error FS0073: internal error: Undefined or unsolved type variable when using records with generic type variables and backgroundTask

[moinessim]

Getting internal error when trying to compile generic type that uses backgroundTask expression.

open System.Text.Json

type Dto = {
    DtoValue : string
    Key : string
}

type MyGenericType<'Key,'Value> = {
    Value : 'Value
    Key : 'Key
}

type ProblematicType<'Key, 'Value, 'Dto, 'E>( fromDto : 'Dto -> Result<MyGenericType<'Key,'Value>,'E> ) =
    let myTask = 
        backgroundTask {
            let dto =  """{"DtoValue":"1","Key":"key1"}""" |> JsonSerializer.Deserialize<'Dto>
            return fromDto dto |> printfn "%A"
        }
    member __.ContainsKey = fun (key: 'Key) -> true


type MyType = MyGenericType<string,int>

module MyType =
    let fromDto (dto: Dto)  =
        try
            {
                Value = int dto.DtoValue
                Key = dto.Key
            } 
            |> Ok
        with | e -> Error e


let problem = ProblematicType<string,int,Dto,exn>(MyType.fromDto)

Provide the steps required to reproduce the problem:

1. Execute above code in FSI or try to compile in console app with dotnet build.

If possible attach a zip file with the repro case. This often makes it easier for others to reproduce.
The zip file should ideally represent the situation just before the call/step that is problematic.

Expected behavior

It should compile and run successfully.

Actual behavior

      backgroundTask {

--------^^^^^^^^^^^^^^

error FS0073: internal error: Undefined or unsolved type variable: 'Key

Known workarounds

Use task instead of backgroundTask expression.

Related information

.NET SDK (reflecting any global.json):
Version: 6.0.100
Commit: 9e8b04bbff

Runtime Environment:
OS Name: Mac OS X
OS Version: 11.5
OS Platform: Darwin
RID: osx.11.0-x64
Base Path: /nix/store/nwyx15pwbkfqxl818q2nhh3cmnmvygik-dotnet-sdk-6.0.100/sdk/6.0.100/

Host (useful for support):
Version: 6.0.0
Commit: 4822e3c3aa

.NET SDKs installed:
6.0.100 [/nix/store/nwyx15pwbkfqxl818q2nhh3cmnmvygik-dotnet-sdk-6.0.100/sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 6.0.0 [/nix/store/nwyx15pwbkfqxl818q2nhh3cmnmvygik-dotnet-sdk-6.0.100/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 6.0.0 [/nix/store/nwyx15pwbkfqxl818q2nhh3cmnmvygik-dotnet-sdk-6.0.100/shared/Microsoft.NETCore.App]

[dsyme]

Here's a much smaller repro:

let TestFunction<'Dto>() =
        backgroundTask {
            let dto = Unchecked.defaultof<'Dto>
            System.Console.WriteLine(dto)
        }

[TheAngryByrd]

This is also affecting cancellableTask and coldTask in IcedTasks. It is also affecting backgroundTaskResult backgroundTaskOption and cancellableTaskResult in FsToolkit.ErrorHandling. Oddly it is not affecting taskResult and taskOption.

open System.Threading
open System.Threading.Tasks
open FsToolkit.ErrorHandling
open IcedTasks

module Affected =
    let testFunctionCTR<'Dto>() =
            cancellableTaskResult {
                let dto = Unchecked.defaultof<'Dto>
                System.Console.WriteLine(dto)
            }

    let testFunctionCanT<'Dto>() =
            cancellableTask {
                let dto = Unchecked.defaultof<'Dto>
                System.Console.WriteLine(dto)
            }

    let testFunctionCoT<'Dto>() =
            coldTask {
                let dto = Unchecked.defaultof<'Dto>
                System.Console.WriteLine(dto)
            }

    let testFunctionBTR<'Dto>() =
            backgroundTaskResult{
                let dto = Unchecked.defaultof<'Dto>
                System.Console.WriteLine(dto)
            }
    let testFunctionBTO<'Dto>() =
            backgroundTaskOption{
                let dto = Unchecked.defaultof<'Dto>
                System.Console.WriteLine(dto)
            }
module NotAffected =
    let testFunctionTR<'Dto>() =
            taskResult {
                let dto = Unchecked.defaultof<'Dto>
                System.Console.WriteLine(dto)
            }
    let testFunctionTO<'Dto>() =
            taskOption {
                let dto = Unchecked.defaultof<'Dto>
                System.Console.WriteLine(dto)
            }