Move theming settings validation registration into ready method

This avoids premature registration of django checks which could break
django 1.11 startup.

openedx/core/djangoapps/theming/apps.py

 
-import os
-import six
 from django.apps import AppConfig
-from django.conf import settings
-from django.core.checks import Error, Tags, register
 
 
 class ThemingConfig(AppConfig):
     name = 'openedx.core.djangoapps.theming'
     verbose_name = "Theming"
 
-
-@register(Tags.compatibility)
-def check_comprehensive_theme_settings(app_configs, **kwargs):
-    """
-    Checks the comprehensive theming theme directory settings.
-
-    Raises compatibility Errors upon:
-        - COMPREHENSIVE_THEME_DIRS is not a list
-        - theme dir path is not a string
-        - theme dir path is not an absolute path
-        - path specified in COMPREHENSIVE_THEME_DIRS does not exist
-
-    Returns:
-        List of any Errors.
-    """
-    if not getattr(settings, "ENABLE_COMPREHENSIVE_THEMING"):
-        # Only perform checks when comprehensive theming is enabled.
-        return []
-
-    errors = []
-
-    # COMPREHENSIVE_THEME_DIR is no longer supported - support has been removed.
-    if hasattr(settings, "COMPREHENSIVE_THEME_DIR"):
-        theme_dir = settings.COMPREHENSIVE_THEME_DIR
-
-        errors.append(
-            Error(
-                "COMPREHENSIVE_THEME_DIR setting has been removed in favor of COMPREHENSIVE_THEME_DIRS.",
-                hint='Transfer the COMPREHENSIVE_THEME_DIR value to COMPREHENSIVE_THEME_DIRS.',
-                obj=theme_dir,
-                id='openedx.core.djangoapps.theming.E001',
-            )
-        )
-
-    if hasattr(settings, "COMPREHENSIVE_THEME_DIRS"):
-        theme_dirs = settings.COMPREHENSIVE_THEME_DIRS
-
-        if not isinstance(theme_dirs, list):
-            errors.append(
-                Error(
-                    "COMPREHENSIVE_THEME_DIRS must be a list.",
-                    obj=theme_dirs,
-                    id='openedx.core.djangoapps.theming.E004',
-                )
-            )
-        if not all([isinstance(theme_dir, six.string_types) for theme_dir in theme_dirs]):
-            errors.append(
-                Error(
-                    "COMPREHENSIVE_THEME_DIRS must contain only strings.",
-                    obj=theme_dirs,
-                    id='openedx.core.djangoapps.theming.E005',
-                )
-            )
-        if not all([theme_dir.startswith("/") for theme_dir in theme_dirs]):
-            errors.append(
-                Error(
-                    "COMPREHENSIVE_THEME_DIRS must contain only absolute paths to themes dirs.",
-                    obj=theme_dirs,
-                    id='openedx.core.djangoapps.theming.E006',
-                )
-            )
-        if not all([os.path.isdir(theme_dir) for theme_dir in theme_dirs]):
-            errors.append(
-                Error(
-                    "COMPREHENSIVE_THEME_DIRS must contain valid paths.",
-                    obj=theme_dirs,
-                    id='openedx.core.djangoapps.theming.E007',
-                )
-            )
-
-    return errors
+    def ready(self):
+        # settings validations related to theming.
+        from . import checks

openedx/core/djangoapps/theming/checks.py

+"""
+Settings validations for the theming app
+"""
+import os
+import six
+from django.conf import settings
+from django.core.checks import Error, Tags, register
+
+
+@register(Tags.compatibility)
+def check_comprehensive_theme_settings(app_configs, **kwargs):
+    """
+    Checks the comprehensive theming theme directory settings.
+
+    Raises compatibility Errors upon:
+        - COMPREHENSIVE_THEME_DIRS is not a list
+        - theme dir path is not a string
+        - theme dir path is not an absolute path
+        - path specified in COMPREHENSIVE_THEME_DIRS does not exist
+
+    Returns:
+        List of any Errors.
+    """
+    if not getattr(settings, "ENABLE_COMPREHENSIVE_THEMING"):
+        # Only perform checks when comprehensive theming is enabled.
+        return []
+
+    errors = []
+
+    # COMPREHENSIVE_THEME_DIR is no longer supported - support has been removed.
+    if hasattr(settings, "COMPREHENSIVE_THEME_DIR"):
+        theme_dir = settings.COMPREHENSIVE_THEME_DIR
+
+        errors.append(
+            Error(
+                "COMPREHENSIVE_THEME_DIR setting has been removed in favor of COMPREHENSIVE_THEME_DIRS.",
+                hint='Transfer the COMPREHENSIVE_THEME_DIR value to COMPREHENSIVE_THEME_DIRS.',
+                obj=theme_dir,
+                id='openedx.core.djangoapps.theming.E001',
+            )
+        )
+
+    if hasattr(settings, "COMPREHENSIVE_THEME_DIRS"):
+        theme_dirs = settings.COMPREHENSIVE_THEME_DIRS
+
+        if not isinstance(theme_dirs, list):
+            errors.append(
+                Error(
+                    "COMPREHENSIVE_THEME_DIRS must be a list.",
+                    obj=theme_dirs,
+                    id='openedx.core.djangoapps.theming.E004',
+                )
+            )
+        if not all([isinstance(theme_dir, six.string_types) for theme_dir in theme_dirs]):
+            errors.append(
+                Error(
+                    "COMPREHENSIVE_THEME_DIRS must contain only strings.",
+                    obj=theme_dirs,
+                    id='openedx.core.djangoapps.theming.E005',
+                )
+            )
+        if not all([theme_dir.startswith("/") for theme_dir in theme_dirs]):
+            errors.append(
+                Error(
+                    "COMPREHENSIVE_THEME_DIRS must contain only absolute paths to themes dirs.",
+                    obj=theme_dirs,
+                    id='openedx.core.djangoapps.theming.E006',
+                )
+            )
+        if not all([os.path.isdir(theme_dir) for theme_dir in theme_dirs]):
+            errors.append(
+                Error(
+                    "COMPREHENSIVE_THEME_DIRS must contain valid paths.",
+                    obj=theme_dirs,
+                    id='openedx.core.djangoapps.theming.E007',
+                )
+            )
+
+    return errors