Allow users to be in treating_groups/recipient_groups default value (#4898)

This requires a custom source property to go against proper component
isolation, the thing is we know it will be a PrincipalSource and it would only
be prefilled with groups, while we may need to also have some users in that
list if the default value has some. (otherwise to would be cleaned up as
invalid values before presenting the form to the user, removing the users from
the default value, only keeping the groups)

src/collective/dms/basecontent/source.py

@@ -8,6 +8,8 @@ class PrincipalSource(PrincipalSource):
 
     BLACKLIST = ('AuthenticatedUsers', 'Administrators', 'Site Administrators', 'Reviewers')
 
+    extra_default_values = None
+
     def search_principals(self, groups_first=False, **kw):
         if kw:
             results = self.acl_users.searchPrincipals(groups_first=True, **kw)
@@ -15,6 +17,10 @@ class PrincipalSource(PrincipalSource):
             # if no kw, we have been called from source __iter__ because
             # of Chosen widget populate_select attribute is set to True
             results = self.acl_users.searchGroups()
+            if self.extra_default_values:
+                # cf widget.py, CustomAjaxChosenMultiSelectionWidget::source
+                results = list(results)
+                results.extend(self.acl_users.searchUsers(id=self.extra_default_values))
         return [r for r in results if r.get('groupid', None) not in self.BLACKLIST]
 
     def searchGroups(self, **kwargs):

src/collective/dms/basecontent/widget.py

@@ -1,13 +1,34 @@
+import zope.component
+
+from zope.schema.interfaces import ISource, IContextSourceBinder
 from zope.interface import implementer
 import z3c.form.interfaces
 
+from z3c.form import interfaces, util, value
+
 from collective.z3cform.chosen.widget import AjaxChosenMultiSelectionWidget
 
+class CustomAjaxChosenMultiSelectionWidget(AjaxChosenMultiSelectionWidget):
+    @property
+    def source(self):
+        # We have a custom source property because we know it will be a
+        # PrincipalSource and it would only be prefilled with groups,
+        # while we may need to also have some users in that list if the
+        # default value has some. (otherwise to would be cleaned up as invalid
+        # values before presenting the form to the user, removing the users
+        # from the default value, only keeping the groups)
+        source = self.field.bind(self.context).value_type.source
+        adapter = zope.component.queryMultiAdapter(
+                (self.context, self.request, self.form, self.field, self),
+                interfaces.IValue, name='default')
+        if adapter:
+            source.extra_default_values = adapter.get()
+        return source
 
 @implementer(z3c.form.interfaces.IFieldWidget)
 def AjaxChosenMultiFieldWidget(field, request):
     widget = z3c.form.widget.FieldWidget(field,
-        AjaxChosenMultiSelectionWidget(request))
+        CustomAjaxChosenMultiSelectionWidget(request))
     widget.populate_select = True
     widget.ignoreMissing = True
     return widget