Merge pull request #1650 from Carreau/predicatable-extensions

Load extension in predictable order.

notebook/notebookapp.py

@@ -933,7 +933,8 @@ class NotebookApp(JupyterApp):
     nbserver_extensions = Dict({}, config=True,
         help=("Dict of Python modules to load as notebook server extensions."
               "Entry values can be used to enable and disable the loading of"
-              "the extensions.")
+              "the extensions. The extensions will be loaded in alphabetical "
+              "order.")
     )
 
     reraise_server_extension_failures = Bool(
@@ -1193,7 +1194,7 @@ class NotebookApp(JupyterApp):
             if not modulename in self.nbserver_extensions:
                 self.nbserver_extensions[modulename] = True
         
-        for modulename in self.nbserver_extensions:
+        for modulename in sorted(self.nbserver_extensions):
             if self.nbserver_extensions[modulename]:
                 try:
                     mod = importlib.import_module(modulename)

notebook/tests/test_serverextensions.py

@@ -1,4 +1,5 @@
 import os
+import sys
 from unittest import TestCase
 try:
     from unittest.mock import patch
@@ -13,8 +14,17 @@ from traitlets.tests.utils import check_help_all_output
 
 from notebook.serverextensions import toggle_serverextension_python
 from notebook import nbextensions
+from notebook.notebookapp import NotebookApp
 from notebook.nbextensions import _get_config_dir
 
+if sys.version_info > (3,):
+    from types import SimpleNamespace
+else:
+    class SimpleNamespace(object):
+        pass
+
+from collections import OrderedDict
+
 
 def test_help_output():
     check_help_all_output('notebook.serverextensions')
@@ -87,3 +97,43 @@ class TestInstallServerExtension(TestCase):
 
         config = self._get_config()
         assert not config['mockextension']
+
+
+class TestOrderedServerExtension(TestCase):
+    """
+    Test that Server Extensions are loaded _in order_
+    """
+
+    def setUp(self):
+        mockextension1 = SimpleNamespace()
+        mockextension2 = SimpleNamespace()
+
+        def load_jupyter_server_extension(obj):
+            obj.mockI = True
+            obj.mock_shared = 'I'
+
+        mockextension1.load_jupyter_server_extension = load_jupyter_server_extension
+
+        def load_jupyter_server_extension(obj):
+            obj.mockII = True
+            obj.mock_shared = 'II'
+
+        mockextension2.load_jupyter_server_extension = load_jupyter_server_extension
+
+        sys.modules['mockextension2'] = mockextension2
+        sys.modules['mockextension1'] = mockextension1
+
+    def tearDown(self):
+        del sys.modules['mockextension2']
+        del sys.modules['mockextension1']
+
+
+    def test_load_ordered(self):
+        app = NotebookApp()
+        app.nbserver_extensions = OrderedDict([('mockextension2',True),('mockextension1',True)])
+
+        app.init_server_extensions()
+
+        assert app.mockII is True, "Mock II should have been loaded"
+        assert app.mockI is True, "Mock I should have been loaded"
+        assert app.mock_shared == 'II', "Mock II should be loaded after Mock I"