Add free user cap feature flag and availability check

- foundation work for free user cap project

ee/app/controllers/groups/usage_quotas_controller.rb

@@ -15,7 +15,7 @@ class Groups::UsageQuotasController < Groups::ApplicationController
   end
 
   def pending_members
-    render_404 unless @group.user_cap_available?
+    render_404 unless @group.apply_user_cap?
     @hide_search_settings = true
   end
 

ee/app/models/ee/namespace.rb

@@ -301,6 +301,18 @@ module EE
         end
     end
 
+    def on_existing_free_subscription?
+      # this is a side-effect free version of checking if a namespace
+      # is on a free plan - see https://gitlab.com/gitlab-org/gitlab/-/merge_requests/80839#note_851566461
+      strong_memoize(:on_existing_free_subscription) do
+        ::Plan
+          .joins(:hosted_subscriptions)
+          .where(name: ::Plan::FREE)
+          .where(gitlab_subscriptions: { namespace_id: id })
+          .exists?
+      end
+    end
+
     # When a purchasing a GL.com plan for a User namespace
     # we only charge for a single user.
     # This method is overwritten in Group where we made the calculation
@@ -458,6 +470,17 @@ module EE
       ::Feature.enabled?(:saas_user_caps, root_ancestor, default_enabled: :yaml)
     end
 
+    def apply_free_user_cap?
+      return false unless ::Gitlab.com?
+      return false unless root_ancestor.on_existing_free_subscription?
+
+      ::Feature.enabled?(:free_user_cap, root_ancestor, default_enabled: :yaml)
+    end
+
+    def apply_user_cap?
+      user_cap_available? || apply_free_user_cap?
+    end
+
     private
 
     def any_project_with_shared_runners_enabled_with_cte?

ee/app/views/groups/usage_quotas/index.html.haml

@@ -6,7 +6,7 @@
 - page_title s_("UsageQuota|Usage")
 - url_to_purchase_storage = buy_storage_path(@group) if purchase_storage_link_enabled?(@group)
 - buy_addon_target_attr = buy_addon_target_attr(@group) if purchase_storage_link_enabled?(@group)
-- pending_members_page_path = pending_members_group_usage_quotas_path(@group) if @group.user_cap_available?
+- pending_members_page_path = pending_members_group_usage_quotas_path(@group) if @group.apply_user_cap?
 - pending_members_count = Member.in_hierarchy(@group).with_state("awaiting").count
 
 - if show_product_purchase_success_alert?

ee/config/feature_flags/development/free_user_cap.yml

+---
+name: free_user_cap
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/80839
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/352633
+milestone: '14.9'
+type: development
+group: group::conversion
+default_enabled: false

ee/spec/controllers/groups/usage_quotas_controller_spec.rb

@@ -43,7 +43,7 @@ RSpec.describe Groups::UsageQuotasController do
 
     before do
       allow_next_found_instance_of(Group) do |group|
-        allow(group).to receive(:user_cap_available?).and_return(feature_available)
+        allow(group).to receive(:apply_user_cap?).and_return(feature_available)
       end
     end
 

ee/spec/models/ee/namespace_spec.rb

@@ -2207,6 +2207,101 @@ RSpec.describe Namespace do
     end
   end
 
+  describe '#apply_free_user_cap?', :saas do
+    let_it_be(:namespace) { create(:group_with_plan, plan: :free_plan) }
+    let_it_be(:subgroup) {  create(:group, parent: namespace) }
+
+    subject(:apply_free_user_cap?) { namespace.apply_free_user_cap? }
+
+    context 'when not on Gitlab.com' do
+      before do
+        allow(::Gitlab).to receive(:com?).and_return(false)
+      end
+
+      it { is_expected.to be false }
+    end
+
+    context 'when :free_user_cap is disabled' do
+      before do
+        stub_feature_flags(free_user_cap: false)
+      end
+
+      it { is_expected.to be false }
+    end
+
+    context 'when :free_user_cap is enabled' do
+      before do
+        stub_feature_flags(free_user_cap: true)
+      end
+
+      it { is_expected.to be true }
+
+      context 'when the namespace is not a group' do
+        let_it_be(:namespace) do
+          namespace = create(:user).namespace
+          create(:gitlab_subscription, hosted_plan: create(:free_plan), namespace: namespace)
+          namespace
+        end
+
+        it { is_expected.to be true }
+      end
+
+      context 'when it is a non free plan' do
+        let_it_be(:namespace) { create(:group_with_plan, plan: :ultimate_plan) }
+
+        it { is_expected.to be false }
+      end
+
+      context 'when no plan exists' do
+        let_it_be(:namespace) { create(:group) }
+
+        it { is_expected.to be false }
+      end
+    end
+  end
+
+  describe '#apply_user_cap?' do
+    let(:namespace) { build(:namespace) }
+
+    where(:user_cap_available, :apply_free_user_cap, :result) do
+      false | false | false
+      false | true  | true
+      true  | false | true
+      true  | true  | true
+    end
+
+    subject { namespace.apply_user_cap? }
+
+    with_them do
+      before do
+        allow(namespace).to receive(:user_cap_available?).and_return(user_cap_available)
+        allow(namespace).to receive(:apply_free_user_cap?).and_return(apply_free_user_cap)
+      end
+
+      it { is_expected.to eq(result) }
+    end
+  end
+
+  describe '#on_existing_free_subscription?', :saas do
+    it 'returns true with a free plan' do
+      namespace = create(:group_with_plan, plan: :free_plan)
+
+      expect(namespace.on_existing_free_subscription?).to be(true)
+    end
+
+    it 'returns false when the plan is not free' do
+      namespace = create(:group_with_plan, plan: :ultimate_plan)
+
+      expect(namespace.on_existing_free_subscription?).to be(false)
+    end
+
+    it 'returns false when there is no plan' do
+      namespace = create(:namespace)
+
+      expect(namespace.on_existing_free_subscription?).to be(false)
+    end
+  end
+
   def create_project(repository_size:, lfs_objects_size:, repository_size_limit:)
     create(:project, namespace: namespace, repository_size_limit: repository_size_limit).tap do |project|
       create(:project_statistics, project: project, repository_size: repository_size, lfs_objects_size: lfs_objects_size)