CartesianSet.equals always returns false for other Set types

[Marcono1234]

Version

32.1.3-jre

Description

The internal class CartesianSet returned by Sets.cartesianProduct implements equals in a way that it is never equal to any other Set type because it calls super.equals which is actually Object.equals (and therefore checks for object identity).
That does not seem intended.

Example

Object o1 = ImmutableSet.of(ImmutableList.of(1, 2));
Object o2 = Sets.cartesianProduct(ImmutableList.of(
    ImmutableSet.of(1), ImmutableSet.of(2)
));

System.out.println("o1.equals(o2): " + o1.equals(o2));
System.out.println("o2.equals(o1): " + o2.equals(o1));

[eamonnmcmanus]

That definitely looks like a violation of the contract of Set.equals. It's been like that for 15 years, so probably it hasn't mattered in practice? Still, I think we could have fallback logic for this case. It could just check that the other set has the right size and that the CartesianSet contains all of the other set's elements.

As far as I can see, CartesianSet.hashCode() does follow the contract for Set.hashCode().

[eamonnmcmanus]

Actually, not quite 15 years, but 11, since this commit changed the parent type from AbstractSet to ForwardingCollection.