rust/README.md

# rustfmt [![Build Status](https://travis-ci.org/rust-lang-nursery/rustfmt.svg)](https://travis-ci.org/rust-lang-nursery/rustfmt) [![Build Status](https://ci.appveyor.com/api/projects/status/github/rust-lang-nursery/rustfmt?svg=true)](https://ci.appveyor.com/project/nrc/rustfmt) [![crates.io](https://img.shields.io/crates/v/rustfmt-nightly.svg)](https://crates.io/crates/rustfmt-nightly)

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](Contributing.md).

We are changing the default style used by rustfmt. There is an ongoing [RFC
process][fmt rfcs]. The last version using the old style was 0.8.6. From 0.9
onwards, the RFC style is the default. If you want the old style back, you can
use [legacy-rustfmt.toml](legacy-rustfmt.toml) as your rustfmt.toml.

The current `master` branch uses libsyntax (part of the compiler). It is
published as `rustfmt-nightly`. The `syntex` branch uses Syntex instead of
libsyntax, it is published (for now) as `rustfmt`. Most development happens on
the `master` branch, however, this only supports nightly toolchains. If you use
stable or beta Rust toolchains, you must use the Syntex version (which is likely
to be a bit out of date). Version 0.1 of rustfmt-nightly is forked from version
0.9 of the syntex branch.


## Quick start

Currently, you can use `rustfmt` on nightly and beta. Rust 1.24 stable will work,
but we're not quite there yet!

To install:

```
rustup component add rustfmt-preview --toolchain=nightly
```

If `nightly` is your default toolchain, you can leave the `--toolchain` off.

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

```
cargo +nightly fmt
```

If `nightly` is your default toolchain, you can leave off the `+nightly`.

## Installation

```
rustup component add rustfmt-preview --toolchain=nightly
```

If you don't have a nightly toolchain, you can add it using rustup:

```
rustup install nightly
```

You can make the nightly toolchain the default by running:

```
rustup default nightly
```

If you choose not to do that you'll have to run rustfmt using `rustup run ...`
or by adding `+nightly` to the cargo invocation.

## 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`, `checkstyle`, and `plain`.

* `overwrite` Is the default and overwrites the original files _without_ creating backups.
* `replace` Overwrites the original files after creating backups of the files.
* `display` Will print the formatted files to stdout.
* `plain` Also writes to stdout, but with no metadata.
* `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=overwrite` 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 syntactically 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](https://github.com/rust-lang/rust.vim#formatting-with-rustfmt)
* [Emacs](https://github.com/rust-lang/rust-mode)
* [Sublime Text 3](https://packagecontrol.io/packages/RustFmt)
* [Atom](atom.md)
* Visual Studio Code using [vscode-rust](https://github.com/editor-rs/vscode-rust), [vsc-rustfmt](https://github.com/Connorcpu/vsc-rustfmt) or [rls_vscode](https://github.com/jonathandturner/rls_vscode) through RLS.

## 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:

```yaml
language: rust
before_script:
- rustup toolchain install nightly
- rustup component add --toolchain nightly rustfmt-preview
- which rustfmt || cargo install --force rustfmt-nightly
script:
- cargo +nightly fmt --all -- --write-mode=diff
- cargo build
- cargo test
```

## 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
visual style previews, [Configurations.md](Configurations.md).

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

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 [Configurations.md](Configurations.md) for details.


## Tips

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

    ```rust
    #[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. You can generate a file containing the default configuration with
  `rustfmt --dump-default-config 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.

* If you get an error like `error while loading shared libraries` while starting
  up rustfmt you should try the following:

  On Linux:

  ```
  export LD_LIBRARY_PATH=$(rustc --print sysroot)/lib:$LD_LIBRARY_PATH
  ```

  On MacOS:

  ```
  export DYLD_LIBRARY_PATH=$(rustc --print sysroot)/lib:$DYLD_LIBRARY_PATH
  ```

  On Windows (Git Bash/Mingw):

  ```
  export PATH=$(rustc --print sysroot)/lib/rustlib/x86_64-pc-windows-gnu/lib/:$PATH
  ```

  (Substitute `x86_64` by `i686` and `gnu` by `msvc` depending on which version of rustc was used to install rustfmt).

## License

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

See [LICENSE-APACHE](LICENSE-APACHE) and [LICENSE-MIT](LICENSE-MIT) for details.

[rust]: https://github.com/rust-lang/rust
[fmt rfcs]: https://github.com/rust-lang-nursery/fmt-rfcs
[style guide]: https://github.com/rust-lang-nursery/fmt-rfcs/blob/master/guide/guide.md