Do not warn if .flat() has more than one parameter or if the one parameter is not 1

[MrHen]

Fixes #315.

A follow up question is if we should warn / fix on .flat(1) which is default flattening behavior but I wanted to get the fix out quickly.

[sindresorhus]

Yes, we should report and fix .flat(1).

[fisker]

and also undefined ? maybe also "1"?

according to , https://tc39.github.io/proposal-flatMap/#sec-Array.prototype.flat

Any value can ToInteger equals to 1, all the same

[sindresorhus]

@fisker Nah. No one would actually pass in that. Not worth caring about.

[fisker]

make sense

[fisker]

on second thought, most people also not pass 1, how about not check arguments at all, instead maybe make a new rule to check flat argument ?

[sindresorhus]

on second thought, most people also not pass 1, how about not check arguments at all, instead maybe make a new rule to check flat argument ?

A rule that checks arguments for built-ins in general sounds useful, but would be very fragile without type information. Better to just use TypeScript then.