Code review comment for lp:~alan-griffiths/miral/encapsulate-mir-PromptSession

> (Almost) there's something with the signal/slot mechanism that still
> requires the complete type for mir::scene::PromptSession.

It's not ideal, but Qt refuses to let signal/slot connections work with types that are forward declared. Qt wants to check if the type is registered with the metatype system at compile time. Can't avoid it.

General change looks ok, however I'd prefer if you adopted the Qt style in PromptSession, e.g.
std::shared_ptr<mir::scene::PromptSession> const& promptSession
  -> const std::shared_ptr<mir::scene::PromptSession> &promptSession
and not use the newer C++ style "auto foo() -> bool"