Is there a way for a knitr engine to delete a file after a latex render

[ryanzomorrodi]

Description

I have a custom knitr engine as part of sasquatch that creates tex, image, and a sty files, which are required to render the final output.

I figured out how to embed the tex and image files within the knitr output so that those files so that those files can be deleted before the render; however, the style file needs to be there for the tex output to be rendered by the latex engine.

Is there a way I can delete the style file produced by the engine after the latex render finishes?

Here is a minimal version of what I would be talking about:

---
format: pdf
---


```{r, output = FALSE}
custom_engine <- function(options) {
  writeLines(
    c(
      "\\NeedsTeXFormat{LaTeX2e}", 
      "\\ProvidesPackage{highlight}[2025/04/11 Simple text highlighting]", 
      "\\RequirePackage{xcolor}",
      "\\newcommand{\\highlight}[1]{\\colorbox{yellow}{#1}}",
      "\\endinput"
    ),
    "style.sty"
  )
  options$results <- "asis"

  knitr::engine_output(
    options, 
    code = "", 
    out = "This is \\highlight{important} text."
   )
}
style_dependency <- list(
  name = "style",
  options = NULL,
  extra_lines = NULL
)
class(style_dependency) <- "latex_dependency"
knitr::knit_meta_add(list(style_dependency))

knitr::knit_engines$set(custom = custom_engine)
```


```{custom}
whatever
```

Now, there is a style.sty file in the same directory as qmd file. I would prefer it didn't exist.

Options I considered:

• on.exit() - R exits before the quarto render so deleting the file on exit would cause the quarto file not to render
• post-render yaml option - since this is part of an engine provided to the user through a package, I cannot control the user's quarto yaml (at least I think I can't)

[mcanouil]

First, don't use R inline syntax for code cell options. Simple rule is: there is nothing but the language between the brackets. Quarto uses YAML style.

```{r}
#| output: false

instead of

```{r, output = FALSE}

Regarding your question, use post-render script.

[ryanzomorrodi]

I would use a post rendered script, but this is part of a package, so I'd have to get the user to write it all out within their own yaml, unless there's a way for R to change the quarto's yaml

Options I considered:

• on.exit() - R exits before the quarto render so deleting the file on exit would cause the quarto file not to render
• post-render yaml option - since this is part of an engine provided to the user through a package, I cannot control the user's quarto yaml (at least I think I can't)

[mcanouil]

If you don't want or cannot use post-render, and want to do it in R, then it's unrelated to Quarto CLI.

[arnaudgallou]

Check out the withr package, it has internal functions that allow you to defer an operation when knitr exists or retrieve knitr's exist frame. You can copy the code and reuse it in your package (see https://r-pkgs.org/license.html#sec-code-you-bundle to properly license the code and credit their authors).

You can use defer_knitr(), or if you want to bundle less code in your package you can make use of knitr_exit_frame(). For example:

frame <- knitr_exit_frame(parent.frame())
withr::defer(expr, envir = frame)

Note that I opened an issue some months ago to ask the developers if they could export defer_knitr(). Hopefully we'll be able to use that function in the future without having to copy its source code.