Source Generator Issue with v8.4.1+ in Visual Studio 2022

[Banane9]

Hello everyone, I have scoured Google in search of anyone experiencing the same problem, but I haven't found anything - so I'm making this discussion post to see if anyone has any ideas how to solve this problem or figure out more details before creating a full issue.

Project Setup

WPF Application targeting .NET 8 for Windows, using Visual Studio 2022.
Also referencing some Serilog packages and WPF-UI, but I don't think those are relevant.

What Works

When referencing CommunityToolkit.Mvvm package at version 8.4.0 (or below), everything works as it should: Properties for fields have observable properties generated for them, etc. No issues while editing, builds work fine too.

Problem

When updating the package to version 8.4.1 or 8.4.2, the source generator doesn't seem to be working properly anymore. Me and multiple other people across multiple projects are not getting the observable properties generated during editing. This means Visual Studio constantly complains about those being missing wherever they're used (hundreds to thousands of errors with a lot of files open) - but everything works perfectly fine when compiling.

Curiously, the new versions are working fine for someone using Visual Studio 2026 - whether he's using that or Visual Studio 2022.
I also tried clearing the cache, deleting the bin/obj folders, etc., but it keeps coming up with the missing properties during editing.

[Sergio0694]

Are you able to share a minimal repro?

[Banane9]

Sure, here you go, but it's literally just the WPF Template with a CommunityToolkit.Mvvm PackageReference and an [ObservableObject] and example-[ObservableProperty] in the MainWindow.xaml.cs.

Screenshot of MainWindow.xaml.cs, even after a successful compile:

[Banane9]

Any ideas? 😅

I did try installing VS 2026 on my laptop too, and it worked there... but made VS 2022 just not compile anymore at all (thanks, Microsoft)

[Sergio0694]

Works fine for me. Are you using an old .NET SDK by any chance? IIRC there was some issue in some XAML precompile target that wasn't passing the source generators to it. Can you try building with the latest .NET SDK and checking?

[Banane9]

Sorry for the late reply, forgot that this was still open.

While your screenshot of the build output wasn't really useful, since that was always clean anyways, the SDK did seem to be the problem.

I deinstalled the 10.0.1xx version I had and installed 10.0.204 and with that it started working as it should. Testing with a colleague who had the same issue, installing 10.0.301 alone didn't help, we had to deinstall 10.0.109 too. Then it magically started working, even though 10.0.301 had already been what was showing up when running dotnet --version in the developer powershell in VS.