QObject: give some TLC to dumpRecursive()

In no particular order:

- use the variable field width feature of QString::asprintf() to
  generate the indentation implicitly, instead of fill()ing a
  QByteArray with the desired number of spaces

- just default-construct 'flags', don't assign an empty string

- use qUtf16Printable() to avoid funneling UTF-16 data through 8-bit
  encodings

- use a C++11 ranged for instead of a counted loop

- remove a pointless isEmpty() guard (the loop won't execute when the
  children().isEmpty())

- avoid copying object->children() (returns by cref, so it's also ok
  to stuff it directly into the ranged for loop).

Add a test.

Pick-to: 6.3
Change-Id: Ie7314713cb48de7e890cdee0760c0361dd24fd18
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qobject.cpp

@@ -4205,12 +4205,9 @@ QList<QByteArray> QObject::dynamicPropertyNames() const
 static void dumpRecursive(int level, const QObject *object)
 {
     if (object) {
-        QByteArray buf;
-        buf.fill(' ', level / 2 * 8);
-        if (level % 2)
-            buf += "    ";
-        QString name = object->objectName();
-        QString flags = QLatin1String("");
+        const int indent = level * 4;
+        const QString name = object->objectName();
+        QString flags;
 #if 0
         if (qApp->focusWidget() == object)
             flags += 'F';
@@ -4224,13 +4221,10 @@ static void dumpRecursive(int level, const QObject *object)
             }
         }
 #endif
-        qDebug("%s%s::%s %s", (const char*)buf, object->metaObject()->className(), name.toLocal8Bit().data(),
-               flags.toLatin1().data());
-        QObjectList children = object->children();
-        if (!children.isEmpty()) {
-            for (int i = 0; i < children.size(); ++i)
-                dumpRecursive(level+1, children.at(i));
-        }
+        qDebug("%*s%s::%ls %ls", indent, "", object->metaObject()->className(),
+               qUtf16Printable(name), qUtf16Printable(flags));
+        for (auto child : object->children())
+            dumpRecursive(level + 1, child);
     }
 }
 

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

@@ -108,6 +108,7 @@ private slots:
     void deleteSelfInSlot();
     void disconnectSelfInSlotAndDeleteAfterEmit();
     void dumpObjectInfo();
+    void dumpObjectTree();
     void connectToSender();
     void qobjectConstCast();
     void uniqConnection();
@@ -3413,6 +3414,32 @@ void tst_QObject::dumpObjectInfo()
     a.dumpObjectInfo(); // should not crash
 }
 
+void tst_QObject::dumpObjectTree()
+{
+    QObject a;
+    Q_SET_OBJECT_NAME(a);
+
+    QTimer b(&a);
+    Q_SET_OBJECT_NAME(b);
+
+    QObject c(&b);
+    Q_SET_OBJECT_NAME(c);
+
+    QFile f(&a);
+    Q_SET_OBJECT_NAME(f);
+
+    const char * const output[] = {
+        "QObject::a ",
+        "    QTimer::b ",
+        "        QObject::c ",
+        "    QFile::f ",
+    };
+    for (const char *line : output)
+        QTest::ignoreMessage(QtDebugMsg, line);
+
+    a.dumpObjectTree();
+}
+
 class ConnectToSender : public QObject
 { Q_OBJECT
     public slots: