From 99010bab18de0c15fff0cb2fb7e3580d176108d0 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Thu, 15 Oct 2020 02:26:51 -0500
Subject: [PATCH] Permit event trackers to accept an empty list of entities or
 domains (#41857)

---
 homeassistant/helpers/event.py | 17 +++++++++++
 tests/helpers/test_event.py    | 52 ++++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+)

diff --git a/homeassistant/helpers/event.py b/homeassistant/helpers/event.py
index b6d59bb500c..33d2082c99e 100644
--- a/homeassistant/helpers/event.py
+++ b/homeassistant/helpers/event.py
@@ -233,6 +233,9 @@ def async_track_state_change_event(
     care about the state change events so we can
     do a fast dict lookup to route events.
     """
+    entity_ids = _async_string_to_lower_list(entity_ids)
+    if not entity_ids:
+        return _remove_empty_listener
 
     entity_callbacks = hass.data.setdefault(TRACK_STATE_CHANGE_CALLBACKS, {})
 
@@ -277,6 +280,11 @@ def async_track_state_change_event(
     return remove_listener
 
 
+@callback
+def _remove_empty_listener() -> None:
+    """Remove a listener that does nothing."""
+
+
 @callback
 def _async_remove_indexed_listeners(
     hass: HomeAssistant,
@@ -309,6 +317,9 @@ def async_track_entity_registry_updated_event(
 
     Similar to async_track_state_change_event.
     """
+    entity_ids = _async_string_to_lower_list(entity_ids)
+    if not entity_ids:
+        return _remove_empty_listener
 
     entity_callbacks = hass.data.setdefault(TRACK_ENTITY_REGISTRY_UPDATED_CALLBACKS, {})
 
@@ -381,6 +392,9 @@ def async_track_state_added_domain(
     action: Callable[[Event], Any],
 ) -> Callable[[], None]:
     """Track state change events when an entity is added to domains."""
+    domains = _async_string_to_lower_list(domains)
+    if not domains:
+        return _remove_empty_listener
 
     domain_callbacks = hass.data.setdefault(TRACK_STATE_ADDED_DOMAIN_CALLBACKS, {})
 
@@ -424,6 +438,9 @@ def async_track_state_removed_domain(
     action: Callable[[Event], Any],
 ) -> Callable[[], None]:
     """Track state change events when an entity is removed from domains."""
+    domains = _async_string_to_lower_list(domains)
+    if not domains:
+        return _remove_empty_listener
 
     domain_callbacks = hass.data.setdefault(TRACK_STATE_REMOVED_DOMAIN_CALLBACKS, {})
 
diff --git a/tests/helpers/test_event.py b/tests/helpers/test_event.py
index bb0d17d7b0e..14b208b68d4 100644
--- a/tests/helpers/test_event.py
+++ b/tests/helpers/test_event.py
@@ -486,6 +486,19 @@ async def test_async_track_state_change_event(hass):
     unsub_throws()
 
 
+async def test_async_track_state_change_event_with_empty_list(hass):
+    """Test async_track_state_change_event passing an empty list of entities."""
+    unsub_single = async_track_state_change_event(
+        hass, [], ha.callback(lambda event: None)
+    )
+    unsub_single2 = async_track_state_change_event(
+        hass, [], ha.callback(lambda event: None)
+    )
+
+    unsub_single2()
+    unsub_single()
+
+
 async def test_async_track_state_added_domain(hass):
     """Test async_track_state_added_domain."""
     single_entity_id_tracker = []
@@ -568,6 +581,32 @@ async def test_async_track_state_added_domain(hass):
     unsub_throws()
 
 
+async def test_async_track_state_added_domain_with_empty_list(hass):
+    """Test async_track_state_added_domain passing an empty list of domains."""
+    unsub_single = async_track_state_added_domain(
+        hass, [], ha.callback(lambda event: None)
+    )
+    unsub_single2 = async_track_state_added_domain(
+        hass, [], ha.callback(lambda event: None)
+    )
+
+    unsub_single2()
+    unsub_single()
+
+
+async def test_async_track_state_removed_domain_with_empty_list(hass):
+    """Test async_track_state_removed_domain passing an empty list of domains."""
+    unsub_single = async_track_state_removed_domain(
+        hass, [], ha.callback(lambda event: None)
+    )
+    unsub_single2 = async_track_state_removed_domain(
+        hass, [], ha.callback(lambda event: None)
+    )
+
+    unsub_single2()
+    unsub_single()
+
+
 async def test_async_track_state_removed_domain(hass):
     """Test async_track_state_removed_domain."""
     single_entity_id_tracker = []
@@ -2876,3 +2915,16 @@ async def test_async_track_entity_registry_updated_event_with_a_callback_that_th
     unsub2()
 
     assert event_data[0] == {"action": "create", "entity_id": "switch.puppy_feeder"}
+
+
+async def test_async_track_entity_registry_updated_event_with_empty_list(hass):
+    """Test async_track_entity_registry_updated_event passing an empty list of entities."""
+    unsub_single = hass.helpers.event.async_track_entity_registry_updated_event(
+        [], ha.callback(lambda event: None)
+    )
+    unsub_single2 = hass.helpers.event.async_track_entity_registry_updated_event(
+        [], ha.callback(lambda event: None)
+    )
+
+    unsub_single2()
+    unsub_single()