Add option to the `no-nested-ternary` rule that allows parens wrapped nested ternaries

We’ve been discussing it over at sindresorhus/xo#12 and concluded it might be nice to have a rule where no-nested-ternary wouldn’t trigger if the nested ternary is wrapped in parenthesis.

We agreed the following ‘unreadable’ and ambiguous code

var foo = i > 5 ? true : i < 100 ? true : false;

could be improved by adding parenthesis.

var foo = i > 5 ? true : (i < 100 ? true : false);

As it stands, ESLint catches both as nested ternaries.

---

There also comes the issue of logic. The following is correct logic; platform === 'linux' isn’t evaluated unless opts.dash is falsey.

var file = opts.dash ? '-' : (platform === 'linux' ? '/dev/stdin' : '/proc/self/fd/0');

Alternatively, the logic would have to be

var file;
if (opts.dash) {
  file = '-';
} else {
  file = platform === 'linux' ? '/dev/stdin' : '/proc/self/fd/0';
}

which is much less than ideal.

---

It’d be nice if there was an option for allowing parenthesis wrapped nested ternary expressions, i.e.

{'no-nested-ternary': [2, {allowParensWrapped: true}]

// @sindresorhus

[wmertens]

It is hard to avoid nested ternaries in React JSX expressions since it is the only available flow control inside them short of creating an immediately-evaluated function.

The only other alternative is preparing the result beforehand, which can be confusing and hard to maintain.

When doing multi-line ternaries, it also helps with figuring out nesting, somewhat.

I think that allowing parens around ternaries is an acceptable trade-off here…

<div>{isFoo ? (isBar ? "barred foo" : <Foo />) : <Whee />}</div>

and multiline

<div>{isFoo ? (
  isBar ? (
    "barred foo"
  ) : (
    <Foo />
  )
) : (
  <Whee />
)}</div>

[nzakas]

The problem with that is that it would allow parens around all ternaries, not just nested ones.