Crates
The crate_type attribute can be used to tell the compiler whether a crate is
a binary or a library (and even which type of library), and the crate_name
attribute can be used to set the name of the crate.
However, it is important to note that both the crate_type and crate_name
attributes have no effect whatsoever when using Cargo, the Rust package
manager. Since Cargo is used for the majority of Rust projects, this means
real-world uses of crate_type and crate_name are relatively limited.
When the crate_type attribute is used, we no longer need to pass the
--crate-type flag to rustc.
$ rustc lib.rs
$ ls lib*
library.rlib