Add test to validate new behavior

core/lib/tests/drop-in-async-context.rs

@@ -0,0 +1,50 @@
+#[macro_use] extern crate rocket;
+
+use rocket::{Rocket, Build, build, fairing::AdHoc, Orbit};
+
+struct AsyncDropInAsync;
+
+impl Drop for AsyncDropInAsync {
+    fn drop(&mut self) {
+        // Attempt to fetch the current runtime while dropping
+        // Pools in rocket_sync_db_pools (and maybe rocket_db_pools)
+        // do use this capability. They spawn tasks to asyncronously
+        // complete shutdown of the pool, which triggers the same panic.
+        let _ = rocket::tokio::runtime::Handle::current();
+    }
+}
+
+fn rocket() -> Rocket<Build> {
+    build().manage(AsyncDropInAsync).attach(AdHoc::on_liftoff(
+        "Shutdown immediately",
+        |rocket: &Rocket<Orbit>| Box::pin(async {
+            rocket.shutdown().notify();
+        }
+    )))
+}
+
+mod launch {
+    #[launch]
+    fn launch() -> _ {
+        super::rocket()
+    }
+    #[test]
+    fn test_launch() {
+        main();
+    }
+}
+
+mod main {
+    #[rocket::main]
+    async fn main() {
+        super::rocket().launch().await.unwrap();
+    }
+    #[test]
+    fn test_main() {
+        main();
+    }
+    #[test]
+    fn test_execute() {
+        rocket::execute(super::rocket().launch()).unwrap();
+    }
+}