(Added on AUG 20, 2014)

Since the update of Octopress source code, this post won’t make sense anymore. I can’t find a way to use MathJax in category list entries anymore because category in plugins/category_generator.rb and plugins/category_list_tag.rb have both been changed to lower case. I don’t know how to track the Ruby code to revert it.

Background

I imported some posts in my old blog on WordPress.com, and some categories like “$\rm \LaTeX$-Suite” weren’t displayed properly. Moreover, the link for some categories like “C/C++” was dead in Watson’s Category List Plugin.

Unlike two months ago¹, I now think that it’s better for me to find out why the catergory list failed to generate a correct URL for a category page, but the default links for category pages in the blog archive are right.

I certainly know the precise location of the part of plugins/category_list_tag.rb that has generated the erroneous links for some category pages.

category_url = File.join(category_dir, category.gsub(/_|\P{Word}/, '-').gsub(/-{2,}/, '-').downcase)

Finding the solution

I tried to browse the code in plugins/category_generator.rb to find out Octopress’s way of generating the URL of categories and what’s wrong with the above method to extract category_url.

At the beginning, I saw category_dir, and used * and n in Vim to explore the script. I did so because in plugins/category_list_tag.rb, category_dir was a part of category_url. I jumped through the category_dirs for a few times since they weren’t related to the generation of the URL for a category page. When the cursor was at line 109, I discovered the word category.to_url. I typed * on to_url, and was brought to line 176. This category.to_url was in category_link method. From the <a> tag inside this method, I’m sure that I should give to_url a try.

"<a class='category' href='/#{dir}/#{category.to_url}/'>#{category}</a>"

Verifying my guess

To test if my guess is correct, I used to most primitive method for debugging: insert puts category + ": " + category.to_url below the line that defined category_url in plugins/category_list_tag.rb. After that, I generated and previewed the site.

For the terminal output, I could see that catergory was the name of the a category, while category_url was part of the correct URL for a category page. Therefore, in plugins/category_list_tag.rb, the method that generated category_url should be changed like this:

category_url = File.join(category_dir, category.to_url)

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