error[E0015]: calls in constant functions are limited to constant functions, tuple structs and tuple variants
  --> $DIR/issue-56164.rs:3:18
   |
LL | const fn foo() { (||{})() }
   |                  ^^^^^^^^

error: function pointers are not allowed in const fn
  --> $DIR/issue-56164.rs:8:5
   |
LL |     input()
   |     ^^^^^^^

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0015`.