Parsing an inline link causes processor to crash for certain matches

[rymsha]

Recently we started to to see such error.

Downgrading to asciidoctor/docker-asciidoctor:1.66 helps, so the bug must be since Asciidoctor version 2.0.21

/usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/substitutors.rb:540:in `+': no implicit conversion of nil into String (TypeError)

          target = $3 + $6
                        ^^
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/substitutors.rb:540:in `block in sub_macros'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/substitutors.rb:535:in `gsub'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/substitutors.rb:535:in `sub_macros'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/substitutors.rb:102:in `block in apply_subs'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/substitutors.rb:91:in `each'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/substitutors.rb:91:in `apply_subs'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/table.rb:358:in `text'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/table.rb:378:in `content'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/converter/html5.rb:906:in `block (3 levels) in convert_table'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/converter/html5.rb:896:in `each'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/converter/html5.rb:896:in `block (2 levels) in convert_table'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/converter/html5.rb:894:in `each'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/converter/html5.rb:894:in `block in convert_table'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/converter/html5.rb:891:in `each'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/converter/html5.rb:891:in `convert_table'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/converter/html5.rb:81:in `convert'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/abstract_block.rb:76:in `convert'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/abstract_block.rb:85:in `block in content'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/abstract_block.rb:85:in `map'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/abstract_block.rb:85:in `content'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/converter/html5.rb:426:in `convert_section'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/converter/html5.rb:55:in `convert'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/abstract_block.rb:76:in `convert'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/abstract_block.rb:85:in `block in content'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/abstract_block.rb:85:in `map'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/abstract_block.rb:85:in `content'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/converter/html5.rb:425:in `convert_section'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/converter/html5.rb:55:in `convert'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/abstract_block.rb:76:in `convert'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/abstract_block.rb:85:in `block in content'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/abstract_block.rb:85:in `map'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/abstract_block.rb:85:in `content'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/document.rb:1012:in `content'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/converter/html5.rb:227:in `convert_document'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/converter/html5.rb:85:in `convert'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/document.rb:956:in `convert'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/convert.rb:118:in `convert'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/convert.rb:190:in `block in convert_file'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/convert.rb:190:in `open'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/convert.rb:190:in `convert_file'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/cli/invoker.rb:129:in `block in invoke!'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/cli/invoker.rb:112:in `each'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/lib/asciidoctor/cli/invoker.rb:112:in `invoke!'
	from /usr/lib/ruby/gems/3.2.0/gems/asciidoctor-2.0.22/bin/asciidoctor:15:in `<top (required)>'
	from /usr/bin/asciidoctor:25:in `load'
	from /usr/bin/asciidoctor:25:in `<main>'

[mojavelinux]

There's a known issue when invalid syntax is used, such as:

<<https://example.com,Example>>

Can you confirm whether this is the use case that is triggering this error for you, or is there another syntax that is also causing it?

This issue is related to the fix for the following issue #4468. There is always a risk when modifying the parsing regular expressions that it will introduce unexpected match errors that aren't covered by the test suite.

[rymsha]

Yes it was the case
Changed
<<link:https://www.unix.com/man-page/linux/5/crontab,format>>
to
link:https://www.unix.com/man-page/linux/5/crontab[format]

[mojavelinux]

Thanks. That's good to know.

You should know that the link: prefix is redundant when the target is a URL. That's because https: is recognized as a macro prefix already. See https://docs.asciidoctor.org/asciidoc/latest/macros/link-macro/#when-to-use-the-link-macro