Fully implement IPluginBase::initialize()

We can now pass host contexts around.

README.md

@@ -18,7 +18,7 @@ imcomplete list of things that still have to be done before this can be used:
 - Left to implement:
   - `YaHostApplicationHostImpl::createComponent`.
   - `IPluginFactory3::setHostContext()` using the same host application context proxy method.
-  - The rest of `IComponent`'s functions after implementing `intialize()`
+  - The rest of `IComponent`'s functions
   - `IPluginFactory3::setHostContext()`
   - All other mandatory interfaces
   - All other optional interfaces

src/common/communication/vst3.h

@@ -180,7 +180,7 @@ class Vst3MessageHandler : public AdHocSocketHandler<Thread> {
                 // always know for sure that the function returns the correct
                 // type, and we can scrap a lot of boilerplate elsewhere.
                 std::visit(
-                    [&]<typename T>(const T object) {
+                    [&]<typename T>(T object) {
                         typename T::Response response = callback(object);
 
                         if (logging) {

src/wine-host/bridges/vst3.cpp

@@ -20,6 +20,8 @@
 
 #include <public.sdk/source/vst/hosting/module_win32.cpp>
 
+#include "vst3-impls/host-application.h"
+
 Vst3Bridge::Vst3Bridge(MainContext& main_context,
                        std::string plugin_dll_path,
                        std::string endpoint_base_dir)
@@ -67,18 +69,39 @@ void Vst3Bridge::run() {
             },
             [&](const YaComponent::Destruct& request)
                 -> YaComponent::Destruct::Response {
-                std::lock_guard lock(component_instances_mutex);
+                std::scoped_lock lock(
+                    component_instances_mutex,
+                    component_host_application_context_instance_mutex);
                 component_instances.erase(request.instance_id);
+                if (component_host_application_context_instances.contains(
+                        request.instance_id)) {
+                    component_host_application_context_instances.erase(
+                        request.instance_id);
+                }
 
                 return Ack{};
             },
-            [&](const YaComponent::Initialize& request)
+            [&](YaComponent::Initialize& request)
                 -> YaComponent::Initialize::Response {
-                // TODO: If `request.host_context_args` has a value, we should
-                //       initialize a proxy object and pass a pointer to that
-                //       instead
+                // If we got passed a host context, we'll create a proxy object
+                // and pass that to the initialize function. This object should
+                // be cleaned up again during `YaComponent::Destruct`.
+                Steinberg::FUnknown* context = nullptr;
+                if (request.host_application_context_args) {
+                    // TODO: Is this safe? These Steinberg smart pointers are
+                    //       scary
+                    component_host_application_context_instances
+                        [request.instance_id] =
+                            Steinberg::owned(new YaHostApplicationHostImpl(
+                                *this,
+                                std::move(
+                                    *request.host_application_context_args)));
+                    context = component_host_application_context_instances
+                        [request.instance_id];
+                }
+
                 return component_instances[request.instance_id]->initialize(
-                    nullptr);
+                    context);
             },
             [&](const YaComponent::Terminate& request)
                 -> YaComponent::Terminate::Response {

src/wine-host/bridges/vst3.h

@@ -108,4 +108,19 @@ class Vst3Bridge : public HostBridge {
     std::map<size_t, Steinberg::IPtr<Steinberg::Vst::IComponent>>
         component_instances;
     std::mutex component_instances_mutex;
+
+    /**
+     * If an `IHostApplication` was passed during
+     * `{IPluginBase,IComponent}::initialize()`, then we'll store a proxy object
+     * here. The instance ID is the same as the corresponding instance ID in
+     * `component_instances`. When an instance gets removed from
+     * `component_instances`, it should also be removed from here.
+     *
+     * XXX: If it turns out we need to keep track of more of these kinds of
+     *      objects, then we should create a wrapper so that everything can stay
+     *      in `component_instances`
+     */
+    std::map<size_t, Steinberg::IPtr<YaHostApplication>>
+        component_host_application_context_instances;
+    std::mutex component_host_application_context_instance_mutex;
 };