| use clippy_utils::diagnostics::span_lint_and_sugg; |
| use clippy_utils::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 |
| ); |
| } |
| } |
| } |
| } |