[Rd] Correct use of tools::R_user_dir() in packages?

[Dirk Eddelbuettel]

On 27 June 2023 at 15:36, Carl Boettiger wrote:
| tools::R_user_dir() provides configurable directories for R packages
| to write persistent information consistent with standard best
| practices relative to each supported operating systems for
| applications to store data, config, and cache information
| respectively.  These standard best practices include writing to
| directories in the users home filespace, which is also specifically
| against CRAN policy.
| 
| These defaults can be overridden by setting the environmental
| variables R_USER_DATA_DIR , R_USER_CONFIG_DIR, R_USER_CACHE_DIR,
| respectively.
| 
| If R developers should be using the locations provided by
| tools::R_user_dir() in packages, why does CRAN's check procedure not
| set these three environmental variables to CRAN compliant location by
| default (e.g. tempdir())?
| 
| In order to comply with CRAN policy, a package developer can obviously
| set these environmental variables themselves within the call for every
| example, every unit test, and every vignette.  Is this the recommended
| approach or is there a better technique?

My use evolved to something like this (from in this case r2u, but similar in
a few other packages)

    .defaultConfigFile <- function() {
        pkgdir <- tools::R_user_dir(packageName())      # ~/.local/share/R/ + package
        if (dir.exists(pkgdir)) {
            fname <- file.path(pkgdir, "config.dcf")
            if (file.exists(fname)) {
                return(fname)
            }
        }
        return("")
    }

You can then create config reader and writers functions that have a file
argument (set to the above) whicg you can override in tests with tempfile()
allowing you to write and then read.

Given the 'thou shalt not write to $HOME' rule, I often have parameter
getters with default values which, if a config file is found (with the name
per the helper above), also read it and use it to override the defaults.
Works for me, and is lightweight via a 'using batteries included'
zero-depends approach.

Dirk

-- 
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