Auto-linking infix operators from in Changelog

[MichaelChirico]

Redirecting from Rdatatable/data.table#3677

pkgdown is good at matching foo() in NEWS to link to ?foo in the reference section, but it appears to miss infix operators like %foo% --> ?`%foo%.

[jayhesselberth]

I had a look and it's a little tricky because single backticks are used for two purposes in this case: marking code in markdown, and parsing infix operators in R.

So when you write `%in%` in markdown, it gets translated to <code>%in%</code>, which lacks the backticks, which are required for R to parse correctly.

If you use double backticks in markdown (`` ?`%in%` ``), then help for %in% is linked correctly. But a bare function link does not work (`` `%in%` ``) (missing the ?), and it would be annoying to use double backticks everywhere anyway.

I think we'd have to modify the HTML tweaking code to check whether <code>%in%</code> was a backticked infix operator (in the markdown version) and then link it as if it were.

[MichaelChirico]

I don't think I follow the pkgdown internals well enough to follow exactly, could you help to point to the code that's driving this?

grepping for <code>%[^%]*%</code> would seem to be pretty straightforward, so there must be a gap in understanding when/how the reference linking is applied