Use IndexOfAnyValues in Regex.Escape (#78667)

* Use IndexOfAnyValues in Regex.Escape

* NET8_0_OR_GREATER => NET7_0_OR_GREATER

src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexParser.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Buffers;
 using System.Collections;
 using System.Collections.Generic;
 using System.Diagnostics;
@@ -149,18 +150,13 @@ public static RegexReplacement ParseReplacement(string pattern, RegexOptions opt
         /// </summary>
         public static string Escape(string input)
         {
-            for (int i = 0; i < input.Length; i++)
-            {
-                if (IsMetachar(input[i]))
-                {
-                    return EscapeImpl(input, i);
-                }
-            }
-
-            return input;
+            int indexOfMetachar = IndexOfMetachar(input.AsSpan());
+            return indexOfMetachar < 0
+                ? input
+                : EscapeImpl(input.AsSpan(), indexOfMetachar);
         }
 
-        private static string EscapeImpl(string input, int i)
+        private static string EscapeImpl(ReadOnlySpan<char> input, int indexOfMetachar)
         {
             // For small inputs we allocate on the stack. In most cases a buffer three
             // times larger the original string should be sufficient as usually not all
@@ -171,12 +167,18 @@ private static string EscapeImpl(string input, int i)
                 new ValueStringBuilder(stackalloc char[EscapeMaxBufferSize]) :
                 new ValueStringBuilder(input.Length + 200);
 
-            char ch = input[i];
-            vsb.Append(input.AsSpan(0, i));
-
-            do
+            while (true)
             {
-                vsb.Append('\\');
+                vsb.Append(input.Slice(0, indexOfMetachar));
+                input = input.Slice(indexOfMetachar);
+
+                if (input.IsEmpty)
+                {
+                    break;
+                }
+
+                char ch = input[0];
+
                 switch (ch)
                 {
                     case '\n':
@@ -193,23 +195,16 @@ private static string EscapeImpl(string input, int i)
                         break;
                 }
 
+                vsb.Append('\\');
                 vsb.Append(ch);
-                i++;
-                int lastpos = i;
+                input = input.Slice(1);
 
-                while (i < input.Length)
+                indexOfMetachar = IndexOfMetachar(input);
+                if (indexOfMetachar < 0)
                 {
-                    ch = input[i];
-                    if (IsMetachar(ch))
-                    {
-                        break;
-                    }
-
-                    i++;
+                    indexOfMetachar = input.Length;
                 }
-
-                vsb.Append(input.AsSpan(lastpos, i - lastpos));
-            } while (i < input.Length);
+            }
 
             return vsb.ToString();
         }
@@ -2081,6 +2076,27 @@ internal static int MapCaptureNumber(int capnum, Hashtable? caps) =>
             // '  a  b  c  d  e  f  g  h  i  j  k  l  m  n  o  p  q  r  s  t  u  v  w  x  y  z  {  |  }  ~
                0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, Q, S, 0, 0, 0};
 
+#if NET7_0_OR_GREATER
+        private static readonly IndexOfAnyValues<char> s_metachars =
+            IndexOfAnyValues.Create("\t\n\f\r #$()*+.?[\\^{|");
+
+        private static int IndexOfMetachar(ReadOnlySpan<char> input) =>
+            input.IndexOfAny(s_metachars);
+#else
+        private static int IndexOfMetachar(ReadOnlySpan<char> input)
+        {
+            for (int i = 0; i < input.Length; i++)
+            {
+                if (IsMetachar(input[i]))
+                {
+                    return i;
+                }
+            }
+
+            return -1;
+        }
+#endif
+
         /// <summary>Returns true for those characters that terminate a string of ordinary chars.</summary>
         private static bool IsSpecial(char ch) => ch <= '|' && Category[ch] >= S;