//! lint on indexing and slicing operations use crate::consts::{constant, Constant}; use crate::utils; use crate::utils::higher; use crate::utils::higher::Range; use rustc::hir::*; use rustc::lint::*; use rustc::ty; use syntax::ast::RangeLimits; /// **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:** /// ```rust /// let x = [1,2,3,4]; /// /// // Bad /// x[9]; /// &x[2..9]; /// /// // Good /// x[0]; /// x[3]; /// ``` declare_clippy_lint! { pub OUT_OF_BOUNDS_INDEXING, correctness, "out of bounds constant indexing" } /// **What it does:** Checks for usage of indexing or slicing. Does not report /// on arrays if we can tell that the indexing or slicing operations are in /// bounds. /// /// **Why is this bad?** Indexing and slicing can panic at runtime and there are /// safe alternatives. /// /// **Known problems:** Hopefully none. /// /// **Example:** /// ```rust /// // 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]; /// &y[10..100]; /// &y[10..]; /// &y[..100]; /// /// // Good /// y[2]; /// &y[2..]; /// &y[..2]; /// &y[0..3]; /// y.get(10); /// y.get(10..100); /// y.get(10..); /// y.get(..100); /// ``` declare_clippy_lint! { pub INDEXING_SLICING, pedantic, "indexing/slicing usage" } #[derive(Copy, Clone)] pub struct IndexingSlicing; impl LintPass for IndexingSlicing { fn get_lints(&self) -> LintArray { lint_array!(INDEXING_SLICING, OUT_OF_BOUNDS_INDEXING) } } impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IndexingSlicing { fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) { if let ExprIndex(ref array, ref index) = &expr.node { let ty = cx.tables.expr_ty(array); if let Some(range) = higher::range(cx, index) { // Ranged indexes, i.e. &x[n..m], &x[n..], &x[..n] and &x[..] if let ty::TyArray(_, s) = ty.sty { let size: u128 = s.assert_usize(cx.tcx).unwrap().into(); // Index is a constant range. if let Some((start, end)) = to_const_range(cx, range, size) { if start > size || end > size { utils::span_lint( cx, OUT_OF_BOUNDS_INDEXING, expr.span, "range is out of 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. }; utils::span_help_and_lint( cx, INDEXING_SLICING, expr.span, "slicing may panic.", help_msg, ); } else { // Catchall non-range index, i.e. [n] or [n << m] if let ty::TyArray(_, s) = ty.sty { let size: u128 = s.assert_usize(cx.tcx).unwrap().into(); // Index is a constant uint. if let Some((Constant::Int(const_index), _)) = constant(cx, cx.tables, index) { if size <= const_index { utils::span_lint( cx, OUT_OF_BOUNDS_INDEXING, expr.span, "const index is out of bounds", ); } // Else index is in bounds, ok. return; } } utils::span_help_and_lint( cx, INDEXING_SLICING, expr.span, "indexing may panic.", "Consider using `.get(n)` or `.get_mut(n)` instead", ); } } } } /// Returns an option containing a tuple with the start and end (exclusive) of /// the range. fn to_const_range<'a, 'tcx>( cx: &LateContext<'a, 'tcx>, range: Range, array_size: u128, ) -> Option<(u128, u128)> { let s = range .start .map(|expr| constant(cx, cx.tables, expr).map(|(c, _)| c)); let start = match s { Some(Some(Constant::Int(x))) => x, Some(_) => return None, None => 0, }; let e = range .end .map(|expr| constant(cx, cx.tables, expr).map(|(c, _)| c)); let end = match e { Some(Some(Constant::Int(x))) => if range.limits == RangeLimits::Closed { x + 1 } else { x }, Some(_) => return None, None => array_size, }; Some((start, end)) }