QQuickText: fix inflated implicitWidth with maximumLineCount

When a Text element uses StyledText with <br> tags, maximumLineCount,
wrapMode: Wrap, and elide: ElideRight, constraining its width could
cause implicitWidth to grow far beyond the correct value.

The root cause is twofold:

1. The loop that creates unwrapped lines for implicit width calculation
used '<=' instead of '<', causing one extra line to be created and
finalized beyond maximumLineCount paragraphs.

2. The multiline-elide code path creates a trailing line via
createLine() to compute the elided text. That line is left unfinalized,
so endLayout() finalizes it at QFIXED_MAX width, inflating
maximumWidth(). Finalize it at zero width right after use.

Fixes: QTBUG-142933
Change-Id: I64bab9512b8400ed63a4dda709259488a2b49a21
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
(cherry picked from commit 021778a0ad7d5758cee5f5592017e46b4e12171d)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 49 insertions, 2 deletions

diff --git a/src/quick/items/qquicktext.cpp b/src/quick/items/qquicktext.cpp
index 22518ca5a5..5a65f170c4 100644
--- a/src/quick/items/qquicktext.cpp
+++ b/src/quick/items/qquicktext.cpp
@@ -980,12 +980,19 @@ QRectF QQuickTextPrivate::setupTextLayout(qreal *const baseline)
                         if (eos != -1)  // There's an abbreviated string available
                             break;
 
-                        const QTextLine nextLine = layout.createLine();
+                        QTextLine nextLine = layout.createLine();
                         elideText = wrappedLine
                                 ? elidedText(line.width(), line, &nextLine)
                                 : elidedText(line.width(), line);
                         elideStart = line.textStart();
                         // elideEnd isn't required for right eliding.
+
+                        // nextLine starts beyond maximumLineCount and is only
+                        // needed for the elide calculation above. Finalize it
+                        // at zero width so endLayout() won't give it QFIXED_MAX
+                        // width, which would inflate maximumWidth().
+                        if (nextLine.isValid())
+                            nextLine.setLineWidth(0);
                     } else {
                         br = unelidedRect;
                         height = naturalHeight;
@@ -1024,9 +1031,10 @@ QRectF QQuickTextPrivate::setupTextLayout(qreal *const baseline)
                         : layoutText.size();
                 if (eol < layoutText.size() && layoutText.at(eol) != QChar::LineSeparator)
                     line = layout.createLine();
-                for (; line.isValid() && unwrappedLineCount <= maxLineCount; ++unwrappedLineCount)
+                for (; line.isValid() && unwrappedLineCount < maxLineCount; ++unwrappedLineCount)
                     line = layout.createLine();
             }
+
             layout.endLayout();
 
             const qreal naturalWidth = layout.maximumWidth();
diff --git a/tests/auto/quick/qquicktext/tst_qquicktext.cpp b/tests/auto/quick/qquicktext/tst_qquicktext.cpp
index 78b5d2220d..42ff11d99e 100644
--- a/tests/auto/quick/qquicktext/tst_qquicktext.cpp
+++ b/tests/auto/quick/qquicktext/tst_qquicktext.cpp
@@ -102,6 +102,7 @@ private slots:
     void implicitSize();
     void implicitSizeChangeRewrap();
     void implicitSizeMaxLineCount();
+    void implicitWidthAfterWidthChange();
     void dependentImplicitSizes();
     void contentSize();
     void implicitSizeBinding_data();
@@ -2487,6 +2488,44 @@ void tst_qquicktext::implicitSizeMaxLineCount()
     QCOMPARE_EQ(textObject->implicitWidth(), referenceWidth);
 }
 
+// implicitWidth should not grow after width is constrained and then released
+void tst_qquicktext::implicitWidthAfterWidthChange()
+{
+    // Test that implicitWidth remains stable when the item width is constrained
+    // and then released, for StyledText with <br> tags, maximumLineCount, wrap, and elide.
+    QScopedPointer<QQuickText> textObject(new QQuickText);
+    textObject->setTextFormat(QQuickText::StyledText);
+    textObject->setText(QStringLiteral("First line<br>Second line<br>"
+                                       "11111111111111111111111111111111111111111111111111111111111"
+                                       "11111111111111111111111111111111111111111"));
+    textObject->setMaximumLineCount(2);
+    textObject->setWrapMode(QQuickText::Wrap);
+    textObject->setElideMode(QQuickText::ElideRight);
+    textObject->componentComplete();
+
+    // Get the unconstrained implicitWidth
+    const qreal originalImplicitWidth = textObject->implicitWidth();
+    QVERIFY(originalImplicitWidth > 0);
+
+    // Constrain the width to something narrow enough to trigger wrapping
+    const qreal narrowWidth = originalImplicitWidth * 0.3;
+    textObject->setWidth(narrowWidth);
+
+    // The implicitWidth should not change just because we constrained the width
+    const qreal constrainedImplicitWidth = textObject->implicitWidth();
+    QCOMPARE_EQ(constrainedImplicitWidth, originalImplicitWidth);
+
+    // Now widen the width back
+    textObject->setWidth(originalImplicitWidth * 2);
+    const qreal widenedImplicitWidth = textObject->implicitWidth();
+    QCOMPARE_EQ(widenedImplicitWidth, originalImplicitWidth);
+
+    // Release the width constraint entirely
+    textObject->resetWidth();
+    const qreal afterImplicitWidth = textObject->implicitWidth();
+    QCOMPARE_EQ(afterImplicitWidth, originalImplicitWidth);
+}
+
 void tst_qquicktext::dependentImplicitSizes()
 {
     QQmlComponent component(&engine, testFile("implicitSizes.qml"));