A function to help migrate old and outdated theme settings after a theme update

jnt-migration.php

<?php

/**
 * This function handles updating old settings that are now outdated and should
 * only fire on theme updates and activations.
 *
 * @since Crush 3.0.7
 */
function jnt_migrate_settings() {

  /**
   * CRUSH 3.0.7 <-- theme version purely for reference
   *
   * Sidebar_autoheight was a checkbox, but now it's a select and named
   * slightly differently. If the user HAD it turned on, lets update
   * the new setting for them and remove the old outdated setting. This
   * will save them having to do it themselves in the customizer.
   */

  // first check to make sure the old settings still exists
  if( isset( get_theme_mod('sidebar_autoheight') ) ) {

    // the autoheight was on
    if( get_theme_mod('sidebar_autoheight')==1) {
      set_theme_mod( 'sidebar_height', 'stretch' );

    // the autoheight was off
    } else {
      set_theme_mod( 'sidebar_height', 'off' ) {
    }

    // delete the old setting and prevent any of this from firing again
    remove_theme_mod( 'sidebar_autoheight' );

  }

  // now simply keep adding settings that need updating each theme update.

}

// we want to fire the above function only after a theme activation or update
add_action('after_switch_theme','jnt_migrate_settings');

?>