Useful D7 custom functions

custom.admin_menu.inc

<?php

/**
 * @file
 * Administration menu integration for the custom module.
 */

/**
 * Implements hook_admin_menu_cache_info().
 */
function custom_admin_menu_cache_info() {
  $caches['bootstrap'] = array(
    'title' => t('Bootstrap'),
    'callback' => 'custom_admin_menu_cache_flush_bootstrap',
  );
  $caches['entity'] = array(
    'title' => t('Entity'),
    'callback' => 'entity_info_cache_clear',
  );
  $caches['field'] = array(
    'title' => t('Field'),
    'callback' => 'field_cache_clear',
  );
  $caches['all'] = array(
    'title' => t('ALL THE THINGS!'),
    'callback' => 'drupal_flush_all_caches',
  );
  return $caches;
}

/**
 * Cache callback to clear the bootstrap cache.
 */
function custom_admin_menu_cache_flush_bootstrap() {
  cache_clear_all('*', 'cache_bootstrap', TRUE);
}

/**
 * Implements hook_admin_menu_output_alter().
 */
function custom_admin_menu_output_alter(array &$content) {
  // @todo Remove when http://drupal.org/node/1899474 is fixed.
  unset($content['icon']['icon']['devel-variables']);
  if (module_exists('devel')) {
    $devel_tree = menu_tree_all_data('devel');
    if ($devel_tree = admin_menu_links_menu($devel_tree)) {
      $content['icon']['icon']['devel'] = array(
        '#title' => t('Devel'),
        '#href' => '#',
        '#options' => array(
          'external' => TRUE,
        ),
      ) + $devel_tree;
    }
  }
}

custom.block.inc

<?php

/**
 * @file
 * Block integration for the custom module.
 */

/**
 * Implements hook_block_view().
 */
function custom_block_view($delta) {
  $function = 'custom_block_view_' . strtr($delta, '-', '_');
  if (function_exists($function)) {
    return $function();
  }
}

custom.drush.inc

<?php

/**
 * @file
 * Drush integration for the custom module.
 */

/**
 * Implements hook_drush_cache_clear().
 */
function custom_drush_cache_clear(&$types) {
  if (drush_drupal_major_version() >= 7) {
    $types['bootstrap'] = 'custom_drush_cache_clear_bootstrap';
    // @todo Remove when http://drupal.org/node/1899468 is fixed.
    if (drush_has_boostrapped(DRUSH_BOOTSTRAP_DRUPAL_FULL)) {
      $types['entity'] = 'entity_info_cache_clear';
      $types['field'] = 'field_cache_clear';
    }
  }
}

/**
 * Clears the bootstrap cache.
 */
function custom_local_drush_cache_clear_bootstrap() {
  cache_clear_all('*', 'cache_bootstrap', TRUE);
}

custom.module

<?php

/**
 * Implements hook_hook_info_alter().
 */
function custom_hook_info(&$info) {
  // Add modulename.group.inc support for most core hooks.
  $groups['block'] = array('block_configure', 'block_info', 'block_info_alter', 'block_list_alter', 'block_save', 'block_view', 'block_view_alter');
  $groups['comment'] = array('comment_delete', 'comment_insert', 'comment_load', 'comment_presave', 'comment_publish', 'comment_unpublish', 'comment_update', 'comment_view', 'comment_view_alter');
  $groups['cron'] = array('cron', 'cron_queue_info', 'cron_queue_info_alter');
  $groups['date'] = array('date_formats', 'date_formats_alter', 'date_format_types', 'date_format_types_alter');
  $groups['entity'] = array('entity_delete', 'entity_info', 'entity_info_alter', 'entity_insert', 'entity_load', 'entity_prepare_view', 'entity_presave', 'entity_query_alter', 'entity_update', 'entity_view' ,'entity_view_alter');
  $groups['file'] = array('file_copy', 'file_delete', 'file_download', 'file_download_access', 'file_download_access_alter', 'file_insert', 'file_load', 'file_mimetype_mapping_alter', 'file_move', 'file_presave', 'file_update', 'file_url_alter', 'file_validate');
  $groups['image'] = array('image_default_styles', 'image_effect_info', 'image_effect_info_alter', 'image_styles_alter', 'image_style_delete', 'image_style_flush', 'image_style_save', 'image_toolkits');
  // Contrib modules.
  $groups['admin_menu'] = array('admin_menu_replacements', 'admin_menu_output_build', 'admin_menu_output_alter', 'admin_menu_map', 'admin_menu_map_alter', 'admin_menu_cache_info');
  foreach ($groups as $group => $hooks) {
    $info += array_fill_keys($hooks, array('group' => $group));
  }
}

/**
 * Implements hook_menu().
 */
function custom_menu() {
  $items = array();
  return $items;
}

/**
 * Implements hook_menu_alter().
 */
function custom_menu_alter(&$items) {
  // Make the delete page for nodes show up as a tab.
  $items['node/%node/delete']['context'] = MENU_CONTEXT_PAGE | MENU_CONTEXT_INLINE;
}

/**
 * Implements hook_node_view().
 */
function custom_node_view($node, $view_mode, $langcode) {
  if (module_exists('comment') && $view_mode == 'teaser') {
    _custom_node_add_unpublished_comments_link($node, $langcode);
  }
}

function _custom_node_add_unpublished_comments_link($node, $langcode) {
  if ($node->comment != COMMENT_NODE_HIDDEN && user_access('administer comments')) {
    $unpublished_count = db_query('SELECT COUNT(cid) FROM {comment} WHERE nid = :nid AND status = :status', array(
      ':nid' => $node->nid,
      ':status' => COMMENT_NOT_PUBLISHED,
    ))->fetchField();
    if (!empty($unpublished_count)) {
      $node->content['links']['comment']['#links']['comment-unpublished-comments'] = array(
        'title' => format_plural($unpublished_count, '1 unpublished comment', '@count unpublished comments', array(), array('langcode' => $langcode)),
        'href' => "node/$node->nid",
        'fragment' => 'comments',
      );
    }
  }
}

/**
 * Filter an array of node objects based if the results of node_access().
 */
function custom_array_filter_node_access(array $nodes, $op = 'view', $account = NULL) {
  $return = array();
  foreach ($nodes as $node) {
    if (node_access($op, $node, $account)) {
      $return[$node->nid] = $node;
    }
  }
  return $return;
}

/**
 * Returns a specific field value, column, and delta.
 *
 * @param $entity_type
 *   The type of $entity; e.g., 'node' or 'user'.
 * @param $entity
 *   The entity containing the data to be displayed.
 * @param $field_name
 *   The field to retrieve.
 * @param $column
 *   The column in the field data to retrieve. Default is NULL which will
 *   return the entire field's data array.
 * @param $delta
 *   The specific delta of the field values to return. Default is 0. If NULL is
 *   provided then all the field delta values will be returned.
 *
 * @return
 *   A field value, or an array of field values, or NULL if no field values
 *   were available.
 *
 * @see field_get_items()
 * @see custom_array_extract_values()
 */
function custom_field_get_value($entity_type, $entity, $field_name, $column = NULL, $delta = 0) {
  if (!empty($entity) && $items = field_get_items($entity_type, $entity, $field_name)) {
    if (isset($column)) {
      $items = custom_extract_nested_values_to_array($items, array($column));
    }

    if (isset($delta)) {
      if (isset($items[$delta])) {
        return $items[$delta];
      }
    }
    else {
      return $items;
    }
  }
}

/**
 * Extract array values out from an array of field items.
 *
 * @param $entity_type
 *   The entity type
 * @param $entity
 *   An entity object of type $entity_type.
 * @param $field
 *   A field name.
 * @param $key
 *   A key to pass into custom_array_extract_values().
 *
 * @return
 *   An array of field values.
 *
 * @see custom_array_extract_values()
 * @see field_get_items()
 */
function custom_field_extract_values($entity_type, $entity, $field, $column) {
  if (!empty($entity) && $items = field_get_items($entity_type, $entity, $field)) {
    return custom_extract_nested_values_to_array($items, array($column));
  }
  return array();
}

/**
 * Find the delta value of a field item's value.
 *
 * @param $entity_type
 *   The entity type
 * @param $entity
 *   An entity object of type $entity_type.
 * @param $field
 *   A field name.
 * @param $column
 *   The column that should have its value compared to $value.
 * @param $value
 *   The field value to compare to.
 *
 * @return
 *   The delta value of the field value if found, which can evaluate to zero.
 *   If the field value is not found, FALSE will be returned.
 */
function custom_field_get_value_delta($entity_type, $entity, $field, $column, $value) {
  if (!empty($entity) && $items = field_get_items($entity_type, $entity, $field)) {
    foreach ($items as $delta => $item) {
      if (isset($item[$column]) && $item[$column] == $value) {
        return $delta;
      }
    }
  }
  
  return FALSE;
}

/**
 * Check if an entity's field has a specific delta value.
 *
 * @param $entity_type
 *   The entity type
 * @param $entity
 *   An entity object of type $entity_type.
 * @param $field
 *   A field name.
 * @param $delta
 *   A delta value to check.
 *
 * @return bool
 *   TRUE is the entity's field has a value with the specific delta, or FALSE
 *   otherwise.
 */
function custom_field_has_delta($entity_type, $entity, $field, $delta) {
  if (!empty($entity) && $items = field_get_items($entity_type, $entity, $field)) {
    return !empty($items[$delta]);
  }
}

/**
 * Duplicate of field_view_value() that extracts $item automatically by delta.
 *
 * @see field_view_value()
 */
function custom_field_view_value($entity_type, $entity, $field_name, $delta = 0, $display = array(), $langcode = NULL) {
  $output = array();

  if ($item = custom_field_get_value($entity_type, $entity, $field_name, NULL, $delta)) {
    // Determine the langcode that will be used by language fallback.
    $langcode = field_language($entity_type, $entity, $field_name, $langcode);

    // Push the item as the single value for the field, and defer to
    // field_view_field() to build the render array for the whole field.
    $clone = clone $entity;
    $clone->{$field_name}[$langcode] = array($item);
    $elements = field_view_field($entity_type, $clone, $field_name, $display, $langcode);

    // Extract the part of the render array we need.
    $output = isset($elements[0]) ? $elements[0] : array();
    if (isset($elements['#access'])) {
      $output['#access'] = $elements['#access'];
    }
  }

  return $output;
}

/**
 * Filter an array of objects or nested arrays by a variable depth value.
 *
 * @param array $items
 *   An array of objects or arrays to filter.
 * @param array $parents
 *   An array of parent keys of the value, starting with the outermost key.
 * @param mixed $value
 *   A value or array of values to match using custom_get_nested_value().
 *
 * @return array
 *   An array of items that matched nested value $value.
 */
function custom_filter_by_nested_value(array $items, array $parents, $value) {
  $return = array();
  foreach ($items as $key => $item) {
    $key_exists = FALSE;
    $found_value = custom_get_nested_value($item, $parents, $key_exists);
    if ($key_exists) {
      if (is_array($value) && in_array($found_value, $value)) {
        $return[$key] = $item;
      }
      elseif ($found_value == $value) {
        $return[$key] = $item;
      }
    }
  }
  return $return;
}

/**
 * Retrieves a value from an object or nested array with variable depth.
 *
 * This is a copy of drupal_array_get_nested_value() but with added support
 * for objects.
 *
 * @param mixed $item
 *   The array or object from which to get the value.
 * @param array $parents
 *   An array of parent keys of the value, starting with the outermost key.
 * @param bool $key_exists
 *   (optional) If given, an already defined variable that is altered by
 *   reference if all the keys in $parents were found.
 *
 * @return mixed
 *   The requested nested value. Possibly NULL if the value is NULL or not all
 *   nested parent keys exist. $key_exists is altered by reference and is a
 *   Boolean that indicates whether all nested parent keys exist (TRUE) or not
 *   (FALSE). This allows to distinguish between the two possibilities when
 *   NULL is returned.
 */
function custom_get_nested_value($item, array $parents, &$key_exists = NULL) {
  $ref = $item;
  foreach ($parents as $parent) {
    if (is_array($ref) && array_key_exists($parent, $ref)) {
      $ref = &$ref[$parent];
    }
    elseif (is_object($ref) && property_exists($ref, $parent)) {
      $ref = $ref->$parent;
    }
    elseif (is_object($ref) && method_exists($ref, '__get') && $ref->__get($parent) !== NULL) {
      // Support objects that override the __get magic method.
      // This also doesn't support if $ref->$parent exists but is set to NULL.
      $ref = $ref->$parent;
    }
    else {
      $key_exists = FALSE;
      return NULL;
    }
  }
  $key_exists = TRUE;
  return $ref;
}

/**
 * Extract an associative key/value array from an array of arrays or objects.
 *
 * @param $items
 *   An array of objects or arrays.
 * @param array $value_parents
 *   An array of parent keys of the value, starting with the outermost key.
 * @param array $key_parents
 *   (optional) An array of parent keys of the key to return for each item,
 *   starting with the outermost key. If not provided, the key of the item in
 *   $items will be used as the returned key. 
 */
function custom_extract_nested_values_to_array(array $items, array $value_parents, array $key_parents = NULL) {
  $return = array();
  foreach ($items as $index => $item) {
    $key = isset($key_parents) ? custom_get_nested_value($item, $key_parents) : $index;
    $return[$key] = custom_get_nested_value($item, $value_parents);
  }
  return $return;
}

/**
 * Attempt to load the current node. This is useful for sites that use Panels for node pages.
 */
function custom_get_current_node($check_access = FALSE) {
  $node = &drupal_static(__FUNCTION__);

  if (!isset($node)) {
    $node = FALSE;
    if (preg_match('/node\/(\d+)/', current_path, $matches)) {
      $node = node_load($matches[1]);

      if ($check_access && !node_access('view', $node)) {
        $node = FALSE;
      }
    }
  }

  return $node;
}

/**
 * Add an array of classes to the body.
 *
 * @param $classes
 *   A string or an array of class strings to add.
 */
function custom_add_class($classes, $hook = 'body') {
  if (!is_array($classes)) {
    $classes = array($classes);
  }

  $static = &drupal_static('custom_classes', array());
  if (!isset($static[$hook]['add'])) {
    $static[$hook]['add'] = array();
  }
  foreach ($classes as $class) {
    $static[$hook]['add'][] = $class;
  }
}

/**
 * Remove an array of classes from the body.
 *
 * @param $classes
 *   A string or an array of class strings to remove.
 */
function custom_remove_class($classes, $hook = 'body') {
  if (!is_array($classes)) {
    $classes = array($classes);
  }

  $static = &drupal_static('custom_classes', array());
  if (!isset($static[$hook]['remove'])) {
    $static[$hook]['remove'] = array();
  }
  foreach ($classes as $class) {
    $static[$hook]['remove'][] = $class;
  }
}

/**
 * Implements hook_process()
 *
 * This essentially works like panels_preprocess_html().
 */
function custom_process(&$variables, $hook) {
  if (!isset($variables['classes'])) {
    return;
  }

  $classes = drupal_static('custom_classes', array());
  if (!empty($classes[$hook]['add'])) {
    $add_classes = array_map('drupal_clean_css_identifier', $classes[$hook]['add']);
    $variables['classes_array'] = array_unique(array_merge($variables['classes_array'], $add_classes));
  }
  if (!empty($classes[$hook]['remove'])) {
    $remove_classes = array_map('drupal_clean_css_identifier', $classes[$hook]['remove']);
    $variables['classes_array'] = array_diff($variables['classes_array'], $remove_classes);
  }
  // Since this runs after template_process(), we need to re-implode the
  // classes array.
  $variables['classes'] = implode(' ', $variables['classes_array']);
}

/**
 * Implements hook_ajax_render_alter().
 */
function custom_ajax_render_alter() {
  // Disable XHProf module on any AJAX requests.
  // @todo Remove when http://drupal.org/node/1485190 is fixed.
  $GLOBALS['conf']['xhprof_enabled'] = FALSE;
}

/**
 * A lightweight version of entity save for field values only.
 */
custom_entity_fields_update($entity_type, $entity) {
  list($id) = entity_extract_ids($entity_type, $entity);
  if (empty($id)) {
    trigger_error('Cannot call custom_entity_fields_update() on a new entity.');
    return FALSE;
  }

  // Some modules use the original property.
  if (!isset($entity->original)) {
    $entity->original = $entity;
  }

  // Ensure that file_field_update() will not trigger additional usage.
  unset($entity->revision);

  // Invoke the field presave and update hooks.
  field_attach_presave($entity_type, $entity);
  field_attach_update($entity_type, $entity);

  // Clear the cache for this entity now.
  entity_get_controller($entity_type)->resetCache(array($id));
}

function custom_get_fields_by_type($type) {
  $fields = array();
  foreach (field_info_field_map() as $field_name => $field_map) {
    if ($field_map['type'] == $type) {
      $fields[$field_name] = field_info_field($field_name);
    }
  }
  return $fields;
}

FYI I've taken all the reusable API functions and wrapped them up into an updateable module called helper: http://drupal.org/project/helper. I will likely not be maintaining this gist anymore.