Included substitution is inconsistent with Typesafe Config

[ghost]

Per https://github.com/lightbend/config/blob/main/HOCON.md#includes :

Recall that substitution happens as a final step, after parsing. It should be done for the entire app's configuration, not for single files in isolation. Therefore, if an included file contains substitutions, they must be "fixed up" to be relative to the app's configuration root.

Maybe it's not 100% clear how this should be interpreted, but if we take these files:

main.conf:

include "included"

a = main

included.conf:

a = included
b = ${a}

And load main.conf, then Typesafe Config produces:

{
  "a": "main",
  "b": "main"
}

But hocon-rs 0.9.0:

{
  "a": "main",
  "b": "included"
}

hocon-rs sets b to main only if main.conf explicitly duplicates the assignment:

include "included"

a = main
b = ${a}

but that defeats the purpose of including files with default values.