I think there should be two crates in rust-land. The answer by @soc makes sense for apps, as the article discusses. Many (most?) people building Rust programs aren't making apps and so shouldn't be using this crate, which clearly and definitively only supports MacOS "Apps".
What does making a different choice for GUI and CLI apps achieve, other than making it impossible to ever have a single coherent place to look/synchronise/etc?
XDG's spec doesn't make such a distinction, so you’re advocating for a new competing standard.
I don't think Apple’s documentation intends to cover command line programs, but… in the absence of any concrete rule, putting your files where most programs on the system do is a reasonable choice, and that place will never be ~/.config/ on macOS.
Apps like homebrew that default to the library but support XDG_CONFIG_HOME if explicitly set, are a decent compromise, though.
Not in Apple's nomenclature, it isn't. An App specifically refers to a folder named ".app" with an info.plist and a binary inside of it. It can also contain a bunch of other metadata and application data. To apple, a "CLI app" as you call it is just the binary (a single file).
But the real distinction is that the "Apple App" manages its preferences in-app. The "CLI app" does not, the user is expected to manage this configuration themselves.
