Repro steps

Provide the steps required to reproduce the problem:

open System
open System.Threading.Tasks

[<EntryPoint>]
let main _ =

    let rec loop (x: int) = async {
        do! Task.CompletedTask |> Async.AwaitTask
        Console.WriteLine x
        return! loop(x+1)
    }
    
    Async.RunSynchronously (loop 0)
    0

with

<PackageReference Update="FSharp.Core" Version="5.0.2"/>

dotnet run -c Release (both Release and Debug are affected)

Expected behavior

It should work

Actual behavior

Stack Overflow!

Known workarounds

1. You could downgrade to 5.0.0 (Implicit in net5 SDK) or to 5.0.1 to make it work again:

<PackageReference Update="FSharp.Core" Version="5.0.0"/>

2. OR Change Completed task to fake async with real continuation

do! Task.CompletedTask |> Async.AwaitTask

to

do! Task.Delay 1 |> Async.AwaitTask

Related information

Call stack shows that all COMPLETED tasks continuations started its trampoline on a stack of previous trampoline which causes SO.

It actually crashed production system which was working on Pulsar.Client.Dotnet (it currently using 5.0.2)

I also tried to find related changes with GitHub help:
https://github.com/dotnet/fsharp/compare/5.0.0..5.0.2

But I couldn't find any related to FSharp.Core tags.

• macOs
• .NET5

UPDATED: 5.0.1 also works ok. So regression was introduced between 5.0.1 and 5.0.2

UPDATED2: suspect PR
#11142