Code shared from the Rust Playground

playground.rs

extern crate serde;
#[macro_use]
extern crate serde_derive; // 1.0.80
extern crate serde_json;
extern crate chrono; // 0.4.6

use std::collections::BTreeMap;
use std::fmt::Display;
use chrono::{DateTime,Utc};
use std::str::FromStr;
use serde::de::{Deserialize, Deserializer};


#[serde(deny_unknown_fields)]
#[derive(Deserialize, Debug)]
struct Container {
    #[serde(deserialize_with="from_str")]
    creation: DateTime<Utc>,
    #[serde(deserialize_with="from_str")]
    items: BTreeMap<DateTime<Utc>, Item>
}
#[serde(deny_unknown_fields)]
#[derive(Deserialize, Debug)]
struct Item{
    id: u8
}

fn from_str<'de, T, D>(deserializer: D) -> Result<T, D::Error>
    where T: FromStr,
          T::Err: Display,
          D: Deserializer<'de>
{
    let s = String::deserialize(deserializer)?;
    T::from_str(&s).map_err(serde::de::Error::custom)
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn test() {
        let data = r#"
            {   "creation": "2018-05-20".
                "items": {
                    "2018-10-19": {
                        "id": 10
                    },
                    "2018-10-20": {
                        "id": 20
                    }
                }
            }
        "#;
        let v = serde_json::from_str::<Container>(data);
        println!("Test");
    }
}