Fixed #8033 -- Explained app registry error during translation setup

Thanks Tim Graham and Aymeric Augustin for the review.

3 files changed, 16 insertions, 3 deletions

diff --git a/django/apps/registry.py b/django/apps/registry.py
index 41095bd41e..492a97f603 100644
--- a/django/apps/registry.py
+++ b/django/apps/registry.py
@@ -4,7 +4,7 @@ import sys
 import threading
 import warnings
 
-from django.core.exceptions import ImproperlyConfigured
+from django.core.exceptions import AppRegistryNotReady, ImproperlyConfigured
 from django.utils import lru_cache
 from django.utils.deprecation import RemovedInDjango19Warning
 from django.utils._os import upath
@@ -116,7 +116,7 @@ class Apps(object):
         Raises an exception if the registry isn't ready.
         """
         if not self.ready:
-            raise RuntimeError("App registry isn't ready yet.")
+            raise AppRegistryNotReady()
 
     def get_app_configs(self):
         """
diff --git a/django/core/exceptions.py b/django/core/exceptions.py
index cf4aea0f36..552b0067c3 100644
--- a/django/core/exceptions.py
+++ b/django/core/exceptions.py
@@ -12,6 +12,11 @@ class DjangoRuntimeWarning(RuntimeWarning):
     pass
 
 
+class AppRegistryNotReady(Exception):
+    """The django.apps registry is not populated yet"""
+    pass
+
+
 class ObjectDoesNotExist(Exception):
     """The requested object does not exist"""
     silent_variable_failure = True
diff --git a/django/utils/translation/trans_real.py b/django/utils/translation/trans_real.py
index 71445cb365..56a0da2639 100644
--- a/django/utils/translation/trans_real.py
+++ b/django/utils/translation/trans_real.py
@@ -11,6 +11,7 @@ import warnings
 
 from django.apps import apps
 from django.conf import settings
+from django.core.exceptions import AppRegistryNotReady
 from django.dispatch import receiver
 from django.test.signals import setting_changed
 from django.utils.deprecation import RemovedInDjango19Warning
@@ -160,7 +161,14 @@ class DjangoTranslation(gettext_module.GNUTranslations):
 
     def _add_installed_apps_translations(self):
         """Merges translations from each installed app."""
-        for app_config in reversed(list(apps.get_app_configs())):
+        try:
+            app_configs = reversed(list(apps.get_app_configs()))
+        except AppRegistryNotReady:
+            raise AppRegistryNotReady(
+                "The translation infrastructure cannot be initialized before the "
+                "apps registry is ready. Check that you don't make non-lazy "
+                "gettext calls at import time.")
+        for app_config in app_configs:
             localedir = os.path.join(app_config.path, 'locale')
             translation = self._new_gnu_trans(localedir)
             self.merge(translation)