process.argv vanishing when --import flag used

[bpstrngr]

Version

20.9.0

Platform

linux-x64

I'm trying to upgrade from the old --loader to the new --import flag for module customization hooks now, but i'm encountering an issue with process.argv going missing when the --import flag is used (both in the loader registration worker, and the main process), unlike without the flag being used:


( for full picture, this is where the hooks get called in each case: )

I have seen similar occur with the --watch flag not being present in execArgv when used, but that is less critical and i can imagine a reason for it.
Is there a reason for process.argv disappearing with --import modules?
Tested with Node 20.9 and 21.1, happens in both versions.

Additional information

first reported under --import flag's concluded feature request: #40110 (comment)

[aduh95]

Could you share a minimal repro? Please note that images makes it very hard fir folks using screen reader, or those unable to decipher text with your color scheme – it also makes it pointlessly harder to copy paste your code to debug the issue.

[bpstrngr]

@aduh95 Thanks for looking, so the only thing to see in the screenshots is the commands being run, which are:
node ./loader.js 1 2 3
and
node --import=./loader.js ./loader.js 1 2 3,
the first of which has process.argv available as passed,
but the second loses them from at least version 20.9,
given a loader.js file with such contents:

// loader.js
 if(process.execArgv.some(flag=>flag.startsWith("--import")))
 // register loader module. 
 await Promise.all(["module","worker_threads"].map(module=>
 import(module))).then(([{register},{MessageChannel}])=>
 [new MessageChannel(),import.meta.url].reduce(({port1,port2},parentURL)=>
 register(new URL(parentURL).pathname,parentURL,{data:{socket:port2},transferList:[port2]})));
 else console.trace(process.argv);

 export function initialize({socket}){console.trace(process.argv);socket.postMessage("Module interface ready");}
 
 export function resolve(source,context,next){console.trace(process.argv);return next(source,context);}

expected logs:
['/path/to/node', '/path/to/loader.js', '1', '2', '3']
actual:
['/path/to/node']

[aduh95]

I think it is your responsibility to pass the argv from the main thread to the loader thread.

/cc @nodejs/loaders

[bpstrngr]

@aduh95 ah right argv are actually intact on the main thread - i just got used to the main thread running the resolution with the old --loader flag, and thought the worker was only alive during the loader registration/initialization. It all actually remains on a separate thread now, got it. So it's a similar reason to why that --watch flag disappears from execArgv on the main thread itself too.

Now i'll just need to figure out how to get the result of what i use the argv for in module resolution back to the main thread somehow... hope it's possible.

Thanks!