nixos/powerdns: replace extraConfig with settings option

[aanderse]

Motivation for this change

#144575

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• 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/)
• 22.05 Release Notes (or backporting 21.11 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
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

[rnhmjoj]

The type is bit more complex than this: there are options accepting a list of values, for example.
You should be able to reuse the functions I've defined for pdns-recursor, which seems to be using the same syntax. We could move them to a common file and import them in both modules.

[aanderse]

ping @infinisil - there are several pieces of powerdns related software that all uses the same configuration format. This format is different enough from existing formats (ini) that it doesn't quite match anything we have. Should I add a new pkgs.formats.pdns format, or abstract this somewhere else?

Thanks!

[infinisil]

I think unless we have a clear specification or some indication that two programs use the same format, we shouldn't abstract this. In this case it seems to be simple enough that we can just define the formats inline in the modules themselves. I guess we could add a types.oneOrMore at some point though. Fyi I think this should maybe rather be oneOrMore = type: coercedTo type singleton (listOf type), so that merging works between single and multiple elements.

[aanderse]

Thanks for the answer @infinisil.