code: private void checkConditionalForwardsExpressions(ClassDeclaration jclass)
              throws FatalCompileTimeException
      {
          // Get simple actions in the Controller annotation.
          List simpleActions =
                  CompilerUtils.getAnnotationArrayValue(jclass, CONTROLLER_TAG_NAME, SIMPLE_ACTIONS_ATTR, true);
  
          if (simpleActions != null) {
              HashSet expressionsFound = new HashSet();
              for (Iterator j = simpleActions.iterator(); j.hasNext();) {
                  AnnotationInstance sa = (AnnotationInstance) j.next();
                  List conditionalForwards = CompilerUtils.getAnnotationArray(sa, CONDITIONAL_FORWARDS_ATTR, true);
  
                  if (conditionalForwards != null) {
                      for (Iterator k = conditionalForwards.iterator(); k.hasNext();) {
                          AnnotationInstance cf = (AnnotationInstance) k.next();
                          String expression = CompilerUtils.getString(cf, CONDITION_ATTR, true);
                          assert expression != null;
  
                          if (expressionsFound.contains(expression)) {
                              String name = CompilerUtils.getString(sa, NAME_ATTR, true);
                              getDiagnostics().addWarning(cf, "warning.duplicate-conditional-forward-expression",expression, name);
                          }
                          else {
                              expressionsFound.add(expression);
                          }
                      }
                  }
                  expressionsFound.clear();
              }
          }
      }
docs: Check for duplicate expressions in conditional forwards of the
  simple action annotations.