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.

Quick start

To install:

cargo install rustfmt

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

cargo fmt

Installation

Note: this method currently requires you to be running cargo 0.6.0 or newer.

cargo install rustfmt

or if you're using rustup.rs

rustup run nightly cargo install rustfmt

Usually cargo-fmt, which enables usage of Cargo subcommand cargo fmt, is installed alongside rustfmt. To only install rustfmt run

cargo install --no-default-features rustfmt

Installing from source

To install from source, first checkout to the tag or branch you want to install, then issue

cargo install --path  .

This will install rustfmt in your ~/.cargo/bin. Make sure to add ~/.cargo/bin directory to your PATH variable.

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'll probably want to specify the write mode. Currently, there are modes for diff, replace, overwrite, display, coverage, and checkstyle.

replace Is the default and overwrites the original files after creating backups of the files.
overwrite Overwrites the original files without creating backups.
display Will print the formatted files to stdout.
diff Will print a diff between the original files and formatted files to stdout. Will also exit with an error code if there are any differences.
checkstyle Will output the lines that need to be corrected as a checkstyle XML file, that can be used by tools like Jenkins.

The write mode can be set by passing the --write-mode flag on the command line. For example rustfmt --write-mode=display src/filename.rs

cargo fmt uses --write-mode=replace by default.

If you want to restrict reformatting to specific sets of lines, you can use the --file-lines option. Its argument is a JSON array of objects with file and range properties, where file is a file name, and range is an array representing a range of lines like [7,13]. Ranges are 1-based and inclusive of both end points. Specifying an empty array will result in no files being formatted. For example,

rustfmt --file-lines '[
    {"file":"src/lib.rs","range":[7,13]},
    {"file":"src/lib.rs","range":[21,29]},
    {"file":"src/foo.rs","range":[10,11]},
    {"file":"src/foo.rs","range":[15,15]}]'

would format lines 7-13 and 21-29 of src/lib.rs, and lines 10-11, and 15 of src/foo.rs. No other files would be formatted, even if they are included as out of line modules from src/lib.rs.

If rustfmt successfully reformatted the code it will exit with 0 exit status. Exit status 1 signals some unexpected error, like an unknown option or a failure to read a file. Exit status 2 is returned if there are syntax errors in the input files. rustfmt can't format syntatically invalid code. Finally, exit status 3 is returned if there are some issues which can't be resolved automatically. For example, if you have a very long comment line rustfmt doesn't split it. Instead it prints a warning and exits with 3.

You can run rustfmt --help for more information.

Running Rustfmt from your editor

Vim
Emacs
Sublime Text 3
Atom
Visual Studio Code using RustyCode or vsc-rustfmt

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 --write-mode=diff instructs rustfmt to exit with an error code if the input is not formatted correctly. It will also print any found differences.

A minimal Travis setup could look like this:

language: rust
cache: cargo
before_script:
- export PATH="$PATH:$HOME/.cargo/bin"
- which rustfmt || cargo install rustfmt
script:
- cargo fmt -- --write-mode=diff
- cargo build
- cargo test

Note that using cache: cargo is optional but highly recommended to speed up the installation.

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 --config-help for the options which are available, or if you prefer to see source code, src/config.rs.

By default, Rustfmt uses a style which (mostly) conforms to the Rust style guidelines. There are many details which the style guidelines do not cover, and in these cases we try to adhere to a style similar to that used in the Rust repo. Once Rustfmt is more complete, and able to re-format large repositories like Rust, we intend to go through the Rust RFC process to nail down the default style in detail.

If there are styling choices you don't agree with, we are usually happy to add options covering different styles. File an issue, or even better, submit a PR.

Tips

For things you do not want rustfmt to mangle, use one of

#[rustfmt_skip]  // requires nightly and #![feature(custom_attribute)] in crate root
#[cfg_attr(rustfmt, rustfmt_skip)]  // works in stable

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.
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.

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.

nrc / rustfmt