WordPress: Output a list of taxonomy terms, then highlight the terms the belong to the current post. Updated to use in_array() to add a "current" CSS class to terms that the current post has. This way we don't have to worry about keeping up with terms in the CSS. Hooray for logic! #snippet #WordPress

get-highlight-terms.php

<?php
/*
As the title implies, this will give you a way to

1. output a complete list of terms for a given taxonomy (nothing special there) 
2. highlight the terms that the current post has (the magic!)

Probably need to figure out a better way to echo out the url of the term archive page...
*/

  $post_terms = get_terms('custom_taxonomy'); // get all terms in taxonomy
  $post_current_terms = wp_get_post_terms( $post->ID, 'custom_taxonomy', array('fields' => 'slugs') ); // get terms current post has
?>
<footer class="custom-taxonomy">
  <?php foreach( $post_terms as $post_term ) : 
    $post_term_slug = $post_term->slug;
  ?>
    <a <?php if ( in_array($post_term_slug, $post_current_terms) ) { echo 'class="current"'; } ?> href="<?php echo site_url() . '/taxonomy-slug/'. $post_term->slug; ?>"><?php echo $post_term->name; ?></a>
  <?php endforeach; ?>
</footer>

highlight-terms-action.php

<?php

  /* The same idea as above, but put into an action that can be hooked into */
  
  // adding the action
  add_action('after_single_project_content', 'fstop_highlight_terms', 10);
  
  // creating the function
  function fstop_highlight_terms(){
    // make sure we're getting current the post loop data
    global $post;

    // get all the terms in the given taxonomy
    $post_terms = get_terms('custom_taxonomy');

    // get only the given taxonomy terms assigned to the current post
    $post_current_terms = wp_get_post_terms( $post->ID, 'custom_taxonomy', array('fields' => 'slugs') ); 

    // start the taxonomy term output
    echo '<footer class="taxonomy-slug">';

    // loop through all givent taxonomy terms
    foreach( $post_terms as $post_term ) : 
      // set a variable equal to the individual term slug, which we'll use to check against the current post's terms
      $post_term_slug = $post_term->slug;

      //start echoing out the terms as links
      echo '<a '; // need the space after to separate it from the class

      // check each term against the current post's assigned terms, if there's a match, add 'class="current" '
      if ( in_array($post_term_slug, $post_current_terms) ) { 
        echo 'class="current" '; // need the space after to separate it from the href
      }

      // echo out the rest of the link to the term archive page. There may be a better way to do this...
      echo 'href="' . site_url() . '/taxonomy-slug/' . $post_term->slug . '">' . $post_term->name . '</a>';

    endforeach;

    echo '</footer>';
    // profit?
  }
  
  // put a do_action() in your template files wherever you want this to output
  do_action('after_single_project_content');
?>