edit/revertCell (#268)

// edit/dispose -------------------------------------------------------------------------------
export interface EditDisposeParams extends IEditSessionOperationParams { }
export interface EditDisposeResult { }

* Initial plumbing for edit/revertCell

* Implementation of revert cell in the parents of the row edit base

* Adding unit tests

src/Microsoft.SqlTools.ServiceLayer/EditData/UpdateManagement/RowCreate.cs

@@ -27,7 +27,7 @@ namespace Microsoft.SqlTools.ServiceLayer.EditData.UpdateManagement
         private const string InsertCompleteScript = "{0} VALUES ({1})";
         private const string InsertCompleteOutput = "{0} OUTPUT {1} VALUES ({2})";
 
-        private readonly CellUpdate[] newCells;
+        internal readonly CellUpdate[] newCells;
 
         /// <summary>
         /// Creates a new Row Creation edit to the result set
@@ -159,6 +159,21 @@ namespace Microsoft.SqlTools.ServiceLayer.EditData.UpdateManagement
             return string.Format(InsertCompleteScript, start, joinedValues);
         }
 
+        /// <summary>
+        /// Reverts a cell to an unset value.
+        /// </summary>
+        /// <param name="columnId">The ordinal ID of the cell to reset</param>
+        /// <returns>The default value for the column, or null if no default is defined</returns>
+        public override string RevertCell(int columnId)
+        {
+            // Validate that the column can be reverted
+            Validate.IsWithinRange(nameof(columnId), columnId, 0, newCells.Length - 1);
+
+            // Remove the cell update from list of set cells
+            newCells[columnId] = null;
+            return null;                // @TODO: Return default value when we have support checked in
+        }
+
         /// <summary>
         /// Sets the value of a cell in the row to be added
         /// </summary>