resolves #4580 don't leave behind empty line inside skipped condition…

…al (PR #4582)

CHANGELOG.adoc

@@ -66,6 +66,10 @@ Improvements::
   * Return `nil` if name passed to `Asciidoctor::SafeMode.value_for_name` is not recognized (#3526)
   * Modify default stylesheet to honor text-* roles on quote blocks
 
+Bug Fixes::
+
+  * Don't leave behind empty line inside skipped preprocessor conditional (#4580)
+
 == 2.0.22 (2024-03-08) - @mojavelinux
 
 Improvements::

lib/asciidoctor/reader.rb

@@ -807,6 +807,10 @@ def process_line line
     return line unless @process_lines
 
     if line.empty?
+      if @skipping
+        shift
+        return nil
+      end
       @look_ahead += 1
       return line
     end

test/reader_test.rb

@@ -2232,6 +2232,19 @@ def process reader, target, attributes
         assert_equal 4, reader.lineno
       end
 
+      test 'peek_line returns nil if contents of skipped conditional is empty line' do
+        input = <<~'EOS'
+        ifdef::foobar[]
+
+        endif::foobar[]
+        EOS
+
+        doc = Asciidoctor::Document.new input
+        reader = doc.reader
+        assert_equal 1, reader.lineno
+        assert_nil reader.peek_line
+      end
+
       test 'ifdef with defined attribute includes content' do
         input = <<~'EOS'
         ifdef::holygrail[]
@@ -2541,6 +2554,19 @@ def process reader, target, attributes
         assert_equal 'Our quest is complete!', result
       end
 
+      test 'ifdef around empty line does not introduce extra line' do
+        input = <<~'EOS'
+        before
+        ifdef::no-such-attribute[]
+
+        endif::[]
+        after
+        EOS
+
+        result = (Asciidoctor::Document.new input).reader.read
+        assert_equal %(before\nafter), result
+      end
+
       test 'should log warning if endif is unmatched' do
         input = <<~'EOS'
         Our quest is complete!