clippy 0.0.208

A bunch of helpful lints to avoid common pitfalls in Rust
error: enum with no variants
 --> $DIR/empty_enum.rs:7:1
  |
7 | enum Empty {}
  | ^^^^^^^^^^^^^
  |
  = note: `-D empty-enum` implied by `-D warnings`
help: consider using the uninhabited type `!` or a wrapper around it
 --> $DIR/empty_enum.rs:7:1
  |
7 | enum Empty {}
  | ^^^^^^^^^^^^^

error: aborting due to previous error