Escaped # not rendered in headings when it's last character

[anthonyfok]

@hagbarddenstore has kindly reported "Escaped # not rendered in headings when it's last character" at gohugoio/hugo#879 as a Hugo issue, though it belongs to the realm of Blackfriday. I have reproduced @hagbarddenstore's report verbatim below:

---

Example Markdown:

# Broken heading \#

This produces the following HTML:

<h1>Broken heading</h1>

But if I add something after the escaped # it will be rendered.

# Working heading \# with escaped signs...

And this renders the following HTML:

<h1>Working heading # with escaped signs...</h1>

Escaping the # sign works everywhere else, but not as the last character.

The bug can be avoided by simply appending a space as the last character, but that's kind of icky.

[anthonyfok]

For a wider perspective, it appears that various Markdown engines exhibit different behaviours in your test case:

John Gruber's original Markdown.pl and GitHub Flavored Markdown (GFM)

# Broken heading \# gives <h1>Broken heading \</h1>, hence

Broken heading \

Kramdown

# Broken heading \# gives <h1 id="broken-heading-">Broken heading #</h1>, i.e.

Broken heading #

which matches your desired output.

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I haven't tested the other Markdown engines yet. It seems that out of the three, only Kramdown got it right?

Note that http://daringfireball.net/projects/markdown/syntax#backslash does mention that the backslash may be used to escape the # hash mark character.

Nevertheless, I think it may be a good idea for Blackfriday to follow one of the behaviours above. 😉