Nested render confuses RStudio

2015-08-06_nested-render-confuses-rstudio.Rmd

---
output:
  html_document
---

```{r setup, echo = FALSE}
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)
```

*UPDATE: JJ provided the magic missing piece, so this gist now shows a successful attempt at nested render, complete with expected RStudio behavior. This gist relates to [issue #491 on rstudio/rmarkdown](https://github.com/rstudio/rmarkdown/issues/491).*

I have some R commands into a file `foo.R`:

```{r define-demo-code}
demo_code <- c(
  "(y <- 1:4)",
  "mean(y)"
)
writeLines(demo_code, "foo.R")
```

I want to cause `foo.R` to be rendered, in the process of rendering THIS file.

It is already well-known that a chunk like this will NOT work (see [issue #248](https://github.com/rstudio/rmarkdown/issues/248))

```{r eval = FALSE}
## not run
rmarkdown::render("foo.R")
```

It produces this error:

```
Error in env$metadata <- list() : 
  cannot change value of locked binding for 'metadata'
Calls: <Anonymous>
Execution halted
```

Thanks to that issue, however, I learned a trick: create a wrapper script and use `devtools::clean_source()` to execute that in a fresh R environment. *Thanks to [an exchange with JJ](https://github.com/rstudio/rmarkdown/issues/491) I learned another thing: use `quiet = TRUE` inside `render()` to keep it from emitting messages that cause the RStudio IDE to display the rendered child instead of parent.*

```{r render-via-wrapper}
## implementing JJ's suggestion to use 'quiet' arg to suppress message output
writeLines('rmarkdown::render("foo.R", "md_document", quiet = TRUE)',
           "render_wrapper.R")
devtools::clean_source("render_wrapper.R", quiet = TRUE)
file.remove("render_wrapper.R")
```

Which does indeed cause `foo.R` to be rendered to `foo.md`:

```{r}
list.files(pattern = "foo")
```

~~But if you render *this document* via the Knit button in RStudio, the preview window pops up `foo.md`, not an HTML preview of *this document*. Which is weird. This document is successfully compiled to `.html` but you have to visit it in the file browser and "View in Web Browser".~~

And indeed Just Works. The End.

Note that clean_source() has been deprecated in favor of the callr package.

how do I use the clean_source function now?