error[E0121]: the placeholder `_` is not allowed within types on item signatures for constants
  --> $DIR/issue-104768.rs:1:10
   |
LL | const A: &_ = 0_u32;
   |          ^^
   |          |
   |          not allowed in type signatures
   |          help: replace with the correct type: `u32`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0121`.