Fix issue 140

This allows for a view function to return something like:

    jsonify(error="error msg"), 400

CHANGES

@@ -45,6 +45,9 @@ Relase date to be decided, codename to be chosen.
 - The :meth:`flask.render_template` method now accepts a either an iterable of
   template names or a single template name.  Previously, it only accepted a
   single template name.  On an iterable, the first template found is rendered.
+- View functions can now return a tuple with the first instance being an
+  instance of :class:`flask.Response`.  This allows for returning
+  ``jsonify(error="error msg"), 400`` from a view function.
 
 
 Version 0.8.1

flask/app.py

@@ -1361,7 +1361,21 @@ class Flask(_PackageBoundObject):
         if isinstance(rv, basestring):
             return self.response_class(rv)
         if isinstance(rv, tuple):
-            return self.response_class(*rv)
+            if len(rv) > 0 and isinstance(rv[0], self.response_class):
+                original = rv[0]
+                new_response = self.response_class('', *rv[1:])
+                if len(rv) < 3:
+                    # The args for the response class are
+                    # response=None, status=None, headers=None,
+                    # mimetype=None, content_type=None, ...
+                    # so if there's at least 3 elements the rv
+                    # tuple contains header information so the
+                    # headers from rv[0] "win."
+                    new_response.headers = original.headers
+                new_response.response = original.response
+                return new_response
+            else:
+                return self.response_class(*rv)
         return self.response_class.force_type(rv, request.environ)
 
     def create_url_adapter(self, request):

flask/testsuite/basic.py

@@ -659,6 +659,35 @@ class BasicFunctionalityTestCase(FlaskTestCase):
             self.assert_equal(rv.data, 'W00t')
             self.assert_equal(rv.mimetype, 'text/html')
 
+    def test_make_response_with_response_instance(self):
+        app = flask.Flask(__name__)
+        with app.test_request_context():
+            rv = flask.make_response(
+                flask.jsonify({'msg': 'W00t'}), 400)
+            self.assertEqual(rv.status_code, 400)
+            self.assertEqual(rv.data,
+                             '{\n  "msg": "W00t"\n}')
+            self.assertEqual(rv.mimetype, 'application/json')
+
+            rv = flask.make_response(
+                flask.Response(''), 400)
+            self.assertEqual(rv.status_code, 400)
+            self.assertEqual(rv.data, '')
+            self.assertEqual(rv.mimetype, 'text/html')
+
+            rv = flask.make_response(
+                flask.Response('', headers={'Content-Type': 'text/html'}),
+                400, None, 'application/json')
+            self.assertEqual(rv.status_code, 400)
+            self.assertEqual(rv.headers['Content-Type'], 'application/json')
+
+            rv = flask.make_response(
+                flask.Response('', mimetype='application/json'),
+                400, {'Content-Type': 'text/html'})
+            self.assertEqual(rv.status_code, 400)
+            self.assertEqual(rv.headers['Content-Type'], 'text/html')
+
+
     def test_url_generation(self):
         app = flask.Flask(__name__)
         @app.route('/hello/<name>', methods=['POST'])