| //! lint on indexing and slicing operations |
| |
| use clippy_utils::consts::{constant, Constant}; |
| use clippy_utils::diagnostics::{span_lint, span_lint_and_then}; |
| use clippy_utils::higher; |
| use rustc_ast::ast::RangeLimits; |
| use rustc_hir::{Expr, ExprKind}; |
| use rustc_lint::{LateContext, LateLintPass}; |
| use rustc_middle::ty; |
| use rustc_session::impl_lint_pass; |
| |
| 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. |
| /// |
| /// ### Example |
| /// ```rust,no_run |
| /// let x = [1, 2, 3, 4]; |
| /// |
| /// x[9]; |
| /// &x[2..9]; |
| /// ``` |
| /// |
| /// Use instead: |
| /// ```no_run |
| /// # let x = [1, 2, 3, 4]; |
| /// // Index within bounds |
| /// |
| /// x[0]; |
| /// x[3]; |
| /// ``` |
| #[clippy::version = "pre 1.29.0"] |
| 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. |
| /// |
| /// ### Example |
| /// ```rust,no_run |
| /// // Vector |
| /// let x = vec![0; 5]; |
| /// |
| /// x[2]; |
| /// &x[2..100]; |
| /// |
| /// // Array |
| /// let y = [0, 1, 2, 3]; |
| /// |
| /// &y[10..100]; |
| /// &y[10..]; |
| /// ``` |
| /// |
| /// Use instead: |
| /// ```no_run |
| /// # #![allow(unused)] |
| /// |
| /// # let x = vec![0; 5]; |
| /// # let y = [0, 1, 2, 3]; |
| /// x.get(2); |
| /// x.get(2..100); |
| /// |
| /// y.get(10); |
| /// y.get(10..100); |
| /// ``` |
| #[clippy::version = "pre 1.29.0"] |
| pub INDEXING_SLICING, |
| restriction, |
| "indexing/slicing usage" |
| } |
| |
| impl_lint_pass!(IndexingSlicing => [INDEXING_SLICING, OUT_OF_BOUNDS_INDEXING]); |
| |
| #[derive(Copy, Clone)] |
| pub struct IndexingSlicing { |
| suppress_restriction_lint_in_const: bool, |
| } |
| |
| impl IndexingSlicing { |
| pub fn new(suppress_restriction_lint_in_const: bool) -> Self { |
| Self { |
| suppress_restriction_lint_in_const, |
| } |
| } |
| } |
| |
| impl<'tcx> LateLintPass<'tcx> for IndexingSlicing { |
| fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { |
| if self.suppress_restriction_lint_in_const && cx.tcx.hir().is_inside_const_context(expr.hir_id) { |
| return; |
| } |
| |
| if let ExprKind::Index(array, index, _) = &expr.kind { |
| let note = "the suggestion might not be applicable in constant blocks"; |
| let ty = cx.typeck_results().expr_ty(array).peel_refs(); |
| if let Some(range) = higher::Range::hir(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_target_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_then(cx, INDEXING_SLICING, expr.span, "slicing may panic", |diag| { |
| diag.help(help_msg); |
| |
| if cx.tcx.hir().is_inside_const_context(expr.hir_id) { |
| diag.note(note); |
| } |
| }); |
| } else { |
| // Catchall non-range index, i.e., [n] or [n << m] |
| if let ty::Array(..) = ty.kind() { |
| // Index is a const block. |
| if let ExprKind::ConstBlock(..) = index.kind { |
| return; |
| } |
| // Index is a constant uint. |
| if let Some(constant) = constant(cx, cx.typeck_results(), index) { |
| // only `usize` index is legal in rust array index |
| // leave other type to rustc |
| if let Constant::Int(off) = constant |
| && off <= usize::MAX as u128 |
| && let ty::Uint(utype) = cx.typeck_results().expr_ty(index).kind() |
| && *utype == ty::UintTy::Usize |
| && let ty::Array(_, s) = ty.kind() |
| && let Some(size) = s.try_eval_target_usize(cx.tcx, cx.param_env) |
| { |
| // get constant offset and check whether it is in bounds |
| let off = usize::try_from(off).unwrap(); |
| let size = usize::try_from(size).unwrap(); |
| |
| if off >= size { |
| span_lint(cx, OUT_OF_BOUNDS_INDEXING, expr.span, "index is out of bounds"); |
| } |
| } |
| // Let rustc's `const_err` lint handle constant `usize` indexing on arrays. |
| return; |
| } |
| } |
| |
| span_lint_and_then(cx, INDEXING_SLICING, expr.span, "indexing may panic", |diag| { |
| diag.help("consider using `.get(n)` or `.get_mut(n)` instead"); |
| |
| if cx.tcx.hir().is_inside_const_context(expr.hir_id) { |
| diag.note(note); |
| } |
| }); |
| } |
| } |
| } |
| } |
| |
| /// 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(cx: &LateContext<'_>, range: higher::Range<'_>, array_size: u128) -> (Option<u128>, Option<u128>) { |
| let s = range.start.map(|expr| constant(cx, cx.typeck_results(), expr)); |
| 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)); |
| 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) |
| } |