In this appendix, we'll talk about some additional tools that are provided by the Rust project, and are useful when developing Rust code.

rustfmt is a tool that can re-format your code according to community norms. Many projects use rustfmt to prevent arguments about which style to use when writing Rust: just do what the tool does!

rustfmt is not at 1.0 yet, but a preview is available for you to use in the meantime. Please give it a try and let us know how it goes!

To install rustfmt:

$ rustup component add rustfmt-preview

This will give you both rustfmt and cargo-fmt, similar to how Rust gives you both rustc and cargo. To take any Cargo project and format it:

$ cargo fmt

If you’ve written code in Rust before, you’ve probably seen a compiler warning before. For example, consider this code:

fn do_something() {}

fn main() {
    for i in 0..100 {
        do_something();
    }
}

Here, we’re calling do_something a hundred times. But we never use the variable i. And so Rust warns:

> cargo build
   Compiling myprogram v0.1.0 (file:///projects/myprogram)
warning: unused variable: `i`
 --> src\main.rs:4:9
  |
4 |     for i in 1..100 {
  |         ^ help: consider using `_i` instead
  |
  = note: #[warn(unused_variables)] on by default

    Finished dev [unoptimized + debuginfo] target(s) in 0.50s

See how it suggests that we use _i as a name instead? We can automatically apply that suggestion with cargo fix:

> cargo fix
    Checking myprogram v0.1.0 (file:///projects/myprogram)
      Fixing src\main.rs (1 fix)
    Finished dev [unoptimized + debuginfo] target(s) in 0.59s

If we look at src\main.rs again, we’ll see that the code has changed:

fn do_something() {}

fn main() {
    for _i in 0..100 {
        do_something();
    }
}

We’re now using _i, and the warning will no longer appear.

cargo fix can also be used to transition your code between different editions of Rust. Editions are covered in Appendix H.

clippy is a bunch of lints to catch common mistakes and improve your Rust code.

clippy is not at 1.0 yet, but a preview is available for you to use in the meantime. Please give it a try and let us know how it goes!

To install clippy:

$ rustup component add clippy-preview

To take any Cargo project and run clippy's lints on it:

$ cargo clippy

To help IDE integration, the Rust project distributes rls, the Rust Language Server, as in http://langserver.org/. This can be used by different clients, such as the Rust plugin for Visual Studio: Code.

The rls is not at 1.0 yet, but a preview is available for you to use in the meantime. Please give it a try and let us know how it goes!

To install the rls:

$ rustup component add rls-preview

Then, install the language server support in your particular IDE, and it should all work.