rustc::metadata::filesearch
pub fn rust_path() -> Vec<Path>
Returns the value of RUST_PATH, as a list of Paths. Includes default entries for, if they exist: $HOME/.rust DIR/.rust for any DIR that's the current working directory or an ancestor of it
Prefix searches with a type followed by a colon (e.g.
fn:) to restrict the search to a given type.
Accepted types are: fn, mod,
struct (or str), enum,
trait, typedef (or
tdef).