From 5fb4e1e674de000d66fcf448807c6f977ace0f74 Mon Sep 17 00:00:00 2001
From: Stanislav Lashmanov <slashmanov@gitlab.com>
Date: Sun, 7 Dec 2025 22:51:05 +0400
Subject: [PATCH] Provide code review ID for diff files

The ID will be the source of truth for marking files as viewed during MR code review
---
 app/serializers/diff_file_entity.rb                | 1 +
 app/serializers/diff_file_metadata_entity.rb       | 1 +
 lib/gitlab/diff/file.rb                            | 5 +++++
 spec/lib/gitlab/diff/file_spec.rb                  | 6 ++++++
 spec/serializers/diff_file_entity_spec.rb          | 4 ++++
 spec/serializers/diff_file_metadata_entity_spec.rb | 1 +
 6 files changed, 18 insertions(+)

diff --git a/app/serializers/diff_file_entity.rb b/app/serializers/diff_file_entity.rb
index d575fbf32c1cf2..fe9b22ad0d965e 100644
--- a/app/serializers/diff_file_entity.rb
+++ b/app/serializers/diff_file_entity.rb
@@ -8,6 +8,7 @@ class DiffFileEntity < DiffFileBaseEntity
 
   expose :added_lines
   expose :removed_lines
+  expose :code_review_id
 
   expose :load_collapsed_diff_url, if: ->(diff_file, options) { options[:merge_request] } do |diff_file|
     merge_request = options[:merge_request]
diff --git a/app/serializers/diff_file_metadata_entity.rb b/app/serializers/diff_file_metadata_entity.rb
index 772b549314e149..ac22fadfb50230 100644
--- a/app/serializers/diff_file_metadata_entity.rb
+++ b/app/serializers/diff_file_metadata_entity.rb
@@ -12,4 +12,5 @@ class DiffFileMetadataEntity < Grape::Entity
   expose :submodule?, as: :submodule
   expose :file_identifier_hash
   expose :file_hash
+  expose :code_review_id
 end
diff --git a/lib/gitlab/diff/file.rb b/lib/gitlab/diff/file.rb
index 3f6ada6e60b23a..2d46c4bc829370 100644
--- a/lib/gitlab/diff/file.rb
+++ b/lib/gitlab/diff/file.rb
@@ -262,6 +262,11 @@ def file_identifier_hash
         Digest::SHA1.hexdigest(file_identifier)
       end
 
+      def code_review_id
+        Digest::SHA1.hexdigest("#{file_identifier}-#{blob&.id}")
+      end
+      strong_memoize_attr :code_review_id
+
       def diffable?
         diffable_by_attribute? && !text_with_binary_notice?
       end
diff --git a/spec/lib/gitlab/diff/file_spec.rb b/spec/lib/gitlab/diff/file_spec.rb
index 4c44779a4bd326..64fe394cdb3a28 100644
--- a/spec/lib/gitlab/diff/file_spec.rb
+++ b/spec/lib/gitlab/diff/file_spec.rb
@@ -455,6 +455,12 @@ def delete_file(file_name)
     end
   end
 
+  describe '#code_review_id' do
+    it 'returns a hash' do
+      expect(diff_file.code_review_id).to match(/\A[0-9a-f]{40}\z/)
+    end
+  end
+
   context 'diff file stats' do
     let(:diff_file) do
       described_class.new(diff, diff_refs: commit.diff_refs, repository: project.repository, stats: stats)
diff --git a/spec/serializers/diff_file_entity_spec.rb b/spec/serializers/diff_file_entity_spec.rb
index 2aeffecbcc828e..01b455c08b40ec 100644
--- a/spec/serializers/diff_file_entity_spec.rb
+++ b/spec/serializers/diff_file_entity_spec.rb
@@ -90,5 +90,9 @@
     end
   end
 
+  it 'exposes code_review_id' do
+    expect(subject[:code_review_id]).to match(/\A[0-9a-f]{40}\z/)
+  end
+
   it_behaves_like 'diff file with conflict_type'
 end
diff --git a/spec/serializers/diff_file_metadata_entity_spec.rb b/spec/serializers/diff_file_metadata_entity_spec.rb
index 7e8695b10f0d08..d4a55a8a4260d0 100644
--- a/spec/serializers/diff_file_metadata_entity_spec.rb
+++ b/spec/serializers/diff_file_metadata_entity_spec.rb
@@ -22,6 +22,7 @@
         :submodule,
         :file_identifier_hash,
         :file_hash,
+        :code_review_id,
         :conflict_type
       )
     end
-- 
GitLab