Improve support for knitr::spin(format = 'qmd')

[kylebutts]

The approach taken here had the goal of not touching the original spin code, so that this only impacts format = 'qmd' and did so as simply as possible.

To do this, I find the any code chunk that starts with #| and prepend a # %% for the previous line. This prevents converting each option passed with #| from creating a new chunk.

Perhaps this could be integrated more deeply with how knitr::spin works, but this is the simplest solution.

@cderv

[kylebutts]

Example:

library(devtools)
load_all()

spin_w_tempfile = function(..., format = "Rmd") {
  tmp = tempfile(fileext = ".R")
  writeLines(c(...), tmp)
  spinned = spin(tmp, knit = FALSE, format = format)
  result = readLines(spinned)
  file.remove(c(tmp, spinned))
  result
}

print_result = function(s) {
  cat(paste0(s, collapse = "\n"))
}

block = c(
  "# %% ",
  "#| echo: false",
  "#| message: false",
  "#| include: false",
  "1+1 ",
  "#| eval: false",
  "1+1",
  "",
  "#' # Header",
  "#' Text",
  "#| include: false",
  "1+1"
)

block |> process_block_for_qmd() |> print_result()
#> # %% 
#> #| echo: false
#> #| message: false
#> #| include: false
#> 1+1 
#> # %%
#> #| eval: false
#> 1+1
#> 
#> #' # Header
#> #' Text
#> # %%
#> #| include: false
#> 1+1

[yihui]

Thank you very much! I don't have time to review this PR at the moment, but I feel the for loops might be unnecessary if you take advantage of rle(). Here is a short function (ninja code) that I just wrote for your reference:

# find the position of the starting `#|` in a consecutive block of `#|` comments
comment_start = function(x) {
  i = startsWith(x, '#| ')
  r = rle(i)
  l = r$lengths
  j = cumsum(l) - l + 1
  j[r$values]
}

Test:

block = c(
    "# %% ",
    "#| echo: false",
    "#| message: false",
    "#| include: false",
    "1+1 ",
    "#| eval: false",
    "1+1",
    "",
    "#' # Header",
    "#' Text",
    "#| include: false",
    "1+1"
)
comment_start(block)
#> [1]  2  6 11

Then you look back one line and see if that line starts with the rc pattern (such as # %%). If not, add # %%.

[kylebutts]

Correct on both points @yihui! The rle solution is nice, thank you.

[yihui]

I just finished revising this PR. Thanks!

[yihui]

This function is too complicated. Essentially what we need is add # %%\n to the lines comment_start(block) (excluding the lines opt + 1) in block. Like this:

i = setdiff(comment_start(block), opt + 1)
block[i] = paste0('# %%\n', block[i])

There is no need to use loops.

[yihui]

I forgot to mention that I remove the limitation to qmd, i.e., this idea should work for any formats (Rnw, Rhtml, etc.). That's because the #| comments are not special to qmd. They work for all knitr document formats.

block = c(
  "# %% ",
  "#| echo: false",
  "#| message: false",
  "#| include: false",
  "1+1 ",
  "#| eval: false",
  "1+1",
  "",
  "#' # Header",
  "#' Text",
  "#| include: false",
  "1+1"
)

cat(spin(text = block, knit = FALSE), sep = '\n')

```{r}
#| echo: false
#| message: false
#| include: false
1+1 
```
```{r}
#| eval: false
1+1
```

# Header
Text

```{r}
#| include: false
1+1
```

cat(spin(text = block, knit = FALSE, format = 'Rnw'), sep = '\n')

\documentclass{article}
\begin{document}

<<>>=
#| echo: false
#| message: false
#| include: false
1+1 
@
<<>>=
#| eval: false
1+1
@

# Header
Text

<<>>=
#| include: false
1+1
@

\end{document}