Implement IPluginFactory3::setHostContext()

Now the plugin factories are fully implemented (at least, functionality
wise, we still can't create most kinds of objects).

src/common/serialization/vst3.h

@@ -61,7 +61,8 @@ using ControlRequest = std::variant<YaComponent::Construct,
                                     YaComponent::Destruct,
                                     YaComponent::Initialize,
                                     YaComponent::Terminate,
-                                    YaPluginFactory::Construct>;
+                                    YaPluginFactory::Construct,
+                                    YaPluginFactory::SetHostContext>;
 
 template <typename S>
 void serialize(S& s, ControlRequest& payload) {

src/common/serialization/vst3/component.h

@@ -43,7 +43,8 @@
  * for everything other than the edit controller's class ID.
  *
  * TODO: I think it's expected that components also implement `IAudioProcessor`
- *       and `IConnectionPoint`.
+ *       and `IConnectionPoint`. We should use the same approach as in the
+ *       plugin factory to implement multiple, possibly optional, interfaces.
  */
 class YaComponent : public Steinberg::Vst::IComponent {
    public:
@@ -57,7 +58,7 @@ class YaComponent : public Steinberg::Vst::IComponent {
          * Read arguments from an existing implementation.
          */
         ConstructArgs(Steinberg::IPtr<Steinberg::Vst::IComponent> component,
-                      size_t isntance_id);
+                      size_t instance_id);
 
         /**
          * The unique identifier for this specific instance.

src/common/serialization/vst3/host-application.cpp

@@ -20,7 +20,7 @@ YaHostApplication::ConstructArgs::ConstructArgs() {}
 
 YaHostApplication::ConstructArgs::ConstructArgs(
     Steinberg::IPtr<Steinberg::Vst::IHostApplication> context,
-    size_t component_instance_id)
+    std::optional<size_t> component_instance_id)
     : component_instance_id(component_instance_id) {
     Steinberg::Vst::String128 name_array;
     if (context->getName(name_array) == Steinberg::kResultOk) {

src/common/serialization/vst3/host-application.h

@@ -48,16 +48,15 @@ class YaHostApplication : public Steinberg::Vst::IHostApplication {
          * Read arguments from an existing implementation.
          */
         ConstructArgs(Steinberg::IPtr<Steinberg::Vst::IHostApplication> context,
-                      size_t component_isntance_id);
+                      std::optional<size_t> component_instance_id);
 
         /**
          * The unique instance identifier of the component this host context has
-         * been passed to and thus belongs to.
-         *
-         * TODO: When we implement `IPluginFactory3::setHostContext()` this
-         *       should be made optional.
+         * been passed to and thus belongs to, if we are handling
+         * `IpluginBase::initialize()`. When handling
+         * `IPluginFactory::setHostContext()` this will be empty.
          */
-        native_size_t component_instance_id;
+        std::optional<native_size_t> component_instance_id;
 
         /**
          * For `IHostApplication::getName`.
@@ -66,7 +65,10 @@ class YaHostApplication : public Steinberg::Vst::IHostApplication {
 
         template <typename S>
         void serialize(S& s) {
-            s.value8b(component_instance_id);
+            s.ext(component_instance_id, bitsery::ext::StdOptional{},
+                  [](S& s, native_size_t& instance_id) {
+                      s.value8b(instance_id);
+                  });
             s.ext(name, bitsery::ext::StdOptional{},
                   [](S& s, std::u16string& name) {
                       s.text2b(name, std::extent_v<Steinberg::Vst::String128>);

src/common/serialization/vst3/plugin-factory.h

@@ -25,6 +25,7 @@
 
 #include "../../bitsery/ext/vst3.h"
 #include "base.h"
+#include "host-application.h"
 
 // TODO: After implementing one or two more of these, abstract away some of the
 //       nasty bits
@@ -155,10 +156,26 @@ class YaPluginFactory : public Steinberg::IPluginFactory3 {
     // From `IPluginFactory3`
     tresult PLUGIN_API
     getClassInfoUnicode(int32 index, Steinberg::PClassInfoW* info) override;
+
     /**
-     * We'll pass a `IHostApplication` to the Windows VST3 plugin's factory when
-     * this is called so it can send messages.
+     * Message to pass through a call to `IPluginFactory3::setHostContext()` to
+     * the Wine plugin host. A proxy `YaHostApplication` should be created on
+     * the Wine plugin host and then passed as an argument to
+     * `IPluginFactory3::setHostContext()`. If the host called
+     * `IPluginFactory3::setHostContext()` with something other than an
+     * `IHostApplication*`, we return an error immediately and log the call.
      */
+    struct SetHostContext {
+        using Response = UniversalTResult;
+
+        YaHostApplication::ConstructArgs host_application_context_args;
+
+        template <typename S>
+        void serialize(S& s) {
+            s.object(host_application_context_args);
+        }
+    };
+
     virtual tresult PLUGIN_API
     setHostContext(Steinberg::FUnknown* context) override = 0;