Markdown writer: Omit space before CodeBlock class

[jtojnar]

When trying to use pandoc as a Markdown formatter, it will insert a space between class part of info-string:

pandoc/src/Text/Pandoc/Writers/Markdown.hs

Line 593 in 0f79a1f

(_,cls:_,_) -> " " <> literal cls

This is pretty uncommon in real life Markdown documents in my experience. The CommonMark spec itself has a first example of fenced code block with a language tag without space.

Taking GitHub code search results as a proxy for popularity, we see the spaceless version is 18× more common:

• https://github.com/search?utf8=%E2%9C%93&q=%2F^\s*```\w%2F+language%3AMarkdown&type=Code&l=Markdown
• https://github.com/search?utf8=%E2%9C%93&q=%2F^\s*```%20\w%2F+language%3AMarkdown&type=Code&l=Markdown

In pandoc codebase, they are roughly equally represented outside of tests:

$ rg '^\s*```\w' --glob !test | wc -l
41
$ rg '^\s*``` \w' --glob !test | wc -l
53

I propose removing the space from the Markdown writer.

I can open a PR if this is desired.

[jgm]

I like it better with the space. Both are valid, and the space is harmless.