When I load HALion 7.0.0.290 VST3 Intel on macOS 13.2.1 in the JUCE AudioPluginHost application, all output buses are initially activated.
If I right-click on HALion, select “Configure Audio IO”, and then select output bus 2 and disable it, the host crashes after applying the layout.
Debugging, I see that the host is correctly deactivating the plug-in, and calling activateBus on each input and output bus with the expected state. Then, during processing, the host is passing nullptr for each of the audio channels in the deactivated bus, which is explicitly allowed here: VST 3 Interfaces: AudioBusBuffers Struct Reference - “if an audio bus is currently inactive, the actual sample buffer addresses are safe to be null.”
I believe that this is a bug in HALion 7 VST3. If it is crashing due to writing to a deactivated/null bus, then it is not correctly implementing the VST3 spec.
Please can you confirm this bug? Let me know if I missed any important details.