Presence of an expression index causes problems when removing indexes

[benubois]

Steps to reproduce

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"
  # Activate the gem you are reporting the issue against.
  gem "activerecord", "5.0.0.1"
  gem "pg"
end

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

# Ensure backward compatibility with Minitest 4
Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection("postgres://postgres@localhost:5432/test")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :users, force: true do |t|
    t.text :email
    t.string :token
  end
  execute "CREATE UNIQUE INDEX index_users_on_lower_email ON users (LOWER(email))"
  add_index :users, :token, unique: true
end

class BugTest < Minitest::Test
  def test_remove_index
    ActiveRecord::Base.connection.remove_index :users, :token
  end
end

Expected behavior

I think this should run without throwing any exceptions.

Actual behavior

This throws a NoMethodError exception.

BugTest#test_remove_index:
NoMethodError: undefined method `join' for "lower(email)":String
Did you mean?  JSON
    /Users/ben/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/activerecord-5.0.0.1/lib/active_record/connection_adapters/abstract/schema_statements.rb:1210:in `block in index_name_for_remove'
    /Users/ben/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/activerecord-5.0.0.1/lib/active_record/connection_adapters/abstract/schema_statements.rb:1215:in `block (2 levels) in index_name_for_remove'
    /Users/ben/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/activerecord-5.0.0.1/lib/active_record/connection_adapters/abstract/schema_statements.rb:1215:in `each'
    /Users/ben/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/activerecord-5.0.0.1/lib/active_record/connection_adapters/abstract/schema_statements.rb:1215:in `all?'
    /Users/ben/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/activerecord-5.0.0.1/lib/active_record/connection_adapters/abstract/schema_statements.rb:1215:in `block in index_name_for_remove'
    /Users/ben/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/activerecord-5.0.0.1/lib/active_record/connection_adapters/abstract/schema_statements.rb:1215:in `select'
    /Users/ben/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/activerecord-5.0.0.1/lib/active_record/connection_adapters/abstract/schema_statements.rb:1215:in `index_name_for_remove'
    /Users/ben/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/activerecord-5.0.0.1/lib/active_record/connection_adapters/postgresql/schema_statements.rb:563:in `remove_index'
    bug.rb:37:in `test_remove_index'

System configuration

Rails version:
5.0.0.1

Ruby version:
2.3.1

Postgres version:
9.5.0.0

It looks like index_name_for_remove is expecting i.columns to be an array of strings, but in the case of an expression index it is just a string.

This was added in 8ceb883 by @greysteil.

[utilum]

The test reproduces on my machine.

[uaihebert]

I was able to find where the problem is:

For the index created by the SQL command the returned columns value is a pure string. That is why is breaking when we fire the query.

When I get home I will fix it. ( :