Fixed #8245 -- Added a LOADING flag to autodiscover to prevent an admin.py module with errors from raising a spurious AlreadyRegistered exception in a subsequent call to autodiscover.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9680 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/contrib/admin/__init__.py

@@ -2,12 +2,26 @@ from django.contrib.admin.options import ModelAdmin, HORIZONTAL, VERTICAL
 from django.contrib.admin.options import StackedInline, TabularInline
 from django.contrib.admin.sites import AdminSite, site
 
+# A flag to tell us if autodiscover is running.  autodiscover will set this to
+# True while running, and False when it finishes.
+LOADING = False
+
 def autodiscover():
     """
     Auto-discover INSTALLED_APPS admin.py modules and fail silently when
     not present. This forces an import on them to register any admin bits they
     may want.
     """
+    # Bail out if autodiscover didn't finish loading from a previous call so
+    # that we avoid running autodiscover again when the URLConf is loaded by
+    # the exception handler to resolve the handler500 view.  This prevents an
+    # admin.py module with errors from re-registering models and raising a
+    # spurious AlreadyRegistered exception (see #8245).
+    global LOADING
+    if LOADING:
+        return
+    LOADING = True
+
     import imp
     from django.conf import settings
 
@@ -38,3 +52,5 @@ def autodiscover():
         # Step 3: import the app's admin file. If this has errors we want them
         # to bubble up.
         __import__("%s.admin" % app)
+    # autodiscover was successful, reset loading flag.
+    LOADING = False

tests/regressiontests/bug8245/admin.py

@@ -0,0 +1,7 @@
+from django.contrib import admin
+
+from models import Story
+
+
+admin.site.register(Story)
+raise Exception("Bad admin module")

tests/regressiontests/bug8245/models.py

@@ -0,0 +1,4 @@
+from django.db import models
+
+class Story(models.Model):
+    title = models.CharField(max_length=10)

tests/regressiontests/bug8245/tests.py

@@ -0,0 +1,23 @@
+from unittest import TestCase
+
+from django.contrib import admin
+
+
+class Bug8245Test(TestCase):
+    """
+    Test for bug #8245 - don't raise an AlreadyRegistered exception when using
+    autodiscover() and an admin.py module contains an error.
+    """
+
+    def test_bug_8245(self):
+        # The first time autodiscover is called, we should get our real error.
+        try:
+            admin.autodiscover()
+        except Exception, e:
+            self.failUnlessEqual(str(e), "Bad admin module")
+        else:
+            self.fail(
+                'autodiscover should have raised a "Bad admin module" error.')
+        # Calling autodiscover again should bail out early and not raise an
+        # AlreadyRegistered error.
+        admin.autodiscover()