Add feature flag support to Pages (#8149)

* Add 'feature_flag' field to pages table, form

* Add 'exist?' to FeatureFlag

* Test for feature flag when loading custom pages

* Refactor FeatureFlag.enabled? to check both boolean and user gates

* Ugly test fixes

* PR feedback and refactoring

* PR refactor: don't require database table!

app/controllers/pages_controller.rb

@@ -4,6 +4,8 @@ class PagesController < ApplicationController
 
   def show
     @page = Page.find_by!(slug: params[:slug])
+    not_found unless FeatureFlag.accessible?(@page.feature_flag_name, current_user)
+
     set_surrogate_key_header "show-page-#{params[:slug]}"
   end
 

app/controllers/stories_controller.rb

@@ -111,8 +111,12 @@ class StoriesController < ApplicationController
       Honeycomb.add_field("stories_route", "org")
       handle_organization_index
     elsif @page
-      Honeycomb.add_field("stories_route", "page")
-      handle_page_display
+      if FeatureFlag.accessible?(@page.feature_flag_name, current_user)
+        Honeycomb.add_field("stories_route", "page")
+        handle_page_display
+      else
+        not_found
+      end
     else
       Honeycomb.add_field("stories_route", "user")
       handle_user_index

app/helpers/feature_flag.rb

@@ -1,7 +1,9 @@
 module FeatureFlag
-  extend self # rubocop:disable Style/ModuleFunction
+  class << self
+    delegate :enabled?, :exist?, to: Flipper
 
-  def enabled?(feature_name, *args)
-    Flipper[feature_name].enabled?(*args)
+    def accessible?(feature_flag_name, *args)
+      feature_flag_name.blank? || !exist?(feature_flag_name) || enabled?(feature_flag_name, *args)
+    end
   end
 end

app/models/page.rb

@@ -18,6 +18,10 @@ class Page < ApplicationRecord
     is_top_level_path ? "/#{slug}" : "/page/#{slug}"
   end
 
+  def feature_flag_name
+    "page_#{slug}"
+  end
+
   private
 
   def evaluate_markdown

app/views/internal/pages/_form.html.erb

@@ -23,7 +23,7 @@
       </div>
       <div class="form-group">
         <% if @page.social_image_url %>
-          <img src="<%= @page.social_image_url%>" style="max-width:500px;display:block" />
+          <img src="<%= @page.social_image_url %>" style="max-width:500px;display:block" />
         <% end %>
         <%= form.label :social_image %>
         <%= form.file_field :social_image, class: "form-control" %>
@@ -38,6 +38,24 @@
         <%= form.check_box :is_top_level_path %>
         <p>(Determines if it is accessible by <code>/page-slug</code> vs <code>/page/page-slug</code>) Be careful! ⚠️</p>
       </div>
+      <div class="form-group">
+        <p>
+          <b><%= link_to "Feature Flag", "/internal/feature_flags" %></b>
+          <span class="badge badge-<%= FeatureFlag.exist?(@page.feature_flag_name) ? "success" : "warning" %>">
+            <%= FeatureFlag.exist?(@page.feature_flag_name) ? "Present" : "Not Present" %>
+          </span>
+          </br>
+          <% if FeatureFlag.exist?(@page.feature_flag_name) %>
+            Access to this page is being guarded by the feature flag <code><%= @page.feature_flag_name %></code>.
+            <%= link_to "Modify flag here", "/internal/feature_flags/features/#{@page.feature_flag_name}" %>
+          <% else %>
+            Everyone has access. Optionally guard access to this page by creating feature <code><%= @page.feature_flag_name %></code>
+            <%= link_to "here", "/internal/feature_flags/features/" %>
+          <% end %>
+          </br>
+          
+        </p>
+      </div>
       <%= form.submit class: "btn btn-primary float-right" %>
     <% end %>
   </div>

spec/helpers/feature_flag_spec.rb

@@ -0,0 +1,66 @@
+require "rails_helper"
+
+UserStruct = Struct.new(:flipper_id)
+
+describe FeatureFlag, type: :helper do
+  describe ".enabled?" do
+    it "calls Flipper's enabled? method" do
+      allow(Flipper).to receive(:enabled?).with("foo")
+
+      described_class.enabled?("foo")
+
+      expect(Flipper).to have_received(:enabled?).with("foo")
+    end
+  end
+
+  describe ".exist?" do
+    it "calls Flipper's exist? method" do
+      allow(Flipper).to receive(:exist?).with("foo")
+
+      described_class.exist?("foo")
+
+      expect(Flipper).to have_received(:exist?).with("foo")
+    end
+  end
+
+  describe ".accessible?" do
+    let(:user) { UserStruct.new(flipper_id: 1) }
+
+    it "returns false when flag doesn't exist" do
+      expect(described_class.accessible?("missing_flag")).to be_truthy # rubocop:disable Rspec/PredicateMatcher
+    end
+
+    it "returns true when flag is empty" do
+      expect(described_class.accessible?("")).to be_truthy # rubocop:disable Rspec/PredicateMatcher
+    end
+
+    it "returns true when flag is nil" do
+      expect(described_class.accessible?(nil)).to be_truthy # rubocop:disable Rspec/PredicateMatcher
+    end
+
+    context "when flag exists and is set to off" do
+      before { Flipper.disable("flag") }
+
+      it "returns false" do
+        expect(described_class.accessible?("flag")).to be_falsy # rubocop:disable Rspec/PredicateMatcher
+      end
+
+      it "returns true when flag is on for user" do
+        Flipper.enable_actor("flag", user)
+        expect(described_class.accessible?("flag", user)).to be_truthy # rubocop:disable Rspec/PredicateMatcher
+      end
+    end
+
+    context "when flag exists and is set to on" do
+      before { Flipper.enable("flag") }
+
+      it "returns true" do
+        expect(described_class.accessible?("flag")).to be_truthy # rubocop:disable Rspec/PredicateMatcher
+      end
+
+      it "returns true for a user" do
+        expect(described_class.accessible?("flag", user)).to be_truthy # rubocop:disable Rspec/PredicateMatcher
+      end
+    end
+  end
+end