feat(sdk): Implement EventHandlerContext for tuples.

This patch implements `EventHandlerContext` for tuples where each part
implements `EventHandlerContext` itself.

crates/matrix-sdk/src/event_handler/context.rs

@@ -107,3 +107,38 @@ impl<T> Deref for Ctx<T> {
         &self.0
     }
 }
+
+// `EventHandlerContext` for tuples.
+
+impl EventHandlerContext for () {
+    fn from_data(_data: &EventHandlerData<'_>) -> Option<Self> {
+        Some(())
+    }
+}
+
+macro_rules! impl_context_for_tuple {
+    ( $( $ty:ident ),* $(,)? ) => {
+        #[allow(non_snake_case)]
+        impl< $( $ty ),* > EventHandlerContext for ( $( $ty ),* , )
+        where
+            $( $ty : EventHandlerContext, )*
+        {
+            fn from_data(data: &EventHandlerData<'_>) -> Option<Self> {
+                $(
+                    let $ty = $ty ::from_data(data)?;
+                )*
+
+                Some(( $( $ty ),* , ))
+            }
+        }
+    };
+}
+
+impl_context_for_tuple!(A);
+impl_context_for_tuple!(A, B);
+impl_context_for_tuple!(A, B, C);
+impl_context_for_tuple!(A, B, C, D);
+impl_context_for_tuple!(A, B, C, D, E);
+impl_context_for_tuple!(A, B, C, D, E, F);
+impl_context_for_tuple!(A, B, C, D, E, F, G);
+impl_context_for_tuple!(A, B, C, D, E, F, G, H);

crates/matrix-sdk/src/event_handler/mod.rs

@@ -753,6 +753,20 @@ mod tests {
         Ok(())
     }
 
+    #[async_test]
+    #[allow(dependency_on_unit_never_type_fallback)]
+    async fn test_add_event_handler_with_tuples() -> crate::Result<()> {
+        let client = logged_in_client(None).await;
+
+        client.add_event_handler(
+            |_ev: OriginalSyncRoomMemberEvent, (_room, _client): (Room, Client)| future::ready(()),
+        );
+
+        // If it compiles, it works. No need to assert anything.
+
+        Ok(())
+    }
+
     #[async_test]
     #[allow(dependency_on_unit_never_type_fallback)]
     async fn test_remove_event_handler() -> crate::Result<()> {