error[E0601]: main function not found

error[E0593]: function is expected to take 1 argument, but it takes 2 arguments
  --> $DIR/issue-47706.rs:21:18
   |
16 |     pub fn new(foo: Option<i32>, _: ()) -> Foo {
   |     ------------------------------------------ takes 2 arguments
...
21 |         self.foo.map(Foo::new)
   |                  ^^^ expected function that takes 1 argument

error: aborting due to 2 previous errors