error[E0562]: `impl Trait` is not allowed in the type of variable bindings
  --> $DIR/issue-58504.rs:10:16
   |
LL |     let gens: [impl Coroutine<Return=!, Yield=()>;2] = [ mk_gen(), mk_gen() ];
   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: `impl Trait` is only allowed in arguments and return types of functions and methods

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0562`.