[WikiPages] Prevent renaming wiki pages for help pages (#666)

app/models/help_page.rb

@@ -7,6 +7,7 @@ class HelpPage < ApplicationRecord
   validate :wiki_page_exists
   after_destroy :invalidate_cache
   after_save :invalidate_cache
+  belongs_to :wiki, class_name: "WikiPage", foreign_key: "wiki_page", primary_key: "title"
 
   def invalidate_cache
     Cache.delete("help_index")
@@ -14,7 +15,7 @@ class HelpPage < ApplicationRecord
   end
 
   def wiki_page_exists
-    errors.add(:wiki_page, "must exist") if WikiPage.find_by(title: wiki_page).blank?
+    errors.add(:wiki_page, "must exist") if wiki.blank?
   end
 
   def pretty_title

app/models/wiki_page.rb

@@ -19,6 +19,7 @@ class WikiPage < ApplicationRecord
   before_destroy :validate_not_used_as_help_page
   before_destroy :log_destroy
   before_save :log_changes
+  after_save :update_help_page, if: :saved_change_to_title?
 
   attr_accessor :skip_secondary_validations, :edit_reason
   array_attribute :other_names
@@ -27,13 +28,7 @@ class WikiPage < ApplicationRecord
   has_one :tag, foreign_key: "name", primary_key: "title"
   has_one :artist, foreign_key: "name", primary_key: "title"
   has_many :versions, -> { order("wiki_page_versions.id ASC") }, class_name: "WikiPageVersion", dependent: :destroy
-
-  def validate_not_used_as_help_page
-    if HelpPage.find_by(wiki_page: title).present?
-      errors.add(:wiki_page, "is used by a help page")
-      throw :abort
-    end
-  end
+  has_one :help_page, foreign_key: "wiki_page", primary_key: "title"
 
   def log_destroy
     ModAction.log(:wiki_page_delete, {wiki_page: title, wiki_page_id: id})
@@ -127,8 +122,22 @@ class WikiPage < ApplicationRecord
     end
   end
 
+  module HelpPageMethods
+    def validate_not_used_as_help_page
+      if help_page.present?
+        errors.add(:wiki_page, "is used by a help page")
+        throw :abort
+      end
+    end
+
+    def update_help_page
+      HelpPage.find_by(wiki_page: title_before_last_save)&.update(wiki_page: title)
+    end
+  end
+
   extend SearchMethods
   include ApiMethods
+  include HelpPageMethods
 
   def user_not_limited
     allowed = CurrentUser.can_wiki_edit_with_reason
@@ -147,7 +156,12 @@ class WikiPage < ApplicationRecord
   end
 
   def validate_rename
-    return if !will_save_change_to_title? || skip_secondary_validations
+    return unless will_save_change_to_title?
+    if !CurrentUser.user.is_admin? && HelpPage.find_by(wiki_page: title_was).present?
+      errors.add(:title, "is used as a help page and cannot be changed")
+      return
+    end
+    return if skip_secondary_validations
 
     tag_was = Tag.find_by_name(Tag.normalize_name(title_was))
     if tag_was.present? && tag_was.post_count > 0

test/factories/help_page.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+FactoryBot.define do
+  factory(:help_page) do
+    sequence(:name) { |n| "help_page_#{n}" }
+    association :wiki, factory: :wiki_page
+  end
+end

test/unit/wiki_page_test.rb

@@ -97,5 +97,43 @@ class WikiPageTest < ActiveSupport::TestCase
         assert_not_equal(@wiki_page.creator_id, version.updater_id)
       end
     end
+
+    context "for a help page" do
+      setup do
+        @janitor = create(:janitor_user)
+        @admin = create(:admin_user)
+        as(@admin) do
+          @help = create(:help_page)
+          @wiki = @help.wiki
+        end
+      end
+
+      should "not allow the title to be changed by janitors" do
+        as(@janitor) do
+          @title = @wiki.title
+          @wiki.update(title: "new_title")
+          assert_equal(["Title is used as a help page and cannot be changed"], @wiki.errors.full_messages)
+          assert_equal(@title, @wiki.reload.title)
+          assert_equal(@title, @help.reload.wiki_page)
+        end
+      end
+
+      should "allow the title to be changed by admins" do
+        as(@admin) do
+          @wiki.update(title: "new_title")
+          assert_equal([], @wiki.errors.full_messages)
+          assert_equal("new_title", @wiki.reload.title)
+          assert_equal("new_title", @help.reload.wiki_page)
+        end
+      end
+
+      should "not allow deleting the wiki page" do
+        as(@admin) do
+          @wiki.destroy
+          assert_equal(["Wiki page is used by a help page"], @wiki.errors.full_messages)
+          assert_not_nil(WikiPage.find_by(id: @wiki.id))
+        end
+      end
+    end
   end
 end