On Mon, Oct 25, 2021 at 5:53 PM Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx> wrote:
There's definitely a bug in this somewhere because if the last command
executed by the final subshell [is] an anonymous function call:
zsh -fc '...; ( () { return 123 } )'
then the zshexit hook is NEVER called.
When an anonymous function (or probably any function) calls "exit", we
pass through this bit of code in builtin.c bin_break():
5719 *
5720 * If we are already exiting... give this all up as
5721 * a bad job.
5722 */
5723 if (stopmsg || (zexit(0, ZEXIT_DEFERRED), !stopmsg)) {
5724 retflag = 1;
5725 breaks = loops;
5726 exit_pending = 1;
5727 exit_level = locallevel;
5728 exit_val = num;
With ZEXIT_DEFERRED, zexit() always bails out here:
5842 /* Positive shell_exiting means we have been here before */
5843 if (from_where == ZEXIT_DEFERRED ||
5844 (shell_exiting++ && from_where != ZEXIT_NORMAL))
5845 return;
We then eventually call zexit(exit_val, ZEXIT_NORMAL) from doshfunc().
If instead the function calls "return 123" and is the last command in
the subshell, we pass through this branch of execcmd_exec():
4239 if (forked) {
4240 /*
4241 * So what's going on here then? Well, I'm glad you asked.
[...]
4263 */
4264 for (i = 0; i < 10; i++)
4265 if (fdtable[i] != FDT_UNUSED)
4266 close(i);
4267 closem(FDT_UNUSED, 1);
4268 if (thisjob != -1)
4269 waitjobs();
4270 _realexit();
4271 }
The call to _realexit() bypasses the hook. This is the expected
behavior for "falling off the end" of a subshell, rather than
explicitly "exit"-ing.
However, in
zsh -fc '( () { return 123 } )'
the parent shell optimizes away the subshell and we arrive here:
3596 /*
3597 * If we are in a subshell environment anyway, say
we're forked,
3598 * even if we're actually not forked because we know the
3599 * subshell is exiting. This ensures SHLVL reflects
the current
3600 * shell, and also optimises out any save/restore we'd need to
3601 * do if we were returning to the main shell.
3602 */
3603 if (type == WC_SUBSH)
3604 forked = 1;
This should not happen when there is an exit trap or an exit hook, I
think? However, I'm not following the comment reference to SHLVL --
why would it not reflect the correct thing? I suppose the actual
correct thing is higher up the call stack, where we should not assert
that the subshell is exiting if the parent shell still has traps or
hooks to process, so that we really have forked here.
As to this:
You can avoid that by having the subshell end with "return 123"
instead of "exit 123", except for some reason (possibly a bug) when
the -c option is used in which case return behaves like exit again.
bin_break() treats "return" as synonymous with "exit" here:
5683 case BIN_RETURN:
5684 if ((isset(INTERACTIVE) && isset(SHINSTDIN))
5685 || locallevel || sourcelevel) {
[...]
5699 return lastval;
5700 }
5701 zexit(num, ZEXIT_NORMAL); /* else treat return as
logout/exit */
To Tycho's original question, this means there is no way to have an
exit hook or trap called exactly when the original shell exits. You
can't forcibly finish a subshell before it "falls off the end" without
possibly invoking the trap and hook, and you can't even reliably test
$ZSH_SUBSHELL inside the hook, because the parent might optimize out a
fork without decrementing that.
[[ $sysparams[pid] = $$ ]] almost gets there, except that you can't
assure the hook itself won't be skipped by a function that calls exit.