RFR: JDK-8304959: Public API in javafx.css.Match should not return private API class PseudoClassState [v2]

[John Hendrikx]

On Sat, 8 Apr 2023 20:33:43 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

>> The class `PseudoClassState` is private API, but was exposed erroneously in the CSS API. Instead, `Set<PseudoClass>` should have been used. This PR corrects this.
>
> John Hendrikx has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Ensure Set PseudoClass and StyleClass are immutable in CSS API
>   
>   Updated documentation, fixed warnings and removed some unnecessary code

I think this is the best that can be done for now.  There are still some mutable aspects to `Selector` (you can change the `Rule` and the ordinal of one).  I'm really not quite sure why it is done that way, it seems there was may have been some vision that these classes could be used to "edit" a stylesheet -- something that's probably best done with a different set of classes to avoid burdening regular read-only CSS work with editable variants, requiring defensive copying everywhere.

Ideally, `Selector` and `Match` would have been interfaces, and the private code should work with the CSS classes only through those.  Changing them to interfaces now seems impossible, it's not binary compatible, and I don't see a deprecation route to get there.

However, it is still possible to improve the situation a bit (in another PR perhaps), as the private code only requires a few additional methods to be made public API on `Selector` to remove its direct dependencies on `SimpleSelector` and `CompoundSelector`:

- getName() which returns the java class name to which the selector is applied
- getId() returns the CSS id (if any) of a Selector
- getStyleClassSet() returns the (immutable) style classes of a Selector

These three methods are implemented by `SimpleSelector`, but not by `CompoundSelector`.  Instead, its last selector is extracted (which is always a `SimpleSelector`) and the methods are called on those. These methods could be made part of `Selector`, then `CompoundSelector` implements them by directing them to its last `SimpleSelector`, and the private code would not need to care about the selector type anymore. These selector classes could then be hidden completely.

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PR Comment: https://git.openjdk.org/jfx/pull/1070#issuecomment-1500980591