.NET Core mixed F# and C# project Intellisense not working

Question

Problem

Given:

• macOS 10.13.6
• VSCode 1.40.1
  • C# package (powered by Omnisharp) 1.21.7
  • Ionide-fsharp 4.3.1
• Mono 6.4.0.198 ( mono --version ) (installed via brew cask install mono-mdk or installed via the official macOS package)
• MSBuild 16.3.0 ( msbuild -version )

I seem to be unable to get intellisense working on VS Code in a project that has to use F# from C#. I have a project in F# and one in C#. And the C# one has a reference to the F# one (to use some of the symbols contained in it).

Everything runs and builds correctly

What I did is this:

• dotnet add reference the F# project to the C# project
• dotnet restore the solution that contains both
• dotnet build
• dotnet run

And everything works fine on the command line.

On the other hand on VSCode I get "missing reference" errors for symbols defined in the F# project.

What have I tried?

I tried every combination of the following sets:

1. Install Mono 6.4.0 (Visual Studio channel)
2. Install Mono 6.4.0 (Stable channel)
3. Install Mono from homebrew ( brew install mono )
4. Install Mono from homebrew ( brew cask install mono-mdk )

and:

1. Set "omnisharp.useGlobalMono": "always" in my settings.json for VS Code
2. Set "omnisharp.useGlobalMono": "auto" in my settings.json` for VS Code

Between each attempt I have:

• Cleaned all bin and obj folders from every project
• Uninstalled other versions of Mono and MSBuild

References

I've read the following references but none of the solutions worked:

• https://github.com/OmniSharp/omnisharp-vscode/issues/1623
• https://github.com/OmniSharp/omnisharp-roslyn/issues/1008
• https://github.com/OmniSharp/omnisharp-vscode/issues/371
• https://github.com/OmniSharp/omnisharp-vscode/issues/2075

Answer 1

Neither OmniSharp nor Ionide recognize or handle mixed C#/F# solutions. Doing so would be an enormous amount of work - the equivalent machinery in Visual Studio is built by a fully staffed team, something open source plugins cannot afford to do.

Answer 2

Try changing settings for F# Extension, "Fsac Runtime" to "Net"
or "Mono" can't remember... don;t have a Mac right now

It did it for me few days ago