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use clippy_utils::{diagnostics::span_lint_and_sugg, peel_blocks};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{Body, ExprKind, Impl, ImplItemKind, Item, ItemKind, Node};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// ### What it does
/// Checks for empty `Drop` implementations.
///
/// ### Why is this bad?
/// Empty `Drop` implementations have no effect when dropping an instance of the type. They are
/// most likely useless. However, an empty `Drop` implementation prevents a type from being
/// destructured, which might be the intention behind adding the implementation as a marker.
///
/// ### Example
/// ```rust
/// struct S;
///
/// impl Drop for S {
/// fn drop(&mut self) {}
/// }
/// ```
/// Use instead:
/// ```rust
/// struct S;
/// ```
#[clippy::version = "1.62.0"]
pub EMPTY_DROP,
restriction,
"empty `Drop` implementations"
}
declare_lint_pass!(EmptyDrop => [EMPTY_DROP]);
impl LateLintPass<'_> for EmptyDrop {
fn check_item(&mut self, cx: &LateContext<'_>, item: &Item<'_>) {
if_chain! {
if let ItemKind::Impl(Impl {
of_trait: Some(ref trait_ref),
items: [child],
..
}) = item.kind;
if trait_ref.trait_def_id() == cx.tcx.lang_items().drop_trait();
if let impl_item_hir = child.id.hir_id();
if let Some(Node::ImplItem(impl_item)) = cx.tcx.hir().find(impl_item_hir);
if let ImplItemKind::Fn(_, b) = &impl_item.kind;
if let Body { value: func_expr, .. } = cx.tcx.hir().body(*b);
let func_expr = peel_blocks(func_expr);
if let ExprKind::Block(block, _) = func_expr.kind;
if block.stmts.is_empty() && block.expr.is_none();
then {
span_lint_and_sugg(
cx,
EMPTY_DROP,
item.span,
"empty drop implementation",
"try removing this impl",
String::new(),
Applicability::MaybeIncorrect
);
}
}
}
}
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