A Source Generator should add code to the compilation of a WPF application when one of the app's XAML files is declaring an app-local namespace

[dev-mano]

Versions Used:

VS versions 16.8.2 and 16.9.0 Preview 1.0
Microsoft.CodeAnalysis.Analyzers version 3.3.1
Microsoft.CodeAnalysis.CSharp.Workspaces version 3.8.0

Steps to Reproduce:

1. Create a new project using the 'WPF App (.NET)' template in VS
2. Add a source generator to the project as described in the Source Generators Cookbook
3. Manually add code to the app that depends on code generated by the source generator in order to compile correctly, e.g. by implementing an interface like INotifyPropertyChanged, as shown in the Source Generators Cookbook examples.
4. Compile the project.

Expected Behavior:

The source generator adds code to the compilation and the build succeeds.

Actual Behavior:

The build emits error messages due to missing code that the source generator was supposed to generate, but didn't.
The build will succeed though if the following, not used 'local' namespace declaration is removed from app.xaml:
xmlns:local="clr-namespace:NameOfWpfApp"

The behavior is the same for these flavors of .NET used by the test app: .NET Core 3.1, .NET 5, .NET Framework 4.7.2.

[jaredpar]

@chsienki is the same WPF issue that we are fixing for 16.9?

[chsienki]

Yes, I believe this is the same issue as dotnet/wpf#3404

I'm not sure why removing the namespace makes it succeed, but I assume it causes the generated XAML code to not reference something it is failing with. This isn't a Roslyn issue, but a WPF one. Closing as a dupe of the above issue.