FIX: Remove anonymous users from users directory (#28892)

Anonymous users are "shadow" users created when an existing real user desires to post anonymously. This feature is off by default, but it can be enabled via the `allow_anonymous_posting` site setting. Those shadow users shouldn't be included in the users directory (`/u`).

app/models/directory_item.rb

@@ -162,7 +162,11 @@ class DirectoryItem < ActiveRecord::Base
                   #{Array.new(column_names.count, 0).join(", ")}
               FROM users u
               LEFT JOIN directory_items di ON di.user_id = u.id AND di.period_type = :period_type
-              WHERE di.id IS NULL AND u.id > 0 AND u.silenced_till IS NULL AND u.active
+              WHERE di.id IS NULL AND u.id > 0 AND u.silenced_till IS NULL AND u.active AND NOT EXISTS(
+                SELECT 1
+                FROM anonymous_users
+                WHERE anonymous_users.user_id = u.id
+              )
               #{SiteSetting.must_approve_users ? "AND u.approved" : ""}
             ",
       period_type: period_types[period_type],

db/post_migrate/20240912210450_delete_anonymous_users_from_directory_items.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class DeleteAnonymousUsersFromDirectoryItems < ActiveRecord::Migration[7.1]
+  def up
+    DB.exec(<<~SQL)
+      DELETE FROM directory_items
+      USING anonymous_users
+      WHERE directory_items.user_id = anonymous_users.user_id
+    SQL
+  end
+end

spec/models/directory_item_spec.rb

@@ -182,5 +182,22 @@ RSpec.describe DirectoryItem do
         expect(DirectoryItem.where(user_id: user.id).count).to eq(0)
       end
     end
+
+    context "with anonymous posting" do
+      fab!(:user)
+      fab!(:group) { Fabricate(:group, users: [user]) }
+
+      before do
+        SiteSetting.allow_anonymous_posting = true
+        SiteSetting.anonymous_posting_allowed_groups = group.id.to_s
+      end
+
+      it "doesn't create records for anonymous users" do
+        anon = AnonymousShadowCreator.get(user)
+        DirectoryItem.refresh!
+        expect(DirectoryItem.where(user_id: anon.id)).to be_blank
+        expect(DirectoryItem.where(user_id: user.id)).to be_present
+      end
+    end
   end
 end