OH, yeah, yeah, I pasted it wrongly, in my code it’s actually build_flags = -DUSB_MIDI (or build_flags = -USB_MIDI, the same), but it keeps throwing the exception: error: 'usbMIDI was not declared in this scope. I’ve seen this error before in Arduino IDE, when USB type is not properly set to MIDI.
By the way the same problem can be reproduced with Atom IDE, if you click “Build” from the graphical interface OR open a console window from IDE and type pio run.