Add a task to clean up workflow's closed projects

If something goes wrong during the run of a workflow and the error is
not correctly caught (yet), the workflow_run can stay in 'running'
status forever and the temporary project created by the workflow is not
removed as expected.

Apart from fixing the errors, we need to ensure we clean up those
projects. This rake task is introduced for that purpose.

As the artifacts were never created, we rely on the workflow_run's
payload information to get part of the project name (repository name and
the PR number).

src/api/lib/tasks/workflows.rake

@@ -0,0 +1,33 @@
+namespace :workflows do
+  desc 'Remove projects that were not closed as expected and set workflow run status to running'
+  task cleanup_non_closed_projects: :environment do
+    workflow_runs = WorkflowRun.where(status: 'running')
+                               .select do |workflow_run|
+                                 workflow_run.hook_event.in?(['pull_request', 'Merge Request Hook']) &&
+                                   workflow_run.hook_action.in?(['closed', 'close', 'merge'])
+                               end
+
+    puts "There are #{workflow_runs.count} workflow runs affected"
+
+    workflow_runs.each do |workflow_run|
+      projects = Project.where('name LIKE ?', "%#{target_project_name_postfix(workflow_run)}")
+
+      # If there is more than one project, we don't know which of them is the one related to the current
+      # workflow run (as we only can get the postfix, we don't have the full project name).
+      next if projects.count > 1
+
+      # If there is no project to remove (previously removed), the workflow run should change the status anyway.
+      User.get_default_admin.run_as { projects.first.destroy } if projects.count == 1
+      workflow_run.update(status: 'success')
+    rescue StandardError => e
+      Airbrake.notify("Failed to remove project created by the workflow: #{e}")
+      next
+    end
+  end
+end
+
+# If the name of the project created by the workflow is "home:Iggy:iggy:hello_world:PR-68", its postfix
+# is "iggy:hello_world:PR-68". This is the only information we can extract from the workflow_run.
+def target_project_name_postfix(workflow_run)
+  ":#{workflow_run.repository_name.tr('/', ':')}:PR-#{workflow_run.event_source_name}" if workflow_run.repository_name && workflow_run.event_source_name
+end

src/api/spec/lib/tasks/workflows_spec.rb

@@ -0,0 +1,76 @@
+require 'rails_helper'
+
+# rubocop:disable RSpec/DescribeClass
+RSpec.describe 'workflows' do
+  # rubocop:enable RSpec/DescribeClass
+  include_context 'rake'
+
+  let!(:admin_user) { create(:admin_user, login: 'Admin') }
+  let(:gitlab_request_headers) do
+    <<~END_OF_HEADERS
+      HTTP_X_GITLAB_EVENT: Merge Request Hook
+    END_OF_HEADERS
+  end
+  let(:github_request_payload_opened) do
+    <<~END_OF_REQUEST
+      {
+        "action": "opened",
+        "pull_request": {
+          "number": 1
+        },
+        "repository": {
+          "full_name": "iggy/hello_world"
+        }
+      }
+    END_OF_REQUEST
+  end
+  let(:github_request_payload_closed) do
+    <<~END_OF_REQUEST
+      {
+        "action": "closed",
+        "pull_request": {
+          "number": 2
+        },
+        "repository": {
+          "full_name": "iggy/hello_world"
+        }
+      }
+    END_OF_REQUEST
+  end
+  let(:gitlab_request_payload_merge) do
+    <<~END_OF_REQUEST
+      {
+        "object_kind": "merge_request",
+        "event_type": "merge_request",
+        "object_attributes": {
+          "iid": 3,
+          "action": "merge"
+        },
+        "repository": {
+          "name": "iggy/test"
+        }
+      }
+    END_OF_REQUEST
+  end
+
+  let!(:project_iggy_hello_world_pr1) { create(:project, name: 'home:Iggy:iggy:hello_world:PR-1') }
+  let!(:project_iggy_hello_world_pr2) { create(:project, name: 'home:Iggy:iggy:hello_world:PR-2') }
+  let!(:project_iggy_test_pr3) { create(:project, name: 'home:Iggy:iggy:test:PR-3') }
+
+  let!(:workflow_run_running_pr_opened) { create(:running_workflow_run, request_payload: github_request_payload_opened) }
+  let!(:workflow_run_succeeded_pr_opened) { create(:succeeded_workflow_run, request_payload: github_request_payload_opened) }
+  let!(:workflow_run_failed_pr_opened) { create(:failed_workflow_run, request_payload: github_request_payload_opened) }
+  let!(:workflow_run_running_pr_closed) { create(:running_workflow_run, request_payload: github_request_payload_closed) }
+  let!(:another_workflow_run_running_pr_closed) { create(:running_workflow_run, request_payload: github_request_payload_closed) }
+  let!(:workflow_run_running_pr_merge) { create(:running_workflow_run, request_headers: gitlab_request_headers, request_payload: gitlab_request_payload_merge) }
+
+  describe 'cleanup_non_closed_projects' do
+    let(:task) { 'workflows:cleanup_non_closed_projects' }
+
+    it { expect { rake_task.invoke }.to change(WorkflowRun.where(status: 'running'), :count).from(4).to(1) }
+
+    # The workflow runs defined above will create two target projects that should be deleted
+    # because the corresponding PR or MR are closed/merged.
+    it { expect { rake_task.invoke }.to change(Project, :count).from(3).to(1) }
+  end
+end