Code review comment for lp:mir/0.22

I wonder if this could break some C++ ABI that passes a MirEvent pointer/ref as a parameter?

diff -r 0.21/include/client/mir_toolkit/events/event.h 0.22/include/client/mir_toolkit/events/event.h
63c63
< typedef union MirEvent MirEvent;
---
> typedef struct MirEvent MirEvent;