Flush the bus info cache in more places

The current approach 'works', but better err on the safe side. Once this
caching layer is no longer necessary we should just remove it.

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

@@ -63,6 +63,12 @@ bool Vst3PluginProxyImpl::unregister_context_menu(size_t context_menu_id) {
     return context_menus.erase(context_menu_id);
 }
 
+void Vst3PluginProxyImpl::clear_bus_cache() {
+    if (processing_bus_cache) {
+        processing_bus_cache.emplace();
+    }
+}
+
 tresult PLUGIN_API Vst3PluginProxyImpl::setAudioPresentationLatencySamples(
     Steinberg::Vst::BusDirection dir,
     int32 busIndex,
@@ -80,6 +86,8 @@ tresult PLUGIN_API Vst3PluginProxyImpl::setBusArrangements(
     int32 numIns,
     Steinberg::Vst::SpeakerArrangement* outputs,
     int32 numOuts) {
+    clear_bus_cache();
+
     // NOTE: Ardour passes a null pointer when `numIns` or `numOuts` is 0, so we
     //       need to work around that
     return bridge.send_audio_processor_message(
@@ -311,20 +319,11 @@ Vst3PluginProxyImpl::activateBus(Steinberg::Vst::MediaType type,
 
 tresult PLUGIN_API Vst3PluginProxyImpl::setActive(TBool state) {
     // HACK: Even though we have implemented this cache specifically for REAPER,
-    //       REAPER mixes up `IComponent::setActive` and
-    //       `IAudioProcessor::setProcessing`. `IAudioProcessor::setProcessing`
-    //       is called before setting up bus arrangements, so without this the
-    //       cache would be filled with default data rather than the bus
-    //       arrangement chosen by REAPER. So now our workaround to get
-    //       acceptable performance in REAPER needs a workaround of its ownn.
-    //       Great!
-    // TODO: We probably also need a reset on
-    //       `IComponentHandler::restartComponent()`
-    if (state) {
-        processing_bus_cache.emplace();
-    } else {
-        processing_bus_cache.reset();
-    }
+    //       REAPER doesn't use `IComponent::setProcessing` properly and calls
+    //       it before doing setting up input and output busses. So now our
+    //       workaround to get acceptable performance in REAPER needs a
+    //       workaround of its ownn.  Great!
+    clear_bus_cache();
 
     return bridge.send_audio_processor_message(
         YaComponent::SetActive{.instance_id = instance_id(), .state = state});

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

@@ -54,6 +54,25 @@ class Vst3PluginProxyImpl : public Vst3PluginProxy {
      */
     bool unregister_context_menu(size_t context_menu_id);
 
+    /**
+     * Clear the bus count and information cache. We need this cache for REAPER
+     * as it makes `num_inputs + num_outputs + 2` function calls to retrieve
+     * this information every single processing cycle. For plugins with a lot of
+     * outputs this really adds up. According to the VST3 workflow diagrams bus
+     * information cannot change anymore once `IAudioProcessor::setProcessing()`
+     * has been called, but REAPER doesn't quite follow the spec here and it
+     * will set bus arrangements and activate the plugin only after it's called
+     * `IAudioProcessor::setProcessing()`. Because of that we'll have to
+     * manually flush this cache when the stores information potentially becomes
+     * invalid.
+     *
+     * HACK: Once REAPER stops calling these functions, we should remove this
+     *       caching layer ASAP as it can only cause issues
+     *
+     * @see processing_bus_cache
+     */
+    void clear_bus_cache();
+
     // From `IAudioPresentationLatency`
     tresult PLUGIN_API
     setAudioPresentationLatencySamples(Steinberg::Vst::BusDirection dir,

src/plugin/bridges/vst3.cpp

@@ -85,9 +85,15 @@ Vst3PluginBridge::Vst3PluginBridge()
                 },
                 [&](const YaComponentHandler::RestartComponent& request)
                     -> YaComponentHandler::RestartComponent::Response {
-                    return plugin_proxies.at(request.owner_instance_id)
-                        .get()
-                        .component_handler->restartComponent(request.flags);
+                    Vst3PluginProxyImpl& proxy_object =
+                        plugin_proxies.at(request.owner_instance_id).get();
+
+                    // To err on the safe side, we'll just always clear out bus
+                    // info cache whenever a plugin requests a restart
+                    proxy_object.clear_bus_cache();
+
+                    return proxy_object.component_handler->restartComponent(
+                        request.flags);
                 },
                 [&](const YaComponentHandler2::SetDirty& request)
                     -> YaComponentHandler2::SetDirty::Response {