GuillaumeGomez / rustfmt

Format Rust code

rustfmt

• Quick start
  • On the Stable toolchain
  • On the Nightly toolchain
  • Installing from source
• Usage
  • Running cargo fmt
  • Running rustfmt directly
  • Verifying code is formatted
  • Exit codes
• Configuring Rustfmt
  • Differences in rustfmt versions
    • Default formatting of submodules
    • Construction of config options
  • Rust's Editions
• Limitations
• Running Rustfmt from your editor
• Checking style on a CI server
• How to build and test
• Tips
• License

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) and verify its status using another repository. The status of that repository's build is reported by the "travis example" badge above.

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

Installing from source

To install from source (nightly required), first checkout to the tag or branch for the version of rustfmt you want.

The easiest way to install is via cargo make

cargo make install

Alternatively, you can run cargo install directly as long as you set the required environment variables and features.

export CFG_RELEASE=nightly
export CFG_RELEASE_CHANNEL=nightly
cargo install --path . --force --locked --features rustfmt,cargo-fmt

(Windows users can use set to specify the environment variable values)

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

Usage

Please use rustfmt --help to see information about available arguments.

Running cargo fmt

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.

Exit codes

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).

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 the config website for all available options.

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 on any channel. Unstable options are always available on nightly, but can only be used on stable and beta with an explicit opt-in (starting in Rustfmt v2.0).

Unstable options are not available on stable/beta with Rustfmt v1.x.

See the configuration documentation on the Rustfmt GitHub page for details (look for the unstable_features section).

Differences in rustfmt versions

Default formatting of submodules

On an invocation rustfmt lib.rs, rustfmt 1.x would format both "lib.rs" and any out-of-file submodules referenced in "lib.rs", unless the skip_children configuration option was true.

With rustfmt 2.x, this behavior requires the --recursive flag (#3587). By default, out-of-file submodules of given files are not formatted.

Note that this only applies to the rustfmt binary, and does not impact cargo fmt.

Construction of config options

Rustfmt 1.x uses only the configuration options declared in the rustfmt configuration file nearest the directory rustfmt is invoked.

Rustfmt 2.x merges configuration options from all configuration files in all parent directories, with configuration files nearer the current directory having priority.

Please see Configurations for more information and #3881 for the motivating issue.

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".

Limitations

Rustfmt tries to work on as much Rust code as possible. Sometimes, the code doesn't even need to compile! However, there are some things that Rustfmt can't do or can't do well. The following list enumerates such limitations:

• A program where any part of the program does not parse (parsing is an early stage of compilation and in Rust includes macro expansion).
• Any fragment of a program (i.e., stability guarantees only apply to whole programs, even where fragments of a program can be formatted today).
• Bugs in Rustfmt (like any software, Rustfmt has bugs, we do not consider bug fixes to break our stability guarantees).

Running Rustfmt from your editor

• Vim
• Emacs
• Sublime Text 3
• Atom
• Visual Studio Code using vscode-rust, vsc-rustfmt or rls_vscode through RLS.
• 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 -- --check

See this blog post for more info.

How to build and test

We recommend using cargo make when working with the rustfmt codebase.

You can alternatively use cargo directly, but you'll have to set the CFG_RELEASE and CFG_RELEASE_CHANNEL environment variables and also provide the corresponding features.

For example:

export CFG_RELEASE=1.45.0-nightly
export CFG_RELEASE_CHANNEL=nightly

(Windows users can use set to specify the environment variable values)

To build with cargo make:

cargo make build

Or alternatively with cargo directly:

cargo build --all-features
# or
CFG_RELEASE_CHANNEL=nightly CFG_RELEASE=1.45.0-nightly cargo build --all-features

To run tests with cargo make:

cargo make test

Or alternatively with cargo directly:

cargo test --all-features
# or
CFG_RELEASE_CHANNEL=nightly CFG_RELEASE=1.45.0-nightly cargo test --all-features

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

Tips

• 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
  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.