# Parser and pretty printer for Rust [![Build Status][4]][5] [![Windows build status][7]][8]

`language-rust` aspires to efficiently and accurately parse and pretty print the [Rust language][0].
The underlying AST structures are also intended to be as similar as possible to the [`libsyntax` AST
`rustc`][10] uses itself. When `language-rust` and `rustc` have diverging AST, the divergence should
be detailed in the documentation.

A typical use looks like:

```haskell
>>> :set -XTypeApplications +t
>>> import Language.Rust.Syntax

>>> -- Sample use of the parser
>>> import Language.Rust.Parser
>>> let inp = inputStreamFromString "fn main () { println!(\"Hello world!\"); }"
inp :: InputStream
>>> let sourceFile = parse' @(SourceFile Span) inp
sourceFile :: SourceFile Span

>>> -- Sample use of the pretty printer
>>> import Language.Rust.Pretty
>>> pretty' sourceFile
fn main() {
  println!("Hello world!");
}
it :: Doc b
```

## Building

### Cabal

With Cabal and GHC, run

    cabal install happy --constraint 'happy >= 1.19.8'
    cabal install alex
    cabal configure
    cabal build

### Stack

With the [Stack][1] tool installed, run

    stack init
    stack build

The second command is responsible for pulling in all of the dependencies (including executable
tools like [Alex][2], [Happy][3], and GHC itself) and then compiling everything. If Stack complains
about the version of Happy installed, you can explicitly install a recent one with `stack install
happy-1.19.8`.

## Evolution of Rust

As Rust evolves, so will `language-rust`. We will make a best effort to support unstable features
from nightly as they come out, but in general will only target compatibility with stable.

## Bugs

Please report any bugs to the [github issue tracker][9].

### Parser

Any difference between what is accepted by the `rustc` parser and the `language-rust` parser
indicates

  * a bug in `language-rust` (this is almost always the case)
  * a bug in `rustc`
  * that there is a newer version of `rustc` which made a breaking change to this syntax

If the AST/parser of `rustc` changes, the `rustc-tests` test suite should start failing - it
compares the JSON AST debug output of `rustc` to our parsed AST.

### Pretty printer

For the pretty printer, bugs are a bit tougher to list exhaustively. Suggestions for better layout
algorithms are most welcome! The [`fmt-rfcs`][6] repo is loosely used as the reference for "correct"
pretty printing.

[0]: https://www.rust-lang.org/en-US/
[1]: https://docs.haskellstack.org/en/stable/README/
[2]: https://hackage.haskell.org/package/alex
[3]: https://hackage.haskell.org/package/happy
[4]: https://travis-ci.org/harpocrates/language-rust.svg?branch=master
[5]: https://travis-ci.org/harpocrates/language-rust
[6]: https://github.com/rust-lang-nursery/fmt-rfcs
[7]: https://ci.appveyor.com/api/projects/status/um8dxklqmubvn091/branch/master?svg=true
[8]: https://ci.appveyor.com/project/harpocrates/language-rust/branch/master
[9]: https://github.com/harpocrates/language-rust/issues
[10]: https://github.com/rust-lang/rust/blob/master/src/libsyntax/ast.rs