ContextHandlers: Add is_allowed_type

Orange/widgets/settings.py

@@ -33,6 +33,7 @@
 import itertools
 import logging
 import warnings
+from typing import List
 
 from orangewidget.settings import (
     Setting, SettingProvider, SettingsHandler, ContextSetting,
@@ -77,6 +78,11 @@ def __init__(self, *, match_values=0, first_match=True, **kwargs):
                 .format(name), OrangeDeprecationWarning
             )
 
+    @classmethod
+    def is_allowed_type(cls, setting):
+        return ContextHandler.is_allowed_type(setting) \
+               or setting.type in (Variable, List[Variable])
+
     def encode_domain(self, domain):
         """
         domain: Orange.data.domain to encode
@@ -276,7 +282,8 @@ def open_context(self, widget, classes):
                 classes = classes.values
             else:
                 classes = None
-
+        if classes is not None:
+            classes = tuple(classes)
         super().open_context(widget, classes)
 
     def new_context(self, classes):