Improved error message to help diagnose invalid winmd files

[kennykerr]

This is a small targeted improvement to the diagnostics produced by cppwinrt.exe to help apply the blame accurately when encountering types in a winmd that use non-WinRT types in an ABI context. For example, given this invalid C++/CX code (that sadly compiles):

namespace BadCppCxComponent
{
    public ref struct Class sealed
    {
        Class()
        {
        }

        Platform::Type^ GetInvalidType()
        {
            return nullptr;
        }
    };
}

The cppwinrt compiler now produces a more helpful diagnostic pinpointing the source of the problem:

C:\scratch>cppwinrt.exe -in BadCppCxComponent.winmd
 error: Type 'System.Type' could not be found
 method: GetInvalidType
 type: BadCppCxComponent.__IClassPublicNonVirtuals
 database: C:\scratch\BadCppCxComponent.winmd

Given a large winmd with hundreds of types, this can make a world of difference.

[DefaultRyan]

Nice. The other place where this sort of thing frequently seems to comes up is when trying to resolve base types. Any chance of adding an improved diagnostic there as well?

[kennykerr]

Thanks Ryan, send me the repro steps for that scenario I can certainly add something to help diagnose.