# Swift {#swift}

The Swift compiler is provided by the `swift` package:

```sh
# Compile and link a simple executable.
nix-shell -p swift --run 'swiftc -' <<< 'print("Hello world!")'
# Run it!
./main
```

The `swift` package also provides the `swift` command, with some caveats:

- Swift Package Manager (SwiftPM) is packaged separately as `swiftpm`. If you
  need functionality like `swift build`, `swift run`, `swift test`, you must
  also add the `swiftpm` package to your closure.
- On Darwin, the `swift repl` command requires an Xcode installation. This is
  because it uses the system LLDB debugserver, which has special entitlements.

## Module search paths {#ssec-swift-module-search-paths}

Like other toolchains in Nixpkgs, the Swift compiler executables are wrapped
to help Swift find your application's dependencies in the Nix store. These
wrappers scan the `buildInputs` of your package derivation for specific
directories where Swift modules are placed by convention, and automatically
add those directories to the Swift compiler search paths.

Swift follows different conventions depending on the platform. The wrappers
look for the following directories:

- On Darwin platforms: `lib/swift/macosx`
  (If not targeting macOS, replace `macosx` with the Xcode platform name.)
- On other platforms: `lib/swift/linux/x86_64`
  (Where `linux` and `x86_64` are from lowercase `uname -sm`.)
- For convenience, Nixpkgs also adds `lib/swift` to the search path.
  This can save a bit of work packaging Swift modules, because many Nix builds
  will produce output for just one target any way.

## Core libraries {#ssec-swift-core-libraries}

In addition to the standard library, the Swift toolchain contains some
additional 'core libraries' that, on Apple platforms, are normally distributed
as part of the OS or Xcode. These are packaged separately in Nixpkgs, and can
be found (for use in `buildInputs`) as:

- `swiftPackages.Dispatch`
- `swiftPackages.Foundation`
- `swiftPackages.XCTest`

## Packaging with SwiftPM {#ssec-swift-packaging-with-swiftpm}

Nixpkgs includes a small helper `swiftpm2nix` that can fetch your SwiftPM
dependencies for you, when you need to write a Nix expression to package your
application.

The first step is to run the generator:

```sh
cd /path/to/my/project
# Enter a Nix shell with the required tools.
nix-shell -p swift swiftpm swiftpm2nix
# First, make sure the workspace is up-to-date.
swift package resolve
# Now generate the Nix code.
swiftpm2nix
```

This produces some files in a directory `nix`, which will be part of your Nix
expression. The next step is to write that expression:

```nix
{
  stdenv,
  swift,
  swiftpm,
  swiftpm2nix,
  fetchFromGitHub,
}:

let
  # Pass the generated files to the helper.
  generated = swiftpm2nix.helpers ./nix;
in

stdenv.mkDerivation (finalAttrs: {
  pname = "myproject";
  version = "0.0.0";

  src = fetchFromGitHub {
    owner = "nixos";
    repo = "myproject";
    tag = finalAttrs.version;
    hash = "";
  };

  # Including SwiftPM as a nativeBuildInput provides a buildPhase for you.
  # This by default performs a release build using SwiftPM, essentially: