libtest's junit formatter does not produce valid XML for doctests

[therealfrauholle]

This issue is related to #85563. The junit formatter of libtest does not produce correct XML for some doctests. Take the following as an example:

use std::marker::PhantomData;


pub struct WithGeneric<A> {
    marker: PhantomData<A>
}

impl<A> WithGeneric<A> {
    /// 
    /// This is a doctest:
    /// 
    /// ```
    /// let _ = hello_world::WithGeneric::<()>::new();
    /// ```
    /// 
    pub fn new() -> Self {
        WithGeneric { marker: PhantomData }
    }
}

When running cargo +nightly-2022-07-26 test --doc -- -Z unstable-options --format junit, the following (invalid) XML is generated (formatted with an external tool):

<?xml version="1.0" encoding="UTF-8"?>
<testsuites>
	<testsuite name="test" package="test" id="0" errors="0" failures="0" tests="1" skipped="0" >
		<testcase classname="src/lib.rs" name="WithGeneric<A>::new (line 12)" time="0"/>
		<system-out/>
		<system-err/>
	</testsuite>
</testsuites>

The XML is invalid because of the name attribute of the testcase element. It contains the invalid characters < and >, which should be escaped to < and > as far as I understand.

Proposed solution

In a quick and dirty way I would implement something similar to what the JSON formatter does to escape the strings to valid XML attributes - I just did not have time to make a PR so far.

Apart from that I never contributed to this repository, nor am I specifically familiar with libtest. What would it take to implement the serialization based on serde and a crate like serde_xml_rs? Could I just add these crates as a dependency? I feel like this would be much cleaner than just repeating what the json formatter does.

[bjorn3]

What would it take to implement the serialization based on serde and a crate like serde_xml_rs?

The standard library can't use proc macros as that would break cross-compilation. This means that using serde_derive is not an option. Using serde without it is somewhat awkward. Serialization is less awkward than deserialization, but still somewhat awkward. Looks like serde_xml_rs uses xml-rs for the actual xml parsing and serialization, so using xml-rs directly would be an option, if not for the fact that xml-rs uses the doc_comment proc macro. Other than this, xml-rs is mostly self-contained, so a rewrite to remove the doc_comment proc macro would be possible I think.

[5225225]

Other than this, xml-rs is mostly self-contained, so a rewrite to remove the doc_comment proc macro would be possible I think.

xml-rs only uses that proc macro for tests. It's to test that the Readme.md's code examples run fine. They'd very likely take a PR to remove it, seeing as it's test only, bumping the MSRV and using #[doc = include("Readme.md")] mod readme_test {} be fine.

However, xml-rs seems unmaintained. So, maybe best not.

Manually implementing XML escaping ourselves would probably be the easiest option. There's also quick-xml. No idea if that uses a proc macro.