xml serde read translates optional attributes with value "" to None

[francisdb]

If you want to be able to make a difference between attribute missing and attribute empty "" should serialize to Some("") but those attributes deserialize to None.
(useful for roundtrips where the output should be equal to input with small change applied)

use serde::{Deserialize, Serialize};

#[derive(Debug, Deserialize, Serialize, PartialEq, Eq)]
struct Name {
    #[serde(rename = "@first_name", skip_serializing_if = "Option::is_none")]
    first_name: Option<String>,
    #[serde(rename = "@second_name", skip_serializing_if = "Option::is_none")]
    second_name: Option<String>,
}

#[test]
fn read_and_write() {
    let expected = Name {
        first_name: Some("aaa".to_string()),
        second_name: Some("".to_string()),
    };

    let name =
        quick_xml::de::from_str::<Name>(r#"<Name first_name="aaa" second_name=""/>"#).unwrap();

    assert_eq!(expected, name);

    let s = quick_xml::se::to_string(&name).unwrap();

    assert_eq!(r#"<Name first_name="aaa" second_name=""/>"#, s);
}

fails with

thread 'read_and_write' panicked at tests/tezt.rs:21:5:
assertion `left == right` failed
  left: Name { first_name: Some("aaa"), second_name: Some("") }
 right: Name { first_name: Some("aaa"), second_name: None }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

I found similar issues that are marked as fixed: #252 and #527

[Mingun]

Yes, the problem only on Deserializer side, it is not tested in tests for #252. Probably should be an easy fix.

[francisdb]

If you want I can have a look at a PR this evening, however I see you self-assigned this?

[Mingun]

I'd looked at this. The current behavior was selected to match serde_json behavior which translates { "a": null } to a: None. In XML the closest analogues to null is empty value of attribute. But maybe we need to review this again.

[francisdb]

Json { "a": "" } will probably give you a: Some("") which is similar to what this issue is going for?

The tricky part is that for json both { "a": null } and {} will return a: None so its impossible to do a round trip keeping exact equal representation. For xml there is no such issue.

[francisdb]

Great, thanks @Mingun
I see a 0.31.0 release was made but it seems to be missing on crates.io?
https://crates.io/crates/quick-xml