| //! 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.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::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.tables(), 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.tables(), 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.tables(), 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) |
| } |