Allow "SkipGeneratedSourcesCheck" for specific generator when a test is using multiple generators

[Youssef1313]

I have a case where I'm testing two generators in the same test, but I only want to verify the generated sources for one of them.

Currently, there is no way to do so.

[Youssef1313]

@sharwell Is this a reasonable request? If you can suggest an API shape, I can try to implement this.

[sharwell]

Can you provide more information about why it doesn't work to just validate both?

[sharwell]

Eventually, the incremental testing features should allow selecting and validating the outputs from a specific generator. Those APIs haven't been designed yet though.

[Youssef1313]

@sharwell Scenario:

• Uno Platform generates C# from XAML via a source generator.
• CommunityToolkit.Mvvm helps implementing Mvvm pattern and generates observable property by their own source generators.

If I try to use a property generated by Mvvm in XAML file (e.g, in x:Bind), the XAML source generator can't see that info and fails to generate.

I'm working around that by unoplatform/uno#11854. The trick is that I'm adding code to anticipate what will be generated instead of failing. https://github.com/unoplatform/uno/blob/284f2a4401b0efe75ac0ccb0ba31093de7821ba8/src/SourceGenerators/Uno.UI.SourceGenerators/XamlGenerator/ThirdPartyGenerators/CommunityToolkitMvvm/MvvmTypeProvider.cs

In tests, I'm referencing both Uno's XAML generator and CommunityToolkit.Mvvm's observable property generator. But it doesn't make sense to test the actual output from CommunityToolkit.Mvvm:

1. It's not code I care about as long as it compiles properly.
2. I don't want to have to update the expected output when I update the package version.
3. It needed unnecessary tweak to CSGenerator that you suggested for some who asked. unoplatform/uno@284f2a4

[sharwell]

I don't have any immediate plans to implement this, but I'll keep the use case in mind when we're building the new API to test incrementality.