Deprecate reflection class name to accept a class

The idea of `class_name` as an option of reflection is that passing a
string would allow us to lazy autoload the class.

Using `belongs_to :client, class_name: Customer` is eagerloading models more than necessary
and creating possible circular dependencies.

3 files changed, 11 insertions, 3 deletions

diff --git a/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb b/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
index 54fb61d6a5..efd2124679 100644
--- a/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
@@ -86,8 +86,10 @@ class DeveloperWithSymbolClassName < Developer
   has_and_belongs_to_many :projects, class_name: :ProjectWithSymbolsForKeys
 end
 
-class DeveloperWithConstantClassName < Developer
-  has_and_belongs_to_many :projects, class_name: ProjectWithSymbolsForKeys
+ActiveSupport::Deprecation.silence do
+  class DeveloperWithConstantClassName < Developer
+    has_and_belongs_to_many :projects, class_name: ProjectWithSymbolsForKeys
+  end
 end
 
 class DeveloperWithExtendOption < Developer
diff --git a/activerecord/test/cases/reflection_test.rb b/activerecord/test/cases/reflection_test.rb
index 0ef51272b9..2444eccab1 100644
--- a/activerecord/test/cases/reflection_test.rb
+++ b/activerecord/test/cases/reflection_test.rb
@@ -404,6 +404,12 @@ class ReflectionTest < ActiveRecord::TestCase
     assert_equal Client, Firm.reflect_on_association(:unsorted_clients_with_symbol).klass
   end
 
+  def test_class_for_class_name
+    assert_deprecated do
+      assert_predicate ActiveRecord::Reflection.create(:has_many, :clients, nil, { class_name: Client }, Firm), :validate?
+    end
+  end
+
   def test_join_table
     category = Struct.new(:table_name, :pluralize_table_names).new("categories", true)
     product = Struct.new(:table_name, :pluralize_table_names).new("products", true)
diff --git a/activerecord/test/models/user.rb b/activerecord/test/models/user.rb
index 47649e0a77..c099c57e37 100644
--- a/activerecord/test/models/user.rb
+++ b/activerecord/test/models/user.rb
@@ -5,7 +5,7 @@ class User < ActiveRecord::Base
   has_secure_token :auth_token
 
   has_and_belongs_to_many :jobs_pool,
-    class_name: Job,
+    class_name: "Job",
     join_table: "jobs_pool"
 end