Support machine global directory

[timfish]

There's currently no way to get a machine global (ie. non user/home scoped) data directory. This is useful for examples if you want to download large files that can be shared between users.

This would look something like:

• Windows %PROGRAMDATA% (C:\ProgramData on Win10)
• macOS /Library/Application Support
• Linux $XDG_DATA_DIRS

This is currently supported by app-dirs via SharedData but the crate is unmaintained.

Would you be open to accepting a PR for this?

[tesuji]

Thank you for opening this issue.

Would you be open to accepting a PR for this?

Yes, you're welcome. But could you talk a bit about the API you planned to add?

I have some thoughts about this:

1. For dirs_next crate, we could either:
   a. Add an enum Location { User, Shared, System } (?), use that enum as a parameter of free functions in dirs_next. But this is a breaking change. So we need to bump major version after doing this.
   b. Add new free functions with shared_ prefix.
2. For directories crate:
   a. Introduce a new SharedDirs struct?

Do you know if any other crates expose the same information?

[timfish]

@lzutao as I said above, app-dirs already exposes this as SharedData but the crate seems unmaintained.

[tesuji]

SharedData is a variant of AppDataType enum.
AppDataType is used as an argument to configure the behavior of
app_dir function and friends.

That would be option 1a I listed above. And that will need a major version bump.
So I would like to hear more about what others think about this issue.