imp: nix -> 2.12.0 for buildkite host/guests to match darwin

Author: johnalotoski

flake.lock

@@ -15,6 +15,7 @@
     # --------------------------------------------------------------
     # --- Auxiliary Nixpkgs ----------------------------------------
     nixpkgs.url = "github:NixOS/nixpkgs";
+    nixpkgs-nix.url = "github:NixOS/nixpkgs";
     capsules = {
       # Until nixago is implemented, as HEAD currently removes fmt hooks
       url = "github:input-output-hk/devshell-capsules/8dcf0e917848abbe58c58fc5d49069c32cd2f585";

flake.nix

@@ -127,7 +127,9 @@ in
           hostAddress = hostIp;
           localAddress = guestIp;
 
-          config = {
+          config = let
+            inherit (self.inputs.nixpkgs-nix.legacyPackages.x86_64-linux.nixVersions) nix_2_12;
+          in {
             imports = [
               # Common guest level config (also applied at host level)
               ./common.nix
@@ -157,6 +159,10 @@ in
             # Ensure we can use same nixpkgs with overlays the host uses
             nixpkgs.pkgs = pkgs;
 
+            # Ensure nix package on buildkite matches darwin buildkite at 2.12.0
+            nix.package = nix_2_12;
+            environment.systemPackages = [nix_2_12];
+
             # Don't try to inherit resolved from the equinix host which won't work
             environment.etc."resolv.conf".text = ''
               nameserver 8.8.8.8

nix/metal/bitteProfile/buildkite/buildkite-agent-containers.nix

@@ -508,6 +508,7 @@ in {
             config,
             ...
           }: let
+            inherit (self.inputs.nixpkgs-nix.legacyPackages.x86_64-linux.nixVersions) nix_2_12;
             cfg = config.services.buildkite-containers;
           in {
             # Temporarily disable nomad to avoid conflict with buildkite resource consumption.
@@ -544,6 +545,10 @@ in {
               in
                 map (n: mkContainer n (toString (10 - n))) (lib.range 1 count);
             };
+
+            # Ensure nix package on buildkite matches darwin buildkite at 2.12.0
+            nix.package = nix_2_12;
+            environment.systemPackages = [nix_2_12];
           })
         ];