Section headings containing spaces in github flavored markdown link to non-existing anchors

[mineo]

Input file a.wiki:

= Test Heading =

text

Pandoc call: pandoc --output=test.md -t gfm --toc --standalone a.wiki

produces

  - [Test Heading](#test_heading)

# Test Heading

text

Online: https://gist.github.com/mineo/2b21f4d1e0ffa062adaef113037c2fb8. The test heading in the TOC links to https://gist.github.com/mineo/2b21f4d1e0ffa062adaef113037c2fb8#test_heading, but clicking on the heading in the document itself changes the anchor in the URL to https://gist.github.com/mineo/2b21f4d1e0ffa062adaef113037c2fb8#test-heading. These are not the same:

diff --git a/a b/b
index ea0a751..3abb72f 100644
--- a/a
+++ b/b
@@ -1 +1 @@
-https://gist.github.com/mineo/2b21f4d1e0ffa062adaef113037c2fb8#test-heading
+https://gist.github.com/mineo/2b21f4d1e0ffa062adaef113037c2fb8#test_heading

Github converts spaces in the heading to hyphens, pandoc converts them to underscores.

[mb21]

Can you try in a github repo? possibly it's different in a gist?

[mineo]

Sure. It's the same in a repository: https://github.com/mineo/markdowntest/blob/master/test.md

[jgm]

The automatic identifiers are created by the reader, not the writer. In this case, the reader format is mediawiki, so mediawiki's scheme for identifiers is used (_ instead of -).

Actually, the extension gfm_auto_identifiers should be usable with mediawiki input (-f mediawiki+gfm_auto_identifiers), but it doesn't quite work because something in the mediawiki reader special-cases a - -> _ conversion. I think I can fix that.