Code shared from the Rust Playground

playground.rs

use serde; // 1.0.90
use serde::ser::{SerializeSeq, Serializer};
use serde::Serialize;
use serde_urlencoded; // 0.5.4

fn main() {
    let p = P {
        ids: vec!["1", "2"],
    };
    println!("{}", serde_urlencoded::to_string(&p).unwrap());
    
    println!("{}", "-".repeat(100));

    let params = Params {
        ids: IdParams(vec!["1", "2"]),
    };
    println!("{}", serde_urlencoded::to_string(&params).unwrap());
}

struct P<'a> {
    ids: Vec<&'a str>,
}

impl<'a> Serialize for P<'a> {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        let mut seq = serializer.serialize_seq(Some(self.ids.len()))?;
        for e in &self.ids {
            seq.serialize_element(&("id", e))?;
        }
        seq.end()
    }
}

struct IdParams<'a>(Vec<&'a str>);

impl<'a> Serialize for IdParams<'a> {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        let mut seq = serializer.serialize_seq(Some(self.0.len()))?;
        for e in &self.0 {
            seq.serialize_element(&("id", e))?;
        }
        seq.end()
    }
}

#[derive(Serialize)]
struct Params<'a> {
    ids: IdParams<'a>,
}