fix: restore signals forwarding to child processes

Reverting the changes introduced in
commit 545f3be, as it inadvertently
disrupted proper signals support

lib/signal-manager.js

@@ -1,9 +1,6 @@
 const runningProcs = new Set()
 let handlersInstalled = false
 
-// NOTE: these signals aren't actually forwarded anywhere. they're trapped and
-// ignored until all child processes have exited. in our next breaking change
-// we should rename this
 const forwardedSignals = [
   'SIGINT',
   'SIGTERM',
@@ -12,8 +9,12 @@ const forwardedSignals = [
 // no-op, this is so receiving the signal doesn't cause us to exit immediately
 // instead, we exit after all children have exited when we re-send the signal
 // to ourselves. see the catch handler at the bottom of run-script-pkg.js
-// istanbul ignore next - this function does nothing
-const handleSignal = () => {}
+const handleSignal = signal => {
+  for (const proc of runningProcs) {
+    proc.kill(signal)
+  }
+}
+
 const setupListeners = () => {
   for (const signal of forwardedSignals) {
     process.on(signal, handleSignal)

test/signal-manager.js

@@ -44,3 +44,24 @@ test('adds only one handler for each signal, removes handlers when children have
 
   t.end()
 })
+
+test('forwards signals to child process', t => {
+  const proc = new EventEmitter()
+  proc.kill = (signal) => {
+    t.equal(signal, signalManager.forwardedSignals[0], 'child receives correct signal')
+    proc.emit('exit', 0)
+    for (const forwarded of signalManager.forwardedSignals) {
+      t.equal(
+        process.listeners(forwarded).includes(signalManager.handleSignal),
+        false, 'listener has been removed')
+    }
+    t.end()
+  }
+
+  signalManager.add(proc)
+  // passing the signal name here is necessary to fake the effects of actually
+  // receiving the signal per nodejs documentation signal handlers receive the
+  // name of the signal as their first parameter
+  // https://nodejs.org/api/process.html#process_signal_events
+  process.emit(signalManager.forwardedSignals[0], signalManager.forwardedSignals[0])
+})