Building notes, projects, and occasional rants


This all started with an article by Marcel Gruenauer "hanekomu", "Repeatedly installing Task::* distributions".

What he wants is a way to tell CPAN this: "install the latest versions of my dependencies".

His solution wont work unfortunately. The code that he gives us will prevent the Task:: module from being installed but it will not guarantee that the latest version of the prereqs will be installed in the following runs.

the reason is simple: if you don't ask for a specific version of your prereqs, CPAN will accept any version, so it will only install each prereq once, the first time.

The perfect solution would be to create a marker on each prereq that would tell the CPAN tool chain that you want the latest version. This does not exist yet. You could probably standardize on version -1 meaning the last one (on a twisted parallel with the last index of Perl lists), but its all speculation. Its just not supported yet.

The next best thing would be to include the version required on each of your prereqs, and keep those values up-to-date to the latest available on CPAN whenever you rebuild your package.

This is a half-way solution. It wont guarantee the latest version at the time your package is installed but it would make sure you get the latest version at the time your package was built on your system before uploading to PAUSE.

This is actually a good compromise given that you are probably listing the versions of the prereqs that you tested your package with on your system.

And, better yet, this half-solution can be automatized. I wrote a Dist::Zilla plugin to do just that. The code is very simple and you can just adapt this into a Module::Install plugin or whatever you use to build your packages.

You can find the code for Dist::Zilla::Plugin::LatestPrereqs at my Github repository for Dist::Zilla tools. Its not on CPAN yet, and for now there are no plans to publish it. The reason is simple: it requires a small patch to the core Dist::Zilla. The patch is a single commit that you can find on Dist::Zilla fork. I've asked Ricardo Signes to accept the patch. If he likes the code, I'll release my plugin after the next Dist::Zilla release.

If you look at the LatestPrereqs code, you'll notice that it is very simple, but it does load the CPAN package and that is a big one. You could write this code directly on your Makefile.PL and have the very latest versions of your prereqs at install time, but this would assume that the system as a properly configured CPAN.

That was a risk that I'm not willing to take on my distributions. If you do it that way, ping me. I would like to follow your module CPAN Testers feed for a while.

Back to Marcel post, if you do need to prevent the install phase for your distribution, then I've also uploaded a Dist::Zilla plugin to do just that: Dist::Zilla::Plugin::MakeMaker::SkipInstall. It might be handy sometimes.