Deal with partially setup packages in the redirect hook.

flask/ext/__init__.py

@@ -57,6 +57,17 @@ class _ExtensionImporter(object):
                 __import__(realname)
             except ImportError:
                 exc_type, exc_value, tb = exc_info()
+                # since we only establish the entry in sys.modules at the
+                # very this seems to be redundant, but if recursive imports
+                # happen we will call into the move import a second time.
+                # On the second invocation we still don't have an entry for
+                # fullname in sys.modules, but we will end up with the same
+                # fake module name and that import will succeed since this
+                # one already has a temporary entry in the modules dict.
+                # Since this one "succeeded" temporarily that second
+                # invocation now will have created a fullname entry in
+                # sys.modules which we have to kill.
+                modules.pop(fullname, None)
                 if self.is_important_traceback(realname, tb):
                     raise exc_type, exc_value, tb
                 continue

flask/testsuite/__init__.py

@@ -134,6 +134,32 @@ class FlaskTestCase(unittest.TestCase):
     def assert_equal(self, x, y):
         return self.assertEqual(x, y)
 
+    def assert_raises(self, exc_type, callable=None, *args, **kwargs):
+        catcher = _ExceptionCatcher(self, exc_type)
+        if callable is None:
+            return catcher
+        with catcher:
+            callable(*args, **kwargs)
+
+
+class _ExceptionCatcher(object):
+
+    def __init__(self, test_case, exc_type):
+        self.test_case = test_case
+        self.exc_type = exc_type
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_value, tb):
+        exception_name = self.exc_type.__name__
+        if exc_type is None:
+            self.test_case.fail('Expected exception of type %r' %
+                                exception_name)
+        elif not issubclass(exc_type, self.exc_type):
+            raise exc_type, exc_value, tb
+        return True
+
 
 class BetterLoader(unittest.TestLoader):
     """A nicer loader that solves two problems.  First of all we are setting

flask/testsuite/ext.py

@@ -8,6 +8,8 @@
     :copyright: (c) 2011 by Armin Ronacher.
     :license: BSD, see LICENSE for more details.
 """
+from __future__ import with_statement
+
 import sys
 import unittest
 from flask.testsuite import FlaskTestCase
@@ -92,6 +94,11 @@ class ExtImportHookTestCase(FlaskTestCase):
         from flask.ext.oldext_package.submodule import test_function
         self.assert_equal(test_function(), 42)
 
+    def test_flaskext_broken_package_no_module_caching(self):
+        for x in xrange(2):
+            with self.assert_raises(ImportError):
+                import flask.ext.broken
+
 
 def suite():
     suite = unittest.TestSuite()

flask/testsuite/test_apps/flask_broken/__init__.py

@@ -0,0 +1,2 @@
+import flask.ext.broken.b
+import missing_module