Without commenting on whether or not this should be implemented I'll note that you can capture this information today when rc.elv is executed using the src builtin. For example, by adding something like this to your rc.elv: var rc-elv-path = (src)[name].

Expanding on this feature request, I think it would be nice to have variables or functions which contain all the different directories of the XDG spec. If the user is still using the ~/.elvish/ directory, then they could all point to the same directory.

This would significantly simplify the work of module authors when there is a need to store data somewhere.

My recommendation is to implement this as variables in the platform module; e.g., platform:xdg-config-home (corresponding to the XDG_CONFIG_HOME env var in the XDG Base Directory spec). Whether or not the xdg- prefix is warranted is debatable but I think it should be present to make the correspondence to the XDG spec env vars crystal clear. The value of each variable would match whatever Elvish decided to use at runtime even if that means using the legacy ~/.elvish path.

Note that the proposed platform:xdg-config-home would not include the final /rc.elv path component -- only the directory containing the rc.elv that was loaded.

I opened issue #1420 when I was surprised that the ~/.config/elvish/rc.elv I synced from my macOS to Windows 10 system was not read on the latter system. I might have found the problem, without resorting to add a fmt.Printf() call to the source, if this issue were resolved. However, in light of the fact that Elvish on MS Windows doesn't (currently) recognize XDG paths is a strong suggestion that the names of the variables to expose this information should be agnostic with regards to the XDG spec. Rather, the names should reflect the use of each value by Elvish.

Note that building elvish from HEAD as I type this will result in this warning if you use github.com/href/elvish-gitstatus:

Warning: ~/.elvish will be ignored from Elvish 0.20.0.

That is because that module has a hardcoded path: var appdir = ~/.elvish/package-data/gitstatus. As I discuss in issue #832 third-party modules really need a way to ask Elvish which dir it is using without having to implement the logic documented in https://elv.sh/ref/command.html.

FWIW, I've been working on implementing this feature. I've decided that the var for this issue should be named platform:config-home. Also, a companion platform:state-home (corresponding to where the Elvish database file is located) also be introduced for use by modules like github.com/href/elvish-gitstatus for its data that normally should be private to a particular machine. I intend to leave exposing module search paths for a future change in order to keep the initial change as small as possible.