drupal_get_filename() always returns pathname of main extension file

drupal_get_filename() always returns the relative pathname of the main extension file now — regardless of whether such a file exists.

Drupal 7

$pathname = drupal_get_filename('module', 'node');
var_dump($pathname);
$pathname = drupal_get_filename('theme', 'stark');
var_dump($pathname);

core/modules/node/node.module
core/themes/stark/stark.info

Drupal 8

$pathname = drupal_get_filename('module', 'node');
var_dump($pathname);
$pathname = drupal_get_filename('theme', 'stark');
var_dump($pathname);

core/modules/node/node.module
core/themes/stark/stark.theme

Note

drupal_get_filename() will most likely be removed prior to the release of Drupal 8.0. It is mostly used internally by Drupal core. If your code relies on it, change it to use the information from respective extension handlers instead; e.g., ModuleHandler::getModuleList().