static File jdkSrcZip() {
  File jdkLocation = new File(getSystemProperty("java.home"));
  if (eqic(jdkLocation.getName(), "jre")) // get our of jre subdir
    jdkLocation = parentFile(jdkLocation);
  ret oneOfTheFiles(
    newFile(jdkLocation, "src.zip"),
    newFile(jdkLocation, "lib/src.zip")); // JDK 10
}