FIX: Move user reindexing into a job (#26753)

In a large forum with millions of users and millions of user_fields
updating the list of dropdown user field options will result in a
502 now due to the large number of fields.

This commit moves the indexing into a job.

app/jobs/regular/index_user_fields_for_search.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+class Jobs::IndexUserFieldsForSearch < Jobs::Base
+  def execute(args)
+    user_field_id = args[:user_field_id]
+    SearchIndexer.queue_users_reindex(
+      UserCustomField.where(name: "user_field_#{user_field_id}").pluck(:user_id),
+    )
+  end
+end

app/models/user_field.rb

@@ -20,9 +20,7 @@ class UserField < ActiveRecord::Base
   end
 
   def queue_index_search
-    SearchIndexer.queue_users_reindex(
-      UserCustomField.where(name: "user_field_#{self.id}").pluck(:user_id),
-    )
+    Jobs.enqueue(:index_user_fields_for_search, user_field_id: self.id)
   end
 
   private

spec/fabricators/user_custom_field_fabricator.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+Fabricator(:user_custom_field) do
+  user
+  name { Fabricate(:user_field).id }
+  value { sequence(:value) { |n| "value#{n}" } }
+end

spec/jobs/index_user_fields_for_search_spec.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+RSpec.describe Jobs::IndexUserFieldsForSearch do
+  subject(:job) { described_class.new }
+
+  before do
+    SearchIndexer.enable
+    Jobs.run_immediately!
+  end
+
+  it "triggers a reindex when executed" do
+    user = Fabricate(:user)
+    user_field = Fabricate(:user_field)
+    Fabricate(:user_custom_field, user: user, name: "user_field_#{user_field.id}")
+
+    job.execute(user_field_id: user_field.id)
+
+    expect(user.reload.user_search_data.version).to eq(SearchIndexer::REINDEX_VERSION)
+  end
+end

spec/models/user_field_spec.rb

@@ -30,4 +30,14 @@ RSpec.describe UserField do
 
     expect(user_field.description).to eq(link)
   end
+
+  it "enqueues index user fields job on save" do
+    user_field = Fabricate(:user_field)
+
+    user_field.update!(description: "tomtom")
+
+    expect(
+      job_enqueued?(job: Jobs::IndexUserFieldsForSearch, args: { user_field_id: user_field.id }),
+    ).to eq(true)
+  end
 end