given:
        def original = jar(testDir.file("original.jar")) {
            manifest {
                multiRelease()
            }

            entry("Foo.class", ORIGINAL_CLASS)
        }

        def transformed = jar(testDir.file("transformed.jar")) {
            manifest {
                multiRelease()
            }

            entry("Foo.class", INSTRUMENTED_CLASS)

     */
    static class ManifestWithDsl extends Manifest {
        /**
         * Configures this Manifest to be Multi-Release.
         */
        void multiRelease() {
            mainAttributes.putValue(JarUtil.MULTI_RELEASE_ATTRIBUTE, "true")
        }
    }

import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;

public class JarUtil {
    // We cannot use Attributes.Name.MULTI_RELEASE as it is only available since Java 9;
    public static final String MULTI_RELEASE_ATTRIBUTE = "Multi-Release";
    // Pattern for JAR entries in the versioned directories.