[build] Add support for JDK 21

[jonpryor]

Context: 5bb0d24
Context: 4273e5c
Context: 0355acf
Context: dotnet/android#9651

Does dotnet/android build with JDK-21? We don't know! But in order to answer that question, dotnet/java-interop needs to be able to build under JDK-21; a'la 5bb0d24:

1. Install JDK-21

2. Run dotnet build -t:Prepare, overriding $(JdksRoot):

   dotnet build -t:Prepare Java.Interop.sln -p:JdksRoot=/Library/Java/JavaVirtualMachines/microsoft-21.jdk/Contents/Home
   

3. Build: dotnet build

Unfortunately, this fails for three reasons:

1. class-parse crashes when processing java.base.jmod.
2. src/Java.Base needs updates to bind JDK-21's java.base.jmod.
3. On Linux and Windows, Gradle 8.1 and JDK-21 don't mix.

~~ class-parse ~~

This only impacts Debug builds of dotnet/java-interop, but:

% dotnet "bin/Debug-net8.0/class-parse.dll" \
  "$HOME/android-toolchain/jdk-21/jmods/java.base.jmod" \
  "-o=obj/Debug-net8.0//mcw/api.xml"
…
Process terminated. Assertion failed.
Unexpected number of method parameters in `Ljdk/internal/org/objectweb/asm/commons/JSRInlinerAdapter$Instantiation;.get(Ljava/lang/Object;)Ljava/lang/Object;`: expected 1, got 0
   at Xamarin.Android.Tools.Bytecode.MethodInfo.UpdateParametersFromMethodParametersAttribute(ParameterInfo[] parameters) in …/src/Xamarin.Android.Tools.Bytecode/Methods.cs:line 308
   …

The assertion?

var pinfo = methodParams.ParameterInfo;
int startIndex = 0;
while (startIndex < pinfo.Count &&
    pinfo [startIndex].AccessFlags.HasFlag (.Synthetic))
  startIndex++;
Debug.Assert (parameters.Length == pinfo.Count - startIndex, …);

This is part of 4273e5c and 0355acf, attempting to "skip over" the constructor parameters which non-static inner classes have which contain the outer class instance:

// Java
class Outer {
  /* non-static */ class Inner {
    public Inner () { … }
  }
}

At the ABI boundary, the Outer.Inner constructor is actually:

/* partial */ class Outer {
  /* partial */ class Inner {
    public Inner (Outer outer) { … }
  }
}

and we need to skip over the first parameter.

Which brings us to
jdk/internal/org/objectweb/asm/commons/JSRInlinerAdapter.Instantiation.get():

% mkdir _x
% unzip $HOME/android-toolchain/jdk-21/jmods/java.base.jmod -d _x
% dotnet bin/Debug-net8.0/class-parse.dll --dump \
  _x/classes/jdk/internal/org/objectweb/asm/commons/JSRInlinerAdapter\$Instantiation.class
…
	8: get (Ljava/lang/Object;)Ljava/lang/Object; Public, Bridge, Synthetic
		Code(6, Unknown[LineNumberTable](6), LocalVariableTableAttribute(LocalVariableTableEntry(Name='this', Descriptor='Ljdk/internal/org/objectweb/asm/commons/JSRInlinerAdapter$Instantiation;', StartPC=0, Index=0)))
		MethodParametersAttribute(MethodParameterInfo(Name='', AccessFlags=Final, Synthetic))

The parameter for JSRInlinerAdapter.Instantiation.get(Object) is Synthetic, causing us to skip over it, which is why we have a parameter mismatch. The thing is, this parameter shouldn't be skipped; the skipping is intended for constructor parameters!

Update the code so that the loop only occurs for constructors. This allows class-parse to not assert, allowing src/Java.Base to build.

~~ Gradle ~~

Via dotnet/android#9651, gradle fails when building tools/java-source-utils, but only on Linux and Windows:

"/mnt/vss/_work/1/s/xamarin-android/external/Java.Interop/build-tools/gradle/gradlew" -d --stacktrace --no-daemon -PjavaSourceVer=11 -PjavaTargetVer=11 jar
…
[org.gradle.internal.buildevents.BuildExceptionReporter]
[org.gradle.internal.buildevents.BuildExceptionReporter] FAILURE: Build failed with an exception.
[org.gradle.internal.buildevents.BuildExceptionReporter]
[org.gradle.internal.buildevents.BuildExceptionReporter] * What went wrong:
[org.gradle.internal.buildevents.BuildExceptionReporter] Could not open settings generic class cache for settings file '/mnt/vss/_work/1/s/xamarin-android/external/Java.Interop/tools/java-source-utils/settings.gradle' (/home/cloudtest/.gradle/caches/8.1.1/scripts/aiw0k2bokig45bv5yvkog3o3j).
[org.gradle.internal.buildevents.BuildExceptionReporter] > BUG! exception in phase 'semantic analysis' in source unit '_BuildScript_' Unsupported class file major version 65
[org.gradle.internal.buildevents.BuildExceptionReporter]
[org.gradle.internal.buildevents.BuildExceptionReporter] * Try:
[org.gradle.internal.buildevents.BuildExceptionReporter] > Run with --scan to get full insights.
[org.gradle.internal.buildevents.BuildExceptionReporter]
[org.gradle.internal.buildevents.BuildExceptionReporter] * Exception is:
[org.gradle.internal.buildevents.BuildExceptionReporter] org.gradle.cache.CacheOpenException: Could not open settings generic class cache for settings file '/mnt/vss/_work/1/s/xamarin-android/external/Java.Interop/tools/java-source-utils/settings.gradle' (/home/cloudtest/.gradle/caches/8.1.1/scripts/aiw0k2bokig45bv5yvkog3o3j).
[org.gradle.internal.buildevents.BuildExceptionReporter] 	at org.gradle.cache.internal.DefaultPersistentDirectoryStore.open(DefaultPersistentDirectoryStore.java:91)
[org.gradle.internal.buildevents.BuildExceptionReporter]  …
[org.gradle.internal.buildevents.BuildExceptionReporter] Caused by: BUG! exception in phase 'semantic analysis' in source unit '_BuildScript_' Unsupported class file major version 65
[org.gradle.internal.buildevents.BuildExceptionReporter] 	at org.gradle.groovy.scripts.internal.DefaultScriptCompilationHandler.compileScript(DefaultScriptCompilationHandler.java:147)
[org.gradle.internal.buildevents.BuildExceptionReporter]  …
[org.gradle.internal.buildevents.BuildExceptionReporter] Caused by: java.lang.IllegalArgumentException: Unsupported class file major version 65
[org.gradle.internal.buildevents.BuildExceptionReporter] 	at groovyjarjarasm.asm.ClassReader.<init>(ClassReader.java:199)

🤔

As per the Gradle Compatibility Matrix, Java 21 requires Gradle 8.5 or later. (No idea why this works on macOS…)

Bump to Gradle 8.12, whic is the current latest stable version.

~~ TODO ~~

While dotnet/java-interop now builds with JDK-21, unit tests don't fully pass. In particular,
tests/Xamarin.Android.Tools.Bytecode-Tests will need to be updated because javac output has changed. (Again.)

Copilot reviewed 4 out of 5 changed files in this pull request and generated no comments.

Files not reviewed (1)

• build-tools/gradle/gradle/wrapper/gradle-wrapper.properties: Language not supported

[jonpryor]

/azp run

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