example of an abstract class pattern failing to work with pub(crate)

abstract-classes.rs

pub(crate) trait EmployeePrivate {
    fn unique_key(&self) -> i32;
}

pub struct Engineer {
    key: i32,
    name: String
}

pub struct EngineeringManager {
    key: i32,
    name: String,
    reports: Vec<i32>
}

// etc...

// ERROR: private type `EmployeePrivate` leaked from public type `Employee`
pub trait Employee: EmployeePrivate {
    fn name(&self) -> &str;

    fn delete(self) {
        let key = self.key(); // should work because every Employee is an EmployeePrivate
        DB::delete_row(key);
    }
}

impl EmployeePrivate for Engineer {
    fn unique_key(&self) -> i32 { self.key }
}

impl Employee for Engineer {
    fn name(&self) -> &str { &self.name }
}

impl EmployeePrivate for EngineeringManager {
    fn unique_key(&self) -> i32 { self.key }
}

impl Employee for EngineeringManager {
    fn name(&self) -> &str { &self.name }
}

pub trait Manager: Employee {
    fn reports(&self) -> &[impl Employee];
}

impl Manager for EngineeringManager {
    // etc...
}