Ability to suppress warnings by type (or just experimental warnings)

[coreyfarrell]

Is your feature request related to a problem? Please describe.
I'd like to suppress experimental warnings while still seeing any other errors. In particular when I am using native ES modules I do not want the experimental warning printed for every process, but I do want unrelated warnings to still be printed.

Describe the solution you'd like
Allow --no-warnings to optionally accept an option string such as --no-warnings=type1,type2. Using --no-warnings without any option would continue to disable all warnings. This would allow --no-warnings=ExperimentalWarning to suppress ExperimentalWarning only.

Describe alternatives you've considered
--no-experimental-warnings or a similarly named new flag could be created. This has the drawback that node --no-experimental-warnings on node.js 13.3.0 exit with an error where --no-warnings=ExperimentalWarnings will not currently error (it causes all warnings to be ignored).

In my own repo which uses ES modules I've created suppress-experimental.cjs which gets loaded with NODE_OPTIONS='--require=./suppress-experimental.cjs':

'use strict';

const {emitWarning} = process;

process.emitWarning = (warning, ...args) => {
	if (args[0] === 'ExperimentalWarning') {
		return;
	}

	if (args[0] && typeof args[0] === 'object' && args[0].type === 'ExperimentalWarning') {
		return;
	}

	return emitWarning(warning, ...args);
};

Obviously patching node.js internals like this is undesirable but it accomplishes my goal.

[JoshMcCullough]

args[0] would point to a string, since the arguments to emitWarning are warning: string | Error, name?: string, ctor?: Function. Are you sure this code is working correctly?

[coreyfarrell]

@JoshMcCullough Yes the code works, note that the parameters for my replacement function are (warning, ...args). I can see how that looks odd but it definitely works.

[JoshMcCullough]

I was suggesting that your args[0] will always be a string since it maps to the 2nd parameter of emitWarning, which is (if the types are correct), name?: string. So the second if block would never be entered -- unless I'm totally missing something here.

[coreyfarrell]

https://nodejs.org/dist/latest/docs/api/process.html#process_process_emitwarning_warning_options shows that process.emitWarning can also take an options object as the second argument. I don't think the ESM warning uses that style call but I still check for it as I want my code to continue working if the ESM warning switches to the options object.