Upgrading the Busy theme to Drupal 8
Back when Drupal 7 was being developed, there was a big inititiative about getting new pretty themes into Drupal core. There were three really good suggestions, one of them being Bartik, which the most people got behind, so it could be finished in time to get into Drupal 7 core. One really good suggestion that couldn't be finished in time was Corolla by Jeff Burnz, which is now a contrib theme. The third suggestion was our theme Busy by eigentor, a theme targeted at corporate websites. Just like Corolla, there wasn't enough time to finish it up for Drupal 7 core. Busy has been a contributed theme ever since, because we didn't want it to get lost only because it didn't make it into Drupal core.
After DrupalCon Portland we got really excited about Drupal 8 so we decided to see how porting Busy would go. Work had to be done to exchange some template variables and rename some files, but it was pretty straightforward and only took a little more than an hour to finish. After twig was moved to core as the new default template engine, some more work had to be done (see "Upgrading a phptemplate theme from Drupal 7 to Drupal 8").
Busy will stay minimally maintained for now, though we might port it to use twig in the future.
If you want a new look for your Drupal 8 site, check out Busy and let us know what you think!
Upgrading a phptemplate theme from Drupal 7 to Drupal 8
So now that twig is in core as the default template engine, how do you port your theme to Drupal 8? We considered converting the theme to twig, but that would take up too much time for now. We just wanted to publish the theme for Drupal 8 as soon as possible. At first of course, we ported the theme to the new structure. These are just a few changes, like renaming the THEME.info file to THEME.info.yml and changing its contents to yml, which is simple. You can check core's bartik.info.yml to see how this needs to be done. Your template.php file is renamed to THEME.theme, the contents of this file didn't have to be changed for Busy. We did have to change some variable names in some of our template files (like the comment template) by referring to core's templates, which are nicely documented within each file. For example, in our comment.tpl.php, we had to replace $picture with $user_picture.
If you have a phptemplate theme, simply add this line to the theme's .info.yml file:
Without this line you will not even be able to activate the theme.
Menus, breadcrumbs, messages
After adding this line, you might still have problems seeing the theme you're used to. In Busy we got fatal errors due to the way we printed the menus in our page.tpl.php. This is what it looks like in Drupal 7:
And this is what we need to do now to print menus like the main menu in your page.tpl.php:
If you want to add classes or ids to the menu, you can do the following in your THEME.theme file (In Drupal 7 this file is called template.php):
Now if you print variables like $messages just using print $messages, you will not get any output. Look through the code in your page.tpl.php for any print $VARIABLE and make it print render($VARIABLE). We had to do this for $breadcrumb and $messages.
Drupal 8's theming system is still under heavy construction and I'm sure there will be more stuff we'll have to change in our template files very soon, but this way works well for now if you are just interested in porting your phptemplate theme to Drupal 8.