Reduce the range walked for formatting content validation (#12384)

Previously, this validation pass would walk over the whole content of the original and changed texts. This change modifies it instead to walk over the affected ranges in the original and changed texts based on the given set of changes.

Author: ToddGrun

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

@@ -60,8 +60,32 @@ public static string GetSubTextString(this SourceText text, TextSpan span)
         return new string(charBuffer, 0, span.Length);
     }
 
-    public static bool NonWhitespaceContentEquals(this SourceText text, SourceText other)
-        => NonWhitespaceContentEquals(text, other, 0, text.Length, 0, other.Length);
+    public static bool NonWhitespaceContentEquals(this SourceText text, ImmutableArray<TextChange> changes)
+    {
+        if (changes.IsEmpty)
+        {
+            return true;
+        }
+
+        // Determine the affected spans in the original and changed source texts
+        var firstChangeSpan = changes[0].Span;
+        var textStart = firstChangeSpan.Start;
+        var textEnd = firstChangeSpan.End;
+
+        for (var i = 1; i < changes.Length; i++)
+        {
+            var changeSpan = changes[i].Span;
+
+            textStart = Math.Min(textStart, changeSpan.Start);
+            textEnd = Math.Max(textEnd, changeSpan.End);
+        }
+
+        var changedText = text.WithChanges(changes);
+        var changedStart = textStart;
+        var changedEnd = textEnd + (changedText.Length - text.Length);
+
+        return text.NonWhitespaceContentEquals(changedText, textStart, textEnd, changedStart, changedEnd);
+    }
 
     public static bool NonWhitespaceContentEquals(
         this SourceText text,

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

@@ -23,9 +23,8 @@ internal sealed class FormattingContentValidationPass(ILoggerFactory loggerFacto
     public Task<bool> IsValidAsync(FormattingContext context, ImmutableArray<TextChange> changes, CancellationToken cancellationToken)
     {
         var text = context.SourceText;
-        var changedText = text.WithChanges(changes);
 
-        if (!text.NonWhitespaceContentEquals(changedText))
+        if (!text.NonWhitespaceContentEquals(changes))
         {
             // Looks like we removed some non-whitespace content as part of formatting. Oops.
             // Discard this formatting result.