Result builder throwing null reference exception

[blair55]

I'm not sure if this is the right place but I've eliminated all libraries other than Expecto which I'm sure is not related. It only exists to help demonstrate.

Repro steps

Checkout this repo and run dotnet run -p tests.
https://github.com/blair55/ResultBuilder-IssueRepro

Expected behavior

The test case should pass.

Actual behavior

The test case fails with System.NullReferenceException: Object reference not set to an instance of an object.

Known workarounds

The issue can be resolved by moving all the code from src/Program.fs into tests/Main.fs and re-pointing the test at the new function.

Related information

Provide any related information

• Operating system: MacOS Sierra 10.12
• Version: dotnet core 2.1.302

[dsyme]

This is an unfortunate known issue when unit-testing Exe projects that don't have an explicit [<EntryPoint>] main method.

Either

1. Change your project to a Library, or
2. Give your Exe project an explicit [<EntryPoint>]

[dsyme]

cc @cartermp for visibility. It would be great if we could somehow give a proper error/warning about this

[blair55]

Thanks @dsyme, have resolved with option 2.

However, I couldn't get option 1 to work?

Happy to close if issue is a dupe.

[cartermp]

@blair55 if your project file is like this it should work:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>netstandard2.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <Compile Include="Program.fs" />
  </ItemGroup>

  <Import Project="..\.paket\Paket.Restore.targets" />
</Project>

[blair55]

@cartermp yep, you're right. Not sure what I was doing earlier but works with that tweak now 👍