Don't add task-list class to lists that have no tasks

Markdown documents can contain multiple lists, some of which might
contain tasks, and some which might not.

Prior to this commit the HTML::Pipeline::TaskList filter added the
'task-list' CSS class to all lists if at least one contained an item
that looked like a task. This made it impossible to style task lists
differently to other lists in the document.

Author: gma

lib/task_list/filter.rb

@@ -54,7 +54,7 @@ class Filter < HTML::Pipeline::Filter
 
     class XPathSelectorFunction
       def self.task_list_item(nodes)
-        nodes if nodes.text =~ ItemPattern
+        nodes.select { |node| node.text =~ ItemPattern }
       end
     end
 
@@ -95,12 +95,13 @@ def render_task_list_item(item)
         item.source.sub(ItemPattern, render_item_checkbox(item)), 'utf-8'
     end
 
-    # Public: Select all task lists from the `doc`.
+    # Public: Select all task list items within `container`.
     #
     # Returns an Array of Nokogiri::XML::Element objects for ordered and
-    # unordered lists.
-    def list_items
-      doc.xpath(ListItemSelector, XPathSelectorFunction)
+    # unordered lists. The container can either be the entire document (as
+    # returned by `#doc`) or an Element object.
+    def list_items(container)
+      container.xpath(ListItemSelector, XPathSelectorFunction)
     end
 
     # Filters the source for task list items.
@@ -112,7 +113,9 @@ def list_items
     #
     # Returns nothing.
     def filter!
-      list_items.reverse.each do |li|
+      list_items(doc).reverse.each do |li|
+        next if list_items(li.parent).empty?
+
         add_css_class(li.parent, 'task-list')
 
         outer, inner =

test/task_list/filter_test.rb

@@ -13,6 +13,14 @@ def setup
     @item_selector = "input.task-list-item-checkbox[type=checkbox]"
   end
 
+  def test_has_no_effect_on_lists_with_no_tasks
+    text = <<-md
+- plain
+- bullets
+    md
+    assert_equal 0, filter(text)[:output].css('ul.task-list').size
+  end
+
   def test_filters_items_in_a_list
     text = <<-md
 - [ ] incomplete