xmlns-prefixed attribute on root element is lost

[jdm]

<!-- before -->
<svg xmlns="http://www.w3.org/2000/svg" xmlns:sodipodi="http://inkscape.sourceforge.net/DTD/sodipodi-0.dtd">
    <sodipodi:namedview>
        ...
    </sodipodi:namedview>

    <path d="..." sodipodi:nodetypes="cccc"/>
</svg>

<!-- after: xmlns:sodipodi moved to child -->
<svg xmlns="http://www.w3.org/2000/svg">
    <sodipodi:namedview xmlns:sodipodi="http://inkscape.sourceforge.net/DTD/sodipodi-0.dtd">
        ...
    </sodipodi:namedview>

    <path d="..." sodipodi:nodetypes="cccc"></path>
</svg>

<!-- before -->
<svg xmlns="http://www.w3.org/2000/svg" xmlns:sodipodi="http://inkscape.sourceforge.net/DTD/sodipodi-0.dtd">
    <path d="..." sodipodi:nodetypes="cccc"/>
</svg>

<!-- after: xmlns:sodipodi removed entirely -->
<svg xmlns="http://www.w3.org/2000/svg">
    <path d="..." sodipodi:nodetypes="cccc"></path>
</svg>

Originally posted by @noahbald in #538 (comment)

[jdm]

It looks like the parsing code stores the namespace data for the node in the treebuilder's namespace stack, but the data about which tag declares a namespace is thrown away. Instead we store the namespace uri for child tags; this is why the xmlns-prefixed attribute jumps to the first child that uses the namespace.

[jdm]

Parsing code that strips out the xmlns attribute:

html5ever/xml5ever/src/tree_builder/mod.rs

Line 347 in feced06

self.declare_ns(attr);

Parsing code that stores the namespace URI on child tags:

html5ever/xml5ever/src/tree_builder/mod.rs

Line 297 in feced06

name.ns = ns_uri;

Serialization code that uses the namespace URI:

html5ever/xml5ever/src/serialize/mod.rs

Line 111 in feced06

self.find_or_insert_ns(name);

[jdm]

Testcase in rcdom/tests/xml-driver.rs:

#[test]
fn weird() {
    assert_serialization(
       r##"<svg xmlns="http://www.w3.org/2000/svg" xmlns:sodipodi="http://inkscape.sourceforge.net/DTD/sodipodi-0.dtd">
    <sodipodi:namedview>
        ...
    </sodipodi:namedview>

    <path d="..." sodipodi:nodetypes="cccc"/>
</svg>"##,
        driver::parse_document(RcDom::default(), Default::default())
            .from_utf8()
            .one(r##"<svg xmlns="http://www.w3.org/2000/svg" xmlns:sodipodi="http://inkscape.sourceforge.net/DTD/sodipodi-0.dtd">
    <sodipodi:namedview>
        ...
    </sodipodi:namedview>

    <path d="..." sodipodi:nodetypes="cccc"/>
</svg>"##.as_bytes()),
    );
}

[jdm]

Current status: I have changes that allow these testcases to pass. However, they cause a lot of xml5lib namespace tests to fail, and Ygg01/xml5lib-tests@3fb8d2b suggests that the current behaviour is intentional. I'm hoping to get in touch with @Ygg01 to better understand what the right behaviour here is.

[jdm]

Branch: https://github.com/servo/html5ever/compare/xmlns-attrs?expand=1

[Ygg01]

Current status: I have changes that allow these testcases to pass. However, they cause a lot of xml5lib namespace tests to fail, and Ygg01/xml5lib-tests@3fb8d2b suggests that the current behaviour is intentional. I'm hoping to get in touch with @Ygg01 to better understand what the right behaviour here is.

Hi Josh. To be honest I don't quite remember the motivation. It's been like 8 years.

The important question is does it goes against XML namespace spec? If not, just change the tests. I'm open to PRs on xml5lib-tests

[Ygg01]

@jdm what are the next steps to close this?

• Do you want me to fix the xml5lib-tests?
• Move xml5lib-tests to the Servo repository, so you can take control over it?
• Make PRs to Ygg01/xm5lib-tests for me to review?