F# Compilation Failure: Multiple references to 'mscorlib.dll' are not permitted

I’m running into a scenario where adding a few NuGet packages to my F# function results in the following error being spit out multiple times during compilation:

2016-12-04T21:05:16.249 commandLineArgs(1,1): error FS215: Multiple references to 'mscorlib.dll' are not permitted

Here’s a project.json that reproduces the issue:

{
    "frameworks": {
        "net46": {
            "dependencies": {
                "FSharp.Data": "2.3.2",
                "FSharp.Data.SqlClient": "1.8.2",
                "Microsoft.Azure.Search": "3.0.1"
            }
        }
    }
}

It’s also worth noting that this happens regardless of what’s in the function itself, so is caused simply by adding the references.

Repro steps

1. Create a new F# function

2. Add the project.json file above

3. 💥

Expected behavior

The function should compile

Actual behavior

The function fails to compile

[fabiocav]

Agreed. The fix will primarily target the .NET package assembly resolver and metadata resolver, but I’ll also make some enhancements to the F# compilation service, including the logging enhancements mentioned above. My goal is to have this (and #890) addressed on the next update, which should happen before the end of the month.

[fabiocav]

@gshackles will have a fix for this ASAP and see if we can squeeze it in with the next release (which also brings some other F# fixes)

@stefan-akelius the process is a bit less “magical” than what described in the post 😃 For NuGet referenced packages, the behavior you get is similar to what you’d get with .NET Core or Visual Studio, where the appropriate package assemblies are referenced, so there’s no special way to reference those assemblies with a #r (or need to do so). I don’t want to hijack the issue, but I would like to hear more about what you dislike with the current process, as we’re always looking to improve (including exposing the right hooks to enable other flows and better integration with other tools like Packet, which is something that has been discussed) if you could either open an issue with more details or contact me directly at [e-mail], that would be great!