Apparent bug when reading multiple nl files with different external function libraries

[Robbybp]

First, thank you for maintaining this library. I am using ASL with a couple libraries of external functions. In a common workflow, I send several nl files to ASL in a sequence, each with its own set of libraries for external functions, which I communicate via the -i argument in the argv array passed to getstops. When an nl file's libraries include more libraries than the previous nl file, I get a function not available error message.

I have attached two nl files that can be used to produce this error: nlfiles.zip. The following code produces the error:

// asl_issue.cpp
#include <stdio.h>
#include <assert.h>
#include "asl_pfgh.h"
#include "getstub.h"

struct ASL_pfgh;
struct Option_Info;

int instantiate_asl(char *nlfile, char *amplfunc){
  printf("Instantiating ASL with file %s and amplfunc %s\n", nlfile, amplfunc);

  ASL_pfgh *asl = (ASL_pfgh *) ASL_alloc(ASL_read_pfgh);
  assert(asl);

  Option_Info* oi = new Option_Info;

  char *argv[] = { 
    (char *)"program_name",
    (char *)"-i",
    amplfunc,
    nlfile,
    NULL,
  };  
  char *stub = getstops(argv, oi);

  FILE *nl = jac0dim(stub, (int)strlen(stub));
  assert(nl);

  int ret = pfgh_read(nl, ASL_findgroups);

  delete oi; 

  return 0;
}

int main(){
  char nlfile1[] = "file1.nl";
  char amplfunc1[] = "/PATH/TO/.idaes/bin/cubic_roots.dylib";
  char nlfile2[] = "file2.nl";
  char amplfunc2[] = ( 
    "/PATH/TO/.idaes/bin/cubic_roots.dylib"
    "\n/PATH/TO/.idaes/bin/functions.dylib"
  );  

  int ret;
  ret = instantiate_asl(nlfile1, amplfunc1);
  ret = instantiate_asl(nlfile2, amplfunc2);

  return 0;
}

which is compiled with the following:

clang++ -o asl_issue \
    -I/PATH/TO/asl/src/solvers/sys.arm64.Darwin \
    asl_issue.cpp \
    /PATH/TO/asl/src/solvers/sys.arm64.Darwin/amplsolver.a

Here, amplsolver.a is compiled by running $ ./configure && make CFLAGS=-fPIC in the asl/src/solvers directory.

As the above suggests, I have prepared this example using Mac with Apple silicon. However, I have noticed this behavior on Linux as well (but have not tested the above example on Linux).
When I change the above code so that the first instantiate_asl call uses both function libraries, i.e.:

  int ret;
  ret = instantiate_asl(nlfile1, amplfunc2);
  ret = instantiate_asl(nlfile2, amplfunc2);

the program runs without error.

The nl files attached depend on libraries distributed by IDAES. They are typically downloaded by the idaes-pse Python package and put in the $HOME/.idaes/bin directory, via:

$ pip install idaes-pse
$ idaes get-extensions

Let me know if this is in fact a bug. I believe I am using the -i argument correctly.