+declare_clippy_lint! {
+ /// **What it does:** Checks for `std::mem::replace` on a value of type
+ /// `T` with `T::default()`.
+ ///
+ /// **Why is this bad?** `std::mem` module already has the method `take` to
+ /// take the current value and replace it with the default value of that type.
+ ///
+ /// **Known problems:** None.
+ ///
+ /// **Example:**
+ /// ```rust
+ /// let mut text = String::from("foo");
+ /// let replaced = std::mem::replace(&mut text, String::default());
+ /// ```
+ /// Is better expressed with:
+ /// ```rust
+ /// let mut text = String::from("foo");
+ /// let taken = std::mem::take(&mut text);
+ /// ```
+ pub MEM_REPLACE_WITH_DEFAULT,
+ style,
+ "replacing a value of type `T` with `T::default()` instead of using `std::mem::take`"
+}
+
+impl_lint_pass!(MemReplace =>
+ [MEM_REPLACE_OPTION_WITH_NONE, MEM_REPLACE_WITH_UNINIT, MEM_REPLACE_WITH_DEFAULT]);
+
+fn check_replace_option_with_none(cx: &LateContext<'_>, src: &Expr<'_>, dest: &Expr<'_>, expr_span: Span) {
+ if let ExprKind::Path(ref replacement_qpath) = src.kind {
+ // Check that second argument is `Option::None`
+ if match_qpath(replacement_qpath, &paths::OPTION_NONE) {
+ // Since this is a late pass (already type-checked),
+ // and we already know that the second argument is an
+ // `Option`, we do not need to check the first
+ // argument's type. All that's left is to get
+ // replacee's path.
+ let replaced_path = match dest.kind {
+ ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mut, ref replaced) => {
+ if let ExprKind::Path(QPath::Resolved(None, ref replaced_path)) = replaced.kind {
+ replaced_path
+ } else {
+ return;
+ }
+ },
+ ExprKind::Path(QPath::Resolved(None, ref replaced_path)) => replaced_path,
+ _ => return,
+ };
+
+ let mut applicability = Applicability::MachineApplicable;
+ span_lint_and_sugg(
+ cx,
+ MEM_REPLACE_OPTION_WITH_NONE,
+ expr_span,
+ "replacing an `Option` with `None`",
+ "consider `Option::take()` instead",
+ format!(
+ "{}.take()",
+ snippet_with_applicability(cx, replaced_path.span, "", &mut applicability)
+ ),
+ applicability,
+ );
+ }
+ }
+}
+
+fn check_replace_with_uninit(cx: &LateContext<'_>, src: &Expr<'_>, dest: &Expr<'_>, expr_span: Span) {
+ if_chain! {
+ // check if replacement is mem::MaybeUninit::uninit().assume_init()
+ if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(src.hir_id);
+ if cx.tcx.is_diagnostic_item(sym::assume_init, method_def_id);
+ then {
+ let mut applicability = Applicability::MachineApplicable;
+ span_lint_and_sugg(
+ cx,
+ MEM_REPLACE_WITH_UNINIT,
+ expr_span,
+ "replacing with `mem::MaybeUninit::uninit().assume_init()`",
+ "consider using",
+ format!(
+ "std::ptr::read({})",
+ snippet_with_applicability(cx, dest.span, "", &mut applicability)
+ ),
+ applicability,
+ );
+ return;
+ }
+ }
+
+ if_chain! {
+ if let ExprKind::Call(ref repl_func, ref repl_args) = src.kind;
+ if repl_args.is_empty();
+ if let ExprKind::Path(ref repl_func_qpath) = repl_func.kind;
+ if let Some(repl_def_id) = cx.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def_id();
+ then {
+ if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, repl_def_id) {
+ let mut applicability = Applicability::MachineApplicable;
+ span_lint_and_sugg(
+ cx,
+ MEM_REPLACE_WITH_UNINIT,
+ expr_span,
+ "replacing with `mem::uninitialized()`",
+ "consider using",
+ format!(
+ "std::ptr::read({})",
+ snippet_with_applicability(cx, dest.span, "", &mut applicability)
+ ),
+ applicability,
+ );
+ } else if cx.tcx.is_diagnostic_item(sym::mem_zeroed, repl_def_id) &&
+ !cx.typeck_results().expr_ty(src).is_primitive() {
+ span_lint_and_help(
+ cx,
+ MEM_REPLACE_WITH_UNINIT,
+ expr_span,
+ "replacing with `mem::zeroed()`",
+ None,
+ "consider using a default value or the `take_mut` crate instead",
+ );
+ }
+ }
+ }
+}
+
+/// Returns true if the `def_id` associated with the `path` is recognized as a "default-equivalent"
+/// constructor from the std library
+fn is_default_equivalent_ctor(cx: &LateContext<'_>, def_id: DefId, path: &QPath<'_>) -> bool {
+ let std_types_symbols = &[
+ sym::string_type,
+ sym::vec_type,
+ sym::vecdeque_type,
+ sym::LinkedList,
+ sym::hashmap_type,
+ sym::BTreeMap,
+ sym::hashset_type,
+ sym::BTreeSet,
+ sym::BinaryHeap,
+ ];