Power sets are broken for ES6

[michaelmior]

Describe the bug
The power set function is broken in ES6 (at least, as transformed via Babel).

To Reproduce

$ cat .babelrc
{
  "presets": ["@babel/preset-env"]
}
$ babel-node
babel > require('set-extensions');
{}
babel > Set.power(new Set([1,2,3]));
Set(8) {
  Set(1) { 3 },
  Set(2) { 3, 2 },
  Set(2) { 3, 1 },
  Set(3) { 3, 2, 1 },
  Set(0) {},
  Set(1) { 1 },
  Set(1) { 2 },
  Set(1) { 3 }
}

Expected behavior
The set {2, 1} should be included in the power set.

Desktop (please complete the following information):

• OS: macOS Catalina 10.15.6
• Browser: node.js
• Version: v14.8.0

Additional context

• babel-node version: 7.8.4
• set-extensions version: 1.4.1
• @babel/core version: 7.11.6
• @babel/preset-env version: 7.11.5

[jankapunkt]

hi @michaelmior thank you for the bug report. I will investigate and will use this as a chance to revive this package.

[jankapunkt]

This revealed another bug in Set.prototype.equal, where

Set {
  Set { 1, 2, 3 },
  Set { 1, 2 },
  Set { 1, 3 },
  Set { 2, 3 },
  Set { 1 },
  Set { 2 },
  Set { 3 },
  Set {}
}

and

Set {
  Set { 3 },
  Set { 3, 2 },
  Set { 3, 1 },
  Set { 3, 2, 1 },
  Set {},
  Set { 1 },
  Set { 2 },
  Set { 3 }
}

are evualuated as equal, while in fact they are not.

[jankapunkt]

Another bug is that there should be no doubled entries of Set { 3 }. It is right to assume, that these are two totally different instances and therefore pass the checks but their absolute value representation are the same (Set { 3 } should be considered equal to Set { 3 }). So the Set.prototype.has function is also involved here.

The has function is not involved, as it works correct. The add function is rather affected:

const set = (...args) => new Set(args)

const set1 = set(3)
const set2 = set(3)

const set3 = set()
set3.add(set1)
set3.has(set1) // true
set3.has(set2) // true

set3.add(set2) // should skip set2
set3 // Set { Set { 3 }, Set { 3 } }

[jankapunkt]

@michaelmior I added you as collaborator. If you accept I can assign you to review the PR #51 which attempts to fix the issue.

[jankapunkt]

Implemented, via #51