Foo {{category template}} becomes <p>Foo</p><p><meta....></p> but in a comment :Foo {{category template}} puts the <meta> tag inside the list item as expected?

Apparently this is a very specific bug, where a category template is added *after a signature* in the *first comment in a thread* (the one not inside a list item), and in that case the category gets moved down.

Foo ~~~~ [[Category:Book]]
: Bar ~~~~ [[Category:Book]]

->

<p>Foo ~~~~ </p>
<link rel="mw:PageProp/Category" href="./Category:Book">
<dl>
    <dd>Bar ~~~~
        <link rel="mw:PageProp/Category" href="./Category:Book">
    </dd>
</dl>

Note the category gets hoisted out of the <p> but not the <dd>. I think we saw something similar to this before. It would be nice if Parsoid was consistent and kept the category in the paragraph. The category is in the paragraph if there is text after it.

In Parsoid this is WTUtils::isRenderingTransparentNode(), which seems to include:

• HTML comments
• "SOL-transparent links": <link> tags with rel attributes matching /(?:^|\s)mw:PageProp\/(?:Category|redirect|Language)(?=$|\s)/
• <meta> tags which don't have `typeof="mw:StartTag" or "mw:EndTag" (these are orphaned literal HTML tags; they might be stripped before Parsoid emits its final HTML)
• Fallback ID spans: <span typeof="mw:FallbackId"> (found inside headings, you can probably ignore these)

Skipping HTML comments, <meta>, and <link> tags should be good enough, I think.

For context:

• All suspicious diffs with the {{RMCategory}} template: 2020-09-03, 2020-09-17, 2020-11-24, 2020-11-24, 2020-11-29, 2020-11-30.
• The markup seems to be generated by substing https://zh.wikipedia.org/wiki/Template:RM (apparently done by Twinkle)

Change 645576 had a related patch set uploaded (by Bartosz Dziewoński; owner: Bartosz Dziewoński):
[mediawiki/extensions/DiscussionTools@master] Handle category links like comments (rendering-transparent nodes)

https://gerrit.wikimedia.org/r/645576

Change 645576 merged by jenkins-bot:
[mediawiki/extensions/DiscussionTools@master] Handle category links like comments (rendering-transparent nodes)

https://gerrit.wikimedia.org/r/645576

A particularly complex case we should add to the integration tests:

https://en.wikipedia.org/?diff=993157834

A closing div, followed by a comment, empty tracking template and category

Looks like we need to include empty spans (tracking templates) in the list: https://en.wikipedia.beta.wmflabs.org/w/index.php?title=User_talk%3ATestuser451716&type=revision&diff=464008&oldid=464007

Change 647219 had a related patch set uploaded (by Esanders; owner: Esanders):
[mediawiki/extensions/DiscussionTools@master] Skip over empty inline nodes (e.g. tracking templates)

https://gerrit.wikimedia.org/r/647219

Change 647219 merged by jenkins-bot:
[mediawiki/extensions/DiscussionTools@master] Skip over empty inline templates (e.g. tracking templates)

https://gerrit.wikimedia.org/r/647219

Working as expected it seems. On the diff view, the reply is now being placed right beneath the first comment that includes the category template.

The diff view: