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use clippy_utils::diagnostics::span_lint_hir;
use if_chain::if_chain;
use rustc_hir::{Impl, Item, ItemKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::sym;
declare_clippy_lint! {
/// ### What it does
/// Checks for manual re-implementations of `PartialEq::ne`.
///
/// ### Why is this bad?
/// `PartialEq::ne` is required to always return the
/// negated result of `PartialEq::eq`, which is exactly what the default
/// implementation does. Therefore, there should never be any need to
/// re-implement it.
///
/// ### Example
/// ```rust
/// struct Foo;
///
/// impl PartialEq for Foo {
/// fn eq(&self, other: &Foo) -> bool { true }
/// fn ne(&self, other: &Foo) -> bool { !(self == other) }
/// }
/// ```
#[clippy::version = "pre 1.29.0"]
pub PARTIALEQ_NE_IMPL,
complexity,
"re-implementing `PartialEq::ne`"
}
declare_lint_pass!(PartialEqNeImpl => [PARTIALEQ_NE_IMPL]);
impl<'tcx> LateLintPass<'tcx> for PartialEqNeImpl {
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
if_chain! {
if let ItemKind::Impl(Impl { of_trait: Some(ref trait_ref), items: impl_items, .. }) = item.kind;
if !cx.tcx.has_attr(item.owner_id.to_def_id(), sym::automatically_derived);
if let Some(eq_trait) = cx.tcx.lang_items().eq_trait();
if trait_ref.path.res.def_id() == eq_trait;
then {
for impl_item in *impl_items {
if impl_item.ident.name == sym::ne {
span_lint_hir(
cx,
PARTIALEQ_NE_IMPL,
impl_item.id.hir_id(),
impl_item.span,
"re-implementing `PartialEq::ne` is unnecessary",
);
}
}
}
};
}
}
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