Hydra fails at runtime due to buildPerlPackage changes

[lopsided98]

Describe the bug

Hydra fails at runtime due to missing transitive dependencies. This occurs because 9e60fef removed nix-support/propagated-user-env-packages from all Perl packages. Hydra uses buildEnv to create an environment with all its Perl packages, and propagated-user-env-packages used to cause all the transitive dependencies to be pulled into the environment, but this no longer happens.

As suggested by @conferno, I tried replacing buildEnv with perl.withPackages, but this does not work because the Perl wrapper clobbers PERL5LIB, which prevents Hydra from adding its own Perl files to PERL5LIB.

To Reproduce
Steps to reproduce the behavior:

nix-build nixos/tests/hydra

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute:
  - hydra
# a list of nixos modules affected by the problem
module:
  - hydra

cc @volth @Ma27

[Ma27]

The overall issue might be solved in the Perl infrastructure of nixpkgs, however I experienced exactly this when I prepared a Hydra bump last weekend (but lacked time to dig in). I'll prepare a PR to unbreak Hydra now, but don't have a strong opinion about how to fix this perl-wide.

[lopsided98]

rt might have the same problem. I'm not sure if all transitive dependencies are explicitly included there.

[Ma27]

Thanks a lot for the insights @volth!

The list of hydra's perl deps looks crafted manually including all transitive dependencies. As the time went on, the list got out of sync but nothing was broken, because buildEnv magically resolved perl dependencies, silently inserting missing ones. It might be nice, but the implicit magic is confusing. It resolves perl dependencies, but not python's, not ruby's, not lua'a

I actually tried to add all transitive perl dependencies of Hydra, but this escalated pretty quickly and I decided that this isn't a feasible approach since tracking the entire dependency graph makes the package IMHO rather hard to maintain.

the code below should restore old behavior (just by adding a single word instead of ~10 lines on bash which also shadowed postFixup defined in buildPerlPackage), also being language-independent and giving an explicit hint of what is going on:

Agreed. This revert would cause a pretty big rebuild and I just don't think that's worth the effort.

IMHO it would be fine to add lib.closePropagation to automatically resolve all paths for now (to get Hydra fixed on master). Sooner or later someone (probably me as package-maintainer 😅 ) should take a closer look at the dependency-list to clean up outdated stuff.

As release isn't affected I'd also be fine to wait until the third solution works fine for us though.

[Ma27]

This should be fixed, at least with #83600 or probably even earlier. I'm currently running Hydra on 20.03 without any issues now. If you encounter further issues, feel free to ping me to reopen!