Use OS-native config, cache home directories

[Earnestly]

Maintainer's notes:

• A Pre-RFC has been started that splits out the first half of t his work (making the paths configurable) to have a smaller, more focused conversation

---

For Linux-like systems, we should be using XDG. See arch's wiki for a non-exhaustive list of software with varying degrees of compliance.

For Windows, everything should go in ~/appdata/locallow or ~/appdata/local,since ~/.cargo is just a cache, AFAICT. This is FOLDERID_LocalAppData for SHGetKnownFolderPath, CSIDL_LOCAL_APPDATA for SHGetFolderPath, and %LOCALAPPDATA% in the environment.

[0X1A]

Have been stumped by this as well. Looked for Cargo's config in ~/.config/cargo only to find nothing. Don't really understand why Cargo places its config in ~/.cargo and the environment variable
CARGO_HOME, while nice is entirely useless. If the user's XDG is not set then it would be fine to place in ~/.cargo.

[Earnestly]

@0X1A If the respective XDG_* variables are not set, they should fallback
to the appropriate defaults as defined by the specification. The unfortunate
legacy behaviour cargo needlessly introduced will likely just add the code
bloat.

[Yamakaky]

Is someone working on this ? The more we wait, the more difficult it will be to change the default.

[0X1A]

@Yamakaky AFAIK there isn't anything being done about it

[whitequark]

You can use my xdg crate to implement this.

[nagisa]

cargo install now installs into ~/.cargo/bin.

[whitequark]

... and it really should use ~/.local/bin; there's precedent already in the behavior pip install --user, at least.