prefix position_column w/ table name in higher/lower item queries

Joining the relation returned by `#higher_items` or `#lower_items`
to a table also having `position_column` would result in an
ambiguous column error

lib/acts_as_list/active_record/acts/list.rb

@@ -255,8 +255,8 @@ def higher_items(limit=nil)
           limit ||= acts_as_list_list.count
           position_value = send(position_column)
           acts_as_list_list.
-            where("#{position_column} < ?", position_value).
-            where("#{position_column} >= ?", position_value - limit).
+            where("#{acts_as_list_class.table_name}.#{position_column} < ?", position_value).
+            where("#{acts_as_list_class.table_name}.#{position_column} >= ?", position_value - limit).
             limit(limit).
             order("#{quoted_table_name}.#{quoted_position_column} ASC")
         end
@@ -273,8 +273,8 @@ def lower_items(limit=nil)
           limit ||= acts_as_list_list.count
           position_value = send(position_column)
           acts_as_list_list.
-            where("#{position_column} > ?", position_value).
-            where("#{position_column} <= ?", position_value + limit).
+            where("#{acts_as_list_class.table_name}.#{position_column} > ?", position_value).
+            where("#{acts_as_list_class.table_name}.#{position_column} <= ?", position_value + limit).
             limit(limit).
             order("#{quoted_table_name}.#{quoted_position_column} ASC")
         end

test/test_joined_list.rb

@@ -0,0 +1,64 @@
+require 'helper'
+
+ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
+ActiveRecord::Schema.verbose = false
+
+class Section < ActiveRecord::Base
+  has_many :items
+  acts_as_list
+
+  scope :visible, -> { where(visible: true) }
+end
+
+class Item < ActiveRecord::Base
+  belongs_to :section
+  acts_as_list scope: :section
+
+  scope :visible, -> { where(visible: true).joins(:section).merge(Section.visible) }
+end
+
+class JoinedTestCase < Minitest::Test
+  def setup
+    ActiveRecord::Base.connection.create_table :sections do |t|
+      t.column :position, :integer
+      t.column :visible, :boolean, default: true
+    end
+
+    ActiveRecord::Base.connection.create_table :items do |t|
+      t.column :position, :integer
+      t.column :section_id, :integer
+      t.column :visible, :boolean, default: true
+    end
+
+    ActiveRecord::Base.connection.schema_cache.clear!
+    [Section, Item].each(&:reset_column_information)
+    super
+  end
+
+  def teardown
+    ActiveRecord::Base.connection.tables.each do |table|
+      ActiveRecord::Base.connection.drop_table(table)
+    end
+    super
+  end
+end
+
+# joining the relation returned by `#higher_items` or `#lower_items` to another table
+# previously could result in ambiguous column names in the query
+class TestHigherLowerItems < JoinedTestCase
+  def test_higher_items
+    section = Section.create
+    item1 = Item.create section: section
+    item2 = Item.create section: section
+    item3 = Item.create section: section
+    assert_equal item3.higher_items.visible, [item1, item2]
+  end
+
+  def test_lower_items
+    section = Section.create
+    item1 = Item.create section: section
+    item2 = Item.create section: section
+    item3 = Item.create section: section
+    assert_equal item1.lower_items.visible, [item2, item3]
+  end
+end