Fix media_player grouping while media_player is off (#58070)

Co-authored-by: Erik Montnemery <erik@montnemery.com>

homeassistant/components/media_player/__init__.py

@@ -896,11 +896,14 @@ class MediaPlayerEntity(Entity):
     @property
     def state_attributes(self):
         """Return the state attributes."""
-        if self.state == STATE_OFF:
-            return None
-
         state_attr = {}
 
+        if self.support_grouping:
+            state_attr[ATTR_GROUP_MEMBERS] = self.group_members
+
+        if self.state == STATE_OFF:
+            return state_attr
+
         for attr in ATTR_TO_PROPERTY:
             value = getattr(self, attr)
             if value is not None:
@@ -909,9 +912,6 @@ class MediaPlayerEntity(Entity):
         if self.media_image_remotely_accessible:
             state_attr["entity_picture_local"] = self.media_image_local
 
-        if self.support_grouping:
-            state_attr[ATTR_GROUP_MEMBERS] = self.group_members
-
         return state_attr
 
     async def async_browse_media(

tests/components/media_player/test_init.py

@@ -4,6 +4,7 @@ from unittest.mock import patch
 
 from homeassistant.components import media_player
 from homeassistant.components.websocket_api.const import TYPE_RESULT
+from homeassistant.const import ATTR_ENTITY_ID, STATE_OFF
 from homeassistant.setup import async_setup_component
 
 
@@ -183,3 +184,27 @@ async def test_media_browse(hass, hass_ws_client):
     assert msg["type"] == TYPE_RESULT
     assert msg["success"]
     assert msg["result"] == {"bla": "yo"}
+
+
+async def test_group_members_available_when_off(hass):
+    """Test that group_members are still available when media_player is off."""
+    await async_setup_component(
+        hass, "media_player", {"media_player": {"platform": "demo"}}
+    )
+    await hass.async_block_till_done()
+
+    # Fake group support for DemoYoutubePlayer
+    with patch(
+        "homeassistant.components.demo.media_player.YOUTUBE_PLAYER_SUPPORT",
+        media_player.SUPPORT_GROUPING | media_player.SUPPORT_TURN_OFF,
+    ):
+        await hass.services.async_call(
+            "media_player",
+            "turn_off",
+            {ATTR_ENTITY_ID: "media_player.bedroom"},
+            blocking=True,
+        )
+
+    state = hass.states.get("media_player.bedroom")
+    assert state.state == STATE_OFF
+    assert "group_members" in state.attributes