[YAML] !include tag support

[drzraf]

Description
SymfonyCloud's configuration supports a YAML !include "custom" tag.

It would be useful as part of the YAML component.

Example

tls:
    client_certificate_authorities:
        - !include
            type: string
            path: file1.key

[Doqnach]

See also #30343

[carsonbot]

Thank you for this suggestion.
There has not been a lot of activity here for a while. Would you still like to see this feature?

[stof]

I don't think there is anything to do here in the yaml parser. The Symfony Cloud parser is implementing an include feature at its own layer that gets represented with a tag in the yaml (and parsed as TaggedValue), which is how tags are working in the spec.

The yaml spec itself does not have a concept of yaml-controlled includes (which would also require defining a resolution algorithm to find files, while the yaml parser deals with a string input, not with files). And expanding the scope of what yaml is is out of scope of the yaml component.

[drzraf]

Fair enough.
Do you know if that ParserExtension's code is already published somewhere so it can be reused?
It may even find its way into another Symfony *bridge* component: It's a useful Yaml extension and I'm pretty sure it's already very generic with few SymfonyCloud's path hardcoded.