$ rails new example
$ cd example
# I don't use Node.js, so:
$ sed -i '/rubyracer/s/^# //' Gemfile
$ bundle install

$ ./bin/rails g model topic subject:string body:text bumped_at:datetime
$ ./bin/rails db:migrate
$ ./bin/rails g migration AddIndexOnTopics

# Edit the migration file so it becomes:
class AddIndexOnTopics < ActiveRecord::Migration[5.1]
  def change
    add_index :topics, :bumped_at, order: {bumped_at: :desc}
  end
end

$ ./bin/rails db:migrate
$ grep INDEX log/development.log
   (3.1ms)  CREATE  INDEX "index_topics_on_bumped_at" ON "topics" ("bumped_at" DESC)
$ sqlite3 db/development.sqlite3
SQLite version 3.8.7.1 2014-10-29 13:59:56
Enter ".help" for usage hints.
sqlite> .fullschema
CREATE TABLE "schema_migrations" ("version" varchar NOT NULL PRIMARY KEY);
CREATE TABLE "ar_internal_metadata" ("key" varchar NOT NULL PRIMARY KEY, "value" varchar, "created_at" datetime NOT NULL, "updated_at" datetime NOT NULL);
CREATE TABLE "topics" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "subject" varchar, "body" text, "bumped_at" datetime, "created_at" datetime NOT NULL, "
updated_at" datetime NOT NULL);
CREATE INDEX "index_topics_on_bumped_at" ON "topics" ("bumped_at" DESC);
/* No STAT tables available */
sqlite>

$ grep -A1 -B1 index db/schema.rb
    t.datetime "updated_at", null: false
    t.index ["bumped_at"], name: "index_topics_on_bumped_at"
  end

$ ./bin/rails db:drop
$ ./bin/rails db:schema:load
$ grep INDEX log/development.log|tail -1
   (10.5ms)  CREATE  INDEX "index_topics_on_bumped_at" ON "topics" ("bumped_at")
$ sqlite3 db/development.sqlite3
SQLite version 3.8.7.1 2014-10-29 13:59:56
Enter ".help" for usage hints.
sqlite> .fullschema
CREATE TABLE "topics" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "subject" varchar, "body" text, "bumped_at" datetime, "created_at" datetime NOT NULL, "
updated_at" datetime NOT NULL);
CREATE INDEX "index_topics_on_bumped_at" ON "topics" ("bumped_at");
CREATE TABLE "schema_migrations" ("version" varchar NOT NULL PRIMARY KEY);
CREATE TABLE "ar_internal_metadata" ("key" varchar NOT NULL PRIMARY KEY, "value" varchar, "created_at" datetime NOT NULL, "updated_at" datetime NOT NULL);
/* No STAT tables available */
sqlite>

$ ruby -v
ruby 2.4.2p198 (2017-09-14 revision 59899) [x86_64-linux]
$ rails -v
Rails 5.1.4