Android SDK build scripts

[marcprux]

Following up on swiftlang/github-workflows#106 and swiftlang/swift#80788, this PR contains a new swift-docker/swift-ci/sdks/android/ folder with scripts that will build and upload a full stand-alone Swift Android Swift SDK. It is modeled after the structure of the swift-ci/sdks/static-linux build scripts.

Running

The top-level ./build script installs a host toolchain and the Android NDK, and then invokes scripts/fetch-source.sh which will fetch tagged sources for libxml2, curl, boringssl, and swift.

It then applies some patches and invokes scripts/build.sh, which will build the sources for each of the specified architectures. Finally, it combines the NDK and the newly built SDKs into a single artifactbundle.

Specifying Architectures

By default all the supported Android architectures (aarch64, x86_64, aarmv7) will be built, but this can be reduced in order to speed up the build. This can be useful, e.g., as part of a CI that validates a pull request, as building a single architecture takes around 30 minutes on a standard ubuntu-24.04 GitHub runner, whereas building for all the architectures takes over an hour.

To build an artifactbundle for just the x86_64 architecture, run:

TARGET_ARCHS=x86_64 ./build

Installing and validating the SDK

The .github/workflows/pull_request.yml workflow will create and upload an installable SDK named something like: swift-6.1-RELEASE_android-0.1.artifactbundle.tar.gz. The results of one of the workflow runs can be seen at https://github.com/swift-android-sdk/swift-docker/actions/runs/14603885089

The workflow will also install the SDK locally and use swift-android-action to build and test various Swift packages in an Android emulator.

[marcprux]

I've updated this PR to build the SDK without including the Android NDK. In order to accommodate this, there is now a post-install scripts/setup-android-sdk.sh that will need to be run manually after the swift sdk install … command. This will find the NDK based on the standard ANDROID_NDK_HOME environment variable and create links from the NDK into the path specified by swift-sdk.json's sdkRootPath, as well as pulling in the swiftrt.o to work around swiftlang/swift#79621.

The latest result of the build for the 6.2 nightly can be seen at: https://github.com/skiptools/swift-android-toolchain/releases/tag/6.2-DEVELOPMENT-SNAPSHOT-2025-05-07-a

[marcprux]

To clarify what the post-install script is doing, following is a result of the output of the command with the default NDK directory:

zap org.swift.swiftpm/swift-sdks % tree swift-6.2-DEVELOPMENT-SNAPSHOT-2025-05-07-a-android-0.1.artifactbundle/swift-android/ndk-sysroot
└── usr
    ├── include -> ~/Library/Android/sdk/ndk/27.0.12077973/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include
    └── lib
        ├── aarch64-linux-android -> ~/Library/Android/sdk/ndk/27.0.12077973/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/aarch64-linux-android
        ├── arm-linux-androideabi -> ~/Library/Android/sdk/ndk/27.0.12077973/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/arm-linux-androideabi
        ├── x86_64-linux-android -> ~/Library/Android/sdk/ndk/27.0.12077973/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/x86_64-linux-android
        ├── swift
        │   └── android
        │       ├── aarch64
        │       │   └── swiftrt.o -> ../../../../../../swift-resources/usr/lib/swift-aarch64/android/aarch64/swiftrt.o
        │       ├── armv7
        │       │   └── swiftrt.o -> ../../../../../../swift-resources/usr/lib/swift-armv7/android/armv7/swiftrt.o
        │       └── x86_64
        │           └── swiftrt.o -> ../../../../../../swift-resources/usr/lib/swift-x86_64/android/x86_64/swiftrt.o
        └── swift_static
            └── android
                ├── aarch64
                │   └── swiftrt.o -> ../../../../../../swift-resources/usr/lib/swift_static-aarch64/android/aarch64/swiftrt.o
                ├── armv7
                │   └── swiftrt.o -> ../../../../../../swift-resources/usr/lib/swift_static-armv7/android/armv7/swiftrt.o
                └── x86_64
                    └── swiftrt.o -> ../../../../../../swift-resources/usr/lib/swift_static-x86_64/android/x86_64/swiftrt.o

Alternative NDK locations can be specified by overriding the ANDROID_NDK_HOME, like so:

zap org.swift.swiftpm/swift-sdks % ANDROID_NDK_HOME="/opt/homebrew/share/android-ndk" swift-6.2-DEVELOPMENT-SNAPSHOT-2025-05-07-a-android-0.1.artifactbundle/swift-android/scripts/setup-android-sdk.sh
setup-android-sdk.sh: success: ndk-sysroot linked to Android SDK

zap org.swift.swiftpm/swift-sdks % tree swift-6.2-DEVELOPMENT-SNAPSHOT-2025-05-07-a-android-0.1.artifactbundle/swift-android/ndk-sysroot
└── usr
    ├── include -> /opt/homebrew/share/android-ndk/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include
    └── lib
        ├── aarch64-linux-android -> /opt/homebrew/share/android-ndk/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/aarch64-linux-android
        ├── arm-linux-androideabi -> /opt/homebrew/share/android-ndk/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/arm-linux-androideabi
        ├── x86_64-linux-android -> /opt/homebrew/share/android-ndk/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/x86_64-linux-android
        ├── swift
        │   └── android
        │       ├── aarch64
        │       │   └── swiftrt.o -> ../../../../../../swift-resources/usr/lib/swift-aarch64/android/aarch64/swiftrt.o
        │       ├── armv7
        │       │   └── swiftrt.o -> ../../../../../../swift-resources/usr/lib/swift-armv7/android/armv7/swiftrt.o
        │       └── x86_64
        │           └── swiftrt.o -> ../../../../../../swift-resources/usr/lib/swift-x86_64/android/x86_64/swiftrt.o
        └── swift_static
            └── android
                ├── aarch64
                │   └── swiftrt.o -> ../../../../../../swift-resources/usr/lib/swift_static-aarch64/android/aarch64/swiftrt.o
                ├── armv7
                │   └── swiftrt.o -> ../../../../../../swift-resources/usr/lib/swift_static-armv7/android/armv7/swiftrt.o
                └── x86_64
                    └── swiftrt.o -> ../../../../../../swift-resources/usr/lib/swift_static-x86_64/android/x86_64/swiftrt.o

[marcprux]

As of 72964f5, the Android SDK is now being built in a Docker container.

[marcprux]

@shahmishal I'm hoping to get feedback on this PR and whether you think the .artifactbundles it creates are suitable candidates for an official release. Happy to answer any questions about it or provide additional documentation. I've been uploading the 6.2 snapshot artifacts from this workflow to https://github.com/skiptools/swift-android-toolchain/releases in case you want to try it out yourself.