Fsharp: Compile error: "primDestForallTy: not a forall type"

[JoakimSjo]

On _dotnet build_ or _dotnet run yarn-watch_ compiler fails with an internal error.

Repro steps

1. Clone my repository from here

2. Run _dotnet build_ or _dotnet run yarn-watch_ inside "src" folder.

Expected behavior

Compilation succede.

Actual behavior

Compilation fails with following error:

Microsoft (R) Build Engine version 15.9.20+g88f5fadfbe for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  Restore completed in 24.31 ms for /Users/joakimsjohaug/Projects/fsharp/nobina/app/src/app.fsproj.
  Restore completed in 48.86 ms for /Users/joakimsjohaug/Projects/fsharp/nobina/app/src/app.fsproj.
error FS0192 : internal error : primDestForallTy: not a forall type [/Users/joakimsjohaug/Projects/fsharp/nobina/app/src/app.fsproj]

Build FAILED.

error FS0192 : internal error : primDestForallTy: not a forall type [/Users/joakimsjohaug/Projects/fsharp/nobina/app/src/app.fsproj]
    0 Warning(s)
    1 Error(s)

Time Elapsed 00:00:04.90

Related information

• Operating system: macOS 10.14.4
• Branch: master
• .NET: 2.2.103
• Editing Tools: Visual Studio Code

[forki]

I looked at this yesterday and it's easy to reproduce. Unfortunately it
does not show line numbers. It also does not reproduce in the IDE. Only if
you run a build. I tried to make the repro smaller but failed.

Joakim Sjøhaug [e-mail] schrieb am Sa., 13. Apr. 2019,
23:57:

On dotnet build or dotnet run yarn-watch compiler fails with an
internal error.
Repro steps

1.

Clone my repository from here
https://github.com/JoakimSjo/fable-react-nobinaApp
2.

Run dotnet build or dotnet run yarn-watch inside "src" folder.

Expected behavior

Compilation succede.
Actual behavior

Compilation fails with following error:

Microsoft (R) Build Engine version 15.9.20+g88f5fadfbe for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

Restore completed in 24.31 ms for /Users/joakimsjohaug/Projects/fsharp/nobina/app/src/app.fsproj.
Restore completed in 48.86 ms for /Users/joakimsjohaug/Projects/fsharp/nobina/app/src/app.fsproj.
error FS0192 : internal error : primDestForallTy: not a forall type [/Users/joakimsjohaug/Projects/fsharp/nobina/app/src/app.fsproj]

Build FAILED.

error FS0192 : internal error : primDestForallTy: not a forall type [/Users/joakimsjohaug/Projects/fsharp/nobina/app/src/app.fsproj]
0 Warning(s)
1 Error(s)

Time Elapsed 00:00:04.90

Related information

• Operating system: macOS 10.14.4
• Branch: master
• .NET: 2.2.103
• Editing Tools: Visual Studio Code

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[TIHan]

I can look at this one.

[cartermp]

@JoakimSjo Do you still see this one? The repro has some older dependencies and it could be that a fix is in place, but not present in the current project.

[Zaid-Ajaj]

I just came across this issue and have no idea where to go from here :/ using latest net5 sdk and it seems like another FSharp.Core version resolution issue.

[dsyme]

I just came across this issue and have no idea where to go from here :/ using latest net5 sdk and it seems like another FSharp.Core version resolution issue.

Could you make a minimal repro? And try changing referenced FSharp.Core to see if that makes a difference? Also --langversion:4.7

Just anything to reduce the matrix of possibilities and causes

[dsyme]

Also, it may be possible to propagate a range parameter down to primDestForallTy to give a better location error on this failure.

[cartermp]

I've only ever seen this manifest in fable projects (via bug reports) and so there is likely some subtle issue in the interplay of FSharp.Core there

[ThisFunctionalTom]

We have the same issue in our project and we found out following:

• We use sdk 3.1 to compile our solution
• We have this problem only with our Client.fsproj (it is a Fable project referencing Fable.Core 3.2.0)
• When compiling Client.fsproj we get "primDestForallTy" error
• When we changed reference in Client.fsproj to Fable.Core 3.1.6 everything works
• Fable.Core 3.2.0 depends on FSharp.Core >= 5.0
• Fable.Core 3.1.6 depends on FSharp.Core >= 4.7.1

TLDR: Changing reference to Fable.Core 3.1.6 solved our problem 😅

I hope this information can help finding the issue.

[ThisFunctionalTom]

I followed the trail and made a smallest repro I could come up with.

In the App.fs if you comment out Program.withDebugger compilation works and with this line it does not.

module App

open Elmish
open Elmish.React

#if DEBUG
open Elmish.Debug
#endif

Program.mkProgram Index.init Index.update Index.view
|> Program.withReactSynchronous "elmish-app"
// #if DEBUG
// |> Program.withDebugger
// #endif
|> Program.run

also with Fable.Core 3.1.6 compilation works and with 3.2.0 it does not.

<?xml version="1.0" encoding="utf-8"?>
<Project Sdk="Microsoft.NET.Sdk">
    <PropertyGroup>
        <TargetFramework>netcoreapp3.1</TargetFramework>
    </PropertyGroup>
    <ItemGroup>
        <Compile Include="Index.fs" />
        <Compile Include="App.fs" />
    </ItemGroup>
    <ItemGroup>
      <PackageReference Include="Fable.Core" Version="3.1.6" />
      <PackageReference Include="Fable.Elmish" Version="3.1.0" />
      <PackageReference Include="Fable.Elmish.Debugger" Version="3.2.0" />
      <PackageReference Include="Fable.Elmish.React" Version="3.0.1" />
      <PackageReference Include="Fable.React" Version="7.2.0" />
    </ItemGroup>
</Project>

So, I guess it has to be something with Fable.Core 3.2.0 and implementation of Program.withDebugger in Fable.Elmish.Debugger.

[ThisFunctionalTom]

I tried following:
Remove Fable.Elmish.Debugger nuget package and add the two source files Fable.Import.fs and Elmish.Debugger.fs from elmish/debugger repo branch v3.x to my project and then everything works again. 🤔