notes on what to do with page preprocessing

theme.php

<?php
function template_preprocess_page(&$variables) {
  $language_interface = language(LANGUAGE_TYPE_INTERFACE); // DC
  $site_config = config('system.site'); // DC

  // Move some variables to the top level for themer convenience and template cleanliness.
  $variables['show_messages'] = $variables['page']['#show_messages']; // Bad

  foreach (system_region_list($GLOBALS['theme']) as $region_key => $region_name) {
    if (!isset($variables['page'][$region_key])) {
      $variables['page'][$region_key] = array();
    }
  }

  // Set up layout variable.
  $variables['layout'] = 'none'; // BAD
  if (!empty($variables['page']['sidebar_first'])) {
    $variables['layout'] = 'first'; // BAD
  }
  if (!empty($variables['page']['sidebar_second'])) {
    $variables['layout'] = ($variables['layout'] == 'first') ? 'both' : 'second'; // BAD
  }

  $variables['base_path']         = base_path(); // Shouldn't be a variable *IN* the template
  $variables['front_page']        = url(); // Gives you a link to the frontpage; this should go away given blocks that encapsulates any such links
  $variables['feed_icons']        = drupal_get_feeds(); // wtf? put it in a block.
  $variables['language']          = $language_interface; // should go somewhere else, a product of the bizarre passing of data to the html template
  $variables['language']->dir     = $language_interface->direction ? 'rtl' : 'ltr'; // ibid
  $variables['logo']              = theme_get_setting('logo'); // should be in the block
  $variables['main_menu']         = theme_get_setting('toggle_main_menu') ? menu_main_menu() : array(); // move to block
  $variables['secondary_menu']    = theme_get_setting('toggle_secondary_menu') ? menu_secondary_menu() : array(); // move to block
  $variables['action_links']      = menu_local_actions(); // move to a block
  $variables['site_name']         = (theme_get_setting('toggle_name') ? check_plain($site_config->get('name')) : ''); // GOOD
  $variables['site_slogan']       = (theme_get_setting('toggle_slogan') ? filter_xss_admin($site_config->get('slogan')) : ''); // move to a block
  $variables['tabs']              = menu_local_tabs(); // move to a block

  if ($node = menu_get_object()) {
    $variables['node'] = $node; // this is shitty global-grabbing, but technically unlikely to break cache
  }

  // Populate the page template suggestions.
  if ($suggestions = theme_get_suggestions(arg(), 'page')) {
    $variables['theme_hook_suggestions'] = $suggestions; // bad, duplicates the pattern that pluggable layouts is itself trying to do
  }
}

/**
 * Process variables for page.tpl.php
 *
 * Perform final addition of variables before passing them into the template.
 * To customize these variables, simply set them in an earlier step.
 *
 * @see template_preprocess_page()
 * @see page.tpl.php
 */
function template_process_page(&$variables) {
  if (!isset($variables['breadcrumb'])) {
    // Build the breadcrumb last, so as to increase the chance of being able to
    // re-use the cache of an already rendered menu containing the active link
    // for the current page.
    // @see menu_tree_page_data()
    $variables['breadcrumb'] = theme('breadcrumb', array('breadcrumb' => drupal_get_breadcrumb())); // move to a block
  }
  if (!isset($variables['title'])) {
    $variables['title'] = drupal_get_title(); // move to a block
  }

  // Generate messages last in order to capture as many as possible for the
  // current page.
  if (!isset($variables['messages'])) {
    $variables['messages'] = $variables['show_messages'] ? theme('status_messages') : ''; // necessary until moved to block
  }
}