VST3 Client: Add host API checks to setBusArrangements and activateBus

modules/juce_audio_plugin_client/VST3/juce_VST3_Wrapper.cpp

@@ -2338,6 +2338,8 @@ public:
     //==============================================================================
     tresult PLUGIN_API setActive (TBool state) override
     {
+        active = (state != 0);
+
         if (! state)
         {
             getPluginInstance().releaseResources();
@@ -2904,6 +2906,9 @@ public:
 
     tresult PLUGIN_API activateBus (Vst::MediaType type, Vst::BusDirection dir, Steinberg::int32 index, TBool state) override
     {
+        // The host is misbehaving! The plugin must be deactivated before setting new arrangements.
+        jassert (! active);
+
         if (type == Vst::kEvent)
         {
            #if JucePlugin_WantsMidiInput
@@ -2979,6 +2984,13 @@ public:
     tresult PLUGIN_API setBusArrangements (Vst::SpeakerArrangement* inputs, Steinberg::int32 numIns,
                                            Vst::SpeakerArrangement* outputs, Steinberg::int32 numOuts) override
     {
+        if (active)
+        {
+            // The host is misbehaving! The plugin must be deactivated before setting new arrangements.
+            jassertfalse;
+            return kResultFalse;
+        }
+
         auto numInputBuses  = pluginInstance->getBusCount (true);
         auto numOutputBuses = pluginInstance->getBusCount (false);
 
@@ -3536,6 +3548,8 @@ private:
     AudioBuffer<float>  emptyBufferFloat;
     AudioBuffer<double> emptyBufferDouble;
 
+    bool active = false;
+
    #if JucePlugin_WantsMidiInput
     std::atomic<bool> isMidiInputBusEnabled { true };
    #endif