Use the lazy-trees branch of Nix

flake.lock

@@ -23,16 +23,16 @@
         "nixpkgs-regression": "nixpkgs-regression"
       },
       "locked": {
-        "lastModified": 1661606874,
+        "lastModified": 1668607642,
-        "narHash": "sha256-9+rpYzI+SmxJn+EbYxjGv68Ucp22bdFUSy/4LkHkkDQ=",
+        "narHash": "sha256-lNnk5thRq43XPcA+5KwoHgdsKf3urmE4B2xzHokVMbc=",
-        "owner": "NixOS",
+        "owner": "edolstra",
         "repo": "nix",
-        "rev": "11e45768b34fdafdcf019ddbd337afa16127ff0f",
+        "rev": "561440bd6ddebd53d7b42bced22cb78fd607a6de",
         "type": "github"
       },
       "original": {
-        "owner": "NixOS",
+        "owner": "edolstra",
-        "ref": "2.11.0",
+        "ref": "lazy-trees",
         "repo": "nix",
         "type": "github"
       }

flake.nix

@@ -2,7 +2,7 @@
   description = "A Nix-based continuous build system";
 
   inputs.nixpkgs.follows = "nix/nixpkgs";
-  inputs.nix.url = "github:NixOS/nix/2.11.0";
+  inputs.nix.url = "github:edolstra/nix/lazy-trees";
 
   outputs = { self, nixpkgs, nix }:
     let

src/hydra-eval-jobs/hydra-eval-jobs.cc

@@ -129,7 +129,7 @@ static void worker(
             LockFlags {
                 .updateLockFile = false,
                 .useRegistries = false,
-                .allowMutable = false,
+                .allowUnlocked = false,
             });
 
         callFlake(state, lockedFlake, *vFlake);