@teh, thanks for your PR! By analyzing the history of the files in this pull request, we identified @obadz, @edolstra and @ericsagnes to be potential reviewers.

As I mentioned on the mailinglist the following implementation might be more efficient:

{ sourceByRegex = src: regexes: builtins.filterSource (path: type:
      let relPath = lib.removePrefix (toString src + "/") (toString path);
      in builtins.match (concatStringsSep "|" (map (r: "(${r})") regexes)) relPath != null)
    src;
}

But I'm not sure so this has to be benchmarked. But we can always do that later.

Regarding tests, I see there's <nixpkgs/lib/tests/release.nix>. Maybe you can hook up a test in there?

I'm not a huge fan of concatStringsSep "|" because that breaks when users use | in their own regex. If speed becomes an issue I think we should move this to builtins. What do you think?

I did put parenthesis around the individual regexes so that the | from users didn't clash. Although I agree that speed isn't a big priority now.

nix-build pkgs/top-level/release.nix -A lib-tests does something but it always succeeds, even if I intentionally break a test.

Even with parenthesis I can write )|( . It's unlikely but I don't feel we need to introduce a potentially unsound behaviour when the number of regexes is usually pretty small, and we always have the escape hatch of introducing a builtin.

Ok agreed.