Test Plan for Runtime Async

[333fred]

Test plan for runtime-generated async state machines

Runtime open issues: dotnet/runtime#109632
Runtime specification: https://github.com/dotnet/runtime/blob/main/docs/design/specs/runtime-async.md
Compiler implementation plan: https://github.com/dotnet/roslyn/blob/main/docs/compilers/CSharp/Runtime%20Async%20Design.md

Included in .NET 10 (feature in preview)

• turning feature on (see IsRuntimeAsyncEnabledIn)
  • presence of required AsyncHelpers APIs in corlib
  • honor RuntimeAsyncMethodGenerationAttribute attribute for override
  • check presence of feature flag runtime-async=on
  • check for return type
• codegen for async methods
  • set method flag MethodImplOptions.Async
  • calls optimized with Await
    • selection of appropriate helper
  • calls using AwaitAwaiter/UnsafeAwaitAwaiter
  • await in catch/finally
  • await using
  • await foreach
  • ref local lifting (Runtime async support for hoisting by-refs #79763)
• methods of validation
  • direct IL verification
  • verifier (caught some issues, although verification rules not yet updated to understand return value expectations: ILVerify support for runtime async runtime#118042)
• block unsupported scenarios for .NET 10 RC1
• disallow application of MethodImplOptions.Async in source
• public APIs
  • IOperation (no impact)
  • GetAwaitExpressionInfo
• consider removing or downgrading the "no await" warning (related issue) Remove CS1998 warning entirely and remove dependent C# code fix providers #80144
• analyzer work for RequiresPreviewFeatures (honor attribute on helper APIs)

Post-.NET 10

• PDBs/symbols for debugging (Debug experience for runtime async #79793)
  • sequence points
• instrumentation
• dynamic (Runtime async support for dynamic #79762)
• disallow directly calling MethodImplOptions.Async methods in some cases?
• disallow directly calling AsyncHelpers helper methods?
• manual smoke testing of various scenarios (debugging, EE, EnC)
• execution (pending availability of new runtime, Verify runtime execution of runtime async tests #79791)
• ensure that every async test also covers runtime-async
• remove RuntimeAsyncMethodGenerationAttribute and DOTNET_RuntimeAsync once feature is stable
• replace feature flag with a real switch and make the SDK set it by default
• use real MethodImplOptions.Async flag (Use MethodImplAttributes.Async #79792)
• partner validation (driven by runtime team)
• follow-up on public announcement
• codegen for async iterator methods (notes)

Async-iterators

• codegen
• debug info/symbols
• EnC