Summary of Changes

At the moment, the JApplicationCms class allows us to retrive all messages attached to the object via $app->getMessageQueue(). This method clears the messages from the session, so we'll get no duplicates (what is great), but the methods also attach/keeps the messages itself. So after a redirect all the messages will be outputted again. (https://github.com/joomla/joomla-cms/blob/staging/libraries/cms/application/cms.php#L1052).

This is very unhandy, if you want to change the error messages, like (as easy example):

$app = JFactory::getApplication();

$messages = $app->getMessageQueue();

foreach ($messages as $message)
{
    $app->enqueueMessage('Prefix: ' . $message['message'], $message['type']);
}

The complex picture where this could appear is:

• You have an profile plugin with an onUserBeforeSave and an onContentPrepareForm event.
• The onContentPrepareForm extends the user profile form with a image upload
• The onUserBeforeSave validates the file with the JMediaHelper class

The problem is now: if an error raises in the JHelperMedia class (https://github.com/joomla/joomla-cms/blob/staging/libraries/cms/helper/media.php), it will use $app->enqueMessage(...) to "communicate" this errors (e.g. https://github.com/joomla/joomla-cms/blob/staging/libraries/cms/helper/media.php#L59). The profile saving method looks for errors in the user model and attach a prefix (https://github.com/joomla/joomla-cms/blob/staging/components/com_users/controllers/profile.php#L162), so any plugin has to raise/throw it's own errors to interact with this call (https://github.com/joomla/joomla-cms/blob/staging/libraries/joomla/user/user.php#L786).

So the way is:

1. Let JHelperMedia validate the file
2. Check $app->getMessageQueue() for existing errors and throw them
3. The user object catchs them and gives them to the model/controller, which attach it as prefix
4. The error will be outputted (what is OK)
5. the "old" error will also be outputted (what is very annoying)

Solution: see this patch. An additional parameter which clears the application message queue and prevent double output.

Testing Instructions

Call somewhere

$app = JFactory::getApplication();
$app->enqueueMessage('Foo', 'notice');
$app->getMessageQueue(true);
$app->redirect(JRoute::_('index.php'));

Expected result (After patch)

The message does not appear

Actual result (Before patch)

The message appears

Documentation Changes Required