control panel throws exception if accessed before addon upgrade step that adds field (controlpanel serializer so it handles schemas with new fields by returning field default)

src/plone/restapi/serializer/controlpanels/__init__.py

@@ -1,5 +1,7 @@
 from plone.dexterity.interfaces import IDexterityContent
 from plone.registry.interfaces import IRegistry
+from plone.registry.interfaces import IRecordsProxy
+from plone.registry.recordsproxy import RecordsProxy
 from plone.restapi.controlpanels import IControlpanel
 from plone.restapi.interfaces import IFieldSerializer
 from plone.restapi.interfaces import ISerializeToJson
@@ -12,12 +14,15 @@
 from zope.interface import alsoProvides
 from zope.interface import implementer
 from zope.interface import noLongerProvides
+from zope.schema.interfaces import IField
 
 import zope.schema
 
 
 SERVICE_ID = "@controlpanels"
 
+_marker = object()
+
 
 @implementer(ISerializeToJsonSummary)
 @adapter(IControlpanel)
@@ -82,7 +87,14 @@ def __call__(self):
             self.controlpanel, self.controlpanel.context, self.controlpanel.request
         )
 
-        proxy = self.registry.forInterface(self.schema, prefix=self.schema_prefix)
+        # We use a special proxy and check=False just in case the schema has a new field before an upgrade happens
+        # Note this doesn't yet handle if a schema field changes type, or the options change
+        proxy = self.registry.forInterface(
+            self.schema,
+            prefix=self.schema_prefix,
+            check=False,
+            # factory=DefaultRecordsProxy,
+        )
 
         # Temporarily provide IDexterityContent, so we can use DX field
         # serializers
@@ -113,3 +125,34 @@ def __call__(self):
             "schema": json_schema,
             "data": json_data,
         }
+
+
+@implementer(IRecordsProxy)
+class DefaultRecordsProxy(RecordsProxy):
+    """Modified RecordsProxy which returns defaults if values missing"""
+
+    def __getattr__(self, name):
+        if not self.__dict__ or name in self.__dict__.keys():
+            return super(RecordsProxy, self).__getattr__(name)
+        if name not in self.__schema__:
+            raise AttributeError(name)
+        value = self.__registry__.get(self.__prefix__ + name, _marker)
+        if value is _marker:
+            # Instead of returning missing_value we return the default
+            # so if this is an upgrade the registry will eventually be
+            # set with the default on next save.
+            field = self.__schema__[name]
+            if IField.providedBy(field):
+                field = field.bind(self)
+                value = field.default
+            else:
+                value = self.__schema__[name].default
+
+        return value
+
+    def __setattr__(self, name, value):
+        if name in self.__schema__:
+            full_name = self.__prefix__ + name
+            self.__registry__[full_name] = value
+        else:
+            self.__dict__[name] = value

src/plone/restapi/tests/test_services_controlpanels.py

@@ -4,12 +4,15 @@
 from plone.app.testing import TEST_USER_ID
 from plone.restapi.testing import PLONE_RESTAPI_DX_FUNCTIONAL_TESTING
 from plone.restapi.testing import RelativeSession
+from zope.component import getUtility
+from plone.registry.interfaces import IRegistry
+import transaction
+
 
 import unittest
 
 
 class TestControlpanelsEndpoint(unittest.TestCase):
-
     layer = PLONE_RESTAPI_DX_FUNCTIONAL_TESTING
 
     def setUp(self):
@@ -119,3 +122,37 @@ def test_get_usergroup_control_panel(self):
         # This control panel does not exist in Plone 5
         response = self.api_session.get("/@controlpanels/usergroup")
         self.assertEqual(200, response.status_code)
+
+    def test_get_schema_with_new_field(self):
+        # simulate startup with a change registry schema to ensure it doesn't break
+
+        registry = getUtility(IRegistry)
+        registry.records._values[
+            "plone.ext_editor"
+        ] = True  # ensure it's not the default
+        transaction.commit()
+
+        response = self.api_session.get("/@controlpanels/editing")
+        old_data = response.json()["data"]
+        self.assertEqual(old_data["ext_editor"], True)
+
+        # It's too hard to add another field so lets delete the registry data to
+        # simulate what it's like starting when the schema has a field and no
+        # data in the registry for it
+        # del registry.records['plone.available_editors']
+        del registry.records["plone.ext_editor"]
+        transaction.commit()
+
+        response = self.api_session.get("/@controlpanels/editing")
+        old_data = response.json()["data"]
+        self.assertEqual(old_data["ext_editor"], None)
+
+        # ensure there is no problem trying to set missing registry entries
+        new_values = {
+            "ext_editor": not old_data["ext_editor"],
+        }
+        response = self.api_session.patch("/@controlpanels/editing", json=new_values)
+
+        # check if the values changed
+        response = self.api_session.get("/@controlpanels/editing")
+        self.assertNotEqual(response.json(), old_data)