refactor(core): allow restart logic to be triggered using an event

[erikian]

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Summarize your changes:
This allows the restart event to be triggered from anywhere in Forge and should make it possible for @caoxiemeihao to address the process.stdin.emit issue mentioned in #3203 (comment):

Ideally, we should instead expose additional start logic from the @electron-forge/core API to expose this functionality so that plugins can hook into it.

At first, I was thinking of creating a dedicated EventEmitter instance for this, but process is an event emitter and is available everywhere, so that makes things simpler if a bit hacky.

[BlackHole1]

LGTM. PTAL @caoxiemeihao

[caoxiemeihao]

Great! 👍

[MarshallOfSound]

This still feels side-effecty/hacky. Like, we're still emitting a random string on a random emitter. This should just be a method exposed via forge core, or plugin base that can be called normally

[erikian]

we're still emitting a random string on a random emitter

What about:

// at the top-level of the module
const restartAppEventEmitter = new EventEmitter()

// ...
if (interactive) {
  restartAppEventEmitter.on('restart', async () => {
    if (lastSpawned) {
      console.info(chalk.cyan('\nRestarting App\n'));
      lastSpawned.restarted = true;
      lastSpawned.kill('SIGTERM');
      lastSpawned.emit('restarted', await forgeSpawnWrapper());
    }
  });

  process.stdin.on('data', async (data) => {
    if (data.toString().trim() === 'rs') {
      restartApp();
    }
  });

  process.stdin.resume();
}
// ...

export function restartApp() {
  restartAppEventEmitter.emit('restart');
}

This would work without consumers directly emitting anything and still allows us to keep the logic simple.

[erikian]

Here's the alternative I mentioned in my previous comment: 3a3cf97. I believe using some form of event-based approach is the best option here — the restart logic depends on variables that are inside the scope of the enclosing start function, and exposing a restartApp method without using events would involve declaring those variables at the top-level of the module and then assigning them from the start function so restartApp can also access them, which is much uglier IMO.

[caoxiemeihao]

Implemented in #3468