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;
12 use rustc_span::symbol::sym;
14 declare_clippy_lint! {
15 /// **What it does:** Checks for `mem::replace()` on an `Option` with
18 /// **Why is this bad?** `Option` already has the method `take()` for
19 /// taking its current value (Some(..) or None) and replacing it with
22 /// **Known problems:** None.
28 /// let mut an_option = Some(0);
29 /// let replaced = mem::replace(&mut an_option, None);
31 /// Is better expressed with:
33 /// let mut an_option = Some(0);
34 /// let taken = an_option.take();
36 pub MEM_REPLACE_OPTION_WITH_NONE,
38 "replacing an `Option` with `None` instead of `take()`"
41 declare_clippy_lint! {
42 /// **What it does:** Checks for `mem::replace(&mut _, mem::uninitialized())`
43 /// and `mem::replace(&mut _, mem::zeroed())`.
45 /// **Why is this bad?** This will lead to undefined behavior even if the
46 /// value is overwritten later, because the uninitialized value may be
47 /// observed in the case of a panic.
49 /// **Known problems:** None.
55 ///# fn may_panic(v: Vec<i32>) -> Vec<i32> { v }
57 /// #[allow(deprecated, invalid_value)]
58 /// fn myfunc (v: &mut Vec<i32>) {
59 /// let taken_v = unsafe { mem::replace(v, mem::uninitialized()) };
60 /// let new_v = may_panic(taken_v); // undefined behavior on panic
61 /// mem::forget(mem::replace(v, new_v));
65 /// The [take_mut](https://docs.rs/take_mut) crate offers a sound solution,
66 /// at the cost of either lazily creating a replacement value or aborting
67 /// on panic, to ensure that the uninitialized value cannot be observed.
68 pub MEM_REPLACE_WITH_UNINIT,
70 "`mem::replace(&mut _, mem::uninitialized())` or `mem::replace(&mut _, mem::zeroed())`"
73 declare_clippy_lint! {
74 /// **What it does:** Checks for `std::mem::replace` on a value of type
75 /// `T` with `T::default()`.
77 /// **Why is this bad?** `std::mem` module already has the method `take` to
78 /// take the current value and replace it with the default value of that type.
80 /// **Known problems:** None.
84 /// let mut text = String::from("foo");
85 /// let replaced = std::mem::replace(&mut text, String::default());
87 /// Is better expressed with:
89 /// let mut text = String::from("foo");
90 /// let taken = std::mem::take(&mut text);
92 pub MEM_REPLACE_WITH_DEFAULT,
94 "replacing a value of type `T` with `T::default()` instead of using `std::mem::take`"
97 declare_lint_pass!(MemReplace =>
98 [MEM_REPLACE_OPTION_WITH_NONE, MEM_REPLACE_WITH_UNINIT, MEM_REPLACE_WITH_DEFAULT]);
100 fn check_replace_option_with_none(cx: &LateContext<'_, '_>, src: &Expr<'_>, dest: &Expr<'_>, expr_span: Span) {
101 if let ExprKind::Path(ref replacement_qpath) = src.kind {
102 // Check that second argument is `Option::None`
103 if match_qpath(replacement_qpath, &paths::OPTION_NONE) {
104 // Since this is a late pass (already type-checked),
105 // and we already know that the second argument is an
106 // `Option`, we do not need to check the first
107 // argument's type. All that's left is to get
109 let replaced_path = match dest.kind {
110 ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mut, ref replaced) => {
111 if let ExprKind::Path(QPath::Resolved(None, ref replaced_path)) = replaced.kind {
117 ExprKind::Path(QPath::Resolved(None, ref replaced_path)) => replaced_path,
121 let mut applicability = Applicability::MachineApplicable;
124 MEM_REPLACE_OPTION_WITH_NONE,
126 "replacing an `Option` with `None`",
127 "consider `Option::take()` instead",
130 snippet_with_applicability(cx, replaced_path.span, "", &mut applicability)
138 fn check_replace_with_uninit(cx: &LateContext<'_, '_>, src: &Expr<'_>, expr_span: Span) {
139 if let ExprKind::Call(ref repl_func, ref repl_args) = src.kind {
141 if repl_args.is_empty();
142 if let ExprKind::Path(ref repl_func_qpath) = repl_func.kind;
143 if let Some(repl_def_id) = cx.tables.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def_id();
145 if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, repl_def_id) {
148 MEM_REPLACE_WITH_UNINIT,
150 "replacing with `mem::uninitialized()`",
152 "consider using the `take_mut` crate instead",
154 } else if cx.tcx.is_diagnostic_item(sym::mem_zeroed, repl_def_id) &&
155 !cx.tables.expr_ty(src).is_primitive() {
158 MEM_REPLACE_WITH_UNINIT,
160 "replacing with `mem::zeroed()`",
162 "consider using a default value or the `take_mut` crate instead",
170 fn check_replace_with_default(cx: &LateContext<'_, '_>, src: &Expr<'_>, dest: &Expr<'_>, expr_span: Span) {
171 if let ExprKind::Call(ref repl_func, _) = src.kind {
173 if !in_external_macro(cx.tcx.sess, expr_span);
174 if let ExprKind::Path(ref repl_func_qpath) = repl_func.kind;
175 if let Some(repl_def_id) = cx.tables.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def_id();
176 if match_def_path(cx, repl_def_id, &paths::DEFAULT_TRAIT_METHOD);
180 MEM_REPLACE_WITH_DEFAULT,
182 "replacing a value of type `T` with `T::default()` is better expressed using `std::mem::take`",
184 if !in_macro(expr_span) {
185 let suggestion = format!("std::mem::take({})", snippet(cx, dest.span, ""));
187 diag.span_suggestion(
191 Applicability::MachineApplicable
201 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MemReplace {
202 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
204 // Check that `expr` is a call to `mem::replace()`
205 if let ExprKind::Call(ref func, ref func_args) = expr.kind;
206 if let ExprKind::Path(ref func_qpath) = func.kind;
207 if let Some(def_id) = cx.tables.qpath_res(func_qpath, func.hir_id).opt_def_id();
208 if match_def_path(cx, def_id, &paths::MEM_REPLACE);
209 if let [dest, src] = &**func_args;
211 check_replace_option_with_none(cx, src, dest, expr.span);
212 check_replace_with_uninit(cx, src, expr.span);
213 check_replace_with_default(cx, src, dest, expr.span);