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use rustc::mir::interpret::ConstValue;
use rustc::ty::{self, ConstKind};
use rustc_hir::*;
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_tool_lint, impl_lint_pass};
use if_chain::if_chain;
use crate::rustc_target::abi::LayoutOf;
use crate::utils::{snippet, span_lint_and_help};
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.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust,ignore
/// let a = [0u32; 1_000_000];
/// ```
pub LARGE_STACK_ARRAYS,
pedantic,
"allocating large arrays on stack may cause stack overflow"
}
pub struct LargeStackArrays {
maximum_allowed_size: u64,
}
impl LargeStackArrays {
#[must_use]
pub fn new(maximum_allowed_size: u64) -> Self {
Self { maximum_allowed_size }
}
}
impl_lint_pass!(LargeStackArrays => [LARGE_STACK_ARRAYS]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LargeStackArrays {
fn check_expr(&mut self, cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
if_chain! {
if let ExprKind::Repeat(_, _) = expr.kind;
if let ty::Array(element_type, cst) = cx.tables.expr_ty(expr).kind;
if let ConstKind::Value(val) = cst.val;
if let ConstValue::Scalar(element_count) = val;
if let Ok(element_count) = element_count.to_machine_usize(&cx.tcx);
if let Ok(element_size) = cx.layout_of(element_type).map(|l| l.size.bytes());
if self.maximum_allowed_size < element_count * element_size;
then {
span_lint_and_help(
cx,
LARGE_STACK_ARRAYS,
expr.span,
&format!(
"allocating a local array larger than {} bytes",
self.maximum_allowed_size
),
&format!(
"consider allocating on the heap with `vec!{}.into_boxed_slice()`",
snippet(cx, expr.span, "[...]")
),
);
}
}
}
}
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