A representation of the user and group databases

This can be used to handle /etc/passwd and related files. Typically, you would:

• Create an instance early in the main phase
• Add things to it as needed (next to the associated packages)
• Apply it at the end of the main phase

A rough example:

// Mappings for the IDs that systemd auto-assigns inconsistently from computer to computer
const USER_MAPPING = [("systemd-journald", 900), /* ... */]
const GROUP_MAPPING = [("systemd-journald", 900), /* ... */]

pub async fn phase_main(props, cmds, package_managers) {
   let passwd = passwd::Passwd::new(USER_MAPPING, GROUP_MAPPING)?;

   let files = package_managers.files();
   // These two files MUST come first as other files later on refer to them,
   // and we are not order independent (unlike the real sysusers.d).
   passwd.add_from_sysusers(files, "systemd", "/usr/lib/sysusers.d/basic.conf")?;
   passwd.add_from_sysusers(files, "filesystem", "/usr/lib/sysusers.d/arch.conf")?;

   // Various other packages and other changes ...
   passwd.add_from_sysusers(files, "dbus", "/usr/lib/sysusers.d/dbus.conf")?;
   // ...

   // Add human user
   let me = passwd::User::new(1000, "me", "me", "");
   me.shell = "/bin/zsh";
   me.home = "/home/me";
   passwd.add_user_with_group(me);
   passwd.add_user_to_groups("me", ["wheel", "optical", "uucp", "users"]);

   // Don't store passwords in your git repo, load them from the system instead
   passwd.passwd_from_system(["me", "root"]);

   // Give root a login shell, we don't want /usr/bin/nologin!
   passwd.update_user("root", |user| {
       user.shell = "/bin/zsh";
       user
   });

   // Deal with the IDs not matching (because the mappings were created
   // before konfigkoll was in use for example)
   passwd.align_ids_with_system()?;

   // Apply changes
   passwd.apply(cmds)?;
}