Create framework for build prerequisites

Introduces the concept of Prerequisites for a CI build.
If a build has unmet prerequisites it will go through the
:preparing state before being made available to a runner.

There are no actual prerequisites yet, so current
behaviour is unchanged.

3 files changed, 68 insertions, 1 deletions

diff --git a/spec/models/ci/build_spec.rb b/spec/models/ci/build_spec.rb
index 9ca4241d7d8..b31c4fcceb3 100644
--- a/spec/models/ci/build_spec.rb
+++ b/spec/models/ci/build_spec.rb
@@ -186,6 +186,37 @@ describe Ci::Build do
     end
   end
 
+  describe '#enqueue' do
+    let(:build) { create(:ci_build, :created) }
+
+    subject { build.enqueue }
+
+    before do
+      allow(build).to receive(:any_unmet_prerequisites?).and_return(has_prerequisites)
+      allow(Ci::PrepareBuildService).to receive(:perform_async)
+    end
+
+    context 'build has unmet prerequisites' do
+      let(:has_prerequisites) { true }
+
+      it 'transitions to preparing' do
+        subject
+
+        expect(build).to be_preparing
+      end
+    end
+
+    context 'build has no prerequisites' do
+      let(:has_prerequisites) { false }
+
+      it 'transitions to pending' do
+        subject
+
+        expect(build).to be_pending
+      end
+    end
+  end
+
   describe '#actionize' do
     context 'when build is a created' do
       before do
@@ -344,6 +375,18 @@ describe Ci::Build do
 
         expect(build).to be_pending
       end
+
+      context 'build has unmet prerequisites' do
+        before do
+          allow(build).to receive(:prerequisites).and_return([double])
+        end
+
+        it 'transits to preparing' do
+          subject
+
+          expect(build).to be_preparing
+        end
+      end
     end
   end
 
@@ -2928,6 +2971,20 @@ describe Ci::Build do
     end
   end
 
+  describe 'state transition: any => [:preparing]' do
+    let(:build) { create(:ci_build, :created) }
+
+    before do
+      allow(build).to receive(:prerequisites).and_return([double])
+    end
+
+    it 'queues BuildPrepareWorker' do
+      expect(Ci::BuildPrepareWorker).to receive(:perform_async).with(build.id)
+
+      build.enqueue
+    end
+  end
+
   describe 'state transition: any => [:pending]' do
     let(:build) { create(:ci_build, :created) }
 
diff --git a/spec/models/ci/pipeline_spec.rb b/spec/models/ci/pipeline_spec.rb
index d35caac33dc..2ac056f63b2 100644
--- a/spec/models/ci/pipeline_spec.rb
+++ b/spec/models/ci/pipeline_spec.rb
@@ -1804,7 +1804,11 @@ describe Ci::Pipeline, :mailer do
 
     context 'on prepare' do
       before do
-        build.prepare
+        # Prevent skipping directly to 'pending'
+        allow(build).to receive(:prerequisites).and_return([double])
+        allow(Ci::BuildPrepareWorker).to receive(:perform_async)
+
+        build.enqueue
       end
 
       it { is_expected.to eq('preparing') }
diff --git a/spec/models/commit_status_spec.rb b/spec/models/commit_status_spec.rb
index 1d241bf6000..e2b7f5c6ee2 100644
--- a/spec/models/commit_status_spec.rb
+++ b/spec/models/commit_status_spec.rb
@@ -489,6 +489,12 @@ describe CommitStatus do
 
       it { is_expected.to be_script_failure }
     end
+
+    context 'when failure_reason is unmet_prerequisites' do
+      let(:reason) { :unmet_prerequisites }
+
+      it { is_expected.to be_unmet_prerequisites }
+    end
   end
 
   describe 'ensure stage assignment' do