error using MacPorts zlib, not present with system zlib?

[Adam Mercer]

Hi

Not sure of the correct place to discuss this but in tracking down a
build issue with a port I've found an interesting issue with MacPorts
zlib.

This simple test code illustrates the problem:

[ram at mimir tmp]$ cat test.c
#include <stdio.h>
#include <stdlib.h>
#include <zlib.h>

int main(void)
{
  void *file;
  int c;

  file = gzopen("test.dat.gz", "r");
  if (file == Z_NULL)
  {
    fprintf(stderr, "unable to open file\n");
    exit(1);
  }

  c = gzgetc(file);

  fprintf(stdout, "c = %c\n", c);

  gzclose(file);
}
[ram at mimir tmp]$ zcat test.dat.gz
test
file

If I compile this against the system zlib then it works as expected:

[ram at mimir tmp]$ clang -o test test.c -lz
[ram at mimir tmp]$ ./test
c = t

But not against the MacPorts zlib:

[ram at mimir tmp]$ clang -o test test.c -I/opt/local/include -L/opt/local/lib -lz
test.c:17:7: error: member reference base type 'void' is not a structure or
      union
  c = gzgetc(file);
      ^~~~~~~~~~~~
/opt/local/include/zlib.h:1655:11: note: instantiated from:
    ((g)->have ? ((g)->have--, (g)->pos++, *((g)->next)++) : gzgetc_(g))
     ~~~  ^
test.c:17:7: error: member reference base type 'void' is not a structure or
      union
  c = gzgetc(file);
      ^~~~~~~~~~~~
/opt/local/include/zlib.h:1655:24: note: instantiated from:
    ((g)->have ? ((g)->have--, (g)->pos++, *((g)->next)++) : gzgetc_(g))
                  ~~~  ^
test.c:17:7: error: member reference base type 'void' is not a structure or
      union
  c = gzgetc(file);
      ^~~~~~~~~~~~
/opt/local/include/zlib.h:1655:37: note: instantiated from:
    ((g)->have ? ((g)->have--, (g)->pos++, *((g)->next)++) : gzgetc_(g))
                               ~~~  ^
test.c:17:7: error: member reference base type 'void' is not a structure or
      union
  c = gzgetc(file);
      ^~~~~~~~~~~~
/opt/local/include/zlib.h:1655:51: note: instantiated from:
    ((g)->have ? ((g)->have--, (g)->pos++, *((g)->next)++) : gzgetc_(g))
                                             ~~~  ^
4 errors generated.
[ram at mimir tmp]$

Does anyone know why MacPorts zlib treats this as an error but the
system version doesn't?

Cheers

Adam