rawHtml: raw MathML children of an MDX JSX `<math>` element reparse in HTML content

[gtritchie]

Split out from #283 (the fix for #249), where it was noted as a follow-up. Same family as #249, for the other foreign-content namespace.

What happens

With rawHtml enabled, reparse_children_into (crates/satteri-ast/src/hast/from_html.rs) reparses an MDX JSX element's children in an <svg> fragment context when the element is named svg (#283), and in the HTML <template> context otherwise. A JSX element named math falls into the second case, so raw MathML under it is read as HTML: /> means nothing on an unknown HTML element, so <mspace width="1em"/> stays open and swallows the following siblings. Inside a real raw <math> html5ever enters the MathML namespace and handles the self-closing tag.

Attribute names are unaffected: MathML attributes use the HTML schema in property-information and here, so unlike #249 this is structural only (self-closing, nesting, and the MathML text/HTML integration points).

Repro

npx tsx repro.mts from packages/satteri:

import { mdxToJs, markdownToHast, defineMdastPlugin } from "satteri";

const inject = defineMdastPlugin({
  name: "inject",
  paragraph() {
    return { type: "html", value: '<mspace width="1em"/><mi>x</mi>' };
  },
});

console.log(
  mdxToJs("<math>\n\ntext\n\n</math>\n", { mdastPlugins: [inject], features: { rawHtml: true } }).code,
);
console.log(JSON.stringify(markdownToHast('<math><mspace width="1em"/><mi>x</mi></math>', { features: { rawHtml: true } })));

Output (main and #283):

_jsx(_components.math, { children: _jsx(_components.mspace, {
    width: "1em",
    children: _jsx(_components.mi, { children: "x" })
}) })

versus the same markup inside raw <math>, where mspace and mi are siblings:

{"tagName":"math","children":[{"tagName":"mspace","properties":{"width":"1em"},"children":[]},{"tagName":"mi","children":[{"type":"text","value":"x"}]}]}

Reach

Not reachable from MDX markup alone (HTML-looking syntax is JSX there). It needs a plugin-injected html node as a child of a JSX <math> element, compiled with features: { rawHtml: true }.

Sketch of a fix

The narrow version mirrors #283: add HtmlSpace::MathMl with a MathML-namespace <math> context element, and enter it for a JSX element named math. But the context is currently a single in_svg: bool threaded through EmitTask, emit, emit_arena_node, and reparse_children_into, and a second namespace does not fit a bool. The shape that scales is to thread the enclosing element's QualName instead (for a stitch, the parsed parent's own name; for a JSX element, its name in the inherited namespace; <template> for component names), hand it to parse_fragment as the context element, and derive in_svg for the serializer from it. That also lets html5ever decide the integration points (foreignObject, annotation-xml, MathML text integration points) instead of the hand-written is_html_integration_point list from #283.

Test coverage

None: the from_html.rs reparse tests and the rawHtml conformance cases have no MathML-under-MDX case; the existing mathml conformance case has the <math> tag inside the raw text itself.