Create a helper method and revert change to shared code, just in case

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Extensions/SourceTextExtensions.cs

@@ -322,4 +322,17 @@ internal static class SourceTextExtensions
 
         return lfCount > crlfCount;
     }
+
+    public static ImmutableArray<TextChange> GetTextChangesArray(this SourceText newText, SourceText oldText)
+    {
+        var list = newText.GetTextChanges(oldText);
+
+        // Fast path for the common case. The base SourceText.GetTextChanges method returns an ImmutableArray
+        if (list is ImmutableArray<TextChange> array)
+        {
+            return array;
+        }
+
+        return list.ToImmutableArray();
+    }
 }

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Formatting/Passes/CSharpFormattingPass.cs

@@ -2,7 +2,6 @@
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Linq;
 using System.Threading;
@@ -63,9 +62,7 @@ internal sealed class CSharpFormattingPass(
 
         _logger.LogTestOnly($"Generated C#:\r\n{context.CSharpSourceText}");
 
-        var finalChanges = changedText.GetTextChanges(originalText);
-
-        return finalChanges.ToImmutableArray();
+        return changedText.GetTextChangesArray(originalText);
     }
 
     private async Task<ImmutableArray<TextChange>> FormatCSharpAsync(FormattingContext context, CancellationToken cancellationToken)

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Formatting/Passes/CSharpOnTypeFormattingPass.cs

@@ -177,7 +177,7 @@ internal sealed class CSharpOnTypeFormattingPass(
         }
 
         // Now that we have made all the necessary changes to the document. Let's diff the original vs final version and return the diff.
-        var finalChanges = cleanedText.GetTextChanges(originalText).ToImmutableArray();
+        var finalChanges = cleanedText.GetTextChangesArray(originalText);
 
         finalChanges = await AddUsingStatementEditsIfNecessaryAsync(context, codeDocument, csharpText, changes, originalTextWithChanges, finalChanges, cancellationToken).ConfigureAwait(false);
 

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Formatting/Passes/HtmlFormattingPassBase.cs

@@ -45,9 +45,7 @@ internal abstract class HtmlFormattingPassBase(ILogger logger) : IFormattingPass
             _logger.LogTestOnly($"After AdjustRazorIndentation:\r\n{changedText}");
         }
 
-        var finalChanges = changedText.GetTextChanges(originalText);
-
-        return finalChanges.ToImmutableArray();
+        return changedText.GetTextChangesArray(originalText);
     }
 
     private static ImmutableArray<TextChange> AdjustRazorIndentation(FormattingContext context)

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Formatting/Passes/RazorFormattingPass.cs

@@ -1,7 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
-using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics.CodeAnalysis;
 using System.Threading;
@@ -43,9 +42,7 @@ internal sealed class RazorFormattingPass : IFormattingPass
         // Compute the final combined set of edits
         changedText = changedText.WithChanges(razorChanges);
 
-        var finalChanges = changedText.GetTextChanges(originalText);
-
-        return finalChanges.ToImmutableArray();
+        return changedText.GetTextChangesArray(originalText);
     }
 
     private static ImmutableArray<TextChange> FormatRazor(FormattingContext context, RazorSyntaxTree syntaxTree)

src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/ReadOnlyListExtensions.cs

@@ -59,11 +59,6 @@ internal static class ReadOnlyListExtensions
 
     public static ImmutableArray<T> ToImmutableArray<T>(this IReadOnlyList<T> list)
     {
-        if (list is ImmutableArray<T> array)
-        {
-            return array;
-        }
-
         return list switch
         {
             [] => [],