A heredoc following a comment that ends with a full-stop . is not highlighted properly.

    let(:source) do
      # Empty lines should make no difference.
      <<~RUBY
        if #{condition}
          #{body}

        end
      RUBY
    end

Removing the full-stop . at the end of the comment allows the heredoc to be highlighted as expected:

Unfortunately, I can't think of a way to fix this in a well-performing manner as I think it would require look-behind assertions to check if the preceding dot is part of a comment.