Bring in patch from Rails to expose public attr readers on BatchEnume…

…rator

app/jobs/concerns/maintenance_tasks/task_job_concern.rb

@@ -37,17 +37,14 @@ def build_enumerator(_run, cursor:)
       when ActiveRecord::Relation
         enumerator_builder.active_record_on_records(collection, cursor: cursor)
       when ActiveRecord::Batches::BatchEnumerator
-        if collection.instance_variable_get(:@start) ||
-          collection.instance_variable_get(:@finish)
+        if collection.start || collection.finish
           raise ArgumentError, "#{@task.class.name}#collection cannot support "\
             "a batch enumerator with the +start+ or +finish+ options."
         end
-        relation = collection.instance_variable_get(:@relation)
-        batch_size = collection.instance_variable_get(:@of)
         enumerator_builder.active_record_on_batch_relations(
-          relation,
+          collection.relation,
           cursor: cursor,
-          batch_size: batch_size,
+          batch_size: collection.batch_size,
         )
       when Array
         enumerator_builder.build_array_enumerator(collection, cursor: cursor)

lib/maintenance_tasks.rb

@@ -7,6 +7,8 @@
 require "job-iteration"
 require "maintenance_tasks/engine"
 
+require "patches/active_record_batch_enumerator"
+
 # The engine's namespace module. It provides isolation between the host
 # application's code and the engine-specific code. Top-level engine constants
 # and variables are defined under this module.

lib/patches/active_record_batch_enumerator.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+# TODO: Remove this patch once all supported Rails versions include the changes
+# upstream - https://github.com/rails/rails/pull/42312/commits/a031a43d969c87542c4ee8d0d338d55fcbb53376
+module ActiveRecordBatchEnumerator
+  # The primary key value from which the BatchEnumerator starts,
+  #   inclusive of the value.
+  attr_reader :start
+
+  # The primary key value at which the BatchEnumerator ends,
+  #   inclusive of the value.
+  attr_reader :finish
+
+  # The relation from which the BatchEnumerator yields batches.
+  attr_reader :relation
+
+  # The size of the batches yielded by the BatchEnumerator.
+  def batch_size
+    @of
+  end
+end
+
+ActiveRecord::Batches::BatchEnumerator.include(ActiveRecordBatchEnumerator)