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Author: ajaybhargavb

src/Microsoft.AspNetCore.Razor.Language/Legacy/SpanEditHandler.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using Microsoft.AspNetCore.Razor.Language.Syntax;
 
@@ -115,6 +116,10 @@ protected virtual SyntaxNode UpdateSpan(SyntaxNode target, SourceChange change)
             {
                 newTarget = Syntax.InternalSyntax.SyntaxFactory.UnclassifiedTextLiteral(builder.ToList()).CreateRed(target.Parent, target.Position);
             }
+            else
+            {
+                Debug.Fail($"The type {target?.GetType().Name} is not a supported span node.");
+            }
 
             var context = target.GetSpanContext();
             newTarget = context != null ? newTarget?.WithSpanContext(context) : newTarget;

src/Microsoft.AspNetCore.Razor.Language/Syntax/LegacySyntaxNodeExtensions.cs

@@ -190,8 +190,13 @@ public static IEnumerable<SyntaxNode> FlattenSpans(this SyntaxNode node)
                 throw new ArgumentNullException(nameof(node));
             }
 
-            var spanNodes = node.DescendantNodes().Where(n => n.IsSpanKind());
-            return spanNodes;
+            foreach (var child in node.DescendantNodes())
+            {
+                if (child.IsSpanKind())
+                {
+                    yield return child;
+                }
+            }
         }
 
         public static SyntaxNode PreviousSpan(this SyntaxNode node)