error[E0277]: `fn() {main}` can't be used as a const parameter type
  --> $DIR/const_param_ty_bad.rs:7:11
   |
LL |     check(main);
   |     ----- ^^^^ the trait `ConstParamTy` is not implemented for fn item `fn() {main}`
   |     |
   |     required by a bound introduced by this call
   |
note: required by a bound in `check`
  --> $DIR/const_param_ty_bad.rs:4:18
   |
LL | fn check(_: impl std::marker::ConstParamTy) {}
   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `check`
help: use parentheses to call this function
   |
LL |     check(main());
   |               ++

error[E0277]: `[closure@$DIR/const_param_ty_bad.rs:8:11: 8:13]` can't be used as a const parameter type
  --> $DIR/const_param_ty_bad.rs:8:11
   |
LL |     check(|| {});
   |     ----- ^^^^^ the trait `ConstParamTy` is not implemented for closure `[closure@$DIR/const_param_ty_bad.rs:8:11: 8:13]`
   |     |
   |     required by a bound introduced by this call
   |
note: required by a bound in `check`
  --> $DIR/const_param_ty_bad.rs:4:18
   |
LL | fn check(_: impl std::marker::ConstParamTy) {}
   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `check`
help: use parentheses to call this closure
   |
LL |     check(|| {}());
   |                ++

error[E0277]: `fn()` can't be used as a const parameter type
  --> $DIR/const_param_ty_bad.rs:9:11
   |
LL |     check(main as fn());
   |     ----- ^^^^^^^^^^^^ the trait `ConstParamTy` is not implemented for `fn()`
   |     |
   |     required by a bound introduced by this call
   |
note: required by a bound in `check`
  --> $DIR/const_param_ty_bad.rs:4:18
   |
LL | fn check(_: impl std::marker::ConstParamTy) {}
   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `check`
help: use parentheses to call this function pointer
   |
LL |     check(main as fn()());
   |                       ++

error[E0277]: `&mut ()` can't be used as a const parameter type
  --> $DIR/const_param_ty_bad.rs:10:11
   |
LL |     check(&mut ());
   |     ----- ^^^^^^^ the trait `ConstParamTy` is not implemented for `&mut ()`
   |     |
   |     required by a bound introduced by this call
   |
   = note: `ConstParamTy` is implemented for `&()`, but not for `&mut ()`
note: required by a bound in `check`
  --> $DIR/const_param_ty_bad.rs:4:18
   |
LL | fn check(_: impl std::marker::ConstParamTy) {}
   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `check`
help: consider removing the leading `&`-reference
   |
LL -     check(&mut ());
LL +     check(());
   |

error[E0277]: `*mut ()` can't be used as a const parameter type
  --> $DIR/const_param_ty_bad.rs:11:11
   |
LL |     check(&mut () as *mut ());
   |     ----- ^^^^^^^^^^^^^^^^^^ the trait `ConstParamTy` is not implemented for `*mut ()`
   |     |
   |     required by a bound introduced by this call
   |
   = help: the trait `ConstParamTy` is implemented for `()`
note: required by a bound in `check`
  --> $DIR/const_param_ty_bad.rs:4:18
   |
LL | fn check(_: impl std::marker::ConstParamTy) {}
   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `check`

error[E0277]: `*const ()` can't be used as a const parameter type
  --> $DIR/const_param_ty_bad.rs:12:11
   |
LL |     check(&() as *const ());
   |     ----- ^^^^^^^^^^^^^^^^ the trait `ConstParamTy` is not implemented for `*const ()`
   |     |
   |     required by a bound introduced by this call
   |
   = help: the trait `ConstParamTy` is implemented for `()`
note: required by a bound in `check`
  --> $DIR/const_param_ty_bad.rs:4:18
   |
LL | fn check(_: impl std::marker::ConstParamTy) {}
   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `check`

error: aborting due to 6 previous errors

For more information about this error, try `rustc --explain E0277`.