88 lines
3.0 KiB
Rust
88 lines
3.0 KiB
Rust
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use clippy_utils::source::snippet;
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use clippy_utils::{diagnostics::span_lint_and_sugg, ty::implements_trait};
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use rustc_errors::Applicability;
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use rustc_hir::{Expr, ExprKind, LangItem, MatchSource, QPath};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_tool_lint, impl_lint_pass};
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use rustc_target::abi::Size;
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declare_clippy_lint! {
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/// ### What it does
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/// It checks for the size of a `Future` created by `async fn` or `async {}`.
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///
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/// ### Why is this bad?
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/// Due to the current [unideal implemention](https://github.com/rust-lang/rust/issues/69826) of `Generator`,
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/// large size of a `Future` may cause stack overflows.
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///
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/// ### Example
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/// ```rust
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/// async fn wait(f: impl std::future::Future<Output = ()>) {}
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///
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/// async fn big_fut(arg: [u8; 1024]) {}
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///
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/// pub async fn test() {
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/// let fut = big_fut([0u8; 1024]);
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/// wait(fut).await;
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/// }
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/// ```
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///
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/// `Box::pin` the big future instead.
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///
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/// ```rust
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/// async fn wait(f: impl std::future::Future<Output = ()>) {}
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///
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/// async fn big_fut(arg: [u8; 1024]) {}
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///
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/// pub async fn test() {
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/// let fut = Box::pin(big_fut([0u8; 1024]));
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/// wait(fut).await;
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/// }
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/// ```
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#[clippy::version = "1.68.0"]
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pub LARGE_FUTURES,
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pedantic,
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"large future may lead to unexpected stack overflows"
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}
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#[derive(Copy, Clone)]
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pub struct LargeFuture {
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future_size_threshold: u64,
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}
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impl LargeFuture {
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pub fn new(future_size_threshold: u64) -> Self {
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Self { future_size_threshold }
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}
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}
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impl_lint_pass!(LargeFuture => [LARGE_FUTURES]);
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impl<'tcx> LateLintPass<'tcx> for LargeFuture {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
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if matches!(expr.span.ctxt().outer_expn_data().kind, rustc_span::ExpnKind::Macro(..)) {
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return;
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}
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if let ExprKind::Match(expr, _, MatchSource::AwaitDesugar) = expr.kind {
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if let ExprKind::Call(func, [expr, ..]) = expr.kind
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&& let ExprKind::Path(QPath::LangItem(LangItem::IntoFutureIntoFuture, ..)) = func.kind
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&& let ty = cx.typeck_results().expr_ty(expr)
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&& let Some(future_trait_def_id) = cx.tcx.lang_items().future_trait()
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&& implements_trait(cx, ty, future_trait_def_id, &[])
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&& let Ok(layout) = cx.tcx.layout_of(cx.param_env.and(ty))
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&& let size = layout.layout.size()
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&& size >= Size::from_bytes(self.future_size_threshold)
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{
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span_lint_and_sugg(
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cx,
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LARGE_FUTURES,
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expr.span,
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&format!("large future with a size of {} bytes", size.bytes()),
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"consider `Box::pin` on it",
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format!("Box::pin({})", snippet(cx, expr.span, "..")),
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Applicability::Unspecified,
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);
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}
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}
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}
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}
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