Update merge request's merge_commit for branch update

Analyze new commits graph to determine each commit's merge commit.

Fix "merged with [commit]" info for merge requests being merged
automatically by other actions.

Allow analyzing upto the relevant commit

3 files changed, 95 insertions, 0 deletions

diff --git a/spec/lib/gitlab/branch_push_merge_commit_analyzer_spec.rb b/spec/lib/gitlab/branch_push_merge_commit_analyzer_spec.rb
new file mode 100644
index 00000000000..45e182358df
--- /dev/null
+++ b/spec/lib/gitlab/branch_push_merge_commit_analyzer_spec.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::BranchPushMergeCommitAnalyzer do
+  let(:project) { create(:project, :repository) }
+  let(:oldrev) { 'merge-commit-analyze-before' }
+  let(:newrev) { 'merge-commit-analyze-after' }
+  let(:commits) { project.repository.commits_between(oldrev, newrev).reverse }
+
+  subject { described_class.new(commits) }
+
+  describe '#get_merge_commit' do
+    let(:expected_merge_commits) do
+      {
+        '646ece5cfed840eca0a4feb21bcd6a81bb19bda3' => '646ece5cfed840eca0a4feb21bcd6a81bb19bda3',
+        '29284d9bcc350bcae005872d0be6edd016e2efb5' => '29284d9bcc350bcae005872d0be6edd016e2efb5',
+        '5f82584f0a907f3b30cfce5bb8df371454a90051' => '29284d9bcc350bcae005872d0be6edd016e2efb5',
+        '8a994512e8c8f0dfcf22bb16df6e876be7a61036' => '29284d9bcc350bcae005872d0be6edd016e2efb5',
+        '689600b91aabec706e657e38ea706ece1ee8268f' => '29284d9bcc350bcae005872d0be6edd016e2efb5',
+        'db46a1c5a5e474aa169b6cdb7a522d891bc4c5f9' => 'db46a1c5a5e474aa169b6cdb7a522d891bc4c5f9'
+      }
+    end
+
+    it 'returns correct merge commit SHA for each commit' do
+      expected_merge_commits.each do |commit, merge_commit|
+        expect(subject.get_merge_commit(commit)).to eq(merge_commit)
+      end
+    end
+
+    context 'when relevant_commit_ids is provided' do
+      let(:relevant_commit_id) { '8a994512e8c8f0dfcf22bb16df6e876be7a61036' }
+      subject { described_class.new(commits, relevant_commit_ids: [relevant_commit_id]) }
+
+      it 'returns correct merge commit' do
+        expected_merge_commits.each do |commit, merge_commit|
+          subject = described_class.new(commits, relevant_commit_ids: [commit])
+          expect(subject.get_merge_commit(commit)).to eq(merge_commit)
+        end
+      end
+    end
+  end
+end
diff --git a/spec/services/merge_requests/refresh_service_spec.rb b/spec/services/merge_requests/refresh_service_spec.rb
index d29a1091d95..493d3eb7392 100644
--- a/spec/services/merge_requests/refresh_service_spec.rb
+++ b/spec/services/merge_requests/refresh_service_spec.rb
@@ -621,4 +621,53 @@ describe MergeRequests::RefreshService do
       @fork_build_failed_todo.reload
     end
   end
+
+  describe 'updating merge_commit' do
+    let(:service) { described_class.new(project, user) }
+    let(:user) { create(:user) }
+    let(:project) { create(:project, :repository) }
+
+    let(:oldrev) { TestEnv::BRANCH_SHA['merge-commit-analyze-before'] }
+    let(:newrev) { TestEnv::BRANCH_SHA['merge-commit-analyze-after'] } # Pretend branch is now updated
+
+    let!(:merge_request) do
+      create(
+        :merge_request,
+        source_project: project,
+        source_branch: 'merge-commit-analyze-after',
+        target_branch: 'merge-commit-analyze-before',
+        target_project: project,
+        merge_user: user
+      )
+    end
+
+    let!(:merge_request_side_branch) do
+      create(
+        :merge_request,
+        source_project: project,
+        source_branch: 'merge-commit-analyze-side-branch',
+        target_branch: 'merge-commit-analyze-before',
+        target_project: project,
+        merge_user: user
+      )
+    end
+
+    subject { service.execute(oldrev, newrev, 'refs/heads/merge-commit-analyze-before') }
+
+    it "updates merge requests' merge_commits" do
+      expect(Gitlab::BranchPushMergeCommitAnalyzer).to receive(:new).and_wrap_original do |original_method, commits|
+        expect(commits.map(&:id)).to eq(%w{646ece5cfed840eca0a4feb21bcd6a81bb19bda3 29284d9bcc350bcae005872d0be6edd016e2efb5 5f82584f0a907f3b30cfce5bb8df371454a90051 8a994512e8c8f0dfcf22bb16df6e876be7a61036 689600b91aabec706e657e38ea706ece1ee8268f db46a1c5a5e474aa169b6cdb7a522d891bc4c5f9})
+
+        original_method.call(commits)
+      end
+
+      subject
+
+      merge_request.reload
+      merge_request_side_branch.reload
+
+      expect(merge_request.merge_commit.id).to eq('646ece5cfed840eca0a4feb21bcd6a81bb19bda3')
+      expect(merge_request_side_branch.merge_commit.id).to eq('29284d9bcc350bcae005872d0be6edd016e2efb5')
+    end
+  end
 end
diff --git a/spec/support/helpers/test_env.rb b/spec/support/helpers/test_env.rb
index 1f00cdf7e92..d52c40ff4f1 100644
--- a/spec/support/helpers/test_env.rb
+++ b/spec/support/helpers/test_env.rb
@@ -54,6 +54,9 @@ module TestEnv
     'add_images_and_changes'             => '010d106',
     'update-gitlab-shell-v-6-0-1'        => '2f61d70',
     'update-gitlab-shell-v-6-0-3'        => 'de78448',
+    'merge-commit-analyze-before'        => '1adbdef',
+    'merge-commit-analyze-side-branch'   => '8a99451',
+    'merge-commit-analyze-after'         => '646ece5',
     '2-mb-file'                          => 'bf12d25',
     'before-create-delete-modify-move'   => '845009f',
     'between-create-delete-modify-move'  => '3f5f443',