Fix SearchValues fixer introducing slight changes for edge case inputs

Author: MihaZupan

src/NetAnalyzers/CSharp/Microsoft.NetCore.Analyzers/Performance/CSharpUseSearchValues.Fixer.cs

@@ -89,6 +89,19 @@ protected override SyntaxNode GetDeclaratorInitializer(SyntaxNode syntax)
                     values.Count <= 128 &&                  // Arbitrary limit to avoid emitting huge literals
                     !ContainsAnyComments(creationSyntax))   // Avoid removing potentially valuable comments
                 {
+                    if (isByte)
+                    {
+                        foreach (char c in values)
+                        {
+                            if (c > 127)
+                            {
+                                // We shouldn't turn non-ASCII byte values into Utf8StringLiterals as that may change behavior.
+                                // e.g. (byte)'ÿ' means 0xFF, but "ÿ"u8 is two bytes (0xC3, 0xBF) that encode that character in UTF8.
+                                return null;
+                            }
+                        }
+                    }
+
                     string valuesString = string.Concat(values);
                     string stringLiteral = SymbolDisplay.FormatLiteral(valuesString, quote: true);
 

src/NetAnalyzers/UnitTests/Microsoft.NetCore.Analyzers/Performance/UseSearchValuesTests.cs

@@ -771,6 +771,42 @@ private void TestMethod(string text)
             await VerifyCodeFixAsync(LanguageVersion.CSharp7_3, source, expected);
         }
 
+        [Fact]
+        public async Task TestCodeFixerDoesNotUseUtf8StringLiteralsForNonAsciiChars()
+        {
+            string source =
+                """
+                using System;
+                using System.Buffers;
+
+                internal sealed class Test
+                {
+                    private void TestMethod(ReadOnlySpan<byte> span)
+                    {
+                        _ = span.IndexOfAny([|new[] { (byte)'ÿ', (byte)'a', (byte)'e', (byte)'i', (byte)'o', (byte)'u' }|]);
+                    }
+                }
+                """;
+
+            string expected =
+                """
+                using System;
+                using System.Buffers;
+
+                internal sealed class Test
+                {
+                    private static readonly SearchValues<byte> s_myBytes = SearchValues.Create(new[] { (byte)'ÿ', (byte)'a', (byte)'e', (byte)'i', (byte)'o', (byte)'u' });
+
+                    private void TestMethod(ReadOnlySpan<byte> span)
+                    {
+                        _ = span.IndexOfAny(s_myBytes);
+                    }
+                }
+                """;
+
+            await VerifyCodeFixAsync(LanguageVersion.CSharp11, source, expected);
+        }
+
         [Fact]
         public static async Task TestCodeFixerDoesNotRemoveTheOriginalMemberIfPublic()
         {