Canonical definitions of home_dir, cargo_home, and rustup_home.

This provides the definition of home_dir used by Cargo and rustup, as well functions to find the correct value of CARGO_HOME and RUSTUP_HOME.

The definition of home_dir provided by the standard library is incorrect because it considers the HOME environment variable on Windows. This causes surprising situations where a Rust program will behave differently depending on whether it is run under a Unix emulation environment like Cygwin or MinGW. Neither Cargo nor rustup use the standard libraries definition - they use the definition here.

This crate further provides two functions, cargo_home and rustup_home, which are the canonical way to determine the location that Cargo and rustup store their data.

See rust-lang/rust#43321.

License

MIT/Apache-2.0