Serde: duplicate field in base struct and flattened struct

What it does

Warns when a conflicting field name is present in both a struct and in a flattened field.

I open an issue in the serde repo https://github.com/serde-rs/serde/issues/1820 and they suggested me to open it here

Categories (optional)

• Kind: Not sure

Avoid uncertainty about which field will be the one becoming serialized

Example

pub struct Base {
    #[serde(flatten)]
    pub flattened: Option<Flattened>,
    pub name: String,
}

pub struct Flattened {
    pub name: String,
}

Could issue a clippy warning suggesting to delete one of the fields named name or rename.

Start from the Rust example in this issue and review how serde flattening creates a conflict between the base and flattened structs. Determine the intended warning when both contain a field named name, and consider the suggested remedies of deleting or renaming one field. Done means the conflict is detected and the warning clearly identifies the duplicate field.