users: don't set inviter field; clear inviter field for most users.

* Don't set the inviter field for newly promoted users, or for Gold/Plat
  upgrades.

* Clear the inviter field for paid Gold/Plat upgrades, and for users who
  have a feedback or a modaction listing who invited them. This leaves
  about 600 remaining users with an inviter field with no other record
  of who invited them.

See #4750.

app/logical/user_promotion.rb

@@ -18,7 +18,6 @@ class UserPromotion
     user.level = new_level
     user.can_upload_free = can_upload_free unless can_upload_free.nil?
     user.can_approve_posts = can_approve_posts unless can_approve_posts.nil?
-    user.inviter = promoter
 
     create_user_feedback
     create_dmail

app/models/user_upgrade.rb

@@ -119,7 +119,7 @@ class UserUpgrade < ApplicationRecord
     end
 
     def upgrade_recipient!
-      recipient.update!(level: level, inviter: User.system)
+      recipient.update!(level: level)
     end
 
     def create_mod_action!

script/fixes/076_clear_inviters.rb

@@ -0,0 +1,28 @@
+#!/usr/bin/env ruby
+
+require_relative "../../config/environment"
+
+User.transaction do
+  # Clear inviter for users who were listed as invited by Albert. Most of these
+  # are very old Gold upgrades. Others are old accounts who probably weren't
+  # invited by Albert himself.
+  p User.where(inviter_id: 1).count
+  User.where(inviter_id: 1).update_all(inviter_id: nil)
+
+  # Clear inviter for older Gold and Platinum upgrades where the user was listed as having invited themselves.
+  p User.where("inviter_id = id").count
+  User.where("inviter_id = id").update_all(inviter_id: nil)
+
+  # Clear inviter for newer Gold and Platinum upgrades where the user was listed as being invited by DanbooruBot.
+  p User.where(inviter_id: User.system.id).count
+  User.where(inviter_id: User.system.id).update_all(inviter_id: nil)
+
+  # Clear inviter for users where there is a promotion feedback from the inviter.
+  p User.joins(:feedback).where.not(inviter_id: nil).where_regex(:body, "^(You have been promoted|You gained the ability|Promoted from|Promoted by)").where("inviter_id = user_feedback.creator_id").count
+  User.joins(:feedback).where.not(inviter_id: nil).where_regex(:body, "^(You have been promoted|You gained the ability|Promoted from|Promoted by)").where("inviter_id = user_feedback.creator_id").update_all(inviter_id: nil)
+
+  # Clear inviter for users where there is a promotion modaction from the inviter.
+  sql = "JOIN (SELECT (regexp_matches(description, '/users/([0-9]+)'))[1]::integer as user_id, * FROM mod_actions) AS subquery ON subquery.user_id = users.id"
+  p User.joins(sql).where("subquery.category": [7, 8, 9, 19]).where("users.inviter_id = subquery.creator_id").count
+  User.joins(sql).where("subquery.category": [7, 8, 9, 19]).where("users.inviter_id = subquery.creator_id").update_all(inviter_id: nil)
+end