settings: Group {default,prod,dev}_settings as configured_settings.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

docs/subsystems/settings.md

@@ -69,11 +69,14 @@ In a production environment, we have:
   `zproject/settings.py`.
 
 * `zproject/settings.py` is the main Django settings file for Zulip.
-  It contains all the settings that are constant for all Zulip
+  It imports everything from `zproject/configured_settings.py`, and
+  contains all the settings that are constant for all Zulip
   installations (e.g. configuration for logging, static assets,
-  middleware, etc.).  It has a line `from prod_settings
-  import *`, which in a prod environment has the effect of importing
-  `/etc/zulip/settings.py` (via a symlink).
+  middleware, etc.).
+
+* `zproject/configured_settings.py` imports everything from
+  `zproject/default_settings.py`, then in a prod environment imports
+  `/etc/zulip/settings.py` via a symlink.
 
 * `zproject/default_settings.py` has the default values for the settings the
   user would set in `/etc/zulip/settings.py`.

tools/linter_lib/pyflakes.py

@@ -21,6 +21,7 @@ def check_pyflakes(files: List[str], options: argparse.Namespace) -> bool:
 
         ("settings.py", "settings import *' used; unable to detect undefined names"),
         ("settings.py", "may be undefined, or defined from star imports"),
+        ("settings.py", "settings.*' imported but unused"),
 
         # Sphinx adds `tags` specially to the environment when running conf.py.
         ("docs/conf.py", "undefined name 'tags'"),

zproject/configured_settings.py

@@ -0,0 +1,16 @@
+########################################################################
+# DEFAULT VALUES FOR SETTINGS
+########################################################################
+
+# For any settings that are not set in the site-specific configuration file
+# (/etc/zulip/settings.py in production, or dev_settings.py or test_settings.py
+# in dev and test), we want to initialize them to sane defaults.
+from .default_settings import *  # isort: skip
+
+# Import variables like secrets from the prod_settings file
+# Import prod_settings after determining the deployment/machine type
+from .config import PRODUCTION
+if PRODUCTION:
+    from .prod_settings import *  # isort: skip
+else:
+    from .dev_settings import *  # isort: skip

zproject/settings.py

@@ -2,14 +2,22 @@
 ########################################################################
 # Here's how settings for the Zulip project work:
 #
+# * configured_settings.py imports default_settings.py, which contains
+#   default values for settings configurable in prod_settings.py.
+#
+# * configured_settings.py imports prod_settings.py, and any site-specific
+#   configuration belongs there.  The template for prod_settings.py is
+#   prod_settings_template.py.
+#
 # * settings.py contains non-site-specific and settings configuration
-# for the Zulip Django app.
-# * settings.py imports prod_settings.py, and any site-specific configuration
-# belongs there.  The template for prod_settings.py is prod_settings_template.py
+#   for the Zulip Django app.
 #
 # See https://zulip.readthedocs.io/en/latest/subsystems/settings.html for more information
 #
 ########################################################################
+
+from .configured_settings import *  # isort: skip
+
 from copy import deepcopy
 import os
 import time
@@ -81,22 +89,6 @@ GENERATE_STRIPE_FIXTURES = False
 # process /etc/boto.cfg.
 os.environ['BOTO_CONFIG'] = '/etc/zulip/boto.cfg'
 
-########################################################################
-# DEFAULT VALUES FOR SETTINGS
-########################################################################
-
-# For any settings that are not set in the site-specific configuration file
-# (/etc/zulip/settings.py in production, or dev_settings.py or test_settings.py
-# in dev and test), we want to initialize them to sane defaults.
-from .default_settings import *
-
-# Import variables like secrets from the prod_settings file
-# Import prod_settings after determining the deployment/machine type
-if PRODUCTION:
-    from .prod_settings import *
-else:
-    from .dev_settings import *
-
 # These are the settings that we will check that the user has filled in for
 # production deployments before starting the app.  It consists of a series
 # of pairs of (setting name, default value that it must be changed from)