Fix #4359: Allow builders to move small (artist) tags manually.

Allow builders to approve artist alias BURs. The BUR must contain only
artist aliases or mass updates and each artist must have less than 100
posts.

app/logical/bulk_update_request_processor.rb

@@ -117,6 +117,22 @@ class BulkUpdateRequestProcessor
     []
   end
 
+  def is_tag_move_allowed?
+    tokens.all? do |type, *args|
+      case type
+      when :create_alias
+        BulkUpdateRequestProcessor.is_tag_move_allowed?(args[0], args[1])
+      when :mass_update
+        lhs = PostQueryBuilder.new(args[0])
+        rhs = PostQueryBuilder.new(args[1])
+
+        lhs.is_simple_tag? && rhs.is_simple_tag? && BulkUpdateRequestProcessor.is_tag_move_allowed?(args[0], args[1])
+      else
+        false
+      end
+    end
+  end
+
   def to_dtext
     tokens.map do |token|
       case token[0]
@@ -132,5 +148,15 @@ class BulkUpdateRequestProcessor
     end.join("\n")
   end
 
+  private
+
+  def self.is_tag_move_allowed?(antecedent_name, consequent_name)
+    antecedent_tag = Tag.find_by_name(Tag.normalize_name(antecedent_name))
+    consequent_tag = Tag.find_by_name(Tag.normalize_name(consequent_name))
+
+    (antecedent_tag.blank? || antecedent_tag.empty? || (antecedent_tag.artist? && antecedent_tag.post_count <= 100)) &&
+    (consequent_tag.blank? || consequent_tag.empty? || (consequent_tag.artist? && consequent_tag.post_count <= 100))
+  end
+
   memoize :tokens
 end

app/models/bulk_update_request.rb

@@ -136,6 +136,10 @@ class BulkUpdateRequest < ApplicationRecord
     @processor ||= BulkUpdateRequestProcessor.new(script, forum_topic_id: forum_topic_id, skip_secondary_validations: skip_secondary_validations)
   end
 
+  def is_tag_move_allowed?
+    processor.is_tag_move_allowed?
+  end
+
   def is_pending?
     status == "pending"
   end

app/policies/bulk_update_request_policy.rb

@@ -8,7 +8,7 @@ class BulkUpdateRequestPolicy < ApplicationPolicy
   end
 
   def approve?
-    user.is_admin? && !record.is_approved?
+    unbanned? && !record.is_approved? && (user.is_admin? || (user.is_builder? && record.is_tag_move_allowed?))
   end
 
   def destroy?

app/views/bulk_update_requests/_bur_edit_links.html.erb

@@ -1,8 +1,6 @@
 <%# bur %>
 
-<% if policy(bur).approve? %>
-  <%= link_to "Approve", approve_bulk_update_request_path(bur), remote: true, method: :post, "data-confirm": "Are you sure you want to approve this bulk update request?" %> |
-<% end %>
+<%= link_to_if policy(bur).approve?, "Approve", approve_bulk_update_request_path(bur), remote: true, method: :post, "data-confirm": "Are you sure you want to approve this bulk update request?" %> |
 <% if policy(bur).destroy? %>
   <%= link_to "Reject", bur, remote: true, method: :delete, "data-confirm": "Are you sure you want to reject this bulk update request?" %> |
 <% end %>

test/functional/bulk_update_requests_controller_test.rb

@@ -4,6 +4,7 @@ class BulkUpdateRequestsControllerTest < ActionDispatch::IntegrationTest
   context "BulkUpdateRequestsController" do
     setup do
       @user = create(:user)
+      @builder = create(:builder_user)
       @admin = create(:admin_user)
       @bulk_update_request = create(:bulk_update_request, user: @user)
     end
@@ -121,6 +122,33 @@ class BulkUpdateRequestsControllerTest < ActionDispatch::IntegrationTest
         end
       end
 
+      context "for a builder" do
+        should "fail for a large artist move" do
+          create(:tag, name: "artist1", category: Tag.categories.artist, post_count: 1000)
+          @bulk_update_request = create(:bulk_update_request, script: "create alias artist1 -> artist2")
+
+          post_auth approve_bulk_update_request_path(@bulk_update_request), @builder
+
+          assert_response 403
+          assert_equal("pending", @bulk_update_request.reload.status)
+          assert_equal(false, TagAlias.where(antecedent_name: "artist1", consequent_name: "artist2").exists?)
+        end
+
+        should "succeed for a small artist move" do
+          create(:tag, name: "artist1a", category: Tag.categories.artist, post_count: 10)
+          create(:tag, name: "artist1b", category: Tag.categories.general, post_count: 0)
+          create(:tag, name: "artist2a", category: Tag.categories.artist, post_count: 20)
+          @bulk_update_request = create(:bulk_update_request, script: "mass update artist1a -> artist1b\ncreate alias artist2a -> artist2b")
+
+          post_auth approve_bulk_update_request_path(@bulk_update_request), @builder
+
+          assert_redirected_to(bulk_update_requests_path)
+          assert_equal("approved", @bulk_update_request.reload.status)
+          assert_equal(@builder, @bulk_update_request.approver)
+          assert_equal(true, TagAlias.where(antecedent_name: "artist2a", consequent_name: "artist2b").exists?)
+        end
+      end
+
       context "for an admin" do
         should "succeed" do
           post_auth approve_bulk_update_request_path(@bulk_update_request), @admin