Add missing event trigger

luigi/worker.py

@@ -583,10 +583,11 @@ def _add(self, task, is_complete):
         else:
             try:
                 deps = task.deps()
-            except Exception:
+            except Exception as ex:
                 formatted_traceback = traceback.format_exc()
                 self.add_succeeded = False
                 self._log_dependency_error(task, formatted_traceback)
+                task.trigger_event(Event.BROKEN_TASK, task, ex)
                 self._email_dependency_error(task, formatted_traceback)
                 return
             status = PENDING

test/event_callbacks_test.py

@@ -36,6 +36,15 @@ def run(self):
             raise DummyException()
 
 
+class TaskWithBrokenDependency(Task):
+
+    def requires(self):
+        raise DummyException()
+
+    def run(self):
+        pass
+
+
 class TaskWithCallback(Task):
 
     def run(self):
@@ -88,6 +97,22 @@ def test_failure(self):
         self.assertEqual(len(exceptions), 1)
         self.assertTrue(isinstance(exceptions[0], DummyException))
 
+    def test_broken_dependency(self):
+        failures = []
+        exceptions = []
+
+        @TaskWithBrokenDependency.event_handler(Event.BROKEN_TASK)
+        def failure(task, exception):
+            failures.append(task)
+            exceptions.append(exception)
+
+        t = TaskWithBrokenDependency()
+        build([t], local_scheduler=True)
+
+        self.assertEqual(failures, [t])
+        self.assertEqual(len(exceptions), 1)
+        self.assertTrue(isinstance(exceptions[0], DummyException))
+
     def test_custom_handler(self):
         dummies = []