Empty chunks can not be knitted when caching is enabled

[holgerbrandl]

1. Create a fake myscript.Rmd with an empty chunk (using ` instead of the backtick for sure)

backtick-backick-backtick{r }
backtick-backick-backtick

2. And then try it to knit it with caching being enabled

opts_chunk$set(cache = TRUE)
knit2html("myscript.Rmd")

knit2html seems to be blocked and runs forever.

This may look like a very artificial use-case but it occurs for me frequently when knitr::spining R-scripts: Whenever spin() encounters an R comment wrapped by 2 markdown lines, it creates an empty chunk. E.g.

#'  # some title
### comment

#' some other markdown

However, I think spin is working correctly here by ignoring the comment and trimming away empty lines within the chunk. knit2html should be more robust and process empty chunks even if caching is enabled. It does so if caching is disabled.

I'm using R v3.1 with knitr v1.8

[yihui]

Thanks. Just fixed it. Please install the development versions of markdown and knitr:

devtools::install_github(c('rstudio/markdown', 'yihui/knitr'))

[github-actions]

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