D29210: [NestedListHelper] Fix indentation of selection, add tests

[Igor Poboiko]

poboiko added inline comments.

INLINE COMMENTS

> dfaure wrote in nestedlisthelper.cpp:225
> should the opposite happen? delete the list when decreasing indentation?
> 
> Or is that what the blkFmt.setObjectIndex(-1); is about?
> A comment there would be useful...
> 
> To me setObjectIndex(-1) sounds like it could kill any kind of embedded object there.... but I might be wrong.

We indeed delete it when decreasing, but here `delta > 0`, which corresponds to increasing :)

Regarding `setObjectIndex()`: it does indeed look like magic, and I don't totally understand it either. It was there, however, and it is also present in the official Qt `TextEdit` example, where it's used when item is removed from the list.
I've found more explicit way: just remove the block from list and set it's indentation to zero, it seems to be working well.

REVISION DETAIL
  https://phabricator.kde.org/D29210

To: poboiko, #frameworks, dfaure, mlaurent
Cc: kde-frameworks-devel
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