R devel - Jun 2023 - Correct use of tools::R_user_dir() in packages?

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?

Thanks for any clarification!

Regards,

Carl

---
Carl Boettiger
http://carlboettiger.info/

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

-- 
dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org

Carl,

I think your statement is false, the whole point of R_user_dir() is for packages
to have a well-defined location that is allowed - from CRAN policy:

"For R version 4.0 or later (hence a version dependency is required or only
conditional use is possible), packages may store user-specific data,
configuration and cache files in their respective user directories obtained from
tools::R_user_dir(), provided that by default sizes are kept as small as
possible and the contents are actively managed (including removing outdated
material)."

Cheers,
Simon

> On 28/06/2023, at 10:36 AM, Carl Boettiger <cboettig at gmail.com>
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?
> 
> Thanks for any clarification!
> 
> Regards,
> 
> Carl
> 
> ---
> Carl Boettiger
> http://carlboettiger.info/
> 
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