Merge pull request #51948 from justinko/issue-51938

Restore inferred association class with the same modularized name

activerecord/lib/active_record/reflection.rb

@@ -428,17 +428,21 @@ def autosave=(autosave)
       # a new association object. Use +build_association+ or +create_association+
       # instead. This allows plugins to hook into association object creation.
       def klass
-        @klass ||= compute_class(compute_name(class_name))
+        @klass ||= _klass(class_name)
+      end
+
+      def _klass(class_name) # :nodoc:
+        if active_record.name.demodulize == class_name
+          return compute_class("::#{class_name}") rescue NameError
+        end
+
+        compute_class(class_name)
       end
 
       def compute_class(name)
         name.constantize
       end
 
-      def compute_name(name) # :nodoc:
-        active_record.name.demodulize == name ? "::#{name}" : name
-      end
-
       # Returns +true+ if +self+ and +other_aggregation+ have the same +name+ attribute, +active_record+ attribute,
       # and +other_aggregation+ has an options hash assigned to it.
       def ==(other_aggregation)
@@ -986,7 +990,7 @@ def through_reflection?
       end
 
       def klass
-        @klass ||= delegate_reflection.compute_class(compute_name(class_name))
+        @klass ||= delegate_reflection._klass(class_name)
       end
 
       # Returns the source of the through reflection. It checks both a singularized

activerecord/test/cases/reflection_test.rb

@@ -208,6 +208,18 @@ def test_reflection_klass_with_same_demodularized_different_modularized_name
     assert_equal Nested::User, reflection.klass
   end
 
+  def test_reflection_klass_with_same_modularized_name
+    reflection = ActiveRecord::Reflection.create(
+      :has_many,
+      :nested_users,
+      nil,
+      {},
+      Nested::NestedUser
+    )
+
+    assert_equal Nested::NestedUser, reflection.klass
+  end
+
   def test_aggregation_reflection
     reflection_for_address = AggregateReflection.new(
       :address, nil, { mapping: [ %w(address_street street), %w(address_city city), %w(address_country country) ] }, Customer

activerecord/test/models/user.rb

@@ -28,4 +28,8 @@ module Nested
   class User < ActiveRecord::Base
     self.table_name = "users"
   end
+
+  class NestedUser < ActiveRecord::Base
+    has_many :nested_users
+  end
 end