error: circular modules: $DIR/circular_modules_hello.rs -> $DIR/circular_modules_main.rs -> $DIR/circular_modules_hello.rs
  --> $DIR/circular_modules_main.rs:2:1
   |
LL | mod circular_modules_hello;
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0425]: cannot find function `say_hello` in module `circular_modules_hello`
  --> $DIR/circular_modules_main.rs:9:29
   |
LL |     circular_modules_hello::say_hello();
   |                             ^^^^^^^^^ not found in `circular_modules_hello`
   |
help: consider importing this function
   |
LL | use circular_modules_hello::say_hello;
   |

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0425`.