Stop throwing for unsupported options in `Worker`'s `execArgv` and `env.NODE_OPTIONS`.

Version

v17.2.0

Platform

No response

Subsystem

worker_threads

What steps will reproduce the bug?

Consider this test.js file:

const { isMainThread, Worker } = require("worker_threads");

if (isMainThread) {
  new Worker(__filename, {
    // execArgv: process.execArgv
  });
} else {
  console.log("Hello from the worker!", process.execArgv);
}

NOTE: --experimental-json-modules and --title are just examples

Run these two commands:

node --experimental-json-modules test.js
node --experimental-json-modules --title foo test.js

They will log

Hello from the worker! [ '--experimental-json-modules' ]
Hello from the worker! [ '--experimental-json-modules', '--title', 'foo' ]

Now, uncomment the execArgv: process.execArgv line and run the two commands again. The first command will still log

Hello from the worker! [ '--experimental-json-modules' ]

however, the second one throws:

Error [ERR_WORKER_INVALID_EXEC_ARGV]: Initiated Worker with invalid execArgv flags: --title
    at new NodeError (node:internal/errors:371:5)
    at new Worker (node:internal/worker:191:13)
    at Object.<anonymous> (/home/nicolo/Documenti/dev/babel/babel/test.js:4:3)
    at Module._compile (node:internal/modules/cjs/loader:1097:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1149:10)
    at Module.load (node:internal/modules/cjs/loader:975:32)
    at Function.Module._load (node:internal/modules/cjs/loader:822:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
    at node:internal/main/run_main_module:17:47 {
  code: 'ERR_WORKER_INVALID_EXEC_ARGV'
}

This mans that the default behavior of the Worker execArgv option is not to inherit execArgv from the parent thread (contrary to what the documentation says).

Why would you want to explicitly pass execArgv: process.execArgv anyway?

A few days ago I was trying to implement a require hook that internally uses a Worker, and in order to avoid registering it recursively in an infinite worker-spawn loop I tried to filter out the --require flag:

new Worker(workerFile, {
  execArgv: process.execArgv.filter((val, i, argv) => val === "--requrie" || argv[i-1] === "--requrie"),
});

this seemed to work, until it crashed in a test that was using the --expose_gc option.

Today, I found the exact same problem in jest-worker (a Jest subpackage that is often also used outside of Jest): https://github.com/facebook/jest/pull/12103 was opened because jest-worker didn't work when running Node.js with --max_old_space_size.

Since Node.js doesn't provide the list of flags supported by workers progrmmatically (and I didn't find it in the docs either 😅) there is no way to filter the execArgv used by a worker.

What is the current behavior?

I initially expected the real default behavior to be something like execArgv: process.execArgv.filter(isSupportedByWorker), but it looks like it's not either. Consider for example the --expose_gc (which is disallowed in workers) option with this example:

const { isMainThread, Worker } = require("worker_threads");

if (isMainThread) {
  new Worker(__filename);
} else {
  console.log("Hello from the worker!", process.execArgv, globalThis.gc);
}

If you run node --expose_gc test.js, it will log

Hello from the worker! [ '--expose_gc' ] [Function: gc]

You can see that the gc function is present. This means that the disallowed flags are not ignored (and not even "ignored but still used to populate the process.execArgv array): they are used and affect the runtime behavior.

How often does it reproduce? Is there a required condition?

Only for the options marked as "unsupported" in workers.

What is the expected behavior?

I see four possible solutions:

• Just ignore the unsupported options
• Never throw, but warn when passing an unsupported option to a worker (potentially even if it's passed by default without an explicit execArgv).
• Only throw if the unsupported option is not also used as an execArgv of the parent thread.
• Always throw for unsupported options (so that execArgv: process.execArgv becomes the default behavior), and provide a Worker.filterExecArgv utility that removes disallowed options, and that I would have used like

  Worker.filterExecArgv(process.execArgv).filter((val, i, argv) => val === "--requrie" || argv[i-1] === "--requrie")
  

If the current behavior is expected, then the docs should be updated to mention that the default value cannot be replicated by explicitly passing an execArgv option.

What do you see instead?

No response

Additional information

No response

Start with the test.js worker_threads reproductions using --experimental-json-modules, --title, and --expose_gc, then read the Worker execArgv documentation and entry point. The issue presents several incompatible behavior choices, so first establish the intended handling for unsupported execArgv and env.NODE_OPTIONS; done should include matching behavior and coverage.