docs(wrapperModules.nushell): add notes about the differences to normal config file placement

[Noah765]

See https://www.nushell.sh/book/configuration.html#flag-behavior.

Outdated summary

The problem with setting the `--config` flag is that the configuration is loaded even in non-interactive environments. See https://www.nushell.sh/book/configuration.html#scenarios.

Note that this is a breaking change since it changes $nu.default-config-dir and affects the location of the history file, which has to be set to a non-Nix store location using $env.config.history.path. If you feel like this trade-off isn't worthwhile or have any suggestions, please suggest them or close this PR.

[BirdeeHub]

Hey! Sorry, took me a bit to get to this.

I recognize that the current nushell module is not great and will need to be improved.

However I am hesitant to export XDG_CONFIG_HOME for a whole shell. For many programs this is not so important, but this is a shell, and it will thus affect all the programs you launch using the shell. Is there a way we can use a different variable, or reset it before any of the user provided config and runtime code gets called?

[Noah765]

Hey! Sorry, took me a bit to get to this.

Don't worry — you're doing a great job here, and it's just a hobby project after all!

However I am hesitant to export XDG_CONFIG_HOME for a whole shell. For many programs this is not so important, but this is a shell, and it will thus affect all the programs you launch using the shell. Is there a way we can use a different variable, or reset it before any of the user provided config and runtime code gets called?

I don't think there is another variable that can be used to configure the config path, and I cannot think of a way to reset XDG_CONFIG_HOME without using more flags which would change the behavior of Nushell in more unexpected ways. Furthermore, $nu.default-config-dir is set to $XDG_CONFIG_HOME/nushell at startup and cannot be changed.
See https://github.com/nushell/nushell/blob/main/crates/nu-path/src/helpers.rs#L22 and https://github.com/nushell/nushell/blob/main/src/config_files.rs#L58.

I believe that using the --config and --env-config is the least destructive option, so I updated this PR to add some clarifying documentation.