serde-sated（相邻标记枚举反序列化[带未标记变体]）

此包提供衍生宏，用于在反序列化相邻标记枚举变体时覆盖 serde::Deserialize 的默认行为，并使用未标记值作为后备。

默认 Deserialize 有什么问题？

看看下面的代码

use serde::{Deserialize, Serialize};
use serde_json::json;

#[derive(Debug, Deserialize, Serialize)]
#[serde(tag = "resourceType", content = "resource")]
pub enum ResourceStruct {
    Number(u64),
    String(String),
    Complex(Complex),
    #[serde(untagged)]
    Unknown(serde_json::Value),
}

#[derive(Debug, Deserialize, Serialize)]
pub struct Complex {
    pub a: u64,
    pub b: u64,
}

#[test]
fn deserialize_json() {
    let missing_field_b_in_complex_variant = json!({
        "resourceType": "Complex",
        "resource": {
            "a": 2000
        }
    });

    let result = serde_json::from_value::<ResourceStruct>(missing_field_b_in_complex_variant).unwrap();
    eprintln!("Resource: {:#?}", result);
}

这将打印

Resource: Unknown(
    Object {
        "resource": Object {
            "a": Number(2000),
        },
        "resourceType": String("Complex"),
    },
)

如您所见，Complex 变体中缺少字段 "b" 导致 serde 默认到未标记变体。

解决方案

这可能不是预期的行为 - 此 crate 允许更改此行为，而不是默认到未标记变体，它将返回正确的错误。

让我们将 ResourceStruct derive 属性更改为使用 serde_sated::deserialize_enum_with_untagged_as_fallback

use serde::{Deserialize, Serialize};
use serde_json::json;
use serde_sated::deserialize_enum_with_untagged_as_fallback;

#[derive(Debug, deserialize_enum_with_untagged_as_fallback, Serialize)]
#[serde(tag = "resourceType", content = "resource")]
pub enum ResourceStruct {
    Number(u64),
    String(String),
    Complex(Complex),
    #[serde(untagged)]
    Unknown(serde_json::Value),
}

#[derive(Debug, Deserialize, Serialize)]
pub struct Complex {
    pub a: u64,
    pub b: u64,
}

#[test]
fn deserialize_json() {
    let missing_field_b_in_complex_variant = json!({
        "resourceType": "Complex",
        "resource": {
            "a": 2000
        }
    });

    let result = serde_json::from_value::<ResourceStruct>(missing_field_b_in_complex_variant);
    eprintln!("Resource: {:#?}", result);
}

现在结果将是

Resource: Err(
    Error("missing field `b`", line: 0, column: 0),
)