Drupal: File upload required?

Question

For some reason, my form breaks when I try to make a file upload required. Here is the code for it:

$form_id = "upload_form";

$form[$form_id] = array (
    '#type' => 'fieldset',
    '#description' => t('This is a utility to import nodes from a Comma Separated Value file. To begin, pick a node type, and upload a CSV.'),
);

$form[$form_id]['type'] = array(
    '#title' => t('Enter node type'),
    '#type' => 'textfield',
//      '#autocomplete_path' => '', TODO: autocomplete for node types
    '#required' => TRUE,
    '#description' => t('This node type should already exist. If it doesn\'t, create it first.'),
);

$form[$form_id]['upload'] = array(
    '#type' => 'file',
    '#title' => t('Upload CSV file'),
//      '#size' => 40,
    '#description' => t('This will not work for a non-CSV file.'),
//      '#required' => TRUE, TODO: breaks it. why?
);

$form[$form_id]['submit'] = array(
    '#type' => 'submit',
    '#value' => t('Submit'),
);

$form['#attributes'] = array('enctype' => 'multipart/form-data');

On a Drupal support site, someone says that it's impossible to make file uploads required. Is this true?

Answer 1

This is my workaround to make file field required:

<?    
    // A piece of form that defines the file field
    $form['attachment'] = array(
        '#type' => 'file',
        '#title' => t('Title'),
        //'#required' => TRUE,  // check this manually
    );

    // Form validation hook
    function yourformname_validate($form, &$form_state) {
        // Validate file
        $validators = array(
            'file_validate_extensions' => array('doc txt pdf'), // does not work for user 1
            'file_validate_size' => array(1000000, 0),
        );
        $file = file_save_upload('attachment', $validators, file_directory_path());
        if ($file) {
             $form_state['values']['attachment'] = $file; // drupal file object
        }
        else{
             form_set_error('attachment', "File is required");
        }
    }
?>

Answer 2

I'm not a Drupal expert but you could check if the $_FILES variable exists, no?