--- /dev/null
+//! lint on indexing and slicing operations
+
+use crate::consts::{constant, Constant};
+use crate::utils::{higher, span_lint, span_lint_and_help};
+use rustc_ast::ast::RangeLimits;
+use rustc_hir::{Expr, ExprKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty;
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+declare_clippy_lint! {
+ /// **What it does:** Checks for out of bounds array indexing with a constant
+ /// index.
+ ///
+ /// **Why is this bad?** This will always panic at runtime.
+ ///
+ /// **Known problems:** Hopefully none.
+ ///
+ /// **Example:**
+ /// ```no_run
+ /// # #![allow(const_err)]
+ /// let x = [1, 2, 3, 4];
+ ///
+ /// // Bad
+ /// x[9];
+ /// &x[2..9];
+ ///
+ /// // Good
+ /// x[0];
+ /// x[3];
+ /// ```
+ pub OUT_OF_BOUNDS_INDEXING,
+ correctness,
+ "out of bounds constant indexing"
+}
+
+declare_clippy_lint! {
+ /// **What it does:** Checks for usage of indexing or slicing. Arrays are special cases, this lint
+ /// does report on arrays if we can tell that slicing operations are in bounds and does not
+ /// lint on constant `usize` indexing on arrays because that is handled by rustc's `const_err` lint.
+ ///
+ /// **Why is this bad?** Indexing and slicing can panic at runtime and there are
+ /// safe alternatives.
+ ///
+ /// **Known problems:** Hopefully none.
+ ///
+ /// **Example:**
+ /// ```rust,no_run
+ /// // Vector
+ /// let x = vec![0; 5];
+ ///
+ /// // Bad
+ /// x[2];
+ /// &x[2..100];
+ /// &x[2..];
+ /// &x[..100];
+ ///
+ /// // Good
+ /// x.get(2);
+ /// x.get(2..100);
+ /// x.get(2..);
+ /// x.get(..100);
+ ///
+ /// // Array
+ /// let y = [0, 1, 2, 3];
+ ///
+ /// // Bad
+ /// &y[10..100];
+ /// &y[10..];
+ /// &y[..100];
+ ///
+ /// // Good
+ /// &y[2..];
+ /// &y[..2];
+ /// &y[0..3];
+ /// y.get(10);
+ /// y.get(10..100);
+ /// y.get(10..);
+ /// y.get(..100);
+ /// ```
+ pub INDEXING_SLICING,
+ restriction,
+ "indexing/slicing usage"
+}
+
+declare_lint_pass!(IndexingSlicing => [INDEXING_SLICING, OUT_OF_BOUNDS_INDEXING]);
+
+impl<'tcx> LateLintPass<'tcx> for IndexingSlicing {
+ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+ if let ExprKind::Index(ref array, ref index) = &expr.kind {
+ let ty = cx.typeck_results().expr_ty(array).peel_refs();
+ if let Some(range) = higher::range(index) {
+ // Ranged indexes, i.e., &x[n..m], &x[n..], &x[..n] and &x[..]
+ if let ty::Array(_, s) = ty.kind() {
+ let size: u128 = if let Some(size) = s.try_eval_usize(cx.tcx, cx.param_env) {
+ size.into()
+ } else {
+ return;
+ };
+
+ let const_range = to_const_range(cx, range, size);
+
+ if let (Some(start), _) = const_range {
+ if start > size {
+ span_lint(
+ cx,
+ OUT_OF_BOUNDS_INDEXING,
+ range.start.map_or(expr.span, |start| start.span),
+ "range is out of bounds",
+ );
+ return;
+ }
+ }
+
+ if let (_, Some(end)) = const_range {
+ if end > size {
+ span_lint(
+ cx,
+ OUT_OF_BOUNDS_INDEXING,
+ range.end.map_or(expr.span, |end| end.span),
+ "range is out of bounds",
+ );
+ return;
+ }
+ }
+
+ if let (Some(_), Some(_)) = const_range {
+ // early return because both start and end are constants
+ // and we have proven above that they are in bounds
+ return;
+ }
+ }
+
+ let help_msg = match (range.start, range.end) {
+ (None, Some(_)) => "consider using `.get(..n)`or `.get_mut(..n)` instead",
+ (Some(_), None) => "consider using `.get(n..)` or .get_mut(n..)` instead",
+ (Some(_), Some(_)) => "consider using `.get(n..m)` or `.get_mut(n..m)` instead",
+ (None, None) => return, // [..] is ok.
+ };
+
+ span_lint_and_help(cx, INDEXING_SLICING, expr.span, "slicing may panic", None, help_msg);
+ } else {
+ // Catchall non-range index, i.e., [n] or [n << m]
+ if let ty::Array(..) = ty.kind() {
+ // Index is a constant uint.
+ if let Some(..) = constant(cx, cx.typeck_results(), index) {
+ // Let rustc's `const_err` lint handle constant `usize` indexing on arrays.
+ return;
+ }
+ }
+
+ span_lint_and_help(
+ cx,
+ INDEXING_SLICING,
+ expr.span,
+ "indexing may panic",
+ None,
+ "consider using `.get(n)` or `.get_mut(n)` instead",
+ );
+ }
+ }
+ }
+}
+
+/// Returns a tuple of options with the start and end (exclusive) values of
+/// the range. If the start or end is not constant, None is returned.
+fn to_const_range<'tcx>(
+ cx: &LateContext<'tcx>,
+ range: higher::Range<'_>,
+ array_size: u128,
+) -> (Option<u128>, Option<u128>) {
+ let s = range
+ .start
+ .map(|expr| constant(cx, cx.typeck_results(), expr).map(|(c, _)| c));
+ let start = match s {
+ Some(Some(Constant::Int(x))) => Some(x),
+ Some(_) => None,
+ None => Some(0),
+ };
+
+ let e = range
+ .end
+ .map(|expr| constant(cx, cx.typeck_results(), expr).map(|(c, _)| c));
+ let end = match e {
+ Some(Some(Constant::Int(x))) => {
+ if range.limits == RangeLimits::Closed {
+ Some(x + 1)
+ } else {
+ Some(x)
+ }
+ },
+ Some(_) => None,
+ None => Some(array_size),
+ };
+
+ (start, end)
+}
projects / rustc.git / blobdiff