QObject: allow calling findChild() without a name

Add an overload of findChild() without a name argument to be able to
call the function with options value only.

[ChangeLog][QtCore][QObject] Added findChild() overload taking no name.

Task-number: QTBUG-103986
Change-Id: Id06b6041408fcf4cc1eeba975afce03f3a28f858
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

src/corelib/doc/snippets/code/src_corelib_kernel_qobject.cpp

@@ -366,7 +366,7 @@ QPushButton *button = parentWidget->findChild<QPushButton *>("button1", Qt::Find
 
 
 //! [42]
-QListWidget *list = parentWidget->findChild<QListWidget *>(QString(), Qt::FindDirectChildrenOnly);
+QListWidget *list = parentWidget->findChild<QListWidget *>(Qt::FindDirectChildrenOnly);
 //! [42]
 
 

src/corelib/kernel/qobject.cpp

@@ -2022,6 +2022,24 @@ void QObject::killTimer(int id)
     \sa findChildren()
 */
 
+/*!
+    \fn template<typename T> T *QObject::findChild(Qt::FindChildOptions options) const
+    \overload
+    \since 6.7
+
+    Returns the child of this object that can be cast into type T, or
+    \nullptr if there is no such object.
+    The search is performed recursively, unless \a options specifies the
+    option FindDirectChildrenOnly.
+
+    If there is more than one child matching the search, the most-direct ancestor
+    is returned. If there are several most-direct ancestors, the first child in
+    children() will be returned. In that case, it's better to use findChildren()
+    to get the complete list of all children.
+
+    \sa findChildren()
+*/
+
 /*!
     \fn template<typename T> QList<T> QObject::findChildren(QAnyStringView name, Qt::FindChildOptions options) const
 

src/corelib/kernel/qobject.h

@@ -140,7 +140,7 @@ public:
     void killTimer(int id);
 
     template<typename T>
-    T findChild(QAnyStringView aName = {}, Qt::FindChildOptions options = Qt::FindChildrenRecursively) const
+    T findChild(QAnyStringView aName, Qt::FindChildOptions options = Qt::FindChildrenRecursively) const
     {
         typedef typename std::remove_cv<typename std::remove_pointer<T>::type>::type ObjType;
         return static_cast<T>(qt_qFindChild_helper(this, aName, ObjType::staticMetaObject, options));
@@ -156,6 +156,12 @@ public:
         return list;
     }
 
+    template<typename T>
+    T findChild(Qt::FindChildOptions options = Qt::FindChildrenRecursively) const
+    {
+        return findChild<T>({}, options);
+    }
+
     template<typename T>
     QList<T> findChildren(Qt::FindChildOptions options = Qt::FindChildrenRecursively) const
     {

tests/auto/corelib/kernel/qobject/tst_qobject.cpp

@@ -510,6 +510,12 @@ void tst_QObject::qobject_castTemplate()
     QVERIFY(!::qobject_cast<ReceiverObject*>(o.data()));
 }
 
+class DerivedObj : public QObject {
+    Q_OBJECT
+public:
+    using QObject::QObject;
+};
+
 void tst_QObject::findChildren()
 {
     QObject o;
@@ -769,7 +775,20 @@ void tst_QObject::findChildren()
     l = o.findChildren<QObject*>(QRegularExpression("^harry$"), Qt::FindDirectChildrenOnly);
     QCOMPARE(l.size(), 0);
 
+    DerivedObj dr1(&o111);
+    DerivedObj dr2(&o111);
+    Q_SET_OBJECT_NAME(dr1);
+    Q_SET_OBJECT_NAME(dr2);
+
     // empty and null string check
+    op = o.findChild<QObject*>(Qt::FindDirectChildrenOnly);
+    QCOMPARE(op, &o1);
+    op = o.findChild<QTimer*>(Qt::FindDirectChildrenOnly);
+    QCOMPARE(op, &t1);
+    op = o.findChild<DerivedObj*>(Qt::FindDirectChildrenOnly);
+    QCOMPARE(op, nullptr);
+    op = o.findChild<DerivedObj*>(Qt::FindChildrenRecursively);
+    QCOMPARE(op, &dr1);
     op = o.findChild<QObject*>(QString(), Qt::FindDirectChildrenOnly);
     QCOMPARE(op, &o1);
     op = o.findChild<QObject*>("", Qt::FindDirectChildrenOnly);