SYSLIB diagnostics for regex source generation

The following table shows the diagnostic IDs for regex source-generation analyzers in .NET 7 and later versions. SYSLIB1045 automatically alerts you to places that you can use source generation to generate the regular expression engine implementation at compile time. The remaining diagnostics alert you to errors related to usage of the source generator.

Diagnostic ID	Description
SYSLIB1040	Invalid GeneratedRegexAttribute usage.
SYSLIB1041	Multiple GeneratedRegexAttribute attributes were applied to the same method, but only one is allowed.
SYSLIB1042	The specified regular expression is invalid.
SYSLIB1043	A GeneratedRegexAttribute method must be partial, parameterless, non-generic, and non-abstract, and return Regex.
SYSLIB1044	The regex generator couldn't generate a complete source implementation for the specified regular expression due to an internal limitation. See the explanation in the generated source for more details.
SYSLIB1045	Use GeneratedRegexAttribute to generate the regular expression implementation at compile time.

For more information about source generation for regular expressions, see .NET regular expression source generators.

Suppress warnings

It's recommended that you use one of the workarounds when possible. However, if you cannot change your code, you can suppress the warning through a #pragma directive or a <NoWarn> project setting. If the SYSLIB1XXX source generator diagnostic doesn't surface as an error, you can suppress the warning in code or in your project file.

To suppress the warnings in code (replace the diagnostic ID as necessary):

// Disable the warning.
#pragma warning disable SYSLIB1006

// Code that generates compiler diagnostic.
// ...

// Re-enable the warning.
#pragma warning restore SYSLIB1006

To suppress the warnings in a project file (replace the diagnostic IDs as necessary):

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
   <TargetFramework>net10.0</TargetFramework>
   <!-- NoWarn below suppresses SYSLIB1002 project-wide -->
   <NoWarn>$(NoWarn);SYSLIB1002</NoWarn>
   <!-- To suppress multiple warnings, you can use multiple NoWarn elements -->
   <NoWarn>$(NoWarn);SYSLIB1002</NoWarn>
   <NoWarn>$(NoWarn);SYSLIB1006</NoWarn>
   <!-- Alternatively, you can suppress multiple warnings by using a semicolon-delimited list -->
   <NoWarn>$(NoWarn);SYSLIB1002;SYSLIB1006;SYSLIB1007</NoWarn>
  </PropertyGroup>
</Project>

See also

• .NET regular expression source generators