Twenty Ten child themes and twentyten_the_page_number

Fatal error: Call to undefined function twentyten_the_page_number() in wp-content/themes/my-child-theme/header.php on line 8

Twenty Ten, the new default theme in WordPress 3.0, is a phenomenal theme that makes a great parent theme. This site indeed uses Twenty Ten, with a lightweight child theme that changes some of the styling and has a small functions.php file to add a few small touches of functionality.

When Twenty Ten was first committed to WordPress trunk, core contributors and committers swooped in and started making line-by-line incremental improvements. The new default theme was, by and large, why WordPress 3.0 had some incredible innovations for theme developers, with custom backgrounds, headers, and menus; get_template_part(); and other features. It’s because we became theme developers ourselves.

An pre-release version of Twenty Ten contained a function called twentyten_the_page_number(). It was redundant, and thus removed before WordPress 3.0 and Twenty Ten 1.1 were shipped. But a few child themes were already expecting this function to be available, causing them to break.

Today, 42 days after the release of 3.0, we’ve released WordPress 3.0.1. With it, we’ve packaged Twenty Ten 1.1. But there are still some individuals out there who want to leverage a child theme that still expects this function to exist. This a short plugin will fix it for you.

Rethinking template tags in plugins

Some plugins offer their own template tags that the blogger can add to their theme where they’d like to display it. Some may even be loaded with an array of arguments to further customize the options. We’ll stick to a simple myplugin_related_posts() template tag as an example throughout.

Usually, these plugins can’t or aren’t willing to take advantage of hooks, such as appending information to the post content, or widgets. That’s okay, especially so when they also offer those alternatives, but also include a theme template tag.

I want to rethink this process. Some bloggers are weary of modifying templates, some plugins’ instructions are plain dangerous, and some bloggers would love to take advantage of a plugin, but it doesn’t allow much flexibility with its output.

Take this as an example:

// Add this to your theme

But, what happens when myplugin is deactivated? That function suddenly no longer exists, and the blog blows up. Of course, most plugin authors realize this, and encourage this instead:

// Add this to your theme
if ( function_exists( 'myplugin_related_posts' ) )

Not bad, but clunky. How can we do this better?

Using Hooks for Template Tags

Dion Hulse blew my mind away when he mentioned this method to me a few months ago. Sure, all developers use hooks on a regular basis, but the ingenuity of using a hook as a template tag was too good to resist.

As an example:

// Add this to your theme
do_action( 'myplugin_related_posts' );

Wow, how cool is that? Look ma, clean code! And no fatal errors! Now all the plugin author needs to do is add their existing template tag to that action:

add_action( 'myplugin_related_posts', 'myplugin_related_posts' );

And, if the plugin author doesn’t provide that, then you can do it yourself in your theme’s functions.php, right next to perhaps other filters and actions that modify or add to the hundreds of template tags built into WordPress.

What’s to stop you from adding arguments?

// Add this to your theme
do_action( 'myplugin_related_posts', array( 'count' => 5 ) );

Or, what’s to stop you from removing, replacing, or adding additional callbacks to the same hook?

If the template tag returns a result and needs to be echoed, you can attach the tag to a filter instead:

echo apply_filters( 'myplugin_get_related_posts', '' );

There are a handful of reasons why I really like this method:

One, it requires no effort for the plugin author to passively support this, as most template tags can already be used as callbacks. To actively support this, they can include an add_action call in their plugin, for the times the hook exists.

They don’t need to require the use of a hook, of course — the widget, template tag, hook, etc., all can be supplied, and the user can choose what to use.

Two, administrators can do this themselves by tying the template tag to a hook on their own. They may need their own wrapper function to support more complex tags, but it’s generally worth it.

Three, if the hook doesn’t exist in the theme, then the plugin’s add_action doesn’t do anything. The converse is that if the callback doesn’t exist, then the action hook doesn’t do anything. No fatal errors.

Four, it encourages plugins and themes to play nice with each other through clean, flexible, and robust methods.

Of course, the template-tag-as-a-callback method is only for those situations where the tag needs to be placed in a particular spot. There’s nothing stopping you from taking the template tag provided by the author and simply leveraging the existing hooks system to append the HTML to the post using the the_content filter.

Leverage the WordPress plugin API and reap the benefits.

Google Summer of Code idea

I am strongly considering applying for the Google Summer of Code with WordPress. As a core developer, I’m in a unique position, because a stated goal of GSoC is to increase participation in the open source community, recruit contributors, and identify possible future committers. (I’m also the only student on the commit team as far as I know, though Dion Hulse was a GSoC student for two years.)

I was not contributing to core during last year’s GSoC term, and I’ve only really thought about applying to GSoC in the last few months. In the end, the powers that be have said I am welcome to apply. With that out of the way, I now need to come up with a project. I’ve thought about it for a while, and I’ve had a few good ideas, but nothing that I feel I can stretch out over a summer. Problem is, a typical project — one that may span several months of iterations under normal circumstances — might be something I could complete in a caffeine-powered weekend.* A few people I spoke to said that’s definitely something I need to consider.

An Advanced Theme Revisioning System

A project on theme revisions is something that has been on the official WordPress list of ideas since last year. My proposal would put this idea on steroids. Continue reading Google Summer of Code idea