Fix possibly corrupted log clusters when using custom tab stops

The calculateTabWidth() can trigger shaping of the item, which can
cause the layout data to be reallocated, so we need to update the
local pointers to it, like we do when we explicitly invoke the
shaper.

[ChangeLog][Text] Fixed problems with text layout when using custom
tab stops.

Task-number: QTBUG-43126
Change-Id: Ifaeeeb4bfb1a55e6638b12b444f53d2679d3d1e6
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>

src/gui/text/qtextlayout.cpp

@@ -1776,6 +1776,11 @@ void QTextLine::layout_helper(int maxGlyphs)
 
             QFixed x = line.x + line.textWidth + lbh.tmpData.textWidth + lbh.spaceData.textWidth;
             QFixed tabWidth = eng->calculateTabWidth(item, x);
+            attributes = eng->attributes();
+            if (!attributes)
+                return;
+            lbh.logClusters = eng->layoutData->logClustersPtr;
+            lbh.glyphs = eng->shapedGlyphs(&current);
 
             lbh.spaceData.textWidth += tabWidth;
             lbh.spaceData.length++;

tests/auto/gui/text/qtextlayout/tst_qtextlayout.cpp

@@ -116,6 +116,7 @@ private slots:
     void boundingRectForSetLineWidth();
     void glyphLessItems();
     void justifyTrailingSpaces();
+    void layoutWithCustomTabStops();
 
     // QTextLine stuff
     void setNumColumnsWrapAtWordBoundaryOrAnywhere();
@@ -2050,5 +2051,38 @@ void tst_QTextLayout::nbsp()
     layout.endLayout();
 }
 
+void tst_QTextLayout::layoutWithCustomTabStops()
+{
+    QScopedPointer<QTextLayout> textLayout(new QTextLayout);
+    QList<QTextOption::Tab> tabStops;
+
+    const int tabWidth = 18;
+    const int maxTabPos = 2500;
+    for (int tabPos = tabWidth; tabPos < maxTabPos; tabPos += tabWidth)
+        tabStops << QTextOption::Tab(tabPos, QTextOption::LeftTab);
+
+    QTextOption textOption;
+    textOption.setTabs(tabStops);
+    textLayout->setTextOption(textOption);
+
+    textLayout->setText(QStringLiteral("\ta aa aa aa aa aa aa"));
+
+    textLayout->beginLayout();
+    textLayout->createLine();
+    textLayout->endLayout();
+
+    qreal shortWidth = textLayout->maximumWidth();
+
+    textLayout->setText(QStringLiteral("\ta aa aa aa aa aa aa aa aa aa aa aa aa a"));
+
+    textLayout->beginLayout();
+    textLayout->createLine();
+    textLayout->endLayout();
+
+    qreal longWidth = textLayout->maximumWidth();
+
+    QVERIFY(longWidth > shortWidth);
+}
+
 QTEST_MAIN(tst_QTextLayout)
 #include "tst_qtextlayout.moc"