src/share/classes/com/sun/tools/javac/model/JavacElements.java

*** 758,767 ****
--- 758,777 ----
  
      public Name getName(CharSequence cs) {
          return names.fromString(cs.toString());
      }
  
+     @Override
+     public boolean isFunctionalInterface(TypeElement element) {
+         if (element.getKind() != ElementKind.INTERFACE)
+             return false;
+         else {
+             TypeSymbol tsym = cast(TypeSymbol.class, element);
+             return types.isFunctionalInterface(tsym);
+         }
+     }
+ 
      /**
       * Returns the tree node and compilation unit corresponding to this
       * element, or null if they can't be found.
       */
      private Pair<JCTree, JCCompilationUnit> getTreeAndTopLevel(Element e) {