Incorrect default type should not be allowed

[sindresorhus]

The parser should not allow setting the incorrect type for default.

yargs([], {number: ['foo'], default: {foo: 'x'}});
//=> { _: [], foo: 'x' }

The above should not be allowed as we defined foo as a number, but the default is set to a string. This should throw an error to prevent mistakes.

[bcoe]

@sindresorhus all of the validation currently happens inside of yargs (https://github.com/yargs/yargs/blob/master/lib/validation.js). Challenges to implementing this feature in yargs-parser, from yargs' point of view are:

1. would need to figure out a way to handle translations, even though all the language files are in yargs.
2. would probably need to refactor the validation.js in yargs, moving some of the logic towards `yargs-parser.

I think this could be a really interesting task for someone.

[bcoe]

refreshing myself with how we handle other strings, we do already have support for translations in yargs-parser, which is good:

  var __ = opts.__ || function (str) {
    return util.format.apply(util, Array.prototype.slice.call(arguments))
  }

[sindresorhus]

would need to figure out a way to handle translations, even though all the language files are in yargs.

Give the errors a unique .code property code and then detect that in Yargs. yargs-parser should not do translations.

[bcoe]

@sindresorhus I was about to reply; since this is a development time error, not a user-land error, I wonder fi we could get away with a throw in this one case, even though we're not throwing for any other errors currently in the parser.

[sindresorhus]

Yes, throwing would be the correct thing to do here. It's a developer-error, not a end-user error. Throw early.

[bcoe]

@sindresorhus, @juergba has been starting to add some more early validation checks in yargs-parser, this seems like an ideal candidate for one.

[bcoe]

see: #301

[Eomm]

If it doesn't cost too much effort, would you mind to keep an option to coerce the values as it was in previous versions of the module?

An example use case is to save the user's default in the env and then use process.env to define the yargs-parser defaults.