#!/bin/sh
# Is SIGINT deliverable to this process tree?
#
# WHY THIS EXISTS. A shell running a command in the background without
# job control sets SIGINT (and SIGQUIT) to SIG_IGN in the child; nohup
# adds SIGHUP. SIG_IGN is inherited across fork AND survives exec, so
# the disposition reaches every descendant --- cargo, a test binary, and
# anything either of them spawns. Tests that signal a child then wait
# for it to die will hang until their own deadline and report that as a
# teardown defect. One lane spent nine framing revisions on exactly that
# misreading; see docs/gpu-probe-sigint-framing.md §4c.
#
# INTERFACE (docs/gpu-probe-sigint-framing.md §7c). Callers rely on
# these three statuses and MUST NOT re-derive the classification:
#
#   0  safe     SIGINT is deliverable.        No diagnostic.
#   1  ignored  SIGINT is inherited SIG_IGN.  Canonical diagnostic.
#   2  error    Undecidable.                  Distinct diagnostic.
#
# `error` is never folded into `ignored`. "Your environment ignores
# SIGINT" and "the guard could not run" are different problems, and
# conflating them fails callers for the wrong reason.
#
# THE PROBE. A child sends itself SIGINT. Deliverable => the trap runs
# => 23. Ignored => the kill is a no-op => the child falls through to
# `exit 0`. The `|| exit 24` arms matter: without them a FAILED kill
# would also fall through to `exit 0` and be misread as `ignored`,
# which is the one wrong answer this helper exists to avoid.
#
# POSIX shell only --- trap, kill, $$ --- so no /proc and no sigaction:
# the mechanism is not Linux-specific and adds no unsafe code.

probe_status=0
sh -c 'trap "exit 23" 2 || exit 24; kill -INT "$$" || exit 24; exit 0' \
  || probe_status=$?

case "$probe_status" in
    23) exit 0 ;;
    0)
        echo 'pmacs: SIGINT is ignored; run this command with SIGINT deliverable' >&2
        exit 1
        ;;
    *)
        echo "pmacs: could not determine whether SIGINT is deliverable (probe status $probe_status)" >&2
        exit 2
        ;;
esac