Format Rust code
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README.md

rustfmt Build Status Build Status crates.io Travis Configuration Status

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

Limitations

Rustfmt tries to work on as much Rust code as possible. Sometimes, the code
doesn’t even need to compile! As we approach a 1.0 release we are also 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).

Installation

rustup component add rustfmt

Installing from source

To install from source (nightly required), 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 can run rustfmt --help for information about available arguments.

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 1.24.0 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

cargo build to build.

cargo test --manifest-path rustfmt-core/Cargo.toml 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]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

  • 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.