Display Previous Next Navigation Links via Shortcode

cpt-navigation-shortcode.php

// 
// For simplicity, the code below assumes that the CPT is 'project'
// 
// TODO: Improve further.
// ------------------------------------------------
add_shortcode('project-navigation', function(){
	$html = '';
	$prev_post_link = '';
	$next_post_link = '';	

	if( is_singular('project') ) {
		$prev_post = get_previous_post();
		if ( $prev_post ){
			$prev_post_link = '<a href="' . get_permalink( $prev_post ) . '">'. $prev_post->post_title . '</a>';
		}

		$next_post = get_next_post();
		if ( $next_post ){
			$next_post_link = '<a href="' . get_permalink( $next_post ) . '">'. $next_post->post_title . '</a>';
		}

		$html .= '<div class="post-nav">';
		$html .= '<div class="alignleft prev-next-post-nav">' . $prev_post_link . '</div>';
		$html .= '<div class="alignright prev-next-post-nav">' . $next_post_link . '</div>';
		$html .= '</div>';
	}
	
	return $html;
});