RDoc crashes when nested class inherits via superclass constant lookup

[skatkov]

RDoc crashes with NoMethodError: undefined method 'name' for nil when parsing a valid nested class whose superclass is resolved through the containing class's inheritance chain.

Ruby executes the file correctly, but RDoc fails in RDoc::Parser::Ruby#add_module_or_class.

Reproduction

Create a clean directory with this Gemfile:

source "https://rubygems.org"

gem "rdoc", "8.0.0"
gem "prism", "1.9.0"

Create repro.rb:

module Example
  class Base
    class Connection
    end
  end

  class Docker < Base
    class Connection < Example::Docker::Connection
    end
  end
end

Install dependencies:

bundle install

Verify that the Ruby is valid:

ruby -c repro.rb
ruby -I. -rrepro -e 'p Example::Docker::Connection.superclass'

Output:

Syntax OK
Example::Base::Connection

Run RDoc:

bundle exec rdoc --debug --force-output --output=doc repro.rb

Actual Behavior

RDoc crashes:

The internal error was:

  (NoMethodError) undefined method 'name' for nil

rdoc-8.0.0/lib/rdoc/parser/ruby.rb:810:in `RDoc::Parser::Ruby#add_module_or_class'
rdoc-8.0.0/lib/rdoc/parser/ruby.rb:966:in `RDoc::Parser::Ruby::RDocVisitor#visit_class_node'
prism-1.9.0/lib/prism/node.rb:4085:in `Prism::ClassNode#accept'

The failing line in RDoc is:

elsif (mod.superclass.is_a?(String) || mod.superclass.name == "Object") &&

mod.superclass is nil in this case.

Expected Behavior

RDoc should generate documentation without crashing and record:

Example::Docker::Connection < Example::Base::Connection

If we switch to YARD, it can handle this case just fine.

Explanation

When Ruby evaluates:

class Connection < Example::Docker::Connection

the new Example::Docker::Connection constant has not yet been assigned. Constant lookup therefore finds the inherited Example::Base::Connection constant through Example::Docker < Example::Base.

RDoc appears not to handle this inherited constant lookup while constructing its class metadata.

Real-World Example

This occurs in the kitchen-docker gem, due to following code:

class Docker < Kitchen::Transport::Base
  class Connection < Kitchen::Transport::Docker::Connection
  end
end

Source: lib/kitchen/transport/docker.rb.

See here:
https://github.com/test-kitchen/kitchen-docker