Avoid keeping config dir in path (#107760)

homeassistant/loader.py

@@ -1177,8 +1177,12 @@ def _async_mount_config_dir(hass: HomeAssistant) -> None:
 
     Async friendly but not a coroutine.
     """
-    if hass.config.config_dir not in sys.path:
-        sys.path.insert(0, hass.config.config_dir)
+
+    sys.path.insert(0, hass.config.config_dir)
+    with suppress(ImportError):
+        import custom_components  # pylint: disable=import-outside-toplevel  # noqa: F401
+    sys.path.remove(hass.config.config_dir)
+    sys.path_importer_cache.pop(hass.config.config_dir, None)
 
 
 def _lookup_path(hass: HomeAssistant) -> list[str]:

tests/test_loader.py

@@ -873,3 +873,14 @@ async def test_async_suggest_report_issue(
         )
         == report_issue
     )
+
+
+async def test_config_folder_not_in_path(hass):
+    """Test that config folder is not in path."""
+
+    # Verify that we are unable to import this file from top level
+    with pytest.raises(ImportError):
+        import check_config_not_in_path  # noqa: F401
+
+    # Verify that we are able to load the file with absolute path
+    import tests.testing_config.check_config_not_in_path  # noqa: F401

tests/testing_config/check_config_not_in_path.py

@@ -0,0 +1 @@
+"""File that should not be possible to import via direct import."""