Restore 'set -b'/'set -o notify' functionality (#74)

'set -b' had no effect; it should cause the shell to notify job
state changes immediately instead of waiting for the next prompt.

This fixes a regression that was introduced in ksh93t 2008-07-25.
The bugfix is from: https://github.com/att/ast/pull/1089

src/cmd/ksh93/sh/jobs.c:
- Save the tty wait state and avoid changing it if TTYWAIT was
  already on to avoid breaking 'set -b'.
  The last 'sh_offstate' is inside of an '#if' directive because it
  is only required when ksh is compiled with SHOPT_COSHELL enabled.

src/cmd/ksh93/tests/pty.sh:
- Add a regression test for 'set -b' in interactive shells.

NEWS

@@ -3,6 +3,10 @@ For full details, see the git log at: https://github.com/ksh93/ksh
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2020-07-14:
+
+- Fixed a bug that caused 'set -b' to have no effect.
+
 2020-07-13:
 
 - Fixed a fork bomb that could occur when the vi editor was sent SIGTSTP

src/cmd/ksh93/include/version.h

@@ -17,4 +17,4 @@
 *                  David Korn <dgk@research.att.com>                   *
 *                                                                      *
 ***********************************************************************/
-#define SH_RELEASE	"93u+m 2020-07-13"
+#define SH_RELEASE	"93u+m 2020-07-14"

src/cmd/ksh93/sh/jobs.c

@@ -344,6 +344,7 @@ int job_reap(register int sig)
 	int nochild=0, oerrno, wstat;
 	Waitevent_f waitevent = shp->gd->waitevent;
 	static int wcontinued = WCONTINUED;
+	int was_ttywait_on;
 #if SHOPT_COSHELL
 	Cojob_t		*cjp;
 	int		cojobs;
@@ -374,11 +375,13 @@ int job_reap(register int sig)
 		flags = WUNTRACED|wcontinued;
 	shp->gd->waitevent = 0;
 	oerrno = errno;
+	was_ttywait_on = sh_isstate(SH_TTYWAIT); /* save tty wait state */
 	while(1)
 	{
 		if(!(flags&WNOHANG) && !sh.intrap && job.pwlist)
 		{
-			sh_onstate(SH_TTYWAIT);
+			if(!was_ttywait_on)
+				sh_onstate(SH_TTYWAIT);
 			if(waitevent && (*waitevent)(-1,-1L,0))
 				flags |= WNOHANG;
 		}
@@ -404,7 +407,8 @@ int job_reap(register int sig)
 		}
 #endif /* SHOPT_COSHELL */
 		pid = waitpid((pid_t)-1,&wstat,flags);
-		sh_offstate(SH_TTYWAIT);
+		if(!was_ttywait_on)
+			sh_offstate(SH_TTYWAIT);
 #if SHOPT_COSHELL
 	cojob:
 #endif /* SHOPT_COSHELL */
@@ -559,6 +563,10 @@ int job_reap(register int sig)
 		}
 #endif
 	}
+#if SHOPT_COSHELL
+	if(!was_ttywait_on)
+		sh_offstate(SH_TTYWAIT); /* only required after 'goto cojob' in the while loop */
+#endif
 	if(errno==ECHILD)
 	{
 		errno = oerrno;

src/cmd/ksh93/tests/pty.sh

@@ -549,5 +549,16 @@ r ^:test-2: true string\\r\\n$
 !
 done
 
+# err_exit #
+tst $LINENO <<"!"
+L notify job state changes
+
+# 'set -b' should immediately notify the user about job state changes.
+
+p :test-1:
+w set -b; sleep .01 &
+u Done
+!
+
 # ======
 exit $((Errors<125?Errors:125))