getopt: use name supplied with '-n' to report error

On Windows:

   $ getopt -o a -n my_script -- -z
   getopt: unknown option -- z

On Linux:

   $ getopt -o a -n my_script -- -z
   my_script: unknown option -- z

The difference arises because the Mingw-w64 implementation of
getopt(3) uses __argv[0] to report errors, not the first element
of the argument array passed to it.

Make __argv[0] point to the name supplied with the '-n' option to
match behaviour when glibc getopt(3) is used.

(GitHub issue #274)

1 files changed, 5 insertions, 0 deletions

diff --git a/util-linux/getopt.c b/util-linux/getopt.c
index 4148586d3..42e0a2730 100644
--- a/util-linux/getopt.c
+++ b/util-linux/getopt.c
@@ -412,6 +412,11 @@ int getopt_main(int argc, char **argv)
                         bb_simple_error_msg_and_die("missing optstring argument");
         }
 
+#if ENABLE_PLATFORM_MINGW32
+        // Mingw-w64 getopt(3) uses __argv[0] in error messages, not the
+        // first element of its argument array.
+        __argv[0] =
+#endif
         argv[n] = name ? name : argv[0];
         return generate_output(argv + n, argc - n, optstr, long_options);
 }