Flattened fields

[glebpom]

It seems that ignored fields are not detected if the structure contains the flattened field. It probably relates to the serde issue, that flatten and deny_unkown_fields cannot be combined (https://github.com/jonasbb/serde-rs.github.io/commit/af0e2e68c98cd2a8411cf194156aabb8316f9cea). Is there a way to make serde-ignored work with flattened fields?

[d4h0]

I just ran into the same problem. Here is an example that demonstrates the issue:

use serde::Deserialize;

#[derive(Debug, Deserialize)]
struct Test1 {}

#[derive(Debug, Deserialize)]
struct Test2 {
    #[serde(flatten)]
    more: More,
}

#[derive(Debug, Deserialize)]
struct More {
    anything: u16,
}

fn test<'de, T: Deserialize<'de> + std::fmt::Debug>(json: &'de str) -> Option<String> {
    let jd = &mut serde_json::Deserializer::from_str(json);

    let mut unknown = None;

    let _: T = serde_ignored::deserialize(jd, |path| {
        unknown.replace(path.to_string());
    })
    .unwrap();

    unknown
}

fn main() {
    // Succeeds:
    assert_eq!(test::<Test1>(r#"{"test1": 42}"#), Some("test1".to_string()));

    // Fails:
    assert_eq!(
        test::<Test2>(r#"{"anything": 42, "test2": 42}"#),
        Some("test2".to_string())
    );
}

[brianc118]

Perhaps something like this can be a workaround? I'm just not sure if it's something we can reliably depend on.

use std::collections::BTreeMap as Map;
use serde_json::Value;
use serde::{Serialize, Deserialize};

#[derive(Debug, Serialize, Deserialize)]
struct Inner {
    a: u32,
    b: String,
}

#[derive(Debug, Serialize, Deserialize)]
struct InnerWithExtra {
    #[serde(flatten)]
    inner: Inner,
    #[serde(flatten)]
    other: Map<String, Value>,
}

fn main() {
    let x: InnerWithExtra = serde_json::from_str(
        r#"{
            "a": 123, 
            "b": "foo",
            "unknown": "mystery"
        }"#
    ).unwrap();
    println!("{:?}", x);
}