If a class annotated with "[Subclass<GObject.Object>]" is in the global namespace, then the GObject-2.0.Integration source generator fails. The generated .cs source file fails to compile, with an error like this:

GObject-2.0.Integration/GObject.Integration.SourceGenerator.Generator/ItemData.Subclass.g.cs(1,11): error CS1001: Identifier expected

That's because the generated .cs file begins with this, which is not valid C#:

namespace <global namespace>;

To see this problem, edit the GridView sample by removing the line "namespace GridViewSample;" from CustomObjectGridViewWindow.cs and StringListGridViewWindow.cs, then try to build it.