feat: Support ANDROID_NDK_ROOT as fallback for ANDROID_NDK_HOME

[organicnz]

Problem

The Swift SDK only checks ANDROID_NDK_HOME to locate the NDK. However, Android Studio and Gradle use ANDROID_NDK_ROOT as the standard. This causes friction for developers with existing Android environments.

Who is affected

• Android Studio users (IDE sets ANDROID_NDK_ROOT)
• CI/CD pipelines (GitHub Actions Android setup uses ANDROID_NDK_ROOT)
• Teams with mixed Kotlin/Swift Android projects

Current behavior

echo $ANDROID_NDK_ROOT  # /Users/dev/Library/Android/sdk/ndk/27.0.12077973
./setup-android-sdk.sh
# error: ANDROID_NDK_HOME not set

Proposed Solution

Check both environment variables with ANDROID_NDK_HOME taking precedence:

ANDROID_NDK="${ANDROID_NDK_HOME:-$ANDROID_NDK_ROOT}"

if [ -z "$ANDROID_NDK" ]; then
    echo "error: Set ANDROID_NDK_HOME or ANDROID_NDK_ROOT"
    exit 1
fi

Benefits

• Zero friction for existing Android developers
• Works out-of-the-box with Android Studio
• CI/CD pipelines work without extra config
• Backwards compatible
• One-line fix

Environment

• OS: 26.2 (25C56) (Tahoe)
• Shell: zsh
• Swift: 6.3-DEVELOPMENT-SNAPSHOT
• Android NDK: r27d
• Swift SDK for Android: 6.3 snapshot

[finagolfin]

This is filed in the wrong place, as this SDK does not provide or use such a script but bundles the NDK sysroot in the SDK bundle.

@marcprux, what do you think about updating the official SDK snapshots in this way upstream?

[marcprux]

@marcprux, what do you think about updating the official SDK snapshots in this way upstream?

I think the problem is that when building packages for Android, ANDROID_NDK_ROOT must not be set, due to swiftlang/swift-driver#1879 (comment) (see also swiftlang/swift-build#495 (comment)).

[finagolfin]

Oh, that's right, Marc, I got those mixed up, thanks for the reminder. 👍

Tarlan, we currently explicitly do not use that Android env variable you want in the official SDK snapshots or here because of long-standing bugs in how swift-driver then accesses files in the NDK sysroot. We hope to get that fixed soon, so that env variable won't have such unfortunate side effects, but until then you'll have to avoid setting it.