Skip 'off-by-one' adjustment in block length during undo operation

The adjustment of block length with 'off-by-one' affects content
length during undo operation. The issue occurs when we perform undo
operation for a set of group blocks that have same fragment
position. Since their positions are same, group block change
(QTextDocumentPrivate::documentChange) with respect to insertion
doesn't affect document block length and further adjustment to
'off-by-one' without considering this leads to incorrect document
content change information (such as invalid information with regard
to characters removed).

This patch skips adjustment of group block length during undo
operation.

Amends 8fbedf2196a292fe2affcf83ddc846b9c852772a

Fixes: QTBUG-113865
Pick-to: 6.7 6.6 6.5 6.2 5.15
Change-Id: I315dcf01ba5b2f4ed6d95e9d6910d82848374aef
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/gui/text/qtextdocument_p.cpp b/src/gui/text/qtextdocument_p.cpp
index 0718300d37..3c1fc04d4b 100644
--- a/src/gui/text/qtextdocument_p.cpp
+++ b/src/gui/text/qtextdocument_p.cpp
@@ -349,8 +349,10 @@ int QTextDocumentPrivate::insert_block(int pos, uint strPos, int format, int blo
     QTextBlockGroup *group = qobject_cast<QTextBlockGroup *>(objectForFormat(blockFormat));
     if (group) {
         group->blockInserted(QTextBlock(this, b));
-        docChangeOldLength--;
-        docChangeLength--;
+        if (command != QTextUndoCommand::BlockDeleted) {
+            docChangeOldLength--;
+            docChangeLength--;
+        }
     }
 
     QTextFrame *frame = qobject_cast<QTextFrame *>(objectForFormat(formats.format(format)));