Error accessing System.Configuration.ConfigurationManager in F# Script and F# Interactive on Visual Studio 16.8.0

[alexchro93]

In Visual Studio 16.8.0 error FS0039 is encountered when trying to access System.Configuration.ConfigurationManager after bringing in the NuGet package via #r "nuget: System.Configuration.ConfigurationManager".

Repro steps

1. Paste the following code in to an F# Scrip file in Visual Studio.

//
// ==== Bring in Dependency ====
//

#r "nuget: System.Configuration.ConfigurationManager"

//
// ==== Set Environment ====
//

System.Configuration.ConfigurationManager.AppSettings.Item "Environment" <- "LOCAL"

//
// ==== Get Environment ====
//

let env = System.Configuration.ConfigurationManager.AppSettings.Item "Environment"

match env with
| "LOCAL" -> printf $"In LOCAL environment"
| _ -> printf $"Environment unknown"

2. The following error appears in Visual Studio editor

3. Try to execute in F# interactive, the following error is shown

4. If you run the script via command line, everything works

Expected behavior

Expected to be able to execute above code in F# Interactive Window

Actual behavior

Cannot execute above code in F# Interactive Window

Known workarounds

I can just execute via command line, but that's no fun.

Related information

• Windows 10 Version 1909
• dotnet SDK 5.1.100
• Visual Studio 16.8.0

[cartermp]

Offhand this looks to be a quirk related to differences in dotnet fsi and fsi.exe, the latter of which is used by Visual Studio.

[KevinRansom]

The desktop build of fsi doesn't preload System.Configuration.dll, and never has.

To make this work on desktop FSI, add this at the top of the script:
#r @"C:\Windows\Microsoft.NET\Framework\v4.0.30319\System.Configuration.dll"

C:\Program Files (x86)\Microsoft Visual Studio\2019\Community>fsi

Microsoft (R) F# Interactive version 11.0.0.0 for F# 5.0
Copyright (c) Microsoft Corporation. All Rights Reserved.

For help type #help;;

> #r @"C:\Windows\Microsoft.NET\Framework\v4.0.30319\System.Configuration.dll"
- #r "nuget: System.Configuration.ConfigurationManager"
- open System.Configuration
- System.Configuration.ConfigurationManager.AppSettings.Item "Environment" <- "LOCAL";;

--> Referenced 'C:\Windows\Microsoft.NET\Framework\v4.0.30319\System.Configuration.dll' (file may be locked by F# Interactive process)

[Loading C:\Users\codec\AppData\Local\Temp\nuget\2408--83596b72-a4c3-4bc9-87f9-5c2a043adedd\Project.fsproj.fsx]
namespace FSI_0002.Project

val it : unit = ()

>

I will look at a fix in the product.