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/**

 * @test

 * @summary Verify the defining class loader of each module never delegates

 *          to its child class loader.

 * @run testng/othervm --add-modules=ALL-SYSTEM VerifyModuleDelegation

 */

import java.lang.module.ModuleDescriptor;

import java.util.Set;

import static java.util.stream.Collectors.toSet;

import org.testng.annotations.*;

import static org.testng.Assert.*;

public class VerifyModuleDelegation {

    private static final String JAVA_BASE = "java.base";

    private static final ModuleDescriptor BASE

        = ModuleDescriptor.newModule(JAVA_BASE).build();

    private static final Set<ModuleDescriptor> MREFS

            = ModuleLayer.boot().modules().stream().map(Module::getDescriptor)

                .collect(toSet());

    private void check(ModuleDescriptor md, ModuleDescriptor ref) {

        assertTrue(md.requires().size() == ref.requires().size());

        assertTrue(md.requires().containsAll(ref.requires()));

    }

    @Test

    public void checkJavaBase() {

        ModuleDescriptor md =

                MREFS.stream()

                     .filter(d -> d.name().equals(JAVA_BASE))

                     .findFirst().orElseThrow(Error::new);

        check(md, BASE);

    }

    @Test

    public void checkLoaderDelegation() {

        ModuleLayer boot = ModuleLayer.boot();

        MREFS.stream()

             .forEach(md -> md.requires().stream().forEach(req ->

                 {

                     // check if M requires D and D's loader must be either the

                     // same or an ancestor of M's loader

                     ClassLoader loader1 = boot.findLoader(md.name());

                     ClassLoader loader2 = boot.findLoader(req.name());

                     if (loader1 != loader2 && !isAncestor(loader2, loader1)) {

                     }

                 }));

    }

    // Returns true if p is an ancestor of cl i.e. class loader 'p' can

    // be found in the cl's delegation chain

    private static boolean isAncestor(ClassLoader p, ClassLoader cl) {

        if (p != null && cl == null) {

            return false;

        }

        ClassLoader acl = cl;

        do {

            acl = acl.getParent();

            if (p == acl) {

                return true;

            }

        } while (acl != null);

        return false;

    }

}