Always show post excerpts

rcp-always-show-excerpt.php

<?php

/**
 * Always show an excerpt.
 * 
 * @param null|array|string $value    The value get_metadata() should return - a single metadata value, or an array of values.
 * @param int               $post_id  Object ID.
 * @param string            $meta_key Meta key.
 * @param bool              $single   Whether to return only the first value of the specified $meta_key.
 *
 * @return bool|null|array|string
 */
function ag_rcp_always_show_excerpt( $value, $post_id, $meta_key, $single ) {

	if ( 'rcp_show_excerpt' == $meta_key && $single ) {
		return true;
	}

	return $value;

}

add_filter( 'get_post_metadata', 'ag_rcp_always_show_excerpt', 10, 4 );