types.attrs: merge non-conflicting values only

[abbradar]

Motivation for this change

Avoid silent conflicting redefinitions of option values.

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.

[infinisil]

With the introduction of types.anything and soon types.raw, we should deprecate types.attrs. As such I don't think it makes sense to change types.attrs anymore, especially in a backwards-incompatible way.

[abbradar]

It makes sense, yeah. I propose then to replace all usage of attrs in NixOS with attrsOf anything to safely merge conflicting values (I was actually bitten by this in production, and IMHO noone expects current behaviour), and add a deprecation warning. What do you think?

[abbradar]

Reading more of the linked issues I see that we already have the deprecation in mind. Great news! Let's close this PR; I don't think it's relevant.