Mezzanine dynamic settings overwriting new ALLOWED_HOSTS behaviour

[bors-ltd]

Hello,

Since Django 1.9.11 and 1.10.3, ALLOWED_HOSTS is now checked in debug environment too, with the convenient behaviour of interpreting [] (or any false value) to the usual localhost environment.

But Mezzanine dynamic settings in turn replace the [] I explicitly set in my local settings to SitesAllowedHosts().

The warning message says You haven't defined the ALLOWED_HOSTS settings which is not really correct when [] has a meaning.

I ran into this because I imported a production database dump and I opened http://localhost:8000 but the database contains a Site with the production URL.

I could fix this with:

diff --git a/mezzanine/utils/conf.py b/mezzanine/utils/conf.py
index 402309ef..f0fd35ec 100644
--- a/mezzanine/utils/conf.py
+++ b/mezzanine/utils/conf.py
@@ -57,7 +57,7 @@ def set_dynamic_settings(s):
                             and s['MIDDLEWARE'] is not None \
                             else 'MIDDLEWARE_CLASSES'
 
-    if not s.get("ALLOWED_HOSTS", []):
+    if s.get("ALLOWED_HOSTS") is None:
         warn("You haven't defined the ALLOWED_HOSTS settings, which "
              "Django requires. Will fall back to the domains "
              "configured as sites.")

But the warning would never appear because the default settings already set ALLOWED_HOSTS to a not-None value: https://github.com/stephenmcd/mezzanine/blob/master/mezzanine/project_template/project_name/settings.py#L95

What should we do about it? Completely remove ALLOWED_HOSTS from settings.py because it should only be set in local_settings.py? Explicitly setting ALLOWED_HOSTS = SitesAllowedHosts() in the project template?

[jerivas]

I think we should align with Django's behavior 👍