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## Appendix D - Useful Development Tools
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:
```console
$ 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:
```console
$ 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][rustfmt].
[rustfmt]: https://github.com/rust-lang/rustfmt
### 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:
<span class="filename">Filename: src/main.rs</span>
```rust
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:
```console
$ 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`:
```console
$ 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:
<span class="filename">Filename: src/main.rs</span>
```rust
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:
```console
$ rustup component add clippy
```
To run Clippy’s lints on any Cargo project, enter the following:
```console
$ cargo clippy
```
For example, say you write a program that uses an approximation of a
mathematical constant, such as pi, as this program does:
<span class="filename">Filename: src/main.rs</span>
```rust
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:
```text
error: approximate value of `f{32, 64}::consts::PI` found. Consider using it directly
--> src/main.rs:2:13
|
2 | let x = 3.1415;
| ^^^^^^
|
= note: #[deny(clippy::approx_constant)] on by default
= help: for further information visit https://rust-lang-nursery.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:
<span class="filename">Filename: src/main.rs</span>
```rust
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][clippy].
[clippy]: https://github.com/rust-lang/rust-clippy
### IDE Integration Using `rust-analyzer`
To help IDE integration, the Rust community recommends using
[`rust-analyzer`][rust-analyzer]<!-- ignore -->. This tool is a set of
compiler-centric utilities that speaks the [Language Server Protocol][lsp]<!--
ignore -->, 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][vscode].
[lsp]: http://langserver.org/
[vscode]: https://marketplace.visualstudio.com/items?itemName=rust-lang.rust-analyzer
Visit the `rust-analyzer` project’s [home page][rust-analyzer] 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.
[rust-analyzer]: https://rust-analyzer.github.io
|
