Link Reference Definition Followed by Hyphen Underline

[joegm]

Input:

[foo]: bar
---

cmark gives me this:

$ cmark
[foo]: bar
---

<p>---</p>

This is different to the output in dingus:

<p></p>
<hr />

I'd say that this is also incorrect because of the empty paragraph, but obviously at least one of cmark/commonmark.js is doing the wrong thing here.

I'm not certain what this should render to per the spec, but I think it should be interpreted as a link reference definition followed by a thematic break, and should render as just <hr />.

[jgm]

This is because of the parsing algorithm; we parse lines into a paragraph, and then try parsing the beginning as reference definitions. The remainder is treated as paragraph text. It doesn't conform to the spec strictly; it was a shortcut to avoid backtracking.

See discussion under commonmark/commonmark-spec#688