do not reinvoke exception views if an exception hits the execution po…

…licy

See Pylons#3468

src/pyramid/router.py

@@ -273,7 +273,4 @@ def __call__(self, environ, start_response):
 
 def default_execution_policy(environ, router):
     with router.request_context(environ) as request:
-        try:
-            return router.invoke_request(request)
-        except Exception:
-            return request.invoke_exception_view(reraise=True)
+        return router.invoke_request(request)

tests/test_router.py

@@ -1561,7 +1561,7 @@ def dummy_policy(environ, router):
         self.assertEqual(resp.status_code, 200)
         self.assertEqual(resp.body, b'foo')
 
-    def test_execution_policy_handles_exception(self):
+    def test_execution_policy_bubbles_exception(self):
         from pyramid.interfaces import IViewClassifier
         from pyramid.interfaces import IExceptionViewClassifier
         from pyramid.interfaces import IRequest
@@ -1591,8 +1591,7 @@ class Exception2(Exception):
         environ = self._makeEnviron(PATH_INFO='/archives/action1/article1')
         start_response = DummyStartResponse()
         router = self._makeOne()
-        result = router(environ, start_response)
-        self.assertEqual(result, ["Hello, world"])
+        self.assertRaises(Exception2, lambda: router(environ, start_response))
 
     def test_request_context_with_statement(self):
         from pyramid.threadlocal import get_current_request