Add tests and fix bug with adding links at finish action

Author: westonruter

plugins/optimization-detective/class-od-template-optimization-context.php

@@ -18,7 +18,6 @@
  * @since n.e.x.t
  *
  * @property-read OD_URL_Metric_Group_Collection $url_metric_group_collection URL Metric group collection.
- * @property-read OD_Tag_Visitor_Registry        $tag_visitor_registry        Tag visitor registry.
  * @property-read positive-int|null              $url_metrics_id              ID for the od_url_metrics post which provided the URL Metrics in the collection.
  * @property-read array<string, mixed>           $normalized_query_vars       Normalized query vars.
  * @property-read non-empty-string               $url_metrics_slug            Slug for the od_url_metrics post.

plugins/optimization-detective/optimization.php

@@ -349,15 +349,6 @@ function od_optimize_template_output_buffer( string $buffer ): string {
 		$visited_tag_state->reset();
 	} while ( $processor->next_tag( array( 'tag_closers' => 'skip' ) ) );
 
-	// Send any preload links in a Link response header and in a LINK tag injected at the end of the HEAD.
-	if ( count( $link_collection ) > 0 ) {
-		$response_header_links = $link_collection->get_response_header();
-		if ( ! is_null( $response_header_links ) && ! headers_sent() ) {
-			header( $response_header_links, false );
-		}
-		$processor->append_head_html( $link_collection->get_html() );
-	}
-
 	// Inject detection script.
 	// TODO: When optimizing above, if we find that there is a stored LCP element but it fails to match, it should perhaps set $needs_detection to true and send the request with an override nonce. However, this would require backtracking and adding the data-od-xpath attributes.
 	if ( $needs_detection ) {
@@ -373,5 +364,15 @@ function od_optimize_template_output_buffer( string $buffer ): string {
 	 */
 	do_action( 'od_finish_template_optimization', $template_optimization_context );
 
+	// Send any preload links in a Link response header and in a LINK tag injected at the end of the HEAD.
+	// Additional links may have been added at the od_finish_template_optimization action, so this must come after.
+	if ( count( $link_collection ) > 0 ) {
+		$response_header_links = $link_collection->get_response_header();
+		if ( ! is_null( $response_header_links ) && ! headers_sent() ) {
+			header( $response_header_links, false );
+		}
+		$processor->append_head_html( $link_collection->get_html() );
+	}
+
 	return $processor->get_updated_html();
 }