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 https://github.com/serde-rs/serde/pull/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.

[ibotty]

I just want to ignore the tag altogether, preferably without having a dummy field. I'll try the fix (or "fix") later.

[oli-obk]

@indiv0 with the serde-pr you can do Option<String>:

• missing tag => None
• <plaintext/> => Some("")
• <plaintext></plaintext> => Some("")
• <plaintext>text</plaintext> => Some("text")

or if you just use a String:

• missing tag => ""
• <plaintext/> => ""
• <plaintext></plaintext> => ""
• <plaintext>text</plaintext> => "text"

[indiv0]

OK awesome I think that'll work. I'll test it tomorrow.

[oli-obk]

The branch has been merged. It's not been published yet, but you can use the serde github repo as a dependency in your code, serde-xml should then pull that in automatically.

[SamWhited]

Is there anything blocking this fix from being released? I'm also running into this issue, but would prefer not to depend on a GitHub dep if possible. I'd be happy to help unblock if possible.

[oli-obk]

@SamWhited this is not a serde_xml issue, but a serde issue, serde has been released a while ago, all you need to do is update your serde dependency to the most recent 0.8 branch.

[SamWhited]

I see; I thought I was on 0.9.1, but maybe not, I'll check when I'm next at my desk. Sorry for the noise and confusion.

EDIT: I was on 0.8.23 after all.