src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/codegen/Lower.java

*** 95,104 ****
--- 95,105 ----
   */
  @Logger(name="lower")
  final class Lower extends NodeOperatorVisitor<BlockLexicalContext> implements Loggable {
  
      private final DebugLogger log;
+     private final boolean es6;
  
      // Conservative pattern to test if element names consist of characters valid for identifiers.
      // This matches any non-zero length alphanumeric string including _ and $ and not starting with a digit.
      private static final Pattern SAFE_PROPERTY_NAME = Pattern.compile("[a-zA-Z_$][\\w$]*");
  
*** 142,151 ****
--- 143,153 ----
                  return block.setIsTerminal(this, false);
              }
          });
  
          this.log = initLogger(compiler.getContext());
+         this.es6 = compiler.getScriptEnvironment()._es6;
      }
  
      @Override
      public DebugLogger getLogger() {
          return log;
*** 255,266 ****
          if (!forNode.isForIn() && isAlwaysTrue(test)) {
              newForNode = forNode.setTest(lc, null);
          }
  
          newForNode = checkEscape(newForNode);
!         if(newForNode.isForIn()) {
!             // Wrap it in a block so its internally created iterator is restricted in scope
              addStatementEnclosedInBlock(newForNode);
          } else {
              addStatement(newForNode);
          }
          return newForNode;
--- 257,269 ----
          if (!forNode.isForIn() && isAlwaysTrue(test)) {
              newForNode = forNode.setTest(lc, null);
          }
  
          newForNode = checkEscape(newForNode);
!         if(!es6 && newForNode.isForIn()) {
!             // Wrap it in a block so its internally created iterator is restricted in scope, unless we are running
!             // in ES6 mode, in which case the parser already created a block to capture let/const declarations.
              addStatementEnclosedInBlock(newForNode);
          } else {
              addStatement(newForNode);
          }
          return newForNode;