Comment parent template variables are built twice

Updated: Comment #7

Problem/Motivation

When using threaded comments, template_preprocess_comment() in comment.module loads the parent comment when rendering every comment in the thread.This duplicates a lot of the preparation of the comment variables that's already been done when rendering the actual parent comment, assuming it's done on the same page. That's likely to be a noticeable regression when you have a lot of threaded comments on a page, for example on groups.drupal.org. We should look at finding way to re-use the variables created for the parent comment I think.

Proposed resolution

• create a repeatable test case (generating a number of threaded comments)
• provide an initial xhprof profiling run for benchmarking
• look at finding way to re-use the variables created for rendering the parent comment
• review the variables which get created in this preprocess and remove any which are not used in the template

Remaining tasks

Everything.

Related Issues

• Part of #1744302: [meta] Resolve known performance regressions in Drupal 8 →
• Follow up of #1272870: No semantics for nested comments / bad for screen-readers →

Original report by catch

Follow-up from [#1272870:79]

+  if ($comment->pid > 0) {
+    // Fetch and store the parent comment information for use in templates.
+    $comment_parent = comment_load($comment->pid);
+    $variables['parent_comment'] = $comment_parent;
+    $variables['parent_author'] = theme('username', array('account' => $comment_parent));
+    $variables['parent_created'] = format_date($comment_parent->created);
+    $variables['parent_changed'] = format_date($comment_parent->changed);
+    $uri_parent = $comment_parent->uri();
+    $uri_parent['options'] += array('attributes' => array('class' => 'permalink', 'rel' => 'bookmark'));
+    $variables['parent_title'] = l($comment_parent->subject, $uri_parent['path'], $uri_parent['options']);
+    $variables['parent_permalink'] = l(t('Parent permalink'), $uri_parent['path'], $uri_parent['options']);
+    $variables['parent'] = t('In reply to !parent_title by !parent_username',
+     

This means that if you're using threaded comments, then we're going to duplicate a lot of the preparation of the comment variables (format_date() twice, theme_username() for example), that's already been done when rendering the actual parent comment, assuming it's done on the same page. That's likely to be a noticeable regression when you have a lot of threaded comments on a page, for example on groups.drupal.org. We should look at finding way to re-use the variables created for the parent comment I think.

Also there are variables created here that never get used? Can we just remove those please?