Failure in differentiating call expression to a function object

[vaithak]

Results in the following assertion failure:

ReverseModeVisitor.cpp:1463: clad::StmtDiff clad::ReverseModeVisitor::VisitCallExpr(const clang::CallExpr*): Assertion `!utils::isArrayOrPointerType(arg->getType()) && "Arguments passed by pointers should be covered in pass by " "reference calls"' failed.

Minimal reproducible example (taken from #618) :

# include "clad/Differentiator/Differentiator.h"
# include <iostream>

struct FunObj {
   double operator()(double *x, size_t n)
   {  double ret = 0;
      for (size_t i = 0; i < n; i++) {
         ret += (i+1) * x[i];
      }
      return ret;
   }
};

double f(double *x, size_t n){
  FunObj f_obj;
  return f_obj(x, n);
}

int main() {
   size_t n = 3;
   double x[] = {1.0, 2.0, 3.0};
   double fx = f(x, n);
   std::cout << "f(x, n) = " << fx << "\n";

   auto f_dx = clad::gradient(f, "x");
   double dx[] = {0.0, 0.0, 0.0};
   clad::array_ref<double> dx_ref(dx, n);
   f_dx.execute(x, n, dx_ref);

   for(size_t i = 0; i < n; ++i)
      std::cout << "df/dx[" << i << "] = " << dx[i] << "\n";
   return 0;
}