Re: Zsh spins in endless loop with SIGHUP + read in zshexit

[Bart Schaefer <schaefer@brasslantern.com>]

On Thu, May 13, 2021 at 11:44 AM Peter Stephenson
<p.w.stephenson@ntlworld.com> wrote:
>
> I haven't looked for cases where we're disobeying "exit" from shell code
> owing to the same logic

So besides the one discussed already in this thread, we have:
1) ${unset?error message}
2) return at top level (bin_break + BIN_RETURN)
3) exit (bin_break + BIN_EXIT)
  3a) in a shell function (ZEXIT_DEFERRED)
  3b) at top level (ZEXIT_NORMAL)
4) doshfunc() when not already in an exit trap
5) loop() when (3a) has previously happened
6) init_misc() for "zsh -c somecommand"
7) zsh_main() at end of input (can be canceled by ignoreeof)
8) zpty module at the end of the child thread
9) signal handling for HUP PIPE ALRM and if not interactive INT

(3a) uses zexit in a comma expression, I'm surprised that doesn't
produce a warning for a void function.  That is the only instance of
DEFERRED.

The only time zexit() fails to _exit() is when called recursively,
which I believe can only happen in a trap.  Possible "dangerous" cases
when used in a trap:

(1) could unexpectedly proceed beyond the parameter expansion into the
subsequent shell code.
(2,3) and by extension (4) when used in combination with an "always"
block (this is not clear-cut) would continue the shell code.
(8) would continue into the pty master code if a new zpty were opened.

I haven't tested whether any of these things actually DO fail to
_exit(), just source code examination of what comes downstream in each
circumstance.  When there is no "always", I believe 2 and 3 correctly
end processing of the current function scope.