Add support for _POSIX2_VERSION, which lets you pick which POSIX

version you want the utilities to conform to.  Remove warnings about
failure to conform to a future POSIX version.

(ISO_8601_OPTION): Remove; no longer needed.
All uses changed to back to the corresponding short options.
(short_options): Remove; no longer needed.
(COMMON_SHORT_OPTIONS): New macro.

(usage): Document only the intersection of the
old and new behaviors, to encourage portability.
(main): Parse options using POSIX 1003.1-2001 rules if
conforming to that standard.  Do not warn of obsolete options.

src/date.c

@@ -79,20 +79,13 @@ static int iso_8601_format = 0;
 /* If non-zero, display time in RFC-(2)822 format for mail or news. */
 static int rfc_format = 0;
 
-/* For long options that have no equivalent short option, use a
-   non-character as a pseudo short option, starting with CHAR_MAX + 1.  */
-enum
-{
-  ISO_8601_OPTION = CHAR_MAX + 1
-};
-
-static char const short_options[] = "d:f:I" OPTARG_POSIX "r:Rs:u";
+#define COMMON_SHORT_OPTIONS "Rd:f:r:s:u"
 
 static struct option const long_options[] =
 {
   {"date", required_argument, NULL, 'd'},
   {"file", required_argument, NULL, 'f'},
-  {"iso-8601", optional_argument, NULL, ISO_8601_OPTION},
+  {"iso-8601", optional_argument, NULL, 'I'},
   {"reference", required_argument, NULL, 'r'},
   {"rfc-822", no_argument, NULL, 'R'},
   {"set", required_argument, NULL, 's'},
@@ -134,20 +127,11 @@ Display the current time in the given FORMAT, or set the system date.\n\
 \n\
   -d, --date=STRING         display time described by STRING, not `now'\n\
   -f, --file=DATEFILE       like --date once for each line of DATEFILE\n\
-"), stdout);
-      if (POSIX2_VERSION < 200112)
-	fputs (_("\
   -ITIMESPEC, --iso-8601[=TIMESPEC]  output date/time in ISO 8601 format.\n\
-  -I                        (obsolete) same as -Idate\n\
-"), stdout);
-      else
-	fputs (_("\
-  -I TIMESPEC, --iso-8601[=TIMESPEC]  output date/time in ISO 8601 format.\n\
-"), stdout);
-      fputs(_("\
-                            TIMESPEC=`date' (or missing) for date only,\n\
+                            TIMESPEC=`date' for date only,\n\
                             `hours', `minutes', or `seconds' for date and\n\
                             time to the indicated precision.\n\
+                            --iso-8601 without TIMESPEC defaults to `date'.\n\
 "), stdout);
       fputs (_("\
   -r, --reference=FILE      display the last modification time of FILE\n\
@@ -315,6 +299,9 @@ main (int argc, char **argv)
   int n_args;
   int status;
   int option_specified_date;
+  char const *short_options = (posix2_version () < 200112
+			       ? COMMON_SHORT_OPTIONS "I::"
+			       : COMMON_SHORT_OPTIONS "I:");
 
   program_name = argv[0];
   setlocale (LC_ALL, "");
@@ -337,12 +324,6 @@ main (int argc, char **argv)
 	batch_file = optarg;
 	break;
       case 'I':
-	if (POSIX2_VERSION < 200112 && OBSOLETE_OPTION_WARNINGS
-	    && ! optarg && ! getenv ("POSIXLY_CORRECT"))
-	  error (0, 0,
-		 _("warning: `-I' option is obsolete; use `--iso-8601'"));
-	/* Fall through.  */
-      case ISO_8601_OPTION:
 	iso_8601_format = (optarg
 			   ? XARGMATCH ("--iso-8601", optarg,
 					time_spec_string, time_spec)