Test code to add merge detection on Settings Registry keys

Signed-off-by: Danilo Aimini <82231674+AMZN-daimini@users.noreply.github.com>

Code/Framework/AzCore/AzCore/Component/ComponentApplication.cpp

@@ -728,6 +728,7 @@ namespace AZ
         DestroyReflectionManager();
 
         static_cast<SettingsRegistryImpl*>(m_settingsRegistry.get())->ClearNotifiers();
+        static_cast<SettingsRegistryImpl*>(m_settingsRegistry.get())->ClearMergeEvents();
 
         // Uninit and unload any dynamic modules.
         m_moduleManager->UnloadModules();

Code/Framework/AzCore/AzCore/Settings/SettingsRegistry.h

@@ -123,6 +123,36 @@ namespace AZ
         using NotifyEvent = AZ::Event<AZStd::string_view, Type>;
         using NotifyEventHandler = typename NotifyEvent::Handler;
 
+        using PreMergeEventCallback = AZStd::function<void(AZStd::string_view path, AZStd::string_view rootKey)>;
+        using PostMergeEventCallback = AZStd::function<void(AZStd::string_view path, AZStd::string_view rootKey)>;
+        using PreMergeEvent = AZ::Event<AZStd::string_view, AZStd::string_view>;
+        using PostMergeEvent = AZ::Event<AZStd::string_view, AZStd::string_view>;
+        using PreMergeEventHandler = typename PreMergeEvent::Handler;
+        using PostMergeEventHandler = typename PostMergeEvent::Handler;
+
+        struct ScopedMergeEvent
+        {
+            ScopedMergeEvent(
+                PreMergeEvent& preMergeEvent, PostMergeEvent& postMergeEvent, AZStd::string_view filePath, AZStd::string_view rootKey)
+                : m_preMergeEvent{ preMergeEvent }
+                , m_postMergeEvent{ postMergeEvent }
+                , m_filePath{ filePath }
+                , m_rootKey{ rootKey }
+            {
+                preMergeEvent.Signal(m_filePath, m_rootKey);
+            }
+
+            ~ScopedMergeEvent()
+            {
+                m_postMergeEvent.Signal(m_filePath, m_rootKey);
+            }
+
+            PreMergeEvent& m_preMergeEvent;
+            PostMergeEvent& m_postMergeEvent;
+            AZStd::string_view m_filePath;
+            AZStd::string_view m_rootKey;
+        };
+
         using VisitorCallback =
             AZStd::function<VisitResponse(AZStd::string_view path, AZStd::string_view valueName, VisitAction action, Type type)>;
         //! Base class for the visitor class during traversal over the Settings Registry. The type-agnostic function is always
@@ -169,6 +199,20 @@ namespace AZ
         //! @callback The function to call when an entry gets a new/updated value.
         [[nodiscard]] virtual NotifyEventHandler RegisterNotifier(NotifyCallback&& callback) = 0;
 
+        //! Register a callback that will be called before an entry is merged.
+        //! @callback The function to call when an entry gets a new/updated value.
+        [[nodiscard]] virtual PreMergeEventHandler RegisterPreMergeEvent(const PreMergeEventCallback& callback) = 0;
+        //! Register a callback that will be called before an entry is merged.
+        //! @callback The function to call when an entry gets a new/updated value.
+        [[nodiscard]] virtual PreMergeEventHandler RegisterPreMergeEvent (PreMergeEventCallback&& callback) = 0;
+
+        //! Register a callback that will be called after an entry is merged.
+        //! @callback The function to call when an entry gets a new/updated value.
+        [[nodiscard]] virtual PostMergeEventHandler RegisterPostMergeEvent(const PostMergeEventCallback& callback) = 0;
+        //! Register a callback that will be called after an entry is merged.
+        //! @callback The function to call when an entry gets a new/updated value.
+        [[nodiscard]] virtual PostMergeEventHandler RegisterPostMergeEvent (PostMergeEventCallback&& callback) = 0;
+
         //! Gets the boolean value at the provided path.
         //! @param result The target to write the result to.
         //! @param path The path to the value.

Code/Framework/AzCore/AzCore/Settings/SettingsRegistryImpl.cpp

@@ -229,6 +229,53 @@ namespace AZ
         m_notifiers.DisconnectAllHandlers();
     }
 
+    auto SettingsRegistryImpl::RegisterPreMergeEvent(const PreMergeEventCallback& callback) -> PreMergeEventHandler
+    {
+        PreMergeEventHandler preMergeHandler{ callback };
+        {
+            AZStd::scoped_lock lock(m_settingMutex);
+            preMergeHandler.Connect(m_preMergeEvent);
+        }
+        return preMergeHandler;
+    }
+
+    auto SettingsRegistryImpl::RegisterPreMergeEvent(PreMergeEventCallback&& callback) -> PreMergeEventHandler
+    {
+        PreMergeEventHandler preMergeHandler{ AZStd::move(callback) };
+        {
+            AZStd::scoped_lock lock(m_settingMutex);
+            preMergeHandler.Connect(m_preMergeEvent);
+        }
+        return preMergeHandler;
+    }
+
+    auto SettingsRegistryImpl::RegisterPostMergeEvent(const PostMergeEventCallback& callback) -> PostMergeEventHandler
+    {
+        PostMergeEventHandler postMergeHandler{ callback };
+        {
+            AZStd::scoped_lock lock(m_settingMutex);
+            postMergeHandler.Connect(m_postMergeEvent);
+        }
+        return postMergeHandler;
+    }
+
+    auto SettingsRegistryImpl::RegisterPostMergeEvent(PostMergeEventCallback&& callback) -> PostMergeEventHandler
+    {
+        PostMergeEventHandler postMergeHandler{ AZStd::move(callback) };
+        {
+            AZStd::scoped_lock lock(m_settingMutex);
+            postMergeHandler.Connect(m_postMergeEvent);
+        }
+        return postMergeHandler;
+    }
+
+    void SettingsRegistryImpl::ClearMergeEvents()
+    {
+        AZStd::scoped_lock lock(m_settingMutex);
+        m_preMergeEvent.DisconnectAllHandlers();
+        m_postMergeEvent.DisconnectAllHandlers();
+    }
+
     SettingsRegistryInterface::Type SettingsRegistryImpl::GetType(AZStd::string_view path) const
     {
         if (path.empty())
@@ -1115,6 +1162,8 @@ namespace AZ
             return false;
         }
 
+        ScopedMergeEvent(m_preMergeEvent, m_postMergeEvent, path, rootKey);
+
         JsonSerializationResult::ResultCode mergeResult(JsonSerializationResult::Tasks::Merge);
         if (rootKey.empty())
         {

Code/Framework/AzCore/AzCore/Settings/SettingsRegistryImpl.h

@@ -48,6 +48,12 @@ namespace AZ
         [[nodiscard]] NotifyEventHandler RegisterNotifier(NotifyCallback&& callback) override;
         void ClearNotifiers();
 
+        [[nodiscard]] PreMergeEventHandler RegisterPreMergeEvent(const PreMergeEventCallback& callback) override;
+        [[nodiscard]] PreMergeEventHandler RegisterPreMergeEvent(PreMergeEventCallback&& callback) override;
+        [[nodiscard]] PostMergeEventHandler RegisterPostMergeEvent(const PostMergeEventCallback& callback) override;
+        [[nodiscard]] PostMergeEventHandler RegisterPostMergeEvent(PostMergeEventCallback&& callback) override;
+        void ClearMergeEvents();
+
         bool Get(bool& result, AZStd::string_view path) const override;
         bool Get(s64& result, AZStd::string_view path) const override;
         bool Get(u64& result, AZStd::string_view path) const override;
@@ -103,6 +109,9 @@ namespace AZ
         
         mutable AZStd::recursive_mutex m_settingMutex;
         NotifyEvent m_notifiers;
+        PreMergeEvent m_preMergeEvent;
+        PostMergeEvent m_postMergeEvent;
+
         rapidjson::Document m_settings;
         JsonSerializerSettings m_serializationSettings;
         JsonDeserializerSettings m_deserializationSettings;