error[E0137]: multiple functions with a #[main] attribute
  --> $DIR/E0137.rs:7:1
   |
LL | fn foo() {}
   | ----------- first #[main] function
...
LL | fn f() {}
   | ^^^^^^^^^ additional #[main] function

error: aborting due to previous error

For more information about this error, try `rustc --explain E0137`.