Fix building many things in nix.

Nix 2.30.0 (2025-07-07) changed the build directory from /tmp to /nix/var/nix/builds which broke a number of builds because my ZFS datasets were utf8only. This adds a role to mount tmpfs to /nix/var/nix/builds to restore the old behavior.

nix/configuration/configuration.nix

@@ -14,6 +14,7 @@
     ./roles/base
     ./roles/bluetooth
     ./roles/boot
+    ./roles/build_in_ram
     ./roles/chromecast
     ./roles/chromium
     ./roles/d2
@@ -177,7 +178,6 @@
         (final: prev: {
           grub2 = (final.callPackage ./package/grub { });
         })
-        (disableTests "git")
       ];
 
     # This option defines the first version of NixOS you have installed on this particular machine,

nix/configuration/formats/iso.nix

@@ -16,8 +16,8 @@
     me.buildingPortable = true;
     me.mountPersistence = lib.mkForce false;
     me.optimizations.enable = lib.mkForce false;
-    me.image_based_appliance.enable = true;
 
-    # TODO: image based appliance?
+    # Not doing image_based_appliance because this might be an install ISO, in which case we'd need nix to do the install.
+    # me.image_based_appliance.enable = true;
   };
 }

nix/configuration/hosts/odo/default.nix

@@ -68,6 +68,7 @@
     me.base.enable = true;
     me.bluetooth.enable = true;
     me.boot.enable = true;
+    me.build_in_ram.enable = true;
     me.chromecast.enable = true;
     me.chromium.enable = true;
     me.d2.enable = true;

nix/configuration/hosts/quark/default.nix

@@ -62,6 +62,7 @@
     me.base.enable = true;
     me.bluetooth.enable = true;
     me.boot.enable = true;
+    me.build_in_ram.enable = true;
     me.chromecast.enable = true;
     me.chromium.enable = true;
     me.d2.enable = true;

nix/configuration/hosts/recovery/default.nix

@@ -47,11 +47,16 @@
     # Enable TRIM
     # services.fstrim.enable = lib.mkDefault true;
 
+    me.build_in_ram.enable = true;
+    me.doas.enable = true;
+    me.network.enable = true;
+    me.nvme.enable = true;
     me.recovery.enable = true;
     me.ssh.enable = true;
     me.sshd.enable = true;
     me.user.enable = true;
     me.zfs.enable = true;
     me.zrepl.enable = true;
+    me.zsh.enable = true;
   };
 }

nix/configuration/roles/build_in_ram/default.nix

@@ -0,0 +1,35 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+{
+  imports = [ ];
+
+  options.me = {
+    build_in_ram.enable = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      example = true;
+      description = "Whether we want to install build_in_ram.";
+    };
+  };
+
+  config = lib.mkIf config.me.build_in_ram.enable (
+    lib.mkMerge [
+      {
+        # Nix 2.30.0 (2025-07-07) changed the build directory from /tmp to /nix/var/nix/builds which broke a number of builds because my ZFS datasets were utf8only.
+        fileSystems."/nix/var/nix/builds" = {
+          device = "tmpfs";
+          fsType = "tmpfs";
+          options = [
+            "size=40G" # adjust for your situation and needs
+            "mode=700"
+          ];
+        };
+      }
+    ]
+  );
+}