Flash messages renderer 

The implementation of rendering FlashMessages in the Core has been optimized.

A new class called \TYPO3\CMS\Core\Messaging\FlashMessageRendererResolver has been introduced. This class detects the context and renders the given FlashMessages in the correct output format. It can handle any kind of output format. The Core ships with the following FlashMessageRenderer classes:

• \TYPO3\CMS\Core\Messaging\Renderer\BootstrapRenderer This renderer is used by default in the TYPO3 backend. The output is based on Bootstrap markup.
• \TYPO3\CMS\Core\Messaging\Renderer\ListRenderer This renderer is used by default in the TYPO3 frontend. The output is a simple <ul> list.
• \TYPO3\CMS\Core\Messaging\Renderer\PlaintextRenderer This renderer is used by default in the CLI context. The output is plain text.

All new rendering classes have to implement the \TYPO3\CMS\Core\Messaging\Renderer\FlashMessageRendererInterface interface. If you need a special output format, you can implement your own renderer class and use it:

use TYPO3\CMS\Core\Utility\GeneralUtility;
use MyVendor\SomeExtension\Messaging\MySpecialRenderer;

$out = GeneralUtility::makeInstance(MySpecialRenderer::class)
   ->render($flashMessages);

The Core has been modified to use the new FlashMessageRendererResolver. Any third party extension should use the provided FlashMessageViewHelper or the new FlashMessageRendererResolver class:

use TYPO3\CMS\Core\Utility\GeneralUtility;
use TYPO3\CMS\Core\Messaging\FlashMessageRendererResolver;

$out = GeneralUtility::makeInstance(FlashMessageRendererResolver::class)
   ->resolve()
   ->render($flashMessages);