From fc7999073f8fff21c779d8f356c92c22481338f8 Mon Sep 17 00:00:00 2001
From: Miha Zupan <mihazupan.zupan1@gmail.com>
Date: Mon, 20 May 2024 23:23:25 +0200
Subject: [PATCH] Remove StringBuilder use

---
 src/libraries/Fuzzing/DotnetFuzzing/Assert.cs    | 16 ----------------
 .../Fuzzing/DotnetFuzzing/Fuzzers/UTF8Fuzzer.cs  | 10 +++++-----
 2 files changed, 5 insertions(+), 21 deletions(-)

diff --git a/src/libraries/Fuzzing/DotnetFuzzing/Assert.cs b/src/libraries/Fuzzing/DotnetFuzzing/Assert.cs
index cdb0324eafcb3..810174ccbc131 100644
--- a/src/libraries/Fuzzing/DotnetFuzzing/Assert.cs
+++ b/src/libraries/Fuzzing/DotnetFuzzing/Assert.cs
@@ -1,8 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using System.Text;
-
 namespace DotnetFuzzing;
 
 internal static class Assert
@@ -36,18 +34,4 @@ static void Throw(ReadOnlySpan<T> expected, ReadOnlySpan<T> actual)
             throw new Exception($"Expected={expected[diffIndex]} Actual={actual[diffIndex]} at index {diffIndex}");
         }
     }
-
-    public static void SequenceEqual(ReadOnlySpan<char> expected, StringBuilder actual)
-    {
-        Equal(expected.Length, actual.Length);
-
-        foreach (ReadOnlyMemory<char> chunk in actual.GetChunks())
-        {
-            SequenceEqual(expected.Slice(0, chunk.Length), chunk.Span);
-
-            expected = expected.Slice(chunk.Length);
-        }
-
-        Equal(0, expected.Length);
-    }
 }
diff --git a/src/libraries/Fuzzing/DotnetFuzzing/Fuzzers/UTF8Fuzzer.cs b/src/libraries/Fuzzing/DotnetFuzzing/Fuzzers/UTF8Fuzzer.cs
index 4b35f23ae69bf..b42adc6a70e42 100644
--- a/src/libraries/Fuzzing/DotnetFuzzing/Fuzzers/UTF8Fuzzer.cs
+++ b/src/libraries/Fuzzing/DotnetFuzzing/Fuzzers/UTF8Fuzzer.cs
@@ -16,7 +16,7 @@ internal sealed class UTF8Fuzzer : IFuzzer
     private static readonly Encoding s_encodingWithCustomReplacement =
         Encoding.GetEncoding("utf-8", EncoderFallback.ExceptionFallback, new DecoderReplacementFallback("{BAD}"));
 
-    private static readonly StringBuilder s_replacementStringBuilder = new(4096);
+    private static readonly ArrayBufferWriter<char> s_replacementBufferWriter = new(4096);
 
     public void FuzzTarget(ReadOnlySpan<byte> bytes)
     {
@@ -91,12 +91,12 @@ private static void Test(ReadOnlySpan<byte> input)
 
             using var decodedChars = PooledBoundedMemory<char>.Rent(decoded.Length, PoisonPagePlacement.After);
 
-            StringBuilder builder = s_replacementStringBuilder.Clear();
+            s_replacementBufferWriter.ResetWrittenCount();
 
             while (!utf8.IsEmpty)
             {
                 OperationStatus opStatus = Utf8.ToUtf16(utf8, decodedChars.Span, out int bytesReadJustNow, out int charsWrittenJustNow, replaceInvalidSequences: false, isFinalBlock: true);
-                builder.Append(decodedChars.Span.Slice(0, charsWrittenJustNow));
+                s_replacementBufferWriter.Write(decodedChars.Span.Slice(0, charsWrittenJustNow));
 
                 utf8 = utf8.Slice(bytesReadJustNow);
 
@@ -108,11 +108,11 @@ private static void Test(ReadOnlySpan<byte> input)
                     Rune.DecodeFromUtf8(utf8, out _, out int bytesToSkip);
                     utf8 = utf8.Slice(bytesToSkip);
 
-                    builder.Append("{BAD}");
+                    s_replacementBufferWriter.Write("{BAD}");
                 }
             }
 
-            Assert.SequenceEqual(decoded, builder);
+            Assert.SequenceEqual(decoded, s_replacementBufferWriter.WrittenSpan);
         }
     }