1 files changed, 33 insertions, 1 deletions
diff --git a/app/models/merge_request_diff.rb b/app/models/merge_request_diff.rb
index 24809141570..d23e66b9697 100644
--- a/app/models/merge_request_diff.rb
+++ b/app/models/merge_request_diff.rb
@@ -358,6 +358,7 @@ class MergeRequestDiff < ApplicationRecord
       if comparison
         comparison.diffs_in_batch(batch_page, batch_size, diff_options: diff_options)
       else
+        reorder_diff_files!
         diffs_in_batch_collection(batch_page, batch_size, diff_options: diff_options)
       end
     end
@@ -371,6 +372,7 @@ class MergeRequestDiff < ApplicationRecord
       if comparison
         comparison.diffs(diff_options)
       else
+        reorder_diff_files!
         diffs_collection(diff_options)
       end
     end
@@ -565,7 +567,7 @@ class MergeRequestDiff < ApplicationRecord
   end
 
   def build_merge_request_diff_files(diffs)
-    diffs.map.with_index do |diff, index|
+    sort_diffs(diffs).map.with_index do |diff, index|
       diff_hash = diff.to_hash.merge(
         binary: false,
         merge_request_diff_id: self.id,
@@ -678,6 +680,7 @@ class MergeRequestDiff < ApplicationRecord
 
         rows = build_merge_request_diff_files(diff_collection)
         create_merge_request_diff_files(rows)
+        new_attributes[:sorted] = true
         self.class.uncached { merge_request_diff_files.reset }
       end
 
@@ -719,6 +722,35 @@ class MergeRequestDiff < ApplicationRecord
       repo.keep_around(start_commit_sha, head_commit_sha, base_commit_sha)
     end
   end
+
+  def reorder_diff_files!
+    return unless sort_diffs?
+    return if sorted? || merge_request_diff_files.empty?
+
+    diff_files = sort_diffs(merge_request_diff_files)
+
+    diff_files.each_with_index do |diff_file, index|
+      diff_file.relative_order = index
+    end
+
+    transaction do
+      # The `merge_request_diff_files` table doesn't have an `id` column so
+      # we cannot use `Gitlab::Database::BulkUpdate`.
+      MergeRequestDiffFile.where(merge_request_diff_id: id).delete_all
+      MergeRequestDiffFile.bulk_insert!(diff_files)
+      update_column(:sorted, true)
+    end
+  end
+
+  def sort_diffs(diffs)
+    return diffs unless sort_diffs?
+
+    Gitlab::Diff::FileCollectionSorter.new(diffs).sort
+  end
+
+  def sort_diffs?
+    Feature.enabled?(:sort_diffs, project, default_enabled: false)
+  end
 end
 
 MergeRequestDiff.prepend_if_ee('EE::MergeRequestDiff')