Duplicate column_defaults properly

Backport c517602 to fix #6115

Deleted:
    activerecord/lib/active_record/core.rb

Conflicts:
    activerecord/test/cases/base_test.rb

activerecord/CHANGELOG.md

@@ -1,5 +1,11 @@
 ## Rails 3.2.12 (unreleased) ##
 
+*   Don't update `column_defaults` when calling destructive methods on column with default value.
+    Backport c517602.
+    Fix #6115.
+
+    *Piotr Sarnacki + Aleksey Magusev + Alan Daud*
+
 *   When `#count` is used in conjunction with `#uniq` we perform `count(:distinct => true)`.
     Fix #6865.
 

activerecord/lib/active_record/base.rb

@@ -479,7 +479,8 @@ def relation #:nodoc:
       #   # Instantiates a single new object bypassing mass-assignment security
       #   User.new({ :first_name => 'Jamie', :is_admin => true }, :without_protection => true)
       def initialize(attributes = nil, options = {})
-        @attributes = self.class.initialize_attributes(self.class.column_defaults.dup)
+        defaults = Hash[self.class.column_defaults.map { |k, v| [k, v.duplicable? ? v.dup : v] }]
+        @attributes = self.class.initialize_attributes(defaults)
         @association_cache = {}
         @aggregation_cache = {}
         @attributes_cache = {}

activerecord/test/cases/base_test.rb

@@ -325,6 +325,12 @@ def test_first_or_initialize
     assert parrot.valid?
   end
 
+  def test_default_values_are_deeply_dupped
+    company = Company.new
+    company.description << "foo"
+    assert_equal "", Company.new.description
+  end
+
   def test_load
     topics = Topic.find(:all, :order => 'id')
     assert_equal(4, topics.size)
@@ -2148,7 +2154,7 @@ def test_marshalling_with_associations
   end
 
   def test_attribute_names
-    assert_equal ["id", "type", "ruby_type", "firm_id", "firm_name", "name", "client_of", "rating", "account_id"],
+    assert_equal ["id", "type", "ruby_type", "firm_id", "firm_name", "name", "client_of", "rating", "account_id", "description"],
                  Company.attribute_names
   end
 

activerecord/test/schema/schema.rb

@@ -176,6 +176,7 @@ def create_table(*args, &block)
     t.integer :client_of
     t.integer :rating, :default => 1
     t.integer :account_id
+    t.string :description, :null => false, :default => ""
   end
 
   add_index :companies, [:firm_id, :type, :rating, :ruby_type], :name => "company_index"