Fix friendly names for empty entity name overrides (#181576)

homeassistant/helpers/entity_registry.py

@@ -550,7 +550,7 @@ def _async_get_full_entity_name(
     if name is None and overridden_name is not None:
         full_name = overridden_name
 
-    elif not use_legacy_naming or name is None:
+    elif not use_legacy_naming or not name:
         raw_device_name: str | None = None
         device_name: str | None = None
         parent_device_name: str | None = None

tests/helpers/test_entity.py

@@ -1042,6 +1042,44 @@ async def _test_friendly_name(
     assert state.attributes.get(ATTR_FRIENDLY_NAME) == expected_friendly_name
 
 
+@pytest.mark.parametrize("has_entity_name", [False, True])
+async def test_friendly_name_empty_override_uses_device_name(
+    hass: HomeAssistant,
+    entity_registry: er.EntityRegistry,
+    device_registry: dr.DeviceRegistry,
+    has_entity_name: bool,
+) -> None:
+    """Test an empty name follows the device until the override is reset."""
+    ent = MockEntity(
+        unique_id="empty_name",
+        device_info={
+            "identifiers": {("test", "device")},
+            "name": "Device Bla",
+        },
+        has_entity_name=has_entity_name,
+        name="Temperature",
+    )
+    await _test_friendly_name(hass, ent, "Device Bla Temperature")
+
+    entry = entity_registry.async_update_entity(ent.entity_id, name="")
+    await hass.async_block_till_done()
+    assert hass.states.get(ent.entity_id).attributes[ATTR_FRIENDLY_NAME] == "Device Bla"
+
+    assert entry.device_id is not None
+    device_registry.async_update_device(entry.device_id, name_by_user="Living room")
+    await hass.async_block_till_done()
+    assert (
+        hass.states.get(ent.entity_id).attributes[ATTR_FRIENDLY_NAME] == "Living room"
+    )
+
+    entity_registry.async_update_entity(ent.entity_id, name=None)
+    await hass.async_block_till_done()
+    assert (
+        hass.states.get(ent.entity_id).attributes[ATTR_FRIENDLY_NAME]
+        == "Living room Temperature"
+    )
+
+
 @pytest.mark.parametrize(
     (
         "has_entity_name",

tests/helpers/test_entity_registry.py

@@ -3658,6 +3658,16 @@ async def test_restore_states(
         pytest.param(
             None, None, "Living Room Fan", "Living Room Fan", id="device_rename_applied"
         ),
+        pytest.param(
+            "Temperature", "", None, "Pedestal Fan", id="empty_name_uses_device_name"
+        ),
+        pytest.param(
+            "Temperature",
+            "",
+            "Living Room Fan",
+            "Living Room Fan",
+            id="empty_name_uses_renamed_device",
+        ),
     ],
 )
 async def test_restore_state_uses_device_name(