playing with anyhow and downcasting

main.rs

use anyhow::Context;
use std::error::Error;
use std::fmt;

#[derive(Debug)]
struct FooError {}

impl fmt::Display for FooError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "foo error!")
    }
}

impl Error for FooError {}

fn foo() -> Result<(), FooError> {
    Err(FooError {})
}

fn bar() -> anyhow::Result<()> {
    foo().context("bar trying to foo")?;
    Ok(())
}

fn main() -> anyhow::Result<()> {
    let result = bar();
    if let Err(e) = &result {
        if let Some(foo_error) = e.downcast_ref::<FooError>() {
            println!("Looks like we hit a foo error: {foo_error:?}");
        }
    }
    result
}

Current output:

Looks like we hit a foo error: FooError
Error: bar trying to foo

Caused by:
    foo error!