Implement presenter for pipeline failure reason

app/presenters/ci/pipeline_presenter.rb

 module Ci
   class PipelinePresenter < Gitlab::View::Presenter::Delegated
+    prepend ::EE::Ci::PipelinePresenter
+
     presents :pipeline
 
     def status_title

app/serializers/pipeline_entity.rb

@@ -44,6 +44,8 @@ class PipelineEntity < Grape::Entity
   end
 
   expose :commit, using: CommitEntity
+  expose :yaml_errors, if: -> (pipeline, _) { pipeline.has_yaml_errors? }
+  expose :failure_reason, if: -> (pipeline, _) { pipeline.failure_reason? }
 
   expose :retry_path, if: -> (*) { can_retry? }  do |pipeline|
     retry_project_pipeline_path(pipeline.project, pipeline)
@@ -53,8 +55,6 @@ class PipelineEntity < Grape::Entity
     cancel_project_pipeline_path(pipeline.project, pipeline)
   end
 
-  expose :yaml_errors, if: -> (pipeline, _) { pipeline.has_yaml_errors? }
-
   private
 
   alias_method :pipeline, :object

config/application.rb

@@ -45,6 +45,7 @@ module Gitlab
       #{config.root}/ee/app/models/concerns
       #{config.root}/ee/app/policies
       #{config.root}/ee/app/serializers
+      #{config.root}/ee/app/presenters
       #{config.root}/ee/app/services
       #{config.root}/ee/app/workers
     ])

ee/app/presenters/ee/ci/pipeline_presenter.rb

+module EE
+  module Ci
+    module PipelinePresenter
+      FAILURE_REASONS = {
+        activity_limit_exceeded: 'Pipeline activity limit exceeded!',
+        size_limit_exceeded: 'Pipeline size limit exceeded!'
+      }
+
+      def failure_reason
+        return unless pipeline.failure_reason?
+
+        FAILURE_REASONS[pipeline.failure_reason.to_sym] ||
+          pipeline.failure_reason
+      end
+    end
+  end
+end

spec/ee/spec/presenters/ci/pipeline_presenter_spec.rb

+require 'spec_helper'
+
+describe Ci::PipelinePresenter do
+  set(:project) { create(:project) }
+  set(:pipeline) { create(:ci_pipeline, project: project) }
+
+  subject(:presenter) do
+    described_class.new(pipeline)
+  end
+
+  context '#failure_reason' do
+    context 'when pipeline has failure reason' do
+      it 'represents a failure reason sentence' do
+        pipeline.failure_reason = :activity_limit_exceeded
+
+        expect(presenter.failure_reason)
+          .to eq 'Pipeline activity limit exceeded!'
+      end
+    end
+
+    context 'when pipeline does not have failure reason' do
+      it 'returns nil' do
+        expect(presenter.failure_reason).to be_nil
+      end
+    end
+  end
+end