Easier way to declare default values

[mainrs]

I have a struct with a lot of fields (~ 50-ish). The types are mostly a number, a string or a bool. Is there an easier way to declare the default values then using the default attribute? E.g.:

pub struct Config {
    #[serde(default = "default_some_field")]
    some_field: String, // default value is "edged"
}

fn default_some_field() -> String {
    "edged".into()
}

I expected the argument to be the default value, e.g. default = "edged" where the proc_macro tries to into() into the type of the field. Maybe the current behaviour could be encoded behind a field called default_fn or something.

P.S.: I am not actually sure if the above proposal is currently possible in syn.

Further examples:

pub struct Config {
    #[serde(default = "4")]
    int_field: i32,
    #[serde(default = "true")]
    bool_field: bool,
}

Would all work as expected as the values can properly be converted using into() or parse.

pub struct Config {
    #[serde(default = "seven")]
    int_field: i32,
}

Wouldn't work as seven can't be parsed correctly into a number.

[dtolnay]

Closing as a duplicate of #368.