Fix server-extension paths (3rd time's the charm) (#734)

jupyter_server/extension/application.py

@@ -12,6 +12,7 @@
 from traitlets import default
 from traitlets import Dict
 from traitlets import HasTraits
+from traitlets import Instance
 from traitlets import List
 from traitlets import Unicode
 from traitlets.config import Config
@@ -103,7 +104,7 @@ def _prepare_templates(self):
             loader=FileSystemLoader(self.template_paths),
             extensions=["jinja2.ext.i18n"],
             autoescape=True,
-            **self.jinja2_options
+            **self.jinja2_options,
         )
 
         # Add the jinja2 environment for this extension to the tornado settings.
@@ -162,6 +163,12 @@ class method. This method can be set as a entry_point in
     def _default_open_browser(self):
         return self.serverapp.config["ServerApp"].get("open_browser", True)
 
+    @property
+    def config_file_paths(self):
+        """Look on the same path as our parent for config files"""
+        # rely on parent serverapp, which should control all config loading
+        return self.serverapp.config_file_paths
+
     # The extension name used to name the jupyter config
     # file, jupyter_{name}_config.
     # This should also match the jupyter subcommand used to launch
@@ -200,7 +207,21 @@ def _default_url(self):
     ]
 
     # A ServerApp is not defined yet, but will be initialized below.
-    serverapp = None
+    serverapp = Instance(ServerApp)
+
+    @default("serverapp")
+    def _default_serverapp(self):
+        # load the current global instance, if any
+        if ServerApp.initialized():
+            try:
+                return ServerApp.instance()
+            except Exception:
+                # error retrieving instance, e.g. MultipleInstanceError
+                pass
+
+        # serverapp accessed before it was defined,
+        # declare an empty one
+        return ServerApp()
 
     _log_formatter_cls = LogFormatter
 

jupyter_server/serverapp.py

@@ -104,7 +104,6 @@
     base_flags,
     base_aliases,
 )
-from jupyter_core.paths import jupyter_config_path
 from jupyter_client import KernelManager
 from jupyter_client.kernelspec import KernelSpecManager
 from jupyter_client.session import Session
@@ -2154,11 +2153,7 @@ def find_server_extensions(self):
         # This enables merging on keys, which we want for extension enabling.
         # Regular config loading only merges at the class level,
         # so each level clobbers the previous.
-        config_paths = jupyter_config_path()
-        if self.config_dir not in config_paths:
-            # add self.config_dir to the front, if set manually
-            config_paths.insert(0, self.config_dir)
-        manager = ExtensionConfigManager(read_config_path=config_paths)
+        manager = ExtensionConfigManager(read_config_path=self.config_file_paths)
         extensions = manager.get_jpserver_extensions()
 
         for modulename, enabled in sorted(extensions.items()):

tests/extension/test_app.py

@@ -69,6 +69,14 @@ def test_extensionapp_load_config_file(
     assert mock_extension.mock_trait == "config from file"
 
 
+def test_extensionapp_no_parent():
+    # make sure we can load config files, even when serverapp is not passed
+    # relevant for e.g. shortcuts to config-loading
+    app = MockExtensionApp()
+    assert isinstance(app.config_file_paths, list)
+    assert app.serverapp is not None
+
+
 OPEN_BROWSER_COMBINATIONS = (
     (True, {}),
     (True, {"ServerApp": {"open_browser": True}}),