Lifetime confusion

main.rs

#[macro_use]
extern crate serde_derive;

extern crate csv;
extern crate serde;

use serde::{Serialize, Deserialize};

pub trait Record<'de>: Serialize + Deserialize<'de> {
    fn is_valid(&self) -> Result<(), String>;
}

#[derive(Serialize, Deserialize)]
struct TestRecord<'a> {
    field_one: &'a str,
    field_two: &'a str,
}

impl<'a, 'de: 'a> Record<'de> for TestRecord<'a> {
    fn is_valid(&self) -> Result<(), String> {
        Ok(())
    }
}

fn validate<'de, R>(record: Result<csv::ByteRecord, csv::Error>, index: usize) -> Result<csv::ByteRecord, String>
where
    R: Record<'de>,
{
    let record = record.map_err(|err| {
        format!("[decoding.row.invalid] {}, {:?}\n", index, err)
    })?;

    let deserialized_record = record.deserialize::<R>(None).map_err(|err| {
        format!("[deserializing.row.invalid] {}, {:?}\n", index, err)
    })?;

    match deserialized_record.is_valid() {
        Ok(()) => Ok(record),
        Err(err) => {
            Err(format!(
                "[validation.row.invalid] {}, {:?}\n",
                index,
                err
            ))
        }
    }
}

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