Add Android build job to CI

Installs the matching NDK and Swift Android SDK artifact bundle on
a macOS runner, then builds debug and release for aarch64-android.

Author: colemancda

.github/workflows/swift.yml

@@ -37,3 +37,32 @@ jobs:
       run: swift build -c ${{ matrix.config }}
     - name: Test
       run: swift test -c ${{ matrix.config }}
+
+  android:
+    name: Android
+    runs-on: macos-15
+    strategy:
+      fail-fast: false
+      matrix:
+        config: ["debug", "release"]
+    env:
+      SWIFT_VERSION: "6.3.2"
+      ANDROID_NDK_VERSION: "27.2.12479018"
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+    - name: Install Swift
+      uses: swift-actions/setup-swift@v2
+      with:
+        swift-version: ${{ env.SWIFT_VERSION }}
+    - name: Install Android NDK
+      run: $ANDROID_HOME/cmdline-tools/latest/bin/sdkmanager --install "ndk;${{ env.ANDROID_NDK_VERSION }}"
+    - name: Install Swift SDK for Android
+      run: |
+        curl -L -o android-sdk.artifactbundle.tar.gz "https://download.swift.org/swift-${{ env.SWIFT_VERSION }}-release/android-sdk/swift-${{ env.SWIFT_VERSION }}-RELEASE/swift-${{ env.SWIFT_VERSION }}-RELEASE_android.artifactbundle.tar.gz"
+        CHECKSUM=$(swift package compute-checksum android-sdk.artifactbundle.tar.gz)
+        swift sdk install android-sdk.artifactbundle.tar.gz --checksum "$CHECKSUM"
+        ANDROID_NDK_HOME="$ANDROID_HOME/ndk/${{ env.ANDROID_NDK_VERSION }}" \
+          bash "$HOME/Library/org.swift.swiftpm/swift-sdks/swift-${{ env.SWIFT_VERSION }}-RELEASE_android.artifactbundle/swift-android/scripts/setup-android-sdk.sh"
+    - name: Build
+      run: swift build --swift-sdk aarch64-unknown-linux-android28 -c ${{ matrix.config }}