Fail jobs if its dependency is missing

app/models/ci/build.rb

@@ -139,6 +139,12 @@ module Ci
           Ci::Build.retry(build, build.user)
         end
       end
+
+      before_transition any => [:running] do |build|
+        if !build.empty_dependencies? && build.dependencies.empty?
+          raise Gitlab::Ci::Error::MissingDependencies
+        end
+      end
     end
     def detailed_status(current_user)

app/models/commit_status.rb

@@ -43,7 +43,8 @@ class CommitStatus < ActiveRecord::Base
     script_failure: 1,
     api_failure: 2,
     stuck_or_timeout_failure: 3,
-    runner_system_failure: 4
+    runner_system_failure: 4,
+    missing_dependency_failure: 5
   }
   ##

app/services/ci/register_job_service.rb

@@ -54,6 +54,9 @@ module Ci
           # we still have to return 409 in the end,
           # to make sure that this is properly handled by runner.
           valid = false
+        rescue Gitlab::Ci::Error::MissingDependencies
+          build.drop!(:missing_dependency_failure)
+          valid = false
         end
       end

lib/gitlab/ci/error/missing_dependencies.rb

+module Gitlab
+  module Ci
+    module Error
+      class MissingDependencies < StandardError; end
+    end
+  end
+end

spec/lib/gitlab/ci/error/missing_dependencies_spec.rb

+require 'spec_helper'
+
+describe Gitlab::Ci::Error::MissingDependencies do
+  it { expect(described_class).to be < StandardError }
+end

spec/models/ci/build_spec.rb

@@ -1868,6 +1868,36 @@ describe Ci::Build do
     end
   end
+  describe 'state transition: any => [:running]' do
+    let(:build) { create(:ci_build, :pending, pipeline: pipeline, stage_idx: 1, options: options) }
+
+    context 'when "dependencies" keyword is not defined' do
+      let(:options) { {} }
+
+      it { expect { build.run! }.not_to raise_error }
+    end
+
+    context 'when "dependencies" keyword is empty' do
+      let(:options) { { dependencies: [] } }
+
+      it { expect { build.run! }.not_to raise_error }
+    end
+
+    context 'when "dependencies" keyword is specified' do
+      let(:options) { { dependencies: ['test'] } }
+
+      context 'when a depended job exists' do
+        let!(:pre_build) { create(:ci_build, pipeline: pipeline, name: 'test', stage_idx: 0) }
+
+        it { expect { build.run! }.not_to raise_error }
+      end
+
+      context 'when depended jobs do not exist' do
+        it { expect { build.run! }.to raise_error(Gitlab::Ci::Error::MissingDependencies) }
+      end
+    end
+  end
+
   describe 'state transition when build fails' do
     let(:service) { MergeRequests::AddTodoWhenBuildFailsService.new(project, user) }

spec/services/ci/register_job_service_spec.rb

@@ -276,6 +276,34 @@ module Ci
         end
       end
+      context 'when "dependencies" keyword is specified' do
+        let!(:pre_stage_job) { create(:ci_build, :success, pipeline: pipeline, name: job_name, stage_idx: 0) }
+
+        let!(:pending_job) do
+          create(:ci_build, :pending, pipeline: pipeline, stage_idx: 1, options: { dependencies: ['spec'] } )
+        end
+
+        let(:picked_job) { execute(specific_runner) }
+
+        context 'when a depended job exists' do
+          let(:job_name) { 'spec' }
+
+          it "picks the build" do
+            expect(picked_job).to eq(pending_job)
+          end
+        end
+
+        context 'when depended jobs do not exist' do
+          let(:job_name) { 'robocop' }
+
+          it 'does not pick the build and drops the build' do
+            expect(picked_job).to be_nil
+            expect(pending_job.reload).to be_failed
+            expect(pending_job).to be_missing_dependency_failure
+          end
+        end
+      end
+
       def execute(runner)
         described_class.new(runner).execute.build
       end