2 match_def_path, match_qpath, paths, snippet_with_applicability, span_help_and_lint, span_lint_and_sugg,
4 use if_chain::if_chain;
5 use rustc::declare_lint_pass;
6 use rustc::hir::{BorrowKind, Expr, ExprKind, Mutability, QPath};
7 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
8 use rustc_errors::Applicability;
9 use rustc_session::declare_tool_lint;
11 declare_clippy_lint! {
12 /// **What it does:** Checks for `mem::replace()` on an `Option` with
15 /// **Why is this bad?** `Option` already has the method `take()` for
16 /// taking its current value (Some(..) or None) and replacing it with
19 /// **Known problems:** None.
25 /// let mut an_option = Some(0);
26 /// let replaced = mem::replace(&mut an_option, None);
28 /// Is better expressed with:
30 /// let mut an_option = Some(0);
31 /// let taken = an_option.take();
33 pub MEM_REPLACE_OPTION_WITH_NONE,
35 "replacing an `Option` with `None` instead of `take()`"
38 declare_clippy_lint! {
39 /// **What it does:** Checks for `mem::replace(&mut _, mem::uninitialized())`
40 /// and `mem::replace(&mut _, mem::zeroed())`.
42 /// **Why is this bad?** This will lead to undefined behavior even if the
43 /// value is overwritten later, because the uninitialized value may be
44 /// observed in the case of a panic.
46 /// **Known problems:** None.
52 ///# fn may_panic(v: Vec<i32>) -> Vec<i32> { v }
54 /// #[allow(deprecated, invalid_value)]
55 /// fn myfunc (v: &mut Vec<i32>) {
56 /// let taken_v = unsafe { mem::replace(v, mem::uninitialized()) };
57 /// let new_v = may_panic(taken_v); // undefined behavior on panic
58 /// mem::forget(mem::replace(v, new_v));
62 /// The [take_mut](https://docs.rs/take_mut) crate offers a sound solution,
63 /// at the cost of either lazily creating a replacement value or aborting
64 /// on panic, to ensure that the uninitialized value cannot be observed.
65 pub MEM_REPLACE_WITH_UNINIT,
67 "`mem::replace(&mut _, mem::uninitialized())` or `mem::replace(&mut _, mem::zeroed())`"
70 declare_lint_pass!(MemReplace =>
71 [MEM_REPLACE_OPTION_WITH_NONE, MEM_REPLACE_WITH_UNINIT]);
73 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MemReplace {
74 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
76 // Check that `expr` is a call to `mem::replace()`
77 if let ExprKind::Call(ref func, ref func_args) = expr.kind;
78 if func_args.len() == 2;
79 if let ExprKind::Path(ref func_qpath) = func.kind;
80 if let Some(def_id) = cx.tables.qpath_res(func_qpath, func.hir_id).opt_def_id();
81 if match_def_path(cx, def_id, &paths::MEM_REPLACE);
83 // Check that second argument is `Option::None`
85 if let ExprKind::Path(ref replacement_qpath) = func_args[1].kind {
86 if match_qpath(replacement_qpath, &paths::OPTION_NONE) {
88 // Since this is a late pass (already type-checked),
89 // and we already know that the second argument is an
90 // `Option`, we do not need to check the first
91 // argument's type. All that's left is to get
93 let replaced_path = match func_args[0].kind {
94 ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mutable, ref replaced) => {
95 if let ExprKind::Path(QPath::Resolved(None, ref replaced_path)) = replaced.kind {
101 ExprKind::Path(QPath::Resolved(None, ref replaced_path)) => replaced_path,
105 let mut applicability = Applicability::MachineApplicable;
108 MEM_REPLACE_OPTION_WITH_NONE,
110 "replacing an `Option` with `None`",
111 "consider `Option::take()` instead",
112 format!("{}.take()", snippet_with_applicability(cx, replaced_path.span, "", &mut applicability)),
117 if let ExprKind::Call(ref repl_func, ref repl_args) = func_args[1].kind {
119 if repl_args.is_empty();
120 if let ExprKind::Path(ref repl_func_qpath) = repl_func.kind;
121 if let Some(repl_def_id) = cx.tables.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def_id();
123 if match_def_path(cx, repl_def_id, &paths::MEM_UNINITIALIZED) {
126 MEM_REPLACE_WITH_UNINIT,
128 "replacing with `mem::uninitialized()`",
129 "consider using the `take_mut` crate instead",
131 } else if match_def_path(cx, repl_def_id, &paths::MEM_ZEROED) &&
132 !cx.tables.expr_ty(&func_args[1]).is_primitive() {
135 MEM_REPLACE_WITH_UNINIT,
137 "replacing with `mem::zeroed()`",
138 "consider using a default value or the `take_mut` crate instead",