LaTeX reader does not set 'uri' class on bare external links / autolinks

[gwern]

I was looking into why some of my Arxiv abstracts' URL links to Github (using LaTeX \url{}) looked weird when I expected them to be rendered in inline code markup (because a URL is code, and not natural language), and was surprised to see that it looks like the intended use is for you to set CSS on the uri class that a regular autolink generates:

$ echo 'Code is available at <https://github.com/ibm/sau-explore>' | xclip -in
$ xclip -o | pandoc -f markdown -w html
<p>Code is available at <a href="https://github.com/ibm/sau-explore" class="uri">https://github.com/ibm/sau-explore</a></p>

I didn't see any documentation about the purpose of this class, and am guessing from the changelog & the discussion in #4913 but OK, fair enough. I think it would be good to style the contents of an autolink using inline code formatting since it is a literal formal computer language, and often completely opaque to a human reader, however, I can work with uri class. But then, why isn't uri anywhere in my abstracts...?

Turns out, Pandoc is inconsistent in its treatment of autolinks: the LaTeX reader does not set the class like the Markdown reader does:

$ xclip -o | pandoc -f latex -w html
<p>Code is available at <a href="https://github.com/ibm/sau-explore">https://github.com/ibm/sau-explore</a></p>
$ xclip -o | pandoc -f latex -w markdown | pandoc -f markdown -w html
<p>Code is available at <a href="https://github.com/ibm/sau-explore" class="uri">https://github.com/ibm/sau-explore</a></p>

A check of the AST verifies that the problem is that the LaTeX reader doesn't set the uri class when it reads in & converts the \url{} to an autolink, but the Markdown reader does set it on autolinks:

$ xclip -o | pandoc -f latex -w native
[Para [Str "Code",Space,Str "is",Space,Str "available",Space,Str "at",Space,Link ("",[],[]) [Str "https://github.com/ibm/sau-explore"] ("https://github.com/ibm/sau-explore","")]]
$ xclip -o | pandoc -f latex -w markdown | pandoc -f markdown -w native
[Para [Str "Code",Space,Str "is",Space,Str "available",Space,Str "at",Space,Link ("",["uri"],[]) [Str "https://github.com/ibm/sau-explore"] ("https://github.com/ibm/sau-explore","")]]

So it seems that not all readers which support autolinks remember to set the class. (I haven't checked if this applies to autolinked email addresses as well, but seems likely.)