Follow up to bbe7fe4 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.

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 @@ def self.extended(base)
       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 @@ def _enum_methods_module
           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]
 

activerecord/lib/active_record/validations/uniqueness.rb

@@ -93,7 +93,7 @@ def deserialize_attribute(record, attribute, value)
       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

activerecord/test/cases/enum_test.rb

@@ -252,17 +252,38 @@ def self.name; 'Book'; end
   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