API for MR Jira Issue association

Adds an api for MR <> Jira association.
If the Project of the MR requires Jira Issue
before merge, the Api returns if
reference to Jira Issue has been mentioned in
the MR title or description.

ee/lib/api/entities/merge_request_jira_issue.rb

+# frozen_string_literal: true
+
+module API
+  module Entities
+    class MergeRequestJiraIssue < Grape::Entity
+      expose :is_present do |merge_request|
+        Atlassian::JiraIssueKeyExtractor.has_keys?(merge_request.title, merge_request.description)
+      end
+    end
+  end
+end

ee/lib/api/merge_request_jira_issue.rb

+# frozen_string_literal: true
+
+module API
+  class MergeRequestJiraIssue < ::API::Base
+    before { authenticate_non_get! }
+    before { check_jira_issue_feature_available! }
+
+    feature_category :source_code_management
+
+    helpers do
+      def check_jira_issue_feature_available!
+        not_found! unless user_project.jira_issue_association_required_to_merge_enabled?
+      end
+
+      def present_jira_issue(merge_request)
+        present merge_request, with: ::API::Entities::MergeRequestJiraIssue, current_user: current_user
+      end
+    end
+
+    resource :projects, requirements: ::API::API::NAMESPACE_OR_PROJECT_REQUIREMENTS do
+      segment ':id/merge_requests/:merge_request_iid' do
+        # Get the Jira Issue association for a merge request
+        #
+        # Parameters:
+        #   id (required)                 - The ID of a project
+        #   merge_request_iid (required)  - IID of MR
+        # Examples:
+        #   GET /projects/:id/merge_requests/:merge_request_iid/jira_issue
+        desc 'Get Jira Issue association for merge request'
+        get 'jira_issue' do
+          forbidden! unless can?(current_user, :read_merge_request, user_project)
+          not_found! unless user_project.project_setting.prevent_merge_without_jira_issue
+
+          merge_request = find_merge_request_with_access(params[:merge_request_iid])
+
+          present_jira_issue(merge_request)
+        end
+      end
+    end
+  end
+end

ee/lib/ee/api/api.rb

@@ -39,6 +39,7 @@ module EE
         mount ::API::VulnerabilityIssueLinks
         mount ::API::VulnerabilityExports
         mount ::API::MergeRequestApprovalRules
+        mount ::API::MergeRequestJiraIssue
         mount ::API::ProjectAliases
         mount ::API::Dependencies
         mount ::API::VisualReviewDiscussions

ee/spec/requests/api/merge_request_jira_issue_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe API::MergeRequestJiraIssue do
+  let_it_be(:user) { create(:user) }
+  let_it_be(:project) { create(:project, :public, :repository, creator: user) }
+  let_it_be_with_reload(:merge_request) { create(:merge_request, author: user, source_project: project, target_project: project) }
+
+  describe 'GET /projects/:id/merge_requests/:merge_request_iid/jira_issue' do
+    let(:url) { "/projects/#{project.id}/merge_requests/#{merge_request.iid}/jira_issue" }
+
+    subject { get api(url, current_user) }
+
+    shared_examples 'not found' do
+      specify do
+        subject
+
+        expect(response).to have_gitlab_http_status(:not_found)
+      end
+    end
+
+    context 'when feature is available' do
+      before do
+        stub_licensed_features(jira_issue_association_enforcement: true)
+        stub_feature_flags(jira_issue_association_on_merge_request: true)
+      end
+
+      context 'user does not have access' do
+        let_it_be(:unauthorized_user) { create(:user) }
+        let(:current_user) { unauthorized_user }
+
+        before do
+          project.project_feature.update!(merge_requests_access_level: ProjectFeature::PRIVATE)
+        end
+
+        it 'responds with forbidden' do
+          subject
+
+          expect(response).to have_gitlab_http_status(:forbidden)
+        end
+      end
+
+      context 'user has access' do
+        let(:current_user) { user }
+
+        context 'when jira issue is not required for merge' do
+          before do
+            project.create_project_setting(prevent_merge_without_jira_issue: false)
+          end
+
+          it_behaves_like 'not found'
+        end
+
+        context 'when jira issue is required for merge' do
+          before do
+            project.create_project_setting(prevent_merge_without_jira_issue: true)
+          end
+
+          it 'responds with not found' do
+            subject
+
+            expect(response).to have_gitlab_http_status(:ok)
+          end
+
+          context 'when Jira issue is not provided in MR title/description' do
+            it 'responds with not found' do
+              subject
+
+              expect(json_response["is_present"]).to eq(false)
+            end
+          end
+
+          context 'when Jira issue is provided in MR title' do
+            before do
+              merge_request.update!(title: 'Fix PRODUCT-1234')
+            end
+
+            it 'responds with not found' do
+              subject
+
+              expect(json_response["is_present"]).to eq(true)
+            end
+          end
+
+          context 'when Jira issue is provided in MR description' do
+            before do
+              merge_request.update!(description: 'Jira issue associated: PRODUCT-1234')
+            end
+
+            it 'responds with not found' do
+              subject
+
+              expect(json_response["is_present"]).to eq(true)
+            end
+          end
+        end
+      end
+    end
+
+    context 'when feature is not available' do
+      using RSpec::Parameterized::TableSyntax
+
+      let(:current_user) { user }
+
+      where(:licensed, :feature_flag) do
+        false | true
+        true  | false
+        false | false
+      end
+
+      with_them do
+        before do
+          stub_licensed_features(jira_issue_association_enforcement: licensed)
+          stub_feature_flags(jira_issue_association_on_merge_request: feature_flag)
+        end
+
+        it_behaves_like 'not found'
+      end
+    end
+  end
+end