Rust Formatter (rustfmt)

What the Rust formatter does

This page runs rustfmt (WASM), the same formatter that cargo fmt invokes, compiled for the browser. It parses your file with the Rust compiler’s own parser and reprints it using the 2021 edition and the 2021 style edition, with Unix line endings.

rustfmt changes layout, not meaning. Expect it to:

• put one statement per line and expand blocks, match arms and struct literals
• break long method chains so each .call() starts its own line
• add trailing commas to multi-line struct fields, enum variants and match arms
• sort use declarations and mod items alphabetically, as cargo fmt does by default

Comments and doc comments (///, //!) are kept where you wrote them. The formatter does not type-check or borrow-check anything, so code that would fail cargo build still formats as long as it parses.

Indentation, width and shortcuts

There are no Rust-only switches; the toolbar’s indent and line-width settings map straight onto rustfmt’s tab_spaces, hard_tabs and max_width. One thing catches people out: rustfmt’s own defaults are 4 spaces and 100 columns, while the toolbar opens at 2 spaces and 80. Pick 4 and 100 if the output should match an unconfigured cargo fmt run in CI. A rustfmt.toml from your project is not read, so options like imports_granularity or group_imports cannot be applied here.

Press Ctrl/Cmd+Enter to format, Ctrl/Cmd+Shift+C to copy the result and Ctrl/Cmd+K to jump to another formatter from the command palette. Ctrl/Cmd+Shift+M is the minify shortcut, but Rust has no minified form, so it is not offered on this page.

Macros, errors and other edge cases

Macro calls written with parentheses or square brackets, such as println!(...) or vec![...], are formatted like function calls. Brace-delimited macros (html! { ... }, macro_rules! bodies) are left almost untouched because rustfmt cannot know their grammar.

If the file does not parse, nothing is reformatted: you get the compiler’s message with a line and column instead of half-formatted output. An unclosed delimiter is reported where the file ends, not where the brace was opened, so scan upwards from the last block you edited. Very deep nesting or an unterminated string can make the WebAssembly build abort with a “crashed” message rather than a tidy diagnostic.

Generated code from build.rs or include! files formats fine, which is handy when you need to read what a derive or code generator actually produced. The same goes for the output of cargo expand: paste it here to turn one enormous line of expanded macro code into something you can follow.

Attributes such as #[derive(Debug, Clone)] move onto their own line above the item, and rustfmt normalises spacing inside them. If you want a block left exactly as written, put #[rustfmt::skip] on the item; the formatter honours it here just as it does locally.

Examples

impl Config{pub fn from_env()->Result<Self,String>{let port=std::env::var("PORT").unwrap_or_else(|_|"8080".into()).parse::<u16>().map_err(|e|e.to_string())?;Ok(Self{port,debug:cfg!(debug_assertions)})}}

impl Config {
    pub fn from_env() -> Result<Self, String> {
        let port = std::env::var("PORT")
            .unwrap_or_else(|_| "8080".into())
            .parse::<u16>()
            .map_err(|e| e.to_string())?;
        Ok(Self {
            port,
            debug: cfg!(debug_assertions),
        })
    }
}

enum Shape{Circle{r:f64},Rect{w:f64,h:f64}}
fn area(s:&Shape)->f64{match s{Shape::Circle{r}=>std::f64::consts::PI*r*r,Shape::Rect{w,h}=>w*h}}

enum Shape {
    Circle { r: f64 },
    Rect { w: f64, h: f64 },
}
fn area(s: &Shape) -> f64 {
    match s {
        Shape::Circle { r } => std::f64::consts::PI * r * r,
        Shape::Rect { w, h } => w * h,
    }
}

pub fn largest<T>(items:&[T])->Option<&T> where T:PartialOrd{let mut it=items.iter();let mut best=it.next()?;for x in it{if x>best{best=x;}}Some(best)}

pub fn largest<T>(items: &[T]) -> Option<&T>
where
    T: PartialOrd,
{
    let mut it = items.iter();
    let mut best = it.next()?;
    for x in it {
        if x > best {
            best = x;
        }
    }
    Some(best)
}

Common errors and how to fix them

Related tools

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