Bad error location with flatten tagged enum

[fixcik]

Hi! I attempted to deserialize a structure with a flattened tagged enum. However, when providing incorrect input data, the error's location is not properly indicated.

Code sample:

use serde::{Deserialize, Serialize};

#[derive(Debug, Serialize, Deserialize)]
struct Task {
    id: String,
    #[serde(flatten)]
    task_type: TaskType,
}

#[derive(Debug, Serialize, Deserialize)]
#[serde(tag = "type", content = "params", rename_all = "snake_case")]
enum TaskType {
    Complex(ComplexTaskParams),
}

#[derive(Debug, Serialize, Deserialize)]
struct ComplexTaskParams {
    param_one: String,
    param_two: String,
}

fn main() {
    let yaml = r#"
        id: 1
        type: complex
        params:
            param_one: value_one
            param_two: 123
    "#;

    let task: Task = serde_yaml::from_str(yaml).unwrap();
    print!("{:?}", task);
}

Expected error location of param_two - line: 5, but it's locate start position of Task:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: 
Error("invalid type: integer `123`, expected a string", line: 2, column: 9)', src/main.rs:31:49

[jonasbb]

This is a duplicate of #1183. With flatten the data gets deserialized into an intermediate buffer, advancing the location in the yaml file, but then fails to deserialize the buffer data into the struct.