Propagate mode during config parsing

[Alexey-Borisov]

No description provided.

[apolukhin]

You are adding a recursive evaluation of #something. That's the thing we'd like to avoid as it makes the YAML config a Turing complete programming language

What problem are you trying to solve that is not solvable right now? Please provide a concrete example

[Alexey-Borisov]

There isn't any problem that is impossible to solve with the current implementation.
I ran into this while doing a small refactoring of our configuration. In our tests we currently have configuration like:

fieldA#env: valueA
fieldB#env: valueB

After the refactoring, it became more natural to group these values under a common node in config_vars.yaml and use $root in static_config.yaml:

root:
fieldA#env: valueA
fieldB#env: valueB

However, this is currently not supported.
Of course, we can rewrite the test configuration to avoid this, so this is more a matter of convenience than necessity. When I looked at the implementation, it seemed that allowing nested #env processing wouldn't introduce any obvious issues, so I proposed the change.

[Alexey-Borisov]

Maybe a better solution would be to add an additional mode that allows this kind of recursion and has to be explicitly enabled by the user?