PATCH: pws-18: ERR_EXIT behavior inconsistent with other shells

[Peter Stephenson <pws@ibmth.df.unipi.it>]

Last thing on my to-do list before pws-19:

Clint Adams wrote:
> ARGV0=sh zsh -fexc 'testerrexit() { return 1; }; false || echo simplecommand;
>  testerrexit || echo function'; echo $?
> 
> does this
> 
> + false
> + echo simplecommand
> simplecommand
> + testerrexit
> + return 1
> 1
> 
> Other shells seems to do this
> 
> ARGV0=sh ksh -fexc 'testerrexit() { return 1; }; false || echo simplecommand;
>  te
> sterrexit || echo function'; echo $?
> 
> + false
> + echo simplecommand
> simplecommand
> + testerrexit
> + echo function
> function
> 0

It took me a couple of minutes to work out the logic: any shell stuff which
is followed at any level of execution by a || or && should suppress errexit
until the final set of commands in the chain at the level at which the ||
or && appears.  I originally thought that being in a function was turning
off errexit, but that's not it, and it should apply to { ... } structures
as well as functions (I checked this).  I can't imagine this was anything
other than an oversight in the zsh code, since I don't suppose anybody ever
thought about it before.  The following should make it consistent.

It also keeps it consistent with

% ksh -fec 'false || { false; print two; false; }; print three'

where you don't get the message `two' because in this case the shell exits
at the first `false' on the right.  The rule seems to be `never exit on a
non-zero status left of a || or &&, always exit on the extreme right',
because you also get

% ksh -fec 'false && true; print yes'
yes

where zsh was already consistent with ksh.

--- Src/exec.c.ee	Tue May 18 11:25:25 1999
+++ Src/exec.c	Wed May 19 11:22:10 1999
@@ -697,6 +697,13 @@
     static int donetrap;
     int ret, cj;
     int old_pline_level, old_list_pipe;
+    /*
+     * ERREXIT only forces the shell to exit if the last command in a &&
+     * or || fails.  This is the case even if an earlier command is a
+     * shell function or other current shell structure, so we have to set
+     * noerrexit here if the sublist is not of type END.
+     */
+    int oldnoerrexit = noerrexit;
 
     cj = thisjob;
     old_pline_level = pline_level;
@@ -716,6 +723,8 @@
 
 	/* Loop through code followed by &&, ||, or end of sublist. */
 	while (slist) {
+	    if (!oldnoerrexit)
+		noerrexit = (slist->type != END);
 	    switch (slist->type) {
 	    case END:
 		/* End of sublist; just execute, ignoring status. */
@@ -758,6 +767,8 @@
 	    slist = slist->right;
 	}
 sublist_done:
+
+	noerrexit = oldnoerrexit;
 
 	if (sigtrapped[SIGDEBUG])
 	    dotrap(SIGDEBUG);

-- 
Peter Stephenson <pws@ibmth.df.unipi.it>       Tel: +39 050 844536
WWW:  http://www.ifh.de/~pws/
Dipartimento di Fisica, Via Buonarroti 2, 56127 Pisa, Italy