nixos/jenkinsSlave: install java

Installs Java into the Jenkins agent and allows specifying the JDK/JRE package to use. This is necessary as Jenkins verifies if the agent contains Java installed through the java -fullversion command, which if not, the connection will fail.

nixos/modules/services/continuous-integration/jenkins/slave.nix

@@ -1,4 +1,4 @@
-{ config, lib, ... }:
+{ config, lib, pkgs, ... }:
 with lib;
 let
   cfg = config.services.jenkinsSlave;
@@ -46,6 +46,15 @@ in {
           this is the home of the "jenkins" user.
         '';
       };
+
+      javaPackage = mkOption {
+        default = pkgs.jdk;
+        defaultText = literalExpression "pkgs.jdk";
+        description = ''
+          Java package to install.
+        '';
+        type = types.package;
+      };
     };
   };
 
@@ -64,5 +73,10 @@ in {
         uid = config.ids.uids.jenkins;
       };
     };
+
+    programs.java = {
+      enable = true;
+      package = cfg.javaPackage;
+    };
   };
 }

nixos/tests/jenkins.nix

@@ -90,6 +90,8 @@ import ./make-test-python.nix ({ pkgs, ...} : {
 
     slave.fail("systemctl is-enabled jenkins.service")
 
+    slave.succeed("java -fullversion")
+
     with subtest("jobs are declarative"):
         # Check that jobs are created on disk.
         master.wait_for_unit("jenkins-job-builder")