Make experiments API a filter of features API

- adds gates info with percentage

Changelog: changed
EE: true

doc/api/experiments.md

@@ -29,12 +29,50 @@ Example response:
 ```json
 [
   {
-      "key": "experiment_1",
-      "enabled": true
+    "key": "code_quality_walkthrough",
+    "definition": {
+      "name": "code_quality_walkthrough",
+      "introduced_by_url": "https://gitlab.com/gitlab-org/gitlab/-/merge_requests/58900",
+      "rollout_issue_url": "https://gitlab.com/gitlab-org/gitlab/-/issues/327229",
+      "milestone": "13.12",
+      "type": "experiment",
+      "group": "group::activation",
+      "default_enabled": false
     },
+    "current_status": {
+      "state": "conditional",
+      "gates": [
         {
-      "key": "experiment_2",
-      "enabled": false
+          "key": "boolean",
+          "value": false
+        },
+        {
+          "key": "percentage_of_actors",
+          "value": 25
+        }
+      ]
+    }
+  },
+  {
+    "key": "ci_runner_templates",
+    "definition": {
+      "name": "ci_runner_templates",
+      "introduced_by_url": "https://gitlab.com/gitlab-org/gitlab/-/merge_requests/58357",
+      "rollout_issue_url": "https://gitlab.com/gitlab-org/gitlab/-/issues/326725",
+      "milestone": "14.0",
+      "type": "experiment",
+      "group": "group::activation",
+      "default_enabled": false
+    },
+    "current_status": {
+      "state": "off",
+      "gates": [
+        {
+          "key": "boolean",
+          "value": false
+        }
+      ]
+    }
   }
 ]
 ```

ee/lib/api/experiments.rb

@@ -15,7 +15,9 @@ module API
 
         experiment(:null_hypothesis, canary: true, user: current_user) do |e|
           e.use { bad_request! 'experimentation may not be working right now' }
-          e.try { experiments = Feature::Definition.definitions.values.select { |d| d.attributes[:type] == 'experiment' } }
+          e.try do
+            experiments = Feature::Definition.definitions.values.select { |d| d.attributes[:type] == 'experiment' }
+          end
         end
 
         present experiments, with: EE::API::Entities::Experiment, current_user: current_user

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

@@ -3,17 +3,33 @@
 module EE
   module API
     module Entities
-      class Experiment < ::API::Entities::Feature::Definition
+      class Experiment < Grape::Entity
         expose :key do |definition|
           definition.attributes[:name].gsub(/_experiment_percentage$/, '')
         end
 
-        expose :enabled do |definition|
-          feature(definition).state != :off
+        expose :definition, using: ::API::Entities::Feature::Definition do |feature|
+          ::Feature::Definition.definitions[feature.name.to_sym]
         end
 
-        expose :state do |definition|
-          feature(definition).state
+        class CurrentStatus < Grape::Entity
+          expose :state
+          expose :gates, using: ::API::Entities::FeatureGate do |model|
+            model.gates.map do |gate|
+              value = model.gate_values[gate.key]
+
+              # By default all gate values are populated. Only show relevant ones.
+              if (value.is_a?(Integer) && value == 0) || (value.is_a?(Set) && value.empty?)
+                next
+              end
+
+              { key: gate.key, value: value }
+            end.compact
+          end
+        end
+
+        expose :current_status, using: CurrentStatus do |definition|
+          feature(definition)
         end
 
         private

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

@@ -11,38 +11,65 @@ RSpec.describe EE::API::Entities::Experiment do
   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",
+      definition: {
+        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",
+        milestone: '13.7',
+        type: 'experiment',
+        group: 'group::adoption',
         default_enabled: false
+      },
+      current_status: {
+        state: :off,
+        gates: [
+          {
+            key: :boolean,
+            value: false
+          }
+        ]
+      }
     )
   end
 
   it "understands conditional state and what that means" do
     Feature.enable_percentage_of_time(:null_hypothesis, 1)
 
-    expect(subject).to include(
+    expect(subject[:current_status]).to match({
                                                 state: :conditional,
-      enabled: true
-    )
+                                                gates: [
+                                                  {
+                                                    key: :boolean,
+                                                    value: false
+                                                  },
+                                                  {
+                                                    key: :percentage_of_time,
+                                                    value: 1
+                                                  }
+                                                ]
+                                              })
   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(
+    expect(subject[:current_status]).to match({
                                                 state: :on,
-      enabled: true
-    )
+                                                gates: [
+                                                  {
+                                                    key: :boolean,
+                                                    value: false
+                                                  },
+                                                  {
+                                                    key: :percentage_of_time,
+                                                    value: 100
+                                                  }
+                                                ]
+                                              })
   end
 
   it "truncates the name since some experiments include extra data in their feature flag name" do
-    experiment.attributes[:name] = 'foo_experiment_percentage'
+    allow(experiment).to receive(:attributes).and_return({ name: 'foo_experiment_percentage' })
 
     expect(subject).to include(
       key: 'foo'

ee/spec/requests/api/experiments_spec.rb

@@ -50,14 +50,13 @@ RSpec.describe API::Experiments do
           group.add_developer(user)
         end
 
-        it 'returns the feature flag details' do
+        it 'returns the feature flag details', :aggregate_failures 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,
+            definition: {
               name: 'null_hypothesis',
               introduced_by_url: 'https://gitlab.com/gitlab-org/gitlab/-/merge_requests/45840',
               rollout_issue_url: nil,
@@ -65,19 +64,40 @@ RSpec.describe API::Experiments do
               type: 'experiment',
               group: 'group::adoption',
               default_enabled: false
+            },
+            current_status: {
+              state: :off,
+              gates: [
+                {
+                  key: :boolean,
+                  value: false
+                }
+              ]
+            }
           }.as_json)
         end
 
-        it 'understands the state of the feature flag and what that means for an experiment' do
+        it 'understands the state of the feature flag and what that means for an experiment', :aggregate_failures 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({
+            key: 'null_hypothesis',
+            current_status: {
               state: :conditional,
-            enabled: true,
-            name: 'null_hypothesis'
+              gates: [
+                {
+                  key: :boolean,
+                  value: false
+                },
+                {
+                  key: :percentage_of_actors,
+                  value: 1
+                }
+              ]
+            }
           }.as_json))
         end
 
@@ -127,7 +147,7 @@ RSpec.describe API::Experiments do
             })
           end
 
-          it 'returns a 400 if experimentation seems broken' do
+          it 'returns a 400 if experimentation seems broken', :aggregate_failures do
             # we assume that rendering control would only be done in error.
             stub_experiments(null_hypothesis: :control)