1 //! lint on indexing and slicing operations
3 use crate::consts::{constant, Constant};
4 use crate::utils::{higher, span_lint, span_lint_and_help};
5 use rustc_ast::ast::RangeLimits;
6 use rustc_hir::{Expr, ExprKind};
7 use rustc_lint::{LateContext, LateLintPass};
9 use rustc_session::{declare_lint_pass, declare_tool_lint};
11 declare_clippy_lint! {
12 /// **What it does:** Checks for out of bounds array indexing with a constant
15 /// **Why is this bad?** This will always panic at runtime.
17 /// **Known problems:** Hopefully none.
21 /// # #![allow(const_err)]
22 /// let x = [1, 2, 3, 4];
32 pub OUT_OF_BOUNDS_INDEXING,
34 "out of bounds constant indexing"
37 declare_clippy_lint! {
38 /// **What it does:** Checks for usage of indexing or slicing. Arrays are special cases, this lint
39 /// does report on arrays if we can tell that slicing operations are in bounds and does not
40 /// lint on constant `usize` indexing on arrays because that is handled by rustc's `const_err` lint.
42 /// **Why is this bad?** Indexing and slicing can panic at runtime and there are
43 /// safe alternatives.
45 /// **Known problems:** Hopefully none.
50 /// let x = vec![0; 5];
65 /// let y = [0, 1, 2, 3];
83 "indexing/slicing usage"
86 declare_lint_pass!(IndexingSlicing => [INDEXING_SLICING, OUT_OF_BOUNDS_INDEXING]);
88 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IndexingSlicing {
89 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
90 if let ExprKind::Index(ref array, ref index) = &expr.kind {
91 let ty = cx.tables.expr_ty(array);
92 if let Some(range) = higher::range(cx, index) {
93 // Ranged indexes, i.e., &x[n..m], &x[n..], &x[..n] and &x[..]
94 if let ty::Array(_, s) = ty.kind {
95 let size: u128 = if let Some(size) = s.try_eval_usize(cx.tcx, cx.param_env) {
101 let const_range = to_const_range(cx, range, size);
103 if let (Some(start), _) = const_range {
107 OUT_OF_BOUNDS_INDEXING,
108 range.start.map_or(expr.span, |start| start.span),
109 "range is out of bounds",
115 if let (_, Some(end)) = const_range {
119 OUT_OF_BOUNDS_INDEXING,
120 range.end.map_or(expr.span, |end| end.span),
121 "range is out of bounds",
127 if let (Some(_), Some(_)) = const_range {
128 // early return because both start and end are constants
129 // and we have proven above that they are in bounds
134 let help_msg = match (range.start, range.end) {
135 (None, Some(_)) => "Consider using `.get(..n)`or `.get_mut(..n)` instead",
136 (Some(_), None) => "Consider using `.get(n..)` or .get_mut(n..)` instead",
137 (Some(_), Some(_)) => "Consider using `.get(n..m)` or `.get_mut(n..m)` instead",
138 (None, None) => return, // [..] is ok.
141 span_lint_and_help(cx, INDEXING_SLICING, expr.span, "slicing may panic.", None, help_msg);
143 // Catchall non-range index, i.e., [n] or [n << m]
144 if let ty::Array(..) = ty.kind {
145 // Index is a constant uint.
146 if let Some(..) = constant(cx, cx.tables, index) {
147 // Let rustc's `const_err` lint handle constant `usize` indexing on arrays.
156 "indexing may panic.",
158 "Consider using `.get(n)` or `.get_mut(n)` instead",
165 /// Returns a tuple of options with the start and end (exclusive) values of
166 /// the range. If the start or end is not constant, None is returned.
167 fn to_const_range<'a, 'tcx>(
168 cx: &LateContext<'a, 'tcx>,
169 range: higher::Range<'_>,
171 ) -> (Option<u128>, Option<u128>) {
172 let s = range.start.map(|expr| constant(cx, cx.tables, expr).map(|(c, _)| c));
173 let start = match s {
174 Some(Some(Constant::Int(x))) => Some(x),
179 let e = range.end.map(|expr| constant(cx, cx.tables, expr).map(|(c, _)| c));
181 Some(Some(Constant::Int(x))) => {
182 if range.limits == RangeLimits::Closed {
189 None => Some(array_size),