Raise WorkspaceChanged with a new SourceText even if we have a new sn…

…apshot without changes (#25576)

* Fixed DDRIT failure (#25551)

* made sure we raise workspace changed events even when there is no text change.

this is needed to bring workspace up to date with latest text snapshot after we don't merge 2 text snapshot to 1 source text if content is same.

see this for more detail - #24849

* added comments on why we need to process all text change events

* removed changes empty check. now it is possible to have empty changes.

* remove non-empty from comment since set now can be empty.

src/Compilers/Core/Portable/Text/TextChangeEventArgs.cs

@@ -18,10 +18,10 @@ public class TextChangeEventArgs : EventArgs
         /// </summary>
         /// <param name="oldText">The text before the change.</param>
         /// <param name="newText">The text after the change.</param>
-        /// <param name="changes">A non-empty set of ranges for the change.</param>
+        /// <param name="changes">A set of ranges for the change.</param>
         public TextChangeEventArgs(SourceText oldText, SourceText newText, IEnumerable<TextChangeRange> changes)
         {
-            if (changes == null || changes.IsEmpty())
+            if (changes == null)
             {
                 throw new ArgumentException("changes");
             }
@@ -36,7 +36,7 @@ public TextChangeEventArgs(SourceText oldText, SourceText newText, IEnumerable<T
         /// </summary>
         /// <param name="oldText">The text before the change.</param>
         /// <param name="newText">The text after the change.</param>
-        /// <param name="changes">A non-empty set of ranges for the change.</param>
+        /// <param name="changes">A set of ranges for the change.</param>
         public TextChangeEventArgs(SourceText oldText, SourceText newText, params TextChangeRange[] changes)
             : this(oldText, newText, (IEnumerable<TextChangeRange>)changes)
         {

src/EditorFeatures/Text/Extensions.TextBufferContainer.cs

@@ -100,18 +100,24 @@ public override SourceText CurrentText
             private void OnTextContentChanged(object sender, TextContentChangedEventArgs args)
             {
                 var changed = this.EtextChanged;
-                if (changed != null && args.Changes.Count != 0)
+                if (changed == null)
                 {
-                    // this should convert given editor snapshots to roslyn forked snapshots
-                    var oldText = (SnapshotSourceText)args.Before.AsText();
-                    var newText = SnapshotSourceText.From(args.After);
-                    _currentText = newText;
-
-                    var changes = ImmutableArray.CreateRange(args.Changes.Select(c => new TextChangeRange(new TextSpan(c.OldSpan.Start, c.OldSpan.Length), c.NewLength)));
-                    var eventArgs = new TextChangeEventArgs(oldText, newText, changes);
-                    this.LastEventArgs = eventArgs;
-                    changed(sender, eventArgs);
+                    return;
                 }
+
+                // we should process all changes even though there is no text changes
+                // otherwise, Workspace.CurrentSolution won't move forward to latest ITextSnapshot
+
+                // this should convert given editor snapshots to roslyn forked snapshots
+                var oldText = (SnapshotSourceText)args.Before.AsText();
+                var newText = SnapshotSourceText.From(args.After);
+                _currentText = newText;
+
+                var changes = ImmutableArray.CreateRange(args.Changes.Select(c => new TextChangeRange(new TextSpan(c.OldSpan.Start, c.OldSpan.Length), c.NewLength)));
+                var eventArgs = new TextChangeEventArgs(oldText, newText, changes);
+
+                this.LastEventArgs = eventArgs;
+                changed(sender, eventArgs);
             }
 
             // These are the event args that were last sent from this text container when the text