empty-element tag can't be parsed by codegen

[ibotty]

#[derive(Deserialize, Debug)]
#[serde(rename="a")]
pub struct A {
    b1: String
}

compiled with serde_codegen::expand(&src, &dst), and

extern crate serde;
extern crate serde_xml;

include!(concat!(env!("OUT_DIR"), "/a.rs"));

fn main() {
    // let deserialized: Result<serde_xml::value::Element, serde_xml::Error> = serde_xml::de::from_str(r"<a><b1>v</b1><b2/></a>");
    let deserialized: Result<A, serde_xml::Error> = serde_xml::de::from_str(r"<a><b1>v</b1><b2/></a>");
    println!("deserialized: {:?}", deserialized);
}

Fails with 'SyntaxError(expected end tag, 1, 22))'. Removing the empty-element tag '' let's it work, as is parsing to serde_xml::value::Element.

That is with

"checksum serde 0.8.16 (registry+https://github.com/rust-lang/crates.io-index)" = "1105e65d0a0b212d2d735c8b5a4f6aba2adc501e8ad4497e9f1a39e4c4ac943e"
"checksum serde_codegen 0.8.16 (registry+https://github.com/rust-lang/crates.io-index)" = "446384bcfd7d9276a23b51e9dc14341909ad05377b68ac5da6f83a7a2094bcd0"
"checksum serde_codegen_internals 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)" = "318f7e77aa5187391d74aaf4553d2189f56b0ce25e963414c951b97877ffdcec"
"checksum serde_xml 0.9.1 (registry+https://github.com/rust-lang/crates.io-index)" = "56346e526b0828da6b7a6a867076a6ae22d188ffd7a5511b4ffbd815def0ba95"

[ibotty]

I forgot to mention: adding a unit field b2:() lets it parse it, i.e. using

pub struct A {
    b1: String,
    b2: ()
}

[oli-obk]

Dupe of #19

[oli-obk]

This is simply a feature I haven't gotten around to implement.

[ibotty]

I am not sure it's the same. I can ignore fields (don't mention them) without any problem, but not empty-element tags. I cannot reproduce issue #19, btw.

[oli-obk]

Hmm ok. I'll investigate

[indiv0]

Any progress on this?

I'm not entirely sure if I'm having the same issue, but I have the following types:

pub struct Subpod {
    ...
    pub plaintext: Option<Plaintext>,
    ...
}

pub type Plaintext = String;

and a test which has:

...
<subpod title="">
    ...
    <plaintext/>
</subpod>
...

This test used to run successfully before, but not now. Which makes me think there's been a regression. The test has not been changed.

[oli-obk]

Indeed there were breaking changes, that's why the version was updated.

If your "plaintext" field is always there, but sometimes empty and sometimes not, then you probably need it to be of a newtype type that contains an option.

So something along the lines of

pub struct Subpod {
    ...
    pub plaintext: Plaintext,
    ...
}

#[derive(Deserialize)]
pub struct Plaintext(Option<String>);

This change was necessary, because otherwise we could not have nested options.

[indiv0]

Makes sense why you updated it. However I tried your fix and now I get:

running 6 tests
test model::tests::test_img_deserializer ... ok
test model::tests::test_plaintext_deserializer ... FAILED
test model::tests::test_pod_deserializer ... FAILED
test model::tests::test_infos_deserializer ... ok
test model::tests::test_query_result_deserializer ... FAILED
test model::tests::test_subpod_deserializer ... FAILED

failures:

---- model::tests::test_plaintext_deserializer stdout ----
        thread 'model::tests::test_plaintext_deserializer' panicked at 'called `Result::unwrap()` on an `Err` value: SyntaxError(serde expected some value: Invalid type. Expected `Str`, 0, 0)', ../src/libcore/result.rs:837
note: Run with `RUST_BACKTRACE=1` for a backtrace.

---- model::tests::test_pod_deserializer stdout ----
        thread 'model::tests::test_pod_deserializer' panicked at 'called `Result::unwrap()` on an `Err` value: SyntaxError(serde expected some value: Invalid type. Expected `Str`, 0, 0)', ../src/libcore/result.rs:837

---- model::tests::test_query_result_deserializer stdout ----
        thread 'model::tests::test_query_result_deserializer' panicked at 'called `Result::unwrap()` on an `Err` value: SyntaxError(serde expected some value: Invalid type. Expected `Str`, 0, 0)', ../src/libcore/result.rs:837

---- model::tests::test_subpod_deserializer stdout ----
        thread 'model::tests::test_subpod_deserializer' panicked at 'called `Result::unwrap()` on an `Err` value: SyntaxError(serde expected some value: Invalid type. Expected `Str`, 0, 0)', ../src/libcore/result.rs:837


failures:
    model::tests::test_plaintext_deserializer
    model::tests::test_pod_deserializer
    model::tests::test_query_result_deserializer
    model::tests::test_subpod_deserializer

test result: FAILED. 2 passed; 4 failed; 0 ignored; 0 measured

error: test failed

[oli-obk]

ok, I'll investigate. Stay on an older serde_xml version for now, 0.8 should still work.

[indiv0]

Alright

[oli-obk]

@indiv0 I think the solution is to move away from Option<String> and to String entirely. So your <plaintext/> would deserialize to an empty string.

Although this depends on serde-rs/serde#635 .

Or do you need to be able to distinguish between <plaintext/>, <plaintext></plaintext> and the tag missing entirely?

[indiv0]

Well I'm trying to maintain a wrapper for the WolframAlpha API.

I can't remember if the tag can be missing entirely, but I do need to be able to handle both <plaintext/> and <plaintext>ABC</plaintext> at least. I'll have to check if the tag is ever missing.