RFR: JDK-8304933: BitSet (used for CSS pseudo class states) listener management is incorrect [v2]

[John Hendrikx]

On Mon, 10 Apr 2023 22:07:41 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

>> As with the earlier comment, any changes to the behavior of a null listener should be done separately and not part of this PR.
>
> Alright, I'll file another ticket for that.  The general state of this class is quite poor, as it does not follow any of the contracts of the interfaces it implements (including `Collection`, `Set` and `ObservableSet`).  This is bad because even though this class is an implementation detail, it does get exposed as an `ObservableSet` via `Node#getPseudoClassStates`.  Things that it violates for example are:
> 
>      node.getPseudoClassStates().retainAll(null);   // no exception
> 
> Or:
>    
>      node.getPseudoClassStates().retainAll(set2);   // does nothing if set2 is not a BitSet
> 
> Or:
> 
>      // fails, even if they're the same because `equals` assumes another BitSet     
>     node.getPseudoClassStates().equals(Set.of(PseudoClass.getPseudoClass("armed"));
> 
>      // works:
>      Set.of(PseudoClass.getPseudoClass("armed")).equals(node.getPseudoClassStates());
> 
> Same goes for the hash code value; these are strictly defined for sets, but `BitSet` violates it causing problems when using these sets as keys.  This causes numerous odd problems that I had to track down while implementing #1076 -- I can only assume very few people are using these API's in the wild.

Filed https://bugs.openjdk.org/browse/JDK-8305816 so we don't forget.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1071#discussion_r1162156819