Bug: missing ${variable} support

[Andrei-Pozolotin]

Bug: missing ${variable} support

[andreaTP]

where the variable could come from in your opinion?

[2m]

I have also encountered this limitation. A couple of examples in Akka

 library-extensions = ${?akka.library-extensions} ["akka.serialization.SerializationExtension"]

https://github.com/akka/akka/blob/945440a38d437fa252e67089da020f695cd5c0b4/akka-actor/src/main/resources/reference.conf#L70

and

server-header = akka-http/${akka.http.version}

https://github.com/akka/akka-http/blob/59bd7157621afebce265d1a26c09f3e9ac22ffc8/akka-http-core/src/main/resources/reference.conf#L19

In theory these could be resolved during compilation time.

[andreaTP]

sounds like it will be totally possible to do it both at run and at compile time, I should find the time to look into.

[andreaTP]

I was looking into this, and it looks like it will require an effort:
https://github.com/lightbend/config#concatenation

supporting all these use cases is a lot actually ...

I do not have time in the near future to target this issue but PR are welcome.