Support F# `Async<'T>` as an awaitable type in minimal APIs

I'm opening this as a placeholder to ensure that the changes from https://github.com/dotnet/aspnetcore/pull/46898 make it into the release notes for 9.0. See also: https://github.com/dotnet/aspnetcore/issues/46773.

I see that 8.0 had #28596, so this issue should be linked to the equivalent for 9.0, if there ends up being one.

Additions

• Support F# Async<'T> as an awaitable type in minimal APIs endpoints.

Changes

• New runtime coercions: unit ⇝ void, when unit is the generic type argument of a generic awaitable type. These coercions apply both to minimal APIs endpoints as well as to controller action methods.

  • Task<unit> → Task
  • ValueTask<unit> → ValueTask
  • Async<unit> → Task

  With default serialization settings, endpoints with the return types Task<unit> or ValueTask<unit>, whose response body was formerly the JSON token null, will now return an empty response body instead.

EDIT by @Rick-Anderson to add the following metadata

Page URL

https://learn.microsoft.com/en-us/aspnet/core/fundamentals/minimal-apis?view=aspnetcore-9.0

Content source URL

https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/fundamentals/minimal-apis.md

Document ID

b09824ab-b051-75a1-13b7-b0e281cc46e0

Article author

Rick-Anderson

---

---

Associated WorkItem - 186857