Function project_declaration 

pub fn project_declaration(
    defs: &PackageDeclaration,
    availability: &dyn DocAvailability,
) -> Projection

Narrow defs to what availability allows. A callable stays when every capability its tags name is available, since a call checks each of them. A type stays when a remaining callable reaches it, or when no callable ever did, as with a type a package exports on its own.