Refactor EventFactory and move it out of _impl::

Strictly speaking, EventFactory can be further instantiated if any
client application figures they need a whole new base class for events
and respectively a separate EventFactory specialisation for it.

Where this whole commit started though was a linkage error because I
did not plan to expose Quotient-specific logging categories for linkage
(effectively, usage) from the client code - meanwhile the inline code
of EventFactory uses qDebug(EVENTS), meaning I had to either add
QUOTIENT_API to EVENTS or hide those invocations. This in turn led
to trimming the EventFactory constructor back to trivial implementation
and dropping the guard variable that was supposed to trace duplicate
EventFactory<BaseEventT> objects for the same BaseEventT - with the
reasoning that such situation is not really dangerous (unlike
EventTypeRegistry double-initialisation fiasco, see #413), and at the
same time it can be easily detected in the logs by duplicated factory
method registration messages. And while I was at it, I replaced the
meaningless bool in the return type of EventFactory<>::addMethod with
the slightly more (but still barely) useful reference to the inserted
factory method. One can (in theory) use it now if they need to turn
some event JSON into an object of some specific event type or nullptr
if the event type in the JSON payload doesn't match - but at the same
rate (for now at least) one can call makeIfMatches<EventT>() directly.

With this commit, both Quotest and Quaternion build and link using
either Clang or GCC even under -fvisibility=hidden. However, running
quotest now reproduces #413, which is a matter of event typeId
infrastructure refactoring, coming in further commits.

4 files changed, 88 insertions, 83 deletions

diff --git a/lib/events/event.cpp b/lib/events/event.cpp
index 96be717c..715e7da2 100644
--- a/lib/events/event.cpp
+++ b/lib/events/event.cpp
@@ -27,6 +27,14 @@ QString EventTypeRegistry::getMatrixType(event_type_t typeId)
                                             : QString();
 }
 
+void _impl::EventFactoryBase::logAddingMethod(event_mtype_t matrixType,
+                                              size_t newSize)
+{
+    qDebug(EVENTS) << "Adding factory method for" << matrixType << "events;"
+                   << newSize << "methods will be in the" << name
+                   << "chain";
+}
+
 Event::Event(Type type, const QJsonObject& json) : _type(type), _json(json)
 {
     if (!json.contains(ContentKeyL)
diff --git a/lib/events/event.h b/lib/events/event.h
index 8a0076d0..0aef49f7 100644
--- a/lib/events/event.h
+++ b/lib/events/event.h
@@ -120,80 +120,93 @@ inline event_ptr_tt<EventT> makeEvent(ArgTs&&... args)
 }
 
 namespace _impl {
-    template <class EventT, class BaseEventT>
-    event_ptr_tt<BaseEventT> makeIfMatches(const QJsonObject& json,
-                                           const QString& matrixType)
+    class QUOTIENT_API EventFactoryBase {
+    public:
+        EventFactoryBase(const EventFactoryBase&) = delete;
+
+    protected: // This class is only to inherit from
+        explicit EventFactoryBase(const char* name)
+            : name(name)
+        {}
+        void logAddingMethod(event_mtype_t mtypeId, size_t newSize);
+
+    private:
+        const char* const name;
+    };
+} // namespace _impl
+
+//! \brief A family of event factories to create events from CS API responses
+//!
+//! Each of these factories, as instantiated by event base types (Event,
+//! RoomEvent etc.) is capable of producing an event object derived from
+//! \p BaseEventT, using the JSON payload and the event type passed to its
+//! make() method. Don't use these directly to make events; use loadEvent()
+//! overloads as the frontend for these. Never instantiate new factories
+//! outside of base event classes.
+//! \sa loadEvent, setupFactory, Event::factory, RoomEvent::factory,
+//!     StateEventBase::factory
+template <typename BaseEventT>
+class EventFactory : public _impl::EventFactoryBase {
+private:
+    std::vector<event_ptr_tt<BaseEventT> (*)(const QJsonObject&, const QString&)>
+        methods {};
+
+    template <class EventT>
+    static event_ptr_tt<BaseEventT> makeIfMatches(const QJsonObject& json,
+                                                  const QString& matrixType)
     {
         return QLatin1String(EventT::matrixTypeId()) == matrixType
                    ? makeEvent<EventT>(json)
                    : nullptr;
     }
 
-    //! \brief A family of event factories to create events from CS API responses
+public:
+    explicit EventFactory(const char* fName)
+        : EventFactoryBase { fName }
+    {}
+
+    //! \brief Add a method to create events of a given type
     //!
-    //! Each of these factories, as instantiated by event base types (Event,
-    //! RoomEvent etc.) is capable of producing an event object derived from
-    //! \p BaseEventT, using the JSON payload and the event type passed to its
-    //! make() method. Don't use these directly to make events; use loadEvent()
-    //! overloads as the frontend for these. Never instantiate new factories
-    //! outside of base event classes.
-    //! \sa loadEvent, setupFactory, Event::factory, RoomEvent::factory,
-    //!     StateEventBase::factory
-    template <typename BaseEventT>
-    class EventFactory
-        : private std::vector<event_ptr_tt<BaseEventT> (*)(const QJsonObject&,
-                                                           const QString&)> {
-        // Actual makeIfMatches specialisations will differ in the first
-        // template parameter but that doesn't affect the function type
-    public:
-        explicit EventFactory(const char* name = "")
-            : name(name)
-        {
-            static auto yetToBeConstructed = true;
-            Q_ASSERT(yetToBeConstructed);
-            if (!yetToBeConstructed) // For Release builds that pass Q_ASSERT
-                qCritical(EVENTS)
-                    << "Another EventFactory for the same base type is being "
-                       "created - event creation logic will be splintered";
-            yetToBeConstructed = false;
-        }
-        EventFactory(const EventFactory&) = delete;
-
-        //! \brief Add a method to create events of a given type
-        //!
-        //! Adds a standard factory method (makeIfMatches) for \p EventT so that
-        //! event objects of this type can be created dynamically by loadEvent.
-        //! The caller is responsible for ensuring this method is called only
-        //! once per type.
-        //! \sa makeIfMatches, loadEvent, Quotient::loadEvent
-        template <class EventT>
-        bool addMethod()
-        {
-            this->emplace_back(&makeIfMatches<EventT, BaseEventT>);
-            qDebug(EVENTS) << "Added factory method for"
-                           << EventT::matrixTypeId() << "events;" << this->size()
-                           << "methods in the" << name << "chain by now";
-            return true;
-        }
-
-        auto loadEvent(const QJsonObject& json, const QString& matrixType)
-        {
-            for (const auto& f : *this)
-                if (auto e = f(json, matrixType))
-                    return e;
-            return makeEvent<BaseEventT>(unknownEventTypeId(), json);
-        }
+    //! Adds a standard factory method (makeIfMatches) for \p EventT so that
+    //! event objects of this type can be created dynamically by loadEvent.
+    //! The caller is responsible for ensuring this method is called only
+    //! once per type.
+    //! \sa loadEvent, Quotient::loadEvent
+    template <class EventT>
+    const auto& addMethod()
+    {
+        logAddingMethod(EventT::matrixTypeId(), methods.size() + 1);
+        return methods.emplace_back(&makeIfMatches<EventT>);
+    }
 
-        const char* const name;
-    };
-} // namespace _impl
+    auto loadEvent(const QJsonObject& json, const QString& matrixType)
+    {
+        for (const auto& f : methods)
+            if (auto e = f(json, matrixType))
+                return e;
+        return makeEvent<BaseEventT>(unknownEventTypeId(), json);
+    }
+};
+
+//! \brief Point of customisation to dynamically load events
+//!
+//! The default specialisation of this calls BaseEventT::factory.loadEvent()
+//! and if that fails (i.e. returns nullptr) creates an unknown event of
+//! BaseEventT. Other specialisations may reuse other factories, add validations
+//! common to BaseEventT events, and so on.
+template <class BaseEventT>
+event_ptr_tt<BaseEventT> doLoadEvent(const QJsonObject& json,
+                                     const QString& matrixType)
+{
+    return BaseEventT::factory.loadEvent(json, matrixType);
+}
 
 // === Event ===
 
 class QUOTIENT_API Event {
 public:
     using Type = event_type_t;
-    static inline _impl::EventFactory<Event> factory { "Event" };
+    static inline EventFactory<Event> factory { "Event" };
 
     explicit Event(Type type, const QJsonObject& json);
     explicit Event(Type type, event_mtype_t matrixType,
@@ -273,37 +286,21 @@ using Events = EventsArray<Event>;
 // This macro should be used in a public section of an event class to
 // provide matrixTypeId() and typeId().
 #define DEFINE_EVENT_TYPEID(_Id, _Type)                                        \
-    static QUOTIENT_EXPORT constexpr event_mtype_t matrixTypeId()              \
+    static QUOTIENT_API constexpr event_mtype_t matrixTypeId()              \
     {                                                                          \
         return _Id;                                                            \
     }                                                                          \
-    static QUOTIENT_EXPORT auto typeId() { return Quotient::typeId<_Type>(); } \
+    static QUOTIENT_API auto typeId() { return Quotient::typeId<_Type>(); } \
     // End of macro
 
 // This macro should be put after an event class definition (in .h or .cpp)
 // to enable its deserialisation from a /sync and other
 // polymorphic event arrays
-#define REGISTER_EVENT_TYPE(_Type)                                         \
-    [[maybe_unused]] QUOTIENT_API inline const auto _factoryAdded##_Type = \
-        _Type::factory.addMethod<_Type>();                                 \
+#define REGISTER_EVENT_TYPE(Type_)                                             \
+    [[maybe_unused]] QUOTIENT_API inline const auto& factoryMethodFor##Type_ = \
+        Type_::factory.addMethod<Type_>();                                     \
     // End of macro
 
-// === Event loading ===
-// (see also event_loader.h)
-
-//! \brief Point of customisation to dynamically load events
-//!
-//! The default specialisation of this calls BaseEventT::factory and if that
-//! fails (i.e. returns nullptr) creates an unknown event of BaseEventT.
-//! Other specialisations may reuse other factories, add validations common to
-//! BaseEventT, and so on
-template <class BaseEventT>
-event_ptr_tt<BaseEventT> doLoadEvent(const QJsonObject& json,
-                                     const QString& matrixType)
-{
-    return BaseEventT::factory.loadEvent(json, matrixType);
-}
-
 // === is<>(), eventCast<>() and switchOnType<>() ===
 
 template <class EventT>
diff --git a/lib/events/roomevent.h b/lib/events/roomevent.h
index 3fbb247e..dcee1170 100644
--- a/lib/events/roomevent.h
+++ b/lib/events/roomevent.h
@@ -13,7 +13,7 @@ class RedactionEvent;
 /** This class corresponds to m.room.* events */
 class QUOTIENT_API RoomEvent : public Event {
 public:
-    static inline _impl::EventFactory<RoomEvent> factory { "RoomEvent" };
+    static inline EventFactory<RoomEvent> factory { "RoomEvent" };
 
     // RedactionEvent is an incomplete type here so we cannot inline
     // constructors and destructors and we cannot use 'using'.
diff --git a/lib/events/stateevent.h b/lib/events/stateevent.h
index 6095d628..88da68f8 100644
--- a/lib/events/stateevent.h
+++ b/lib/events/stateevent.h
@@ -19,7 +19,7 @@ inline QJsonObject basicStateEventJson(const QString& matrixTypeId,
 
 class QUOTIENT_API StateEventBase : public RoomEvent {
 public:
-    static inline _impl::EventFactory<StateEventBase> factory { "StateEvent" };
+    static inline EventFactory<StateEventBase> factory { "StateEvent" };
 
     StateEventBase(Type type, const QJsonObject& json);
     StateEventBase(Type type, event_mtype_t matrixType,