Add trigger information for job API

Create new entity called TriggerVariablesEnitity for trigger variables,
to aid reuseablity in the future.

Update JSON schema to include trigger information in the response.

Refactor rspec tests a bit to reduce duplication and for the `context`
to make sense.

closes https://gitlab.com/gitlab-org/gitlab-ce/issues/50989

app/models/ci/build.rb

@@ -40,6 +40,7 @@ module Ci
     delegate :url, to: :runner_session, prefix: true, allow_nil: true
     delegate :terminal_specification, to: :runner_session, allow_nil: true
     delegate :gitlab_deploy_token, to: :project
+    delegate :trigger_short_token, to: :trigger_request, allow_nil: true
 
     ##
     # The "environment" field for builds is a String, and is the unexpanded name!

app/models/ci/trigger_request.rb

@@ -8,6 +8,8 @@ module Ci
     belongs_to :pipeline, foreign_key: :commit_id
     has_many :builds
 
+    delegate :short_token, to: :trigger, prefix: true, allow_nil: true
+
     # We switched to Ci::PipelineVariable from Ci::TriggerRequest.variables.
     # Ci::TriggerRequest doesn't save variables anymore.
     validates :variables, absence: true

app/serializers/build_details_entity.rb

@@ -59,6 +59,12 @@ class BuildDetailsEntity < JobEntity
     raw_project_job_path(project, build)
   end
 
+  expose :trigger, if: -> (*) { build.trigger_request } do
+    expose :trigger_short_token, as: :short_token
+
+    expose :trigger_variables, as: :variables, using: TriggerVariableEntity
+  end
+
   private
 
   def build_failed_issue_options

app/serializers/trigger_variable_entity.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class TriggerVariableEntity < Grape::Entity
+  include RequestAwareEntity
+
+  expose :key, :value, :public
+end

changelogs/unreleased/50989-add-trigger-information-to-job-api.yml

@@ -0,0 +1,5 @@
+---
+title: Add trigger information in job API
+merge_request: 21495
+author:
+type: other

spec/controllers/projects/jobs_controller_spec.rb

@@ -208,6 +208,51 @@ describe Projects::JobsController, :clean_gitlab_redis_shared_state do
       end
     end
 
+    context 'when requesting JSON job is triggered' do
+      let!(:merge_request) { create(:merge_request, source_project: project) }
+      let(:trigger) { create(:ci_trigger, project: project) }
+      let(:trigger_request) { create(:ci_trigger_request, pipeline: pipeline, trigger: trigger) }
+      let(:job) { create(:ci_build, pipeline: pipeline, trigger_request: trigger_request) }
+
+      before do
+        project.add_developer(user)
+        sign_in(user)
+
+        allow_any_instance_of(Ci::Build).to receive(:merge_request).and_return(merge_request)
+      end
+
+      context 'with no variables' do
+        before do
+          get_show(id: job.id, format: :json)
+        end
+
+        it 'exposes trigger information' do
+          expect(response).to have_gitlab_http_status(:ok)
+          expect(response).to match_response_schema('job/job_details')
+          expect(json_response['trigger']['short_token']).to eq 'toke'
+          expect(json_response['trigger']['variables'].length).to eq 0
+        end
+      end
+
+      context 'with variables' do
+        before do
+          create(:ci_pipeline_variable, pipeline: pipeline, key: :TRIGGER_KEY_1, value: 'TRIGGER_VALUE_1')
+
+          get_show(id: job.id, format: :json)
+        end
+
+        it 'exposes trigger information and variables' do
+          expect(response).to have_gitlab_http_status(:ok)
+          expect(response).to match_response_schema('job/job_details')
+          expect(json_response['trigger']['short_token']).to eq 'toke'
+          expect(json_response['trigger']['variables'].length).to eq 1
+          expect(json_response['trigger']['variables'].first['key']).to eq "TRIGGER_KEY_1"
+          expect(json_response['trigger']['variables'].first['value']).to eq "TRIGGER_VALUE_1"
+          expect(json_response['trigger']['variables'].first['public']).to eq false
+        end
+      end
+    end
+
     def get_show(**extra_params)
       params = {
         namespace_id: project.namespace.to_param,

spec/fixtures/api/schemas/job/job_details.json

@@ -1,8 +1,11 @@
 {
-  "allOf": [{ "$ref": "job.json" }],
+  "allOf": [
+    { "$ref": "job.json" }
+  ],
   "description": "An extension of job.json with more detailed information",
   "properties": {
     "artifact": { "$ref": "artifact.json" },
-    "terminal_path": { "type": "string" }
+    "terminal_path": { "type": "string" },
+    "trigger": { "$ref": "trigger.json" }
   }
 }

spec/fixtures/api/schemas/job/trigger.json

@@ -0,0 +1,28 @@
+{
+  "type": "object",
+  "required": [
+    "short_token",
+    "variables"
+  ],
+  "properties": {
+    "short_token": { "type": "string" },
+    "variables": {
+      "type": "array",
+      "items": {
+        "type": "object",
+        "required": [
+          "key",
+          "value",
+          "public"
+        ],
+        "properties": {
+          "key": { "type": "string" },
+          "value": { "type": "string" },
+          "public": { "type": "boolean" }
+        },
+        "additionalProperties": false
+      }
+    }
+  },
+  "additionalProperties": false
+}