• you probably don’t want one-function-per-file, for the reason i’m about to state, but it doesn’t hugely matter

• you’ll need a mod MODNAME; statement and pub use MODNAME::FUNCNAME; statement in lib.rs for each file and function

you can eliminate the second requirement by just doing pub fn FUNCNAME in lib.rs

if users do use CRATENAME::*;, then all top-level items in it become dropped into their global scope. this is generally considered a bad idea, except that prelude modules exist to do exactly this, and it’s pretty common to see mod prelude { pub use common_stuff; } in libraries and use CRATENAME::prelude::*; and consumers. be aware that symbols in the prelude should probably have an identifying prefix slapped on them with an use Name as CrateName rename directive, because they don’t have a namespace anymore

another trick libraries can offer is to say “please import me with use cratename::prelude as cn;” and provide a short abbreviation that is a tolerable namespace prefix. for example, my docs suggest use bitvec::prelude as bv;

As described by Masklinn, yes, Rust does have prebuilt library formats. However, these are mostly used internally, are finnicky for different compiler versions, and cargo still lacks support for them. In fact, crates.io requires libraries to be "open-source" (as in, you provide the source code, you could still have the source code load from some closed-source dependency), and it distributes the source code to whoever downloads the crate. Then, the source code is effectively compiled with your program (this is where rlibs come in to play, but cargo doesn't expose this to the user). This is also why you're able to inspect the source code for pretty much every crate.

Tok:tmp doug$ du -a

8   ./Cargo.toml
8   ./src/bin.rs
8   ./src/lib.rs
16  ./src

Cargo.toml:

[package]
name = "mything"
version = "0.0.1"
authors = ["me <[email protected]>"]

[lib]
name = "mylib"
path = "src/lib.rs"

[[bin]]
name = "mybin"
path = "src/bin.rs"

src/lib.rs:

pub fn test() {
    println!("Test");
}

src/bin.rs:

extern crate mylib; // not needed since Rust edition 2018

use mylib::test;

pub fn main() {
    test();
}