From f01f1943e49ac3a60c54dd3f3009a445474dc412 Mon Sep 17 00:00:00 2001
From: Olivier Goffart <ogoffart@woboq.com>
Date: Sun, 26 Jul 2015 14:14:31 +0200
Subject: [PATCH] Fix compilation error while instantiating operator<<
 explicitly

Task-number: QTBUG-47375
Change-Id: Ibd260de88c174c1aa3833a56b153b8b74d337338
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/io/qdebug.h                     | 14 +++++++++++---
 tests/auto/corelib/io/qdebug/tst_qdebug.cpp |  9 +++++++++
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/src/corelib/io/qdebug.h b/src/corelib/io/qdebug.h
index 59bd32e9a4..3c3ceba249 100644
--- a/src/corelib/io/qdebug.h
+++ b/src/corelib/io/qdebug.h
@@ -278,7 +278,7 @@ template <class T>
 inline typename QtPrivate::QEnableIf<
     QtPrivate::IsQEnumHelper<T>::Value || QtPrivate::IsQEnumHelper<QFlags<T> >::Value,
     QDebug>::Type
-operator<<(QDebug debug, const QFlags<T> &flags)
+qt_QMetaEnum_flagDebugOperator_helper(QDebug debug, const QFlags<T> &flags)
 {
     const QMetaObject *obj = qt_getEnumMetaObject(T());
     const char *name = qt_getEnumName(T());
@@ -289,10 +289,10 @@ template <class T>
 inline typename QtPrivate::QEnableIf<
     !QtPrivate::IsQEnumHelper<T>::Value && !QtPrivate::IsQEnumHelper<QFlags<T> >::Value,
     QDebug>::Type
-operator<<(QDebug debug, const QFlags<T> &flags)
+qt_QMetaEnum_flagDebugOperator_helper(QDebug debug, const QFlags<T> &flags)
 #else // !QT_NO_QOBJECT
 template <class T>
-inline QDebug operator<<(QDebug debug, const QFlags<T> &flags)
+inline QDebug qt_QMetaEnum_flagDebugOperator_helper(QDebug debug, const QFlags<T> &flags)
 #endif
 {
     QDebugStateSaver saver(debug);
@@ -312,6 +312,14 @@ inline QDebug operator<<(QDebug debug, const QFlags<T> &flags)
     return debug;
 }
 
+template<typename T>
+inline QDebug operator<<(QDebug debug, const QFlags<T> &flags)
+{
+    // We have to use an indirection otherwise specialisation of some other overload of the
+    // operator<< the compiler would try to instantiate QFlags<T> for the QEnableIf
+    return qt_QMetaEnum_flagDebugOperator_helper(debug, flags);
+}
+
 #ifdef Q_OS_MAC
 
 // We provide QDebug stream operators for commonly used Core Foundation
diff --git a/tests/auto/corelib/io/qdebug/tst_qdebug.cpp b/tests/auto/corelib/io/qdebug/tst_qdebug.cpp
index 32344f1e26..4e5cfed019 100644
--- a/tests/auto/corelib/io/qdebug/tst_qdebug.cpp
+++ b/tests/auto/corelib/io/qdebug/tst_qdebug.cpp
@@ -625,5 +625,14 @@ void tst_QDebug::threadSafety() const
     }
 }
 
+// Should compile: instentiation of unrelated operator<< should not cause cause compilation
+// error in QDebug operators (QTBUG-47375)
+class TestClassA {};
+class TestClassB {};
+
+template <typename T>
+TestClassA& operator<< (TestClassA& s, T&) { return s; };
+template<> TestClassA& operator<< <TestClassB>(TestClassA& s, TestClassB& l);
+
 QTEST_MAIN(tst_QDebug);
 #include "tst_qdebug.moc"