Fix no-op emission of QComboBox::currentTextChanged

currentTextChanged is emitted when the current index changes
and the current text doesn't.
This can be the case, if
- old and new index have identical text values
- an item is removed below the current index

[ChangeLog][Widgets][QComboBox] emit currentTextChanged only,
if currentText changes.

Add a corresponding test in tst_QComboBox::currentText().

Fixes: QTBUG-113717
Change-Id: I847874f0792b29a2841e50bb82d06ad496fb02c3
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
(cherry picked from commit 9195438a5fd88c676b0fc4abd429bcffa6f97e24)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/widgets/widgets/qcombobox.cpp

@@ -904,8 +904,11 @@ QStyleOptionComboBox QComboBoxPrivateContainer::comboStyleOption() const
     \fn void QComboBox::currentTextChanged(const QString &text)
     \since 5.0
 
-    This signal is sent whenever currentText changes. The new value
-    is passed as \a text.
+    This signal is emitted whenever currentText changes.
+    The new value is passed as \a text.
+
+    \note It is not emitted, if currentText remains the same,
+    even if currentIndex changes.
 */
 
 /*!
@@ -1071,7 +1074,7 @@ void QComboBoxPrivate::_q_dataChanged(const QModelIndex &topLeft, const QModelIn
             lineEdit->setText(text);
             updateLineEditGeometry();
         } else {
-            emit q->currentTextChanged(text);
+            updateCurrentText(text);
         }
         q->update();
 #if QT_CONFIG(accessibility)
@@ -1382,7 +1385,7 @@ void QComboBoxPrivate::_q_emitCurrentIndexChanged(const QModelIndex &index)
     emit q->currentIndexChanged(index.row());
     // signal lineEdit.textChanged already connected to signal currentTextChanged, so don't emit double here
     if (!lineEdit)
-        emit q->currentTextChanged(text);
+        updateCurrentText(text);
 #if QT_CONFIG(accessibility)
     QAccessibleValueChangeEvent event(q, text);
     QAccessible::updateAccessibility(&event);
@@ -2848,6 +2851,15 @@ void QComboBoxPrivate::doHidePopup()
     _q_resetButton();
 }
 
+void QComboBoxPrivate::updateCurrentText(const QString &text)
+{
+    if (text == currentText)
+        return;
+
+    currentText = text;
+    emit q_func()->currentTextChanged(text);
+}
+
 /*!
     Clears the combobox, removing all items.
 

src/widgets/widgets/qcombobox_p.h

@@ -357,6 +357,7 @@ public:
     void updateFocusPolicy();
     void showPopupFromMouseEvent(QMouseEvent *e);
     void doHidePopup();
+    void updateCurrentText(const QString &text);
 
 #ifdef Q_OS_MAC
     void cleanupNativePopup();
@@ -382,6 +383,7 @@ public:
     QPersistentModelIndex currentIndex;
     QPersistentModelIndex root;
     QString placeholderText;
+    QString currentText;
     QRect hoverRect;
     QSize iconSize;
     mutable QSize minimumSizeHint;

tests/auto/widgets/widgets/qcombobox/tst_qcombobox.cpp

@@ -1503,42 +1503,70 @@ void tst_QComboBox::currentTextChanged()
     testWidget->addItems(QStringList() << "foo" << "bar");
     QCOMPARE(testWidget->count(), 2);
 
-    QSignalSpy spy(testWidget, SIGNAL(currentTextChanged(QString)));
+    QSignalSpy textChangedSpy(testWidget, &QComboBox::currentTextChanged);
 
     testWidget->setEditable(editable);
 
     // set text in list
     testWidget->setCurrentIndex(0);
     QCOMPARE(testWidget->currentIndex(), 0);
-    spy.clear();
+    textChangedSpy.clear();
     testWidget->setCurrentText(QString("bar"));
-    QCOMPARE(spy.size(), 1);
-    QCOMPARE(qvariant_cast<QString>(spy.at(0).at(0)), QString("bar"));
+    QCOMPARE(textChangedSpy.size(), 1);
+    QCOMPARE(qvariant_cast<QString>(textChangedSpy.at(0).at(0)), QString("bar"));
 
     // set text not in list
     testWidget->setCurrentIndex(0);
     QCOMPARE(testWidget->currentIndex(), 0);
-    spy.clear();
+    textChangedSpy.clear();
     testWidget->setCurrentText(QString("qt"));
     if (editable) {
-        QCOMPARE(spy.size(), 1);
-        QCOMPARE(qvariant_cast<QString>(spy.at(0).at(0)), QString("qt"));
+        QCOMPARE(textChangedSpy.size(), 1);
+        QCOMPARE(qvariant_cast<QString>(textChangedSpy.at(0).at(0)), QString("qt"));
     } else {
-        QCOMPARE(spy.size(), 0);
+        QCOMPARE(textChangedSpy.size(), 0);
     }
 
     // item changed
     testWidget->setCurrentIndex(0);
     QCOMPARE(testWidget->currentIndex(), 0);
-    spy.clear();
+    textChangedSpy.clear();
     testWidget->setItemText(0, QString("ape"));
-    QCOMPARE(spy.size(), 1);
-    QCOMPARE(qvariant_cast<QString>(spy.at(0).at(0)), QString("ape"));
+    QCOMPARE(textChangedSpy.size(), 1);
+    QCOMPARE(qvariant_cast<QString>(textChangedSpy.at(0).at(0)), QString("ape"));
+
     // change it back
-    spy.clear();
+    textChangedSpy.clear();
     testWidget->setItemText(0, QString("foo"));
-    QCOMPARE(spy.size(), 1);
-    QCOMPARE(qvariant_cast<QString>(spy.at(0).at(0)), QString("foo"));
+    QCOMPARE(textChangedSpy.size(), 1);
+    QCOMPARE(qvariant_cast<QString>(textChangedSpy.at(0).at(0)), QString("foo"));
+
+    // currentIndexChanged vs. currentTextChanged
+    testWidget->clear();
+    testWidget->addItems(QStringList() << "first" << "second" << "third" << "fourth" << "fourth");
+    testWidget->setCurrentIndex(4);
+    textChangedSpy.clear();
+    QSignalSpy indexChangedSpy(testWidget, &QComboBox::currentIndexChanged);
+
+    // Index change w/o text change
+    testWidget->removeItem(3);
+    QCOMPARE(textChangedSpy.count(), 0);
+    QCOMPARE(indexChangedSpy.count(), 1);
+
+    // Index and text change
+    testWidget->setCurrentIndex(0);
+    QCOMPARE(textChangedSpy.count(), 1);
+    QCOMPARE(indexChangedSpy.count(), 2);
+
+    // remove item above current index
+    testWidget->removeItem(2);
+    QCOMPARE(textChangedSpy.count(), 1);
+    QCOMPARE(indexChangedSpy.count(), 2);
+
+    // Text change w/o index change
+    testWidget->setItemText(0, "first class");
+    QCOMPARE(textChangedSpy.count(), 2);
+    QCOMPARE(indexChangedSpy.count(), 2);
 }
 
 void tst_QComboBox::editTextChanged()