Use feature definitions for experiments api

- This is additive only, and generally an internal API.

ee/lib/api/experiments.rb

@@ -11,9 +11,7 @@ module API
         success EE::API::Entities::Experiment
       end
       get do
-        experiments = Gitlab::Experimentation::EXPERIMENTS.keys.map do |experiment_key|
-          { key: experiment_key, enabled: Gitlab::Experimentation.active?(experiment_key) }
-        end
+        experiments = Feature::Definition.definitions.values.select { |d| d.attributes[:type] == 'experiment' }
 
         present experiments, with: EE::API::Entities::Experiment, current_user: current_user
       end

ee/lib/ee/api/entities/experiment.rb

@@ -3,9 +3,24 @@
 module EE
   module API
     module Entities
-      class Experiment < Grape::Entity
-        expose :key
-        expose :enabled
+      class Experiment < ::API::Entities::Feature::Definition
+        expose :key do |definition|
+          definition.attributes[:name].gsub(/_experiment_percentage$/, '')
+        end
+
+        expose :enabled do |definition|
+          feature(definition).state != :off
+        end
+
+        expose :state do |definition|
+          feature(definition).state
+        end
+
+        private
+
+        def feature(definition)
+          @feature ||= ::Feature.get(definition.attributes[:name]) # rubocop:disable Gitlab/AvoidFeatureGet
+        end
       end
     end
   end

ee/spec/lib/ee/api/entities/experiment_spec.rb

@@ -3,12 +3,49 @@
 require 'spec_helper'
 
 RSpec.describe EE::API::Entities::Experiment do
-  describe '#as_json' do
-    let(:experiment) { { key: 'experiment_1', enabled: true } }
-    let(:entity) { described_class.new(experiment) }
+  let(:experiment) { Feature::Definition.get(:null_hypothesis) }
+  let(:entity) { described_class.new(experiment) }
 
-    subject { entity.as_json }
+  subject { entity.as_json }
 
-    it { is_expected.to match({ key: experiment[:key], enabled: experiment[:enabled] }) }
+  it do
+    is_expected.to match(
+      key: "null_hypothesis",
+      state: :off,
+      enabled: false,
+      name: "null_hypothesis",
+      introduced_by_url: "https://gitlab.com/gitlab-org/gitlab/-/merge_requests/45840",
+      rollout_issue_url: nil,
+      milestone: "13.7",
+      type: "experiment",
+      group: "group::adoption",
+      default_enabled: false
+    )
+  end
+
+  it "understands conditional state and what that means" do
+    Feature.enable_percentage_of_time(:null_hypothesis, 1)
+
+    expect(subject).to include(
+      state: :conditional,
+      enabled: true
+    )
+  end
+
+  it "understands state and what that means for if its enabled or not" do
+    Feature.enable_percentage_of_time(:null_hypothesis, 100)
+
+    expect(subject).to include(
+      state: :on,
+      enabled: true
+    )
+  end
+
+  it "truncates the name since some experiments include extra data in their feature flag name" do
+    experiment.attributes[:name] = 'foo_experiment_percentage'
+
+    expect(subject).to include(
+      key: 'foo'
+    )
   end
 end

ee/spec/requests/api/experiments_spec.rb

@@ -6,26 +6,21 @@ RSpec.describe API::Experiments do
   let_it_be(:user) { create(:user) }
   let_it_be(:group) { create(:group, name: 'GitLab.com', path: 'gitlab-com') }
 
+  let(:definition_yaml) { Rails.root.join('config', 'feature_flags', 'experiment', 'null_hypothesis.yml') }
+
   describe 'GET /experiments' do
     context 'when on .com' do
-      let(:experiments) do
-        {
-          experiment_1: {
-            tracking_category: 'something'
-          },
-          experiment_2: {
-            tracking_category: 'something_else'
-          }
-        }
-      end
-
       before do
-        skip_feature_flags_yaml_validation
-        skip_default_enabled_yaml_check
-        stub_const('Gitlab::Experimentation::EXPERIMENTS', experiments)
-        Feature.enable_percentage_of_time('experiment_1_experiment_percentage', 10)
-        Feature.disable('experiment_2_experiment_percentage')
         allow(Gitlab).to receive(:com?).and_return(true)
+
+        definition = YAML.load_file(definition_yaml).deep_symbolize_keys!
+        allow(Feature::Definition.definitions).to receive(:values).and_return([
+          Feature::Definition.new(definition_yaml.to_s, definition),
+          Feature::Definition.new(
+            "foo/non_experiment.yml",
+            definition.merge(type: 'development', name: 'non_experiment')
+          )
+        ])
       end
 
       it 'returns a 401 for anonymous users' do
@@ -49,23 +44,41 @@ RSpec.describe API::Experiments do
         expect(response).to have_gitlab_http_status(:forbidden)
       end
 
-      it 'returns the feature list for gitlab team members' do
-        expected_experiments = [
-          {
-            'key' => 'experiment_1',
-            'enabled' => true
-          },
-          {
-            'key' => 'experiment_2',
-            'enabled' => false
-          }
-        ]
-        group.add_developer(user)
-
-        get api('/experiments', user)
-
-        expect(response).to have_gitlab_http_status(:ok)
-        expect(json_response).to match_array(expected_experiments)
+      context 'for gitlab team members' do
+        before do
+          group.add_developer(user)
+        end
+
+        it 'returns the feature flag details' do
+          get api('/experiments', user)
+
+          expect(response).to have_gitlab_http_status(:ok)
+          expect(json_response).to include({
+            key: "null_hypothesis",
+            state: :off,
+            enabled: false,
+            name: "null_hypothesis",
+            introduced_by_url: "https://gitlab.com/gitlab-org/gitlab/-/merge_requests/45840",
+            rollout_issue_url: nil,
+            milestone: "13.7",
+            type: "experiment",
+            group: "group::adoption",
+            default_enabled: false
+          }.as_json)
+        end
+
+        it 'understands the state of the feature flag and what that means for an experiment' do
+          Feature.enable_percentage_of_actors(:null_hypothesis, 1)
+
+          get api('/experiments', user)
+
+          expect(response).to have_gitlab_http_status(:ok)
+          expect(json_response).to include(hash_including({
+            state: :conditional,
+            enabled: true,
+            name: "null_hypothesis"
+          }.as_json))
+        end
       end
     end