Externally tagged enum variants where all fields have #[serde(default)] should allow being written as a unit variant. #2691
Description
I'm building a program that takes URLs and strips all the tracking parameters and handles redirects and so on. One of the mappers is ExpandShortLink, which just sends a request to the URL being cleaned and returns the URL the server responded with.
I'm trying to support the case where a user wants to specify HTTP headers for a specific ExpandShortLink without requiring that all uses of ExpandShortLink have a default header map (I expect it to be a niche feature).
Basically, I have this code:
use serde::Deserialize;
use serde_json::from_str;
use std::collections::HashMap;
#[derive(Deserialize)]
struct Rule {
// ...
mapper: Mapper
}
#[derive(Deserialize)]
enum Mapper {
// ...
ExpandShortLink {
#[serde(default)]
headers: HashMap<String, String>
}
}
fn main() {
assert!(from_str::<Rule>("{\"mapper\": {\"ExpandShortLink\": {\"headers\": {}}}}").is_ok());
assert!(from_str::<Rule>("{\"mapper\": \"ExpandShortLink\"}").is_ok());
}I would like to have {"mapper": "ExpandShortLink"} and {"mapper": {"ExpandShortLink": {"headers": {}}}} both deserialize to Rule {mapper: Mapper::ExpandShortLink {headers: HashMap::new()}}.