R Markdown code folding doesn't work with bash, Python code chunks

Question

R Markdown now has the option to automatically show or hide code chunks in your .Rmd document. However, this seems to only work with R code chunks.

---
output: 
  html_document: 
    code_folding: hide
---

```{r}
print("This code chunk will be hidden")
```

```{r, engine='bash'}
echo "This code chunk will not be hidden"


```{r, engine='python'}
print "Will this code chunk be hidden?"
```

```{r}
system('uname -srv',intern=T)
sessionInfo()
```

The only solution I have been able to come up with is to hide the code behind a blank tab

---
output: 
  html_document: 
    code_folding: hide
---

```{r}
print("This code chunk will be hidden")
```

# Source code {.tabset .tabset-pills}

## Hide Code

## Show Code

```{r, engine='bash'}
echo "This code chunk will not be hidden"
```

```{r, engine='python'}
print "Will this code chunk be hidden?"
```

```{r}
system('uname -srv',intern=T)
sessionInfo()
```

Is there a better solution to this which will enable code folding for all code chunks?

Answer 1

Maybe R version plays a role here? For me, without any modifications, your code works as expected:

## R version 3.3.3 (2017-03-06)
## Platform: x86_64-apple-darwin13.4.0 (64-bit)
## Running under: macOS Sierra 10.12.6

as for R studio

Version 1.0.136 – © 2009-2016 RStudio, Inc.

Of course, I have changed (from your initial post)

```{r, engine='bash'}
echo "This code chunk will not be hidden"

with

```{r, engine='bash'}
echo "This code chunk will not be hidden"
```

Answer 2

You can fix it in post-production too. I convert Rmd->HTML using rmarkdown::render() (R 3.4.1) and pandoc-1.17.2. The resulting HTML file uses different CSS classes for different languages, but only the <pre> class "sourceCode r" supports folding.

So, just change all non-"r" classes to "r" in the <pre> tags:

perl -i -pe 's/<pre class="sourceCode [^r]+">/<pre class="sourceCode r">/' myfile.html

The appearance of the code in the blocks will not change.