resolves #4268 implicitly attach nested list that has block attribute lines to dlist entry

CHANGELOG.adoc

@@ -73,6 +73,7 @@ Bug Fixes::
   * Don't allow target of include directive to start with a space (to distinguish it from a dlist item) or to end with a space
   * Manify alt text of block image in manpage output (#4401)
   * Adjust font size of term in horizontal dlist to match font size of term in regular dlist
+  * Implicitly attach nested list that starts with block attribute lines to dlist entry (#4268)
 
 == 2.0.18 (2022-10-15) - @mojavelinux
 

lib/asciidoctor/parser.rb

@@ -1443,11 +1443,26 @@ def self.read_lines_for_list_item reader, list_type, sibling_trait = nil, has_te
         # we're being more strict here about the terminator, but I think that's a good thing
         buffer.concat reader.read_lines_until terminator: match.terminator, read_last_line: true, context: nil
         continuation = :inactive
-      # technically BlockAttributeLineRx only breaks if ensuing line is not a list item
-      # which really means BlockAttributeLineRx only breaks if it's acting as a block delimiter
-      # FIXME to be AsciiDoc compliant, we shouldn't break if style in attribute line is "literal" (i.e., [literal])
+      # BlockAttributeLineRx only breaks dlist if ensuing line is not a list item
       elsif dlist && continuation != :active && (BlockAttributeLineRx.match? this_line)
-        break
+        block_attribute_lines = [this_line]
+        while (next_line = reader.peek_line)
+          if is_delimited_block? next_line
+            interrupt = true
+          elsif next_line.empty? || ((next_line.start_with? '[') && (BlockAttributeLineRx.match? next_line))
+            block_attribute_lines << reader.read_line
+            next
+          elsif (AnyListRx.match? next_line) && !(is_sibling_list_item? next_line, list_type, sibling_trait)
+            buffer.concat block_attribute_lines
+          else # rubocop:disable Lint/DuplicateBranch
+            interrupt = true
+          end
+          break
+        end
+        if interrupt
+          reader.unshift_lines block_attribute_lines
+          break
+        end
       elsif continuation == :active && !this_line.empty?
         # literal paragraphs have special considerations (and this is one of
         # two entry points into one)

test/lists_test.rb

@@ -4155,6 +4155,89 @@
       assert_xpath '//*[@class="dlist"]/following-sibling::*[@class="paragraph"]', output, 1
       assert_xpath '//*[@class="dlist"]/following-sibling::*[@class="paragraph"]/p[text()="detached"]', output, 1
     end
+
+    test 'block attribute lines above nested horizontal list does not break list' do
+      input = <<~'EOS'
+      Operating Systems::
+      [horizontal]
+        Linux::: Fedora
+        BSD::: OpenBSD
+
+      Cloud Providers::
+        PaaS::: OpenShift
+        IaaS::: AWS
+      EOS
+
+      output = convert_string_to_embedded input
+      assert_xpath '//dl', output, 2
+      assert_xpath '/*[@class="dlist"]/dl', output, 1
+      assert_xpath '(//dl)[1]/dd', output, 2
+      assert_xpath '((//dl)[1]/dd)[1]//table', output, 1
+      assert_xpath '((//dl)[1]/dd)[2]//table', output, 0
+    end
+
+    test 'block attribute lines above nested list with style does not break list' do
+      input = <<~'EOS'
+      TODO List::
+      * get groceries
+      Grocery List::
+      [square]
+      * bread
+      * milk
+      * lettuce
+      EOS
+
+      output = convert_string_to_embedded input
+      assert_xpath '//dl', output, 1
+      assert_xpath '(//dl)[1]/dd', output, 2
+      assert_xpath '((//dl)[1]/dd)[2]//ul[@class="square"]', output, 1
+    end
+
+    test 'multiple block attribute lines above nested list does not break list' do
+      input = <<~'EOS'
+      Operating Systems::
+      [[variants]]
+      [horizontal]
+        Linux::: Fedora
+        BSD::: OpenBSD
+
+      Cloud Providers::
+        PaaS::: OpenShift
+        IaaS::: AWS
+      EOS
+
+      output = convert_string_to_embedded input
+      assert_xpath '//dl', output, 2
+      assert_xpath '/*[@class="dlist"]/dl', output, 1
+      assert_xpath '(//dl)[1]/dd', output, 2
+      assert_xpath '(//dl)[1]/dd/*[@id="variants"]', output, 1
+      assert_xpath '((//dl)[1]/dd)[1]//table', output, 1
+      assert_xpath '((//dl)[1]/dd)[2]//table', output, 0
+    end
+
+    test 'multiple block attribute lines separated by empty line above nested list does not break list' do
+      input = <<~'EOS'
+      Operating Systems::
+      [[variants]]
+
+      [horizontal]
+
+        Linux::: Fedora
+        BSD::: OpenBSD
+
+      Cloud Providers::
+        PaaS::: OpenShift
+        IaaS::: AWS
+      EOS
+
+      output = convert_string_to_embedded input
+      assert_xpath '//dl', output, 2
+      assert_xpath '/*[@class="dlist"]/dl', output, 1
+      assert_xpath '(//dl)[1]/dd', output, 2
+      assert_xpath '(//dl)[1]/dd/*[@id="variants"]', output, 1
+      assert_xpath '((//dl)[1]/dd)[1]//table', output, 1
+      assert_xpath '((//dl)[1]/dd)[2]//table', output, 0
+    end
   end
 
   context 'Item with text inline' do