Part 1 - Reuse the Same Code

In mid-January, the first version of Backdrop CMS was released. Backdrop is a fork of Drupal that adds some highly-anticipated features and API improvements to the core Drupal platform while focusing on performance, usability, and developer experience.

When an open-source fork makes the news, it's often because it was born from a fierce, acrimonious battle (example: Joomla forking from Mambo); the resulting projects compete with each other on the exact same turf and developers are forced to choose sides. Backdrop's goal, however, is not to destroy or replace the original Drupal project. Rather, it aims to be a "friendly fork" that focuses on Drupal's traditional audience of site builders and developers, an audience which the Backdrop founders believe are being slowly left behind by the Drupal project itself.

Because of this, I expect that many existing Drupal developers will not want to choose between the platforms, but instead will continue working with Drupal while also beginning to use Backdrop. In this series of blog posts, I will explain how a module (or theme) developer can take a Drupal project they currently maintain and support it for Backdrop as well, while keeping duplicate work to a minimum.

  • In part 1 (this post), I'll show how for some modules, the exact same code can be used with both Drupal and Backdrop.
  • In part 2, I'll explain what to do when you want to port a Drupal module to a separate Backdrop version and get it up and running on GitHub.
  • In part 3, I'll explain how to link the Backdrop module to the Drupal.org version and maintain them simultaneously.

Sometimes the Same Exact Code can be Used With Both Drupal and Backdrop

To start things off let's look at Field Reference Delete, a Drupal 7 module I maintain which does some behind-the-scenes cleanup in your database when entities such as nodes or taxonomy terms are deleted on the site. It's a moderately-complex module which makes heavy use of Drupal's field and entity systems.

To make this or any Drupal module work with Backdrop, there is one step that is always required: Adding a backdrop = 1.x line to the .info file to inform Backdrop core that the code is Backdrop-compatible.

Easy enough. The big question is what changes are required beyond that?

Checking for Changes

Although Backdrop is not 100% compatible with Drupal 7 (due to the features and API improvements it adds) it aims to be backwards-compatible as much as possible, for example by including a compatibility layer to allow Drupal functionality that is deprecated in Backdrop to still work correctly.

The Backdrop change records and module conversion guide provide technical advice for developers on how and when to upgrade their code. The biggest changes are probably the configuration management system (Backdrop’s replacement for Drupal 7’s variable API and other configuration that was previously stored in the database) and layout system (which removes much of the functionality of the Drupal 7 Block module in favor of a newer, more powerful Layout module).

If your Drupal 7 module makes heavy use of these systems, it’s likely you’ll want to make some changes in order to work with Backdrop. However, the compatibility layer means that you might not actually need to. For example, Backdrop retains Drupal 7’s variable API (although it is marked as deprecated and is not as powerful as the configuration system which replaces it). So your code might still work even if it uses this system. It really depends on the details of how your module works, so the best advice is to test it out and see what (if anything) is broken.

It’s also worth noting that because Backdrop was forked from an early version of Drupal 8 (not from Drupal 7) it inherited a smattering of changes that were added to Drupal 8 early in the release cycle. Not all of these have made it into the list of Backdrop change records yet, although work is ongoing and people are adding them as they are noticed.

In the case of Field Reference Delete, I tested the module on Backdrop and it worked fine. I also skimmed the change records and module conversion guide mentioned above and didn't see anything that obviously needed to change. Even though entities in Backdrop have been converted to classed objects and the field API has been converted to use the configuration management system, Field Reference Delete’s heavy use of the entity and field systems still didn’t require that any changes be made. All I had to do to get the module working was add that one backdrop = 1.x line to the .info file.

Adding the One Line of Code on Drupal.org

Interestingly enough, since Drupal will happily ignore a backdrop = 1.x line in a module's .info file, it's possible to simply add that code to the Drupal.org version of the module and use the same version of the module for either Drupal or Backdrop. I did that in this issue; the resulting diff is simply this:


diff --git a/field_reference_delete.info b/field_reference_delete.info
...
name = Field reference delete
description = Immediately removes references to a deleted entity from fields stored in an SQL database.
core = 7.x
+backdrop = 1.x

Drupal uses the core = 7.x line to determine Drupal compatibility, and Backdrop uses the backdrop = 1.x line to determine Backdrop compatibility. The 7.x-1.0-beta1 release of Field Reference Delete contains the above change and can be used equally well on a Drupal or Backdrop site. Simple!

There are some downsides to doing this, however:

  • Although no changes to the module code may be strictly required, there are usually optional (and non-backwards-compatible) changes that can be made to better integrate with new Backdrop features.
  • It is hard for Backdrop users and developers to find the module and know that it's compatible with Backdrop. I tried to improve its discoverability by adding a "Backdrop compatibility" tag to the above-mentioned issue, and I also put a note on the project page explaining that Backdrop is supported. These aren't ideal, but should help; perhaps a standard will eventually catch on but there isn't a formal one yet.

Despite these disadvantages, for the time being I'd like to just have one copy of the code for this particular module (hosted in one place), and it's nice to know that's possible.

In part 2 of this series, I’ll take a look at a different module I maintain where it isn’t possible to use the same exact code for Drupal and Backdrop, and I’ll show how I went through the official process for porting my module to Backdrop and getting it hosted on GitHub. Stay tuned!

Further Backdrop Resources

Do you have any thoughts or questions, or experiences of your own trying to port a module to Backdrop? Leave them in the comments.

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