libpq: init at 17.2

[wolfgangwalther]

This creates a separate libpq package as discussed in #61580 (comment).

This brings down the number of rebuilds after updating postgresql to about 1.2k darwin and 2.5k linux. Before, they were ~ around 5k, IIRC.

Unfortunately, we are still not anywhere low enough to be able to merge postgresql updates directly into master. I think the nr. 1 reason for that is postgresqlTestHook - and the fact that many packages use a very simple postgresql server in their build dependencies for the check phase.

The only way to get the number of rebuilds lower would be to package postgresqlTestHook as a separate postgresql derivation. The idea would be, that security related issues are irrelevant for the check phase of other packages - and thus updating this separately could easily go through staging with a certain delay. This derivation could also be one that is built with the minimal feature set, making it slimmer overall.

I still think that introducing libpq is a good thing on it's own, thus this PR.

Closes #61580 and #191920

Things done

• Built on platform(s)
  • x86_64-linux (the directly changed packages)
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

---

Add a 👍 reaction to pull requests you find important.

[wolfgangwalther]

Rebased to resolve merge conflicts.

[Ma27]

I promise, I haven't forgotten about that, I'll do my best to schedule a review soon! :))

[Ma27]

FYI pushed a fix for pdo_pgsql/pgsql exts in PHP.

[wolfgangwalther]

FYI pushed a fix for pdo_pgsql/pgsql exts in PHP.

Seems like that needs some nixfmt, I don't get why, though.

[Ma27]

Fixed.

[Ma27]

The change itself looks good to me.

After re-reading #294504 (comment) I'm not sure if I consider the status quo that bad: packages like psycopg or pdo_pgsql only depend on the lib output at runtime which is effectively libpq already. The static build seems to produce static libraries successfully as well nowadays. Regarding dependency concerns, one may still work with outputChecks.

OTOH with another postgresql package that's then used for the test hook we could allow shipping all server updates to master directly. But then again, we could also ship security updates to staging-next directly to speed things up a bit.

I'm not sure.
I'm slightly leaning towards this solution, but figured it'd make sense to share my thoughts from review before merging (hoping that we didn't discuss this before and I just didn't find the thread again), not after.

[szlend]

Apologies, misclicked 😅