resolves asciidoctor#4033 don't assign nil value to named attribute m…

…apped to absent positional attribute when parsing attrlist

CHANGELOG.adoc

@@ -13,6 +13,12 @@ endif::[]
 This document provides a high-level view of the changes introduced in Asciidoctor by release.
 For a detailed view of what has changed, refer to the {uri-repo}/commits/master[commit history] on GitHub.
 
+== Unreleased
+
+Bug Fixes::
+
+  * Don't assign nil value to named attribute mapped to absent positional attribute when parsing attrlist (#4033)
+
 // tag::compact[]
 == 2.0.14 (2021-04-19) - @mojavelinux
 

lib/asciidoctor/attribute_list.rb

@@ -173,7 +173,7 @@ def parse_attribute index, positional_attrs
       end
     else
       name = @block.apply_subs name if single_quoted && @block
-      if (positional_attr_name = positional_attrs[index])
+      if (positional_attr_name = positional_attrs[index]) && name
         @attributes[positional_attr_name] = name
       end
       # QUESTION should we assign the positional key even when it's claimed by a positional attribute?

test/attribute_list_test.rb

@@ -262,11 +262,10 @@ def doc.apply_subs *args
     assert_equal expected, attributes
   end
 
-  # FIXME this is a negative test that should be updated when the problem is fixed
-  test 'should assign nil to attribute mapped to missing positional attribute' do
+  test 'should not assign nil to attribute mapped to missing positional attribute' do
     attributes = {}
     line = 'alt text,,100'
-    expected = { 1 => 'alt text', 2 => nil, 3 => '100', 'alt' => 'alt text', 'width' => nil, 'height' => '100' }
+    expected = { 1 => 'alt text', 2 => nil, 3 => '100', 'alt' => 'alt text', 'height' => '100' }
     Asciidoctor::AttributeList.new(line).parse_into(attributes, %w(alt width height))
     assert_equal expected, attributes
   end

test/blocks_test.rb

@@ -2590,11 +2590,11 @@ def names
       assert_xpath '/*[@class="imageblock"]//img[@src="images/tiger.png"][@alt="Tiger"][@width="200"][@height="300"]', output, 1
     end
 
-    # FIXME this is a negative test that should be updated when the problem is fixed
-    test 'should output empty width attribute if positional width attribute is empty' do
+    test 'should not output empty width attribute if positional width attribute is empty' do
       input = 'image::images/tiger.png[Tiger,]'
       output = convert_string_to_embedded input
-      assert_xpath '/*[@class="imageblock"]//img[@src="images/tiger.png"][@width=""]', output, 1
+      assert_xpath '/*[@class="imageblock"]//img[@src="images/tiger.png"]', output, 1
+      assert_xpath '/*[@class="imageblock"]//img[@src="images/tiger.png"][@width]', output, 0
     end
 
     test "can convert block image with link" do