Impossible to listen to beforeExit in single-tick --eval

[Fishrock123]

• Version: v2.2.0+ (?)
• Platform: all
• Subsystem: process

The following exits without printing:

node -e "process.on('beforeExit', () => process._rawDebug('hi'))"

However, this does print:

node -e "process.on('beforeExit', () => process._rawDebug('hi')); setImmediate(()=>{})"

I did some debugging and using this patch I get the following output:

diff --git a/lib/events.js b/lib/events.js
index d676580..16ee82c 100644
--- a/lib/events.js
+++ b/lib/events.js
@@ -138,6 +138,8 @@ EventEmitter.prototype.emit = function emit(type) {
   var needDomainExit = false;
   var doError = (type === 'error');

+  // process._rawDebug((new Error()).stack)
+
   events = this._events;
   if (events)
     doError = (doError && events.error == null);
@@ -169,6 +171,9 @@ EventEmitter.prototype.emit = function emit(type) {

   handler = events[type];

+  process._rawDebug('01.5:' + type)
+  process._rawDebug(typeof handler)
+
   if (!handler)
     return false;

@@ -234,6 +239,9 @@ function _addListener(target, type, listener, prepend) {
   }

   if (!existing) {
+    process._rawDebug('@@@@')
+    // process._rawDebug((new Error()).stack)
+    // process._rawDebug(listener.toString())
     // Optimize the case of one listener. Don't need the extra array object.
     existing = events[type] = listener;
     ++target._eventsCount;
diff --git a/lib/internal/process/next_tick.js b/lib/internal/process/next_tick.js
index 529645a..5f43ba0 100644
--- a/lib/internal/process/next_tick.js
+++ b/lib/internal/process/next_tick.js
@@ -138,6 +138,8 @@ function setupNextTick() {
   }

   function nextTick(callback) {
+    process._rawDebug('#####')
+    process._rawDebug((new Error()).stack)
     if (typeof callback !== 'function')
       throw new TypeError('callback is not a function');
     // on the way out, don't bother. it won't get fired anyway.

./node -e "process.on('beforeExit', () => process._rawDebug('hi'))"
@@@@
@@@@
01.5:newListener
function
@@@@
#####
Error
    at process.nextTick (internal/process/next_tick.js:142:24)
    at evalScript (bootstrap_node.js:344:13)
    at run (bootstrap_node.js:110:11)
    at run (bootstrap_node.js:382:7)
    at startup (bootstrap_node.js:109:9)
    at bootstrap_node.js:497:3
01.5:beforeExit
undefined
01.5:newListener
function
@@@@
01.5:exit
undefined

That is, beforeExit fires before the listener is attached.

Turns out that at evalScript (bootstrap_node.js:344:13) leads to this code and comment in evalScript():

    // Defer evaluation for a tick.  This is a workaround for deferred
    // events not firing when evaluating scripts from the command line,
    // see https://github.com/nodejs/node/issues/1600.
    process.nextTick(function() {
      const result = module._compile(script, `${name}-wrapper`);
      if (process._print_eval) console.log(result);
    });

That comment leads back to #1600 - net.listen does not emit 'listening' event when in --eval mode.

That was fixed in 93a44d5 by @bnoordhuis and reviewed by @trevnorris resulting in this code in evalScript().

Not sure how to fix this right now, but it seems like a deeper bug somewhere relating to startup and nextTick.

Refs: #1793 & #1600 & also the older nodejs/node-v0.x-archive#14168

Edit: found by @cxreg

[Fishrock123]

ping @bnoordhuis and @trevnorris

[bnoordhuis]

#8821