Fix `define_attribute_method` with Symbol in AR

This issue is only appear when you try to call `define_attribute_method`
and passing a symbol in Active Record. It does not appear in isolation
in Active Model itself.

Before this patch, when you run `User.define_attribute_method :foo`, you
will get:

    NoMethodError: undefined method `unpack' for :foo:Symbol
        from activerecord/lib/active_record/attribute_methods/read.rb:28:in `define_method_attribute'
        from activerecord/lib/active_record/attribute_methods/primary_key.rb:61:in `define_method_attribute'
        from activemodel/lib/active_model/attribute_methods.rb:292:in `block in define_attribute_method'
        from activemodel/lib/active_model/attribute_methods.rb:285:in `each'
        from activemodel/lib/active_model/attribute_methods.rb:285:in `define_attribute_method'

This patch contains both a fix in Active Model and a test in Active
Record for this error.

1 files changed, 7 insertions, 0 deletions

diff --git a/activerecord/test/cases/attribute_methods_test.rb b/activerecord/test/cases/attribute_methods_test.rb
index 3dc0c0ce53..4d24a980dc 100644
--- a/activerecord/test/cases/attribute_methods_test.rb
+++ b/activerecord/test/cases/attribute_methods_test.rb
@@ -866,6 +866,13 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert subklass.method_defined?(:id), "subklass is missing id method"
   end
 
+  test "define_attribute_method works with both symbol and string" do
+    klass = Class.new(ActiveRecord::Base)
+
+    assert_nothing_raised { klass.define_attribute_method(:foo) }
+    assert_nothing_raised { klass.define_attribute_method("bar") }
+  end
+
   test "read_attribute with nil should not asplode" do
     assert_nil Topic.new.read_attribute(nil)
   end