//! The other half: a `match` on the generated enum stops being exhaustive the
//! moment the form gains a message.
//!
//! `hello.dform` emits one message, `greet`. This matches a variant that is not
//! there — which is the shape of the error an application gets when a message is
//! *removed*; and the missing-arm error is what it gets when one is added.
include!;