Expose head pipeline in the related merge requests

Expose head pipeline for the MR in the api when requesting
related merge requests for an issue and show a detailed
status for the pipeline, which would include:
details_path, favicon, group, icon, label, text, tooltip.

https://gitlab.com/gitlab-org/gitlab-ce/issues/57662#note_152023412

lib/api/entities.rb

@@ -690,6 +690,10 @@ module API
       # Deprecated
       expose :allow_collaboration, as: :allow_maintainer_to_push, if: -> (merge_request, _) { merge_request.for_fork? }
 
+      expose :reference do |merge_request, options|
+        merge_request.to_reference(options[:project])
+      end
+
       expose :web_url do |merge_request|
         Gitlab::UrlBuilder.build(merge_request)
       end
@@ -726,6 +730,8 @@ module API
         merge_request.metrics&.pipeline
       end
 
+      expose :head_pipeline, using: 'API::Entities::Pipeline'
+
       expose :diff_refs, using: Entities::DiffRefs
 
       # Allow the status of a rebase to be determined
@@ -1267,6 +1273,9 @@ module API
       expose :created_at, :updated_at, :started_at, :finished_at, :committed_at
       expose :duration
       expose :coverage
+      expose :detailed_status, using: DetailedStatusEntity do |pipeline, options|
+        pipeline.detailed_status(options[:current_user])
+      end
     end
 
     class PipelineSchedule < Grape::Entity

lib/api/issues.rb

@@ -310,7 +310,7 @@ module API
           .flatten
 
         present paginate(::Kaminari.paginate_array(merge_requests)),
-          with: Entities::MergeRequestBasic,
+          with: Entities::MergeRequest,
           current_user: current_user,
           project: user_project
       end

spec/fixtures/api/schemas/public_api/v4/merge_request.json

@@ -119,6 +119,12 @@
       "merge_status", "sha", "merge_commit_sha", "user_notes_count",
       "should_remove_source_branch", "force_remove_source_branch",
       "web_url", "squash"
-    ]
+    ],
+    "head_pipeline": {
+      "oneOf": [
+        { "type": "null" },
+        { "$ref": "pipeline/detail.json" }
+      ]
+    }
   }
 }

spec/fixtures/api/schemas/public_api/v4/pipeline/basic.json

@@ -13,6 +13,5 @@
     "ref": { "type": "string" },
     "status": { "type": "string" },
     "web_url": { "type": "string" }
-  },
-  "additionalProperties": false
+  }
 }

spec/fixtures/api/schemas/public_api/v4/pipeline/detail.json

+{
+  "type": "object",
+  "allOf": [
+    { "$ref": "basic.json" },
+    {
+      "properties": {
+        "before_sha": { "type": ["string", "null"] },
+        "tag": { "type": ["boolean"] },
+        "yaml_errors": { "type": ["string", "null"] },
+        "user": {
+          "anyOf": [
+            { "type": ["object", "null"] },
+            { "$ref": "../user/basic.json" }
+          ]
+        },
+        "created_at": { "type": ["date", "null"] },
+        "updated_at": { "type": ["date", "null"] },
+        "started_at": { "type": ["date", "null"] },
+        "finished_at": { "type": ["date", "null"] },
+        "committed_at": { "type": ["date", "null"] },
+        "duration": { "type": ["number", "null"] },
+        "coverage": { "type": ["string", "null"] },
+        "detailed_status": {
+          "oneOf": [
+            { "type": "null" },
+            { "$ref": "../../../status/ci_detailed_status.json" }
+          ]
+        }
+      }
+    }
+  ]
+}

spec/requests/api/merge_requests_spec.rb

@@ -729,6 +729,14 @@ describe API::MergeRequests do
   end
 
   describe "GET /projects/:id/merge_requests/:merge_request_iid" do
+    it 'matches json schema' do
+      merge_request = create(:merge_request, :with_test_reports, milestone: milestone1, author: user, assignee: user, source_project: project, target_project: project, title: "Test", created_at: base_time)
+      get api("/projects/#{project.id}/merge_requests/#{merge_request.iid}", user)
+
+      expect(response).to have_gitlab_http_status(200)
+      expect(response).to match_response_schema('public_api/v4/merge_request')
+    end
+
     it 'exposes known attributes' do
       create(:award_emoji, :downvote, awardable: merge_request)
       create(:award_emoji, :upvote, awardable: merge_request)

spec/requests/api/pipelines_spec.rb

@@ -399,6 +399,13 @@ describe API::Pipelines do
 
   describe 'GET /projects/:id/pipelines/:pipeline_id' do
     context 'authorized user' do
+      it 'exposes known attributes' do
+        get api("/projects/#{project.id}/pipelines/#{pipeline.id}", user)
+
+        expect(response).to have_gitlab_http_status(200)
+        expect(response).to match_response_schema('public_api/v4/pipeline/detail')
+      end
+
       it 'returns project pipelines' do
         get api("/projects/#{project.id}/pipelines/#{pipeline.id}", user)