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use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::source::snippet;
use rustc_hir::{Expr, ExprKind, Item, ItemKind, Node};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::layout::LayoutOf;
use rustc_middle::ty::{self, ConstKind};
use rustc_session::{declare_tool_lint, impl_lint_pass};
declare_clippy_lint! {
/// ### What it does
/// Checks for local arrays that may be too large.
///
/// ### Why is this bad?
/// Large local arrays may cause stack overflow.
///
/// ### Example
/// ```rust,ignore
/// let a = [0u32; 1_000_000];
/// ```
#[clippy::version = "1.41.0"]
pub LARGE_STACK_ARRAYS,
pedantic,
"allocating large arrays on stack may cause stack overflow"
}
pub struct LargeStackArrays {
maximum_allowed_size: u128,
}
impl LargeStackArrays {
#[must_use]
pub fn new(maximum_allowed_size: u128) -> Self {
Self { maximum_allowed_size }
}
}
impl_lint_pass!(LargeStackArrays => [LARGE_STACK_ARRAYS]);
impl<'tcx> LateLintPass<'tcx> for LargeStackArrays {
fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
if let ExprKind::Repeat(_, _) = expr.kind
&& let ty::Array(element_type, cst) = cx.typeck_results().expr_ty(expr).kind()
&& let ConstKind::Value(ty::ValTree::Leaf(element_count)) = cst.kind()
&& let Ok(element_count) = element_count.try_to_target_usize(cx.tcx)
&& let Ok(element_size) = cx.layout_of(*element_type).map(|l| l.size.bytes())
&& !cx.tcx.hir().parent_iter(expr.hir_id)
.any(|(_, node)| matches!(node, Node::Item(Item { kind: ItemKind::Static(..), .. })))
&& self.maximum_allowed_size < u128::from(element_count) * u128::from(element_size) {
span_lint_and_help(
cx,
LARGE_STACK_ARRAYS,
expr.span,
&format!(
"allocating a local array larger than {} bytes",
self.maximum_allowed_size
),
None,
&format!(
"consider allocating on the heap with `vec!{}.into_boxed_slice()`",
snippet(cx, expr.span, "[...]")
),
);
}
}
}
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