nCompile with package=TRUE when a free nFunction has an nClass argument fails

[perrydv]

reprex:

nc <- nClass(
  Cpublic = list(
    x = 'numericVector'
  )
)
nf <- nFunction(
  function(obj = 'nc') {
  }
)
comp <- nCompile(nc, nf, package = TRUE) # FAILS
comp$nf(comp$nc$new())

The problem is that RcppExports.cpp needs to see the header file for the nc nClass (which would be nClass_1_ or such), because std::shared_ptr<nClass_1_> appears in the code Rcpp::compileAttributes creates in RcppExports.cpp for nf. We have test coverage of passing nClasses as arguments, but evidently either that happens only for nClass methods (in which case only the new_<type> function for the class is in RcppExports.cpp) or the package=TRUE pathway is not used (in which case nCompile succeeds).

A possible solution would be to generate a standard all.h that can be included simply in RcppExports.cpp and that includes all generated headers.