cc @infinisil @srhb

I don't know why this would cause a rebuild of anything...

As already indicated on IRC, I don't think this fits in nixpkgs and I'd rather see this in something like NUR or Flakes in the future. I think nixpkgs' lib should mainly be reserved for things used in nixpkgs itself.

While I did previously mention how I wouldn't mind nixpkgs being used as a standard library, I think this function is a bit too non-standard for this.

Nixpkgs is also already a too big centralized piece of bloat, adding random functions to it wouldn't help with that. I wouldn't want nixpkgs to become a dumping ground for all kind of unrelated functionality.

@infinisil I hear you. I don't see this as "random functionality" though and I'm curious if there are others who agree with me, hence the PR. I see this almost as "missing feature from nix-build" so therefore it should be ubiquitous.

(I also wonder if mapAttrsNestedRecursiveCond might deserve a home in lib.attrsets though...)

I've convinced myself that this feature set is non-trivial enough that it either a) justifies a real package in nixpkgs or b) doesn't justify one because there are many ways to implement it.

For now I've started a repo which expands a great deal on this PR with more features: https://github.com/3noch/help.nix

It's nice you've extracted this to separate package! Please publish your package in https://nixos.wiki/wiki/Applications, so it is visible. Maybe it fits a separate section "lib extensions"