Fix feature flag check for productivity analytics

Previously the productivity_analytics endpoint would return a 404 if
there was no entry in the features table. This fixes the bug so the
page will be rendered in that case.

ee/changelogs/unreleased/fix-pa-feature-flag-check.yml

+---
+title: Fix feature flag check for productivity analytics
+merge_request: 19025
+author:
+type: fixed

ee/config/routes/analytics.rb

@@ -3,9 +3,7 @@
 namespace :analytics do
   root to: 'analytics#index'
 
-  constraints(::Constraints::FeatureConstrainer.new(Gitlab::Analytics::PRODUCTIVITY_ANALYTICS_FEATURE_FLAG)) do
-    resource :productivity_analytics, only: :show
-  end
+  resource :productivity_analytics, only: :show, constraints: lambda { |req| Gitlab::Analytics.productivity_analytics_enabled? }
 
   constraints(::Constraints::FeatureConstrainer.new(Gitlab::Analytics::CYCLE_ANALYTICS_FEATURE_FLAG)) do
     resource :cycle_analytics, only: :show

ee/spec/routing/analytics_routing_spec.rb

@@ -3,10 +3,36 @@
 require 'spec_helper'
 
 describe 'Analytics' do
-  include RSpec::Rails::RequestExampleGroup
   include Warden::Test::Helpers
 
   it 'redirects to sign_in if user is not authenticated' do
-    expect(get('/-/analytics')).to redirect_to('/users/sign_in')
+    expect(get('/-/analytics')).to route_to('analytics/analytics#index')
+  end
+
+  context 'when user is logged in' do
+    let(:user) { create(:user) }
+
+    before do
+      login_as(user)
+    end
+
+    context 'productivity_analytics feature flag is enabled by default' do
+      it 'succeeds' do
+        # make sure we call this method for checking the feature availability
+        expect(Gitlab::Analytics).to receive(:productivity_analytics_enabled?).and_call_original
+
+        expect(get('/-/analytics/productivity_analytics')).to route_to('analytics/productivity_analytics#show')
+      end
+    end
+
+    context 'productivity_analytics feature flag is disabled' do
+      before do
+        stub_feature_flags(Gitlab::Analytics::PRODUCTIVITY_ANALYTICS_FEATURE_FLAG => false)
+      end
+
+      it 'routes to `not_found`' do
+        expect(get('/-/analytics/productivity_analytics')).to route_to('application#route_not_found', unmatched_route: '-/analytics/productivity_analytics')
+      end
+    end
   end
 end