Reproducible issues with `unscope` when using `joins`

_rails_unscoping_relation.rb

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'

  # At this time, 5.x bundles appear to require the following to be successful.
  gem 'rails',           github: 'rails/rails' # path: '../rails'
  gem 'arel',            github: 'rails/arel',            branch: 'master'
  gem 'rack',            github: 'rack/rack',             branch: 'master'
  gem 'sprockets',       github: 'rails/sprockets',       branch: 'master'
  gem 'sprockets-rails', github: 'rails/sprockets-rails', branch: 'master'
  gem 'sass-rails',      github: 'rails/sass-rails',      branch: 'master'
  gem 'sqlite3'
end

require 'active_record'
require 'minitest/autorun'
require 'logger'

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :aaas do |t|
    t.timestamps null: false
    t.string :foo, null: true
    t.string :bar, null: true
  end

  create_table :bbbs do |t|
    t.timestamps null: false
    t.references :aaa
    t.string :bar, null: true
  end
end

class Aaa < ActiveRecord::Base
  has_one :bbb, inverse_of: :aaa
end

class Bbb < ActiveRecord::Base
  belongs_to :aaa, inverse_of: :bbb
end

class BugTest < Minitest::Test
  def setup_sql
    @literal   = Aaa.joins(:bbb).where('aaa.bar' => 'baz', 'bbb.bar' => 'foo')
    @nested_hash = Aaa.joins(:bbb).where(aaa: { bar: 'baz' }, bbb: { bar: 'foo' })

    @target_query       = 'SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id" WHERE "aaa"."bar" = \'baz\''
    @unscoped_condition = 'AND "bbb"."bar" = \'foo\''
  end

  def test_a_literal_definition_with_prefixed_unscope
    setup_sql
    a = @literal.unscope(where: ['bbb.bar'])

    assert (@target_query == a.to_sql), "Query mismatch.\n  Expected: #{@target_query}\n  Actual:   #{a.to_sql}"
  end

  def test_b_literal_definition_with_unprefixed_unscope
    setup_sql
    b = @literal.unscope(where: ['bar'])

    assert (@target_query == b.to_sql), "Query mismatch.\n  Expected: #{@target_query}\n  Actual:   #{b.to_sql}"
  end

  def test_c_nested_hash_definition_with_prefixed_unscope
    setup_sql
    c = @nested_hash.unscope(where: ['bbb.bar'])

    assert (@target_query == c.to_sql), "Query mismatch.\n  Expected: #{@target_query}\n  Actual:   #{c.to_sql}"
  end

  def test_d_nested_hash_definition_with_unprefixed_unscope
    setup_sql
    d = @nested_hash.unscope(where: ['bar'])

    assert (@target_query == d.to_sql), "Query mismatch.\n  Expected: #{@target_query}\n  Actual:   #{d.to_sql}"
  end
end

output_rails_4_2_4.txt

With gemfile section: 

```ruby
gemfile(true) do
  source 'https://rubygems.org'
  gem 'rails',           '4.2.4'
  gem 'arel',            '6.0.3'
  gem 'sqlite3'
end
```

==========================================================================================================================

-- create_table(:aaas)
D, [2015-09-08T10:29:28.727044 #5973] DEBUG -- :    (0.3ms)  CREATE TABLE "aaas" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "created_at" datetime NOT NULL, "updated_at" datetime NOT NULL, "foo" varchar, "bar" varchar) 
   -> 0.0017s
-- create_table(:bbbs)
D, [2015-09-08T10:29:28.727355 #5973] DEBUG -- :    (0.1ms)  CREATE TABLE "bbbs" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "created_at" datetime NOT NULL, "updated_at" datetime NOT NULL, "aaa_id" integer, "bar" varchar) 
   -> 0.0002s

# Running:

FFFF

Finished in 0.008255s, 484.5526 runs/s, 484.5526 assertions/s.

  1) Failure:
BugTest#test_a_literal_definition_with_prefixed_unscope [unscope_relation.rb:60]:
Query mismatch.
  Expected: SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id" WHERE "aaa"."bar" = 'baz'
  Actual:   SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id" WHERE "aaa"."bar" = 'baz' AND "bbb"."bar" = 'foo'


  2) Failure:
BugTest#test_b_literal_definition_with_unprefixed_unscope [unscope_relation.rb:67]:
Query mismatch.
  Expected: SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id" WHERE "aaa"."bar" = 'baz'
  Actual:   SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id"


  3) Failure:
BugTest#test_c_nested_hash_definition_with_prefixed_unscope [unscope_relation.rb:74]:
Query mismatch.
  Expected: SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id" WHERE "aaa"."bar" = 'baz'
  Actual:   SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id" WHERE "bbb"."bar" = 'foo' AND "aaa"."bar" = 'baz'


  4) Failure:
BugTest#test_d_nested_hash_definition_with_unprefixed_unscope [unscope_relation.rb:81]:
Query mismatch.
  Expected: SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id" WHERE "aaa"."bar" = 'baz'
  Actual:   SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id" WHERE "bbb"."bar" =  AND "aaa"."bar" = 'baz'

output_rails_5_edge.txt

-- create_table(:aaas)
D, [2015-09-08T10:24:08.136343 #2158] DEBUG -- :    (0.3ms)  CREATE TABLE "aaas" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "created_at" datetime NOT NULL, "updated_at" datetime NOT NULL, "foo" varchar, "bar" varchar) 
   -> 0.0032s
-- create_table(:bbbs)
D, [2015-09-08T10:24:08.136741 #2158] DEBUG -- :    (0.1ms)  CREATE TABLE "bbbs" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "created_at" datetime NOT NULL, "updated_at" datetime NOT NULL, "aaa_id" integer, "bar" varchar) 
   -> 0.0003s

# Running:

FFFF

Finished in 0.009412s, 424.9807 runs/s, 424.9807 assertions/s.

  1) Failure:
BugTest#test_a_literal_definition_with_prefixed_unscope [unscope_relation.rb:64]:
Query mismatch.
  Expected: SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id" WHERE "aaa"."bar" = 'baz'
  Actual:   SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id" WHERE "aaa"."bar" = 'baz' AND "bbb"."bar" = 'foo'


  2) Failure:
BugTest#test_b_literal_definition_with_unprefixed_unscope [unscope_relation.rb:71]:
Query mismatch.
  Expected: SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id" WHERE "aaa"."bar" = 'baz'
  Actual:   SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id"


  3) Failure:
BugTest#test_c_nested_hash_definition_with_prefixed_unscope [unscope_relation.rb:78]:
Query mismatch.
  Expected: SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id" WHERE "aaa"."bar" = 'baz'
  Actual:   SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id" WHERE "aaa"."bar" = 'baz' AND "bbb"."bar" = 'foo'


  4) Failure:
BugTest#test_d_nested_hash_definition_with_unprefixed_unscope [unscope_relation.rb:85]:
Query mismatch.
  Expected: SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id" WHERE "aaa"."bar" = 'baz'
  Actual:   SELECT "aaas".* FROM "aaas" INNER JOIN "bbbs" ON "bbbs"."aaa_id" = "aaas"."id"


4 runs, 4 assertions, 4 failures, 0 errors, 0 skips