Convert non-space white space characters to spaces in DNames (#285)

* convert special whitespace characters to spaces

* test

* lint issues

* LF

* pr concerns

src/libraries/Microsoft.PowerFx.Core/Utils/DName.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license.
 
 using System;
+using System.Text;
 
 namespace Microsoft.PowerFx.Core.Utils
 {
@@ -159,11 +160,36 @@ namespace Microsoft.PowerFx.Core.Utils
             }
 
             var fAllSpaces = true;
+            var fHasSpecialWhiteSpaceCharacters = false;
+            
             fModified = false;
 
             for (var i = 0; i < strName.Length; i++)
             {
-                fAllSpaces = fAllSpaces && (strName[i] == ChSpace);
+                var fIsSpace = strName[i] == ChSpace;
+                var fIsWhiteSpace = char.IsWhiteSpace(strName[i]);
+                fAllSpaces = fAllSpaces && fIsWhiteSpace;
+                fHasSpecialWhiteSpaceCharacters |= fIsWhiteSpace && !fIsSpace;
+            }
+
+            if (fHasSpecialWhiteSpaceCharacters)
+            {
+                fModified = true;
+                var builder = new StringBuilder(strName.Length);
+
+                for (var i = 0; i < strName.Length; i++)
+                {
+                    if (char.IsWhiteSpace(strName[i]))
+                    {
+                        builder.Append(ChSpace);
+                    }
+                    else
+                    {
+                        builder.Append(strName[i]);
+                    }
+                }
+
+                strName = builder.ToString();
             }
 
             if (!fAllSpaces)

src/tests/Microsoft.PowerFx.Core.Tests/DNameTests.cs

@@ -0,0 +1,27 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Microsoft.PowerFx.Core.Utils;
+using Xunit;
+
+namespace Microsoft.PowerFx.Core.Tests
+{
+    public sealed class DNameTests
+    {
+        [Theory]
+        [InlineData(" Name   ", " Name   ", false)]
+        [InlineData("Name\bAbcd", "Name\bAbcd", false)]
+        [InlineData("Name\nAbcd", "Name Abcd", true)]
+        [InlineData("   ", "_   ", true)]
+        [InlineData(" \t ", "_   ", true)]
+        public void TestMakeValid(string name, string expected, bool expectedModified)
+        {
+            var result = DName.MakeValid(name, out var modified);
+            Assert.Equal(modified, expectedModified);
+            Assert.Equal(expected, result);
+        }
+    }
+}