Serde ignored

Find out about keys that are ignored when deserializing data. This crate provides a wrapper that works with any existing Serde Deserializer and invokes a callback on every ignored field.

You can use this to warn users about extraneous keys in a config file, for example.

Note that if you want unrecognized fields to be an error, consider using the #[serde(deny_unknown_fields)] attribute instead.

[dependencies]
serde = "1.0"
serde_ignored = "0.1"

use serde::Deserialize;
use std::collections::{BTreeSet as Set, BTreeMap as Map};

#[derive(Debug, PartialEq, Deserialize)]
struct Package {
    name: String,
    dependencies: Map<String, Dependency>,
}

#[derive(Debug, PartialEq, Deserialize)]
struct Dependency {
    version: String,
}

fn main() {
    let j = r#"{
        "name": "demo",
        "dependencies": {
            "serde": {
                "version": "1.0",
                "typo1": ""
            }
        },
        "typo2": {
            "inner": ""
        },
        "typo3": {}
    }"#;

    // Some Deserializer.
    let jd = &mut serde_json::Deserializer::from_str(j);

    // We will build a set of paths to the unused elements.
    let mut unused = Set::new();

    let p: Package = serde_ignored::deserialize(jd, |path| {
        unused.insert(path.to_string());
    }).unwrap();

    // Deserialized as normal.
    println!("{:?}", p);

    // There were three ignored keys.
    let mut expected = Set::new();
    expected.insert("dependencies.serde.typo1".to_owned());
    expected.insert("typo2".to_owned());
    expected.insert("typo3".to_owned());
    assert_eq!(unused, expected);
}

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