Make QMetaTypeInterface constexpr on Windows

This was so far problematic as it gave various link errors. The solution
to that seems to be to make the default constructor of QPairVariantInterfaceImpl
constexpr to get around one set of problems.

The other problem to solve where undefined references to metaobjects. The
reason for that is apparently that QMetaTypeInterface contains a direct
pointer to the meta object, something the linker doesn't like. Adding a
level of indirection by using a function that returns the pointer seems
to solve that problem.

Fixes: QTBUG-88468
Change-Id: I5612ae807ea3b7e49bc40349d8d1fca1be9bd7ee
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 23 insertions, 12 deletions

diff --git a/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.cpp b/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.cpp
index f3d95285dc..503e9b0e33 100644
--- a/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.cpp
+++ b/tests/auto/corelib/kernel/qmetatype/tst_qmetatype.cpp
@@ -413,19 +413,30 @@ void tst_QMetaType::registerGadget(const char *name, const QList<GadgetPropertyT
     meta->d.static_metacall = &GadgetsStaticMetacallFunction;
     meta->d.superdata = nullptr;
     const auto flags = QMetaType::IsGadget | QMetaType::NeedsConstruction | QMetaType::NeedsDestruction;
-    using TypeInfo = QtPrivate::QMetaTypeInterface;
+    struct TypeInfo : public QtPrivate::QMetaTypeInterface
+    {
+        QMetaObject *mo;
+    };
+
     auto typeInfo = new TypeInfo {
-        0, alignof(GenericGadgetType), sizeof(GenericGadgetType), uint(flags), 0, meta, name,
-        [](const TypeInfo *self, void *where) { GadgetTypedConstructor(self->typeId, where, nullptr); },
-        [](const TypeInfo *self, void *where, const void *copy) { GadgetTypedConstructor(self->typeId, where, copy); },
-        [](const TypeInfo *self, void *where, void *copy) { GadgetTypedConstructor(self->typeId, where, copy); },
-        [](const TypeInfo *self, void *ptr) { GadgetTypedDestructor(self->typeId, ptr); },
-        nullptr,
-        nullptr,
-        nullptr,
-        GadgetSaveOperator,
-        GadgetLoadOperator,
-        nullptr
+        {
+            0, alignof(GenericGadgetType), sizeof(GenericGadgetType), uint(flags), 0,
+            [](const QtPrivate::QMetaTypeInterface *self) -> const QMetaObject * {
+                return reinterpret_cast<const TypeInfo *>(self)->mo;
+            },
+            name,
+            [](const QtPrivate::QMetaTypeInterface *self, void *where) { GadgetTypedConstructor(self->typeId, where, nullptr); },
+            [](const QtPrivate::QMetaTypeInterface *self, void *where, const void *copy) { GadgetTypedConstructor(self->typeId, where, copy); },
+            [](const QtPrivate::QMetaTypeInterface *self, void *where, void *copy) { GadgetTypedConstructor(self->typeId, where, copy); },
+            [](const QtPrivate::QMetaTypeInterface *self, void *ptr) { GadgetTypedDestructor(self->typeId, ptr); },
+            nullptr,
+            nullptr,
+            nullptr,
+            GadgetSaveOperator,
+            GadgetLoadOperator,
+            nullptr
+        },
+        meta
     };
     QMetaType gadgetMetaType(typeInfo);
     dynamicGadgetProperties->m_metatype = gadgetMetaType;