{cli} output not captured by quarto slides

[JosiahParry]

Output from the cli package is not captured by reveal js slides.

Desired behavior: output from cli is captured and printed

Reprex:

---
title: "this-dont-work"
format: revealjs
---

## define class with cli print

```{r, echo = TRUE}
print.myclass <- function(x, ...) cli::cli_text(cli::style_bold("this shouldnt work"))

obj <- structure(list(1, 2, 3), class = "myclass")

obj
```

## change the print method

```{r, echo = TRUE}
print.myclass <- function(x, ...) cat("this will work")

obj
```

[jthomasmock]

Try this from Danielle Navarro maybe?

https://blog.djnavarro.net/posts/2021-04-18_pretty-little-clis/

[JosiahParry]

Unfortunately this doesn't work in quarto slides (at least the way im going about it).

---
title: "this-dont-work"
format: revealjs
---

```{r}
options(crayon.enabled = TRUE)
ansi_aware_handler <- function(x, options) {
  paste0(
    "<pre class=\"r-output\"><code>",
    fansi::sgr_to_html(x = x, warn = FALSE, term.cap = "256"),
    "</code></pre>"
  )
}

knitr::knit_hooks$set(
  output = ansi_aware_handler, 
  message = ansi_aware_handler, 
  warning = ansi_aware_handler,
  error = ansi_aware_handler
)

```


## define class with cli print

```{r, echo = TRUE}
print.myclass <- function(x, ...) cli::cli_text(cli::style_bold("this shouldnt work"))

obj <- structure(list(1, 2, 3), class = "myclass")

obj
```

## change the print method

```{r, echo = TRUE}
print.myclass <- function(x, ...) cat("this will work")

obj
```

[mcanouil]

I am not completely sure to fully grasp the extent of what you want to achieve, but you should write a knit_print S3 method and register it, see https://bookdown.org/yihui/rmarkdown-cookbook/opts-render.html#opts-render.

---
format: revealjs
---

```{r}
#| echo: true
#| results: asis
options(crayon.enabled = TRUE)
library(knitr)
knit_print.myclass <- function(x, options) {
  fansi::sgr_to_html(x = cli::style_bold("this should'nt work"), warn = FALSE, term.cap = "256")
}
registerS3method("knit_print", "myclass", knit_print.myclass)

(obj <- structure(list(1, 2, 3), class = "myclass"))

print(obj)
```

[JosiahParry]

The goal is to capture the output of various objects that use {cli} in their print method, so I think the above would be a little much

[mcanouil]

The issue is the call to cli::cli_text(), see an example below:

---
format: revealjs
---

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

## {.smaller}

- Does not work because of `cli::cli_text()`

```{r}
#| echo: true
print.myclass <- function(x, ...) {
  cli::cli_text(cli::style_bold(cli::col_blue("this "), cli::col_red("shouldnt "), " work ..."))
  1 + 1
}

(obj <- structure(list(1, 2, 3), class = "myclass"))
```

- Does ot work because nothing is printing the cli message.

```{r}
#| echo: true
print.myclass <- function(x, ...) {
  cli::style_bold(cli::col_blue("this "), cli::col_red("shouldnt "), "work ...")
  1 + 1
}
obj
```

- Does work properly.

```{r}
#| echo: true
print.myclass <- function(x, ...) {
  cat(cli::style_bold(cli::col_blue("this "), cli::col_red("shouldnt "), "work ..."))
  1 + 1
}
obj
```

[mcanouil]

I am not sure there is a workaround to the following behaviour ...

unfortunately, I am not familiar with cli internals.

[JosiahParry]

real odd! oh well :/ im not sure if it is worth a {cli} bug report or not

[mcanouil]

I do not think it is a bug.

Let's ping/ask @gaborcsardi on this 😇

[cderv]

@JosiahParry if I understand correctly you would like to have CLI output like colors showed in a knitted output ?

cli is working with ANSI coloring and is made for terminal. Neither in R Markdown or Quarto you would get the formatting. I don't think it is a revealjs issue - it will not show any formatting in any format by default. Historically it was a crayon issue r-lib/crayon#24 (comment)

To get ANSI formatting in HTML output, it would require specific handling, which the fansi package used by @mcanouil in his answer is doing (See vignette https://cran.r-project.org/web/packages/fansi/vignettes/sgr-in-rmd.html).
Or some tools like pkgdown and downlit are specifically converting ANSI character for formatting to HTML formatting. Quarto do not by default and integration with downlit needs to be improve (see #3730)

Regarding why printing with cli::cli_text() output shows in format: html and not format: revealjs, this is because cli::cli_text() and probably other cli functions are like message() or warning(). So set message: true or warning: true and you will see them, as revealjs sets warning and message (and echo) to FALSE by default

---
title: "this-dont-work"
format: revealjs
---

## define class with cli print

```{r}
#| echo: true
#| message: true
print.myclass <- function(x, ...) cli::cli_text(cli::style_bold("this shouldnt work"))

obj <- structure(list(1, 2, 3), class = "myclass")

obj
```

## change the print method

```{r}
#| echo: true
print.myclass <- function(x, ...) cat("this will work")

obj
```

Probably cli::cat_*() functions are more comparable to cat() and don't require to activate message: true in revealjs.

Hope it helps understand.

[mcanouil]

@cderv 🤦‍♂️ I did not thought of looking at the default of message, warning, and error.
I did not realise the default was different from html format.

[cderv]

No problem. You can't know everything :)

They are different because space in slide is rare so by default it is better to limit the outputs to only results. Hence the different execute options.

[JosiahParry]

@cderv im not worried about colored output. It would just be nice to have any output. The output format for github_document in Rmarkdown renders {cli} fine enough for my standards :) it's surprising to me that there is nothing though for revealjs

[JosiahParry]

I'll try setting echo and message in the chunks and see how behavior changes

[mcanouil]

@JosiahParry to have all output messages from cli, the following yaml header will do the job. 😉

execute:
  message: true
  warning: true
  error: true

[t-kalinowski]

I wonder if Quarto should/could automatically do the equivalent for R users when it knows the final output format is html:

```{r setup, include = FALSE}
options(cli.num_colors = 256)
fansi::set_knit_hooks(knitr::knit_hooks)
```

Something like this would "just work" for most users.

The equivalent functionality could alternatively be done as post-processing step, if injecting knitr hooks before evaluating code is not desirable. (This might require an update in cli::num_ansi_colors() to make it aware of Quarto's new capability to handle ansi color sequences). In pseudo code:

if(fansi::has_sgr(x))
  x <- fansi::sgr_to_html(fansi::html_esc(x))

[cderv]

Thanks Tomasz ! Are you suggesting to use fansi package logic for knitr engine only, or reimplement the logic in quarto cross-language so that ANSI are handled in HTML output ?

Just to be sure to understand.

We could set a hook for knitr to use, but if so we don't want to depend on the ANSI package in Quarto.

However, is this is only done in R side of Quarto, this could probably also be done directly in rmarkdown as an opt-in or else.

[t-kalinowski]

I think ideally, this would be implemented directly in quarto, so we could get cross-language support from one effort. However, I understand development time is limited, and fansi in R already exists and does most of the hard work.

My pragmatic suggestion is to inject fansi hooks when using the R knitr engine, with the understanding that ansi sequence will only "just work" for users using the knitr engine.

[gaborcsardi]

FWIW cli can convert ANSI tags to HTML, see ?cli::ansi_html. I am pretty sure that there are JS/TS packages that can do this as well, if you want to have in the quarto.