RFR: 8189354: ArrayIndexOutOfBoundsException when listening to selection changes on TreeTableView [v8]

[Ambarish Rapte]

On Tue, 27 Apr 2021 19:18:59 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 one additional commit since the last revision:
> 
>   Use MockListObserver

The fix looks good to me. Performed a regressive testing on TreeTableView and TreeView.  Though there is an existing issue that SelectionModel.getSelectedItems() and SelectionModel.getSelectedIndices() are incorrect when some intermediate change events are received.
Also, I agree with Jeanette on that the two issues in discussion seem different. The AIOOB Exception is not reproducible with TreeView.
But I found another NPE with TreeView which gets fixed by this PR.
Steps:
1. Run the test program attached to [JDK-8189228](https://bugs.openjdk.java.net/browse/JDK-8189228)
2. Select/Click any child of root for instance 4 Item 1
3. Ctrl click the same item to deselect it
-> Observe the NPE
This gets fixed by this PR.

The issues that are currently listed in the bug [JDK-8189228](https://bugs.openjdk.java.net/browse/JDK-8189228) are not reproducible, so it can be closed as cannot reproduce
or 
May be we should update the description of  [JDK-8189228](https://bugs.openjdk.java.net/browse/JDK-8189228) to include this NPE and add that bug to this PR ?

modules/javafx.controls/src/test/java/test/javafx/scene/control/TreeTableViewTest.java line 6654:

> 6652:         root.setExpanded(true);
> 6653: 
> 6654:         TreeTableView<String> treeView = new TreeTableView<>(root);

rename variable as `treeTableView`

modules/javafx.controls/src/test/java/test/javafx/scene/control/TreeViewTest.java line 3704:

> 3702:         observer.check1();
> 3703:         observer.checkAddRemove(0, treeView.getSelectionModel().getSelectedItems(), List.of(c1, c2, c3), 1, 1);
> 3704:     }

These test validate the getRemoved() list. I think we should also have a test for exception.

-------------

Changes requested by arapte (Reviewer).

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