Re: bug: $? after empty command

[Peter Stephenson <p.w.stephenson@ntlworld.com>]

On Fri, 10 Jul 2009 23:05:54 +0100
Peter Stephenson <p.w.stephenson@ntlworld.com> wrote:
> On Fri, 10 Jul 2009 10:02:28 +0100
> Peter Stephenson <pws@csr.com> wrote:
> > On Thu, 9 Jul 2009 21:41:51 +0000 (UTC)
> > Eric Blake <ebb9@byu.net> wrote:
> >> Eric Blake <ebb9 <at> byu.net> writes:
> >>> $ zsh -c 'false; . /dev/null; echo $?'
> >>> 1
> >>> $ zsh -c 'false; ``; echo $?'
> >>> 1
> >> $ zsh -c 'false; sleep& echo $?'
> >> 1
> > 
> > "fn() { }" is valid, and I suspect "fn"
> > logically ought to reset the status, too
> 
> These four were all fairly easy; in each case there is a local context
> where the command in question is being executed in which the status can
> be reset.  There may be a a more generic place, such as execlist(), for
> these to go, but I like the transparency of resetting them locally;
> execlist()/execode() are used in just too many places.

Change of plan:  I woke up in the night and realised that doing it this
way breaks the case

  fn() { print $?; }
  false
  fn

which is a bit strange but perfectly valid and should print "1".

> However, that's a bit craven.

This takes the brave option, but actually it's easy except for the case
of "." which needs a bit more information from down below.  For both
executing a list and sourcing a file line by line we only reset the
status if there is no code to execute.

The case of starting a background function isn't affected, in that case
the foreground code is always empty.

Index: Src/exec.c
===================================================================
RCS file: /cvsroot/zsh/zsh/Src/exec.c,v
retrieving revision 1.167
diff -u -r1.167 exec.c
--- Src/exec.c	10 Jul 2009 22:10:26 -0000	1.167
+++ Src/exec.c	11 Jul 2009 16:32:42 -0000
@@ -1056,6 +1056,10 @@
     /* Loop over all sets of comands separated by newline, *
      * semi-colon or ampersand (`sublists').               */
     code = *state->pc++;
+    if (wc_code(code) != WC_LIST) {
+	/* Empty list; this returns status zero. */
+	lastval = 0;
+    }
     while (wc_code(code) == WC_LIST && !breaks && !retflag && !errflag) {
 	int donedebug;
 
@@ -3513,7 +3517,6 @@
 	return retval;
     }
     /* pid == 0 */
-    lastval = 0;		/* status of empty list is zero */
     child_unblock();
     zclose(pipes[0]);
     redup(pipes[1], 1);
@@ -4261,7 +4264,6 @@
     if (trap_state == TRAP_STATE_PRIMED)
 	trap_return--;
     oldlastval = lastval;
-    lastval = 0;		/* status of empty function is zero */
     oldnumpipestats = numpipestats;
     if (noreturnval) {
 	/*
Index: Src/init.c
===================================================================
RCS file: /cvsroot/zsh/zsh/Src/init.c,v
retrieving revision 1.104
diff -u -r1.104 init.c
--- Src/init.c	10 Jul 2009 22:10:26 -0000	1.104
+++ Src/init.c	11 Jul 2009 16:32:42 -0000
@@ -99,11 +99,11 @@
 /* keep executing lists until EOF found */
 
 /**/
-int
+enum loop_return
 loop(int toplevel, int justonce)
 {
     Eprog prog;
-    int err;
+    int err, non_empty = 0;
 
     pushheap();
     if (!toplevel)
@@ -151,6 +151,7 @@
 	if (hend(prog)) {
 	    int toksav = tok;
 
+	    non_empty = 1;
 	    if (toplevel &&
 		(getshfunc("preexec") ||
 		 paramtab->getnode(paramtab, "preexec" HOOK_SUFFIX))) {
@@ -207,7 +208,11 @@
 	lexrestore();
     popheap();
 
-    return err;
+    if (err)
+	return LOOP_ERROR;
+    if (!non_empty)
+	return LOOP_EMPTY;
+    return LOOP_OK;
 }
 
 static char *cmd;
@@ -1131,7 +1136,6 @@
     fstack.tp = FS_SOURCE;
     funcstack = &fstack;
 
-    lastval = 0;		/* status of empty file is zero */
     if (prog) {
 	pushheap();
 	errflag = 0;
@@ -1141,8 +1145,21 @@
 	    ret = SOURCE_ERROR;
     } else {
 	/* loop through the file to be sourced  */
-	if (loop(0, 0))
+	switch (loop(0, 0))
+	{
+	case LOOP_OK:
+	    /* nothing to do but compilers like a complete enum */
+	    break;
+
+	case LOOP_EMPTY:
+	    /* Empty code resets status */
+	    lastval = 0;
+	    break;
+
+	case LOOP_ERROR:
 	    ret = SOURCE_ERROR;
+	    break;
+	}
     }
     funcstack = funcstack->prev;
     sourcelevel--;
Index: Src/zsh.h
===================================================================
RCS file: /cvsroot/zsh/zsh/Src/zsh.h,v
retrieving revision 1.159
diff -u -r1.159 zsh.h
--- Src/zsh.h	10 Jul 2009 11:08:48 -0000	1.159
+++ Src/zsh.h	11 Jul 2009 16:32:43 -0000
@@ -1726,6 +1726,17 @@
 #define PRINT_WHENCE_FUNCDEF	(1<<9)
 #define PRINT_WHENCE_WORD	(1<<10)
 
+/* Return values from loop() */
+
+enum loop_return {
+    /* Loop executed OK */
+    LOOP_OK,
+    /* Loop executed no code */
+    LOOP_EMPTY,
+    /* Loop encountered an error */
+    LOOP_ERROR
+};
+
 /* Return values from source() */
 
 enum source_return {
Index: Test/A01grammar.ztst
===================================================================
RCS file: /cvsroot/zsh/zsh/Test/A01grammar.ztst,v
retrieving revision 1.24
diff -u -r1.24 A01grammar.ztst
--- Test/A01grammar.ztst	10 Jul 2009 22:10:27 -0000	1.24
+++ Test/A01grammar.ztst	11 Jul 2009 16:32:43 -0000
@@ -553,3 +553,9 @@
 0:Last status of successfully executed "." file is retained
 >1
 >0
+
+  echo 'echo $?' >dot_status
+  false
+  . ./dot_status
+0:"." file sees status from previous command
+>1
Index: Test/C04funcdef.ztst
===================================================================
RCS file: /cvsroot/zsh/zsh/Test/C04funcdef.ztst,v
retrieving revision 1.6
diff -u -r1.6 C04funcdef.ztst
--- Test/C04funcdef.ztst	10 Jul 2009 22:10:27 -0000	1.6
+++ Test/C04funcdef.ztst	11 Jul 2009 16:32:43 -0000
@@ -15,6 +15,13 @@
   fnz
 0:Empty function body resets status
 
+  fn3() { return 3; }
+  fnstat() { print $?; }
+  fn3
+  fnstat
+0:Status is not reset on non-empty function body
+>3
+
   function f$$ () {
     print regress expansion of function names
   }
Index: Test/D08cmdsubst.ztst
===================================================================
RCS file: /cvsroot/zsh/zsh/Test/D08cmdsubst.ztst,v
retrieving revision 1.3
diff -u -r1.3 D08cmdsubst.ztst
--- Test/D08cmdsubst.ztst	10 Jul 2009 22:10:27 -0000	1.3
+++ Test/D08cmdsubst.ztst	11 Jul 2009 16:32:43 -0000
@@ -93,3 +93,8 @@
  false
  ``
 0:Empty command substitution resets status
+
+ false
+ echo `echo $?`
+0:Non-empty command substitution inherits status
+>1


-- 
Peter Stephenson <p.w.stephenson@ntlworld.com>
Web page now at http://homepage.ntlworld.com/p.w.stephenson/