test/jdk/java/lang/invoke/lambda/LambdaHiddenCaller.java

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import java.io.Serializable;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.util.function.IntSupplier;

import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertTrue;

/*
 * @test
 * @bug 8343064
 * @summary Test about when lambda caller/target class is a hidden class
 * @run junit LambdaHiddenCaller
 */
public class LambdaHiddenCaller {
    static Hooks hiddenCaller;

    @BeforeAll
    static void setup() throws Throwable {
        byte[] bytes;
        try (var in = LambdaHiddenCaller.class.getResourceAsStream("HiddenHooks.class")) {
            bytes = in.readAllBytes();
        }
        var hiddenClassLookup = MethodHandles.lookup().defineHiddenClass(bytes, true);
        hiddenCaller = (Hooks) hiddenClassLookup.findConstructor(hiddenClassLookup.lookupClass(), MethodType.methodType(void.class))
                .asType(MethodType.methodType(Hooks.class)).invokeExact();
    }

    @Test
    void testStaticMethod() {
        var is = hiddenCaller.callStaticMethodLambda();
        assertEquals(42, is.getAsInt());
    }

    @Test
    void testSerializableLambda() {
        var is = hiddenCaller.callSerializableLambda();
        assertEquals(42, is.getAsInt());
        assertTrue(Serializable.class.isAssignableFrom(is.getClass()));
        // We do not guarantee serialization functionalities yet
    }
}

/**
 * Hooks to call hidden class methods easily.
 */
interface Hooks {
    IntSupplier callStaticMethodLambda();

    IntSupplier callSerializableLambda();
}

class HiddenHooks implements Hooks {
    private static int compute() {
        return 42;
    }

    @Override
    public IntSupplier callStaticMethodLambda() {
        return HiddenHooks::compute;
    }

    @Override
    public IntSupplier callSerializableLambda() {
        return (IntSupplier & Serializable) HiddenHooks::compute;
    }
}