Invoke-customs are only supported starting with Android O (--min-api 26) warnings

[jpobst]

Our main build produces the following warnings:

_GenerateRuntimeDex16:
"/Users/builder/android-toolchain/jdk-21/bin/java" -classpath "/Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/r8.jar" com.android.tools.r8.D8 --release --no-desugaring --output "obj/Release/release" "/Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime.jar"
Warning in /Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime.jar:mono/MonoPackageManager.class at Lmono/MonoPackageManager;LoadApplication(Landroid/content/Context;)V:
Invoke-customs are only supported starting with Android O (--min-api 26)
Warning in /Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_fastdev.jar:mono/android/incrementaldeployment/IncrementalClassLoader.class at Lmono/android/incrementaldeployment/IncrementalClassLoader;createDelegateClassLoader(Ljava/io/File;Ljava/lang/String;Ljava/util/List;Ljava/lang/ClassLoader;)Lmono/android/incrementaldeployment/IncrementalClassLoader$DelegateClassLoader;:
Invoke-customs are only supported starting with Android O (--min-api 26)
"/Users/builder/android-toolchain/jdk-21/bin/java" -classpath "/Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/r8.jar" com.android.tools.r8.D8 --release --no-desugaring --output "obj/Release/release-net6" "/Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_net6.jar"
Warning in /Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_net6.jar:mono/MonoPackageManager.class at Lmono/MonoPackageManager;LoadApplication(Landroid/content/Context;)V:
Invoke-customs are only supported starting with Android O (--min-api 26)
Warning in /Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_net6.jar:mono/MonoPackageManager.class at Lmono/MonoPackageManager;getNativeLibraryPath(Landroid/content/pm/ApplicationInfo;)Ljava/lang/String;:
Invoke-customs are only supported starting with Android O (--min-api 26)
Warning in /Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_net6.jar:mono/android/incrementaldeployment/IncrementalClassLoader.class at Lmono/android/incrementaldeployment/IncrementalClassLoader;createDelegateClassLoader(Ljava/io/File;Ljava/lang/String;Ljava/util/List;Ljava/lang/ClassLoader;)Lmono/android/incrementaldeployment/IncrementalClassLoader$DelegateClassLoader;:
Invoke-customs are only supported starting with Android O (--min-api 26)
"/Users/builder/android-toolchain/jdk-21/bin/java" -classpath "/Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/r8.jar" com.android.tools.r8.D8 --release --no-desugaring --output "obj/Release/fastdev-net6" "/Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_fastdev_net6.jar"
Warning in /Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_fastdev_net6.jar:mono/android/MultiDexLoader.class at Lmono/android/MultiDexLoader;getDexList(Ljava/lang/String;Ljava/lang/String;)Ljava/util/List;:
Invoke-customs are only supported starting with Android O (--min-api 26)
Warning in /Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_fastdev_net6.jar:mono/MonoPackageManager.class at Lmono/MonoPackageManager;LoadApplication(Landroid/content/Context;)V:
Invoke-customs are only supported starting with Android O (--min-api 26)
Warning in /Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_fastdev_net6.jar:mono/android/MultiDexLoader.class at Lmono/android/MultiDexLoader;attachInfo(Landroid/content/Context;Landroid/content/pm/ProviderInfo;)V:
Invoke-customs are only supported starting with Android O (--min-api 26)
Warning in /Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_fastdev_net6.jar:mono/MonoPackageManager.class at Lmono/MonoPackageManager;getNativeLibraryPath(Landroid/content/pm/ApplicationInfo;)Ljava/lang/String;:
Invoke-customs are only supported starting with Android O (--min-api 26)
Warning in /Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_fastdev_net6.jar:mono/android/incrementaldeployment/IncrementalClassLoader.class at Lmono/android/incrementaldeployment/IncrementalClassLoader;createDelegateClassLoader(Ljava/io/File;Ljava/lang/String;Ljava/util/List;Ljava/lang/ClassLoader;)Lmono/android/incrementaldeployment/IncrementalClassLoader$DelegateClassLoader;:
Invoke-customs are only supported starting with Android O (--min-api 26)
"/Users/builder/android-toolchain/jdk-21/bin/java" -classpath "/Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/r8.jar" com.android.tools.r8.D8 --release --no-desugaring --output "obj/Release/release-clr" "/Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_clr.jar"
Warning in /Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_clr.jar:mono/MonoPackageManager.class at Lmono/MonoPackageManager;LoadApplication(Landroid/content/Context;)V:
Invoke-customs are only supported starting with Android O (--min-api 26)
Warning in /Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_clr.jar:mono/android/incrementaldeployment/IncrementalClassLoader.class at Lmono/android/incrementaldeployment/IncrementalClassLoader;createDelegateClassLoader(Ljava/io/File;Ljava/lang/String;Ljava/util/List;Ljava/lang/ClassLoader;)Lmono/android/incrementaldeployment/IncrementalClassLoader$DelegateClassLoader;:
Invoke-customs are only supported starting with Android O (--min-api 26)
"/Users/builder/android-toolchain/jdk-21/bin/java" -classpath "/Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/r8.jar" com.android.tools.r8.D8 --release --no-desugaring --output "obj/Release/fastdev-clr" "/Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_fastdev_clr.jar"
Warning in /Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_fastdev_clr.jar:mono/android/MultiDexLoader.class at Lmono/android/MultiDexLoader;getDexList(Ljava/lang/String;Ljava/lang/String;)Ljava/util/List;:
Invoke-customs are only supported starting with Android O (--min-api 26)
Warning in /Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_fastdev_clr.jar:mono/MonoPackageManager.class at Lmono/MonoPackageManager;LoadApplication(Landroid/content/Context;)V:
Invoke-customs are only supported starting with Android O (--min-api 26)
Warning in /Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_fastdev_clr.jar:mono/android/MultiDexLoader.class at Lmono/android/MultiDexLoader;attachInfo(Landroid/content/Context;Landroid/content/pm/ProviderInfo;)V:
Invoke-customs are only supported starting with Android O (--min-api 26)
Warning in /Users/builder/azdo/_work/11/s/xamarin-android/bin/Release/lib/packs/Microsoft.Android.Sdk.Darwin/35.99.0/tools/java_runtime_fastdev_clr.jar:mono/android/incrementaldeployment/IncrementalClassLoader.class at Lmono/android/incrementaldeployment/IncrementalClassLoader;createDelegateClassLoader(Ljava/io/File;Ljava/lang/String;Ljava/util/List;Ljava/lang/ClassLoader;)Lmono/android/incrementaldeployment/IncrementalClassLoader$DelegateClassLoader;:
Invoke-customs are only supported starting with Android O (--min-api 26)

These warning appear to be ~new, as they do not happen on our release/9.0.1xx branch.

They began happening sometime before Jan 13 (our CI build logs only go back 2 months.)

We need to ensure that our .NET 10 version still works on API levels prior to 26.

[jpobst]

Per Stack Overflow, this seems to be an issue when you don't set:

android {
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

We changed this here.

It is probably fine when we build desktop Java apps like d8 or manifestmerger.jar, but we may not be able to use it for things that are going to run on Android like java_runtime.jar.

[jonathanpeppers]

Reviewing the r8.jar command in _GenerateRuntimeDex16, I see a couple issues:

• --min-api is omitted, so it would default to API 1
• We are passing --no-desugaring, which leaves all Java features as-is.
• We don't pass the path to android.jar.

I think a combination of these causes the warnings? After fixing them all, I see now warnings from r8.jar anymore:

• [java-runtime] fix Invoke-customs warning #10039

I didn't see why --no-desugaring was initially passed: 4742d50