Merge pull request rails#21158 from lsylvester/only-invoke-mattr_accessor-default-block-once

Prevent the default block for mattr_accessor being called multiple times

Author: rafaelfranca

activesupport/lib/active_support/core_ext/module/attribute_accessors.rb

@@ -206,7 +206,7 @@ def #{sym}=(obj)
   #   Person.class_variable_get("@@hair_colors") # => [:brown, :black, :blonde, :red]
   def mattr_accessor(*syms, &blk)
     mattr_reader(*syms, &blk)
-    mattr_writer(*syms, &blk)
+    mattr_writer(*syms)
   end
   alias :cattr_accessor :mattr_accessor
 end

activesupport/test/core_ext/module/attribute_accessor_test.rb

@@ -76,4 +76,10 @@ def test_should_use_default_value_if_block_passed
     assert_equal 'default_reader_value', @module.defr
     assert_equal 'default_writer_value', @module.class_variable_get('@@defw')
   end
+
+  def test_should_not_invoke_default_value_block_multiple_times
+    count = 0
+    @module.cattr_accessor(:defcount){ count += 1 }
+    assert_equal 1, count
+  end
 end