1 //! lint on indexing and slicing operations
3 use crate::consts::{constant, Constant};
5 use crate::utils::higher;
6 use crate::utils::higher::Range;
8 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
10 use rustc::{declare_tool_lint, lint_array};
11 use syntax::ast::RangeLimits;
13 declare_clippy_lint! {
14 /// **What it does:** Checks for out of bounds array indexing with a constant
17 /// **Why is this bad?** This will always panic at runtime.
19 /// **Known problems:** Hopefully none.
23 /// let x = [1, 2, 3, 4];
33 pub OUT_OF_BOUNDS_INDEXING,
35 "out of bounds constant indexing"
38 declare_clippy_lint! {
39 /// **What it does:** Checks for usage of indexing or slicing. Arrays are special cased, this lint
40 /// does report on arrays if we can tell that slicing operations are in bounds and does not
41 /// lint on constant `usize` indexing on arrays because that is handled by rustc's `const_err` lint.
43 /// **Why is this bad?** Indexing and slicing can panic at runtime and there are
44 /// safe alternatives.
46 /// **Known problems:** Hopefully none.
51 /// let x = vec![0; 5];
66 /// let y = [0, 1, 2, 3];
84 "indexing/slicing usage"
87 #[derive(Copy, Clone)]
88 pub struct IndexingSlicing;
90 impl LintPass for IndexingSlicing {
91 fn get_lints(&self) -> LintArray {
92 lint_array!(INDEXING_SLICING, OUT_OF_BOUNDS_INDEXING)
95 fn name(&self) -> &'static str {
100 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IndexingSlicing {
101 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
102 if let ExprKind::Index(ref array, ref index) = &expr.node {
103 let ty = cx.tables.expr_ty(array);
104 if let Some(range) = higher::range(cx, index) {
105 // Ranged indexes, i.e. &x[n..m], &x[n..], &x[..n] and &x[..]
106 if let ty::Array(_, s) = ty.sty {
107 let size: u128 = s.assert_usize(cx.tcx).unwrap().into();
109 let const_range = to_const_range(cx, range, size);
111 if let (Some(start), _) = const_range {
115 OUT_OF_BOUNDS_INDEXING,
116 range.start.map_or(expr.span, |start| start.span),
117 "range is out of bounds",
123 if let (_, Some(end)) = const_range {
127 OUT_OF_BOUNDS_INDEXING,
128 range.end.map_or(expr.span, |end| end.span),
129 "range is out of bounds",
135 if let (Some(_), Some(_)) = const_range {
136 // early return because both start and end are constants
137 // and we have proven above that they are in bounds
142 let help_msg = match (range.start, range.end) {
143 (None, Some(_)) => "Consider using `.get(..n)`or `.get_mut(..n)` instead",
144 (Some(_), None) => "Consider using `.get(n..)` or .get_mut(n..)` instead",
145 (Some(_), Some(_)) => "Consider using `.get(n..m)` or `.get_mut(n..m)` instead",
146 (None, None) => return, // [..] is ok.
149 utils::span_help_and_lint(cx, INDEXING_SLICING, expr.span, "slicing may panic.", help_msg);
151 // Catchall non-range index, i.e. [n] or [n << m]
152 if let ty::Array(..) = ty.sty {
153 // Index is a constant uint.
154 if let Some(..) = constant(cx, cx.tables, index) {
155 // Let rustc's `const_err` lint handle constant `usize` indexing on arrays.
160 utils::span_help_and_lint(
164 "indexing may panic.",
165 "Consider using `.get(n)` or `.get_mut(n)` instead",
172 /// Returns a tuple of options with the start and end (exclusive) values of
173 /// the range. If the start or end is not constant, None is returned.
174 fn to_const_range<'a, 'tcx>(
175 cx: &LateContext<'a, 'tcx>,
178 ) -> (Option<u128>, Option<u128>) {
179 let s = range.start.map(|expr| constant(cx, cx.tables, expr).map(|(c, _)| c));
180 let start = match s {
181 Some(Some(Constant::Int(x))) => Some(x),
186 let e = range.end.map(|expr| constant(cx, cx.tables, expr).map(|(c, _)| c));
188 Some(Some(Constant::Int(x))) => {
189 if range.limits == RangeLimits::Closed {
196 None => Some(array_size),