Reduce creation of MQTT related discovery tasks (#90801)

* Reduce creation of MQTT related discovery tasks

Most of the branching can avoid creating a task as it
did not need to await for the majority of cases. We
fallback to creating a task for the cases were we do
need to await.

* comment

* revert

homeassistant/components/mqtt/discovery.py

@@ -218,7 +218,8 @@ async def async_start(  # noqa: C901
         discovery_hash = (component, discovery_id)
         if discovery_hash in mqtt_data.discovery_already_discovered or payload:
 
-            async def discovery_done(_: Any) -> None:
+            @callback
+            def discovery_done(_: Any) -> None:
                 pending = mqtt_data.discovery_pending_discovered[discovery_hash][
                     "pending"
                 ]

homeassistant/components/mqtt/mixins.py

@@ -832,8 +832,37 @@ class MqttDiscoveryUpdate(Entity):
             else:
                 await self.async_remove(force_remove=True)
 
-        async def discovery_callback(payload: MQTTDiscoveryPayload) -> None:
+        async def _async_process_discovery_update(
-            """Handle discovery update."""
+            payload: MQTTDiscoveryPayload,
+            discovery_update: Callable[
+                [MQTTDiscoveryPayload], Coroutine[Any, Any, None]
+            ],
+            discovery_data: DiscoveryInfoType,
+        ) -> None:
+            """Process discovery update."""
+            try:
+                await discovery_update(payload)
+            finally:
+                send_discovery_done(self.hass, discovery_data)
+
+        async def _async_process_discovery_update_and_remove(
+            payload: MQTTDiscoveryPayload, discovery_data: DiscoveryInfoType
+        ) -> None:
+            """Process discovery update and remove entity."""
+            self._cleanup_discovery_on_remove()
+            await _async_remove_state_and_registry_entry(self)
+            send_discovery_done(self.hass, discovery_data)
+
+        @callback
+        def discovery_callback(payload: MQTTDiscoveryPayload) -> None:
+            """Handle discovery update.
+
+            If the payload has changed we will create a task to
+            do the discovery update.
+
+            As this callback can fire when nothing has changed, this
+            is a normal function to avoid task creation until it is needed.
+            """
             _LOGGER.debug(
                 "Got update for entity with hash: %s '%s'",
                 discovery_hash,
@@ -846,17 +875,20 @@ class MqttDiscoveryUpdate(Entity):
             if not payload:
                 # Empty payload: Remove component
                 _LOGGER.info("Removing component: %s", self.entity_id)
-                self._cleanup_discovery_on_remove()
+                self.hass.async_create_task(
-                await _async_remove_state_and_registry_entry(self)
+                    _async_process_discovery_update_and_remove(
-                send_discovery_done(self.hass, self._discovery_data)
+                        payload, self._discovery_data
+                    )
+                )
             elif self._discovery_update:
                 if old_payload != self._discovery_data[ATTR_DISCOVERY_PAYLOAD]:
                     # Non-empty, changed payload: Notify component
                     _LOGGER.info("Updating component: %s", self.entity_id)
-                    try:
+                    self.hass.async_create_task(
-                        await self._discovery_update(payload)
+                        _async_process_discovery_update(
-                    finally:
+                            payload, self._discovery_update, self._discovery_data
-                        send_discovery_done(self.hass, self._discovery_data)
+                        )
+                    )
                 else:
                     # Non-empty, unchanged payload: Ignore to avoid changing states
                     _LOGGER.debug("Ignoring unchanged update for: %s", self.entity_id)