WISH: Flag and/or environment variable to declare script requires internet access

[HenrikBengtsson]

Issue

The default assumption is that R has access to the internet. For example, during startup, we might call foghorn to query the CRAN status of R packages we maintain. However, if there is no internet access (e.g. when being off the grid or running in airplane), such calls will fail - often with a long timeout period first.

Suggestion

Add a mechanism to skip startup scripts when there's no internet access. One idea is to introduce an environment variable
NO_INTERNET to be used in file names as:

~/.Rprofile.d/interactive=TRUE/when=daily/package=foghorn,NO_INTERNET!=TRUE.R

This file will be skipped if, and only if:

• NO_INTERNET=TRUE

It will be processed if:

• NO_INTERNET is not defined
• NO_INTERNET is empty
• NO_INTERNET=FALSE
• NO_INTERNET is non-empty and not identical to TRUE
• NO_INTERNET=true
• NO_INTERNET=1
• NO_INTERNET=0

Comment: It would be better if we could detect if an environment variable is defined or not, cf. Issue #89.