mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-24 12:03:28 +00:00
93 lines
3.1 KiB
Rust
93 lines
3.1 KiB
Rust
|
use clippy_utils::diagnostics::span_lint_and_help;
|
||
|
use rustc_hir::intravisit::{walk_expr, walk_fn, FnKind, NestedVisitorMap, Visitor};
|
||
|
use rustc_hir::{Body, Expr, ExprKind, FnDecl, FnHeader, HirId, IsAsync, Item, ItemKind, YieldSource};
|
||
|
use rustc_lint::{LateContext, LateLintPass};
|
||
|
use rustc_middle::hir::map::Map;
|
||
|
use rustc_session::{declare_lint_pass, declare_tool_lint};
|
||
|
use rustc_span::Span;
|
||
|
|
||
|
declare_clippy_lint! {
|
||
|
/// **What it does:** Checks for functions that are declared `async` but have no `.await`s inside of them.
|
||
|
///
|
||
|
/// **Why is this bad?** Async functions with no async code create overhead, both mentally and computationally.
|
||
|
/// Callers of async methods either need to be calling from an async function themselves or run it on an executor, both of which
|
||
|
/// causes runtime overhead and hassle for the caller.
|
||
|
///
|
||
|
/// **Known problems:** None
|
||
|
///
|
||
|
/// **Example:**
|
||
|
///
|
||
|
/// ```rust
|
||
|
/// // Bad
|
||
|
/// async fn get_random_number() -> i64 {
|
||
|
/// 4 // Chosen by fair dice roll. Guaranteed to be random.
|
||
|
/// }
|
||
|
/// let number_future = get_random_number();
|
||
|
///
|
||
|
/// // Good
|
||
|
/// fn get_random_number_improved() -> i64 {
|
||
|
/// 4 // Chosen by fair dice roll. Guaranteed to be random.
|
||
|
/// }
|
||
|
/// let number_future = async { get_random_number_improved() };
|
||
|
/// ```
|
||
|
pub UNUSED_ASYNC,
|
||
|
pedantic,
|
||
|
"finds async functions with no await statements"
|
||
|
}
|
||
|
|
||
|
declare_lint_pass!(UnusedAsync => [UNUSED_ASYNC]);
|
||
|
|
||
|
struct AsyncFnVisitor<'a, 'tcx> {
|
||
|
cx: &'a LateContext<'tcx>,
|
||
|
found_await: bool,
|
||
|
}
|
||
|
|
||
|
impl<'a, 'tcx> Visitor<'tcx> for AsyncFnVisitor<'a, 'tcx> {
|
||
|
type Map = Map<'tcx>;
|
||
|
|
||
|
fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
|
||
|
if let ExprKind::Yield(_, YieldSource::Await { .. }) = ex.kind {
|
||
|
self.found_await = true;
|
||
|
}
|
||
|
walk_expr(self, ex);
|
||
|
}
|
||
|
|
||
|
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
|
||
|
NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
|
||
|
}
|
||
|
}
|
||
|
|
||
|
impl<'tcx> LateLintPass<'tcx> for UnusedAsync {
|
||
|
fn check_item(&mut self, _: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
|
||
|
if let ItemKind::Trait(..) = item.kind {
|
||
|
return;
|
||
|
}
|
||
|
}
|
||
|
fn check_fn(
|
||
|
&mut self,
|
||
|
cx: &LateContext<'tcx>,
|
||
|
fn_kind: FnKind<'tcx>,
|
||
|
fn_decl: &'tcx FnDecl<'tcx>,
|
||
|
body: &Body<'tcx>,
|
||
|
span: Span,
|
||
|
hir_id: HirId,
|
||
|
) {
|
||
|
if let FnKind::ItemFn(_, _, FnHeader { asyncness, .. }, _) = &fn_kind {
|
||
|
if matches!(asyncness, IsAsync::Async) {
|
||
|
let mut visitor = AsyncFnVisitor { cx, found_await: false };
|
||
|
walk_fn(&mut visitor, fn_kind, fn_decl, body.id(), span, hir_id);
|
||
|
if !visitor.found_await {
|
||
|
span_lint_and_help(
|
||
|
cx,
|
||
|
UNUSED_ASYNC,
|
||
|
span,
|
||
|
"unused `async` for function with no await statements",
|
||
|
None,
|
||
|
"consider removing the `async` from this function",
|
||
|
);
|
||
|
}
|
||
|
}
|
||
|
}
|
||
|
}
|
||
|
}
|