Implement POSIX mode for the getopts built-in

When a POSIX shell script that uses getopts is passed one of the
AST self-documentation options (like --help), then the script
aborts and ksh prints a usage message generated from the options
string, which will not contain any self-documentation if it's a
POSIX script. The script is prevented from throwing an error and
showing its own usage message, which may be a lot more informative.
This is a clear incompatibility with the POSIX spec that should be
fixed in the POSIX mode.

We can't fix this purely in ksh93; the libast optget function also
needs to learn about the POSIX mode.

src/lib/libast/include/option.h,
src/lib/libast/misc/optlib.h,
src/lib/libast/misc/optget.c:
- Remove useless padding from Optstate_t; it was ostensibly for ABI
  compatibility with old libast versions, but we abandoned that.
- Add a 'posix' flag to Optstate_t, so ksh93 can set opt_info.posix
  to activate the POSIX mode in optget.
- optget():
  - If the posix flag is set, only process short options with a
    single '-' prefix, as specified by POSIX. This disables the AST
    self-doc options, too.
  - Let the posix flag disable special handling of '-?' as well.

src/cmd/ksh93/bltins/getopts.c:
- b_getopts(): Set the opt_info.posix flag to 1 if the 'posix'
  shell option is on *and* the options string passed does not use
  the extended ksh interface (as flagged by the 'extended'
  variable). This way, scripts running in POSIX mode may still
  optionally offer ksh-style long options and self-documentation
  (for example, many of ksh's own build scripts do this).

Author: McDutchie

NEWS

@@ -9,6 +9,12 @@ Uppercase BUG_* IDs are shell bug IDs as used by the Modernish shell library.
   such as --help or --man, 'getopts' will no longer stop the execution of any
   commands that follow the function call on the same command line.
 
+- The shell's POSIX mode has been amended to disable long options (including
+  --help, etc., which would abort the script), which are incompatible with
+  the POSIX spec and may prevent POSIX scripts from printing their own usage
+  message. This is only disabled if the --posix option is on *and* getopts is
+  given an options string that does not use ksh's extended getopts interface.
+
 2026-04-22:
 
 - Fixed a bug that causes the loss of the contents of all here-documents

src/cmd/ksh93/bltins/getopts.c

@@ -115,13 +115,15 @@ int	b_getopts(int argc,char *argv[],Shbltin_t *context)
 	{
 		sh_popcontext(&buff);
 		sh.st.opterror = 1;
+		opt_info.posix = 0;
 		if(r==0)
 			return 2;
 		pp = (struct checkpt*)sh.jmplist;
 		pp->mode = longjmpmode;
 		sh_exit(2);
 	}
 	opt_info.disc = &disc;
+	opt_info.posix = sh_isoption(SH_POSIX) && !extended;
 	switch(opt_info.index>=0 && opt_info.index<=argc?(opt_info.num= LONG_MIN,flag=optget(argv,options)):0)
 	{
 	    case '?':
@@ -210,5 +212,6 @@ int	b_getopts(int argc,char *argv[],Shbltin_t *context)
 		nv_putval(np, opt_info.arg, NV_RDONLY);
 	sh_popcontext(&buff);
 	opt_info.disc = 0;
+	opt_info.posix = 0;
 	return r;
 }

src/cmd/ksh93/sh.1

@@ -6852,7 +6852,7 @@ is used for each of the parameters that requires
 \f3getopts\fP \*(OK \f3\-a\fP \f2name\^\fP \*(CK \f2optstring vname\^\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK
 Checks
 .I arg
-for legal options.
+for valid options.
 If
 .I arg
 is omitted,
@@ -8137,6 +8137,11 @@ or
 .B TERM
 signal;
 .IP \[bu]
+causes the \fBgetopts\fR built-in command to disable the built-in handling
+of \fB-?\fR and long-form options (including the self-documentation options
+such as \fB--help\fR), unless the options string given to \fBgetopts\fR uses
+the extended interface;
+.IP \[bu]
 disables the special handling of \f3/dev/fd/\fP\f2n\fP in file existence and
 access test operators in \fBtest\fR/\fB[\fR and \fB[[\fR, causing these to
 operate on the file \f3/dev/fd/\fP\f2n\fP in the file system;

src/cmd/ksh93/tests/posix.sh

@@ -248,6 +248,14 @@ for c in a e f g A E F G
 do	printf "%$c" 1.5 2>/dev/null || err_exit "POSIX printf %$c fails to accept floating point operand"
 done >/dev/null
 
+# causes the getopts built-in command to disable the built-in handling of '-?' and long-form
+# options (including the self-documentation options such as --help), unless the options string
+# given to getopts uses the extended interface;
+got=$("$SHELL" -o posix -c 'while getopts x o; do case $o in \?) echo "MY USAGE MESSAGE";; esac; done' sh -\? 2>&1)
+[[ $got == *$'\nMY USAGE MESSAGE' ]] || err_exit "POSIX getopts fails to let script handle -? itself (got $(printf %q "$got"))"
+got=$("$SHELL" -o posix -c 'while getopts x o; do case $o in \?) echo "MY USAGE MESSAGE";; esac; done' sh --help 2>&1)
+[[ $got == *$'\nMY USAGE MESSAGE' ]] || err_exit "POSIX getopts fails to let script handle --help itself (got $(printf %q "$got"))"
+
 # changes the test/[ built-in command to make its deprecated expr1 -a expr2 and expr1 -o expr2 operators work
 # even if expr1 equals "!" or "(" (which means the nonstandard unary -a file and -o option operators cannot
 # be directly negated using ! or wrapped in parentheses);

src/lib/libast/include/option.h

@@ -46,11 +46,8 @@ typedef struct Optdisc_s
 	Optinfo_f	infof;		/* runtime info function	*/
 } Optdisc_t;
 
-/* NOTE: Opt_t member order fixed by a previous binary release */
-
 #ifndef _OPT_PRIVATE_
-#define _OPT_PRIVATE_	\
-	char		pad[3*sizeof(void*)];
+#define _OPT_PRIVATE_
 #endif
 
 typedef struct Opt_s
@@ -67,7 +64,7 @@ typedef struct Opt_s
 	Optdisc_t*	disc;		/* user discipline		*/
 	intmax_t	number;		/* # numeric argument		*/
 	unsigned char	assignment;	/* option arg assignment op	*/
-	unsigned char	pads[sizeof(void*)-1];
+	char		posix;		/* set for POSIX compliance	*/
 	_OPT_PRIVATE_
 } Opt_t;
 

src/lib/libast/misc/optget.c

@@ -323,12 +323,7 @@ static Msg_t		C_LC_MESSAGES_libast[] =
 	{ C("version") },
 };
 
-/*
- * 2007-03-19 move opt_info from _opt_info_ to (*_opt_data_)
- *	      to allow future Opt_t growth
- */
-
-static Opt_t	_opt_info_ = { 0,0,0,0,0,0,0,{0},{0},0,0,0,{0},{0},&state };
+static Opt_t	_opt_info_ = { 0,NULL,NULL,0,NULL,0,0,{0},{0},NULL,0,0,0,&state };
 Opt_t*		_opt_infop_ = &_opt_info_;
 
 Optstate_t*
@@ -4404,7 +4399,21 @@ optget(char** argv, const char* oopts)
 			}
 			if (!(s = argv[opt_info.index]))
 				return 0;
-			if (!prefix)
+			if (opt_info.posix)
+			{
+				/*
+				 * POSIX mode: only short options with single '-' prefix are recognized
+				 */
+
+				if (!prefix || *s != '-')
+				{
+					opt_info.index++;
+					return 0;
+				}
+				prefix = 1;
+				n = 1;
+			}
+			else if (!prefix)
 			{
 				/*
 				 * long with no prefix (dd style)
@@ -4552,7 +4561,7 @@ optget(char** argv, const char* oopts)
 	 *	v	long option value (via =) if w != 0
 	 */
 
-	if (c == '?')
+	if (c == '?' && !opt_info.posix)
 	{
 		/*
 		 * ? always triggers internal help

src/lib/libast/misc/optlib.h

@@ -103,7 +103,6 @@ typedef struct Optstate_s
 } Optstate_t;
 
 #define _OPT_PRIVATE_ \
-	char            pad[2*sizeof(void*)]; \
 	Optstate_t*	state;
 
 #include <error.h>