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
Pick-to: 6.6
Change-Id: I847874f0792b29a2841e50bb82d06ad496fb02c3
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 16 insertions, 4 deletions

diff --git a/src/widgets/widgets/qcombobox.cpp b/src/widgets/widgets/qcombobox.cpp
index 33aa88fffb..32b43ed4fd 100644
--- a/src/widgets/widgets/qcombobox.cpp
+++ b/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.