src/tools/clippy/clippy_lints/src/empty_drop.rs

   1 use clippy_utils::{diagnostics::span_lint_and_sugg, peel_blocks};
   2 use if_chain::if_chain;
   3 use rustc_errors::Applicability;
   4 use rustc_hir::{Body, ExprKind, Impl, ImplItemKind, Item, ItemKind, Node};
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7
   8 declare_clippy_lint! {
   9     /// ### What it does
  10     /// Checks for empty `Drop` implementations.
  11     ///
  12     /// ### Why is this bad?
  13     /// Empty `Drop` implementations have no effect when dropping an instance of the type. They are
  14     /// most likely useless. However, an empty `Drop` implementation prevents a type from being
  15     /// destructured, which might be the intention behind adding the implementation as a marker.
  16     ///
  17     /// ### Example
  18     /// ```rust
  19     /// struct S;
  20     ///
  21     /// impl Drop for S {
  22     ///     fn drop(&mut self) {}
  23     /// }
  24     /// ```
  25     /// Use instead:
  26     /// ```rust
  27     /// struct S;
  28     /// ```
  29     #[clippy::version = "1.62.0"]
  30     pub EMPTY_DROP,
  31     restriction,
  32     "empty `Drop` implementations"
  33 }
  34 declare_lint_pass!(EmptyDrop => [EMPTY_DROP]);
  35
  36 impl LateLintPass<'_> for EmptyDrop {
  37     fn check_item(&mut self, cx: &LateContext<'_>, item: &Item<'_>) {
  38         if_chain! {
  39             if let ItemKind::Impl(Impl {
  40                 of_trait: Some(ref trait_ref),
  41                 items: [child],
  42                 ..
  43             }) = item.kind;
  44             if trait_ref.trait_def_id() == cx.tcx.lang_items().drop_trait();
  45             if let impl_item_hir = child.id.hir_id();
  46             if let Some(Node::ImplItem(impl_item)) = cx.tcx.hir().find(impl_item_hir);
  47             if let ImplItemKind::Fn(_, b) = &impl_item.kind;
  48             if let Body { value: func_expr, .. } = cx.tcx.hir().body(*b);
  49             let func_expr = peel_blocks(func_expr);
  50             if let ExprKind::Block(block, _) = func_expr.kind;
  51             if block.stmts.is_empty() && block.expr.is_none();
  52             then {
  53                 span_lint_and_sugg(
  54                     cx,
  55                     EMPTY_DROP,
  56                     item.span,
  57                     "empty drop implementation",
  58                     "try removing this impl",
  59                     String::new(),
  60                     Applicability::MaybeIncorrect
  61                 );
  62             }
  63         }
  64     }
  65 }