Follow up to bbe7fe41 to fix enum leakage across classes.

The original attempt didn't really fix the problem and wasn't testing the
problematic area. This commit corrected those issues in the original commit.

Also removed the private `enum_mapping_for` method. As `defined_enums` is now a
method, this method doesn't provide much value anymore.

3 files changed, 35 insertions, 11 deletions

diff --git a/activerecord/lib/active_record/enum.rb b/activerecord/lib/active_record/enum.rb
index 167f8b7a49..6e0d19ad31 100644
--- a/activerecord/lib/active_record/enum.rb
+++ b/activerecord/lib/active_record/enum.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/object/deep_dup'
+
 module ActiveRecord
   # Declare an enum attribute where the values map to integers in the database,
   # but can be queried by name. Example:
@@ -70,8 +72,9 @@ module ActiveRecord
       base.defined_enums = {}
     end
 
-    def enum_mapping_for(attr_name) # :nodoc:
-      defined_enums[attr_name.to_s]
+    def inherited(base)
+      base.defined_enums = defined_enums.deep_dup
+      super
     end
 
     def enum(definitions)
@@ -136,7 +139,7 @@ module ActiveRecord
           mod = Module.new do
             private
               def save_changed_attribute(attr_name, value)
-                if (mapping = self.class.enum_mapping_for(attr_name))
+                if (mapping = self.class.defined_enums[attr_name])
                   if attribute_changed?(attr_name)
                     old = changed_attributes[attr_name]
 
diff --git a/activerecord/lib/active_record/validations/uniqueness.rb b/activerecord/lib/active_record/validations/uniqueness.rb
index 71c71cb4b1..ee080451a9 100644
--- a/activerecord/lib/active_record/validations/uniqueness.rb
+++ b/activerecord/lib/active_record/validations/uniqueness.rb
@@ -93,7 +93,7 @@ module ActiveRecord
       end
 
       def map_enum_attribute(klass, attribute, value)
-        mapping = klass.enum_mapping_for(attribute.to_s)
+        mapping = klass.defined_enums[attribute.to_s]
         value = mapping[value] if value && mapping
         value
       end
diff --git a/activerecord/test/cases/enum_test.rb b/activerecord/test/cases/enum_test.rb
index 5157c272ca..3b2f0dfe07 100644
--- a/activerecord/test/cases/enum_test.rb
+++ b/activerecord/test/cases/enum_test.rb
@@ -252,17 +252,38 @@ class EnumTest < ActiveRecord::TestCase
   end
 
   test "enums are distinct per class" do
-    Plane = Class.new(ActiveRecord::Base) do
-      enum status: [:grounded, :operational]
+    klass1 = Class.new(ActiveRecord::Base) do
+      self.table_name = "books"
+      enum status: [:proposed, :written]
+    end
+
+    klass2 = Class.new(ActiveRecord::Base) do
+      self.table_name = "books"
+      enum status: [:drafted, :uploaded]
     end
-    assert_equal({ "proposed" => 0, "written" => 1, "published" => 2 }, Book.statuses)
-    assert_equal({ "grounded" => 0, "operational" => 1 }, Plane.statuses)
+
+    book1 = klass1.proposed.create!
+    book1.status = :written
+    assert_equal ['proposed', 'written'], book1.status_change
+
+    book2 = klass2.drafted.create!
+    book2.status = :uploaded
+    assert_equal ['drafted', 'uploaded'], book2.status_change
   end
 
   test "enums are inheritable" do
-    Encyclopedia = Class.new(Book) do
-      enum status: [:published, :reprinted]
+    subklass1 = Class.new(Book)
+
+    subklass2 = Class.new(Book) do
+      enum status: [:drafted, :uploaded]
     end
-    assert_equal({ "published" => 0, "reprinted" => 1 }, Encyclopedia.statuses)
+
+    book1 = subklass1.proposed.create!
+    book1.status = :written
+    assert_equal ['proposed', 'written'], book1.status_change
+
+    book2 = subklass2.drafted.create!
+    book2.status = :uploaded
+    assert_equal ['drafted', 'uploaded'], book2.status_change
   end
 end