lib.concatMapAttrs: Simplify stack trace

[roberth]

Description of changes

By removing the unnecessary pipe and flip, we get a simpler, shorter stack trace.

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/)
• 23.05 Release Notes (or backporting 22.11 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
• Fits CONTRIBUTING.md.

[infinisil]

@piegamesde might be interested in this as the author of NixOS/rfcs#148

[piegamesde]

@infinisil Thanks, this is an interesting example.

---

On another note, I'd like to see less pull requests of the kind "self-merged after 3 hours", even for simple and straightforward changes

[infinisil]

On another note, I'd like to see less pull requests of the kind "self-merged after 3 hours", even for simple and straightforward changes

Agreed! I would've merged this PR @roberth 🙂

[roberth]

On another note, I'd like to see less pull requests of the kind "self-merged after 3 hours", even for simple and straightforward changes

Ok. Feels unnecessary, but I can think of some arguments. I'll do my part and see how it goes.

rfc 148

Actually I just pulled this commit from #202517 with the intent of removing the trivial stuff to make review easier. I didn't want to bother anyone with review because I thought it was uninteresting and not worth their time. So I got that wrong then.

[piegamesde]

I understand your motivation and don't think merging this PR quickly was inherently bad. It's just that not all Nixpkgs contributors hold themselves up to the same standards, so this kind of thing tends to occasionally go wrong and break things. And it's of course difficult to differentiate here, so the next best thing is to normalize some generous safety margins, even though they might feel (and be) unnecessary in some situations.