src/jdk/nashorn/internal/runtime/arrays/ArrayData.java

*** 105,122 ****
              return ScriptRuntime.EMPTY_ARRAY;
          }
  
          @Override
          public ArrayData ensure(final long safeIndex) {
!             if (safeIndex > 0L) {
                  if (safeIndex >= SparseArrayData.MAX_DENSE_LENGTH) {
                      return new SparseArrayData(this, safeIndex + 1);
                  }
                  //known to fit in int
                  return toRealArrayData((int)safeIndex);
!            }
!            return this;
          }
  
          @Override
          public ArrayData convert(final Class<?> type) {
              return toRealArrayData().convert(type);
--- 105,121 ----
              return ScriptRuntime.EMPTY_ARRAY;
          }
  
          @Override
          public ArrayData ensure(final long safeIndex) {
!             assert safeIndex >= 0L;
              if (safeIndex >= SparseArrayData.MAX_DENSE_LENGTH) {
                  return new SparseArrayData(this, safeIndex + 1);
              }
              //known to fit in int
              return toRealArrayData((int)safeIndex);
! 
          }
  
          @Override
          public ArrayData convert(final Class<?> type) {
              return toRealArrayData().convert(type);
*** 131,142 ****
          public ArrayData delete(final long fromIndex, final long toIndex) {
              return new DeletedRangeArrayFilter(this, fromIndex, toIndex);
          }
  
          @Override
!         public void shiftLeft(final int by) {
!             //nop, always empty or we wouldn't be of this class
          }
  
          @Override
          public ArrayData shiftRight(final int by) {
              return this; //always empty or we wouldn't be of this class
--- 130,141 ----
          public ArrayData delete(final long fromIndex, final long toIndex) {
              return new DeletedRangeArrayFilter(this, fromIndex, toIndex);
          }
  
          @Override
!         public ArrayData shiftLeft(final int by) {
!             return this; //nop, always empty or we wouldn't be of this class
          }
  
          @Override
          public ArrayData shiftRight(final int by) {
              return this; //always empty or we wouldn't be of this class
*** 449,465 ****
      }
  
      /**
       * Shift the array data left
       *
!      * TODO: explore start at an index and not at zero, to make these operations
!      * even faster. Offset everything from the index. Costs memory but is probably
!      * worth it
       *
       * @param by offset to shift
       */
!     public abstract void shiftLeft(final int by);
  
      /**
       * Shift the array right
       *
       * @param by offset to shift
--- 448,464 ----
      }
  
      /**
       * Shift the array data left
       *
!      * TODO: This is used for Array.prototype.shift() which only shifts by 1,
!      * so we might consider dropping the offset parameter.
       *
       * @param by offset to shift
+      * @return New arraydata (or same)
       */
!     public abstract ArrayData shiftLeft(final int by);
  
      /**
       * Shift the array right
       *
       * @param by offset to shift