PHP require_once() warning with hook_menu

Question

I'm writing a small module for learning purpose, where I try to create a module settings form using hook_menu() and form_api.
Everything look good in my code but I still getting this error message :

Warning: require_once(/var/www/html/drupal/modules/system/demo_usernames_form.inc): failed to open stream: No such file or directory in menu_execute_active_handler() (line 515 of /var/www/html/drupal/includes/menu.inc). Warning: require_once(/var/www/html/drupal/modules/system/demo_usernames_form.inc): failed to open stream: No such file or directory in menu_execute_active_handler() (line 515 of /var/www/html/drupal/includes/menu.inc).

function demo_menu(){
    $items[]=array();
    $items['admin/config/people/usernames']=array(
        'title'=>'bad usernames list',
        'description'=>t('configure not allowed usernames'),
        'page_callback'=>'drupal_get_form',
        'page arguments'=>array('demo_usernames_form'),
        'access arguments'=>array('administer site configuration'),
        'file'=>'demo_usernames_form.inc',
        );
    return $items;

function demo_usernames_form($form,&$form_state){
    $form['bad_usernames']=array(
        '#type'=>'textfield',
        '#title'=>'Bad usernames',
        '#default_value'=>variable_get('bad_usernames'),
        '#description'=>t('Enter a list of "bad usernames" separated by commas.  If a user tries to enter one of these usernames either on account creation or when editing their account, the form will display an error message.'),
        );
    return(system_settings_form($form));

}

Answer 1

If you look a bit closer at the path in the error message:

/var/www/html/drupal/modules/system/demo_usernames_form.inc

You'll notice it's trying to find your include file in the system module.

It's happening because the user module's implementation of hook_menu() has this in it:

$items ['admin/config/people'] = array(
  'title' => 'People',
  'description' => 'Configure user accounts.',
  'position' => 'left',
  'weight' => -20,
  'page callback' => 'system_admin_menu_block_page',
  'access arguments' => array('access administration pages'),
  'file' => 'system.admin.inc',
  'file path' => drupal_get_path('module', 'system'),
);

Notice the file path at the bottom, explicitly setting the path Drupal should look for the included file in.

Since properties are inherited from parent paths, and the path of your item sits nicely under that one, you get an implicit file path that you weren't expecting. The result: your module path is no longer consulted when the system tries to find the include file.

To fix, just add the correct file path to your hook_menu() code:

$items['admin/config/people/usernames']=array(
  'title'=>'bad usernames list',
  'description'=>t('configure not allowed usernames'),
  'page_callback'=>'drupal_get_form',
  'page arguments'=>array('demo_usernames_form'),
  'access arguments'=>array('administer site configuration'),
  'file'=>'demo_usernames_form.inc',
  'file path' => drupal_get_path('module', 'demo'),
);

And flush them caches.

Answer 2

it's weird because it's calling "demo_usernames_form.inc" from drupal/modules/system/ not from your module directory in your case demo/. make sure you clear cache. if did't work try to add "file path" and see how it goes, this just for debugging but it should pick the file from your module by default. see more here hook_menu: "file path": The path to the directory containing the file specified in "file". This defaults to the path to the module implementing the hook."