Merge pull request #2195 from Unity-Technologies/6000.0-backport-117367

[6000.0] Fix the System.String.Replace throwing NotImplementedException (mono#20960)

Author: UnityAlex

mcs/class/corlib/Test/System/StringTest.cs

@@ -3221,6 +3221,10 @@ public void Replace()
 
 		// Test replacing null characters (bug #67395)
 		Assert.AreEqual ("is this ok ?", "is \0 ok ?".Replace ("\0", "this"), "should not strip content after nullchar");
+
+		// System.String.Replace fails with NotImplementedException https://github.com/mono/mono/issues/20948
+		Assert.AreEqual ("Original", s1.Replace("o", "O", StringComparison.CurrentCulture), "Replace(string, string, StringComparison)");
+		Assert.AreEqual ("Original", s1.Replace("o", "O", false, CultureInfo.CurrentCulture), "Replace(string, string, bool, CultureInfo)");
 	}
 
 	[Test]

mcs/class/corlib/corefx/CompareInfo.cs

@@ -86,7 +86,7 @@ int LastIndexOfCore (string source, string target, int startIndex, int count, Co
 		unsafe int IndexOfCore (string source, string target, int startIndex, int count, CompareOptions options, int* matchLengthPtr)
 		{
 			if (matchLengthPtr != null)
-				throw new NotImplementedException ();
+				*matchLengthPtr = target.Length;
 
 			return internal_index_switch (source, startIndex, count, target, options, true);
 		}