Add debug output for single enum flags

They have a separate type that we can't recognize directly, but we
can check if we can recognize the QFlags<T> form, though we have to
add a lot of template-conditions to avoid triggering QFlags static
asserts.

Change-Id: I00853682c5376dd3cc411ff151f47bce2389e277
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

2 files changed, 18 insertions, 0 deletions

diff --git a/src/corelib/io/qdebug.h b/src/corelib/io/qdebug.h
index ee8ef679a9..ae1869f89e 100644
--- a/src/corelib/io/qdebug.h
+++ b/src/corelib/io/qdebug.h
@@ -376,6 +376,19 @@ operator<<(QDebug dbg, T value)
     return qt_QMetaEnum_debugOperator(dbg, typename QFlags<T>::Int(value), obj, name);
 }
 
+template<typename T,
+         typename A = typename std::enable_if<std::is_enum<T>::value, void>::type,
+         typename B = typename std::enable_if<sizeof(T) <= sizeof(int), void>::type,
+         typename C = typename std::enable_if<!QtPrivate::IsQEnumHelper<T>::Value, void>::type,
+         typename D = typename std::enable_if<QtPrivate::IsQEnumHelper<QFlags<T>>::Value, void>::type>
+inline QDebug operator<<(QDebug dbg, T value)
+{
+    typedef QFlags<T> FlagsT;
+    const QMetaObject *obj = qt_getEnumMetaObject(FlagsT());
+    const char *name = qt_getEnumName(FlagsT());
+    return qt_QMetaEnum_debugOperator(dbg, typename FlagsT::Int(value), obj, name);
+}
+
 template <class T>
 inline typename std::enable_if<
     QtPrivate::IsQEnumHelper<T>::Value || QtPrivate::IsQEnumHelper<QFlags<T> >::Value,
diff --git a/tests/auto/corelib/kernel/qmetaobject/tst_qmetaobject.cpp b/tests/auto/corelib/kernel/qmetaobject/tst_qmetaobject.cpp
index 9c33dc4c4d..9855bec520 100644
--- a/tests/auto/corelib/kernel/qmetaobject/tst_qmetaobject.cpp
+++ b/tests/auto/corelib/kernel/qmetaobject/tst_qmetaobject.cpp
@@ -1767,6 +1767,11 @@ void tst_QMetaObject::enumDebugStream()
     QTest::ignoreMessage(QtDebugMsg, "QFlags<MyNamespace::MyClass::MyScopedFlag>(MyFlag2|MyFlag3)");
     f3 |= MyNamespace::MyClass::MyScopedFlag::MyFlag3;
     qDebug() << f3;
+
+    // Single flag recognized as enum:
+    QTest::ignoreMessage(QtDebugMsg, "MyNamespace::MyClass::MyFlag1");
+    MyNamespace::MyClass::MyFlag f4 = MyNamespace::MyClass::MyFlag1;
+    qDebug() << f4;
 }
 
 void tst_QMetaObject::inherits_data()