Function show_broken_pkg 

pub fn show_broken_pkg(
    cache: &Cache,
    pkg: &Package<'_>,
    now: bool,
) -> Option<String>

Reference implementation to print broken packages just like apt does.

Returns None if the package is not considered broken

now:

• true = When checking broken packages before modifying the cache.
• false = When checking broken packages after modifying the cache.