src/jdk.compiler/share/classes/com/sun/tools/javac/main/Option.java

*** 39,48 ****
--- 39,49 ----
  import java.util.Iterator;
  import java.util.LinkedHashSet;
  import java.util.Locale;
  import java.util.ServiceLoader;
  import java.util.Set;
+ import java.util.StringJoiner;
  import java.util.TreeSet;
  import java.util.regex.Pattern;
  import java.util.stream.Collectors;
  import java.util.stream.StreamSupport;
  
*** 293,302 ****
--- 294,313 ----
              if (source == null) {
                  throw helper.newInvalidValueException(Errors.InvalidSource(operand));
              }
              super.process(helper, option, operand);
          }
+ 
+         @Override
+         protected void help(Log log) {
+             StringJoiner sj = new StringJoiner(", ");
+             for(Source source :  Source.values()) {
+                 if (source.isSupported())
+                     sj.add(source.name);
+             }
+             super.help(log, log.localize(PrefixKind.JAVAC, descrKey, sj.toString()));
+         }
      },
  
      TARGET("-target", "opt.arg.release", "opt.target", STANDARD, BASIC) {
          @Override
          public void process(OptionHelper helper, String option, String operand) throws InvalidValueException {
*** 304,313 ****
--- 315,334 ----
              if (target == null) {
                  throw helper.newInvalidValueException(Errors.InvalidTarget(operand));
              }
              super.process(helper, option, operand);
          }
+ 
+         @Override
+         protected void help(Log log) {
+             StringJoiner sj = new StringJoiner(", ");
+             for(Target target :  Target.values()) {
+                 if (target.isSupported())
+                     sj.add(target.name);
+             }
+             super.help(log, log.localize(PrefixKind.JAVAC, descrKey, sj.toString()));
+         }
      },
  
      RELEASE("--release", "opt.arg.release", "opt.release", STANDARD, BASIC) {
          @Override
          protected void help(Log log) {