A secret/unintuitive behavior of xdg.*Home options (they can set XDG_*_HOME env vars)

[Andrew15-5]

Hi, I had a question about XDG env vars that I asked at https://matrix.to/#/#users:nixos.org. I wanted to know the best way to set, e.g., xdg.configHome from the set environment.sessionVariables.XDG_CONFIG_HOME. But then people quickly told me a secret that xdg.configHome itself does this already! I was shocked, especially because the documentation doesn't say anything about that. Only the xdg.enable says something related to the XDG.

I think that it would be great if the concrete options a user searches for explain/mention this behavior. Then there should be no confusion and the environment.sessionVariables.XDG_CONFIG_HOME should be unset (generally speaking).