Fix #941 -- allow errorhandlers for HTTPException

flask/app.py

@@ -1360,13 +1360,6 @@ def handle_user_exception(self, e):
         exc_type, exc_value, tb = sys.exc_info()
         assert exc_value is e
 
-        # ensure not to trash sys.exc_info() at that point in case someone
-        # wants the traceback preserved in handle_http_exception.  Of course
-        # we cannot prevent users from trashing it themselves in a custom
-        # trap_http_exception method so that's their fault then.
-        if isinstance(e, HTTPException) and not self.trap_http_exception(e):
-            return self.handle_http_exception(e)
-
         blueprint_handlers = ()
         handlers = self.error_handler_spec.get(request.blueprint)
         if handlers is not None:
@@ -1376,6 +1369,13 @@ def handle_user_exception(self, e):
             if isinstance(e, typecheck):
                 return handler(e)
 
+        # ensure not to trash sys.exc_info() at that point in case someone
+        # wants the traceback preserved in handle_http_exception.  Of course
+        # we cannot prevent users from trashing it themselves in a custom
+        # trap_http_exception method so that's their fault then.
+        if isinstance(e, HTTPException) and not self.trap_http_exception(e):
+            return self.handle_http_exception(e)
+
         reraise(exc_type, exc_value, tb)
 
     def handle_exception(self, e):

flask/testsuite/basic.py

@@ -18,7 +18,7 @@
 from threading import Thread
 from flask.testsuite import FlaskTestCase, emits_module_deprecation_warning
 from flask._compat import text_type
-from werkzeug.exceptions import BadRequest, NotFound
+from werkzeug.exceptions import BadRequest, NotFound, HTTPException
 from werkzeug.http import parse_date
 from werkzeug.routing import BuildError
 
@@ -640,6 +640,24 @@ def error():
         self.assert_equal(rv.status_code, 500)
         self.assert_equal(b'internal server error', rv.data)
 
+    def test_http_error_handling(self):
+        app = flask.Flask(__name__)
+        @app.errorhandler(HTTPException)
+        def error(e):
+            if type(e) is NotFound:
+                return 'not here', 404
+            raise AssertionError(str(e))
+
+        @app.route('/explicit')
+        def explicit():
+            return flask.abort(404)
+
+        c = app.test_client()
+        for rv in (c.get('/not_existing'), c.get('/explicit')):
+            self.assert_equal(rv.data, b'not here')
+            self.assert_equal(rv.status_code, 404)
+
+
     def test_before_request_and_routing_errors(self):
         app = flask.Flask(__name__)
         @app.before_request