Figure out what to do with our uses of builtins.match before Nix 1.12 is released

[copumpkin]

A quick git grep against a recent HEAD reveals that we use builtins.match fairly extensively:

$ git grep builtins.match
lib/filesystem.nix:                          (map (builtins.match pattern) files);
lib/sources.nix:    in lib.any (re: builtins.match re relPath != null) regexes) src;
nixos/modules/services/misc/geoip-updater.nix:          (x: builtins.match ".*\.(gz|xz)$" x == null) cfg.databases) == [];
nixos/modules/services/misc/geoip-updater.nix:          ${toString (builtins.filter (x: builtins.match ".*\.(gz|xz)$" x == null) cfg.databases)};
pkgs/build-support/fetchgit/default.nix:    matched = builtins.match "(.*).git" base;
pkgs/build-support/fetchgit/default.nix:    appendShort = if (builtins.match "[a-f0-9]*" rev) != null
pkgs/build-support/fetchurl/boot.nix:    let m = builtins.match "mirror://([a-z]+)/(.*)" url; in
pkgs/development/idris-modules/default.nix:      m = builtins.match "(.*)\.nix" name;
pkgs/os-specific/linux/kernel/cpu-cgroup-v2-patches/default.nix:  match = builtins.match "(.*)\\.patch" name;
pkgs/top-level/impure.nix:            (builtins.filter (n: builtins.match ".*\.nix" n != null || pathExists (path + ("/" + n + "/default.nix")))

We need to figure out which regexes will be affected by the change (if any) and fix them.

Also, many of them already behave differently between Linux and Darwin (see NixOS/nix#1537), so we should probably do something about those even before 1.12 😄

[mpickering]

I can look at the idris usage of builtins.match but how has it changed in version 1.12?

Eventually I think I will refactor that code anyway to not rely on match at all.

[copumpkin]

It now uses std::regex in C++ which I think has slightly different syntax and behavior from before.

[dezgeg]

Here's one difference which I noticed with non-matching capture groups:

$ nix-build -A nix
/nix/store/6lgqkk4cpcsi3bl2xnk5q0ylsn2vdmvj-nix-1.11.15
$ ./result/bin/nix-instantiate --eval -E 'builtins.match "(x)?(y)?" ""' 
[ ]
$ nix-build -A nixUnstable
/nix/store/h2zl1b3297gwixk26lpvzhmlcdzyl1j9-nix-1.12pre5663_c7af84ce
$ ./result/bin/nix-instantiate --eval -E 'builtins.match "(x)?(y)?" ""' 
[ null null ]

[stale]

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[pennae]

it's been five years. any issues that were likely to ever be discovered probably have been, and if there's anything left this issue probably won't even be remembered by whoever finds it.