From d2766e6671952e74231b0aaf21a8eac324a05d34 Mon Sep 17 00:00:00 2001
From: Daniel Morton <daniel.morton@shopify.com>
Date: Wed, 18 Mar 2020 16:18:37 -0400
Subject: [PATCH] Log when enumerator has nothing to iterate

---
 lib/job-iteration/iteration.rb         | 7 +++++++
 test/unit/active_job_iteration_test.rb | 9 +++++++++
 2 files changed, 16 insertions(+)

diff --git a/lib/job-iteration/iteration.rb b/lib/job-iteration/iteration.rb
index b53fc749..739a6d3e 100644
--- a/lib/job-iteration/iteration.rb
+++ b/lib/job-iteration/iteration.rb
@@ -116,8 +116,10 @@ def interruptible_perform(*arguments)
 
     def iterate_with_enumerator(enumerator, arguments)
       arguments = arguments.dup.freeze
+      found_record = false
       enumerator.each do |object_from_enumerator, index|
         record_unit_of_work do
+          found_record = true
           each_iteration(object_from_enumerator, *arguments)
           self.cursor_position = index
         end
@@ -128,6 +130,11 @@ def iterate_with_enumerator(enumerator, arguments)
         return false
       end
 
+      logger.info(
+        "[JobIteration::Iteration] Enumerator found nothing to iterate! " \
+        "(times_interrupted: #{times_interrupted}, cursor_position: #{cursor_position})"
+      ) unless found_record
+
       true
     end
 
diff --git a/test/unit/active_job_iteration_test.rb b/test/unit/active_job_iteration_test.rb
index 543ee59d..44d5e939 100644
--- a/test/unit/active_job_iteration_test.rb
+++ b/test/unit/active_job_iteration_test.rb
@@ -585,6 +585,15 @@ def test_log_completion_data
       end
     end
 
+    def test_log_no_iterations
+      Product.delete_all
+      push(ActiveRecordIterationJob)
+
+      assert_logged(%([JobIteration::Iteration] Enumerator found nothing to iterate!)) do
+        work_one_job
+      end
+    end
+
     def test_aborting_in_each_iteration_job_will_execute_on_complete_callback
       push(AbortingActiveRecordIterationJob)
       work_one_job