doc: document --no-warnings=<cat1>,<cat2>

[bnoordhuis]

Refs #30810.

Node allows suppression of e.g. experimental warnings with --no-warnings=ExperimentalWarning but that syntax is completely undocumented. Even the warning categories aren't documented anywhere, as far as I can tell.

The way node parses flags means its inversion --warnings=ExperimentalWarning possibly also does something meaningful but I haven't checked.

[jakecastelli]

Hi Ben, I have tried the --no-warnings flag with =<xxWarning> but it looks like it would just suppress all the warnings instead of the one I explicitly set, maybe I used it incorrectly?

The code sample I tested locally:

const EventEmitter = require('events').EventEmitter;

const eventEmitter = new EventEmitter();

for (i = 0; i < 11; i++) {
  eventEmitter.on('', () => {});
}

setTimeout(() => {}, 2 ** 32);

// print:
// (node:87253) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11  listeners added to 
// [EventEmitter]. Use emitter.setMaxListeners() to increase limit
// (Use `node --trace-warnings ...` to show where the warning was created)
// (node:87253) TimeoutOverflowWarning: 4294967296 does not fit into a 32-bit signed integer.
// Timeout duration was set to 1.

I tried --no-warnings=MaxListenersExceededWarning and it also suppressed TimeoutOverflowWarning from setTimeout.

Tested on node 14 and current main branch, same results.

[bnoordhuis]

--no-warnings=... doesn't work at the granularity of individual warning classes, just:

1. categories, of which I believe there are currently only three: DeprecationWarning, ExperimentalWarning and V8; or

2. deprecation numbers; DEP0001, DEP0002, etc.

[jakecastelli]

I have tried --no-warnings=DEP0024 which is deprecation warning for sys

const assert = require('assert');
const sys = require('sys');

try {
  assert.fail('a', 'b')
} catch(err) {}

I would expect the console to suppress the deprecation warning for sys but still show me the DEP0094 which is the deprecation warning for assert.fail with more than 2 args.

However it looks like it has suppressed all the warnings 🤔

Would you mind pointing out where the source code for parsing the flag 🙏 cheers!

[bnoordhuis]

The warning for require('sys') is DEP0025, not DEP0024. :-)

It's possible suppressing specific deprecation warnings no longer works. Like I said, it's functionality that's undocumented and - worse - untested so it quite possibly bitrotted.

[jakecastelli]

Sorry I had a typo, meant to type DEP0025.

I tried to search where this functionality resides in the code base but didn't find it :(

[jagadeeshmeesala]

this will be my first issue to start with, can I take this one?

[bnoordhuis]

Sure, go ahead.

[jagadeeshmeesala]

PR is created for the documentation here #47031 #47031

Please review.

[jagadeeshmeesala]

I have tried to use --no-warnings=ExperimentalWarning and --no-warnings=DeprecationWarning, but it is neither accepting any of the option, basically suppressing all type of warnings. But --no-deprecation command-line flag can be used to suppress deprecation warnings. It is mentioned in the documentation already I just iterated that.

`'use strict';

const EventEmitter = require('events').EventEmitter;

const eventEmitter = new EventEmitter();

for (let i = 0; i < 11; i++) {
  eventEmitter.on('', () => {});
}

setTimeout(() => {}, 2 ** 32);


const assert = require('assert');
const sys = require('sys');

try {
  assert.fail('a', 'b')
} catch(err) {}` 

[Lakshyachitransh]

Hi jagadeeshmeesala if you are not working on this can i take this