Invalid regular expression breaks kresd NixOS module

[puppe]

Describe the bug

There is an error in the kresd NixOS module. The changed regular expression introduced in #153610 is invalid.

error: invalid regular expression '([0-9.]+):([0-9]+)()'

       at /nix/store/ldq0kzflyiy4ip2l1fpdqbhsgcrpal3x-source/nixos/modules/services/networking/kresd.nix:12:13:

           11|   mkListen = kind: addr: let
           12|     al_v4 = builtins.match "([0-9.]+):([0-9]+)()" addr;
             |             ^
           13|     al_v6 = builtins.match "\\[(.+)]:([0-9]+)(%.*|$)" addr;

Steps To Reproduce

Steps to reproduce the behavior:

1. Add the following to a NIxOS configuration: services.kresd.enable = true;
2. Evaluate the configuration.

Expected behavior

I guess, the regular expression should not be invalid and thereby should not cause an error during evaluation.

Additional context

This can also be reproduced in nix repl:

nix-repl> builtins.match "([0-9.]+):([0-9]+)()" "127.0.0.1:53"
error: invalid regular expression '([0-9.]+):([0-9]+)()'

       at «string»:1:1:

            1| builtins.match "([0-9.]+):([0-9]+)()" "127.0.0.1:53"
             | ^
            2|

Notify maintainers

@vcunat

[user@system:~]$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"aarch64-darwin"`
 - host os: `Darwin 21.2.0, macOS 12.1`
 - multi-user?: `yes`
 - sandbox: `no`
 - version: `nix-env (Nix) 2.5.1`
 - channels(root): `"nixpkgs-22.05pre345162.81f05d871fa"`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixpkgs`

[puppe]

Maybe there are differences in builtins.match between Nix 2.3 and Nix 2.5. I have just tested this on another host:

[user@system:~]$ nix-shell -p nix-info --run "nix-info -m"                                                                                                                                                                                                                                                                     
 - system: `"x86_64-linux"`
 - host os: `Linux 5.10.91, NixOS, 21.11 (Porcupine)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.3.16`
 - channels(root): `"nixos-21.11.335288.3ddd960a3b5"`
 - channels(martin): `""`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

[user@system:~]$ nix repl                                                                                                                                                                                                                                                                                                      
Welcome to Nix version 2.3.16. Type :? for help.

nix-repl> builtins.match "([0-9.]+):([0-9]+)()" "127.0.0.1:53"
[ "127.0.0.1" "53" "" ]

Edit: There are differences in builtins.match between Darwin and Linux.

[puppe]

NixOS/nix#1537 might be related.

[puppe]

I submitted a pull request that should fix this. See #156867.

[vcunat]

This is the obnoxious thing that Nix takes the regexp engine from the C++ library, but the standard does not define such details, so different people platforms get different things. On my NixOS the regexp is accepted.

[vcunat]

Just my curiosity: you don't use the code to run kresd on a darwin, right? (just to evaluate a NixOS system)

[puppe]

Just my curiosity: you don't use the code to run kresd on a darwin, right? (just to evaluate a NixOS system)

The Nix expressions are evaluated on my Macbook (aarch64-darwin), and then the derivations are built on a NixOS host (x86_64-linux). See https://nixos.org/manual/nix/stable/advanced-topics/distributed-builds.html and https://nixos.wiki/wiki/Distributed_build for details.

Edit: Yes, I evaluate the kresd module for a NixOS system.