2 in_macro, match_def_path, match_qpath, paths, snippet, snippet_with_applicability, span_lint_and_help,
3 span_lint_and_sugg, span_lint_and_then,
5 use if_chain::if_chain;
6 use rustc_errors::Applicability;
7 use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability, QPath};
8 use rustc_lint::{LateContext, LateLintPass};
9 use rustc_middle::lint::in_external_macro;
10 use rustc_session::{declare_lint_pass, declare_tool_lint};
11 use rustc_span::source_map::Span;
13 declare_clippy_lint! {
14 /// **What it does:** Checks for `mem::replace()` on an `Option` with
17 /// **Why is this bad?** `Option` already has the method `take()` for
18 /// taking its current value (Some(..) or None) and replacing it with
21 /// **Known problems:** None.
27 /// let mut an_option = Some(0);
28 /// let replaced = mem::replace(&mut an_option, None);
30 /// Is better expressed with:
32 /// let mut an_option = Some(0);
33 /// let taken = an_option.take();
35 pub MEM_REPLACE_OPTION_WITH_NONE,
37 "replacing an `Option` with `None` instead of `take()`"
40 declare_clippy_lint! {
41 /// **What it does:** Checks for `mem::replace(&mut _, mem::uninitialized())`
42 /// and `mem::replace(&mut _, mem::zeroed())`.
44 /// **Why is this bad?** This will lead to undefined behavior even if the
45 /// value is overwritten later, because the uninitialized value may be
46 /// observed in the case of a panic.
48 /// **Known problems:** None.
54 ///# fn may_panic(v: Vec<i32>) -> Vec<i32> { v }
56 /// #[allow(deprecated, invalid_value)]
57 /// fn myfunc (v: &mut Vec<i32>) {
58 /// let taken_v = unsafe { mem::replace(v, mem::uninitialized()) };
59 /// let new_v = may_panic(taken_v); // undefined behavior on panic
60 /// mem::forget(mem::replace(v, new_v));
64 /// The [take_mut](https://docs.rs/take_mut) crate offers a sound solution,
65 /// at the cost of either lazily creating a replacement value or aborting
66 /// on panic, to ensure that the uninitialized value cannot be observed.
67 pub MEM_REPLACE_WITH_UNINIT,
69 "`mem::replace(&mut _, mem::uninitialized())` or `mem::replace(&mut _, mem::zeroed())`"
72 declare_clippy_lint! {
73 /// **What it does:** Checks for `std::mem::replace` on a value of type
74 /// `T` with `T::default()`.
76 /// **Why is this bad?** `std::mem` module already has the method `take` to
77 /// take the current value and replace it with the default value of that type.
79 /// **Known problems:** None.
83 /// let mut text = String::from("foo");
84 /// let replaced = std::mem::replace(&mut text, String::default());
86 /// Is better expressed with:
88 /// let mut text = String::from("foo");
89 /// let taken = std::mem::take(&mut text);
91 pub MEM_REPLACE_WITH_DEFAULT,
93 "replacing a value of type `T` with `T::default()` instead of using `std::mem::take`"
96 declare_lint_pass!(MemReplace =>
97 [MEM_REPLACE_OPTION_WITH_NONE, MEM_REPLACE_WITH_UNINIT, MEM_REPLACE_WITH_DEFAULT]);
99 fn check_replace_option_with_none(cx: &LateContext<'_, '_>, src: &Expr<'_>, dest: &Expr<'_>, expr_span: Span) {
100 if let ExprKind::Path(ref replacement_qpath) = src.kind {
101 // Check that second argument is `Option::None`
102 if match_qpath(replacement_qpath, &paths::OPTION_NONE) {
103 // Since this is a late pass (already type-checked),
104 // and we already know that the second argument is an
105 // `Option`, we do not need to check the first
106 // argument's type. All that's left is to get
108 let replaced_path = match dest.kind {
109 ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mut, ref replaced) => {
110 if let ExprKind::Path(QPath::Resolved(None, ref replaced_path)) = replaced.kind {
116 ExprKind::Path(QPath::Resolved(None, ref replaced_path)) => replaced_path,
120 let mut applicability = Applicability::MachineApplicable;
123 MEM_REPLACE_OPTION_WITH_NONE,
125 "replacing an `Option` with `None`",
126 "consider `Option::take()` instead",
129 snippet_with_applicability(cx, replaced_path.span, "", &mut applicability)
137 fn check_replace_with_uninit(cx: &LateContext<'_, '_>, src: &Expr<'_>, expr_span: Span) {
138 if let ExprKind::Call(ref repl_func, ref repl_args) = src.kind {
140 if repl_args.is_empty();
141 if let ExprKind::Path(ref repl_func_qpath) = repl_func.kind;
142 if let Some(repl_def_id) = cx.tables.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def_id();
144 if match_def_path(cx, repl_def_id, &paths::MEM_UNINITIALIZED) {
147 MEM_REPLACE_WITH_UNINIT,
149 "replacing with `mem::uninitialized()`",
150 "consider using the `take_mut` crate instead",
152 } else if match_def_path(cx, repl_def_id, &paths::MEM_ZEROED) &&
153 !cx.tables.expr_ty(src).is_primitive() {
156 MEM_REPLACE_WITH_UNINIT,
158 "replacing with `mem::zeroed()`",
159 "consider using a default value or the `take_mut` crate instead",
167 fn check_replace_with_default(cx: &LateContext<'_, '_>, src: &Expr<'_>, dest: &Expr<'_>, expr_span: Span) {
168 if let ExprKind::Call(ref repl_func, _) = src.kind {
170 if !in_external_macro(cx.tcx.sess, expr_span);
171 if let ExprKind::Path(ref repl_func_qpath) = repl_func.kind;
172 if let Some(repl_def_id) = cx.tables.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def_id();
173 if match_def_path(cx, repl_def_id, &paths::DEFAULT_TRAIT_METHOD);
177 MEM_REPLACE_WITH_DEFAULT,
179 "replacing a value of type `T` with `T::default()` is better expressed using `std::mem::take`",
181 if !in_macro(expr_span) {
182 let suggestion = format!("std::mem::take({})", snippet(cx, dest.span, ""));
188 Applicability::MachineApplicable
198 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MemReplace {
199 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
201 // Check that `expr` is a call to `mem::replace()`
202 if let ExprKind::Call(ref func, ref func_args) = expr.kind;
203 if let ExprKind::Path(ref func_qpath) = func.kind;
204 if let Some(def_id) = cx.tables.qpath_res(func_qpath, func.hir_id).opt_def_id();
205 if match_def_path(cx, def_id, &paths::MEM_REPLACE);
206 if let [dest, src] = &**func_args;
208 check_replace_option_with_none(cx, src, dest, expr.span);
209 check_replace_with_uninit(cx, src, expr.span);
210 check_replace_with_default(cx, src, dest, expr.span);