Fix assertion failure in QCompleter::setCompletionPrefix().

Calling setCompletionPrefix() on a QCompleter from a slot connected
to the editingFinished() signal of the corresponding QLineEdit
could in some cases alter the internal state of the completer in
such a way that an assertion would fail. The fix prevents the
asserting code from being called in this particular state.

Reviewed-by: janarve
Task-number: 246056

2 files changed, 35 insertions, 2 deletions

diff --git a/src/gui/util/qcompleter.cpp b/src/gui/util/qcompleter.cpp
index 8b07163..aeb7e91 100644
--- a/src/gui/util/qcompleter.cpp
+++ b/src/gui/util/qcompleter.cpp
@@ -824,9 +824,9 @@ void QCompleterPrivate::_q_complete(QModelIndex index, bool highlighted)
     Q_Q(QCompleter);
     QString completion;
 
-    if (!index.isValid())
+    if (!index.isValid() || (index.row() >= proxy->engine->matchCount())) {
         completion = prefix;
-    else {
+    } else {
         QModelIndex si = proxy->mapToSource(index);
         si = si.sibling(si.row(), column); // for clicked()
         completion = q->pathFromIndex(si);
diff --git a/tests/auto/qcompleter/tst_qcompleter.cpp b/tests/auto/qcompleter/tst_qcompleter.cpp
index 6434d49..67b9b67 100644
--- a/tests/auto/qcompleter/tst_qcompleter.cpp
+++ b/tests/auto/qcompleter/tst_qcompleter.cpp
@@ -140,6 +140,7 @@ private slots:
     // task-specific tests below me
     void task178797_activatedOnReturn();
     void task189564_omitNonSelectableItems();
+    void task246056_setCompletionPrefix();
 
 private:
     void filter();
@@ -1093,5 +1094,37 @@ void tst_QCompleter::task189564_omitNonSelectableItems()
     QVERIFY(matches2.isEmpty());
 }
 
+class task246056_ComboBox : public QComboBox
+{
+    Q_OBJECT
+public:
+    task246056_ComboBox()
+    {
+        setEditable(true);
+        setInsertPolicy(NoInsert);
+        Q_ASSERT(completer());
+        completer()->setCompletionMode(QCompleter::PopupCompletion);
+        completer()->setCompletionRole(Qt::DisplayRole);
+        connect(lineEdit(), SIGNAL(editingFinished()), SLOT(setCompletionPrefix()));
+    }
+private slots:
+    void setCompletionPrefix() { completer()->setCompletionPrefix(lineEdit()->text()); }
+};
+
+void tst_QCompleter::task246056_setCompletionPrefix()
+{
+    task246056_ComboBox *comboBox = new task246056_ComboBox;
+    comboBox->addItem("");
+    comboBox->addItem("a1");
+    comboBox->addItem("a2");
+    comboBox->show();
+    comboBox->setFocus();
+    QTest::qWait(100);
+    QTest::keyPress(comboBox, 'a');
+    QTest::keyPress(comboBox->completer()->popup(), Qt::Key_Down);
+    QTest::keyPress(comboBox->completer()->popup(), Qt::Key_Down);
+    QTest::keyPress(comboBox->completer()->popup(), Qt::Key_Enter); // don't crash!
+}
+
 QTEST_MAIN(tst_QCompleter)
 #include "tst_qcompleter.moc"