Move settings validation out of startup.py

This also creates a new app common_initialization in order to provide a
place to run initialization code common to both the LMS and CMS.

openedx/core/djangoapps/common_initialization/apps.py

@@ -0,0 +1,14 @@
+"""
+Common initialization app for the LMS and CMS
+"""
+
+from django.apps import AppConfig
+
+
+class CommonInitializationConfig(AppConfig):
+    name = 'openedx.core.djangoapps.common_initialization'
+    verbose_name = 'Common Initialization'
+
+    def ready(self):
+        # Common settings validations for the LMS and CMS.
+        from . import checks

openedx/core/djangoapps/common_initialization/checks.py

@@ -0,0 +1,49 @@
+"""
+Common settings validations for the LMS and CMS.
+
+Only populate this module with general settings validators which do not fit in
+other, more specific djangoapps.  Usually, settings which are widely used
+across the entire LMS or CMS can be validated here.
+"""
+from django.conf import settings
+from django.core.checks import Error, Tags, register
+
+
+@register(Tags.compatibility)
+def validate_lms_root_url_setting(app_configs, **kwargs):
+    """
+    Validates the LMS_ROOT_URL setting.
+    """
+    errors = []
+    if not getattr(settings, 'LMS_ROOT_URL', None):
+        errors.append(
+            Error(
+                'LMS_ROOT_URL is not defined.',
+                id='common.djangoapps.common_initialization.E001',
+            )
+        )
+    return errors
+
+
+@register(Tags.compatibility)
+def validate_marketing_site_setting(app_configs, **kwargs):
+    """
+    Validates marketing site related settings.
+    """
+    errors = []
+    if settings.FEATURES.get('ENABLE_MKTG_SITE'):
+        if not hasattr(settings, 'MKTG_URLS'):
+            errors.append(
+                Error(
+                    'ENABLE_MKTG_SITE is True, but MKTG_URLS is not defined.',
+                    id='common.djangoapps.common_initialization.E002',
+                )
+            )
+        if not settings.MKTG_URLS.get('ROOT'):
+            errors.append(
+                Error(
+                    'There is no ROOT defined in MKTG_URLS.',
+                    id='common.djangoapps.common_initialization.E003',
+                )
+            )
+    return errors