Project namespaces can now be added for module dependencies

Summary

Dependencies are specified in the module .info file (Drupal 7) or .info.yml file (Drupal 8). For projects on drupal.org it is recommended that dependencies now include a project name as follows.

Drupal 7:

dependencies[] = project:module (>=version)

Drupal 8:

dependencies
  - project:module (>=version)

In this form the project name is recommended, the module name is required and the version requirement is optional. Since the project name is not required this is backward compatible with existing code. There is no effect on module installation or dependency calculation in Drupal core.

Before

The dependencies were specified in the following form:

Drupal 7:

dependencies[] = module (>=version)

Drupal 8:

dependencies
  - module (>= 1.x)

In this form the module name is required and the version requirement is optional.

Example

A real example from Drupal 7 is the webform project containing the webform module. A webform_patched project was created that also contains a webform module. Specifying a dependency in the form

dependencies[] = webform (>= 7.x-3.20)

is ambiguous and results in problems. Specifying the dependency in the form

dependencies[] = webform_patched:webform (>= 7.x-3.20)
dependencies[] = drupal:system (>=7.40)

uses the project name which is unique so that the module is uniquely specified. Since project namespaces was added in Drupal 7.40 that also is added as a requirement. There are also numerous examples of modules that have been moved into and out of Drupal core and thus appear in both Drupal core and a contributed project. The php module is an example in Drupal 8 of a module that moved out of Drupal core into the php project.