17.13 R CMD check and vignettes

• We conclude with a discussion of how vignettes are treated by R CMD check. This official checker expects a package bundle created by R CMD build, as described above. In the devtools workflow, we usually rely on devtools::check(), which automatically does this build step for us, before checking the package. R CMD check has various command line options and also consults many environment variables. We’re taking a maximalist approach here, i.e. we describe all the checks that could happen.

• R CMD check does some static analysis of vignette code and scrutinizes the existence, size, and modification times of various vignette-related files. If your vignettes use packages that don’t appear in DESCRIPTION, that is caught here. If files that should exist don’t exist or vice versa, that is caught here. This should not happen if you use the standard vignette workflow outlined in this chapter and is usually the result of some experiment that you’ve done, intentionally or not.

• The vignette code is then extracted into a .R file, using the “tangle” feature of the relevant vignette engine (knitr, in our case), and run. The code originating from chunks marked as eval = FALSE will be commented out in this file and, therefore, is not executed. Then the vignettes are rebuilt from source, using the “weave” feature of the vignette engine (knitr, for us). This executes all the vignette code yet again, except for chunks marked eval = FALSE.