startup::disable()/enable(): Hide/unhide user's startup files

[HenrikBengtsson]

Background

There is no straightforward way to achieve R --vanilla when using RStudio Console - the only approach is to make sure to remove/hide all of ./.Rprofile, ~/.Rprofile, ./.Renviron, and ~/.Renviron (https://community.rstudio.com/t/how-to-do-an-r-vanilla-in-rstudio-console/13601).

Idea

Provide startup::disable() and startup::enable() that hides and unhides startup files from R by renaming them, e.g. to and from ~/.Rprofile.disabled_20181115-212105.

An alternative approach to renaming ~/.Rprofile, is to override it with an empty ./.Rprofile. (Note though that when doing 'Restart R' in the RStudio Console, RStudio used the original working directory from where it was started (defaults to ~) as the working directory, regardless of what getwd() reports.

This should also be agile to any R_ENVIRON, R_ENVIRON_USER, R_PROFILE, and R_PROFILE_USER settings.

There could also be a startup::disable(once = TRUE), which will automatically call startup::enable() the next time R is launched.

If a file cannot be renamed (e.g. due to lacking file privileges), a warning should be produced.

Result

With this, when restarting R / RStudio Console, we'll achieve R --no-init-file --no-environ. Compared to R --vanilla (= R --no-save --no-restore --no-site-file --no-init-file --no-environ), we still pick up site startup files (--no-site-file) and we still restore .RData (--no-restore) [Issue #42].

Limitations

Using startup::disable() will emulate R --vanilla for all future R sessions launched, not just the next one. Thus, one needs to be careful to use this in an environment where one run many R sessions in parallel.