Drush Make and Module Dependencies
Drush make is a wonderful tool for constructing Drupal platforms. A lot of Drupal developers are used to adding a list of modules, a few libraries and theme or 2 then running drush make to build their platform. It all seems pretty easy. What if I told you module developers could make things even easier for site builders?
Some contrib modules depend on third party libraries, and due to various reasons they can't always be stored in git repositories on drupal.org and included in the module release. To solve this problem module developers can include a .make file for their module. Drush recursively processes make files, so the module make file would be processed once found by drush make.
A good example of where this could be useful is the SMTP module, which depends on the LGPL licensed PHPMailer library. The module also requires a patch to be applied to the library, which drush make can apply for us. The following .make file could be included in the SMTP module as smtp.make:
core = 6.x api = 2 libraries[phpmailer][download][type] = "get" libraries[phpmailer][download][url] = "http://downloads.sourceforge.net/project/phpmailer/phpmailer%20for%20php5_6/Previous%20Versions/2.2.1/phpMailer_v2.2.1_.tar.gz" libraries[phpmailer][download][md5] = "0bf75c1bcef8bde6adbebcdc69f1a02d" libraries[phpmailer][directory_name] = "phpmailer" libraries[phpmailer][destination] = "modules/contrib/smtp" libraries[phpmailer][patch][drupal-compatibility][url] = "http://drupalcode.org/project/smtp.git/blob_plain/2acaba97adcad7304c22624ceeb009d358b596e3:/class.phpmailer.php.2.2.1.patch" libraries[phpmailer][patch][drupal-compatibility][md5] = "2d82de03b1a4b60f3b69cc20fae61b76"
Now when the SMTP module is included a normal drush make file it will be downloaded, the PHPMailer library will be downloaded and patched ready for use.
Unfortunately there are some limitations to this approach. Firstly it assumes that the SMTP module will be installed under the modules/contrib directory, which is accepted best practice, but may not suit everyone's needs. When I tested this with the current stable version of drush make (6.x-2.2) it failed, and drush make 6.x-3.x from git needed to be patched. Hopefully a fix for this can be backported to the 6.x-2.x branch and included in a future release.
Update: I have posted the make file for the SMTP module as patch in issue #1159080.