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|
//! 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::{declare_tool_lint, 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:
/// ```rust
/// # 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:
/// ```rust
/// # #![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_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(cx, cx.typeck_results(), index) {
// 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).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)
}
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