Distributing Swift Applications

You’ve created your Swift application. Now, how do you get it to your users?

The easiest way is by using the Swift Flatpak. If you haven’t installed it yet, now’s the time to do so.

Creating a Flatpak

First off, make sure you already know the basics of creating Flatpaks; see the official developer guide for more information.

Let’s use a simple Hello, world! project as our example. Create a Package.swift:

// swift-tools-version:4.0

import PackageDescription

let package = Package(
    name: "example",
    dependencies: [
    ],
    targets: [
        .target(
            name: "example",
            dependencies: []),
    ]
)

and Sources/example/main.swift:

print("Hello, world!")

Now, let’s assume the full application ID will be org.mysite.Hello (Flatpak uses reverse domain name notation for application IDs). Create org.mysite.Hello.json containing the following:

{
  "app-id": "org.mysite.Hello",
  "runtime": "org.freedesktop.Platform",
  "runtime-version": "1.6",
  "sdk": "org.freedesktop.Sdk",
  "sdk-extensions": [
    "org.freedesktop.Sdk.Extension.swift4"
  ],
  "command": "/app/bin/example",
  "modules": [
    {
      "name": "sdk",
      "buildsystem": "simple",
      "sources": [
        {
          "type": "git",
          "path": "https://github.com/myuser/myrepo.git",
          "tag": "HEAD"
        },
        {
          "type": "script",
          "commands": [
            ". /usr/lib/sdk/swift4/enable.sh",
            "swift build -c release",
            "install -Dm 755 .build/release/example /app/bin/example",
            "/usr/lib/sdk/swift4/set-runtime.sh /app/lib /app/bin example"
          ],
          "dest-filename": "build-example.sh"
        }
      ],
      "build-commands": [
        "./build-example.sh"
      ]
    }
  ]
}

Here’s a breakdown of the interesting parts of this file:

• sdk-extensions: This is where the Swift SDK extension is used. The SDK extension “extends” the previously chosen SDK with the Swift compiler and libraries.
• sources: This is where the sources are chosen. The first is just the Git repository of our application, but the second is far more interesting and will be explained below.
• build-commands calls into ./build-example.sh to build our code.

build-example.sh does the following:

• Sources enable.sh to enable use of the Swift SDK extension.
• Builds the application.
• Installs it to /app/bin/example via the install command. Note that Flatpak requires your application to be installed to the /app prefix.
• Calls a script called set-runtime.sh. This script will copy the Swift runtime libraries to the application directory, and it will set the dynamic linker of your application binaries to the library directory. The arguments are as follows:
  • The first is the directory to store the Swift runtime libraries and patched dynamic linker (see Version Warnings for information on why that is necessary).
  • The second is the directory where your application binaries are stored.
  • Any other arguments passed are assumed to be paths to binaries, relative to the second argument (the application directory). These binaries will all have their dynamic linker set to the patched one that doesn’t emit version warnings.