Do not define unset boolean args

[pvdlg]

Proposal to solve xojs/xo#299.

For each boolean arg that doesn't define a default, set it to undefined. After parsing remove the options with a value of undefined.

Unfortunately this doesn't work with minimist due to an unrelated bug when using both default and alias:

minimist(['-f'], {boolean: ['foo'], alias: {f: 'foo'}, default: {foo: null}});
// => {_: [], foo: true, f: [null, true]}
// Should be {_: [], foo: true, f:  true}

minimist(['--foo'], {boolean: ['foo'], alias: {f: 'foo'}, default: {foo: null}});
// => {_: [], foo: true, f: [null, true]}
// Should be {_: [], foo: true, f:  true}

I replaced minimist with yargs-parser to solve this issue.

meow relies on minimist-options to transform the options format. It still works with yargs-parser as the format is the same.

This PR works as a fix for xojs/xo#299 but it might be a desireable to support the other yargs-parser options. That would require to support those option in minimist-options or to replace it.

Not sure if it worth the effort though, as yargs already allow all those options and support the same convenient format as meow via the options function:

const argv = require('yargs')
    .options({
      rainbow: {
	type: 'boolean',
	alias: 'r'
     }
   }).argv;

[sindresorhus]

Does Yargs also default to undefined if boolean is the type and no default is specified?

[pvdlg]

Yards default to false like minimist.
For some reasons minimist ignore {default: undefined} but works with {default: null}.

[sindresorhus]

I'm still a little bit unsure whether undefined when no default is specified for boolean is the best default. It's quite convenient not having to specify default: false for all boolean flags. Maybe we should make this behavior opt-in with a Meow option?

[pvdlg]

OK, we can have an option. We just need to define what's the default.
What is most the common case:

• Wanting the unset boolean arg to not be included in the result options object?
• Or wanting the unset boolean args to be false?

[sindresorhus]

Or wanting the unset boolean args to be false?

This. I've only needed unset options in XO and one other CLI before.

[sindresorhus]

Even when boolean defaults to false, it should still be possible to unset them individually, by setting default: null or default: undefined.

[pvdlg]

Even when boolean defaults to false, it should still be possible to unset them individually, by setting default: null or default: undefined.

That's already the case in the current PR.

So we can add the option booleanDefault, and whatever value set there will be used as default, unless a default is already used.
By default booleanDefault will be false.

[sindresorhus]

So we can add the option booleanDefault, and whatever value set there will be used as default, unless a default is already used.
By default booleanDefault will be false.

Yes! Much better than what I had in mind.

[pvdlg]

I added the booleanDefault option. By default it's false so the default behavior doesn't change.

[pvdlg]

Updated to to yargs-parser@10.0.0

[sindresorhus]

Looks good. Thanks, @pvdlg :)