Add Enum.Parse<T>() polyfill for .NET Framework builds (#5100)

[shaig-mahmudov]

Added a generic Enum.Parse<T> polyfill in the NUnit.Compatibility namespace, wrapped in a #if NETFRAMEWORK conditional. This allows the framework to use the generic API on .NET Framework builds where it is not natively available. Closes #5100

[OsirisTerje]

If you run build and build --target test locally, you will get the same errors you see in the build log here locally. Makes it easier and faster to fix them.

[stevenaw]

Thanks for your interest and prompt PR @shaig-mahmudov.
I've left a few suggestions on how to adjust the code a bit which should allow this to seamlessly "just work".

Terje has also left a few suggestions on how to build and test this locally. There's a few build warnings (which you may be able to see in your IDE too) which are being escalated to errors by our CI build.

[stevenaw]

This might be a "miss" on my part in the original spec. There's ambiguity errors reported by the compiler. You can likely help make them go away by changing this namespace to System so that it matches the namespace of the built-in Enum type.

[stevenaw]

If you convert this to use the C#14 extension member syntax then you can extend static methods onto Enum itself, similar to how we've added some of the classic asserts back onto the Assert class here: https://github.com/nunit/nunit/blob/main/src/NUnitFramework/nunit.framework.legacy/ClassicAssertExtensions.cs#L13-L19

Doing this will then allow you the update elsewhere in the code where we call Enum.Parse(typeof(EnumType), string) to instead call the generic Enum.Parse<EnumType>(string) method seamlessly

[stevenaw]

I'd recommend renaming this to EnumExtensions so that changing the namespace to System doesn't cause conflicts

[shaig-mahmudov]

Hi @stevenaw, I’ve applied the requested changes:
• Namespace: moved from NUnit.Compatibility to System to match the built-in Enum type and avoid ambiguity.
• Extension syntax: updated the implementation to use extension members so Enum.Parse() works seamlessly.
• Class name: renamed to EnumExtensions to avoid potential conflicts.
• Formatting: adjusted generic constraints (SA1127) to match the style guide.
• Local build: verified with dotnet build and dotnet build src/NUnitFramework/framework/nunit.framework.csproj across the relevant target frameworks.

Thanks for the guidance — happy to make further adjustments if needed.

[OsirisTerje]

@shaig-mahmudov Look at the code @stevenaw linked to, or just see image below:

This is the new syntax, and then you get rid of the this Enum _ too.

[stevenaw]

Thanks for your changes @shaig-mahmudov

Terje is right about the new syntax as it will allow these methods to appear as if they are static methods on the built-in Enum class itself despite that they aren't "built-in" on .NET Framework. The goal behind a polyfill like this is to allow code to call a method on all runtimes we support even if it's only built into .NET itself on newer ones.

In other words, we'd want to also able to update these references within this PR:

• nunit/src/NUnitFramework/framework/Internal/RuntimeFramework.cs

  Line 387 in 7cf7343

  return (RuntimeType)Enum.Parse(typeof(RuntimeType), s, true);

• nunit/src/NUnitFramework/framework/Api/FrameworkController.cs

  Line 115 in 7cf7343

  var traceLevel = (InternalTraceLevel)Enum.Parse(typeof(InternalTraceLevel), (string)traceLevelValue, true);

To instead call

• Enum.Parse<RuntimeType>(s, true)
• Enum.Parse<InternalTraceLevel>((string)traceLevelValue, true)

As appropriate without needing any #if NETFRAMEWORK checks around where we call the method.

[shaig-mahmudov]

@dotnet-policy-service agree

[shaig-mahmudov]

Hi @stevenaw, @TerjeP, I've updated the Enum.Parse polyfill as suggested:

• Switched to the extension(Enum) syntax in EnumExtensions.cs.
• Removed the this Enum _ parameter and updated the XML documentation.
• Updated the calls in RuntimeFramework.cs and FrameworkController.cs to use the cleaner Enum.Parse(...) syntax.
• Ready for another look. Thanks!"

[stevenaw]

Thanks @shaig-mahmudov
The extension method itself looks as expected. Can you please check and see if you forgot to commit any other changes on your end? We'd like to update the calls in RuntimeFramework.cs and FrameworkController.cs where we use the old Enum.Parse() to instead call your new version so that it can be used :)

[shaig-mahmudov]

@stevenaw Thanks for the feedback. I’ve updated the enum parsing in FrameworkController.cs and RuntimeFramework.cs to use the generic Enum.Parse<T>(..., true) syntax.

[stevenaw]

Thanks @shaig-mahmudov ! Your changes look good, I appreciate your quick responses to each feedback.
I've pushed a few minor edits just to remove some extra periods in the xmldocs. A final build is running now and I'll merge upon its successful completion.

Thanks for your contribution!

[shaig-mahmudov]

@stevenaw Thanks for the review, edits, and guidance! I appreciate it and I’m happy to contribute to the project.