NoMethodError: undefined method `length' for #<Arel::Nodes::SelectStatement:0x00007f1640044518>

[koic]

Probably related to the change by #2008.

Steps to reproduce

# frozen_string_literal: true

require "bundler/inline"

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

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem "rails", github: "rails/rails", branch: "master"
  gem "activerecord-oracle_enhanced-adapter",  github: "rsim/oracle-enhanced", branch: "master"
  gem "minitest"

  platforms :ruby do
    gem "ruby-oci8"
  end
end

require "active_record"
require "minitest/autorun"
require "logger"
require "active_record/connection_adapters/oracle_enhanced_adapter"

# Set Oracle enhanced adapter specific connection parameters
DATABASE_NAME = ENV["DATABASE_NAME"] || "orcl"
DATABASE_HOST = ENV["DATABASE_HOST"]
DATABASE_PORT = ENV["DATABASE_PORT"]
DATABASE_USER = ENV["DATABASE_USER"] || "oracle_enhanced"
DATABASE_PASSWORD = ENV["DATABASE_PASSWORD"] || "oracle_enhanced"
DATABASE_SYS_PASSWORD = ENV["DATABASE_SYS_PASSWORD"] || "admin"

CONNECTION_PARAMS = {
  adapter: "oracle_enhanced",
  database: DATABASE_NAME,
  host: DATABASE_HOST,
  port: DATABASE_PORT,
  username: DATABASE_USER,
  password: DATABASE_PASSWORD
}

ActiveRecord::Base.establish_connection(CONNECTION_PARAMS)

ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :posts, force: true do |t|
  end

  create_table :comments, force: true do |t|
    t.integer :post_id
  end
end

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

class BugTest < Minitest::Test
  def test_association_stuff
    post = Post.create!
    post.comments << Comment.create!

    assert_equal 1, Comment.where(post_id: Post.select(:id))
  end
end

Expected behavior

No errors.

Actual behavior

Error:
BugTest#test_association_stuff:
NoMethodError: undefined method `length' for #<Arel::Nodes::SelectStatement:0x00007f1640044518>
    /home/vagrant/.rvm/gems/ruby-2.7.2/bundler/gems/oracle-enhanced-662f543d1567/lib/arel/visitors/oracle.rb:144:in `visit_Arel_Nodes_In'
    /home/vagrant/.rvm/gems/ruby-2.7.2/bundler/gems/rails-75a65a905a5d/activerecord/lib/arel/visitors/visitor.rb:30:in `visit'
    /home/vagrant/.rvm/gems/ruby-2.7.2/bundler/gems/rails-75a65a905a5d/activerecord/lib/arel/visitors/to_sql.rb:779:in `block in inject_join'
    /home/vagrant/.rvm/gems/ruby-2.7.2/bundler/gems/rails-75a65a905a5d/activerecord/lib/arel/visitors/to_sql.rb:777:in `each'
    /home/vagrant/.rvm/gems/ruby-2.7.2/bundler/gems/rails-75a65a905a5d/activerecord/lib/arel/visitors/to_sql.rb:777:in `each_with_index'
    /home/vagrant/.rvm/gems/ruby-2.7.2/bundler/gems/rails-75a65a905a5d/activerecord/lib/arel/visitors/to_sql.rb:777:in `inject_join'
    /home/vagrant/.rvm/gems/ruby-2.7.2/bundler/gems/rails-75a65a905a5d/activerecord/lib/arel/visitors/to_sql.rb:177:in `collect_nodes_for'
    /home/vagrant/.rvm/gems/ruby-2.7.2/bundler/gems/rails-75a65a905a5d/activerecord/lib/arel/visitors/to_sql.rb:157:in `visit_Arel_Nodes_SelectCore'
    /home/vagrant/.rvm/gems/ruby-2.7.2/bundler/gems/rails-75a65a905a5d/activerecord/lib/arel/visitors/to_sql.rb:124:in `block in visit_Arel_Nodes_SelectStatement'

System configuration

6.1.0.rc1 (master)
rails/rails@75a65a9

Oracle enhanced adapter version:

6.1.0.alpha (master)
662f543

Ruby version:

ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x86_64-linux]

Oracle Database version:

As far as I can see, this error reproduced on Oracle 11g and 19c.

• Oracle XE 11.2.0-1.0
• Oracle Database 19c Enterprise Edition Release 19.0.0.0.0