fix: respect process.exitCode

[brandonocasey]

Fixes #40

[sindresorhus]

AI review:

The Problem with the Current Patch

The patch always prioritizes process.exitCode over signal-based exit codes, but this might not be the right behavior. Consider these scenarios:

1. User sets process.exitCode = 1 for normal exit handling
2. Process gets killed by SIGTERM (signal 15)
3. Current patch would exit with code 1 instead of 143 (128 + 15)

This loses important information about how the process died. Unix convention uses 128 + signal specifically to distinguish signal-based exits from normal exits.

Better Approach

The intention should probably be more nuanced:

// Respect process.exitCode for graceful exits, but preserve signal info for real signals
const exitCode = (signal > 0) 
  ? 128 + signal  // Real signal - preserve signal-based exit code
  : (typeof process.exitCode === 'number' || typeof process.exitCode === 'string') 
    ? process.exitCode 
    : 0;

Or alternatively, only respect process.exitCode for explicit exits:

const exitCode = (signal === 0 || signal === -128) // exit event or gracefulExit
  ? (typeof process.exitCode === 'number' || typeof process.exitCode === 'string') 
    ? process.exitCode 
    : 0
  : 128 + signal;

The Question

Should process.exitCode = 1 be ignored when the process is killed by SIGTERM? I think it probably should be - the signal-based exit code (143) carries more important information about the termination cause.

[brandonocasey]

The current failure on node 20 is happening for me even in main. The listener appears to be:

function flushSync() {
  workerStdio.stdout[kStdioWantsMoreDataCallback]();
  workerStdio.stderr[kStdioWantsMoreDataCallback]();
}

which comes from node internals: https://github.com/nodejs/node/blob/34cb10b4a25a920b9d38daff64ce4467a996bfc5/lib/internal/bootstrap/switches/is_not_main_thread.js#L49
Seems like the tests need an update in a different pull request. Unless you want me to update them here?

[sindresorhus]

You can just update here.

[timmywil]

This seems to have changed the behavior of gracefulExit(1), which now exits with signal 0. Was that intended? I had to change all calls to

process.exitCode = 1
gracefulExit()

Edit: Sorry, I should have checked the issues first. I went digging into source right away. See #42