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/api/projects/status/github/rust-lang-nursery/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](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to be a bit out of date).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

You must be using the latest nightly compiler toolchain.

To install:

```
cargo install rustfmt-nightly
```

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

```
cargo fmt
```

## Installation

```
cargo install rustfmt-nightly
```

or if you're using [Rustup](https://www.rustup.rs/)

```
rustup update
rustup run nightly cargo install rustfmt-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.

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-nightly
```
## 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 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](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.

(These instructions use the Syntex version of Rustfmt. If you want to use the
nightly version replace `install rustfmt` with `install rustfmt-nightly`,
however you must then only run this with the nightly toolchain).

A minimal Travis setup could look like this:

```yaml
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
visual style previews, [Configurations.md](Configurations.md).

By default, Rustfmt uses a style which conforms to the [Rust style guide][style
guide]. For details that have not yet been formalized through the [style RFC
process][fmt rfcs], we try to adhere to a style similar to that used in the
[Rust repo][rust].

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

    ```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.
* 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
```

## 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