Prevent commits from upstream repositories to be re-processed by forks

app/workers/process_commit_worker.rb

@@ -17,6 +17,7 @@ class ProcessCommitWorker
     project = Project.find_by(id: project_id)
 
     return unless project
+    return if commit_exists_in_upstream?(project, commit_hash)
 
     user = User.find_by(id: user_id)
 
@@ -76,4 +77,16 @@ class ProcessCommitWorker
 
     Commit.from_hash(hash, project)
   end
+
+  private
+
+  # Avoid to re-process commits messages that already exists in the upstream
+  # when project is forked. This will also prevent duplicated system notes.
+  def commit_exists_in_upstream?(project, commit_hash)
+    return false unless project.forked?
+
+    upstream_project = project.forked_from_project
+    commit_id = commit_hash.with_indifferent_access[:id]
+    upstream_project.commit(commit_id).present?
+  end
 end

changelogs/unreleased/issue_19262.yml

+---
+title: Prevent commits from upstream repositories to be re-processed by forks
+merge_request:
+author:

spec/workers/process_commit_worker_spec.rb

@@ -39,6 +39,18 @@ describe ProcessCommitWorker do
 
       worker.perform(project.id, user.id, commit.to_hash)
     end
+
+    context 'when commit already exists in upstream project' do
+      let(:forked) { create(:project, :public) }
+
+      it 'does not process commit message' do
+        create(:forked_project_link, forked_to_project: forked, forked_from_project: project)
+
+        expect(worker).not_to receive(:process_commit_message)
+
+        worker.perform(forked.id, user.id, forked.commit.to_hash)
+      end
+    end
   end
 
   describe '#process_commit_message' do