Macro bail 

macro_rules! bail {
    ( $( $arg:tt )+ ) => { ... };
}

Break out of the current function, returning an internal error.

Example

use apollo_federation::bail;
use apollo_federation::error::FederationError;

fn example() -> Result<(), FederationError> {
    bail!("Something went horribly wrong");
    unreachable!()
}