Expose items for suggesting a pipeline

- this is an incrimental MR that will expose a few objects
  needed for suggesting a pipeline in the front end

app/models/project.rb

@@ -2299,6 +2299,10 @@ class Project < ApplicationRecord
     false
   end
 
+  def uses_default_ci_config?
+    ci_config_path.blank? || ci_config_path == Gitlab::FileDetector::PATTERNS[:gitlab_ci]
+  end
+
   private
 
   def closest_namespace_setting(name)

app/serializers/merge_request_widget_entity.rb

@@ -50,6 +50,19 @@ class MergeRequestWidgetEntity < Grape::Entity
     ci_environments_status_project_merge_request_path(merge_request.project, merge_request)
   end
 
+  expose :merge_request_add_ci_config_path, if: ->(mr, _) { can_add_ci_config_path?(mr) } do |merge_request|
+    project_new_blob_path(
+      merge_request.source_project,
+      merge_request.source_branch,
+      file_name: '.gitlab-ci.yml',
+      commit_message: s_("CommitMessage|Add %{file_name}") % { file_name: Gitlab::FileDetector::PATTERNS[:gitlab_ci] }
+    )
+  end
+
+  expose :human_access do |merge_request|
+    merge_request.project.team.human_max_access(current_user&.id)
+  end
+
   # Rendering and redacting Markdown can be expensive. These links are
   # just nice to have in the merge request widget, so only
   # include them if they are explicitly requested on first load.
@@ -75,6 +88,13 @@ class MergeRequestWidgetEntity < Grape::Entity
     @presenters ||= {}
     @presenters[merge_request] ||= MergeRequestPresenter.new(merge_request, current_user: current_user) # rubocop: disable CodeReuse/Presenter
   end
+
+  def can_add_ci_config_path?(merge_request)
+    merge_request.source_project&.uses_default_ci_config? &&
+      merge_request.all_pipelines.none? &&
+      merge_request.commits_count.positive? &&
+      can?(current_user, :push_code, merge_request.source_project)
+  end
 end
 
 MergeRequestWidgetEntity.prepend_if_ee('EE::MergeRequestWidgetEntity')

spec/models/project_spec.rb

@@ -2095,6 +2095,28 @@ describe Project do
     end
   end
 
+  describe '#uses_default_ci_config?' do
+    let(:project) { build(:project)}
+
+    it 'has a custom ci config path' do
+      project.ci_config_path = 'something_custom'
+
+      expect(project.uses_default_ci_config?).to be_falsey
+    end
+
+    it 'has a blank ci config path' do
+      project.ci_config_path = ''
+
+      expect(project.uses_default_ci_config?).to be_truthy
+    end
+
+    it 'does not have a custom ci config path' do
+      project.ci_config_path = nil
+
+      expect(project.uses_default_ci_config?).to be_truthy
+    end
+  end
+
   describe '#latest_successful_build_for_ref' do
     let(:project) { create(:project, :repository) }
     let(:pipeline) { create_pipeline(project) }

spec/serializers/merge_request_widget_entity_spec.rb

@@ -53,6 +53,94 @@ describe MergeRequestWidgetEntity do
       .to eq("/#{resource.project.full_path}/-/merge_requests/#{resource.iid}.diff")
   end
 
+  describe 'merge_request_add_ci_config_path' do
+    before do
+      project.add_role(user, role)
+    end
+
+    context 'when there are pipelines' do
+      let(:role) { :developer }
+
+      before do
+        create(:ci_empty_pipeline, project: project, sha: resource.all_commit_shas.first, ref: resource.source_branch)
+      end
+
+      it 'no ci config path' do
+        expect(subject[:merge_request_add_ci_config_path]).to be_nil
+      end
+    end
+
+    context 'when there are no pipelines' do
+      context 'when user has permissions' do
+        let(:role) { :developer }
+
+        it 'has add ci config path' do
+          expect(subject[:merge_request_add_ci_config_path])
+            .to eq("/#{resource.project.full_path}/-/new/#{resource.source_branch}?commit_message=Add+.gitlab-ci.yml&file_name=.gitlab-ci.yml")
+        end
+
+        context 'when source project is missing' do
+          before do
+            resource.source_project = nil
+          end
+
+          it 'returns a blank ci config path' do
+            expect(subject[:merge_request_add_ci_config_path]).to be_nil
+          end
+        end
+
+        context 'when there are no commits' do
+          before do
+            allow(resource).to receive(:commits_count).and_return(0)
+          end
+
+          it 'returns a blank ci config path' do
+            expect(subject[:merge_request_add_ci_config_path]).to be_nil
+          end
+        end
+
+        context 'when ci_config_path is customized' do
+          it 'has no path if ci_config_path is not set to our default setting' do
+            project.ci_config_path = 'not_default'
+
+            expect(subject[:merge_request_add_ci_config_path]).to be_nil
+          end
+
+          it 'has a path if ci_config_path unset' do
+            expect(subject[:merge_request_add_ci_config_path]).not_to be_nil
+          end
+
+          it 'has a path if ci_config_path is an empty string' do
+            project.ci_config_path = ''
+
+            expect(subject[:merge_request_add_ci_config_path]).not_to be_nil
+          end
+
+          it 'has a path if ci_config_path is set to our default file' do
+            project.ci_config_path = Gitlab::FileDetector::PATTERNS[:gitlab_ci]
+
+            expect(subject[:merge_request_add_ci_config_path]).not_to be_nil
+          end
+        end
+      end
+
+      context 'when user does not have permissions' do
+        let(:role) { :reporter }
+
+        it 'has add ci config path' do
+          expect(subject[:merge_request_add_ci_config_path]).to be_nil
+        end
+      end
+    end
+  end
+
+  it 'has human access' do
+    project.add_maintainer(user)
+
+    expect(subject[:human_access])
+      .to eq('Maintainer')
+  end
+
   describe 'when source project is deleted' do
     let(:project) { create(:project, :repository) }
     let(:forked_project) { fork_project(project) }