Polymorphic search doesn't take polymorphic type into the query

[Looooong]

Given the polymorphic example from the wiki:

Location.ransack(locatable_of_House_type_number_eq: 100).result

The final query doesn't compare locatable_type = 'House'. This would gives false result, as the House id can match IDs from other polymorphic types as well.

Here is the full specs:

# You can run this file directly using `ruby` command
# Given bundler and rspec 3 are installed globally
# It might be different if you are using rspec 2
require 'bundler/inline'
require 'rspec/autorun'
require 'rspec/core/formatters/progress_formatter'
require 'rspec/core/profiler'

# TODO: Define dependencies
gemfile true do
  source 'https://rubygems.org'
  gem 'sqlite3'
  gem 'rspec-expectations'

  gem 'activerecord', '~> 5.2', require: %w[active_record active_record/relation]
  gem 'activesupport', require: 'active_support/dependencies/autoload'
  gem 'ransack', github: 'activerecord-hackery/ransack', ref: '6434e3bedfbf4cc5d97d33c84d10682970a95083'
end

ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')

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

  create_table :locations, force: true do |t|
    t.references :locatable, polymorphic: true
  end
end

class House < ActiveRecord::Base
  has_one :location, as: :locatable
end

class Location < ActiveRecord::Base
  belongs_to :locatable, polymorphic: true
end

RSpec.describe Location, type: :model do
  it 'queries correctly' do
    expect(Location.ransack(locatable_of_House_type_id_eq: 123).result.to_sql).to eq(<<-SQL.squish)
      SELECT "locations".*
      FROM "locations"
      LEFT OUTER JOIN "houses" ON "houses"."id" = "locations"."locatable_id"
      WHERE "houses"."id" = 123
        AND "locations"."locatable_type" = 'House'
    SQL
end

Output:

Failures:

  1) Location queries correctly
     Failure/Error:
       expect(Location.ransack(locatable_of_House_type_id_eq: 123).result.to_sql).to eq(<<-SQL.squish)
         SELECT \"locations\".*
         FROM \"locations\"
         LEFT OUTER JOIN \"houses\" ON \"houses\".\"id\" = \"locations\".\"locatable_id\"
         WHERE \"houses\".\"id\" = 123
           AND \"locations\".\"locatable_type\" = 'House'
       SQL
     
       expected: "SELECT \"locations\".* FROM \"locations\" LEFT OUTER JOIN \"houses\" ON \"houses\".\"id\" = \"locati...ons\".\"locatable_id\" WHERE \"houses\".\"id\" = 123 AND \"locations\".\"locatable_type\" = 'House'"
            got: "SELECT \"locations\".* FROM \"locations\" LEFT OUTER JOIN \"houses\" ON \"houses\".\"id\" = \"locations\".\"locatable_id\" WHERE \"houses\".\"id\" = 123"
     
       (compared using ==)

[PhilCoggins]

This is a dupe of an issue I opened #1039.

I have tirelessly tried to get this issue addressed, and even tried to fix myself, but the outlook is grim. I have a monkey patch in that issue that will work up to Rails 5.2.3, but anything beyond that, including Rails 6 the monkey patch will not work.

Edit: Also see my comment in this PR that addresses the specific issue with incorrect JOIN being generated #1077 (comment)