Flash messages signals

If we send a signal when a template is rendered why not when a message
is flashed? One real world use case is in tests, this signal should make
flash messages expectation easier to implement.

flask/__init__.py

@@ -34,7 +34,7 @@ from .templating import render_template, render_template_string
 # the signals
 from .signals import signals_available, template_rendered, request_started, \
      request_finished, got_request_exception, request_tearing_down, \
-     appcontext_tearing_down
+     appcontext_tearing_down, message_flashed
 
 # We're not exposing the actual json module but a convenient wrapper around
 # it.

flask/helpers.py

@@ -35,6 +35,7 @@ except ImportError:
 
 from jinja2 import FileSystemLoader
 
+from .signals import message_flashed
 from .globals import session, _request_ctx_stack, _app_ctx_stack, \
      current_app, request
 
@@ -361,6 +362,8 @@ def flash(message, category='message'):
     flashes = session.get('_flashes', [])
     flashes.append((category, message))
     session['_flashes'] = flashes
+    message_flashed.send(current_app._get_current_object(),
+                         message=message, category=category)
 
 
 def get_flashed_messages(with_categories=False, category_filter=[]):

flask/signals.py

@@ -50,3 +50,4 @@ request_finished = _signals.signal('request-finished')
 request_tearing_down = _signals.signal('request-tearing-down')
 got_request_exception = _signals.signal('got-request-exception')
 appcontext_tearing_down = _signals.signal('appcontext-tearing-down')
+message_flashed = _signals.signal('message-flashed')

flask/testsuite/signals.py

@@ -8,6 +8,8 @@
     :copyright: (c) 2011 by Armin Ronacher.
     :license: BSD, see LICENSE for more details.
 """
+from __future__ import with_statement
+
 import flask
 import unittest
 from flask.testsuite import FlaskTestCase
@@ -95,6 +97,31 @@ class SignalsTestCase(FlaskTestCase):
         finally:
             flask.got_request_exception.disconnect(record, app)
 
+    def test_flash_signal(self):
+        app = flask.Flask(__name__)
+        app.config['SECRET_KEY'] = 'secret'
+
+        @app.route('/')
+        def index():
+            flask.flash('This is a flash message', category='notice')
+            return flask.redirect('/other')
+
+        recorded = []
+        def record(sender, message, category):
+            recorded.append((message, category))
+
+        flask.message_flashed.connect(record, app)
+        try:
+            client = app.test_client()
+            with client.session_transaction():
+                client.get('/')
+                self.assert_equal(len(recorded), 1)
+                message, category = recorded[0]
+                self.assert_equal(message, 'This is a flash message')
+                self.assert_equal(category, 'notice')
+        finally:
+            flask.message_flashed.disconnect(record, app)
+
 
 def suite():
     suite = unittest.TestSuite()