Add has_and_belongs_to_many back to reflections hash.

This adds back `has_and_belongs_to_many` reflection to the reflections
hash. Even thought we are not using that internally, as
`Model.reflections` is a public method we need to keep the hash of
reflections coherent.

ad7b5ef is the commit that made
has_and_belongs_to_many became a has_many :through and a has_many.

[fixes #14682]

activerecord/lib/active_record/associations.rb

@@ -1606,6 +1606,9 @@ def destroy_associations
         end
 
         has_many name, scope, hm_options, &extension
+
+        reflection = ActiveRecord::Reflection::AssociationReflection.new(:has_and_belongs_to_many, name, scope, options, self)
+        self.reflections = self.reflections.except(middle_reflection.name).merge!(name => reflection)
       end
     end
   end

activerecord/lib/active_record/reflection.rb

@@ -4,8 +4,10 @@ module Reflection # :nodoc:
     extend ActiveSupport::Concern
 
     included do
+      class_attribute :_reflections
       class_attribute :reflections
       class_attribute :aggregate_reflections
+      self._reflections = {}
       self.reflections = {}
       self.aggregate_reflections = {}
     end
@@ -22,6 +24,7 @@ def self.create(macro, name, scope, options, ar)
     end
 
     def self.add_reflection(ar, name, reflection)
+      ar._reflections = ar._reflections.merge(name => reflection)
       ar.reflections = ar.reflections.merge(name => reflection)
     end
 
@@ -62,7 +65,7 @@ def reflect_on_aggregation(aggregation)
       #   Account.reflect_on_all_associations(:has_many)  # returns an array of all has_many associations
       #
       def reflect_on_all_associations(macro = nil)
-        association_reflections = reflections.values
+        association_reflections = :has_and_belongs_to_many == macro ? reflections.values : _reflections.values
         macro ? association_reflections.select { |reflection| reflection.macro == macro } : association_reflections
       end
 
@@ -77,7 +80,7 @@ def reflect_on_association(association)
 
       # Returns an array of AssociationReflection objects for all associations which have <tt>:autosave</tt> enabled.
       def reflect_on_all_autosave_associations
-        reflections.values.select { |reflection| reflection.options[:autosave] }
+        _reflections.values.select { |reflection| reflection.options[:autosave] }
       end
     end
 

activerecord/test/cases/reflection_test.rb

@@ -200,7 +200,12 @@ def test_association_reflection_in_modules
   end
 
   def test_reflection_should_not_raise_error_when_compared_to_other_object
-    assert_nothing_raised { Firm.reflections[:clients] == Object.new }
+    assert_nothing_raised { Firm._reflections[:clients] == Object.new }
+  end
+
+  def test_has_and_belongs_to_many_reflection
+    assert_equal :has_and_belongs_to_many, Category.reflections[:posts].macro
+    assert_equal :posts, Category.reflect_on_all_associations(:has_and_belongs_to_many).first.name
   end
 
   def test_has_many_through_reflection