`ref` field support in .NET runtimes

[AaronRobinsonMSFT]

There are several moving parts to support ref fields, this issue represents work in the actual runtime.

The high-level tasks for the runtime are below to address the ref fields work.

• CoreCLR support
  • Port specific work from Hackathon project – https://github.com/dotnet/runtime/tree/feature/lowlevelhackathon
  • Add runtime support for ref fields #63985
  • Fix layout and GCInfo for ByRef fields. #64422
  • Prevent placing ref fields on non-pointer boundaries #64520
  • Validate IntPtr and ByRef field overlap #65246
• Mono support
  • Add runtime support for ref fields #63985
  • Prevent placing ref fields on non-pointer boundaries #64520
  • Validate IntPtr and ByRef field overlap #65246
  • Update tests to help uncover CrossGen2 scenario validation #65477
• API Proposal: Add ref field feature support to RuntimeFeature class #64165
• Audit handling of null byrefs in runtime and libraries Box helpers do not handle null-valued managed pointers #70268
• Tooling support
  • GenAPI needs to account for ref fields  #63751
  • [API Proposal]: Support ref fields in System.Reflection.Metadata.Ecma335.BlobEncoder #68309
  • Validate Linker support. Validate that linker correctly handles ref fields linker#2519
• ECMA update – Proposed changes to ECMA 335 for ref field support #63659
• Delete the ByReference<T> type and replace its use with ref fields.
  • Consume Roslyn with ref fields support #71498
• Diagnostics – Ensure SOS and VS can handle these new semantics.
  • Update SOS to resolve first level byref fields diagnostics#2829
  • Ensure ClrInstrumentationEngine handles ref fields microsoft/CLRInstrumentationEngine#464
  • GetTypeFields should return ELEMENT_TYPE_BYREF. #65880
  • EE doesn't display ref fields as expected. roslyn#62157
• C# test cases – Comprehensive collection of testing for the runtime.
• Update CrossGen
  • Add support for byref fields in NativeAOT/crossgen2 #64366
  • Fix layout and GCInfo for ByRef fields. #64422
  • Update tests to help uncover CrossGen2 scenario validation #65477
• Update NativeAOT – CoreCLR and Mono.
  • Add support for byref fields in NativeAOT/crossgen2 #64366
  • Update tests to help uncover CrossGen2 scenario validation #65477
• Language support - Merge features/ref-fields roslyn#62155
  • Low level struct improvements
  • Span<T> safety
  • Proposal for sunsetting restricted types when targeting net7

This contributes to enabling #45152.

[AaronRobinsonMSFT]

/cc @mangod9 @jaredpar @davidwrighton @steveharter @lambdageek @dotnet/interop-contrib @fanyang-mono

[jkotas]

Remove specialized type handling in runtime – Make ArgIterator, RuntimeArgumentHandle, and TypedReference “just types”.

I am not sure what this is about. The runtime does not have any special handling of these types. (Roslyn does - but you have it under separate check box.)

Also in the list should be: Delete the internal ByReference<T> type and replace its use with ref fields.

[jaredpar]

Remove specialized type handling in runtime – Make ArgIterator, RuntimeArgumentHandle, and TypedReference “just types”.

I believe @davidwrighton believes there is some spec work necessary before we can remove the notion of special types. Likely I think we will also need a feature flag in corelib to identify runtimes where Roslyn is safe to remove the notion of restricted types and depend solely on the type definition being correct. But agree bulk of the work here is in Roslyn.

[AaronRobinsonMSFT]

/cc @tommcdon @noahfalk for Diagnostics impact.

[vitek-karas]

We may possibly need dotnet/linker and mono/cecil work - it needs to be able to roundtrip assembly with ref fields correctly. I know it's not specifically about runtime - but it will be needed in order to use it in the runtime (since we run the code through linker during build).

[AaronRobinsonMSFT]

We may possibly need dotnet/linker and mono/cecil work

This was brought up in the initial planning meeting. If I recall, @davidwrighton wasn't sure there should be any impact.