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//! 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. Arrays are special cased, 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
/// // 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);
/// ```
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(..) = ty.sty {
// 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;
}
}
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))
}