From 47c6466d0acc6d8d733b4fdbaf980a60bbfc93ef Mon Sep 17 00:00:00 2001
From: Fabian Kosmale <fabian.kosmale@qt.io>
Date: Tue, 31 Mar 2020 08:48:56 +0200
Subject: [PATCH] QMetaType: create metatype for void

Create a QMetaTypeInterface for void. This allows us differentiate
QMetaType::Unknown from QMetaType::Void. In addition, this will enable
the usage of QMetaMethod::metaReturnType in QMetaMethod::returnType,
and will facilitate using metaReturnType in declarative, which needs to
distinguish between Unknown and Void.

Change-Id: I83296b49587f3deb7ec73e25a33f0d8c98cf8da0
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
---
 src/corelib/kernel/qmetatype.h                | 30 ++++++++++++++-----
 src/corelib/kernel/qmetatype_p.h              |  4 +--
 .../kernel/qmetatype/tst_qmetatype.cpp        | 13 ++++++--
 3 files changed, 34 insertions(+), 13 deletions(-)

diff --git a/src/corelib/kernel/qmetatype.h b/src/corelib/kernel/qmetatype.h
index 60192e4131c..3c7781c8509 100644
--- a/src/corelib/kernel/qmetatype.h
+++ b/src/corelib/kernel/qmetatype.h
@@ -2758,7 +2758,6 @@ QMetaTypeInterface QMetaTypeForType<T>::metaType = {
         }
     })
 };
-#undef QT_METATYPE_CONSTEXPRLAMDA
 
 template<typename T>
 constexpr const decltype(typenameHelper<T>()) QMetaTypeForType<T>::name = typenameHelper<T>();
@@ -2766,7 +2765,28 @@ constexpr const decltype(typenameHelper<T>()) QMetaTypeForType<T>::name = typena
 template<>
 class QMetaTypeForType<void>
 {
+    static const decltype(typenameHelper<void>()) name;
+
+public:
+    static inline QMetaTypeInterface metaType =
+    {
+        /*.revision=*/ 0,
+        /*.size=*/ 0,
+        /*.alignment=*/ 0,
+        /*.flags=*/ 0,
+        /*.metaObject=*/ nullptr,
+        /*.name=*/ "void",
+        /*.typeId=*/ BuiltinMetaType<void>::value,
+        /*.ref=*/ Q_REFCOUNT_INITIALIZE_STATIC,
+        /*.deleteSelf=*/ nullptr,
+        /*.defaultCtr=*/ nullptr,
+        /*.copyCtr=*/ nullptr,
+        /*.moveCtr=*/ nullptr,
+        /*.dtor=*/ nullptr,
+        /*.legacyRegisterOp=*/ nullptr
+    };
 };
+#undef QT_METATYPE_CONSTEXPRLAMDA
 
 #ifndef QT_BOOTSTRAPPED
 #define QT_METATYPE_DECLARE_EXTERN_TEMPLATE_ITER(TypeName, Id, Name)                               \
@@ -2789,11 +2809,7 @@ template<typename T>
 constexpr QMetaTypeInterface *qMetaTypeInterfaceForType()
 {
     using Ty = std::remove_cv_t<std::remove_reference_t<T>>;
-    if constexpr (std::is_same_v<Ty, void>) {
-        return nullptr;
-    } else {
-        return &QMetaTypeForType<Ty>::metaType;
-    }
+    return &QMetaTypeForType<Ty>::metaType;
 }
 
 namespace detail {
@@ -2818,8 +2834,6 @@ constexpr QMetaTypeInterface *qTryMetaTypeInterfaceForType()
     using Tz = std::remove_pointer_t<Ty>;
     if constexpr (!is_complete<Tz, Unique>::value) {
         return nullptr;
-    } else if constexpr (std::is_same_v<Ty, void>) {
-        return nullptr;
     } else {
         return &QMetaTypeForType<Ty>::metaType;
     }
diff --git a/src/corelib/kernel/qmetatype_p.h b/src/corelib/kernel/qmetatype_p.h
index 8e08d84ffdf..2f4d69488ff 100644
--- a/src/corelib/kernel/qmetatype_p.h
+++ b/src/corelib/kernel/qmetatype_p.h
@@ -192,9 +192,7 @@ template<> struct TypeDefinition<QIcon> { static const bool IsAvailable = false;
 template<typename T>
 static QT_PREPEND_NAMESPACE(QtPrivate::QMetaTypeInterface) *getInterfaceFromType()
 {
-    if constexpr (std::is_same_v<T, void>) {
-        return nullptr;
-    } else if constexpr (QtMetaTypePrivate::TypeDefinition<T>::IsAvailable) {
+    if constexpr (QtMetaTypePrivate::TypeDefinition<T>::IsAvailable) {
         return &QT_PREPEND_NAMESPACE(QtPrivate::QMetaTypeForType)<T>::metaType;
     }
     return nullptr;
diff --git a/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.cpp b/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.cpp
index f144aad7e40..d036be55c69 100644
--- a/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.cpp
+++ b/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.cpp
@@ -127,6 +127,7 @@ private slots:
     void operatorEq_data();
     void operatorEq();
     void typesWithInaccessibleDTors();
+    void voidIsNotUnknown();
 };
 
 struct BaseGenericType
@@ -1339,7 +1340,7 @@ void tst_QMetaType::isRegistered_data()
     QTest::addColumn<bool>("registered");
 
     // predefined/custom types
-    QTest::newRow("QMetaType::Void") << int(QMetaType::Void) << false;
+    QTest::newRow("QMetaType::Void") << int(QMetaType::Void) << true;
     QTest::newRow("QMetaType::Int") << int(QMetaType::Int) << true;
 
     int dummyTypeId = qRegisterMetaType<IsRegisteredDummyType>("IsRegisteredDummyType");
@@ -2548,7 +2549,7 @@ void tst_QMetaType::operatorEq_data()
     QTest::newRow("String") << QMetaType(QMetaType::QString)
                             << QMetaType::fromType<const QString &>() << true;
     QTest::newRow("void1") << QMetaType(QMetaType::UnknownType) << QMetaType::fromType<void>()
-                           << true;
+                           << false;
     QTest::newRow("void2") << QMetaType::fromType<const void>() << QMetaType::fromType<void>()
                            << true;
     QTest::newRow("vec1") << QMetaType::fromType<QVector<const int *>>()
@@ -2590,6 +2591,14 @@ void tst_QMetaType::typesWithInaccessibleDTors()
     Q_UNUSED(QMetaType::fromType<WithDeletedDtor>());
 }
 
+void tst_QMetaType::voidIsNotUnknown()
+{
+    QMetaType voidType = QMetaType::fromType<void>();
+    QMetaType voidType2 = QMetaType(QMetaType::Void);
+    QCOMPARE(voidType, voidType2);
+    QVERIFY(voidType != QMetaType(QMetaType::UnknownType));
+}
+
 // Compile-time test, it should be possible to register function pointer types
 class Undefined;