Fix BUG_LOOPRET2 and related return/exit misbehaviour

The 'exit' and 'return' commands without an argument failed to pass
down the exit status of the last-run command when incorporated in a
block with redirection, &&/|| list, 'case' statement, or 'while',
'until' or 'for' loop.

src/cmd/ksh93/bltins/cflow.c:
- Use $?, which is sh.savexit a.k.a. shp->savexit, as the default
  exit status value if there is no argument, instead of
  shp->oldexit. This fixes the default exit status behaviour to
  match POSIX and other shells.

src/cmd/ksh93/include/defs.h,
src/cmd/ksh93/include/shell.h:
- Remove now-unused sh.oldexit (a.k.a. shp->oldexit) private struct
  member. It appeared to fulfill the same function as sh.savexit,
  but in a slightly broken way.
- Move the savexit/$? declaration from the _SH_PRIVATE part of the
  struct definition to the public API part. Since $? uses this,
  it's clearly a publicly exposed value already, and this is
  generally the one to use. (If anything, it's exitval that should
  have been private.) This declares savexit right next to exitval,
  rewriting the comments to clarify the difference between them.

src/cmd/ksh93/sh/fault.c,
src/cmd/ksh93/sh/subshell.c,
src/cmd/ksh93/sh/xec.c:
- Remove assignments to shp->oldexit.

src/cmd/ksh93/tests/basic.sh:
- Add thorough regression tests for the default exit status
  behaviour of 'return' and 'exit' in various lexical contexts.
- Verify that 'for' and 'case' without any command, as well as a
  lone redirection, still correctly reset the exit status to 0.

Fixes: #117

NEWS

@@ -3,6 +3,18 @@ For full details, see the git log at: https://github.com/ksh93/ksh
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2020-09-09:
+
+- Fixed BUG_LOOPRET2 and related bugs. The 'exit' and 'return' commands without
+  an argument now correctly default to passing down the exit status of the
+  last-run command. Tests like the following, in which the last-run command is
+  'false', now correctly output 1 instead of 0:
+	fn() { return || true; }; false; fn; echo "$?"
+	fn() { while return; do true; done; }; false; fn; echo "$?"
+	fn() { for i in 1; do return; done; }; false; fn; echo "$?"
+	fn() { case 1 in 1) return ;; esac; }; false; fn; echo "$?"
+	fn() { { return; } 2>&1; }; false; fn; echo "$?"
+
 2020-09-05:
 
 - Fixed erroneous syntax errors in parameter expansions such as ${var:-wor)d}

TODO

@@ -49,9 +49,3 @@ https://github.com/modernish/modernish/tree/0.16/lib/modernish/cap/
   parameter expansion inserts any IFS separator characters, those characters
   are erroneously interpreted as wildcards when quoted "$*" is used as the
   glob pattern.
-
-- BUG_LOOPRET2: If a 'return' command is given without a status argument
-  within the set of conditional commands in a 'while' or 'until' loop (i.e.,
-  between 'while'/'until' and 'do'), the exit status passed down from the
-  previous command is ignored and the function returns with status 0
-  instead.

src/cmd/ksh93/bltins/cflow.c

@@ -64,7 +64,7 @@ done:
 		errormsg(SH_DICT,ERROR_usage(2),"%s",optusage((char*)0));
 	pp->mode = (**argv=='e'?SH_JMPEXIT:SH_JMPFUN);
 	argv += opt_info.index;
-	n = (((arg= *argv)?(int)strtol(arg, (char**)0, 10):shp->oldexit));
+	n = (arg = *argv) ? (int)strtol(arg, (char**)0, 10) : shp->savexit;
 	if(n<0 || n==256 || n > SH_EXITMASK+shp->gd->sigmax+1)
 			n &= ((unsigned int)n)&SH_EXITMASK;
 	/* return outside of function, dotscript and profile is exit */

src/cmd/ksh93/include/defs.h

@@ -155,7 +155,6 @@ struct shared
 	Sfio_t		*heredocs;	/* current here-doc temp file */ \
 	Sfio_t		*funlog;	/* for logging function definitions */ \
 	int		**fdptrs;	/* pointer to file numbers */ \
-	int		savexit; \
 	char		*lastarg; \
 	char		*lastpath;	/* last alsolute path found */ \
 	int		path_err;	/* last error on path search */ \
@@ -181,7 +180,6 @@ struct shared
 	char		*prefix;	/* prefix for compound assignment */ \
 	sigjmp_buf	*jmplist;	/* longjmp return stack */ \
 	char		*fifo;		/* fifo name for process sub */ \
-	int		oldexit; \
 	pid_t		bckpid;		/* background process id */ \
 	pid_t		cpid; \
 	pid_t		spid; 		/* subshell process id */ \

src/cmd/ksh93/include/shell.h

@@ -140,7 +140,8 @@ struct Shell_s
 	Dt_t		*bltin_tree;    /* for builtin commands */
 	Shscope_t	*topscope;	/* pointer to top-level scope */
 	int		inlineno;	/* line number of current input file */
-	int		exitval;	/* most recent exit value */
+	int		exitval;	/* exit status of the command currently being run */
+	int		savexit;	/* $? == exit status of the last command executed */
 	unsigned char	trapnote;	/* set when trap/signal is pending */
 	char		shcomp;		/* set when running shcomp */
 	unsigned int	subshell;	/* set for virtual subshell */

src/cmd/ksh93/include/version.h

@@ -17,4 +17,4 @@
 *                  David Korn <dgk@research.att.com>                   *
 *                                                                      *
 ***********************************************************************/
-#define SH_RELEASE	"93u+m 2020-09-05"
+#define SH_RELEASE	"93u+m 2020-09-09"

src/cmd/ksh93/sh/fault.c

@@ -614,7 +614,6 @@ void sh_done(void *ptr, register int sig)
 	if(t=shp->st.trapcom[0])
 	{
 		shp->st.trapcom[0]=0; /*should free but not long */
-		shp->oldexit = savxit;
 		sh_trap(t,0);
 		savxit = shp->exitval;
 	}

src/cmd/ksh93/sh/subshell.c

@@ -610,7 +610,6 @@ Sfio_t *sh_subshell(Shell_t *shp,Shnode_t *t, volatile int flags, int comsub)
 		/* trap on EXIT not handled by child */
 		char *trap=shp->st.trapcom[0];
 		shp->st.trapcom[0] = 0;	/* prevent recursion */
-		shp->oldexit = shp->exitval;
 		sh_trap(trap,0);
 		free(trap);
 	}

src/cmd/ksh93/sh/xec.c

@@ -972,8 +972,6 @@ int sh_exec(register const Shnode_t *t, int flags)
 		if(was_monitor&flags)
 			sh_onstate(SH_MONITOR);
 		type = t->tre.tretyp;
-		if(!shp->intrap)
-			shp->oldexit=shp->exitval;
 		shp->exitval=0;
 		shp->lastsig = 0;
 		shp->lastpath = 0;

src/cmd/ksh93/tests/basic.sh

@@ -428,6 +428,88 @@ if	env x-a=y >/dev/null 2>&1
 then	[[ $(env 'x-a=y'  $SHELL -c 'env | grep x-a') == *x-a=y* ]] || err_exit 'invalid environment variables not preserved'
 fi
 
+foo() { return; }
+false
+foo && err_exit "'return' within function does not preserve exit status"
+false
+foo & wait "$!" && err_exit "'return' within function does not preserve exit status (bg job)"
+
+foo() { false; return || :; }
+foo && err_exit "'return ||' does not preserve exit status"
+
+foo() { false; return && :; }
+foo && err_exit "'return &&' does not preserve exit status"
+
+foo() { false; while return; do true; done; }
+foo && err_exit "'while return' does not preserve exit status"
+
+foo() { false; while return; do true; done 2>&1; }
+foo && err_exit "'while return' with redirection does not preserve exit status"
+
+foo() { false; until return; do true; done; }
+foo && err_exit "'until return' does not preserve exit status"
+
+foo() { false; until return; do true; done 2>&1; }
+foo && err_exit "'until return' with redirection does not preserve exit status"
+
+foo() { false; for i in 1; do return; done; }
+foo && err_exit "'return' within 'for' does not preserve exit status"
+
+foo() { false; for i in 1; do return; done 2>&1; }
+foo && err_exit "'return' within 'for' with redirection does not preserve exit status"
+
+foo() { false; { return; } 2>&1; }
+foo && err_exit "'return' within { block; } with redirection does not preserve exit status"
+
+foo() ( exit )
+false
+foo && err_exit "'exit' within function does not preserve exit status"
+false
+foo & wait "$!" && err_exit "'exit' within function does not preserve exit status (bg job)"
+
+foo() ( false; exit || : )
+foo && err_exit "'exit ||' does not preserve exit status"
+
+foo() ( false; exit && : )
+foo && err_exit "'exit &&' does not preserve exit status"
+
+foo() ( false; while exit; do true; done )
+foo && err_exit "'while exit' does not preserve exit status"
+
+foo() ( false; while exit; do true; done 2>&1 )
+foo && err_exit "'while exit' with redirection does not preserve exit status"
+
+foo() ( false; until exit; do true; done )
+foo && err_exit "'until exit' does not preserve exit status"
+
+foo() ( false; until exit; do true; done 2>&1 )
+foo && err_exit "'until exit' with redirection does not preserve exit status"
+
+foo() ( false; for i in 1; do exit; done )
+foo && err_exit "'exit' within 'for' does not preserve exit status"
+
+foo() ( false; for i in 1; do exit; done 2>&1 )
+foo && err_exit "'exit' within 'for' with redirection does not preserve exit status"
+
+foo() ( false; { exit; } 2>&1 )
+foo && err_exit "'exit' within { block; } with redirection does not preserve exit status"
+
+set --
+false
+for i in "$@"; do :; done || err_exit 'empty loop does not reset exit status ("$@")'
+false
+for i do :; done || err_exit 'empty loop does not reset exit status ("$@" shorthand)'
+false
+for i in; do :; done || err_exit "empty loop does not reset exit status (empty 'in' list)"
+
+false
+case 1 in 1) ;; esac || err_exit "empty case does not reset exit status"
+false
+case 1 in 2) echo whoa ;; esac || err_exit "non-matching case does not reset exit status"
+
+false
+2>&1 || err_exit "lone redirection does not reset exit status"
+
 float s=SECONDS
 for i in .1 .2
 do      print $i