RFR: 8189354: ArrayIndexOutOfBoundsException when listening to selection changes on TreeTableView [v3]

[mstr2]

On Sun, 25 Apr 2021 15:35:58 GMT, mstr2 <github.com+43553916+mstr2 at openjdk.org> wrote:

>> This PR fixes the implementation of `ControlUtils.reducingChange`, which incorrectly computed adjacent removed indices, thus resulting in incorrect removal notifications.
>> 
>> Since there were no unit tests for this method, I also added a bunch of tests.
>> 
>> After applying this fix, I can no longer reproduce [JDK-8189354](https://bugs.openjdk.java.net/browse/JDK-8189354) and [JDK-8189228](https://bugs.openjdk.java.net/browse/JDK-8189228).
>
> mstr2 has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Revert changes to MockListObserver
>  - Removed ControlUtils.reducingChange

You're right that removing `ControlUtils.reducingChange` is enough to solve the problem. Maybe the method was created because it might be confusing that, while the indices are often not adjacent, they _are_ (as you correctly say) adjacent with respect to `selectedIndices`.

I have tested the change with [8189354](https://bugs.openjdk.java.net/browse/JDK-8189354) and [8189228](https://bugs.openjdk.java.net/browse/JDK-8189228), and both issues seem to be solved.

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PR: https://git.openjdk.java.net/jfx/pull/480