meta-swift

meta-swift is a Yocto layer for the Swift programming language.

This layer presently supports the latest version of Swift (6.1.3) for several Yocto versions. It should also be compatible with earlier versions of Swift, after updating the version in swift-version.inc. (This may also require changes to swift-native.bb to reflect the different install artifacts.)

Both x86_64 and aarch64 host architectures are supported. The layer follows the convention of matching branch names with their corresponding Yocto release.

The meta-swift layer has been tested with the following Yocto target machines:

• qemuarm
• qemuarm64
• qemux86-64
• beaglebone-yocto
• raspberrypi-armv7
• raspberrypi-armv8
• raspberrypi4-64

Other machines that use x86_64, armv7 or aarch64 target architectures should also work.

Compiling

A good way to get started is to look at the meta-swift-examples repository, which contains scripts and a workspace for building under Docker.

The local CI workflows also provide some examples of how the layer is compiled.

Usage

First, add the meta-swift layer to your project, by checking out the appropriate branch for your Yocto version (e.g. scarthgap) and using bitbake-layers add-layer. (You may also modify bblayers.conf directly.)

Create a new Swift package and include it in your BitBake recipe as follows:

DESCRIPTION = "An example Swift application"
LICENSE = "CLOSED"

SRC_URI = "\
    file://Sources/hello-world/main.swift \
    file://Package.swift \
"

S = "${SWIFT_UNPACKDIR}"
B = "${WORKDIR}/build"

inherit swift

When you inherit the swift class, BitBake does the following:

• Automatically downloads the Swift toolchain for the host architecture and creates a cross-compiling sysroot
• Adds build dependencies for the Swift standard libraries, including Foundation
• Performs the required build steps to build a Swift package

By default, Swift tests are not built. To build them, add:

SWIFT_BUILD_TESTS = "1"

to your recipe.

Note that Yocto will automatically detect and add runtime dependencies for the Swift runtime, so it is not necessary to add them explicitly in your package.

Deployment

The user of this layer must provide their own do_install function for swift packages. An example of this is available in swift-hello-world.bb:

do_install() {
    install -d ${D}${bindir}
    install -m 0755 ${BUILD_DIR}/hello-world ${D}${bindir}
    install -m 0755 ${BUILD_DIR}/hello-worldPackageTests.xctest ${D}${bindir}
}

INSANE_SKIP:${PN} = "buildpaths"
INSANE_SKIP:${PN}-dbg = "buildpaths"

The finished binaries are located in ${BUILD_DIR}. Skipping buildpaths package QA is required on styhead and higher, as these warnings are treated as errors (and the build directory path is often embedded in Swift binaries, a known issue).