Bug 83260

[Yemelyanenko Fyodor]

My assumptions from email below weren't fully correct...
There is RedlineGuard class 
(https://opengrok.libreoffice.org/xref/core/sw/source/core/undo/undobj.cxx#190), 
instance of which is constructed just before UndoImpl called.
Constructor sets RedlineFlags to value, that been during editing, which 
is Undone now, In destructor it sets flags back to their current values. 
This should help Undo mechanism to work properly. But in reality it not 
saves from crushes.
For now I'll do my further investigations on this issue.

------ Исходное сообщение ------
От: "Yemelyanenko Fyodor" <fyodor_e at hotmail.com>
Кому: "libreoffice at lists.freedesktop.org" 
<libreoffice at lists.freedesktop.org>
Отправлено: 22.12.2017 16:56:53
Тема: Bug 83260

>Hello!
>
>I'm working on bug 83260
>(https://bugs.documentfoundation.org/show_bug.cgi?id=83260) and have an
>issue...
>In short, when redlining (change tracking) is ON undo will crush LO
>during some circumstances.
>
>This is connected with redlining implementation in LO. When you toggle
>Show in Edit->Changes->Show and doc already has some deleted 
>paragraphs,
>these paragraph moved from special section of document do document
>section. As a result, such move invalidate Undo indexes and during Undo
>LO will crush in many cases.
>
>For now I see 2 possible solutions:
>1. Rewrite redlining, so Show option will change how doc is viewed, but
>not how it is formed (list of nodes)
>2. When toggling change tracking or show option ON/OFF - clean
>Undo/Redo.
>
>For now, I prefer option 2 :-)
>
>Do we need to warn user, that we going to purge Undo/Redo (say, by
>displaying some warning?)
>Any additional suggestions will be appreciated.
>
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