+ } 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,
+ ];
+
+ if std_types_symbols
+ .iter()
+ .any(|symbol| is_diagnostic_assoc_item(cx, def_id, *symbol))
+ {
+ if let QPath::TypeRelative(_, ref method) = path {
+ if method.ident.name == sym::new {
+ return true;
+ }
+ }
+ }
+
+ false
+}
+
+fn check_replace_with_default(cx: &LateContext<'_>, src: &Expr<'_>, dest: &Expr<'_>, expr_span: Span) {
+ if let ExprKind::Call(ref repl_func, _) = src.kind {
+ if_chain! {
+ if !in_external_macro(cx.tcx.sess, expr_span);
+ 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();
+ if is_diagnostic_assoc_item(cx, repl_def_id, sym::Default)
+ || is_default_equivalent_ctor(cx, repl_def_id, repl_func_qpath);
+
+ then {
+ span_lint_and_then(
+ cx,
+ MEM_REPLACE_WITH_DEFAULT,
+ expr_span,
+ "replacing a value of type `T` with `T::default()` is better expressed using `std::mem::take`",
+ |diag| {
+ if !in_macro(expr_span) {
+ let suggestion = format!("std::mem::take({})", snippet(cx, dest.span, ""));
+
+ diag.span_suggestion(
+ expr_span,
+ "consider using",
+ suggestion,
+ Applicability::MachineApplicable
+ );
+ }
+ }
+ );
+ }
+ }
+ }
+}
+
+const MEM_REPLACE_WITH_DEFAULT_MSRV: RustcVersion = RustcVersion::new(1, 40, 0);
+
+pub struct MemReplace {
+ msrv: Option<RustcVersion>,
+}
+
+impl MemReplace {
+ #[must_use]
+ pub fn new(msrv: Option<RustcVersion>) -> Self {
+ Self { msrv }
+ }
+}
+
+impl<'tcx> LateLintPass<'tcx> for MemReplace {
+ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+ if_chain! {
+ // Check that `expr` is a call to `mem::replace()`
+ if let ExprKind::Call(ref func, ref func_args) = expr.kind;
+ if let ExprKind::Path(ref func_qpath) = func.kind;
+ if let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id();
+ if match_def_path(cx, def_id, &paths::MEM_REPLACE);
+ if let [dest, src] = &**func_args;
+ then {
+ check_replace_option_with_none(cx, src, dest, expr.span);
+ check_replace_with_uninit(cx, src, dest, expr.span);
+ if meets_msrv(self.msrv.as_ref(), &MEM_REPLACE_WITH_DEFAULT_MSRV) {
+ check_replace_with_default(cx, src, dest, expr.span);
+ }