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Swift SDK Generator

Overview

With Swift supporting many different platforms, cross-compilation can boost developer productivity. In certain cases it's the only way to build a Swift package.

SE-0387 proposal introduces Swift SDKs, which bundle together all components required for cross-compilation in a single archive, and make cross builds as easy as running a single command.

Swift SDK authors can assemble such archive manually, but the goal of Swift SDK Generator developed in this repository is to automate this task as much as possible. If you're a platform maintainer, or someone who would like to make cross-compiling easy to your favorite platform, you can tailor the generator source code to your needs and publish a newly generated Swift SDK for users to install.

Requirements

Usage of Swift SDKs requires Swift 5.9, follow installation instructions on swift.org to install it first.

After that, verify that the experimental-sdk command is available:

swift experimental-sdk list

The output will either state that no Swift SDKs are available, or produce a list of those you previously had installed, in case you've used the swift experimental-sdk install command before.

Supported platforms and minimum versions

macOS as a host platform and a few Linux distributions as target platforms are supported by the generator. Support for Linux as a host platform is currently in development. Eventually, the generator will allow cross-compiling between any Linux distributions officially supported by the Swift project.

Platform Supported Version as Host Supported Version as Target
macOS (arm64) ✅ macOS 13.0+ ❌
macOS (x86_64) ✅ macOS 13.0+1 ❌
Ubuntu ⚠️ (WIP) ✅ 20.04 / 22.04
RHEL ⚠️ (WIP) ✅ UBI 9

How to use it

Clone this repository into a directory of your choice and make it the current directory. Build and run it with this command:

swift run swift-sdk-generator make-linux-sdk

This will download required components and produce a Swift SDK for Ubuntu Jammy in the Bundles subdirectory. Follow the steps printed at the end of generator's output for installing the newly generated Swift SDK.

Additional command-line options are available for specifying target platform features, such as Linux distribution name, version, and target CPU architecture. Pass --help flag to see all of the available options:

swift run swift-sdk-generator make-linux-sdk --help

After installing a Swift SDK, verify that it's available to SwiftPM:

swift experimental-sdk list

The output of the last command should contain ubuntu22.04. Note the full Swift SDK ID in the output, we'll refer to it subsequently as <generated_sdk_id>.

Create a new project to verify that the SDK works:

mkdir cross-compilation test
cd cross-compilation-test
swift package init --type executable

Build this project with the SDK:

swift build --experimental-swift-sdk <generated_sdk_id>

Verify that the produced binary is compatible with Linux:

file .build/debug/cross-compilation-test

That should produce output similar to this:

.build/debug/cross-compilation-test: ELF 64-bit LSB pie executable, ARM aarch64, version 1 (SYSV), 
dynamically linked, interpreter /lib/ld-linux-aarch64.so.1, for GNU/Linux 3.7.0, with debug_info, not stripped

You can then copy this binary to a Docker image that has Swift runtime libraries installed. For example, for Ubuntu Jammy and Swift 5.9 this would be swift:5.9-jammy-slim. If you'd like to copy the binary to an arbitrary Ubuntu Jammy system, make sure you pass --static-swift-stdlib flag to swift build, in addition to the --experimental-swift-sdk option.

Building an SDK from a container image

You can base your SDK on a container image, such as one of the official Swift images. By default, the command below will build an SDK based on the Ubuntu Jammy image:

swift run swift-sdk-generator make-linux-sdk --with-docker

To build a RHEL images, use the --linux-distribution-name option. The following command will build a ubi9-based image:

swift run swift-sdk-generator make-linux-sdk --with-docker --linux-distribution-name rhel

You can also specify the base container image by name:

swift run swift-sdk-generator make-linux-sdk --with-docker --from-container-image swift:5.9-jammy

swift run swift-sdk-generator make-linux-sdk --with-docker --linux-distribution-name rhel --from-container-image swift:5.9-rhel-ubi9

Including extra Linux libraries

If your project depends on Linux libraries which are not part of a standard base image, you can build your SDK from a custom container image which includes them.

Prepare a Dockerfile which derives from one of the standard images and installs the packages you need. This example installs SQLite and its dependencies on top of the Swift project's Ubuntu Jammy image:

FROM swift:5.9-jammy
RUN apt update && apt -y install libsqlite3-dev && apt -y clean

Build the new container image:

docker build -t my-custom-image -f Dockerfile .

Finally, build your custom SDK:

swift run swift-sdk-generator make-linux-sdk --with-docker --from-container-image my-custom-image:latest --sdk-name 5.9-ubuntu-with-sqlite

Swift SDK distribution

The .artifactbundle directory produced in the previous section can be packaged as a .tar.gz archive and redistributed in this form. Users of such Swift SDK bundle archive can easily install it with swift experimental-sdk install command, which supports both local file system paths and public http:// and https:// URLs as an argument.

Contributing

There are several ways to contribute to Swift SDK Generator. To learn about the policies, best practices that govern contributions to the Swift project, and instructions for setting up the development environment please read the Contributor Guide.

If you're interested in adding support for a new platform, please open an issue on this repository first so that the best implementation strategy can be discussed before proceeding with an implementation.

Reporting issues

If you have any trouble with the Swift SDK Generator, help is available. We recommend:

When reporting an issue please follow the bug reporting guidelines, they can be found in contribution guide.

If you’re not comfortable sharing your question with the list, contact details for the code owners can be found in CODEOWNERS; however, Swift Forums is usually the best place to go for help.

License

Copyright 2022 - 2024 Apple Inc. and the Swift project authors. Licensed under Apache License v2.0 with Runtime Library Exception.

See https://swift.org/LICENSE.txt for license information.

See https://swift.org/CONTRIBUTORS.txt for Swift project authors.

Footnotes

  1. Since LLVM project doesn't provide pre-built binaries of lld for macOS on x86_64, it will be automatically built from sources by the generator, which will increase its run by at least 15 minutes on recent hardware. You will also need CMake and Ninja preinstalled (e.g. via brew install cmake ninja). ↩