livebook: configurable package and extraPackages

Also fix examples to not include a semicolon in the .env file.

nixos/modules/services/development/livebook.md

@@ -18,7 +18,7 @@ which runs the server.
     port = 20123;
     # See note below about security
     environmentFile = pkgs.writeText "livebook.env" ''
-      LIVEBOOK_PASSWORD = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
+      LIVEBOOK_PASSWORD = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
     '';
   };
 }
@@ -37,3 +37,14 @@ A better approach would be to put the password in some secure
 user-readable location and set `environmentFile = /home/user/secure/livebook.env`.
 
 :::
+
+### Extra dependencies {#module-services-livebook-extra-dependencies}
+
+By default, the Livebook service is run with minimum dependencies, but
+some features require additional packages.  For example, the machine
+learning Kinos require `gcc` and `gnumake`.  To add these, use
+`extraPackages`:
+
+```
+services.livebook.extraPackages = with pkgs; [ gcc gnumake ];
+```

nixos/modules/services/development/livebook.nix

@@ -12,6 +12,8 @@ in
     # future, this can be changed to a system service.
     enableUserService = mkEnableOption "a user service for Livebook";
 
+    package = mkPackageOption pkgs "livebook" { };
+
     environmentFile = mkOption {
       type = types.path;
       description = lib.mdDoc ''
@@ -63,6 +65,15 @@ in
         }
       '';
     };
+
+    extraPackages = mkOption {
+      type = with types; listOf package;
+      default = [ ];
+      description = lib.mdDoc ''
+        Extra packages to make available to the Livebook service.
+      '';
+      example = literalExpression "with pkgs; [ gcc gnumake ]";
+    };
   };
 
   config = mkIf cfg.enableUserService {
@@ -79,9 +90,9 @@ in
               sname = cfg.erlang_node_short_name;
             } // cfg.options);
           in
-          "${pkgs.livebook}/bin/livebook server ${args}";
+            "${cfg.package}/bin/livebook server ${args}";
       };
-      path = [ pkgs.bash ];
+      path = [ pkgs.bash ] ++ cfg.extraPackages;
       wantedBy = [ "default.target" ];
     };
   };

nixos/tests/livebook-service.nix

@@ -11,7 +11,7 @@ import ./make-test-python.nix ({ lib, pkgs, ... }: {
         enableUserService = true;
         port = 20123;
         environmentFile = pkgs.writeText "livebook.env" ''
-          LIVEBOOK_PASSWORD = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
+          LIVEBOOK_PASSWORD = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
         '';
         options = {
           cookie = "chocolate chip";