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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):

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:

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

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

Rustfmt is able to pick up the edition used by reading the Cargo.toml file if executed through the Cargo's formatting tool cargo fmt. Otherwise, the edition needs to be specified in rustfmt.toml, e.g., with edition = "2018".

Tips

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.