pretty_rmd overwrites all lines of chunk with first line in Rmd with single chunk

[yogat3ch]

Reprex:

file.create("test.Rmd")
writeLines('
---
title: "Untitled"
output: html_document
---
```{r, cache = F, echo = F}
library(htmltools)
if (isTRUE(getOption("knitr.in.progress"))) {
  message("I am knitting")
tagList(
  div(id = "include-iframeResizer"),
  htmlDependency(
    name = "iframeResizer",
    version = "4.2.8",
    src = c(href = "https://cdn.jsdelivr.net/npm/iframe-resizer@4.2.8/js/",
            file = "inst"),
    script = "iframeResizer.contentWindow.min.js",
    all_files = F
    )
)
}

```', con = "test.Rmd")

sinew::pretty_rmd("test.Rmd", output = NULL, open_output = FALSE, create_library = FALSE)

Output is:

---
title: "Untitled"
output: html_document
---
```{r, cache = F, echo = F}
library(htmltools)
library(htmltools)
library(htmltools)
library(htmltools)
library(htmltools)
library(htmltools)
library(htmltools)
library(htmltools)
library(htmltools)
library(htmltools)
library(htmltools)
library(htmltools)
library(htmltools)
library(htmltools)
library(htmltools)
library(htmltools)
```

The bug is related to pretty_rmd.R#158 mapply simplifying to matrix when there's just one chunk.

This makes it such that pretty_rmd.R#L167 copies the first line to all lines.

Fixed by #67 by adding SIMPLIFY = FALSE to prevent simplification of output from mapply on an Rmd with a single chunk to an array/matrix.

Does not appear to be an issue when create_library = TRUE and pretty_rmd_library is used instead.