On 06/10/2017 06:03 PM, Florian Pritz via arch-dev-public wrote:

Talking to some folks in #perl pointed me towards a hopefully satisfying solution. I plan to version the architecture specific directories and introduce a libalpm hook that checks for old directories and warns the user by printing a list of affected AUR/cpanplus-dist-arch packages, respectively a list of files for modules installed directly with cpan.

The new directory layout would be "/usr/lib/perl5/$baseversion/{core,vendor,site}_perl" with $baseversion being "5.26" right now. Currently the layout is "/usr/lib/perl5/{core,vendor,site}_perl". The check for old versions would then be rather simple since it just has to look for directories beside the current version.

During the old discussion, Justin raised the issue that if the directories are versioned, perl modules that are not rebuilt will just be missing. This could lead to software not detecting them any more and disabling a feature or using a slower module to do the job.

One possibility to counter this would be to replace the perl executable with a wrapper that performs the check and prints errors to stderr. Optionally it could also exit with an error code rather than continuing to run the script. I'm not sure if I want this or not, but I'm leaning towards a yes since exiting will make the error more difficult to miss.

I kind of feel like users who do the wrong thing should not be catered to. That being said, using a perl directory layout that causes non-rebuilt packages to simply go missing from the perl installation seems like an *excellent* tradeoff of harmless while providing useful functionality. It seems to work well for python, too.

Hooks to warn people when they do the wrong thing seem ugly, but I can't really claim to be extremely bothered if it is as lightweight as a check for existing files/directories, I assume running whenever the perl package is updated... But providing wrapper scripts that hijack the perl binary every time you try to do anything that involves perl is a *terrible idea*, and regardless, if users don't pay attention to pacman output they deserve everything that happens to them. Paying attention to pacman output is non-optional in Arch, last I checked.