Assert failure while trying to iterate fields

A new user question. BTW is there a search for old threads?

I’m getting the failure:

void clang::RecordDecl::LoadFieldsFromExternalStorage() const: Assertion `hasExternalLexicalStorage() && Source && “No external storage?”’ failed.

when trying to iterate over a RecordDecl and not sure even what’s going on let along how to deal with it:

I’m proceeding from the example in

Here is some context:

Thanks in advance for any help