# SwiftSyntax

SwiftSyntax is a set of Swift bindings for the
[libSyntax](https://github.com/apple/swift/tree/master/lib/Syntax) library. It
allows for Swift tools to parse, inspect, generate, and transform Swift source
code.

> Note: SwiftSyntax is still in development, and the API is not guaranteed to
> be stable. It's subject to change without warning.

## Usage

First, install the latest Swift `master` toolchain from
[swift.org](https://swift.org/download/#snapshots). This will
ensure you have the latest version of SwiftSyntax, which is necessary as
SwiftSyntax evolves. Next, select that toolchain in Xcode, using
the File>Toolchains menu.

Then, open a new Swift file or create a new Swift package and
`import SwiftSyntax`. From there, you'll be able to use the SwiftSyntax API.

## Example

This is a program that adds 1 to every integer literal in a Swift file.

```swift
import SwiftSyntax
import Foundation

/// AddOneToIntegerLiterals will visit each token in the Syntax tree, and
/// (if it is an integer literal token) add 1 to the integer and return the
/// new integer literal token.
class AddOneToIntegerLiterals: SyntaxRewriter {
  override func visit(_ token: TokenSyntax) -> Syntax {
    // Only transform integer literals.
    guard case .integerLiteral(let text) = token.tokenKind else {
      return token
    }

    // Remove underscores from the original text.
    let integerText = String(text.filter { ("0"..."9").contains($0) })

    // Parse out the integer.
    let int = Int(integerText)!

    // Return a new integer literal token with `int + 1` as its text.
    return token.withKind(.integerLiteral("\(int + 1)"))
  }
}

let file = CommandLine.arguments[1]
let url = URL(fileURLWithPath: file)
let sourceFile = try SourceFileSyntax.parse(url)
let incremented = AddOneToIntegerLiterals().visit(sourceFile)
print(incremented)
```

This example turns this:

```swift
let x = 2
let y = 3_000
```

into:

```swift
let x = 3
let y = 3001
```