show no changes when there is no change.

src/VisualStudio/Core/Def/Implementation/Preview/ChangeList.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-using Microsoft.CodeAnalysis;
+using System;
 using Microsoft.CodeAnalysis.Editor.Shared.Utilities;
-using Microsoft.VisualStudio.LanguageServices.Implementation.Utilities;
 using Microsoft.VisualStudio.Shell.Interop;
 
 namespace Microsoft.VisualStudio.LanguageServices.Implementation.Preview
 {
     internal partial class ChangeList : ForegroundThreadAffinitizedObject, IVsPreviewChangesList, IVsLiteTreeList
     {
+        public readonly static ChangeList Empty = new ChangeList(Array.Empty<AbstractChange>());
+
         internal AbstractChange[] Changes { get; private set; }
 
         public ChangeList(AbstractChange[] changes)

src/VisualStudio/Core/Def/Implementation/Preview/FileChange.cs

@@ -83,8 +83,8 @@ private ChangeList ComputeChildren(TextDocument left, TextDocument right, Cancel
             var diff = ComputeDiffSpans(diffService, left, right, cancellationToken);
             if (diff.Differences.Count == 0)
             {
-                // There are no changes. Just show the whole document.
-                return GetEntireDocumentAsSpanChange(left);
+                // There are no changes.
+                return ChangeList.Empty;
             }
 
             return GetChangeList(diff, right.Id, oldText, newText);
@@ -240,8 +240,11 @@ private static IHierarchicalDifferenceCollection ComputeDiffSpans(ITextDifferenc
             var oldText = left.GetTextAsync(cancellationToken).WaitAndGetResult(cancellationToken);
             var newText = right.GetTextAsync(cancellationToken).WaitAndGetResult(cancellationToken);
 
+            var oldString = oldText.ToString();
+            var newString = newText.ToString();
+
             // first try, cheapest way.
-            var diffResult = diffService.DiffStrings(oldText.ToString(), newText.ToString(), new StringDifferenceOptions()
+            var diffResult = diffService.DiffStrings(oldString, newString, new StringDifferenceOptions()
             {
                 DifferenceType = StringDifferenceTypes.Line | StringDifferenceTypes.Word,
                 WordSplitBehavior = WordSplitBehavior.WhiteSpaceAndPunctuation
@@ -253,7 +256,7 @@ private static IHierarchicalDifferenceCollection ComputeDiffSpans(ITextDifferenc
             }
 
             // second, try a bit more expansive way
-            return diffService.DiffStrings(oldText.ToString(), newText.ToString(), new StringDifferenceOptions()
+            return diffService.DiffStrings(oldString, newString, new StringDifferenceOptions()
             {
                 DifferenceType = StringDifferenceTypes.Word,
                 WordSplitBehavior = WordSplitBehavior.WhiteSpaceAndPunctuation

src/VisualStudio/Core/Def/Implementation/Preview/PreviewEngine.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Runtime.InteropServices;
@@ -10,6 +11,7 @@
 using Microsoft.CodeAnalysis.Shared.Extensions;
 using Microsoft.VisualStudio.ComponentModelHost;
 using Microsoft.VisualStudio.Editor;
+using Microsoft.VisualStudio.Language.Intellisense;
 using Microsoft.VisualStudio.Shell.Interop;
 using Microsoft.VisualStudio.Text.Differencing;
 using Microsoft.VisualStudio.Text.Editor;
@@ -36,7 +38,7 @@ internal class PreviewEngine : ForegroundThreadAffinitizedObject, IVsPreviewChan
         private PreviewUpdater _updater;
 
         public Solution FinalSolution { get; private set; }
-        public readonly bool ShowCheckBoxes;
+        public bool ShowCheckBoxes { get; private set; }
 
         public PreviewEngine(string title, string helpString, string description, string topLevelItemName, Glyph topLevelGlyph, Solution newSolution, Solution oldSolution, IComponentModel componentModel, bool showCheckBoxes = true) :
             this(title, helpString, description, topLevelItemName, topLevelGlyph, newSolution, oldSolution, componentModel, null, showCheckBoxes)
@@ -134,8 +136,14 @@ public int GetRootChangesList(out object ppIUnknownPreviewChangesList)
             // References (metadata/project/analyzer)
             ReferenceChange.AppendReferenceChanges(projectChanges, this, builder);
 
-            _topLevelChange.Children = new ChangeList(builder.ToArray());
-            ppIUnknownPreviewChangesList = new ChangeList(new[] { _topLevelChange });
+            _topLevelChange.Children = builder.Count == 0 ? ChangeList.Empty : new ChangeList(builder.ToArray());
+            ppIUnknownPreviewChangesList = _topLevelChange.Children.Changes.Length == 0 ? new ChangeList(new[] { new NoChange(this) }) : new ChangeList(new[] { _topLevelChange });
+
+            if (_topLevelChange.Children.Changes.Length == 0)
+            {
+                this.ShowCheckBoxes = false;
+            }
+
             return VSConstants.S_OK;
         }
 
@@ -169,7 +177,11 @@ private void AppendFileChanges(IEnumerable<DocumentId> changedDocuments, ArrayBu
                     linkedDocumentIds.AddRange(rightDocument.GetLinkedDocumentIds());
                 }
 
-                builder.Add(new FileChange(left, right, _componentModel, _topLevelChange, this, _imageService));
+                var fileChange = new FileChange(left, right, _componentModel, _topLevelChange, this, _imageService);
+                if (fileChange.Children.Changes.Length > 0)
+                {
+                    builder.Add(fileChange);
+                }
             }
         }
 
@@ -261,5 +273,43 @@ private static void EditBufferToInitialize(IVsTextView adapter)
 
             Marshal.ThrowExceptionForHR(lines.ReplaceLines(0, 0, piLineIndex, piLineLength, newTextPtr, newText.Length, changes));
         }
+
+        private class NoChange : AbstractChange
+        {
+            public NoChange(PreviewEngine engine) : base(engine)
+            {
+            }
+
+            public override int GetText(out VSTREETEXTOPTIONS tto, out string ppszText)
+            {
+                tto = VSTREETEXTOPTIONS.TTO_DEFAULT;
+                ppszText = ServicesVSResources.NoChanges;
+                return VSConstants.S_OK;
+            }
+
+            public override int GetTipText(out VSTREETOOLTIPTYPE eTipType, out string ppszText)
+            {
+                eTipType = VSTREETOOLTIPTYPE.TIPTYPE_DEFAULT;
+                ppszText = null;
+                return VSConstants.E_FAIL;
+            }
+
+            public override int CanRecurse => 0;
+            public override int IsExpandable => 0;
+
+            internal override void GetDisplayData(VSTREEDISPLAYDATA[] pData)
+            {
+                pData[0].Image = pData[0].SelectedImage = (ushort)StandardGlyphGroup.GlyphInformation;
+            }
+
+            public override int OnRequestSource(object pIUnknownTextView)
+            {
+                return VSConstants.S_OK;
+            }
+
+            public override void UpdatePreview()
+            {
+            }
+        }
     }
 }

src/VisualStudio/Core/Def/ServicesVSResources.Designer.cs

@@ -692,6 +692,15 @@ internal class ServicesVSResources {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to No Changes.
+        /// </summary>
+        internal static string NoChanges {
+            get {
+                return ResourceManager.GetString("NoChanges", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Not a valid value.
         /// </summary>

src/VisualStudio/Core/Def/ServicesVSResources.resx

@@ -462,4 +462,7 @@ Use the dropdown to view and switch to other projects this file may belong to.</
   <data name="EnableAndIgnore" xml:space="preserve">
     <value>Enable and ignore future errors</value>
   </data>
+  <data name="NoChanges" xml:space="preserve">
+    <value>No Changes</value>
+  </data>
 </root>
\ No newline at end of file