Ensure experiment feature flag survival using YML files & persist_used!

- Use "experiment" feature flag type defined in
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/45840
- Add YML definition files for existing experiment feature flags so they
are now compatible with Feature.enabled?(...)
- Use Feature.persist_used!(...) when stubbing experiments for tests to
mark those flags as "in use"

ee/config/feature_flags/experiment/ci_notification_dot_experiment_percentage.yml

+---
+name: ci_notification_dot_experiment_percentage
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/27626
+rollout_issue_url: https://gitlab.com/gitlab-org/growth/team-tasks/-/issues/101
+milestone: '12.10'
+type: experiment
+group: group::expansion
+default_enabled: false

ee/config/feature_flags/experiment/contact_sales_btn_in_app_experiment_percentage.yml

+---
+name: contact_sales_btn_in_app_experiment_percentage
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/38508
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/238207
+milestone: '13.3'
+type: experiment
+group: group::conversion
+default_enabled: true

ee/config/feature_flags/experiment/customize_homepage_experiment_percentage.yml

+---
+name: customize_homepage_experiment_percentage
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/39348
+rollout_issue_url: https://gitlab.com/gitlab-org/growth/team-tasks/-/issues/187
+milestone: '13.4'
+type: experiment
+group: group::expansion
+default_enabled: false

ee/config/feature_flags/experiment/default_to_issues_board_experiment_percentage.yml

+---
+name: default_to_issues_board_experiment_percentage
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/43939
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/268298
+milestone: '13.5'
+type: experiment
+group: group::conversion
+default_enabled: true

ee/config/feature_flags/experiment/group_only_trials_experiment_percentage.yml

+---
+name: group_only_trials_experiment_percentage
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/40564
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/258629
+milestone: '13.5'
+type: experiment
+group: group::conversion
+default_enabled: false

ee/config/feature_flags/experiment/invite_members_empty_group_version_a_experiment_percentage.yml

+---
+name: invite_members_empty_group_version_a_experiment_percentage
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/45689
+rollout_issue_url: https://gitlab.com/gitlab-org/growth/team-tasks/-/issues/280
+milestone: '13.6'
+type: experiment
+group: group::expansion
+default_enabled: false

ee/config/feature_flags/experiment/invite_members_empty_project_version_a_experiment_percentage.yml

+---
+name: invite_members_empty_project_version_a_experiment_percentage
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/49588
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/262014
+milestone: '13.7'
+type: experiment
+group: group::expansion
+default_enabled: false

ee/config/feature_flags/experiment/invite_members_version_a_experiment_percentage.yml

+---
+name: invite_members_version_a_experiment_percentage
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/45689/
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/219239
+milestone: '13.6'
+type: experiment
+group: group::expansion
+default_enabled: false

ee/config/feature_flags/experiment/invite_members_version_b_experiment_percentage.yml

+---
+name: invite_members_version_b_experiment_percentage
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/43900
+rollout_issue_url: https://gitlab.com/gitlab-org/growth/team-tasks/-/issues/214
+milestone: '13.5'
+type: experiment
+group: group::expansion
+default_enabled: false

ee/config/feature_flags/experiment/jobs_empty_state_experiment_percentage.yml

+---
+name: jobs_empty_state_experiment_percentage
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/48686
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/281054
+milestone: '13.7'
+type: experiment
+group: group::activation
+default_enabled: false

ee/config/feature_flags/experiment/onboarding_issues_experiment_percentage.yml

+---
+name: onboarding_issues_experiment_percentage
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/31656/
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/224515
+milestone: '13.0'
+type: experiment
+group: group::conversion
+default_enabled: true

ee/config/feature_flags/experiment/remove_known_trial_form_fields_experiment_percentage.yml

+---
+name: remove_known_trial_form_fields_experiment_percentage
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/45634/
+rollout_issue_url: https://gitlab.com/gitlab-org/growth/team-tasks/-/issues/281
+milestone: '13.7'
+type: experiment
+group: group::conversion
+default_enabled: false

ee/config/feature_flags/experiment/trial_registration_with_social_signin_experiment_percentage.yml

+---
+name: trial_registration_with_social_signin_experiment_percentage
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/45633
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/262853
+milestone: '13.7'
+type: experiment
+group: group::conversion
+default_enabled: false

ee/config/feature_flags/experiment/trimmed_skip_trial_copy_experiment_percentage.yml

+---
+name: trimmed_skip_trial_copy_experiment_percentage
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/48110
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/284956
+milestone: '13.7'
+type: experiment
+group: group::conversion
+default_enabled: false

ee/config/feature_flags/experiment/upgrade_link_in_user_menu_a_experiment_percentage.yml

+---
+name: upgrade_link_in_user_menu_a_experiment_percentage
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/29428
+rollout_issue_url: https://gitlab.com/gitlab-org/growth/team-tasks/-/issues/126
+milestone: '13.0'
+type: experiment
+group: group::expansion
+default_enabled: false

lib/feature/shared.rb

@@ -57,6 +57,8 @@ class Feature
         default_enabled: false,
         example: <<-EOS
           experiment(:my_experiment, project: project, actor: current_user) { ...variant code... }
+          # or
+          Gitlab::Experimentation.in_experiment_group?(:my_experiment, subject: current_user)
         EOS
       }
     }.freeze

lib/gitlab/experimentation/experiment.rb

@@ -3,6 +3,8 @@
 module Gitlab
   module Experimentation
     class Experiment
+      FEATURE_FLAG_SUFFIX = "_experiment_percentage"
+
       attr_reader :key, :tracking_category, :use_backwards_compatible_subject_index
 
       def initialize(key, **params)
@@ -10,7 +12,7 @@ module Gitlab
         @tracking_category = params[:tracking_category]
         @use_backwards_compatible_subject_index = params[:use_backwards_compatible_subject_index]
 
-        @experiment_percentage = Feature.get(:"#{key}_experiment_percentage").percentage_of_time_value # rubocop:disable Gitlab/AvoidFeatureGet
+        @experiment_percentage = Feature.get(:"#{key}#{FEATURE_FLAG_SUFFIX}").percentage_of_time_value # rubocop:disable Gitlab/AvoidFeatureGet
       end
 
       def active?

spec/support/helpers/stub_experiments.rb

 # frozen_string_literal: true
 
 module StubExperiments
+  SUFFIX = Gitlab::Experimentation::Experiment::FEATURE_FLAG_SUFFIX
+
   # Stub Experiment with `key: true/false`
   #
   # @param [Hash] experiment where key is feature name and value is boolean whether active or not.
@@ -11,6 +13,7 @@ module StubExperiments
     allow(Gitlab::Experimentation).to receive(:active?).and_call_original
 
     experiments.each do |experiment_key, enabled|
+      Feature.persist_used!("#{experiment_key}#{SUFFIX}")
       allow(Gitlab::Experimentation).to receive(:active?).with(experiment_key) { enabled }
     end
   end
@@ -25,6 +28,7 @@ module StubExperiments
     allow(Gitlab::Experimentation).to receive(:in_experiment_group?).and_call_original
 
     experiments.each do |experiment_key, enabled|
+      Feature.persist_used!("#{experiment_key}#{SUFFIX}")
       allow(Gitlab::Experimentation).to receive(:in_experiment_group?).with(experiment_key, anything) { enabled }
     end
   end