monkey_patches.py

#################################################################################################################
# Patch the wagtail.admin.forms.pages.PageViewRestrictionForm class to filter groups to only those available
# to the current site. 
#################################################################################################################
def page_view_restriction_init(self, *args, **kwargs):
    super(PageViewRestrictionForm, self).__init__(*args, **kwargs)

    self.fields['groups'].widget = forms.CheckboxSelectMultiple()
    # BEGIN PATCH
    current_site = Site.find_for_request(get_current_request())
    self.fields['groups'].queryset = Group.objects.filter(name__istartswith=current_site.hostname)
    # END PATCH

 
# and now use this method instead of the usual init
wagtail.admin.forms.pages.PageViewRestrictionForm.__init__ = page_view_restriction_init

Further questions showed up that get_current_request is from a custom middleware we have installed - that is a light wrapper around CrquestMiddleware

#python

from crequest.middleware import CrequestMiddleware

def get_current_request(default=None, silent=True, label='__DEFAULT_LABEL__'):
    """
    Returns the current request. This is a more robust form of get_current_request, but it's not backwards compatible,
    so we gave it a different name.

    You can optionally use ``default`` to pass in a dummy request object to act as the default if there is no current
    request, e.g. when ``get_current_request()`` is called during a manage.py command.
    """
    request = CrequestMiddleware.get_request(default)
    if request is None and not silent:
        raise NoCurrentRequestException(
            "{} failed because there is no current request. Try using djunk.utils.FakeCurrentRequest.".format(label)
        )
    return request