src/tools/clippy/clippy_lints/src/undropped_manually_drops.rs

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use clippy_utils::path_res;
   3 use clippy_utils::ty::is_type_lang_item;
   4 use rustc_hir::{lang_items, Expr, ExprKind};
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7 use rustc_span::sym;
   8
   9 declare_clippy_lint! {
  10     /// ### What it does
  11     /// Prevents the safe `std::mem::drop` function from being called on `std::mem::ManuallyDrop`.
  12     ///
  13     /// ### Why is this bad?
  14     /// The safe `drop` function does not drop the inner value of a `ManuallyDrop`.
  15     ///
  16     /// ### Known problems
  17     /// Does not catch cases if the user binds `std::mem::drop`
  18     /// to a different name and calls it that way.
  19     ///
  20     /// ### Example
  21     /// ```rust
  22     /// struct S;
  23     /// drop(std::mem::ManuallyDrop::new(S));
  24     /// ```
  25     /// Use instead:
  26     /// ```rust
  27     /// struct S;
  28     /// unsafe {
  29     ///     std::mem::ManuallyDrop::drop(&mut std::mem::ManuallyDrop::new(S));
  30     /// }
  31     /// ```
  32     #[clippy::version = "1.49.0"]
  33     pub UNDROPPED_MANUALLY_DROPS,
  34     correctness,
  35     "use of safe `std::mem::drop` function to drop a std::mem::ManuallyDrop, which will not drop the inner value"
  36 }
  37
  38 declare_lint_pass!(UndroppedManuallyDrops => [UNDROPPED_MANUALLY_DROPS]);
  39
  40 impl<'tcx> LateLintPass<'tcx> for UndroppedManuallyDrops {
  41     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  42         if_chain! {
  43             if let ExprKind::Call(fun, [arg_0, ..]) = expr.kind;
  44             if path_res(cx, fun).opt_def_id() == cx.tcx.get_diagnostic_item(sym::mem_drop);
  45             let ty = cx.typeck_results().expr_ty(arg_0);
  46             if is_type_lang_item(cx, ty, lang_items::LangItem::ManuallyDrop);
  47             then {
  48                 span_lint_and_help(
  49                     cx,
  50                     UNDROPPED_MANUALLY_DROPS,
  51                     expr.span,
  52                     "the inner value of this ManuallyDrop will not be dropped",
  53                     None,
  54                     "to drop a `ManuallyDrop<T>`, use std::mem::ManuallyDrop::drop",
  55                 );
  56             }
  57         }
  58     }
  59 }