1 //! lint on indexing and slicing operations
3 use clippy_utils::consts::{constant, Constant};
4 use clippy_utils::diagnostics::{span_lint, span_lint_and_then};
5 use clippy_utils::higher;
6 use rustc_ast::ast::RangeLimits;
7 use rustc_hir::{Expr, ExprKind};
8 use rustc_lint::{LateContext, LateLintPass};
10 use rustc_session::{declare_tool_lint, impl_lint_pass};
12 declare_clippy_lint! {
14 /// Checks for out of bounds array indexing with a constant
17 /// ### Why is this bad?
18 /// This will always panic at runtime.
22 /// let x = [1, 2, 3, 4];
30 /// # let x = [1, 2, 3, 4];
31 /// // Index within bounds
36 #[clippy::version = "pre 1.29.0"]
37 pub OUT_OF_BOUNDS_INDEXING,
39 "out of bounds constant indexing"
42 declare_clippy_lint! {
44 /// Checks for usage of indexing or slicing. Arrays are special cases, this lint
45 /// does report on arrays if we can tell that slicing operations are in bounds and does not
46 /// lint on constant `usize` indexing on arrays because that is handled by rustc's `const_err` lint.
48 /// ### Why is this bad?
49 /// Indexing and slicing can panic at runtime and there are
50 /// safe alternatives.
55 /// let x = vec![0; 5];
61 /// let y = [0, 1, 2, 3];
69 /// # #![allow(unused)]
71 /// # let x = vec![0; 5];
72 /// # let y = [0, 1, 2, 3];
79 #[clippy::version = "pre 1.29.0"]
82 "indexing/slicing usage"
85 impl_lint_pass!(IndexingSlicing => [INDEXING_SLICING, OUT_OF_BOUNDS_INDEXING]);
87 #[derive(Copy, Clone)]
88 pub struct IndexingSlicing {
89 suppress_restriction_lint_in_const: bool,
92 impl IndexingSlicing {
93 pub fn new(suppress_restriction_lint_in_const: bool) -> Self {
95 suppress_restriction_lint_in_const,
100 impl<'tcx> LateLintPass<'tcx> for IndexingSlicing {
101 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
102 if self.suppress_restriction_lint_in_const && cx.tcx.hir().is_inside_const_context(expr.hir_id) {
106 if let ExprKind::Index(array, index) = &expr.kind {
107 let note = "the suggestion might not be applicable in constant blocks";
108 let ty = cx.typeck_results().expr_ty(array).peel_refs();
109 if let Some(range) = higher::Range::hir(index) {
110 // Ranged indexes, i.e., &x[n..m], &x[n..], &x[..n] and &x[..]
111 if let ty::Array(_, s) = ty.kind() {
112 let size: u128 = if let Some(size) = s.try_eval_usize(cx.tcx, cx.param_env) {
118 let const_range = to_const_range(cx, range, size);
120 if let (Some(start), _) = const_range {
124 OUT_OF_BOUNDS_INDEXING,
125 range.start.map_or(expr.span, |start| start.span),
126 "range is out of bounds",
132 if let (_, Some(end)) = const_range {
136 OUT_OF_BOUNDS_INDEXING,
137 range.end.map_or(expr.span, |end| end.span),
138 "range is out of bounds",
144 if let (Some(_), Some(_)) = const_range {
145 // early return because both start and end are constants
146 // and we have proven above that they are in bounds
151 let help_msg = match (range.start, range.end) {
152 (None, Some(_)) => "consider using `.get(..n)`or `.get_mut(..n)` instead",
153 (Some(_), None) => "consider using `.get(n..)` or .get_mut(n..)` instead",
154 (Some(_), Some(_)) => "consider using `.get(n..m)` or `.get_mut(n..m)` instead",
155 (None, None) => return, // [..] is ok.
158 span_lint_and_then(cx, INDEXING_SLICING, expr.span, "slicing may panic", |diag| {
161 if cx.tcx.hir().is_inside_const_context(expr.hir_id) {
166 // Catchall non-range index, i.e., [n] or [n << m]
167 if let ty::Array(..) = ty.kind() {
168 // Index is a const block.
169 if let ExprKind::ConstBlock(..) = index.kind {
172 // Index is a constant uint.
173 if let Some(..) = constant(cx, cx.typeck_results(), index) {
174 // Let rustc's `const_err` lint handle constant `usize` indexing on arrays.
179 span_lint_and_then(cx, INDEXING_SLICING, expr.span, "indexing may panic", |diag| {
180 diag.help("consider using `.get(n)` or `.get_mut(n)` instead");
182 if cx.tcx.hir().is_inside_const_context(expr.hir_id) {
191 /// Returns a tuple of options with the start and end (exclusive) values of
192 /// the range. If the start or end is not constant, None is returned.
193 fn to_const_range(cx: &LateContext<'_>, range: higher::Range<'_>, array_size: u128) -> (Option<u128>, Option<u128>) {
196 .map(|expr| constant(cx, cx.typeck_results(), expr).map(|(c, _)| c));
197 let start = match s {
198 Some(Some(Constant::Int(x))) => Some(x),
205 .map(|expr| constant(cx, cx.typeck_results(), expr).map(|(c, _)| c));
207 Some(Some(Constant::Int(x))) => {
208 if range.limits == RangeLimits::Closed {
215 None => Some(array_size),