moving the logic from core to an extension point implementation

core/src/main/java/hudson/model/Run.java

@@ -1878,33 +1878,6 @@ public abstract class Run <JobT extends Job<JobT,RunT>,RunT extends Run<JobT,Run
      */
     public EnvVars getEnvironment(TaskListener log) throws IOException, InterruptedException {
         EnvVars env = getCharacteristicEnvVars();
-        Computer c = Computer.currentComputer();
-        if (c!=null)
-            env = c.getEnvironment().overrideAll(env);
-        String rootUrl = Jenkins.getInstance().getRootUrl();
-        if(rootUrl!=null) {
-            env.put("JENKINS_URL", rootUrl);
-            env.put("HUDSON_URL", rootUrl); // Legacy compatibility
-            env.put("BUILD_URL", rootUrl+getUrl());
-            env.put("JOB_URL", rootUrl+getParent().getUrl());
-        }
-        
-        env.put("JENKINS_HOME", Jenkins.getInstance().getRootDir().getPath() );
-        env.put("HUDSON_HOME", Jenkins.getInstance().getRootDir().getPath() );   // legacy compatibility
-
-        Thread t = Thread.currentThread();
-        if (t instanceof Executor) {
-            Executor e = (Executor) t;
-            env.put("EXECUTOR_NUMBER",String.valueOf(e.getNumber()));
-	    if(e.getOwner() instanceof MasterComputer) {
-		env.put("NODE_NAME", "master");
-	    } else {
-	    	env.put("NODE_NAME",e.getOwner().getName());
-	    }
-            Node n = e.getOwner().getNode();
-            if (n!=null)
-                env.put("NODE_LABELS",Util.join(n.getAssignedLabels()," "));
-        }
 
         for (EnvironmentContributor ec : EnvironmentContributor.all())
             ec.buildEnvironmentFor(this,env,log);

core/src/main/java/jenkins/model/CoreEnvironmentContributor.java

+package jenkins.model;
+
+import hudson.EnvVars;
+import hudson.Extension;
+import hudson.Util;
+import hudson.model.Computer;
+import hudson.model.EnvironmentContributor;
+import hudson.model.Executor;
+import hudson.model.Node;
+import hudson.model.Run;
+import hudson.model.TaskListener;
+import jenkins.model.Jenkins.MasterComputer;
+
+import java.io.IOException;
+
+/**
+ * {@link EnvironmentContributor} that adds the basic set of environment variables that
+ * we've been exposing historically.
+ *
+ * @author Kohsuke Kawaguchi
+ */
+@Extension(ordinal=-100)
+public class CoreEnvironmentContributor extends EnvironmentContributor {
+    @Override
+    public void buildEnvironmentFor(Run r, EnvVars env, TaskListener listener) throws IOException, InterruptedException {
+        Computer c = Computer.currentComputer();
+        if (c!=null)
+            c.getEnvironment().overrideAll(env);
+
+        Jenkins j = Jenkins.getInstance();
+        String rootUrl = j.getRootUrl();
+        if(rootUrl!=null) {
+            env.put("JENKINS_URL", rootUrl);
+            env.put("HUDSON_URL", rootUrl); // Legacy compatibility
+            env.put("BUILD_URL", rootUrl+r.getUrl());
+            env.put("JOB_URL", rootUrl+r.getParent().getUrl());
+        }
+
+        String root = j.getRootDir().getPath();
+        env.put("JENKINS_HOME", root);
+        env.put("HUDSON_HOME", root);   // legacy compatibility
+
+        Thread t = Thread.currentThread();
+        if (t instanceof Executor) {
+            Executor e = (Executor) t;
+            env.put("EXECUTOR_NUMBER", String.valueOf(e.getNumber()));
+            if (e.getOwner() instanceof MasterComputer) {
+                env.put("NODE_NAME", "master");
+            } else {
+                env.put("NODE_NAME", e.getOwner().getName());
+            }
+            Node n = e.getOwner().getNode();
+            if (n != null)
+                env.put("NODE_LABELS", Util.join(n.getAssignedLabels(), " "));
+        }
+    }
+}