error: named variants are not allowed in ProtocolMessage
 --> tests/derive/compile-fail/wrong_usage.rs:9:5
  |
9 |     VariantB { n: u32 },
  |     ^^^^^^^^

error: this variant must contain exactly one field to be valid ProtocolMessage
  --> tests/derive/compile-fail/wrong_usage.rs:11:5
   |
11 |     VariantC(u32, String),
   |     ^^^^^^^^

error: this variant must contain exactly one field to be valid ProtocolMessage
  --> tests/derive/compile-fail/wrong_usage.rs:13:5
   |
13 |     VariantD(),
   |     ^^^^^^^^

error: unit variants are not allowed in ProtocolMessage
  --> tests/derive/compile-fail/wrong_usage.rs:15:5
   |
15 |     VariantE,
   |     ^^^^^^^^

error: only enum may implement ProtocolMessage
  --> tests/derive/compile-fail/wrong_usage.rs:20:1
   |
20 | struct Msg2 {
   | ^^^^^^

error: only enum may implement ProtocolMessage
  --> tests/derive/compile-fail/wrong_usage.rs:26:1
   |
26 | union Msg3 {
   | ^^^^^

error: #[protocol_message] attribute appears more than once
  --> tests/derive/compile-fail/wrong_usage.rs:33:3
   |
33 | #[protocol_message(root = two)]
   |   ^^^^^^^^^^^^^^^^

error: unexpected token
  --> tests/derive/compile-fail/wrong_usage.rs:41:30
   |
41 | #[protocol_message(root = one, blah blah)]
   |                              ^

error: unexpected end of input, expected `root`
  --> tests/derive/compile-fail/wrong_usage.rs:49:20
   |
49 | #[protocol_message()]
   |                    ^