rust/README.md

# rustfmt [![linux](https://github.com/rust-lang/rustfmt/actions/workflows/linux.yml/badge.svg?event=push)](https://github.com/rust-lang/rustfmt/actions/workflows/linux.yml) [![mac](https://github.com/rust-lang/rustfmt/actions/workflows/mac.yml/badge.svg?event=push)](https://github.com/rust-lang/rustfmt/actions/workflows/mac.yml) [![windows](https://github.com/rust-lang/rustfmt/actions/workflows/windows.yml/badge.svg?event=push)](https://github.com/rust-lang/rustfmt/actions/workflows/windows.yml) [![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) and our [Code of
Conduct](CODE_OF_CONDUCT.md).

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

## Quick start

You can run `rustfmt` with Rust 1.24 and above.

### On the Stable toolchain

To install:

```sh
rustup component add rustfmt
```

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

```sh
cargo fmt
```

### On the Nightly toolchain

For the latest and greatest `rustfmt`, nightly is required.

To install:

```sh
rustup component add rustfmt --toolchain nightly
```

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

```sh
cargo +nightly fmt
```

## Limitations

Rustfmt tries to work on as much Rust code as possible. Sometimes, the code
doesn't even need to compile! In general, we are 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).


## 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.
The easiest way to run rustfmt against a project is with `cargo fmt`. `cargo fmt` works on both
single-crate projects and [cargo workspaces](https://doc.rust-lang.org/book/ch14-03-cargo-workspaces.html).
Please see `cargo fmt --help` for usage information.

You can specify the path to your own `rustfmt` binary for cargo to use by setting the`RUSTFMT` 
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.
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](https://marketplace.visualstudio.com/items?itemName=rust-lang.rust-analyzer)
* [IntelliJ or CLion](intellij.md)


## 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):

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

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
--help=config` for the options which are available, or if you prefer to see
visual style previews, [GitHub page](https://rust-lang.github.io/rustfmt/).

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 [GitHub page](https://rust-lang.github.io/rustfmt/) 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:

    ```rust
    #![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:

  ```sh
  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 |
  | 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](LICENSE-APACHE) and [LICENSE-MIT](LICENSE-MIT) for details.

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