Ensure HABTM relationships produce valid class names (Fixes #17119)

activerecord/lib/active_record/associations.rb

@@ -1700,7 +1700,7 @@ module ActiveRecord
         hm_options[:through] = middle_reflection.name
         hm_options[:source] = join_model.right_reflection.name
 
-        [:before_add, :after_add, :before_remove, :after_remove, :autosave, :validate, :join_table].each do |k|
+        [:before_add, :after_add, :before_remove, :after_remove, :autosave, :validate, :join_table, :class_name].each do |k|
           hm_options[k] = options[k] if options.key? k
         end
 

activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb

@@ -98,7 +98,7 @@ module ActiveRecord::Associations::Builder
 
     def middle_options(join_model)
       middle_options = {}
-      middle_options[:class] = join_model
+      middle_options[:class_name] = "#{lhs_model.name}::#{join_model.name}"
       middle_options[:source] = join_model.left_reflection.name
       if options.key? :foreign_key
         middle_options[:foreign_key] = options[:foreign_key]

activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb

@@ -1,5 +1,6 @@
 require "cases/helper"
 require 'models/developer'
+require 'models/computer'
 require 'models/project'
 require 'models/company'
 require 'models/customer'
@@ -80,7 +81,7 @@ end
 
 class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
   fixtures :accounts, :companies, :categories, :posts, :categories_posts, :developers, :projects, :developers_projects,
-           :parrots, :pirates, :parrots_pirates, :treasures, :price_estimates, :tags, :taggings
+           :parrots, :pirates, :parrots_pirates, :treasures, :price_estimates, :tags, :taggings, :computers
 
   def setup_data_for_habtm_case
     ActiveRecord::Base.connection.execute('delete from countries_treaties')
@@ -883,4 +884,12 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     child.special_projects << SpecialProject.new("name" => "Special Project")
     assert child.save, 'child object should be saved'
   end
+
+  def test_habtm_with_reflection_using_class_name_and_fixtures
+    assert_not_nil Developer._reflections['shared_computers']
+    # Checking the fixture for named association is important here, because it's the only way
+    # we've been able to reproduce this bug
+    assert_not_nil File.read(File.expand_path("../../../fixtures/developers.yml", __FILE__)).index("shared_computers")
+    assert_equal developers(:david).shared_computers.first, computers(:laptop)
+  end
 end

activerecord/test/fixtures/computers.yml

@@ -3,3 +3,8 @@ workstation:
   system: 'Linux'
   developer: 1
   extendedWarranty: 1
+
+laptop:
+  system: 'MacOS 1'
+  developer: 1
+  extendedWarranty: 1

activerecord/test/fixtures/developers.yml

@@ -2,6 +2,7 @@ david:
   id: 1
   name: David
   salary: 80000
+  shared_computers: laptop
 
 jamis:
   id: 2

activerecord/test/models/developer.rb

@@ -15,6 +15,8 @@ class Developer < ActiveRecord::Base
 
   accepts_nested_attributes_for :projects
 
+  has_and_belongs_to_many :shared_computers, class_name: "Computer"
+
   has_and_belongs_to_many :projects_extended_by_name,
       -> { extending(DeveloperProjectsAssociationExtension) },
       :class_name => "Project",

activerecord/test/schema/schema.rb

@@ -228,6 +228,11 @@ ActiveRecord::Schema.define do
     t.integer :extendedWarranty, null: false
   end
 
+  create_table :computers_developers, id: false, force: true do |t|
+    t.references :computer
+    t.references :developer
+  end
+
   create_table :contracts, force: true do |t|
     t.integer :developer_id
     t.integer :company_id