pallet-message-queue: add queue pausing (#14318)

* pallet-message-queue: add queue pausing

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Fix build

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Remove check

Otherwise it would not start servicing queues that started paused
and became unpaused afterwards.

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

---------

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

substrate/frame/support/src/traits.rs

@@ -113,7 +113,7 @@ pub use preimages::{Bounded, BoundedInline, FetchResult, Hash, QueryPreimage, St
 mod messages;
 pub use messages::{
 	EnqueueMessage, ExecuteOverweightError, Footprint, NoopServiceQueues, ProcessMessage,
-	ProcessMessageError, ServiceQueues, TransformOrigin,
+	ProcessMessageError, QueuePausedQuery, ServiceQueues, TransformOrigin,
 };
 
 #[cfg(feature = "try-runtime")]

substrate/frame/support/src/traits/messages.rs

@@ -69,8 +69,18 @@ pub trait ProcessMessage {
 pub enum ExecuteOverweightError {
 	/// The referenced message was not found.
 	NotFound,
+	/// The message was already processed.
+	///
+	/// This can be treated as success condition.
+	AlreadyProcessed,
 	/// The available weight was insufficient to execute the message.
 	InsufficientWeight,
+	/// The queue is paused and no message can be executed from it.
+	///
+	/// This can change at any time and may resolve in the future by re-trying.
+	QueuePaused,
+	/// An unspecified error.
+	Other,
 }
 
 /// Can service queues and execute overweight messages.
@@ -220,3 +230,15 @@ where
 		E::footprint(O::get())
 	}
 }
+
+/// Provides information on paused queues.
+pub trait QueuePausedQuery<Origin> {
+	/// Whether this queue is paused.
+	fn is_paused(origin: &Origin) -> bool;
+}
+
+impl<Origin> QueuePausedQuery<Origin> for () {
+	fn is_paused(_: &Origin) -> bool {
+		false
+	}
+}