Force comment pagination on single posts.
Previously, the 'page_comments' toggle allowed users to disable comment
pagination. This toggle was only superficial, however. Even with
'page_comments' turned on, comments_template() loaded all of a post's
comments into memory, and passed them to wp_list_comments() and
Walker_Comment, the latter of which produced markup for only the
current page of comments. In other words, it was possible to enable
'page_comments', thereby showing only a subset of a post's comments on a given
page, but all comments continued to be loaded in the background. This technique
scaled poorly. Posts with hundreds or thousands of comments would load slowly,
or not at all, even when the 'comments_per_page' setting was set to a
reasonable number.
Recent changesets have addressed this problem through more efficient tree-
walking, better descendant caching, and more selective queries for top-level
post comments. The current changeset completes the project by addressing the
root issue: that loading a post causes all of its comments to be loaded too.
Here's the breakdown:
- Comment pagination is now forced. Setting 'page_comments' to false leads to evil things when you have many comments. If you want to avoid pagination, set 'comments_per_page' to something high.
- The 'page_comments' setting has been expunged from options-discussion.php, and from places in the codebase where it was referenced. For plugins relying on 'page_comments', we now force the value to
true with a pre_option filter.
comments_template() now queries for an appropriately small number of comments. Usually, this means the comments_per_page value.
- To preserve the current (odd) behavior for comment pagination links, some unholy hacks have been inserted into
comments_template(). The ugliness is insulated in this function for backward compatibility and to minimize collateral damage. A side-effect is that, for certain settings of 'default_comments_page', up to 2x the value of comments_per_page might be fetched at a time.
- In support of these changes, a
$format parameter has been added to WP_Comment::get_children(). This param allows you to request a flattened array of comment children, suitable for feeding into Walker_Comment.
WP_Query loops are now informed about total available comment counts and comment pages by the WP_Comment_Query (found_comments, max_num_pages), instead of by Walker_Comment.
Aside from radical performance improvements in the case of a post with many
comments, this changeset fixes a bug that caused the first page of comments to
be partial (found_comments % comments_per_page), rather than the last, as
you'd expect.
Props boonebgorges, wonderboymusic.
Fixes #8071.