hydra: hack, update to nix master

hosts/containers/hydra/default.nix

@@ -60,6 +60,22 @@
     }];
   };
 
+  nixpkgs.config.packageOverrides = pkgs: {
+    # HACK: nix-2.5.1 is broken <https://github.com/NixOS/nix/issues/5728>
+    nixUnstable = pkgs.nixUnstable.overrideAttrs (oa: rec {
+      version = "2.6${VERSION_SUFFIX}";
+      VERSION_SUFFIX = "pre20220107_${pkgs.lib.substring 0 7 src.rev}";
+      patches = [];
+      src = pkgs.fetchFromGitHub {
+        owner = "nixos";
+        repo = "nix";
+        rev = "fcddaa4b9b22a910a24a513bc05579a12eb1db41";
+        sha256 = "1v5z2kc9gard6sqxqi73w37x1jfa9ja04svkwr9f1dfj3vl3xygp";
+      };
+    });
+  };
+
+
   # This value determines the NixOS release with which your system is to be
   # compatible, in order to avoid breaking some software such as database
   # servers. You should change this only after NixOS release notes say you

hosts/containers/hydra/hydra.nix

@@ -40,7 +40,15 @@ in {
     hydraURL = "https://hydra.hq.c3d2.de";
     logo = ./c3d2.svg;
     notificationSender = "hydra@spam.works";
-    package = pkgs.hydra-unstable;
+    package = pkgs.hydra-unstable.overrideAttrs (oa: {
+      # HACK for Hydra error: cannot write modified lock file of flake
+      patchPhase = ''
+        ${pkgs.lib.optionalString (oa ? patchPhase) oa.patchPhase}
+
+        substituteInPlace src/script/hydra-eval-jobset \
+          --replace '"nix", "flake", "info"' '"nix", "flake", "info", "--no-write-lock-file"'
+      '';
+    });
     useSubstitutes = true;
   };