Ensure F# Support

[TheCodeTraveler]

Let's ensure that CommunityToolkit.Maui has 1st Class support F# ❤️

In the Xamarin Community Toolkit, we learned that we must make a concerted effort to ensure that our library works with both F# and C# projects:

• [Bug] Cannot build F# project after installing xamarin.communitytoolkit NuGet package xamarin/XamarinCommunityToolkit#1124
• Add F# Project xamarin/XamarinCommunityToolkit#1181
• Fix XCT fails build in F# projects xamarin/XamarinCommunityToolkit#1133

I recommend making the following additions:

• Create CommunityToolkit.Maui.Samples.Fsharp
  • This ensures that the CommunityToolkit.Maui DLL compiles in F# projects
• Keep CommunityToolkit.Maui.UnitTests
  • This will remain our main Unit Test project
• Create CommunityToolkit.Maui.UnitTests.FSharp
  • This unit test project will exclusively test generated code for F# (because CommunityToolkit.Maui.UnitTests cannot accomplish that)

The new sample app, CommunityToolkit.Maui.Samples.Fsharp, doesn't need to replicate CommunityToolkit.Maui.Sample. Rather, it just needs to include a project reference to CommunityToolit.Maui to ensure that both CommunityToolkit.Maui and CommunityToolkit.Maui.Core successfully compile in an F# project.

And the new Unit Test project, CommunityToolkit.Maui.UnitTests.FSharp doesn't need to replicate code from CommunityToolkit.Maui.UnitTests, rather it just needs to test code generated by Source Generators for F#.

[pictos]

If I'm not wrong just C# support Source Generators (SG), so we need to pay attention when adding SG features like

• Implement TextColorTo  #224
  and think how we will work around them

[TheCodeTraveler]

Yes, good catch!

We should probably add an F# Unit Test Project too.

I think this'll structure will allow us to continue to writing our UnitTests in C# while ensuring all Tests pass for F#:

1. Convert CommunityToolkit.Maui.UnitTests to a Shared Project
   • I.e. CommunityToolkit.Maui.UnitTests.csproj -> CommunityToolkit.Maui.UnitTests.shproj
2. Create CommunityToolkit.Maui.UnitTests.Fsharp
   • Include ProjectReference to CommunityToolkit.Maui.UnitTests Shared Project
3. Create CommunityToolkit.Maui.UnitTests.Csharp
   • Include ProjectReference to CommunityToolkit.Maui.UnitTests Shared Project

[TheCodeTraveler]

Dang - I just tried the above architecture in the Add-F#-Unit-Test-Project branch and it doesn't work

tl;dr F# Projects don't compile .cs files

We can see in this screenshot that only UnitTests from the CommunityToolkit.Maui.UnitTests.Csharp project appear in the Test Explorer window.

And when running dotnet test against CommunityToolkit.Maui.UnitTests.Fsharp, we get the following error:

A total of 1 test files matched the specified pattern.
No test is available in /Users/bramin/GitHub/CommunityToolkit.Maui/src/CommunityToolkit.Maui.UnitTests.Fsharp/bin/Debug/net6.0/CommunityToolkit.Maui.UnitTests.Fsharp.dll.

> bramin@Brandons-MacBook-Pro CommunityToolkit.Maui.UnitTests.Fsharp % dotnet test
  Determining projects to restore...
  Restored /Users/bramin/GitHub/CommunityToolkit.Maui/src/CommunityToolkit.Maui.UnitTests.Fsharp/CommunityToolkit.Maui.UnitTests.Fsharp.fsproj (in 537 ms).
  2 of 3 projects are up-to-date for restore.
  CommunityToolkit.Maui.Core -> /Users/bramin/GitHub/CommunityToolkit.Maui/src/CommunityToolkit.Maui.Core/bin/Debug/net6.0/CommunityToolkit.Maui.Core.dll
  CommunityToolkit.Maui -> /Users/bramin/GitHub/CommunityToolkit.Maui/src/CommunityToolkit.Maui/bin/Debug/net6.0/CommunityToolkit.Maui.dll
  CommunityToolkit.Maui.UnitTests.Fsharp -> /Users/bramin/GitHub/CommunityToolkit.Maui/src/CommunityToolkit.Maui.UnitTests.Fsharp/bin/Debug/net6.0/CommunityToolkit.Maui.UnitTests.Fsharp.dll
Test run for /Users/bramin/GitHub/CommunityToolkit.Maui/src/CommunityToolkit.Maui.UnitTests.Fsharp/bin/Debug/net6.0/CommunityToolkit.Maui.UnitTests.Fsharp.dll (.NETCoreApp,Version=v6.0)
Microsoft (R) Test Execution Command Line Tool Version 17.0.0
Copyright (c) Microsoft Corporation.  All rights reserved.

Starting test execution, please wait...
A total of 1 test files matched the specified pattern.
No test is available in /Users/bramin/GitHub/CommunityToolkit.Maui/src/CommunityToolkit.Maui.UnitTests.Fsharp/bin/Debug/net6.0/CommunityToolkit.Maui.UnitTests.Fsharp.dll. Make sure that test discoverer & executors are registered and platform & framework version settings are appropriate and try again.

[TheCodeTraveler]

Here's a new architecture that would still ensure we test all of our code for F# compatibility:

• Create CommunityToolkit.Maui.Samples.Fsharp
  • This ensures that the CommunityToolkit.Maui DLL compiles in F# projects
• Keep CommunityToolkit.Maui.UnitTests
  • This will remain our main Unit Test project
• Create CommunityToolkit.Maui.UnitTests.FSharp
  • This unit test project will exclusively test generated code for F# (because CommunityToolkit.Maui.UnitTests cannot accomplish that)

Going forward, all new PRs that include Source Generators will be required to add Unit Tests to both CommunityToolkit.Maui.UnitTests and CommunityToolkit.Maui.UnitTests.FSharp. And all PRs that don't include Source Generators would only need to add UnitTests to to CommunityToolkit.Maui.UnitTests.

[VladislavAntonyuk]

Looks like F# doesn't support source generators: fsharp/fslang-suggestions#864

We depends on it, right?

[CliffAgius]

Closed as answered