Implement the plugin side if IComponentHandler3

src/plugin/bridges/vst3-impls/plugin-proxy.h

@@ -38,6 +38,22 @@ class Vst3PluginProxyImpl : public Vst3PluginProxy {
     tresult PLUGIN_API queryInterface(const Steinberg::TUID _iid,
                                       void** obj) override;
 
+    /**
+     * Add a context menu created by a call to
+     * `IComponentHandler3::createContextMenu` to our list of registered cotnext
+     * menus. This way we can refer to it later when the plugin calls a function
+     * on the proxy object we'll create for it.
+     */
+    size_t register_context_menu(
+        Steinberg::IPtr<Steinberg::Vst::IContextMenu> menu);
+
+    /**
+     * Unregister a context menu using the ID generated by a previous call to
+     * `register_context_menu()`. This will release the context menu object
+     * returned by the host.
+     */
+    bool unregister_context_menu(size_t context_menu_id);
+
     // From `IAudioPresentationLatency`
     tresult PLUGIN_API
     setAudioPresentationLatencySamples(Steinberg::Vst::BusDirection dir,
@@ -242,6 +258,21 @@ class Vst3PluginProxyImpl : public Vst3PluginProxy {
      */
     Vst3PlugViewProxyImpl* last_created_plug_view = nullptr;
 
+    /**
+     * All context menus created by this object through
+     * `IComponentHandler3::createContextMenu()`. We'll generate a unique
+     * identifier for each context menu just like we do for plugin objects. When
+     * the plugin drops the context menu object, we'll also remove the
+     * corresponding entry for this map causing the original pointer returned by
+     * the host to get dropped a well.
+     *
+     * @see Vst3PluginProxyImpl::register_context_menu
+     * @see Vst3PluginProxyImpl::unregister_context_menu
+     */
+    std::map<size_t, Steinberg::IPtr<Steinberg::Vst::IContextMenu>>
+        context_menus;
+    std::mutex context_menus_mutex;
+
     // The following pointers are cast from `host_context` if
     // `IPluginBase::initialize()` has been called
 
@@ -252,6 +283,8 @@ class Vst3PluginProxyImpl : public Vst3PluginProxy {
 
     Steinberg::FUnknownPtr<Steinberg::Vst::IComponentHandler2>
         component_handler_2;
+    Steinberg::FUnknownPtr<Steinberg::Vst::IComponentHandler3>
+        component_handler_3;
     Steinberg::FUnknownPtr<Steinberg::Vst::IUnitHandler> unit_handler;
 
    private:
@@ -265,4 +298,12 @@ class Vst3PluginProxyImpl : public Vst3PluginProxy {
      * but for the sake of correctness we will.
      */
     Steinberg::IPtr<Steinberg::FUnknown> host_context;
+
+    /**
+     * Used to assign unique identifiers to context menus created by
+     * `IComponentHandler3::CreateContextMenu`.
+     *
+     * @related Vst3PluginProxyImpl::register_context_menu
+     */
+    std::atomic_size_t current_context_menu_id;
 };