Use TYPO3 YamlFileLoader

[sascha-egerer]

Is your feature request related to a problem? Please describe.
TYPO3 has its own YAML file loader that comes with some extra features. It's sad that these features can't be used in ContentBlocks as it does not use the YamlFileLoader implementation of TYPO3, which is based on Symfony YamlFileLoader, but does directly require Symfony YamlFileLoader.

Describe the solution you'd like
Replace Symfony YamlFileLoader with TYPO3 YamlFileLoader

[nhovratov]

Which features exactly do you miss?

[sascha-egerer]

Custom placeholders. We have a placeholder processor %const()% that can be used to read php constants and enums.
Something like %const(My\Namespace\Types\PageTypes::FOLDER)%

By the way: currently symfony/yaml is missing in require section of composer.json. But this would become obsolete if switching to TYPO3 YamlFileLoader.

[nhovratov]

We need to discuss this in the team. The reason behind using the plain Symfony YAML loader, was to discourage using imports and keep the Content Block as simple / stupid as possible. The YAML definition should be the knowledge baseline for everyone. Adding advanced logic is great for developers as you, but will confuse integrators / non-PHP people. Let's keep this issue open for discussion. Maybe we can find a good middleground. As for the composer requirement, I will add it right away, thanks!