Do not serialize a pipeline again when showing a build

This change makes it possible to avoid additional serialization of
entire pipeline when rendering a build details page. Instead we expose
more information from the build entity itself what is much cheaper than
serializing entire pipeline.

Additionally we do not need to serialize `latest?` flag, which involves
multiple Gitaly calls.

app/assets/javascripts/jobs/store/actions.js

@@ -184,16 +184,9 @@ export const receiveTraceError = ({ commit }) => {
 export const requestStages = ({ commit }) => commit(types.REQUEST_STAGES);
 export const fetchStages = ({ state, dispatch }) => {
   dispatch('requestStages');
-
-  axios
-    .get(`${state.job.pipeline_path}.json`)
-    .then(({ data }) => {
-      // Set selected stage
-      dispatch('receiveStagesSuccess', data.details.stages);
-      const selectedStage = data.details.stages.find(stage => stage.name === state.selectedStage);
+  dispatch('receiveStagesSuccess', state.job.pipeline.details.stages);
+  const selectedStage = state.job.pipeline.details.stages.find(stage => stage.name === state.selectedStage);
   dispatch('fetchJobsForStage', selectedStage);
-    })
-    .catch(() => dispatch('receiveStagesError'));
 };
 export const receiveStagesSuccess = ({ commit }, data) =>
   commit(types.RECEIVE_STAGES_SUCCESS, data);

app/serializers/build_details_entity.rb

@@ -8,11 +8,8 @@ class BuildDetailsEntity < JobEntity
   expose :stuck?, as: :stuck
   expose :user, using: UserEntity
   expose :runner, using: RunnerEntity
-
-  # expose :pipeline, using: PipelineEntity
-  expose :pipeline_path do |build|
-    project_pipeline_path(build.project, build.pipeline)
-  end
+  expose :metadata, using: BuildMetadataEntity
+  expose :pipeline, using: PipelineEntity
 
   expose :deployment_status, if: -> (*) { build.starts_environment? } do
     expose :deployment_status, as: :status
@@ -20,8 +17,6 @@ class BuildDetailsEntity < JobEntity
     expose :persisted_environment, as: :environment, with: EnvironmentEntity
   end
 
-  expose :metadata, using: BuildMetadataEntity
-
   expose :artifact, if: -> (*) { can?(current_user, :read_build, build) } do
     expose :download_path, if: -> (*) { build.artifacts? } do |build|
       download_project_job_artifacts_path(project, build)

app/serializers/pipeline_details_entity.rb

 # frozen_string_literal: true
 
 class PipelineDetailsEntity < PipelineEntity
+  expose :flags do
+    expose :latest?, as: :latest
+  end
+
   expose :details do
-    expose :ordered_stages, as: :stages, using: StageEntity
     expose :artifacts, using: BuildArtifactEntity
     expose :manual_actions, using: BuildActionEntity
     expose :scheduled_actions, using: BuildActionEntity

app/serializers/pipeline_entity.rb

@@ -20,7 +20,6 @@ class PipelineEntity < Grape::Entity
   end
 
   expose :flags do
-    expose :latest?, as: :latest
     expose :stuck?, as: :stuck
     expose :auto_devops_source?, as: :auto_devops
     expose :merge_request_event?, as: :merge_request
@@ -34,6 +33,7 @@ class PipelineEntity < Grape::Entity
 
   expose :details do
     expose :detailed_status, as: :status, with: DetailedStatusEntity
+    expose :ordered_stages, as: :stages, using: StageEntity
     expose :duration
     expose :finished_at
   end

spec/serializers/pipeline_entity_spec.rb

@@ -48,8 +48,8 @@ describe PipelineEntity do
       it 'contains flags' do
         expect(subject).to include :flags
         expect(subject[:flags])
-          .to include :latest, :stuck, :auto_devops,
-                      :yaml_errors, :retryable, :cancelable, :merge_request
+          .to include :stuck, :auto_devops, :yaml_errors,
+                      :retryable, :cancelable, :merge_request
       end
     end