Make workflow-basic-steps compatible with Guava 21.0 and newer

src/main/java/org/jenkinsci/plugins/workflow/steps/TimeoutStepExecution.java

@@ -17,9 +17,12 @@
 import java.io.Serializable;
 import java.lang.ref.Reference;
 import java.lang.ref.WeakReference;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
 import java.util.List;
 import java.util.UUID;
 import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
 import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
@@ -188,7 +191,7 @@ private void cancel() {
                             LOGGER.log(Level.WARNING, null, x);
                         }
                     }
-                }, MoreExecutors.sameThreadExecutor());
+                }, newExecutorService());
             }
         } else {
             listener().getLogger().println("Cancelling nested steps due to timeout");
@@ -199,6 +202,30 @@ private void cancel() {
         }
     }
 
+    /**
+     * Returns an {@link ExecutorService} to be used as a parameter in other methods. It calls
+     * {@code MoreExecutors#newDirectExecutorService} or falls back to {@code
+     * MoreExecutors#sameThreadExecutor} for compatibility with older (< 18.0) versions of Guava.
+     *
+     * @since TODO
+     */
+    private static ExecutorService newExecutorService() {
+        try {
+            try {
+                // Guava older than 18
+                Method method = MoreExecutors.class.getMethod("sameThreadExecutor");
+                return (ExecutorService) method.invoke(null);
+            } catch (NoSuchMethodException e) {
+                // TODO Invert this to prefer the newer Guava method once Guava is upgraded in
+                // Jenkins core.
+                Method method = MoreExecutors.class.getMethod("newDirectExecutorService");
+                return (ExecutorService) method.invoke(null);
+            }
+        } catch (IllegalAccessException | InvocationTargetException | NoSuchMethodException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
     @Override public String getStatus() {
         if (killer == null) {
             return "killer task nowhere to be found";