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) [![Travis Configuration Status](https://img.shields.io/travis/davidalber/rustfmt-travis.svg?label=travis%20example)](https://travis-ci.org/davidalber/rustfmt-travis)

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) and our [Code of
Conduct](CODE_OF_CONDUCT.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to be a bit out of date).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.

You can use rustfmt in Travis CI builds. We provide a minimal Travis CI
configuration (see [here](#checking-style-on-a-ci-server)) 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 use `rustfmt` on Rust 1.24 and above.

To install:

```
rustup component add rustfmt-preview
```

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

```
cargo fmt
```

For the latest and greatest `rustfmt` (nightly required):
```
rustup component add rustfmt-preview --toolchain nightly
```
To run:
```
cargo +nightly fmt
```

To format code that requires edition 2018, create a `rustfmt.toml` [configuration](#configuring-rustfmt) file containing:

```toml
edition = "Edition2018"
```

## 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-preview
```

## 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 argument.

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

* [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 `--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):

```yaml
language: rust
rust:
- nightly
before_script:
- rustup component add rustfmt-preview
script:
- cargo fmt --all -- --check
- cargo build
- cargo test
```

See [this blog post](https://medium.com/@ag_dubs/enforcing-style-in-ci-for-rust-projects-18f6b09ec69d)
for more info.

## 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 Rust and #![feature(tool_attributes)] 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 --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.

* 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).

* 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 | 
  | coverage | displays how much of the input file was processed | Yes |
  | checkstyle | emits in a checkstyle format | Yes |

## 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