FSharpCompilerService not working on .NETCore 3.1.12 due to mismatch version of the App ref directory

[gmoneh]

Runtime: .NET Core 3.1.12

When using FSharp Compiler Services (in my case via FsiEvaluationSession.Create() ), a System.IO.DirectoryNotFoundException: 'Could not find a part of the path 'C:\Program Files\dotnet\packs\Microsoft.NETCore.App.Ref\3.1.12\ref'.' is thrown.

The reason for this is the algorithm used to find the ref directory. According to this comment in the FSharp.Compiler.Service/DotNetFrameworkDependencies.fs:

// use the well know location for obj to traverse the file system towards the
//
// packs\Microsoft.NETCore.App.Ref\sdk-version\netcoreappn.n
// we will rely on the sdk-version match on the two paths to ensure that we get the product that ships with the
// version of the runtime we are executing on

The problem is that, in a .NETCore 3.1.12 installation, those do not match, rendering this algorithm incorrect.

On my computer, for example, the location of obj (.NET base implementation) is C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App\3.1.12.

According to the algorithm implemented in the file referenced above, it goes to look for these dependencies at: 'C:\Program Files\dotnet\packs\Microsoft.NETCore.App.Ref\3.1.12\ref', but this directory does not exist. The .NET Core directory on that folder is 'C:\Program Files\dotnet\packs\Microsoft.NETCore.App.Ref\3.1.10\ref'.

[baronfel]

Please open this issue in dotnet/fsharp, this repo is no longer in active development.