Warn when using custom components (#15172)

* Warn when using custom components

* Update text

homeassistant/loader.py

@@ -81,7 +81,7 @@ def get_component(hass, comp_or_platform) -> Optional[ModuleType]:
     potential_paths = ['custom_components.{}'.format(comp_or_platform),
                        'homeassistant.components.{}'.format(comp_or_platform)]
 
-    for path in potential_paths:
+    for index, path in enumerate(potential_paths):
         try:
             module = importlib.import_module(path)
 
@@ -100,6 +100,14 @@ def get_component(hass, comp_or_platform) -> Optional[ModuleType]:
 
             cache[comp_or_platform] = module
 
+            if index == 0:
+                _LOGGER.warning(
+                    'You are using a custom component for %s which has not '
+                    'been tested by Home Assistant. This component might '
+                    'cause stability problems, be sure to disable it if you '
+                    'do experience issues with Home Assistant.',
+                    comp_or_platform)
+
             return module
 
         except ImportError as err:

tests/test_loader.py

@@ -124,3 +124,13 @@ async def test_custom_component_name(hass):
     # Test custom components is mounted
     from custom_components.test_package import TEST
     assert TEST == 5
+
+
+async def test_log_warning_custom_component(hass, caplog):
+    """Test that we log a warning when loading a custom component."""
+    loader.get_component(hass, 'test_standalone')
+    assert \
+        'You are using a custom component for test_standalone' in caplog.text
+
+    loader.get_component(hass, 'light.test')
+    assert 'You are using a custom component for light.test' in caplog.text