XDG user dirs should default to $HOME

[OJFord]

If ${XDG_CONFIG_HOME:-$HOME/.config}/user-dirs.dirs does not exist, or lacks the specified key (e.g. XDG_DOWNLOAD_DIR), the behaviour of xdg-user-dir the CLI program is to output $HOME.

In the same case, the behaviour of dirs::download_dir() (for example) is to return None.

There's no specification as such for '"well known" user directories', but it's implied that this is the intended fall-back behaviour:

Note: To disable a directory, point it to the homedir.

https://www.freedesktop.org/wiki/Software/xdg-user-dirs/

cf. tauri-apps/tauri#3090, xdg-rs/dirs#56 (I opened there as that's what I'm using, via tauri, but it seems to affect dirs too, so I've copied here.)

[soc]

I don't read this sentence of the spec as a fallback behavior, but as a way to disable a directory ("To disable a directory, point it to the homedir.") as they seemingly have used "no entry" for other purposes already.

I believe this is correctly represented with None in Rust. Feel free to reopen if you have further thoughts on this!

[OJFord]

I suppose it depends whether you view the API as 'what has been configured?' (nothing, None) or 'what is the directory to use?' (not configured, $HOME or something sensible).

It'd be nice if these various libraries/tools were consistent on the matter, but having lost context on this I think you're right, it's at best ambiguous, and absent something explicit they never will be.