Annotate unsupported APIs in .Net core as Obsolete - Reflection area

[buyaa-n]

Fixes #50529

As part of #47228 we are annotating APIs not supported in .Net Core with [Obsolete] attribute

[dotnet-issue-labeler]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, to please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[joperezr]

Changes look good, assuming that this has gone through API review and that the breaking change has been approved.

[buyaa-n]

assuming that this has gone through API review and that the breaking change has been approved.

There was no API review, but we had an offline discussion that we want to Obsolete APIs not supported in .Net core for all platforms so that developers get warnings at design time instead of getting PNSE at runtime (from that perspective i think it is not breaking change). We filed issues for each area so that area owners handled it appropriately, main thing the area owners need to consider/make sure is the APIs are really not supported on any platform and not intended/planned to get supported in the future. For the APIs in this PR APIs in Assembly and Type are documented that it is not supported on .NetCore, APIs in StrongNameKeyPair not documented but doesn't look like supported on .Net Core, all of them has no associated issue for future support

[GrabYourPitchforks]

According to source.dot.net, there are only two instantiations of StrongNameKeyPair throughout the entirety of the indexed code bases, and both of them would have thrown PNSE anyway. So for these callers, changing the StrongNameKeyPair ctor is not a breaking change.

https://github.com/dotnet/msbuild/blob/9bcc06cbe19ae2482ab18eab90a82fd079b26897/src/Tasks/StrongNameUtils.cs#L68-L84
https://github.com/dotnet/msbuild/blob/9bcc06cbe19ae2482ab18eab90a82fd079b26897/src/Tasks/StrongNameUtils.cs#L99-L115

[GrabYourPitchforks]

A missing UrlFormat, but otherwise LGTM. Thanks!

[jeffhandley]

It looks like there's a check failing in src/mono/System.Private.CoreLib/src/System/RuntimeTypeHandle.cs where another pragma will be needed. But I preemptively approve based on that getting resolved.

[RussKie]

What course of action should the downstream consumers affected by this change take? E.g. dotnet/winforms is currently broken because StrongNameKeyPair is a part of our public API.

• Do we remove the public API?
• Do we mark it as obsolete? If so, what obsoletion message should we put, as the runtime obsoletion strings aren't available to us.

/cc: @terrajobst

[terrajobst]

You could also just suppress the obsoletion. I doubt anyone would care :-)

[RussKie]

I didn't consider it, that's an option too :)
Thanks!