner_id.to_def_id();
if let hir::ItemKind::Trait(_, _, _, _, _) = item.kind
&& cx.tcx.is_object_safe(def_id)
{
let direct_super_traits_iter = cx.tcx
.super_predicates_of(def_id)
.predicates
.into_iter()
.filter_map(|(pred, _)| pred.to_opt_poly_trait_pred());
if direct_super_traits_iter.count() > 1 {
cx.struct_span_lint(
MULTIPLE_SUPERTRAIT_UPCASTABLE,
cx.tcx.def_span(def_id),
DelayDm(|| {
format!(
"`{}` is object-safe and has multiple supertraits",
item.ident,
)
}),
|diag| diag,
);
}
}
}
}