error[E0308]: mismatched types
 --> $DIR/19-enums-tuple-variant-incomplete.rs:4:9
  |
4 | #[def = "A"]
  |         ^^^
  |         |
  |         expected enum `Foo`, found fn item
  |         expected `Foo` because of return type
  |         help: use parentheses to instantiate this tuple variant: `"A"(_)`
5 | enum Foo {
6 |     A(usize),
  |     -------- fn(usize) -> Foo {Foo::A} defined here
  |
  = note: expected enum `Foo`
          found fn item `fn(usize) -> Foo {Foo::A}`