Don't use this in production!

• It uses lots of unsafe which is documented but has only been reviewed by me
• it needs nightly (#![feature(untagged_unions)] and #![feature(proc_macro_diagnostic)])
• The resulting structs are always repr(C).

What does it do?

It allows you to annotate fields of a struct as private and create variants of the struct that do / don't have those fields. You can then take references to each one.

It also allows you to have attributes on only one one of the structs or both of them and to consume the container to turn it into the private variant.

You may not use cfg on only one of the variants since that would break internal layout guarantees.

Why did you create this?

I wanted automatic compile time guarantees that I don't accidentaly expose private data.

Example:

You can find more examples here.

#![feature(untagged_unions)]
use sanitizeable::{sanitizeable, Sanitizeable};

#[sanitizeable]
#[derive(Debug)]
#[public_attr::derive(serde::Serialize)] // This only derives `serde::Serialize` for the public variant
struct User {
    name: String,
    // This attrribute is only applied to the field on the private type
    #[private_attr::doc = "This is the user's email, make sure to send them a lot of spam"]
    email: String,
    #[private]
    pin: u16,
}

// using `UserPrivate` here would not compile since it does not implement `serde::Serialize`
fn send_user_information<W: std::io::Write>(writer: &mut W, user_data: &UserPublic) {
    eprintln!("sending user {}", user_data.name);
    serde_json::to_writer(writer, user_data).unwrap();

    // dbg!(user_data.pin); // This would not compile
}

fn change_pin(user: &mut UserPrivate, new_pin: u16) {
    user.pin = new_pin;
}

fn main() {
    let mut user_buffer = Vec::new();

    let mut user = User::from_private(UserPrivate {
        name: "A user".into(),
        email: "some@email.com".into(),
        pin: 1337,
    });

    send_user_information(&mut user_buffer, user.public());

    change_pin(user.private_mut(), 42);

    dbg!(user.public());
}

Contributing

If you think this is cool and want to make it useable, feel free to create a PR an Issue or to message me.