Fix 'exit' default status in trap action (re: 092b90d)

Reproducer:

   (trap 'false; exit' EXIT; exit 9); echo $?

Expected output: 9
Actual output: 1

In a trap action, the default exit status passed down by an 'exit'
with no arguments is the exit status of the last command *before*
the trap action.

So, *that* was the point of the sh.oldexit variable removed in
092b90d. BUG_LOOPRET2 was that sh.oldexit was unconditionally used
for the default exit status of 'exit' and 'return' in b_return().

The fix is to restore it, while using it correctly this time (i.e.,
depending on sh.intrap) so that BUG_LOOPRET2 is not introduced.

Thanks to @sckendall2 and @jghub for the bug reports.

Resolves: #667
Resolves: #687

NEWS

@@ -2,6 +2,13 @@ This documents significant changes in the dev branch of ksh 93u+m.
 For full details, see the git log at: https://github.com/ksh93/ksh
 Uppercase BUG_* IDs are shell bug IDs as used by the Modernish shell library.
 
+2023-12-25:
+
+- Fixed a regression in the behavior of 'exit' in a trap action, introduced
+  on 2020-09-09. The default exit status, used when no argument is given to
+  'exit', is now once again the exit status of the last command executed
+  *before* the trap action, as expected.
+
 2023-09-16:
 
 - The 'kill' built-in command was meant to refuse to issue SIGSTOP to the

src/cmd/ksh93/bltins/cflow.c

@@ -76,7 +76,8 @@ int	b_return(int n, char *argv[],Shbltin_t *context)
 	}
 	else
 	{
-		n = sh.savexit;				/* no argument: pass down $? */
+		/* no argument: pass down $? (but in a trap action, pass down the pre-trap $?) */
+		n = sh.intrap ? sh.oldexit : sh.savexit;
 		if(do_exit)
 			n &= SH_EXITMASK;
 	}

src/cmd/ksh93/include/shell.h

@@ -302,6 +302,7 @@ struct Shell_s
 	char		*comdiv;	/* points to sh -c argument */
 	char		*prefix;	/* prefix for compound assignment */
 	sigjmp_buf	*jmplist;	/* longjmp return stack */
+	int		oldexit;	/* saves pre-trap exit status for 'exit' default in trap actions */
 	pid_t		bckpid;		/* background process id */
 	pid_t		cpid;
 	pid_t		spid; 		/* subshell process id */
@@ -310,7 +311,7 @@ struct Shell_s
 	int		topfd;
 	int		savesig;
 	unsigned char	*sigflag;	/* pointer to signal states */
-	char		intrap;
+	char		intrap;		/* set while executing a trap action */
 	char		forked;
 	char		binscript;
 	char		funload;

src/cmd/ksh93/include/version.h

@@ -18,7 +18,7 @@
 
 #define SH_RELEASE_FORK	"93u+m"		/* only change if you develop a new ksh93 fork */
 #define SH_RELEASE_SVER	"1.1.0-alpha"	/* semantic version number: https://semver.org */
-#define SH_RELEASE_DATE	"2023-09-24"	/* must be in this format for $((.sh.version)) */
+#define SH_RELEASE_DATE	"2023-12-25"	/* must be in this format for $((.sh.version)) */
 #define SH_RELEASE_CPYR	"(c) 2020-2023 Contributors to ksh " SH_RELEASE_FORK
 
 /* Scripts sometimes field-split ${.sh.version}, so don't change amount of whitespace. */

src/cmd/ksh93/sh/fault.c

@@ -666,6 +666,7 @@ noreturn void sh_done(int sig)
 	if(t=sh.st.trapcom[0])
 	{
 		sh.st.trapcom[0]=0; /* should free but not long */
+		sh.oldexit = savxit;
 		sh_trap(t,0);
 		savxit = sh.exitval;
 	}

src/cmd/ksh93/sh/subshell.c

@@ -657,6 +657,7 @@ Sfio_t *sh_subshell(Shnode_t *t, volatile int flags, int comsub)
 		/* trap on EXIT not handled by child */
 		char *trap=sh.st.trapcom[0];
 		sh.st.trapcom[0] = 0;	/* prevent recursion */
+		sh.oldexit = sh.exitval;
 		sh_trap(trap,0);
 		free(trap);
 	}

src/cmd/ksh93/sh/xec.c

@@ -901,6 +901,8 @@ int sh_exec(const Shnode_t *t, int flags)
 		sh_offstate(SH_DEFPATH);
 		if(!(flags & sh_state(SH_ERREXIT)))
 			sh_offstate(SH_ERREXIT);
+		if(!sh.intrap)
+			sh.oldexit = sh.exitval;
 		sh.exitval=0;
 		sh.lastsig = 0;
 		sh.chldexitsig = 0;

src/cmd/ksh93/tests/exit.sh

@@ -228,9 +228,21 @@ unset exp got sig
 # ======
 # trap status tests
 
+exp=0
+(trap 'false; exit' EXIT; true; exit)
+let "(got=$?)==exp" || err_exit "pre-trap exit status not preserved (got $got, expected $exp)"
+
 exp=1
-(trap 'false; exit' EXIT; true)
-let "(got=$?)==exp" || err_exit "passing down exit status from EXIT trap failed (got $got, expected $exp)"
+(trap 'true; exit' EXIT; false; exit)
+let "(got=$?)==exp" || err_exit "pre-trap exit status not preserved (got $got, expected $exp)"
+
+exp=7
+(trap 'false; exit 7' EXIT; exit 9)
+let "(got=$?)==exp" || err_exit "explicit exit status in trap not honoured (got $got, expected $exp)"
+
+exp=9
+(trap 'false; exit' EXIT; exit 9)
+let "(got=$?)==exp" || err_exit "explicit exit status outside trap not honoured (got $got, expected $exp)"
 
 # ======
 exit $((Errors<125?Errors:125))