[code-reflection] RFR: BytecodeGenerator support of lambdas [v7]

[Adam Sotona]

On Tue, 16 Apr 2024 13:36:25 GMT, Adam Sotona <asotona at openjdk.org> wrote:

>>> Unfortunately this is a different case. We generate a hidden class with lambda implementation method inside and `LambdaMetafactory` could not (and according to the spec should not) find the class.
>> 
>> I believe they can all be of the same nest, but I suppose`InnerClassLambdaMetafactory` would need to patch the hidden target class instance into the constant pool (in theory it could).
>> 
>> It is aware about the target class being hidden when generating the lambda class name:
>> 
>> 
>>     private static String lambdaClassName(Class<?> targetClass) {
>>         String name = targetClass.getName();
>>         if (targetClass.isHidden()) {
>>             // use the original class name
>>             name = name.replace('/', '_');
>>         }
>>         return name.replace('.', '/') + "$$Lambda";
>>     }
>
> `InnerClassLambdaMetafactory` generates the hidden inner class (for example: `lambda_0x00007ff000189400$$Lambda/0x00007ff000117a08`) and then it all fails with:
> 
> java.lang.ClassNotFoundException: lambda.0x00007ff000189400
> 	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
> 	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
> 	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:525)
> 	at TestBytecode.consume(TestBytecode.java:291)
> 	at java.base/java.lang.invoke.MethodHandle.invokeWithArguments(MethodHandle.java:733)
> 	at TestBytecode.lambda$testGenerate$14(TestBytecode.java:476)
> 	at TestBytecode.permutateAllArgs(TestBytecode.java:412)
> 	at TestBytecode.testGenerate(TestBytecode.java:475)

I've identified `j/l/i/defineHiddenClass/BasicTest::testLambda` is actually not testing a lambda in a hidden class, but rather a MH in a hidden class.
If I modify `j/l/i/defineHiddenClass/src/Lambda` from `Function<Object, String> f = Object::toString;` to `Function<Object, String> f = o -> o.toString();` the test fails with:

java.lang.NoClassDefFoundError: Lambda/0x00007ff00029e800
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:641)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1597)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:641)
	at java.base/java.lang.Thread.run(Thread.java:1575)
Caused by: java.lang.ClassNotFoundException: Lambda.0x00007ff00029e800
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:525)

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PR Review Comment: https://git.openjdk.org/babylon/pull/48#discussion_r1567466713