Problem

Currently, running bundle exec rdoc in the repository root causes the following error:

uh-oh! RDoc had a problem:

Directory doc already exists, but it looks like it isn't an RDoc directory.

Because RDoc doesn't want to risk destroying any of your existing files,
you'll need to specify a different output directory name (using the --op <dir>
option)


run with --debug for full backtrace

Solution

That seems caused by doc directory. Inside it there's rdoc/markup_reference.rb file only.
While this file seems to be processed by Rakefile, it doesn't have to exist in doc directory since the file path is hardcoded.
So moving rdoc/markup_reference.rb file into some other place should be enough.