Added a workaround for a pypy bug in context managers

flask/_compat.py

@@ -71,3 +71,27 @@ def with_metaclass(meta, *bases):
                 return type.__new__(cls, name, (), d)
             return meta(name, bases, d)
     return metaclass('temporary_class', None, {})
+
+
+# Certain versions of pypy have a bug where clearing the exception stack
+# breaks the __exit__ function in a very peculiar way.  This is currently
+# true for pypy 2.2.1 for instance.  The second level of exception blocks
+# is necessary because pypy seems to forget to check if an exception
+# happend until the next bytecode instruction?
+BROKEN_PYPY_CTXMGR_EXIT = False
+if hasattr(sys, 'pypy_version_info'):
+    class _Mgr(object):
+        def __enter__(self):
+            return self
+        def __exit__(self, *args):
+            sys.exc_clear()
+    try:
+        try:
+            with _Mgr():
+                raise AssertionError()
+        except:
+            raise
+    except TypeError:
+        BROKEN_PYPY_CTXMGR_EXIT = True
+    except AssertionError:
+        pass