Yet another fake subshell fix

Yet another fake subshell fix

[Peter William Stephenson]

More ramifications to do with exec'ing the last command in a shell
that's about to exit:  going into a subshell messes up the shell
terminal file descriptor (plus other things), so that builtins are
unhappy.  You can see it with things like

% zsh -fc 'vared DISPLAY'

(useless example, obviously) which I scrupulously made sure worked
when I wrote the patch to delay setting up the terminal in
non-interactive shells.

The answer is simple, correct, and I should have done it when I first
thought about exec'ing the final command: there's no point in trying
to do the fake-exec thing for a builtin or shell command anyway; it
simply removes a bit of post processing by the shell (which you might
be glad of someday).

If there are any problems with this, they must have been there for a
long time, since this is what zsh always used to do with builtins (as
well as every other command).

This would actually fix the previous problems with exit instead of
_exit in 99.99% of cases (we return to, say, getoutput, which handles
$(...), and _exit from there), but the second patch I sent for that
does get everything right so we still need it.  The remaining .01% of
cases are where a nervous user asks for a real `exec read' or what
have you inside a subshell.

*** Src/exec.c~	Wed Nov  8 10:05:22 1995
--- Src/exec.c	Mon Nov 13 17:58:16 1995
***************
*** 1266,1274 ****
       * in a subshell pipeline, or if the shell is no longer needed    *
       * (e.g. the last command after a `-c').  However, if the command *
       * is going into the background, or if we need to trap EXIT or    *
!      * ZERR, then we can't do this.                                   */
  
!     if (last1 && (how & Z_SYNC)
  	&& !sigtrapped[SIGZERR] && !sigtrapped[SIGEXIT]
  	&& execok()) {
  	cmd->flags |= CFLAG_FAKE_EXEC;
--- 1266,1276 ----
       * in a subshell pipeline, or if the shell is no longer needed    *
       * (e.g. the last command after a `-c').  However, if the command *
       * is going into the background, or if we need to trap EXIT or    *
!      * ZERR, then we can't do this.  Also, if it's getting run in the *
!      * current shell, there's no point (and we unnecessarily mess up  *
!      * terminal settings etc.)                                        */
  
!     if (last1 && (how & Z_SYNC) && !is_cursh
  	&& !sigtrapped[SIGZERR] && !sigtrapped[SIGEXIT]
  	&& execok()) {
  	cmd->flags |= CFLAG_FAKE_EXEC;

-- 
Peter Stephenson <pws@ifh.de>       Tel: +49 33762 77366
WWW:  http://www.ifh.de/~pws/       Fax: +49 33762 77330
Deutches Electronen-Synchrotron --- Institut fuer Hochenergiephysik Zeuthen
DESY-IfH, 15735 Zeuthen, Germany.