SPMDestinations

What is this? It's a set of Homebrew formulas (installation packages) to install (and build) Swift cross compilers hosted on macOS. For example it allows you to build a Swift Package Manager package on macOS, but for Ubuntu Linux. Without running anything in Docker.

End of April 2017 Johannes Weiß added custom toolchain support to Swift Package Manager. Johannes also provided a script which shows how to build an Ubuntu toolchain for x86-64.

SPMDestinations splits up the original script into multiple parts and provides the results as Homebrew formulas. This way Homebrew can cache components which are reused for different toolchains, and the installation is much easier.

NOTE: The host system requires a Swift 5.3 installation (e.g. Xcode 12).

Toolchain Installation

SPMDestinations requires Homebrew, get it over here.

Currently those cross compilation toolchains are provided:

• Swift 5.3.1, Ubuntu Xenial (16.04), x86_64
• Swift 5.3.1, Amazon Linux 2, x86_64
• Swift 5.2.5, Ubuntu Xenial (16.04), x86_64
• Swift 5.2.5, Amazon Linux 2, x86_64

Note that the required toolchains are quite big (~500MB compressed each, for host and target system). The scripts clone the respective folders to make things reasonably fast and save space.

brew tap SPMDestinations/tap
brew install spm-dest-5.3-x86_64-ubuntu16.04

This puts the toolchain into:

ls ${HOMEBREW_PREFIX}/lib/swift/dst/x86_64-unknown-linux/
swift-5.3-ubuntu16.04.xtoolchain

On Apple silicon

There are two ways to run Homebrew on Apple silicon, either using Rosetta in /usr/local (arch -x86_64 brew) or natively in /opt/homebrew.

If using the native one, all is the same, for installation using Rosetta:

arch -x86_64 brew tap SPMDestinations/tap
arch -x86_64 brew install spm-dest-5.3-x86_64-ubuntu16.04

Testing the Toolchain

To build an SPM package for a different platform, one just adds the --destination argument, pointing to the desired cross toolchain.

A full example:

mkdir macro-test && cd macro-test
swift package init --type=executable

swift build --destination \
  ${HOMEBREW_PREFIX}/lib/swift/dst/x86_64-unknown-linux/swift-5.3-ubuntu16.04.xtoolchain/destination.json

The built product can be found in .build as usual:

file .build/debug/macro-test
.build/debug/macro-test:                   \
  ELF 64-bit LSB shared object, x86-64,    \
  version 1 (SYSV), dynamically linked,    \
  interpreter /lib64/ld-linux-x86-64.so.2, \
  for GNU/Linux 2.6.32, with debug_info, not stripped

To actually test whether it works, it can be copied over to an actual Linux machine, or run within Docker:

docker run --rm -t                    \
  --name test-x-build                 \
  --volume "${PWD}/.build/debug:/run" \
  --workdir "/run"                    \
  swiftlang/swift:nightly-5.3-xenial  \
  bash -c "LD_LIBRARY_PATH=/usr/lib/swift/linux ./macro-test"
Hello, world!

The LD_LIBRARY_PATH is b0rked in the nightly-5.3-xenial Docker image (doesn't include /usr/lib/swift/linux), hence the explicit setting.

Dev Installation

When building own toolchains a Swift host toolchain is usually required. Plus for Linux targets the LLVM linker (lld). This project provides formulas for both.

They don't do much but grab the toolchains from swift.org and put them into a specific Brew directory. The advantage is that Brew does all the caching.

brew tap SPMDestinations/tap
brew install host-lld-bin-8 swift-xctoolchain-5.3

The full binary clang/llvm toolchains (as used in the original script) are also provided as formulas via brew install clang-llvm-bin-8 (BIG!).

Who

SPMDestinations is brought to you by ZeeZide. We like feedback, GitHub stars, cool contract work, presumably any form of praise you can think of.