mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-22 19:13:29 +00:00
204 lines
6.3 KiB
Rust
204 lines
6.3 KiB
Rust
//! lint on indexing and slicing operations
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use clippy_utils::consts::{constant, Constant};
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use clippy_utils::diagnostics::{span_lint, span_lint_and_help};
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use clippy_utils::higher;
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use rustc_ast::ast::RangeLimits;
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use rustc_hir::{Expr, ExprKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for out of bounds array indexing with a constant
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/// index.
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///
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/// ### Why is this bad?
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/// This will always panic at runtime.
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///
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/// ### Known problems
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/// Hopefully none.
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///
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/// ### Example
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/// ```no_run
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/// # #![allow(const_err)]
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/// let x = [1, 2, 3, 4];
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///
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/// // Bad
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/// x[9];
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/// &x[2..9];
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///
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/// // Good
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/// x[0];
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/// x[3];
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/// ```
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pub OUT_OF_BOUNDS_INDEXING,
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correctness,
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"out of bounds constant indexing"
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}
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for usage of indexing or slicing. Arrays are special cases, this lint
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/// does report on arrays if we can tell that slicing operations are in bounds and does not
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/// lint on constant `usize` indexing on arrays because that is handled by rustc's `const_err` lint.
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///
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/// ### Why is this bad?
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/// Indexing and slicing can panic at runtime and there are
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/// safe alternatives.
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///
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/// ### Known problems
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/// Hopefully none.
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///
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/// ### Example
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/// ```rust,no_run
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/// // Vector
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/// let x = vec![0; 5];
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///
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/// // Bad
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/// x[2];
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/// &x[2..100];
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/// &x[2..];
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/// &x[..100];
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///
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/// // Good
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/// x.get(2);
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/// x.get(2..100);
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/// x.get(2..);
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/// x.get(..100);
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///
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/// // Array
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/// let y = [0, 1, 2, 3];
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///
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/// // Bad
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/// &y[10..100];
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/// &y[10..];
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/// &y[..100];
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///
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/// // Good
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/// &y[2..];
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/// &y[..2];
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/// &y[0..3];
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/// y.get(10);
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/// y.get(10..100);
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/// y.get(10..);
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/// y.get(..100);
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/// ```
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pub INDEXING_SLICING,
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restriction,
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"indexing/slicing usage"
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}
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declare_lint_pass!(IndexingSlicing => [INDEXING_SLICING, OUT_OF_BOUNDS_INDEXING]);
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impl<'tcx> LateLintPass<'tcx> for IndexingSlicing {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if let ExprKind::Index(array, index) = &expr.kind {
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let ty = cx.typeck_results().expr_ty(array).peel_refs();
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if let Some(range) = higher::Range::hir(index) {
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// Ranged indexes, i.e., &x[n..m], &x[n..], &x[..n] and &x[..]
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if let ty::Array(_, s) = ty.kind() {
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let size: u128 = if let Some(size) = s.try_eval_usize(cx.tcx, cx.param_env) {
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size.into()
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} else {
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return;
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};
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let const_range = to_const_range(cx, range, size);
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if let (Some(start), _) = const_range {
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if start > size {
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span_lint(
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cx,
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OUT_OF_BOUNDS_INDEXING,
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range.start.map_or(expr.span, |start| start.span),
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"range is out of bounds",
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);
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return;
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}
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}
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if let (_, Some(end)) = const_range {
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if end > size {
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span_lint(
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cx,
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OUT_OF_BOUNDS_INDEXING,
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range.end.map_or(expr.span, |end| end.span),
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"range is out of bounds",
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);
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return;
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}
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}
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if let (Some(_), Some(_)) = const_range {
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// early return because both start and end are constants
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// and we have proven above that they are in bounds
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return;
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}
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}
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let help_msg = match (range.start, range.end) {
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(None, Some(_)) => "consider using `.get(..n)`or `.get_mut(..n)` instead",
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(Some(_), None) => "consider using `.get(n..)` or .get_mut(n..)` instead",
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(Some(_), Some(_)) => "consider using `.get(n..m)` or `.get_mut(n..m)` instead",
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(None, None) => return, // [..] is ok.
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};
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span_lint_and_help(cx, INDEXING_SLICING, expr.span, "slicing may panic", None, help_msg);
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} else {
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// Catchall non-range index, i.e., [n] or [n << m]
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if let ty::Array(..) = ty.kind() {
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// Index is a constant uint.
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if let Some(..) = constant(cx, cx.typeck_results(), index) {
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// Let rustc's `const_err` lint handle constant `usize` indexing on arrays.
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return;
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}
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}
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span_lint_and_help(
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cx,
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INDEXING_SLICING,
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expr.span,
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"indexing may panic",
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None,
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"consider using `.get(n)` or `.get_mut(n)` instead",
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);
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}
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}
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}
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}
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/// Returns a tuple of options with the start and end (exclusive) values of
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/// the range. If the start or end is not constant, None is returned.
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fn to_const_range<'tcx>(
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cx: &LateContext<'tcx>,
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range: higher::Range<'_>,
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array_size: u128,
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) -> (Option<u128>, Option<u128>) {
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let s = range
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.start
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.map(|expr| constant(cx, cx.typeck_results(), expr).map(|(c, _)| c));
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let start = match s {
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Some(Some(Constant::Int(x))) => Some(x),
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Some(_) => None,
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None => Some(0),
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};
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let e = range
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.end
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.map(|expr| constant(cx, cx.typeck_results(), expr).map(|(c, _)| c));
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let end = match e {
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Some(Some(Constant::Int(x))) => {
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if range.limits == RangeLimits::Closed {
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Some(x + 1)
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} else {
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Some(x)
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}
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},
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Some(_) => None,
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None => Some(array_size),
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};
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(start, end)
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}
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