<svg><template> crashes: Cannot read properties of undefined (reading 'nodeName') #17

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)

Affected package and version

hast-util-from-parse5@8.0.3

Steps to reproduce

import {fromParse5} from 'hast-util-from-parse5'
import {parseFragment} from 'parse5'

fromParse5(parseFragment('<svg><template>x</template></svg>'))

An unclosed <svg><template> is enough, and <math><template> behaves the same:

fromParse5(parseFragment('<svg><template>'))
fromParse5(parseFragment('<math><template>x</template></math>'))

Actual behavior

TypeError: Cannot read properties of undefined (reading 'nodeName')
    at one (lib/index.js:72)
    at element (lib/index.js:204)

Reachable through every HTML→hast path that uses this utility: hast-util-raw (so rehype-raw on markdown containing that raw HTML), hast-util-from-html, and rehype-parse — whole-document mode included.

Expected behavior

No crash; the foreign template converts like any other foreign element.

Cause

element() switches to the template-contents branch on the tag name alone:

if (result.tagName === 'template') {
  const reference = /** @type {DefaultTreeAdapterMap['template']} */ (node)
  // …
  const content = /** @type {Root} */ (one(state, reference.content))

parse5 — per the HTML spec — attaches template contents only to an HTML-namespace template. Inside foreign content a <template> is an ordinary foreign element: its children live in childNodes, and its content is undefined, so one(state, undefined) throws.

Fix

Guard the branch on the field actually being present:

if (result.tagName === 'template' && 'content' in node && node.content !== undefined) {

The foreign template then takes the ordinary element path, and hastscript normalizes its children onto content anyway, so the converted shape matches the HTML form. PR with tests incoming.

Runtime / package manager

Node 22 / npm — but the crash is environment-independent.