Expose if action is playable in JSON

To avoid a manual build action being played (resulting in a 404),
expose `playable?` in the JSON so the frontend can disable/hide the
play button if it's not playable.

app/assets/javascripts/environments/components/environment_item.js

@@ -141,6 +141,7 @@ export default {
           const parsedAction = {
             name: gl.text.humanize(action.name),
             play_path: action.play_path,
+            playable: action.playable,
           };
           return parsedAction;
         });

app/serializers/build_action_entity.rb

@@ -11,4 +11,6 @@ class BuildActionEntity < Grape::Entity
       build.project,
       build)
   end
+
+  expose :playable?, as: :playable
 end

app/serializers/build_entity.rb

@@ -16,6 +16,7 @@ class BuildEntity < Grape::Entity
     path_to(:play_namespace_project_build, build)
   end
+  expose :playable?, as: :playable
   expose :created_at
   expose :updated_at

spec/serializers/build_action_entity_spec.rb

@@ -17,5 +17,9 @@ describe BuildActionEntity do
     it 'contains path to the action play' do
       expect(subject[:path]).to include "builds/#{build.id}/play"
     end
+
+    it 'contains whether it is playable' do
+      expect(subject[:playable]).to eq build.playable?
+    end
   end
 end

spec/serializers/build_entity_spec.rb

@@ -18,6 +18,10 @@ describe BuildEntity do
     expect(subject).not_to include(/variables/)
   end
+  it 'contains whether it is playable' do
+    expect(subject[:playable]).to eq build.playable?
+  end
+
   it 'contains timestamps' do
     expect(subject).to include(:created_at, :updated_at)
   end