"'opt*' redeclared without dllimport attribute: previous dllimport ignored" warnings in Cygwin

[Rangi42]

When I make rgbds in Cygwin x64 on Windows 8.1, it gives these warnings:

$ make
DEFS=-Dlr.type=ielr -Dparse.lac=full -Dparse.error=verbose
In file included from src/asm/main.c:33:
include/extern/getopt.h:29:14: warning: ‘optarg’ redeclared without dllimport attribute: previous dllimport ignored [-Wattributes]
   29 | extern char *optarg;
      |              ^~~~~~
include/extern/getopt.h:30:12: warning: ‘optind’ redeclared without dllimport attribute: previous dllimport ignored [-Wattributes]
   30 | extern int optind, opterr, optopt, optreset;
      |            ^~~~~~
include/extern/getopt.h:30:20: warning: ‘opterr’ redeclared without dllimport attribute: previous dllimport ignored [-Wattributes]
   30 | extern int optind, opterr, optopt, optreset;
      |                    ^~~~~~
include/extern/getopt.h:30:28: warning: ‘optopt’ redeclared without dllimport attribute: previous dllimport ignored [-Wattributes]
   30 | extern int optind, opterr, optopt, optreset;
      |                            ^~~~~~
include/extern/getopt.h:30:36: warning: ‘optreset’ redeclared without dllimport attribute: previous dllimport ignored [-Wattributes]
   30 | extern int optind, opterr, optopt, optreset;
      |                                    ^~~~~~~~
In file included from src/extern/getopt.c:36:
include/extern/getopt.h:29:14: warning: ‘optarg’ redeclared without dllimport attribute: previous dllimport ignored [-Wattributes]
   29 | extern char *optarg;
      |              ^~~~~~
include/extern/getopt.h:30:12: warning: ‘optind’ redeclared without dllimport attribute: previous dllimport ignored [-Wattributes]
   30 | extern int optind, opterr, optopt, optreset;
      |            ^~~~~~
include/extern/getopt.h:30:20: warning: ‘opterr’ redeclared without dllimport attribute: previous dllimport ignored [-Wattributes]
   30 | extern int optind, opterr, optopt, optreset;
      |                    ^~~~~~
include/extern/getopt.h:30:28: warning: ‘optopt’ redeclared without dllimport attribute: previous dllimport ignored [-Wattributes]
   30 | extern int optind, opterr, optopt, optreset;
      |                            ^~~~~~
include/extern/getopt.h:30:36: warning: ‘optreset’ redeclared without dllimport attribute: previous dllimport ignored [-Wattributes]
   30 | extern int optind, opterr, optopt, optreset;
      |                                    ^~~~~~~~

(For some reason they don't come up regarding every instance of #include "extern/getopt.h".)

[ISSOtm]

This is because we're re-implementing getopt. Dunno if/how this could be fixed, barring renaming all the symbols, which I'd like to avoid.

[pinobatch]

I renamed all the symbols when I imported a snapshot of this getopt reimplementation into my own project. See musl_getopt.c in pinobatch/little-things-nes.

[Rangi42]

Renaming all the symbols avoids any dependency on the ones declared by unistd.h. It also makes extern/getopt.c actually used, and thus checked by checkpatch.

(I had tried different combinations of declaring or not declaring some variables as extern, but nothing (a) gave no warnings on Cygwin and (b) compiled on all platforms.)