Factor our configuration resolution mechanism to a separate package so others can use it

[lorenzwalthert]

In my limited understanding, {renv} has a sophisticated configuration resolution mechanism:

user-level configs

Uses R options in the form of renv.config.<name>, or RENV_CONFIG_<NAME>⁠ (with resolving conflicts), e.g. in .Rprofile or .Renviron. These can be accessed in session with renv::config.

project-local settings

Allows two ways of specifying option defaults with resolving conflicts (e.g. in .Rprofile):

options(renv.settings = list(snapshot.type = "all"))
options(renv.settings.snapshot.type = "all")

These can be accessed and changed in session with renv::settings and are persistent within renv/settings.json

The configuration options are well documented leveraging R's helpfile mechanism. I believe resolving project-local and user-level configurations is a very generic functionality for R packages, and many packages have opted to implement their own, using various file formats, heuristics and logic, creating friction for users and maintenance burden for developers. I myself have experimented before (since people have long asked to allow configuring {styler} with a config file), creating a prototype {fallback} that tackles the problem in an even more general way. However, I abandoned that approach due to a lack of time. But I don't think we need to re-invent the wheel for every package anew, it would be great to have a standard way of resolving configuration on a user and project level.

Hence, I was wondering if you'd consider exposing the config resolution mechanism of {renv} in a separate package so other package developers (or even just R users) could use it.