For authored WinRT components, will it be an issue that the new attributes takes an array of types? Array of types aren't allowed as attribute parameters in WinRT components as far as I know, and I remember we specifically hit this issue in the Microsoft Store as well. Unless that restriction was just due to .NET Native specifically and not something about WinRT components per se? 🤔

I assume the analyzer you mentioned would be to warn users if their types are not partial, because the generator wouldn't be able to add the necessary attributes to it?

Right, I believe the type would need to be marked partial for the source generator to add the attribute. There is always the option for the developer themselves to put the attribute if they want and I plan on updating the source generator to detect that and not put it itself.

For authored WinRT components, will it be an issue that the new attributes takes an array of types? Array of types aren't allowed as attribute parameters in WinRT components as far as I know, and I remember we specifically hit this issue in the Microsoft Store as well. Unless that restriction was just due to .NET Native specifically and not something about WinRT components per se? 🤔

Based on this from the docs "The types of a custom attribute's parameters and fields are limited to the WinRT fundamental types, enums, and references to other WinRT types. No other parameter or field type is allowed.", it sounds like array of types might not be allowed on an WinRT attribute. But in this case, the attribute we are putting will not be emitted to the WinMD to project, it will just be on the actual implementation type as a C# attribute (not a WinRT attribute).

This should possibly fix #1270, will need to validate.

Merging these changes for now to unblock my other PRs, but I will probably have an upcoming PR that will slightly change the design here to the below. This will allow to eliminate some of the remaining reflection to get the vftbl ptr and also be a design that we can eventually easily move to static interfaces from C# 11 when we can.

[global::WinRT.WinRTExposedType(typeof(ManagedPropertiesCCW))]
partial class ManagedProperties
{
}

public ManagedPropertiesCCW : IWinRTExposedTypeDetails
{
...
}