[workerd-cxx] enable "expect" attribute (#47)

* [workerd-cxx] enable "expect" attribute

It is relatively new.

Author: mikea

kj-rs/tests/test_futures.rs

@@ -149,10 +149,7 @@ pub async fn new_layered_ready_future_void() -> Result<()> {
 }
 
 // From example at https://doc.rust-lang.org/std/future/fn.poll_fn.html#capturing-a-pinned-state
-async fn naive_select<T>(
-    a: impl Future<Output = T>,
-    b: impl Future<Output = T>,
-) -> T {
+async fn naive_select<T>(a: impl Future<Output = T>, b: impl Future<Output = T>) -> T {
     let (mut a, mut b) = (pin!(a), pin!(b));
     future::poll_fn(move |cx| {
         if let Poll::Ready(r) = a.as_mut().poll(cx) {

syntax/attrs.rs

@@ -159,6 +159,7 @@ pub fn parse(cx: &mut Errors, attrs: Vec<Attribute>, mut parser: Parser) -> Othe
             || attr_path.is_ident("forbid")
             || attr_path.is_ident("deprecated")
             || attr_path.is_ident("must_use")
+            || attr_path.is_ident("expect")
         {
             // https://doc.rust-lang.org/reference/attributes/diagnostics.html
             passthrough_attrs.push(attr);