Useful Development Tools
- Automatic Formatting with
rustfmt
- Fix Your Code with
rustfix
- More Lints with Clippy
- IDE Integration Using
rust-analyzer
In this appendix, we talk about some useful development tools that the Rust project provides. We’ll look at automatic formatting, quick ways to apply warning fixes, a linter, and integrating with IDEs.
Automatic Formatting with rustfmt
The rustfmt
tool reformats your code according to the community code style.
Many collaborative projects use rustfmt
to prevent arguments about which
style to use when writing Rust: everyone formats their code using the tool.
To install rustfmt
, enter the following:
$ rustup component add rustfmt
This command gives you rustfmt
and cargo-fmt
, similar to how Rust gives you
both rustc
and cargo
. To format any Cargo project, enter the following:
$ cargo fmt
Running this command reformats all the Rust code in the current crate. This
should only change the code style, not the code semantics. For more information
on rustfmt
, see its documentation.
Fix Your Code with rustfix
The rustfix tool is included with Rust installations and can automatically fix compiler warnings that have a clear way to correct the problem that’s likely what you want. It’s likely you’ve seen compiler warnings before. For example, consider this code:
Filename: src/main.rs
fn do_something() {} fn main() { for i in 0..100 { do_something(); } }
Here, we’re calling the do_something
function 100 times, but we never use the
variable i
in the body of the for
loop. Rust warns us about that:
$ cargo build
Compiling myprogram v0.1.0 (file:///projects/myprogram)
warning: unused variable: `i`
--> src/main.rs:4:9
|
4 | for i in 0..100 {
| ^ help: consider using `_i` instead
|
= note: #[warn(unused_variables)] on by default
Finished dev [unoptimized + debuginfo] target(s) in 0.50s
The warning suggests that we use _i
as a name instead: the underscore
indicates that we intend for this variable to be unused. We can automatically
apply that suggestion using the rustfix
tool by running the command 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
When we look at src/main.rs again, we’ll see that cargo fix
has changed the
code:
Filename: src/main.rs
fn do_something() {} fn main() { for _i in 0..100 { do_something(); } }
The for
loop variable is now named _i
, and the warning no longer appears.
You can also use the cargo fix
command to transition your code between
different Rust editions. Editions are covered in Appendix E.
More Lints with Clippy
The Clippy tool is a collection of lints to analyze your code so you can catch common mistakes and improve your Rust code.
To install Clippy, enter the following:
$ rustup component add clippy
To run Clippy’s lints on any Cargo project, enter the following:
$ cargo clippy
For example, say you write a program that uses an approximation of a mathematical constant, such as pi, as this program does:
Filename: src/main.rs
fn main() { let x = 3.1415; let r = 8.0; println!("the area of the circle is {}", x * r * r); }
Running cargo clippy
on this project results in this error:
error: approximate value of `f{32, 64}::consts::PI` found
--> src/main.rs:2:13
|
2 | let x = 3.1415;
| ^^^^^^
|
= note: `#[deny(clippy::approx_constant)]` on by default
= help: consider using the constant directly
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#approx_constant
This error lets you know that Rust already has a more precise PI
constant
defined, and that your program would be more correct if you used the constant
instead. You would then change your code to use the PI
constant. The
following code doesn’t result in any errors or warnings from Clippy:
Filename: src/main.rs
fn main() { let x = std::f64::consts::PI; let r = 8.0; println!("the area of the circle is {}", x * r * r); }
For more information on Clippy, see its documentation.
IDE Integration Using rust-analyzer
To help IDE integration, the Rust community recommends using
rust-analyzer
. This tool is a set of
compiler-centric utilities that speaks the Language Server Protocol, which is a specification for IDEs and programming languages to
communicate with each other. Different clients can use rust-analyzer
, such as
the Rust analyzer plug-in for Visual Studio Code.
Visit the rust-analyzer
project’s home page
for installation instructions, then install the language server support in your
particular IDE. Your IDE will gain abilities such as autocompletion, jump to
definition, and inline errors.