Using version of FSharp.Compiler.Service higher than 9.0.1 causes exception

Using a version of FSharp.Compiler.Service (FCS) higher than 9.0.1 in an Azure Function potentially causes runtime exceptions, because the Azure WebJobs SDK relies on FCS 9.0.1. Compilation succeeds, but version 9.0.1 is loaded at runtime instead of 11.0.6, which causes crashes when using functionality available in 11.0.6 but not in 9.0.1.

Repro steps

1. Create an F# Azure Function with manual trigger (or any other).
2. Add a dependency to FSharp.Compiler.Service via project.json, latest version.

{
  "frameworks": {
    "net46":{
      "dependencies": {
        "FSharp.Compiler.Service": "11.0.6"
      }
    }
  }
}

1. In the code, use any feature present in FSC 11.0.6 but not in FSC 9.0.1 (see http://stackoverflow.com/q/42755884/114519 for an example)
2. Save: compilation succeeds
3. Run: exception is triggered, such as:

Exception while executing function: Functions.fsc-1. mscorlib: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.

Expected behavior

Compilation error.

Actual behavior

Successful compilation but runtime exception.

Known workarounds

Reverting to FSC 9.0.1

Related information

The following answer on StackOverflow describes the issue in more detail, with related information: http://stackoverflow.com/a/42894076/114519

• Programming language used: F#
• Links to source: https://github.com/mathias-brandewinder/fsibot-serverless/tree/98d5dc40226358c6e44b73a796197c01eb7658d1/process-mention

I can provide a smaller repro, if needed.

[christopheranderson]

Should improve the error handling on this.

[mathias-brandewinder]

I think warnings would be a great start, this caused quite a bit of head-scratching on my end 😃 More broadly, do you have any advice or plans to support a scenario like this one, where I’d want to use a version of a package that is not the same as the one that ships by default?