Using Swift SDKs to cross-compile Swift packages to Linux

As an Apple app developer, you will be familiar with cross-compiling code for different platforms such as iOS, macOS, tvOS and watchOS with very minimal setup and directly from Xcode.

However, if you try to cross-compile Swift code for any other platform that has Swift support like Linux, you will soon find out that it is an arduous process that involves downloading and installing many files and tools and setting the environment up correctly.

Thankfully, the Swift team at Apple has made this process much easier with the introduction of Swift SDKs.

What are Swift SDKs?

First introduced in the SE-0387 proposal and now built into SPM (from versions of Swift 5.9 and above), Swift SDKs are artifact bundles which contain all necessary files to cross-compile Swift code for specific platforms.

Swift SDKs can be retrieved, installed and used with the same swift command line tool you use to build and run Swift programmes by passing it the experimental-sdk flag:

# List all installed Swift SDKs
swift experimental-sdk list

# Install a Swift SDK
swift experimental-sdk install <bundle-path-or-url>

# Remove an installed SDK
swift experimental-sdk remove <sdk-id-or-bundle-name>

Creating a Swift SDK

Now that you know what Swift SDKs are, let’s see how you can create one using the swift-sdk-generator, an open-source tool created and maintained by Apple.

As it stands, the Swift SDK Generator only supports Linux as a target platform and macOS as a host platform, but the list of supported platforms may grow in the future.