Add ability to block words in usernames (#35407)

db/migrate/20250717003848_create_username_blocks.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+class CreateUsernameBlocks < ActiveRecord::Migration[8.0]
+  def change
+    create_table :username_blocks do |t|
+      t.string :username, null: false
+      t.string :normalized_username, null: false
+      t.boolean :exact, null: false, default: false
+      t.boolean :allow_with_approval, null: false, default: false
+
+      t.timestamps
+    end
+
+    add_index :username_blocks, 'lower(username)', unique: true, name: 'index_username_blocks_on_username_lower_btree'
+    add_index :username_blocks, :normalized_username
+
+    reversible do |dir|
+      dir.up do
+        load Rails.root.join('db', 'seeds', '05_blocked_usernames.rb')
+      end
+    end
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2025_06_27_132728) do
+ActiveRecord::Schema[8.0].define(version: 2025_07_17_003848) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_catalog.plpgsql"
 
@@ -1238,6 +1238,17 @@ ActiveRecord::Schema[8.0].define(version: 2025_06_27_132728) do
     t.datetime "updated_at", null: false
   end
 
+  create_table "username_blocks", force: :cascade do |t|
+    t.string "username", null: false
+    t.string "normalized_username", null: false
+    t.boolean "exact", default: false, null: false
+    t.boolean "allow_with_approval", default: false, null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index "lower((username)::text)", name: "index_username_blocks_on_username_lower_btree", unique: true
+    t.index ["normalized_username"], name: "index_username_blocks_on_normalized_username"
+  end
+
   create_table "users", force: :cascade do |t|
     t.string "email", default: "", null: false
     t.datetime "created_at", precision: nil, null: false

db/seeds/05_blocked_usernames.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+%w(
+  abuse
+  account
+  accounts
+  admin
+  administration
+  administrator
+  admins
+  help
+  helpdesk
+  instance
+  mod
+  moderator
+  moderators
+  mods
+  owner
+  root
+  security
+  server
+  staff
+  support
+  webmaster
+).each do |str|
+  UsernameBlock.create_with(username: str, exact: true).find_or_create_by(username: str)
+end
+
+%w(
+  mastodon
+  mastadon
+).each do |str|
+  UsernameBlock.create_with(username: str, exact: false).find_or_create_by(username: str)
+end