index_exists? doesn't match column names in PostgreSQL for lower(name)

[stanhu]

Steps to reproduce

# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  gem "rails"
  gem "pg"
end

require "active_record"
require "minitest/autorun"
require "logger"

TABLE_NAME = "some_table_name"
INDEX_NAME = "some_index_name"
PG_HOST = '/tmp'

# Make sure to setup your connection config!
conn_config = {
  dbname: "your_database",
  #  host: "host",
  host: PG_HOST,
  port: 5432,
  user: "",
  # password: "password"
}

# Some unique db_name
db_name = "pull_request_test_#{SecureRandom.hex}"

db_conn = PG.connect(conn_config)
db_conn.exec("CREATE DATABASE #{db_name}")

ActiveRecord::Base.logger = Logger.new(STDOUT)
ActiveRecord::Base.establish_connection(adapter: "postgresql", database: db_name, host: PG_HOST)

ActiveRecord::Schema.define do
  create_table TABLE_NAME, force: true do |t|
    t.string :column1
  end

end

class AddIndexToPublicSchema < ActiveRecord::Migration[5.2]
  def up
    add_index TABLE_NAME, 'lower((column1)::text)', name: INDEX_NAME
  end
end

class BugTest < Minitest::Test
  def test_failed_add_index
    AddIndexToPublicSchema.migrate(:up)
    assert ActiveRecord::Base.connection.index_exists?(TABLE_NAME, "lower((column1)::text)", name: INDEX_NAME)
  end
end

This appears to happen because indexes(TABLE_NAME).columns returns lower(column1). However,

rails/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb

Lines 101 to 103 in d3327ca

	column_names = Array(column_name).map(&:to_s)
	checks = []
	checks << lambda { |i| i.columns == column_names }

expects the list of columns to be an array.

The workaround appears to use index_name_exists? to skip the column name check.

Expected behavior

index_exists? returns true.

Actual behavior

index_exists? returns false.

System configuration

Rails version: 5.2.3

Ruby version: 2.6.3