Erm, based on the lack of filenames: it would probably have to be `grep main` ... I guess it would be better to be something like

```rust
fn failure() { fail!() }

fn intermediate() { failure() }

fn main() { intermediate() }
```

and at least grep for `intermediate` to make sure it's actually picking up the call stack. (Best case would be checking `main`, `intermediate` and `failure`.)