Test Android cross compilation on Windows

This also fixes the Android support to recognize an NDK even when an SDK is not present, which might be the case for some installations not driven through Android Studio (for example, NDK as installed by the chocolatey package manager on Windows, or installed manually into some directory).

Author: jakepetroules

.github/scripts/windows_pre_build.ps1

@@ -30,7 +30,7 @@ if ($InstallCMake) {
 }
 
 if (-not $SkipAndroid) {
-    choco install android-ndk
+    choco install -y android-ndk
 
     Import-Module $env:ChocolateyInstall\helpers\chocolateyProfile.psm1
     refreshenv

.github/workflows/pull_request.yml

@@ -17,6 +17,7 @@ jobs:
       linux_pre_build_command: ./.github/scripts/linux_pre_build.sh
       linux_build_command: 'swift test --no-parallel'
       linux_swift_versions: '["nightly-main", "nightly-6.2"]'
+      windows_pre_build_command: 'Invoke-Program .\.github\scripts\windows_pre_build.ps1'
       windows_swift_versions: '["nightly-main"]'
       windows_build_command: 'Invoke-Program swift test --no-parallel'
       enable_linux_static_sdk_build: true

Sources/SWBAndroidPlatform/AndroidSDK.swift

@@ -266,16 +266,16 @@ public import Foundation
     }
 }
 
-fileprivate extension AndroidSDK.NDK {
+extension AndroidSDK.NDK {
     /// The location of the Android NDK based on the `ANDROID_NDK_ROOT` environment variable (falling back to the deprecated but well known `ANDROID_NDK_HOME`).
     /// - seealso: [Configuring NDK Path](https://github.com/android/ndk-samples/wiki/Configure-NDK-Path#terminologies)
-    static var environmentOverrideLocation: AbsolutePath? {
+    internal static var environmentOverrideLocation: AbsolutePath? {
         (getEnvironmentVariable("ANDROID_NDK_ROOT") ?? getEnvironmentVariable("ANDROID_NDK_HOME"))?.nilIfEmpty.map { AbsolutePath($0) } ?? nil
     }
 
     /// Location of the Android NDK installed by the `google-android-ndk-*-installer` family of packages available in Debian 13 "Trixie" and Ubuntu 24.04 "Noble".
     /// These packages are available in non-free / multiverse and multiple versions can be installed simultaneously.
-    static var defaultDebianLocation: AbsolutePath? {
+    fileprivate static var defaultDebianLocation: AbsolutePath? {
         AbsolutePath("/usr/lib/android-ndk")
     }
 }

Sources/SWBAndroidPlatform/Plugin.swift

@@ -26,6 +26,7 @@ public let initializePlugin: PluginInitializationFunction = { manager in
 
 @_spi(Testing) public final class AndroidPlugin: Sendable {
     private let androidSDKInstallations = AsyncCache<OperatingSystem, [AndroidSDK]>()
+    private let androidOverrideNDKInstallation = AsyncCache<OperatingSystem, AndroidSDK.NDK?>()
 
     func cachedAndroidSDKInstallations(host: OperatingSystem) async throws -> [AndroidSDK] {
         try await androidSDKInstallations.value(forKey: host) {
@@ -34,8 +35,22 @@ public let initializePlugin: PluginInitializationFunction = { manager in
         }
     }
 
-    @_spi(Testing) public func effectiveInstallation(host: OperatingSystem) async throws -> (sdk: AndroidSDK, ndk: AndroidSDK.NDK)? {
+    func cachedAndroidOverrideNDKInstallation(host: OperatingSystem) async throws -> AndroidSDK.NDK? {
+        try await androidOverrideNDKInstallation.value(forKey: host) {
+            if let overridePath = AndroidSDK.NDK.environmentOverrideLocation {
+                return try AndroidSDK.NDK(host: host, path: overridePath, fs: localFS)
+            }
+            return nil
+        }
+    }
+
+    @_spi(Testing) public func effectiveInstallation(host: OperatingSystem) async throws -> (sdk: AndroidSDK?, ndk: AndroidSDK.NDK)? {
         guard let androidSdk = try? await cachedAndroidSDKInstallations(host: host).first else {
+            // No SDK, but we might still have a standalone NDK from the env var override
+            if let overrideNDK = try? await cachedAndroidOverrideNDKInstallation(host: host) {
+                return (nil, overrideNDK)
+            }
+
             return nil
         }
 
@@ -63,9 +78,9 @@ struct AndroidEnvironmentExtension: EnvironmentExtension {
     func additionalEnvironmentVariables(context: any EnvironmentExtensionAdditionalEnvironmentVariablesContext) async throws -> [String: String] {
         switch context.hostOperatingSystem {
         case .windows, .macOS, .linux:
-            if let latest = try? await plugin.cachedAndroidSDKInstallations(host: context.hostOperatingSystem).first {
-                let sdkPath = latest.path.path.str
-                let ndkPath = latest.preferredNDK?.path.path.str
+            if let (sdk, ndk) = try? await plugin.effectiveInstallation(host: context.hostOperatingSystem) {
+                let sdkPath = sdk?.path.path.str
+                let ndkPath = ndk.path.path.str
                 return [
                     "ANDROID_HOME": sdkPath,
                     "ANDROID_SDK_ROOT": sdkPath,
@@ -220,7 +235,7 @@ struct AndroidToolchainRegistryExtension: ToolchainRegistryExtension {
     let plugin: AndroidPlugin
 
     func additionalToolchains(context: any ToolchainRegistryExtensionAdditionalToolchainsContext) async throws -> [Toolchain] {
-        guard let toolchainPath = try? await plugin.cachedAndroidSDKInstallations(host: context.hostOperatingSystem).first?.preferredNDK?.toolchainPath else {
+        guard let toolchainPath = try? await plugin.effectiveInstallation(host: context.hostOperatingSystem)?.ndk.toolchainPath else {
             return []
         }