Fix source incompatibility while connecting signals with forward declared arguments

QObject::connect tries to determine if the arguments are registered
metatypes. This used to work even for arguments that were forward
declared. But now, the metatype system tries to call
QtPrivate::IsQEnumHelper<T>::Value to know if it is registered.
That fails on gcc if T is forward declared.

Apparently gcc needs to know the full type of T to pass it in the
ellipsis function, even within a sizeof expression.

So change the ellipsis expression to a template one.

Task-number: QTBUG-44496
Change-Id: I7fa07bd3cde470b134c2ec53b0d581333d16a6f1
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 20 insertions, 1 deletions

diff --git a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
index 94242607f0..263cc5a07a 100644
--- a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
+++ b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
@@ -1,7 +1,7 @@
 /****************************************************************************
 **
 ** Copyright (C) 2015 The Qt Company Ltd.
-** Copyright (C) 2013 Olivier Goffart <ogoffart@woboq.com>
+** Copyright (C) 2015 Olivier Goffart <ogoffart@woboq.com>
 ** Contact: http://www.qt.io/licensing/
 **
 ** This file is part of the test suite of the Qt Toolkit.
@@ -127,6 +127,7 @@ private slots:
     void connectConvert();
     void connectWithReference();
     void connectManyArguments();
+    void connectForwardDeclare();
     void returnValue_data();
     void returnValue();
     void returnValue2_data();
@@ -5208,6 +5209,24 @@ void tst_QObject::connectManyArguments()
     QCOMPARE(ManyArgumentNamespace::count, 12);
 }
 
+class ForwardDeclared;
+
+class ForwardDeclareArguments : public QObject
+{
+    Q_OBJECT
+signals:
+    void mySignal(const ForwardDeclared&);
+public slots:
+    void mySlot(const ForwardDeclared&) {}
+};
+
+void tst_QObject::connectForwardDeclare()
+{
+    ForwardDeclareArguments ob;
+    // it should compile
+    QVERIFY(connect(&ob, &ForwardDeclareArguments::mySignal, &ob, &ForwardDeclareArguments::mySlot, Qt::QueuedConnection));
+}
+
 class ReturnValue : public QObject {
 friend class tst_QObject;
 Q_OBJECT