Definition + setext underline/thematic break, creates loose empty paragraph

[wooorm]

I think this is a bug in commonmark.js:

[a]: b
---

[a]: b
===

On the dingus, it yields:

<p></p>
<hr />
<p>===</p>

Rendered here (cmark-gfm + more GH stuff, likely same as just cmark):

<p>---</p>
<p>===</p>

---

===

• I don’t think a random empty <p></p> should show up, that’s a clear bug.
• I probably think, but this is more vague, that <p>---</p> makes more sense here, as definitions/paragraphs/setext heading underlines interplay weirdly (Mention that link reference definitions are constructed from paragraphs commonmark-spec#605).

[jgm]

One observation: if you change the setext heading line regex to something that will never be matched, the empty p tag disappears. So this is due to some interference with setext heading parsing.

[wooorm]

Similar to what you note, I think the area around definitions/setext headings/lists is very hard to think about. One example: wooorm/markdown-rs#22 (comment). I have no idea what should happen in these cases. Which comes first? Which construct has precedence, and what happens if it doesn’t match

[jgm]

I remember there were some discussions about this -- you could check the tracker (including closed issues) fro commonmark-spec.