Disallow calls to tokio::spawn outside dedicated extension trait

Prevent accidentally spawning a task that could outlive the actor system
and become a zombie.

Any long-lived task should be tied to its owner by keeping RemoteHandle around.

daemon/clippy.toml

@@ -0,0 +1,3 @@
+disallowed-methods = [
+  "tokio::spawn", # tasks can outlive the actor system, prefer spawn_with_handle()
+]

daemon/src/lib.rs

@@ -1,6 +1,5 @@
 #![cfg_attr(not(test), warn(clippy::unwrap_used))]
 #![warn(clippy::disallowed_method)]
-
 use crate::db::load_all_cfds;
 use crate::maker_cfd::{FromTaker, NewTakerOnline};
 use crate::model::cfd::{Cfd, Order, UpdateCfdProposals};

daemon/src/tokio_ext.rs

@@ -10,6 +10,8 @@ where
     F: Future<Output = Result<(), E>> + Send + 'static,
     E: fmt::Display,
 {
+    // we want to disallow calls to tokio::spawn outside FutureExt
+    #[allow(clippy::disallowed_method)]
     tokio::spawn(async move {
         if let Err(e) = future.await {
             tracing::warn!("Task failed: {:#}", e);
@@ -40,6 +42,8 @@ where
         Self: Future<Output = ()> + Send + 'static,
     {
         let (future, handle) = self.remote_handle();
+        // we want to disallow calls to tokio::spawn outside FutureExt
+        #[allow(clippy::disallowed_method)]
         tokio::spawn(future);
         handle
     }