Retrieves the cached term objects for the given object ID.

Upstream functions (like get_the_terms() and is_object_in_term()) are
responsible for populating the object-term relationship cache. The current
function only fetches relationship data that is already in the cache.

function get_object_term_cache( $id, $taxonomy ) {
	$_term_ids = wp_cache_get( $id, "{$taxonomy}_relationships" );

	// We leave the priming of relationship caches to upstream functions.
	if ( false === $_term_ids ) {
		return false;
	}

	// Backward compatibility for if a plugin is putting objects into the cache, rather than IDs.
	$term_ids = array();
	foreach ( $_term_ids as $term_id ) {
		if ( is_numeric( $term_id ) ) {
			$term_ids[] = (int) $term_id;
		} elseif ( isset( $term_id->term_id ) ) {
			$term_ids[] = (int) $term_id->term_id;
		}
	}

	// Fill the term objects.
	_prime_term_caches( $term_ids );

	$terms = array();
	foreach ( $term_ids as $term_id ) {
		$term = get_term( $term_id, $taxonomy );
		if ( is_wp_error( $term ) ) {
			return $term;
		}

		$terms[] = $term;
	}

	return $terms;
}