{% url ... %} template tag may fail when not using a settings module

[Simon Sapin]

When using django.conf.settings.configure(...) instead of a settings module as ​documented, settings.SETTINGS_MODULE is set to None.

The {% url ... %} template tag is implemented as following, in django.template.defaulttags.URLNode.render :

        # Try to look up the URL twice: once given the view name, and again
        # relative to what we guess is the "main" app. If they both fail, 
        # re-raise the NoReverseMatch unless we're using the 
        # {% url ... as var %} construct in which cause return nothing.
        url = ''
        try:
            url = reverse(self.view_name, args=args, kwargs=kwargs)
        except NoReverseMatch:
            project_name = settings.SETTINGS_MODULE.split('.')[0]
            try:
                url = reverse(project_name + '.' + self.view_name,
                              args=args, kwargs=kwargs)
            except NoReverseMatch:
                if self.asvar is None:
                    raise

In some cases (for example in the admin templates), it will execute this : settings.SETTINGS_MODULE.split('.') which raises AttributeError: 'NoneType' object has no attribute 'split'.
Instead, it should check for settings.SETTINGS_MODULE being None before using it.

As a workaround, set SETTINGS_MODULE to some module name. This module needs to exist, as it is imported by other parts of Django, but does not need to actually contain the settings (which are set with django.conf.settings.configure)

[Simon Sapin]

The described workaround is bad as it breaks django.core.management.execute_from_command_line (ie manage.py) by causing it to raise RuntimeError: Settings already configured.

Instead, i added the following to my url config, so that {% url django-admindocs-docroot as docroot %} wouldn't fail in the admin :

(r'^admin/doc/', include('django.contrib.admindocs.urls')),

[Jacob]

Duplicate of #9005