rustfmt

A tool for formatting Rust code according to style guidelines.

If you'd like to help out (and you should, it's a fun project!), see Contributing.md and our Code of Conduct.

You can use rustfmt in Travis CI builds. We provide a minimal Travis CI configuration (see here).

Quick start

You can run rustfmt with Rust 1.24 and above.

On the Stable toolchain

To install:

rustup component add rustfmt

To run on a cargo project in the current working directory:

cargo fmt

On the Nightly toolchain

For the latest and greatest rustfmt, nightly is required.

To install:

rustup component add rustfmt --toolchain nightly

To run on a cargo project in the current working directory:

cargo +nightly fmt

Limitations

Rustfmt tries to work on as much Rust code as possible. Sometimes, the code doesn't even need to compile! In general, we are looking to limit areas of instability; in particular, post-1.0, the formatting of most code should not change as Rustfmt improves. However, there are some things that Rustfmt can't do or can't do well (and thus where formatting might change significantly, even post-1.0). We would like to reduce the list of limitations over time.

The following list enumerates areas where Rustfmt does not work or where the stability guarantees do not apply (we don't make a distinction between the two because in the future Rustfmt might work on code where it currently does not):

• a program where any part of the program does not parse (parsing is an early stage of compilation and in Rust includes macro expansion).
• Macro declarations and uses (current status: some macro declarations and uses are formatted).
• Comments, including any AST node with a comment 'inside' (Rustfmt does not currently attempt to format comments, it does format code with comments inside, but that formatting may change in the future).
• Rust code in code blocks in comments.
• Any fragment of a program (i.e., stability guarantees only apply to whole programs, even where fragments of a program can be formatted today).
• Code containing non-ascii unicode characters (we believe Rustfmt mostly works here, but do not have the test coverage or experience to be 100% sure).
• Bugs in Rustfmt (like any software, Rustfmt has bugs, we do not consider bug fixes to break our stability guarantees).

Running

You can run Rustfmt by just typing rustfmt filename if you used cargo install. This runs rustfmt on the given file, if the file includes out of line modules, then we reformat those too. So to run on a whole module or crate, you just need to run on the root file (usually mod.rs or lib.rs). Rustfmt can also read data from stdin. Alternatively, you can use cargo fmt to format all binary and library targets of your crate.

You can run rustfmt --help for information about available arguments. The easiest way to run rustfmt against a project is with cargo fmt. cargo fmt works on both single-crate projects and cargo workspaces. Please see cargo fmt --help for usage information.

You can specify the path to your own rustfmt binary for cargo to use by setting theRUSTFMT environment variable. This was added in v1.4.22, so you must have this version or newer to leverage this feature (cargo fmt --version)

Running rustfmt directly

To format individual files or arbitrary codes from stdin, the rustfmt binary should be used. Some examples follow:

• rustfmt lib.rs main.rs will format "lib.rs" and "main.rs" in place
• rustfmt will read a code from stdin and write formatting to stdout
  • echo "fn main() {}" | rustfmt would emit "fn main() {}".

For more information, including arguments and emit options, see rustfmt --help.

Verifying code is formatted

When running with --check, Rustfmt will exit with 0 if Rustfmt would not make any formatting changes to the input, and 1 if Rustfmt would make changes. In other modes, Rustfmt will exit with 1 if there was some error during formatting (for example a parsing or internal error) and 0 if formatting completed without error (whether or not changes were made).

Running Rustfmt from your editor

• Vim
• Emacs
• Sublime Text 3
• Atom
• Visual Studio Code
• IntelliJ or CLion

Checking style on a CI server

To keep your code base consistently formatted, it can be helpful to fail the CI build when a pull request contains unformatted code. Using --check instructs rustfmt to exit with an error code if the input is not formatted correctly. It will also print any found differences. (Older versions of Rustfmt don't support --check, use --write-mode diff).

A minimal Travis setup could look like this (requires Rust 1.31.0 or greater):

language: rust
before_script:
- rustup component add rustfmt
script:
- cargo build
- cargo test
- cargo fmt --all -- --check

See this blog post for more info.

How to build and test

cargo build to build.

cargo test to run all tests.

To run rustfmt after this, use cargo run --bin rustfmt -- filename. See the notes above on running rustfmt.

Configuring Rustfmt

Rustfmt is designed to be very configurable. You can create a TOML file called rustfmt.toml or .rustfmt.toml, place it in the project or any other parent directory and it will apply the options in that file. See rustfmt --help=config for the options which are available, or if you prefer to see visual style previews, GitHub page.

By default, Rustfmt uses a style which conforms to the Rust style guide that has been formalized through the style RFC process.

Configuration options are either stable or unstable. Stable options can always be used, while unstable ones are only available on a nightly toolchain, and opt-in. See GitHub page for details.

Rust's Editions

The edition option determines the Rust language edition used for parsing the code. This is important for syntax compatibility but does not directly control formatting behavior (see Style Editions).

When running cargo fmt, the edition is automatically read from the Cargo.toml file. However, when running rustfmt directly, the edition defaults to 2015. For consistent parsing between rustfmt and cargo fmt, you should configure the edition in your rustfmt.toml file:

edition = "2018"

Style Editions

This option is inferred from the edition if not specified.

See Rust Style Editions for details on formatting differences between style editions. rustfmt has a default style edition of 2015 while cargo fmt infers the style edition from the edition set in Cargo.toml. This can lead to inconsistencies between rustfmt and cargo fmt if the style edition is not explicitly configured.

To ensure consistent formatting, it is recommended to specify the style_edition in a rustfmt.toml configuration file. For example:

style_edition = "2024"

Tips

• To ensure consistent parsing between cargo fmt and rustfmt, you should configure the edition in your rustfmt.toml file.

• To ensure consistent formatting between cargo fmt and rustfmt, you should configure the style_edition in your rustfmt.toml file.

• For things you do not want rustfmt to mangle, use #[rustfmt::skip]

• To prevent rustfmt from formatting a macro or an attribute, use #[rustfmt::skip::macros(target_macro_name)] or #[rustfmt::skip::attributes(target_attribute_name)]

  Example:

  #![rustfmt::skip::attributes(custom_attribute)]
  
  #[custom_attribute(formatting , here , should , be , Skipped)]
  #[rustfmt::skip::macros(html)]
  fn main() {
      let macro_result1 = html! { <div>
  Hello</div>
      }.to_string();
  

• When you run rustfmt, place a file named rustfmt.toml or .rustfmt.toml in target file directory or its parents to override the default settings of rustfmt. You can generate a file containing the default configuration with rustfmt --print-config default rustfmt.toml and customize as needed.

• After successful compilation, a rustfmt executable can be found in the target directory.

• If you're having issues compiling Rustfmt (or compile errors when trying to install), make sure you have the most recent version of Rust installed.

• You can change the way rustfmt emits the changes with the --emit flag:

  Example:

  cargo fmt -- --emit files
  

  Options:

  Flag	Description	Nightly Only
  files	overwrites output to files	No
  stdout	writes output to stdout	No
  coverage	displays how much of the input file was processed	Yes
  checkstyle	emits in a checkstyle format	Yes
  json	emits diffs in a json format	Yes

License

Rustfmt is distributed under the terms of both the MIT license and the Apache License (Version 2.0).

See LICENSE-APACHE and LICENSE-MIT for details.