[Bug] GenerateReferenceAssemblySource drops constraint

[terrajobst]

A community member pointed out to me that System.Enum.GetNames<TEnum>() dropped the Enum constraint while the implementation still has it.

Running Git Blame revealed that this changed in e5d59bd by @jkotas.

It looks like the tool has dropped this constraint but not in all cases.

It would be good to understand why that is so we don't inadvertently change the reference assemblies.

[ericstj]

We need to add APICompat support to check these: dotnet/sdk#39659

The latest GenAPI handles this scenario. I tested with a standalone lib that exposes a similar API and it emits:

        public static string[] GetNames<TEnum>()
            where TEnum : struct, System.Enum { throw null; }

So this gets fixed when we fix dotnet/sdk#31088

[jkotas]

It looks like the tool has dropped this constraint but not in all cases.

The genapi tooling has number of issues.

The reformatting was motivated by work on new unrelated APIs. I wanted the ref sources to be auto-generated, but then noticed a lot of formatting inconsistencies in System.Runtime ref sources. I tried to keep just the style changes only and revert everything else, but missed this one.

Thank you FlashOver for catching it!

[jkotas]

Fixed by #100844

The underlying problem is duplicate of issues listed in #100843 (comment) .