ANSI colours with downlit

[mccarthy-m-g]

Does Quarto support ANSI colours in R output? This is handled by downlit in R packages like pkgdown and "just works". Quarto uses downlit for code linking when code-link: true, but this doesn't make colours work.

For example, in this reprex the output will just be plain text, but it should be coloured.

---
title: "Reprex"
format:
  html:
    code-link: true
---

```{r}
#| collapse = TRUE
cat(cli::col_red("This is red"), "\n")
cat(cli::col_blue("This is blue"), "\n")

message(cli::col_green("This is green"))

warning(cli::style_bold("This is bold"))
```

[cscheid]

I don't know the interaction between knitr, downlit, and cli::col_* well enough to say what's going wrong, but the markdown we're getting back from knitr doesn't have any color annotations in it (I got this by simply adding keep-md: true to your example):

---
title: "Reprex"
format:
  html:
    code-link: true
    keep-md: true
---


::: {.cell}

```{.r .cell-code}
cat(cli::col_red("This is red"), "\n")
## This is red
cat(cli::col_blue("This is blue"), "\n")
## This is blue

message(cli::col_green("This is green"))
## This is green

warning(cli::style_bold("This is bold"))
## Warning: This is bold
```
:::

[cscheid]

@cderv would you know how this all works by any chance?

[cderv]

This is handled by downlit in R packages like pkgdown and "just works"

@mccarthy-m-g This is only working in pkgdown context right ? Or do you also get coloring working in R Markdown document ?

cli does ANSI coloring, and not HTML coloring. So to make in work in a HTML rendered document, downlit is converting to HTML highlighting (with help of fansi 📦. Moreover, I think by default cli function deactivate ANSI coloring in a knitting context. So it needs to be reactivated to be then handled by downlit.

Also I believe pkgdown is doing a special post processing before downlit as ANSI escape character can be lost otherwise.

All that above explain that this does not "just works" currently with Quarto.

Can you confirm that it works for you only in pkgdown context ? From there, I'll know where to look to try improve this behavior. From my test, it does not work either in R Markdown, only in pkgdown special handling.

By the fansi can be used directly to convert from ANSI with a knitr hooks. See https://github.com/brodieG/fansi#rmarkdown
It applies with Quarto too.

Example to illustrate how this works:

---
title: "Reprex"
format: html
---

```{r}
#| comment: ''
#| results: asis
#| echo: false
old_hook <- fansi::set_knit_hooks(knitr::knit_hooks, which = c("output", "warning", "error", "message"))
options(crayon.enabled = TRUE)
```

```{r}
cat(cli::col_red("This is red"), "\n")
cat(cli::col_blue("This is blue"), "\n")

message(cli::col_green("This is green"))

warning(cli::style_bold("This is bold"))
```

Hope it helps understand. But anyway, I'll think about how improving this with code_link: true as indeed downlit is supposed to handle the ANSI conversion to HTML and CSS.

[cscheid]

I knew you'd know everything about this inside and out 🙇‍♂️

[mccarthy-m-g]

This is excellent, thank you @cderv!

Just for reference in case anyone else is trying this, you can also set options(cli.num_colors = 256) if you need more than the 8 default colours.

@cscheid Do you want me to file an issue re: supporting ANSI colours when code_link: true?

[cderv]

Do you want me to file an issue re: supporting ANSI colours when code_link: true?

yes please do, this will be easier to follow. However, I feel this is something that should be dealt with in the R packages.

Can you confirm that it works for you only in pkgdown context ?

I am still interesting by this answer 😄

[mccarthy-m-g]

Done!

I tested with pkgdown, rmarkdown, and distill: Only pkgdown gives colour output natively.

[cderv]

Ok this confirm my understanding. We probably could try do something in rmarkdown natively when downlit is used.