Allow isolated projects to read from cache / copy into isolated library

[kdkavanagh]

Related to #555

Would be helpful to have a way to override the project's settings.dcf at runtime, or provide use.cache as an argument to restore and eliminate any ambiguity. Since isolate() modifies the settings.dcf file, other processes activating the same project (but using differently library paths - HPC-style usecase) will not be able to use the cache. In other words, is there a way to make the cache setting a property of the library path rather than a property of the renv project?

Perhaps a way to say "Use the cache, but copy instead of symlink" during restore would be sufficient, effectively isolating w/o disabling the cache

[kevinushey]

It looks like renv does have a mechanism for setting project settings without persisting them. For example:

renv::settings$use.cache(FALSE, persist = FALSE)

Would that be sufficient for your case?

[kdkavanagh]

Not quite - That certainly helps for manually disabling the cache for some invocation, however isolate() itself disables the cache and persists the change w/o giving the user that control. Additionally, I'd like the ability to restore from the cache, but actually copy the packages into the library instead of symlinking. In other words, isolate() but without disabling the cache in the project settings OR restore() forcing it to use the cache

[kevinushey]

Got it -- thanks for elaborating. I've added the ability to control whether renv uses symlinks in the development version of renv -- you can set:

options(renv.config.cache.symlinks = FALSE)

to instruct renv to copy, rather than link, from the cache when appropriate. (You can set this in the project .Rprofile, or renv/settings.R, if you'd like the option to be tied to that particular project)

In addition, renv::isolate() now only copies symlinked packages from the cache back into the project library; it does not also set the associated project setting.