Fix setting brightness to 0 in HomeKit when the On characteristic is not sent (#129201)

Author: bdraco

homeassistant/components/homekit/type_lights.py

@@ -171,16 +171,20 @@ def _async_send_events(self, _now: datetime) -> None:
         events = []
         service = SERVICE_TURN_ON
         params: dict[str, Any] = {ATTR_ENTITY_ID: self.entity_id}
+        has_on = CHAR_ON in char_values
 
-        if CHAR_ON in char_values:
+        if has_on:
             if not char_values[CHAR_ON]:
                 service = SERVICE_TURN_OFF
             events.append(f"Set state to {char_values[CHAR_ON]}")
 
         brightness_pct = None
         if CHAR_BRIGHTNESS in char_values:
             if char_values[CHAR_BRIGHTNESS] == 0:
-                events[-1] = "Set state to 0"
+                if has_on:
+                    events[-1] = "Set state to 0"
+                else:
+                    events.append("Set state to 0")
                 service = SERVICE_TURN_OFF
             else:
                 brightness_pct = char_values[CHAR_BRIGHTNESS]

tests/components/homekit/test_type_lights.py

@@ -226,6 +226,24 @@ async def test_light_brightness(
     assert len(events) == 3
     assert events[-1].data[ATTR_VALUE] == f"Set state to 0, brightness at 0{PERCENTAGE}"
 
+    hk_driver.set_characteristics(
+        {
+            HAP_REPR_CHARS: [
+                {
+                    HAP_REPR_AID: acc.aid,
+                    HAP_REPR_IID: char_brightness_iid,
+                    HAP_REPR_VALUE: 0,
+                },
+            ]
+        },
+        "mock_addr",
+    )
+    await _wait_for_light_coalesce(hass)
+    assert call_turn_off
+    assert call_turn_off[0].data[ATTR_ENTITY_ID] == entity_id
+    assert len(events) == 4
+    assert events[-1].data[ATTR_VALUE] == f"Set state to 0, brightness at 0{PERCENTAGE}"
+
     # 0 is a special case for homekit, see "Handle Brightness"
     # in update_state
     hass.states.async_set(