Exempt MemberNotNullWhen from genapi ref assembly requirements

[stephentoub]

As with MemberNotNull, MemberNotNullWhen is an implementation detail when it refers to a private member (even when attributed on a public API). The tooling shouldn't require it in reference assemblies, as in such situations it a) isn't meaningful to a consumer and b) leaks implementation details.

Fixes #67198 (comment)
cc: @bartonjs, @SteveDunn

[ghost]

Tagging subscribers to this area: @dotnet/area-infrastructure-libraries
See info in area-owners.md if you want to be subscribed.

Issue Details

---

As with MemberNotNull, MemberNotNullWhen is an implementation detail when it refers to a private member (even when attributed on a public API). The tooling shouldn't require it in reference assemblies, as in such situations it a) isn't meaningful to a consumer and b) leaks implementation details.

Fixes #67198 (comment)
cc: @bartonjs, @SteveDunn

Author:	stephentoub
Assignees:	stephentoub
Labels:	area-Infrastructure-libraries
Milestone:	-

[SteveDunn]

Thanks for this @stephentoub ! Should DisallowNullAttribute also be added? I added it to my PR and it fixed the compilation error I was getting:

error : Compat issues with assembly System.Security.Cryptography.Xml:
error : CannotRemoveAttribute : Attribute 'System.Diagnostics.CodeAnalysis.DisallowNullAttribute' exists on parameter 'value' on member 'System.Security.Cryptography.Xml.EncryptedReference.Uri.set(System.String)' in the implementation but not the reference

[stephentoub]

Should DisallowNullAttribute also be added?

No, that's part of the public signature. The tooling was highlighting a bug in your PR: you have DisallowNull in the implementation but you're missing it in the ref; you need to add it to the ref.