Merge pull request #14459 from CyrusNajmabadi/nullTextViewLinesRC

Be resilient to being called while the text view is being initialized.

src/EditorFeatures/Core/Implementation/Classification/SemanticClassificationUtilities.cs

@@ -106,7 +106,8 @@ internal static class SemanticClassificationUtilities
             return true;
         }
 
-        private static async Task ClassifySpansAsync(TaggerContext<IClassificationTag> context, DocumentSnapshotSpan spanToTag,
+        private static async Task ClassifySpansAsync(
+            TaggerContext<IClassificationTag> context, DocumentSnapshotSpan spanToTag,
             IEditorClassificationService classificationService, ClassificationTypeMap typeMap)
         {
             try

src/EditorFeatures/Core/Shared/Extensions/ITextViewExtensions.cs

@@ -326,6 +326,12 @@ public static bool TryMoveCaretToAndEnsureVisible(this ITextView textView, Virtu
         /// </summary>
         public static SnapshotSpan? GetVisibleLinesSpan(this ITextView textView, ITextBuffer subjectBuffer, int extraLines = 0)
         {
+            // No point in continuing if the text view has been closed.
+            if (textView.IsClosed)
+            {
+                return null;
+            }
+
             // If we're being called while the textview is actually in the middle of a layout, then 
             // we can't proceed.  Much of the text view state is unsafe to access (and will throw).
             if (textView.InLayout)
@@ -333,6 +339,13 @@ public static bool TryMoveCaretToAndEnsureVisible(this ITextView textView, Virtu
                 return null;
             }
 
+            // During text view initialization the TextViewLines may be null.  In that case we can't
+            // get an appropriate visisble span.
+            if (textView.TextViewLines == null)
+            {
+                return null;
+            }
+
             // Determine the range of text that is visible in the view.  Then map this down to the
             // bufffer passed in.  From that, determine the start/end line for the buffer that is in
             // view.