Panicking

When an unrecoverable error happens in Rust, the program panics. There are several ways that panics can be handled, but it usually ends up with your program exiting (crashing).

Let's try it. Add this before the "hello world" message:

#![allow(unused)]
fn main() {
panic!("Oh no!");
}

We should observe two things:

1. Compiler gives us "unreachable statement" warning for the code after panic!().
2. When we run our program, it doesn't appear to do anything.

Let's fix point 2 by displaying the panic information. First, let's import error macro from the log crate:

#![allow(unused)]
fn main() {
use log::{info, error};
}

Then, modify the panic handler, located just after import statements, like so:

1. Give a name to the PanicInfo variable. In Rust, we use _ when we have unused variables that we don't want to name.
2. Print the panic info using the error!() macro.

#![allow(unused)]
fn main() {
#[panic_handler]
fn panic(panic_info: &core::panic::PanicInfo) -> ! {
    error!("{panic_info}");
    loop {}
}
}

Now, we get a useful message about why our program crashed:

ERROR - panicked at src/bin/main.rs:32:9:
Oh no!

Finally, don't forget to delete the panic!() call before proceeding to the next section!