How to fix bar2() concisely? (bar1 is not concise)

gistfile1.txt

fn foo() -> Result<(), std::io::Error> {
    Ok(())
}

// Compiles, but verbose (using map_err).
fn bar1() -> Result<(), Box<dyn std::error::Error>> {
    foo().map_err(|e| e.into())
}

// Does not compile.
fn bar2() -> Result<(), Box<dyn std::error::Error>> {
    foo()
}