This is a quirk in the reporting. When the assembly is missing from ref it seems like it misses getting the identifier correct. @ViktorHofer - probably a bug in APICompat's logging. Here's some sample output around this:

tePackage.targets(39,5): error CP0004: Assembly with name 'left' does not exist at System.ServiceModel.Duplex.
    C:\src\dotnet\wcf\.dotnet\sdk\10.0.100-alpha.1.24573.1\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.ApiCompat.ValidatePackage.targets(39,5): error CP0001: Type 'System.ServiceModel.CallbackBehaviorAttribute' exists on lib/netstandard2.0/System.ServiceModel.Duplex.dll but not on left

Probably we can rebase this PR on @mconnew which should fix these missing assemblies.

I think this is another bug in API compat tooling. WSTrustTokenParameters has the new keyword because when the class was first introduced, the base class didn't have a KeySize property. The base class did have a KeySize property exposed on NetFx and was brought back, so the definition in WSTrustTokenParameters needed the new keyword so that it didn't become binary incompatible. This hasn't changed single 6.1.0.

Yeah, it does seem to be off:

CP0002: Member 'System.Nullable<int> System.ServiceModel.Federation.WSTrustTokenParameters.KeySize.get' exists on [Baseline] lib/net8.0/System.ServiceModel.Federation.dll but not on lib/netstandard2.0/System.ServiceModel.Federation.dll

This has to do with comparing the previous net8.0 asset with the new netstandard2.0 asset. You'll only face this issue across this one baseline comparison. Details here dotnet/sdk#46834.

The next version will be 8.1.2. It looks like @HongGit doesn't update this version number until we're ready to build, so the comparison should be with 8.1.1 and not 8.1.0.

This looks like a genuine problem, this api is listed in the netstandard reference assembly but isn't public on .NET Framework, so should only be in our net8 reference assembly.

@ericstj, do you know what's going on with these three? As far as I can tell, these are correct. The CP0008 error means a base interface was removed from the interface hierarchy from one of the compared sides. Is this caused by Attribute no longer implementing the interface _Attribute? Is this an API compat tool bug as the interface is defined on Attribute, which is external to these packages so isn't a difference between WCF Client packages.

I'll have a closer look at this and the others. The logged messages give a bit more context - @ViktorHofer has improved human readability of the suppression files in later 10.0 releases.

A lot of times you still need to look at the metadata to understand what's going on. I'll have a review and add detail by mid-day tomorrow.

Yeah, it's System.Runtime.InteropServices._Attribute

Type 'System.Web.Services.Configuration.XmlFormatExtensionAttribute' does not implement interface 'System.Runtime.InteropServices._Attribute' on ref/netstandard2.0/System.Web.Services.Description.dll but it does on lib/net462/System.Web.Services.Description.dll

The reason we flag it is because when folks use references (ref folder) we do a strict comparison, because we expect folks want to expose all public API in their references that are in the lib. They can then suppress those that differ.

This particular package has this structure:

lib\net462
lib\netstandard2.0
ref\netstandard2.0

As a result, when looking at the lib\net462 implementation and say "all it's public API should be exposed by it's reference" - the ref\netstandard2.0 one. We see that _Attribute is not there -- thus this error.

You're doing a couple things I'd advise against:

1. If you use ref - you should really aim for 1/1 references with lib. Especially when it comes to netframework - to avoid the need to bring in the giant netstandard support facade set.
2. Don't use ref if you don't have to. We've really shied away from using ref just because there are too many .NET Framework design time tools that don't work well with reference assemblies. We only use ref for our targeting packs anymore.