[arch-general] [arch-dev-public] libalpm hook and wrapper for detecting broken perl modules

[Eli Schwartz]

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.

-- 
Eli Schwartz

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