Fix bug with IndexOf

Author: linkdotnet

CHANGELOG.md

@@ -9,6 +9,9 @@ All notable changes to **ValueStringBuilder** will be documented in this file. T
 ### Added
 -   Added `Reverse` function
 
+### Changed
+-   Fixed a bug where two empty strings return the wrong value in (Last)IndexOf
+
 ## [1.12.2] - 2023-02-21
 
 ### Changed

src/LinkDotNet.StringBuilder/NaiveSearch.cs

@@ -49,6 +49,11 @@ public static ReadOnlySpan<int> FindAll(ReadOnlySpan<char> text, ReadOnlySpan<ch
     /// <returns>The index of the found <paramref name="word"/> in <paramref name="text"/> or -1 if not found.</returns>
     public static int FindFirst(ReadOnlySpan<char> text, ReadOnlySpan<char> word)
     {
+        if (text.IsEmpty && word.IsEmpty)
+        {
+            return 0;
+        }
+
         if (text.IsEmpty || word.IsEmpty)
         {
             return -1;
@@ -86,6 +91,11 @@ public static int FindFirst(ReadOnlySpan<char> text, ReadOnlySpan<char> word)
     /// <returns>The index of the found <paramref name="word"/> in <paramref name="text"/> or -1 if not found.</returns>
     public static int FindLast(ReadOnlySpan<char> text, ReadOnlySpan<char> word)
     {
+        if (text.IsEmpty && word.IsEmpty)
+        {
+            return 0;
+        }
+
         if (text.IsEmpty || word.IsEmpty)
         {
             return -1;

tests/LinkDotNet.StringBuilder.UnitTests/ValueStringBuilderTests.cs

@@ -206,6 +206,16 @@ public void ShouldReturnMinusOneIfNotFound()
         index.Should().Be(-1);
     }
 
+    [Fact]
+    public void ShouldReturnZeroIfBothEmpty()
+    {
+        using var stringBuilder = new ValueStringBuilder();
+
+        var index = stringBuilder.IndexOf(string.Empty);
+
+        index.Should().Be(0);
+    }
+
     [Fact]
     public void ShouldReturnMinusOneWordIsLongerThanString()
     {
@@ -307,6 +317,16 @@ public void ShouldReturnZeroWhenEmptyStringInIndexOf()
         index.Should().Be(0);
     }
 
+    [Fact]
+    public void ShouldReturnZeroIfBothEmptyLastIndexOf()
+    {
+        using var stringBuilder = new ValueStringBuilder();
+
+        var index = stringBuilder.LastIndexOf(string.Empty);
+
+        index.Should().Be(0);
+    }
+
     [Fact]
     public void ShouldReturnZeroWhenEmptyStringInLastIndexOf()
     {