How to add external packages and run in rust compiler?

Question

I am compiling and building an example program using rust. I chose rustc instead of cargo for compiling because it being a simple personal test project. So far using rustc for compiling and building executable worked fine but when I tried to add an external rand package its giving me this error

1 | extern crate rand;
  | ^^^^^^^^^^^^^^^^^^ can't find crate

This is the full code

extern crate rand;

use rand::Rng;

fn main() {
    for x in 1..11 {
        let random_number = rand::thread_rng()
            .gen_range(1, 101);
        println!("{} -> {}", x, random_number)
    }
}

How can I add external packages and run with rustc?

Answer 1

This is possible without Cargo, but you'll have to do what it normally does for you.

1. Download all the dependencies.
2. Compile all the dependencies with rustc using the correct flags.

rand v0.7.3
├── getrandom v0.1.14
│   ├── cfg-if v0.1.10
│   └── libc v0.2.66
├── libc v0.2.66 (*)
├── rand_chacha v0.2.1
│   ├── c2-chacha v0.2.3
│   │   └── ppv-lite86 v0.2.6
│   └── rand_core v0.5.1
│       └── getrandom v0.1.14 (*)
└── rand_core v0.5.1 (*)

rand isn't too bad, with only 8 transitive dependencies (including rand itself, not including duplicates). Still, you'll have to go to crates.io or github and download the correct version of the source for each.

Then comes compiling. The minimum you'll have to do to compile your own binary is rustc -L dependency=/path/to/dependency/dir src/main.rs. But remember that you have to do this for each of the 8 dependencies, and all of those have their own external dependencies. You'll also need to figure out the right order to compile them.

Moveover, some crates have their own settings in their Cargo.toml that have to be respected. Some crates even have a build script that needs to be compiled and run (libc is an example in this dependency tree).

---

Alternatively, you could just put

[dependencies]
rand = "0.7.3"

in your Cargo.toml and run cargo build. Your choice. Cargo is one of the nicest things about Rust, so I suggest you use it.

---

P.S. To see what exactly cargo is doing, run cargo clean to remove any already compiled dependencies. Then run cargo build --verbose (or cargo build -vv if you're brave). You'll see all the flags that get passed to rustc, scripts that get run and everything else.

Answer 2

I wanted to expand on @SCappella's answer. I would encourage you to use cargo as well. If you are familiar with package managers from other languages such as JS, PHP, or Python, you might be interested in cargo edit.

It allows you to run commands cargo add rand (latest version), cargo add rand@0.7.3 (specific version), cargo upgrade rand (upgrade only rand), cargo upgrade (upgrade all dependencies) in CLI instead of editing Cargo.toml file directly.

To install it, run cargo install cargo-edit, and then read the documentation on the website on how you can use it.