StringBuilder.Replace with ReadOnlySpan<char>

src/libraries/System.Private.CoreLib/src/System/Text/StringBuilder.cs

@@ -1841,6 +1841,17 @@
         /// </remarks>
         public StringBuilder Replace(string oldValue, string? newValue) => Replace(oldValue, newValue, 0, Length);
 
+        /// <summary>
+        /// Replaces all instances of one read-only character span with another in this builder.
+        /// </summary>
+        /// <param name="oldValue">The read-only character span to replace.</param>
+        /// <param name="newValue">The read-only character span to replace <paramref name="oldValue"/> with.</param>
+        /// <remarks>
+        /// If <paramref name="newValue"/> is <c>null</c>, instances of <paramref name="oldValue"/>
+        /// are removed from this builder.
+        /// </remarks>
+        public StringBuilder Replace(ReadOnlySpan<char> oldValue, ReadOnlySpan<char> newValue) => Replace(oldValue, newValue, 0, Length);
+
         /// <summary>
         /// Determines if the contents of this builder are equal to the contents of another builder.
         /// </summary>
@@ -1950,6 +1961,25 @@
         /// are removed from this builder.
         /// </remarks>
         public StringBuilder Replace(string oldValue, string? newValue, int startIndex, int count)
+        {
+            ArgumentException.ThrowIfNullOrEmpty(oldValue);
+
+            ReadOnlySpan<char> newValueSpan = (newValue == null) ? ReadOnlySpan<char>.Empty : newValue.AsSpan();
+            return Replace(oldValue.AsSpan(), newValueSpan, startIndex, count);
+        }
+
+        /// <summary>
+        /// Replaces all instances of one read-only character span with another in part of this builder.
+        /// </summary>
+        /// <param name="oldValue">The read-only character span to replace.</param>
+        /// <param name="newValue">The read-only character span to replace <paramref name="oldValue"/> with.</param>
+        /// <param name="startIndex">The index to start in this builder.</param>
+        /// <param name="count">The number of characters to read in this builder.</param>
+        /// <remarks>
+        /// If <paramref name="newValue"/> is <c>null</c>, instances of <paramref name="oldValue"/>
+        /// are removed from this builder.
+        /// </remarks>
+        public StringBuilder Replace(ReadOnlySpan<char> oldValue, ReadOnlySpan<char> newValue, int startIndex, int count)
         {
             int currentLength = Length;
             if ((uint)startIndex > (uint)currentLength)
@@ -1960,9 +1990,10 @@
             {
                 throw new ArgumentOutOfRangeException(nameof(count), SR.ArgumentOutOfRange_IndexMustBeLessOrEqual);
             }
-            ArgumentException.ThrowIfNullOrEmpty(oldValue);
-
-            newValue ??= string.Empty;
+            if (oldValue.Length == 0)
+            {
+                throw new ArgumentException(SR.Arg_EmptySpan, nameof(oldValue));
+            }
 
             var replacements = new ValueListBuilder<int>(stackalloc int[128]); // A list of replacement positions in a chunk to apply
 
@@ -2225,7 +2256,7 @@
         /// <remarks>
         /// This routine is very efficient because it does replacements in bulk.
         /// </remarks>
-        private void ReplaceAllInChunk(ReadOnlySpan<int> replacements, StringBuilder sourceChunk, int removeCount, string value)
+        private void ReplaceAllInChunk(ReadOnlySpan<int> replacements, StringBuilder sourceChunk, int removeCount, ReadOnlySpan<char> value)
         {
             Debug.Assert(!replacements.IsEmpty);
 
@@ -2251,7 +2282,7 @@
             while (true)
             {
                 // Copy in the new string for the ith replacement
-                ReplaceInPlaceAtChunk(ref targetChunk!, ref targetIndexInChunk, ref value.GetRawStringData(), value.Length);
+                ReplaceInPlaceAtChunk(ref targetChunk!, ref targetIndexInChunk, ref MemoryMarshal.GetReference<char>(value), value.Length);
                 int gapStart = replacements[i] + removeCount;
                 i++;
                 if ((uint)i >= replacements.Length)
@@ -2289,7 +2320,7 @@
         /// <param name="indexInChunk">The index in <paramref name="chunk"/> at which the substring starts.</param>
         /// <param name="count">The logical count of the substring.</param>
         /// <param name="value">The prefix.</param>
-        private bool StartsWith(StringBuilder chunk, int indexInChunk, int count, string value)
+        private bool StartsWith(StringBuilder chunk, int indexInChunk, int count, ReadOnlySpan<char> value)
         {
             for (int i = 0; i < value.Length; i++)
             {

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -14925,6 +14925,8 @@ public void CopyTo(int sourceIndex, System.Span<char> destination, int count) {
         public System.Text.StringBuilder Replace(char oldChar, char newChar, int startIndex, int count) { throw null; }
         public System.Text.StringBuilder Replace(string oldValue, string? newValue) { throw null; }
         public System.Text.StringBuilder Replace(string oldValue, string? newValue, int startIndex, int count) { throw null; }
+        public System.Text.StringBuilder Replace(ReadOnlySpan<char> oldValue, ReadOnlySpan<char> newValue) { throw null; }
+        public System.Text.StringBuilder Replace(ReadOnlySpan<char> oldValue, ReadOnlySpan<char> newValue, int startIndex, int count) { throw null; }
         void System.Runtime.Serialization.ISerializable.GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
         public override string ToString() { throw null; }
         public string ToString(int startIndex, int length) { throw null; }

src/libraries/System.Runtime/tests/System/Text/StringBuilderTests.cs

@@ -1775,6 +1775,84 @@ public static void Replace_String_Invalid()
             AssertExtensions.Throws<ArgumentOutOfRangeException>("count", () => builder.Replace("a", "b", 4, 2)); // Count + start index > builder.Length
         }
 
+        [Theory]
+        [InlineData("", "a", "!", 0, 0, "")]
+        [InlineData("aaaabbbbccccdddd", "a", "!", 0, 16, "!!!!bbbbccccdddd")]
+        [InlineData("aaaabbbbccccdddd", "a", "!", 2, 3, "aa!!bbbbccccdddd")]
+        [InlineData("aaaabbbbccccdddd", "a", "!", 4, 1, "aaaabbbbccccdddd")]
+        [InlineData("aaaabbbbccccdddd", "aab", "!", 2, 2, "aaaabbbbccccdddd")]
+        [InlineData("aaaabbbbccccdddd", "aab", "!", 2, 3, "aa!bbbccccdddd")]
+        [InlineData("aaaabbbbccccdddd", "aa", "!", 0, 16, "!!bbbbccccdddd")]
+        [InlineData("aaaabbbbccccdddd", "aa", "$!", 0, 16, "$!$!bbbbccccdddd")]
+        [InlineData("aaaabbbbccccdddd", "aa", "$!$", 0, 16, "$!$$!$bbbbccccdddd")]
+        [InlineData("aaaabbbbccccdddd", "aaaa", "!", 0, 16, "!bbbbccccdddd")]
+        [InlineData("aaaabbbbccccdddd", "aaaa", "$!", 0, 16, "$!bbbbccccdddd")]
+        [InlineData("aaaabbbbccccdddd", "a", "", 0, 16, "bbbbccccdddd")]
+        [InlineData("aaaabbbbccccdddd", "b", null, 0, 16, "aaaaccccdddd")]
+        [InlineData("aaaabbbbccccdddd", "aaaabbbbccccdddd", "", 0, 16, "")]
+        [InlineData("aaaabbbbccccdddd", "aaaabbbbccccdddd", "", 16, 0, "aaaabbbbccccdddd")]
+        [InlineData("aaaabbbbccccdddd", "aaaabbbbccccdddde", "", 0, 16, "aaaabbbbccccdddd")]
+        [InlineData("aaaaaaaaaaaaaaaa", "a", "b", 0, 16, "bbbbbbbbbbbbbbbb")]
+        public static void Replace_CharSpan(string value, string oldValue, string newValue, int startIndex, int count, string expected)
+        {
+            StringBuilder builder;
+            if (startIndex == 0 && count == value.Length)
+            {
+                // Use Replace(ReadOnlySpan<char>, ReadOnlySpan<char>)
+                builder = new StringBuilder(value);
+                builder.Replace(oldValue.AsSpan(), newValue.AsSpan());
+                Assert.Equal(expected, builder.ToString());
+            }
+            // Use Replace(ReadOnlySpan<char>, ReadOnlySpan<char>, int, int)
+            builder = new StringBuilder(value);
+            builder.Replace(oldValue.AsSpan(), newValue.AsSpan(), startIndex, count);
+            Assert.Equal(expected, builder.ToString());
+        }
+
+        [Fact]
+        public static void Replace_CharSpan_StringBuilderWithMultipleChunks()
+        {
+            StringBuilder builder = StringBuilderWithMultipleChunks();
+            builder.Replace("a".AsSpan(), "b".AsSpan(), builder.Length - 10, 10);
+            Assert.Equal(new string('a', builder.Length - 10) + new string('b', 10), builder.ToString());
+        }
+
+        [Fact]
+        public static void Replace_CharSpan_StringBuilderWithMultipleChunks_WholeString()
+        {
+            StringBuilder builder = StringBuilderWithMultipleChunks();
+            builder.Replace(builder.ToString().AsSpan(), "".AsSpan());
+            Assert.Same(string.Empty, builder.ToString());
+        }
+
+        [Fact]
+        public static void Replace_CharSpan_StringBuilderWithMultipleChunks_LongString()
+        {
+            StringBuilder builder = StringBuilderWithMultipleChunks();
+            builder.Replace((builder.ToString() + "b").AsSpan(), "".AsSpan());
+            Assert.Equal(s_chunkSplitSource, builder.ToString());
+        }
+
+        [Fact]
+        public static void Replace_CharSpan_Invalid()
+        {
+            var builder = new StringBuilder(0, 5);
+            builder.Append("Hello");
+
+            AssertExtensions.Throws<ArgumentException>("oldValue", () => builder.Replace(new char[0].AsSpan(), new char[] { 'a' }.AsSpan())); // Old value is empty
+            AssertExtensions.Throws<ArgumentException>("oldValue", () => builder.Replace(new char[0].AsSpan(), new char[] { 'a' }.AsSpan(), 0, 0)); // Old value is empty
+
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("requiredLength", () => builder.Replace(new char[] { 'o' }.AsSpan(), new char[] { 'o', 'o' }.AsSpan())); // New length > builder.MaxCapacity
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("requiredLength", () => builder.Replace(new char[] { 'o' }.AsSpan(), new char[] { 'o', 'o' }.AsSpan(), 0, 5)); // New length > builder.MaxCapacity
+
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => builder.Replace(new char[] { 'a' }.AsSpan(), new char[] { 'b' }.AsSpan(), -1, 0)); // Start index < 0
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("count", () => builder.Replace(new char[] { 'a' }.AsSpan(), new char[] { 'b' }.AsSpan(), 0, -1)); // Count < 0
+
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => builder.Replace(new char[] { 'a' }.AsSpan(), new char[] { 'b' }.AsSpan(), 6, 0)); // Count + start index > builder.Length
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("count", () => builder.Replace(new char[] { 'a' }.AsSpan(), new char[] { 'b' }.AsSpan(), 5, 1)); // Count + start index > builder.Length
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("count", () => builder.Replace(new char[] { 'a' }.AsSpan(), new char[] { 'b' }.AsSpan(), 4, 2)); // Count + start index > builder.Length
+        }
+
         [Theory]
         [InlineData("Hello", 0, 5, "Hello")]
         [InlineData("Hello", 2, 3, "llo")]