[Rd] vignette/knitr help

[Mick Jordan]

I need some help understanding a problem running the tests on the 
'digest' package. Initially, I got the message that the 'knitr' package 
was needed to run vignettes:

Running vignettes for package ‘digest’
Error in loadVignetteBuilder(vigns$pkgdir) :
   vignette builder 'knitr' not found

So I installed the knitr package and all its dependents (‘mime’, 
‘stringi’, ‘magrittr’, ‘evaluate’, ‘formatR’, ‘highr’, ‘markdown’, 
‘stringr’, ‘yaml’) . Now I get some different warnings:

Running vignettes for package ‘digest’
   Running ‘sha1.Rmd’
Warning messages:
1: In readLines(if (is.character(input2)) { :
   cannot open file 'sha1.Rmd': No such file or directory
2: In engine$weave(file, quiet = TRUE, encoding = enc) :
   The vignette engine knitr::rmarkdown is not available, because the 
rmarkdown package is not installed. Please install it.
3: In readLines(con) :
   cannot open file 'sha1.Rmd': No such file or directory

So why is sha1.Rmd missing? And why is it complaining about rmarkdown? 
Or more precisely why did it not install it as a dependent? It installed 
plain markdown.

Mick Jordan