When creating a binary crate with a src/main.rs and #[derive(Deserialize, Serialize)], running cargo doc on it will result in new doc items for generated constants:

use serde::{Deserialize, Serialize};

#[derive(Deserialize, Serialize)]
struct Dummy {
}

fn main() {
    println!("Hello, world!");
}

This is because Cargo runs with --document-private-items internally for src/main.rs. If you put the same code in a src/lib.rs the private items will not be documented by default, so you won't see them there for default cargo doc.
The items will be visible both for src/lib.rs and src/main.rs if the struct itself is pub.

I believe the generated _IMPL_{}_FOR_{} constants should not be visible in rustdoc and this merge request seems to fix the issue for me.