Fix EXIT trap not called when shell is exiting under numerous circumstances

[tmoschou]

Problem

EXIT traps are never called when the shell is exiting under numerous circumstances.

1. ERR_EXIT (set -e) set and a command fails inside a function
   zsh -e -c 'trap "echo Trap" EXIT; f() { false; }; f'

2. ${unsetvar?message}/${unsetvar:?message} used inside a function in a non-interactive shell
   zsh -c 'trap "echo Trap" EXIT; f() { echo ${unset?oops}; }; f'

3. NO_UNSET (set -u) set and an unset variable is referenced (inside a function or not)
   zsh -u -c 'trap "echo Trap" EXIT; echo $unset'

In all cases, expected: Trap on stdout. Actual: Trap missing.

This contradicts the documentation and user expectation that EXIT can be relied on for clean-up (e.g. lock files, temporary files, etc.) when the shell is exiting. Additionally bash handles these cases as you would expect, always firing the EXIT trap.

Zsh also fails to fire nested local-scoped EXIT traps in these cases. However swapping false for exit 1 does cause all EXIT traps to fire correctly bottom-up:

set -e
trap "echo Trap1" EXIT
f1() {
    trap "echo Trap2" EXIT
    f2() {
        trap "echo Trap3" EXIT
        false  # replace with `exit 1` to see all traps fire
    }
    f2
}
f1

• Expected: Trap3, Trap2, Trap1
• Actual: Trap3

Note that EXIT traps specifically are local by default (LOCA_TRAPS behavior), unless POSIX_TRAPS is set.

Root cause

When a function is entered, starttrapscope() saves and unsets sigtrapped[SIGEXIT]. Normally endtrapscope() restores it when the function returns.

ERR_EXIT: When ERR_EXIT triggers inside a function, execlist() called realexit() directly — bypassing endtrapscope() — so saved EXIT traps were never restored or executed.

${var:?}: The paramsubst() handler called _exit(1) (subshell) or zexit() (main process) directly, similarly bypassing the function unwind and endtrapscope(). Additionally, errflag (set by zerr()) prevented dotrapargs() from executing the EXIT trap even when the unwind did reach endtrapscope().

NO_UNSET: paramsubst() and getmathparam() set errflag via zerr() and returned, but errflag blocked dotrapargs() in endtrapscope() from running EXIT traps at each function level. The shell eventually exited via the main loop without unwinding through function scopes.

Fix

Reuse the same exit_pending unwind mechanism as the exit builtin, so that endtrapscope() runs at each function level and all nested EXIT traps are executed bottom-up, matching the behaviour of an explicit exit call.

• ERR_EXIT / ${var:?}: call set_exit_pending() instead of realexit() / zexit() when inside a function, so the exit unwinds through each scope.
• NO_UNSET and other zerr()-based errors: in endtrapscope(), convert errflag-driven exits to exit_pending in non-interactive shells, so all EXIT traps fire during the unwind. This is a single central check rather than patching each error site.
• Extract set_exit_pending() to consolidate the repeated unwind setup (trap_state, retflag, breaks, exit_pending, exit_level, exit_val).
• Extract restore_saved_trap() from endtrapscope() to reduce duplication in the trap restoration logic.
• Clear errflag in endtrapscope() when exit_pending, so EXIT traps can fire even when the exit was triggered by an error. This mirrors what zexit() already does before calling dotrap(SIGEXIT).

Test plan

• Added regression tests in Test/C03traps.ztst for ERR_EXIT, ${var:?}, and NO_UNSET — both top-level and nested function cases
• Full test suite passes (67 successful, 1 pre-existing failure in E02, 2 skipped)
• Manual verification — all now print Trap:

  ./Src/zsh -f -o err_exit -c 'trap "echo Trap" EXIT; f() { false; }; f'
  ./Src/zsh -f -c 'trap "echo Trap" EXIT; f() { echo ${unset:?oops}; }; f'
  ./Src/zsh -f -u -c 'trap "echo Trap" EXIT; echo $unset'
  ./Src/zsh -f -u -c 'trap "echo Trap" EXIT; f() { echo $unset; }; f'
  

• Verified POSIX_TRAPS still behaves correctly (EXIT traps are global, not function-scoped):
  ./Src/zsh -f -o posix_traps -e -c 'trap "echo A" EXIT; f() { trap "echo B" EXIT; }; f; false'