Pandoc-style R code fences do not get downlit syntax highlighting

[mattwarkentin]

Hi,

I was playing around some more and I noticed that if you use pandoc-style code fences but mark them as R code, then they do not get the same syntax hightlighting as R Markdown R code chunks. I suppose this makes sense since downlit is only used on an R Markdown code chunk that has the "R" engine (if (downlit && options$engine == "R")), and any code contained in code fences are handed off to pandoc for syntax highlighting.

Seems like this could be a bit tricky to handle, perhaps using a regex, but not impossible. Perhaps the recommendation should just be to use proper R Markdown chunks and set eval = FALSE to get consistent highlighting for documents using downlit (@hadley thoughts?).

Just thought I would share this observation, feel free to close the issue if you think it's not worth acting on. This issue can at least serve as a reminder of why this may crop up in some cases.

In the example below, chunk 1 has default pandoc highlighting, while chunk 2 and 3 are formatted the same using downlit.

---
title: "My Website"
description: |
  Welcome to the website. I hope you enjoy it!
site: distill::distill_website
---

```r
1 + 2
```

```{r eval=FALSE}
1 + 2
```

```{r}
1 + 2
```

[jjallaire]

Yes, I agree that the best way here is eval = FALSE

[cderv]

This could maybe change in the future when support in rmarkdown is done not by a knitr hook in a way it could be used by other formats based on the html_document format. Related to rstudio/rmarkdown#1941
Still working on it as some challenges still needs to be dealt with