Remove process.exit(1) from babel-node

[dword-design]

Because it breaked graceful shutdown of the sub process. For example, if you have an express server, catch the SIGINT signal and process.exit(0) after closing the server, the command would always return exit code 1. This PR allows the subprocess to decide how to exit itself.

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/10596/

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/10596/

[mgreenw]

This makes sense 👍I'm still worried about the functionality here because I don't think this change fixes #8526 where the SIGINT signal gets sent to the child process twice. Should line 106 be removed entirely such that babel-node (the parent process) does not even handle SIGINT at all?

[nicolo-ribaudo]

Should line 106 be removed entirely such that babel-node (the parent process) does not even handle SIGINT at all?

Probably yes, but I'm not an expert on this topic.
I think that currently we are doing this:

1. Spawn babel-node
   1.i Spawn user's program
   1.ii Ctrl+C
   1.iii SIGINT
2. SIGINT (it bubbles to the parent process?)
   2.i Forward SIGINT to the child process
3. process.exit(1)

[mgreenw]

I'm not exactly sure what would happen if the SIGINT for some reason never got sent to the child process. Because the parent is dead, wouldn't the child get reaped at some point?

I think the initial SIGINT from the Ctrl-C should be plenty to alert the child that it should die, and the parent re-sending the signal (2.i in @nicolo-ribaudo's chart) does not make sense and should be removed.

[nicolo-ribaudo]

I think that this PR is ok as-is.

I did some experiments around processes management at https://gist.github.com/nicolo-ribaudo/e6dd1806e184aea49a824d1dea2d0001, which simluates what this PR does.
You can run node main.js and kill one of the processes by running kill -SIGINT 12345 (replace 12345 with the correct PID).

If I kill the child process (which is what running Ctrl+C in @babel/node does), I get this output:

Main process is pid 23024
Child process is pid 23031
Child process killed
Child process is exiting...
Child process exited. code: 0, signal: null
Main process is exiting...

If I kill the main process, I get this output:

Main process is pid 23183
Child process is pid 23190
Main process killed
Killing child process...
Child process killed
Child process is exiting...
Child process exited. code: 0, signal: null
Main process is exiting...

As you can see, the child process doesn't receive SIGINT twice (so this PR also fixes #8526).

You can change EXITCODE in child.js to check that the exit code of the child process is not changed by. the main process.

If you comment lines 24-25 of main.js (#9758 (comment)) and kill the main process, the child process will stay alive. On the other hand, even with those lines the child process won't receive SIGINT twice (#8526).

[mgreenw]

@nicolo-ribaudo Thanks for doing that testing! It looks like this kills two birds with one stone.

[JLHwung]

Thanks