crayon/cli output in vignettes when comment=""

[jeroen]

Follow up on: #1858.
Vignettes that set a custom output prefix (instead of ##) for example the empty string:

knitr::opts_chunk$set(comment = "")

This has the unexpected side-effect that ansi codes do not get escaped anymore. A tibble will print a lot of escape sequences:

tibble::as_tibble(iris)

[38;5;246m# A tibble: 150 × 5
[39m
   Sepal.Length Sepal.Width Petal.Length Petal.Width Species
          
[3m
[38;5;246m<dbl>
[39m
[23m       
[3m
[38;5;246m<dbl>
[39m
[23m        
[3m
[38;5;246m<dbl>
[39m
[23m       
[3m
[38;5;246m<dbl>
[39m
[23m 
[3m
[38;5;246m<fct>
[39m
[23m  

[38;5;250m 1
[39m          5.1         3.5          1.4         0.2 setosa 

[38;5;250m 2
[39m          4.9         3            1.4         0.2 setosa 

[38;5;250m 3
[39m          4.7         3.2          1.3         0.2 setosa 

[38;5;250m 4
[39m          4.6         3.1          1.5         0.2 setosa 

[38;5;250m 5
[39m          5           3.6          1.4         0.2 setosa 

[38;5;250m 6
[39m          5.4         3.9          1.7         0.4 setosa 

[38;5;250m 7
[39m          4.6         3.4          1.4         0.3 setosa 

[38;5;250m 8
[39m          5           3.4          1.5         0.2 setosa 

[38;5;250m 9
[39m          4.4         2.9          1.4         0.2 setosa 

[38;5;250m10
[39m          4.9         3.1          1.5         0.1 setosa 

[38;5;246m# … with 140 more rows
[39m

[maelle]

downlit only escapes comments so any custom output prefix that doesn't start with # will get this.

Wasn't there some discussion of whether rmarkdown itself could run downlit via a hook? 🤔

[maelle]

For reference rstudio/rmarkdown#1881

[hadley]

Yeah, we had to use a regexp for this, so you'll need to deliberately suppress crayon in your vignette.

[maelle]

But if rmarkdown supported downlit, could the regexp become useless? I.e. the highlighting & escaping would be done as a knitr output hook or so?

[hadley]

@maelle right, but I think we're some distance from that.

[hadley]

I'm closing this since supporting arbitrary comment prefixes is still a long way away, still a lot of work, and still not requested by that many people.