Breaking: #67546 - Cleanup Flash message rendering in FlashMessageQueue

See forge#67546

Description

The rendering of flash messages has changed when using the view helper. Now the rendering output of \TYPO3\CMS\Core\Messaging\FlashMessageQueue::renderFlashMessages() is adapted to being exactly the same.

Impact

Extensions using the rendered output of \TYPO3\CMS\Core\Messaging\FlashMessageQueue::renderFlashMessages() and in addition using HTML tags in flash messages for styling purposes will get their HTML flash message output properly HTML encoded. Thus the HTML tags will be visible in the rendered flash message output.

Since \TYPO3\CMS\Backend\Template\DocumentTemplate also uses this rendering type, modules using this class will also be affected.

Affected Installations

All extensions that use modules with \TYPO3\CMS\Backend\Template\DocumentTemplate or are using \TYPO3\CMS\Core\Messaging\FlashMessageQueue::renderFlashMessages() directly.

Migration

Remove all HTML from flash messages.