What's the purpose of adding TypeForwardedTo attributes?

[0xced]

In #86 you said

generate type forwards to ensure things work as expected in multi-targeting scenarios

Could you please elaborate a little bit more on this? What exact problem does it solve to add TypeForwardedTo attributes in target frameworks where the type exists?

For example, when multi-targeting net7.0;net6.0;netstandard2.0 the source generator produces this for .NET 6 and .NET 7 targets:

[assembly: global::System.Runtime.CompilerServices.TypeForwardedTo(typeof(global::System.Runtime.CompilerServices.IsExternalInit))]

If I add <PolySharpExcludeTypeForwardedToDeclarations>true</PolySharpExcludeTypeForwardedToDeclarations> they are not generated and everything seems to work fine. Am I missing something?

[OwnageIsMagic]

In case you generate attributes as public in lib A and have reference to them in another lib B (or generate as internal and use reflection).
With this attribute lib A will always have definition of IsExternalInitAttribute (real or forwarded). Without it, there is a possibility of TypeLoadException in some edge cases if A and B are updated separately, but I wold say in any sane deploy scheme this should not be a problem. Or maybe I missing something obvious.

[OwnageIsMagic]

Like if you publish lib A ver 1, but in ver 2 change PolySharp settings, so this type is no longer generated.
Lib B is transitive dep of app have dependency on A.v1, and app have direct dep on lib A.v2 -- assembly redirection would kick in and choose A.v2 and lib B will throw TypeLoadException.

[WeihanLi]

Find a document about the type forwarding, hope it helps
https://learn.microsoft.com/en-us/dotnet/standard/assembly/type-forwarding