SYSLIB0052: APIs that support obsolete mechanisms for Regex extensibility are obsolete

The following Regex and RegexRunner APIs are obsolete, starting in .NET 8. Calling them in code generates warning SYSLIB0052 at compile time. These APIs supported the now obsolete CompileToAssembly.

• Regex.InitializeReferences()
• Regex.UseOptionC()
• Regex.UseOptionR()
• RegexRunner.CharInSet(Char, String, String)
• RegexRunner.Scan(Regex, String, Int32, Int32, Int32, Int32, Boolean)
• RegexRunner.Scan(Regex, String, Int32, Int32, Int32, Int32, Boolean, TimeSpan)

Workaround

N/A

Suppress a warning

If you must use the obsolete APIs, you can suppress the warning in code or in your project file.

To suppress only a single violation, add preprocessor directives to your source file to disable and then re-enable the warning.

// Disable the warning.
#pragma warning disable SYSLIB0052

// Code that uses obsolete API.
// ...

// Re-enable the warning.
#pragma warning restore SYSLIB0052

To suppress all the SYSLIB0052 warnings in your project, add a <NoWarn> property to your project file.

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
   ...
   <NoWarn>$(NoWarn);SYSLIB0052</NoWarn>
  </PropertyGroup>
</Project>

For more information, see Suppress warnings.