Fixed request context preservation and teardown handler interaction.

flask/ctx.py

@@ -235,6 +235,10 @@ class RequestContext(object):
         # is pushed the preserved context is popped.
         self.preserved = False
 
+        # remembers the exception for pop if there is one in case the context
+        # preservation kicks in.
+        self._preserved_exc = None
+
         # Functions that should be executed after the request on the response
         # object.  These will be called before the regular "after_request"
         # functions.
@@ -296,7 +300,7 @@ class RequestContext(object):
         # functionality is not active in production environments.
         top = _request_ctx_stack.top
         if top is not None and top.preserved:
-            top.pop()
+            top.pop(top._preserved_exc)
 
         # Before we push the request context we have to ensure that there
         # is an application context.
@@ -331,9 +335,18 @@ class RequestContext(object):
         clear_request = False
         if not self._implicit_app_ctx_stack:
             self.preserved = False
+            self._preserved_exc = None
             if exc is None:
                 exc = sys.exc_info()[1]
             self.app.do_teardown_request(exc)
+
+            # If this interpreter supports clearing the exception information
+            # we do that now.  This will only go into effect on Python 2.x,
+            # on 3.x it disappears automatically at the end of the exception
+            # stack.
+            if hasattr(sys, 'exc_clear'):
+                sys.exc_clear()
+
             request_close = getattr(self.request, 'close', None)
             if request_close is not None:
                 request_close()
@@ -356,6 +369,7 @@ class RequestContext(object):
         if self.request.environ.get('flask._preserve_context') or \
            (exc is not None and self.app.preserve_context_on_exception):
             self.preserved = True
+            self._preserved_exc = exc
         else:
             self.pop(exc)