static int classFileVersionToJavaVersion(S version) {
  ret classFileVersionToJavaVersion(parseFirstInt(version));
}

static int classFileVersionToJavaVersion(int majorVersion) {
  if (majorVersion < 45) ret -1; // bad input
  // Java 2 through 11, probably for newer versions this works too
  int j = majorVersion-44;
  if (j > 11) print("Warning: Please upgrade function classFileVersionToJavaVersion for JDK 12+");
  ret j;
}