Allow to use only defined feature flags

This changes the API for feature flags to:
- allow to use only defined feature flags
- allow to skip this validation with `?force=1`
- returns information if the feature flag is defined

doc/api/features.md

@@ -37,7 +37,8 @@ Example response:
         "key": "boolean",
         "value": false
       }
-    ]
+    ],
+    "definition": null
   },
   {
     "name": "my_user_feature",
@@ -47,7 +48,15 @@ Example response:
         "key": "percentage_of_actors",
         "value": 34
       }
-    ]
+    ],
+    "definition": {
+      "name": "my_user_feature",
+      "introduced_by_url": "https://gitlab.com/gitlab-org/gitlab/-/merge_requests/40880",
+      "rollout_issue_url": "https://gitlab.com/gitlab-org/gitlab/-/issues/244905",
+      "group": "group::ci",
+      "type": "development",
+      "default_enabled": false
+    }
   },
   {
     "name": "new_library",
@@ -57,7 +66,45 @@ Example response:
         "key": "boolean",
         "value": true
       }
-    ]
+    ],
+    "definition": null
+  }
+]
+```
+
+## List all feature definitions
+
+Get a list of all feature definitions.
+
+```plaintext
+GET /features/definitions
+```
+
+```shell
+curl --header "PRIVATE-TOKEN: <your_access_token>" "https://gitlab.example.com/api/v4/features/definitions"
+```
+
+Example response:
+
+```json
+[
+  {
+    "name": "api_kaminari_count_with_limit",
+    "introduced_by_url": "https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/23931",
+    "rollout_issue_url": null,
+    "milestone": "11.8",
+    "type": "ops",
+    "group": "group::ecosystem",
+    "default_enabled": false
+  },
+  {
+    "name": "marginalia",
+    "introduced_by_url": null,
+    "rollout_issue_url": null,
+    "milestone": null,
+    "type": "ops",
+    "group": null,
+    "default_enabled": false
   }
 ]
 ```
@@ -81,6 +128,7 @@ POST /features/:name
 | `user` | string | no | A GitLab username |
 | `group` | string | no | A GitLab group's path, for example `gitlab-org` |
 | `project` | string | no | A projects path, for example `gitlab-org/gitlab-foss` |
+| `force` | boolean | no | Skip feature flag validation checks, ie. YAML definition |
 
 Note that you can enable or disable a feature for a `feature_group`, a `user`,
 a `group`, and a `project` in a single API call.
@@ -104,7 +152,15 @@ Example response:
       "key": "percentage_of_time",
       "value": 30
     }
-  ]
+  ],
+  "definition": {
+    "name": "my_user_feature",
+    "introduced_by_url": "https://gitlab.com/gitlab-org/gitlab/-/merge_requests/40880",
+    "rollout_issue_url": "https://gitlab.com/gitlab-org/gitlab/-/issues/244905",
+    "group": "group::ci",
+    "type": "development",
+    "default_enabled": false
+  }
 }
 ```
 
@@ -133,7 +189,15 @@ Example response:
       "key": "percentage_of_actors",
       "value": 42
     }
-  ]
+  ],
+  "definition": {
+    "name": "my_user_feature",
+    "introduced_by_url": "https://gitlab.com/gitlab-org/gitlab/-/merge_requests/40880",
+    "rollout_issue_url": "https://gitlab.com/gitlab-org/gitlab/-/issues/244905",
+    "group": "group::ci",
+    "type": "development",
+    "default_enabled": false
+  }
 }
 ```
 

ee/spec/requests/api/features_spec.rb

@@ -18,7 +18,10 @@ RSpec.describe API::Features, stub_feature_flags: false do
   end
 
   describe 'POST /feature' do
-    let(:feature_name) { 'my_feature' }
+    let(:feature_name) do
+      Feature::Definition.definitions
+        .values.find(&:development?).name
+    end
 
     context 'when running on a Geo primary node' do
       before do
@@ -43,6 +46,14 @@ RSpec.describe API::Features, stub_feature_flags: false do
 
         expect(response).to have_gitlab_http_status(:bad_request)
       end
+
+      context 'when force=1 is set' do
+        it 'allows to change state' do
+          post api("/features/#{feature_name}", admin), params: { value: 'true', force: true }
+
+          expect(response).to have_gitlab_http_status(:created)
+        end
+      end
     end
   end
 

lib/api/entities/feature.rb

@@ -17,6 +17,16 @@ module API
           { key: gate.key, value: value }
         end.compact
       end
+
+      class Definition < Grape::Entity
+        ::Feature::Definition::PARAMS.each do |param|
+          expose param
+        end
+      end
+
+      expose :definition, using: Definition do |feature|
+        ::Feature::Definition.definitions[feature.name.to_sym]
+      end
     end
   end
 end

lib/api/features.rb

@@ -46,6 +46,15 @@ module API
         present features, with: Entities::Feature, current_user: current_user
       end
 
+      desc 'Get a list of all feature definitions' do
+        success Entities::Feature::Definition
+      end
+      get :definitions do
+        definitions = ::Feature::Definition.definitions.values.map(&:to_h)
+
+        present definitions, with: Entities::Feature::Definition, current_user: current_user
+      end
+
       desc 'Set the gate value for the given feature' do
         success Entities::Feature
       end
@@ -56,6 +65,7 @@ module API
         optional :user, type: String, desc: 'A GitLab username'
         optional :group, type: String, desc: "A GitLab group's path, such as 'gitlab-org'"
         optional :project, type: String, desc: 'A projects path, like gitlab-org/gitlab-ce'
+        optional :force, type: Boolean, desc: 'Skip feature flag validation checks, ie. YAML definition'
 
         mutually_exclusive :key, :feature_group
         mutually_exclusive :key, :user
@@ -63,7 +73,7 @@ module API
         mutually_exclusive :key, :project
       end
       post ':name' do
-        validate_feature_flag_name!(params[:name])
+        validate_feature_flag_name!(params[:name]) unless params[:force]
 
         feature = Feature.get(params[:name]) # rubocop:disable Gitlab/AvoidFeatureGet
         targets = gate_targets(params)

lib/feature.rb

@@ -136,8 +136,6 @@ class Feature
     end
 
     def register_definitions
-      return unless check_feature_flags_definition?
-
       Feature::Definition.reload!
     end
 

lib/feature/definition.rb

@@ -13,6 +13,12 @@ class Feature
       end
     end
 
+    TYPES.each do |type, _|
+      define_method("#{type}?") do
+        attributes[:type].to_sym == type
+      end
+    end
+
     def initialize(path, opts = {})
       @path = path
       @attributes = {}
@@ -94,6 +100,10 @@ class Feature
         @definitions = load_all!
       end
 
+      def has_definition?(key)
+        definitions.has_key?(key.to_sym)
+      end
+
       def valid_usage!(key, type:, default_enabled:)
         if definition = definitions[key.to_sym]
           definition.valid_usage!(type_in_code: type, default_enabled_in_code: default_enabled)
@@ -119,10 +129,6 @@ class Feature
       private
 
       def load_all!
-        # We currently do not load feature flag definitions
-        # in production environments
-        return [] unless Gitlab.dev_or_test_env?
-
         paths.each_with_object({}) do |glob_path, definitions|
           load_all_from_path!(definitions, glob_path)
         end