"non-binding let on a synchronization lock"
}
-declare_lint_pass!(LetUnderscore => [LET_UNDERSCORE_MUST_USE, LET_UNDERSCORE_LOCK]);
+declare_clippy_lint! {
+ /// **What it does:** Checks for `let _ = <expr>`
+ /// where expr has a type that implements `Drop`
+ ///
+ /// **Why is this bad?** This statement immediately drops the initializer
+ /// expression instead of extending its lifetime to the end of the scope, which
+ /// is often not intended. To extend the expression's lifetime to the end of the
+ /// scope, use an underscore-prefixed name instead (i.e. _var). If you want to
+ /// explicitly drop the expression, `std::mem::drop` conveys your intention
+ /// better and is less error-prone.
+ ///
+ /// **Known problems:** None.
+ ///
+ /// **Example:**
+ ///
+ /// Bad:
+ /// ```rust,ignore
+ /// struct Droppable;
+ /// impl Drop for Droppable {
+ /// fn drop(&mut self) {}
+ /// }
+ /// {
+ /// let _ = Droppable;
+ /// // ^ dropped here
+ /// /* more code */
+ /// }
+ /// ```
+ ///
+ /// Good:
+ /// ```rust,ignore
+ /// {
+ /// let _droppable = Droppable;
+ /// /* more code */
+ /// // dropped at end of scope
+ /// }
+ /// ```
+ pub LET_UNDERSCORE_DROP,
+ pedantic,
+ "non-binding let on a type that implements `Drop`"
+}
+
+declare_lint_pass!(LetUnderscore => [LET_UNDERSCORE_MUST_USE, LET_UNDERSCORE_LOCK, LET_UNDERSCORE_DROP]);
const SYNC_GUARD_PATHS: [&[&str]; 3] = [
&paths::MUTEX_GUARD,
if let PatKind::Wild = local.pat.kind;
if let Some(ref init) = local.init;
then {
- let init_ty = cx.tables().expr_ty(init);
+ let init_ty = cx.typeck_results().expr_ty(init);
let contains_sync_guard = init_ty.walk().any(|inner| match inner.unpack() {
GenericArgKind::Type(inner_ty) => {
SYNC_GUARD_PATHS.iter().any(|path| match_type(cx, inner_ty, path))
"consider using an underscore-prefixed named \
binding or dropping explicitly with `std::mem::drop`"
)
- } else if is_must_use_ty(cx, cx.tables().expr_ty(init)) {
+ } else if init_ty.needs_drop(cx.tcx, cx.param_env) {
+ span_lint_and_help(
+ cx,
+ LET_UNDERSCORE_DROP,
+ local.span,
+ "non-binding `let` on a type that implements `Drop`",
+ None,
+ "consider using an underscore-prefixed named \
+ binding or dropping explicitly with `std::mem::drop`"
+ )
+ } else if is_must_use_ty(cx, cx.typeck_results().expr_ty(init)) {
span_lint_and_help(
cx,
LET_UNDERSCORE_MUST_USE,