From dd9709d179788acec8046ee7ddbeed18cb7bd1cf Mon Sep 17 00:00:00 2001
From: Boone Gorges <boonebgorges@gmail.com>
Date: Thu, 1 Oct 2015 03:11:30 +0000
Subject: [PATCH] Simplify pagination logic in `comments_template()`.

[34561] "fixed" the problem of newest-first comments showing fewer than
'per_page' comments on the post permalink when the total number of comments
was not divisible by 'per_page'. See #29462. But this fix caused numerous
other problems. First, comment pages reported by `get_page_of_comment()`
(which expects comment pages to be filled oldest-first) were no longer correct.
Second, and more seriously, the new logic caused comments to be shifted
between pages, making their permalinks non-permanent.

The current changeset reverts the changed behavior. In order to preserve the
performance improvements introduced in [34561], an additional query must be
performed when 'default_comments_page=newest' and 'cpage=0' (ie, you're viewing
the post permalink). A nice side effect of this revert is that we no longer
need the hacks required to determine proper comment pagination, introduced in
[34561].

See #8071. See #34073.
Built from https://develop.svn.wordpress.org/trunk@34729


git-svn-id: http://core.svn.wordpress.org/trunk@34693 1a063a9b-81f0-0310-95a4-ce76da25c4cd
---
 wp-includes/comment-template.php | 74 +++++++-------------------------
 wp-includes/version.php          |  2 +-
 2 files changed, 16 insertions(+), 60 deletions(-)

diff --git a/wp-includes/comment-template.php b/wp-includes/comment-template.php
index bad4a14ea4..a0cf16dfcf 100644
--- a/wp-includes/comment-template.php
+++ b/wp-includes/comment-template.php
@@ -1240,74 +1240,30 @@ function comments_template( $file = '/comments.php', $separate_comments = false
 		$per_page = (int) get_option( 'comments_per_page' );
 	}
 
-	/*
-	 * For legacy reasons, higher page numbers always mean more recent comments, regardless of sort order.
-	 * Since we don't have full pagination info until after the query, we use some tricks to get the
-	 * right comments for the current page.
-	 *
-	 * Abandon all hope, ye who enter here!
-	 */
-	$flip_comment_order = $trim_comments_on_page= false;
+	$comment_args['order']  = 'ASC';
 	$comment_args['number'] = $per_page;
 	$page = (int) get_query_var( 'cpage' );
-	if ( 'newest' === get_option( 'default_comments_page' ) ) {
-		if ( $page ) {
-			$comment_args['order'] = 'ASC';
 
-			/*
-			 * We don't have enough data (namely, the total number of comments) to calculate an
-			 * exact offset. We'll fetch too many comments, and trim them as needed
-			 * after the query.
-			 */
-			$offset = ( $page - 2 ) * $per_page;
-			if ( 0 > $offset ) {
-				// `WP_Comment_Query` doesn't support negative offsets.
-				$comment_args['offset'] = 0;
-			} else {
-				$comment_args['offset'] = $offset;
-			}
-
-			// Fetch double the number of comments we need.
-			$comment_args['number'] += $per_page;
-			$trim_comments_on_page = true;
-		} else {
-			$comment_args['order'] = 'DESC';
-			$comment_args['offset'] = 0;
-			$flip_comment_order = true;
-		}
+	if ( $page ) {
+		$comment_args['offset'] = ( $page - 1 ) * $per_page;
+	} elseif ( 'oldest' === get_option( 'default_comments_page' ) ) {
+		$comment_args['offset'] = 0;
 	} else {
-		$comment_args['order'] = 'ASC';
-		if ( $page ) {
-			$comment_args['offset'] = ( $page - 1 ) * $per_page;
-		} else {
-			$comment_args['offset'] = 0;
-		}
+		// If fetching the first page of 'newest', we need a top-level comment count.
+		$top_level_query = new WP_Comment_Query();
+		$top_level_count = $top_level_query->query( array(
+			'count'   => true,
+			'orderby' => false,
+			'post_id' => $post->ID,
+			'parent'  => 0,
+		) );
+
+		$comment_args['offset'] = ( ceil( $top_level_count / $per_page ) - 1 ) * $per_page;
 	}
 
 	$comment_query = new WP_Comment_Query( $comment_args );
 	$_comments = $comment_query->comments;
 
-	// Delightful pagination quirk #1: `wp_list_comments()` expects the order to be wrong, so we make it wrong.
-	if ( $flip_comment_order ) {
-		$_comments = array_reverse( $_comments );
-	}
-
-	// Delightful pagination quirk #2: reverse chronological order requires page shifting.
-	if ( $trim_comments_on_page ) {
-		// Correct the value of max_num_pages, which is wrong because we manipulated the per_page 'number'.
-		$comment_query->max_num_pages = ceil( $comment_query->found_comments / $per_page );
-
-		// Identify the number of comments that should appear on page 1.
-		$page_1_count = $comment_query->found_comments - ( ( $comment_query->max_num_pages - 1 ) * $per_page );
-
-		// Use that value to shift the matched comments.
-		if ( 1 === $page ) {
-			$_comments = array_slice( $_comments, 0, $page_1_count );
-		} else {
-			$_comments = array_slice( $_comments, $page_1_count, $per_page );
-		}
-	}
-
 	// Trees must be flattened before they're passed to the walker.
 	$comments_flat = array();
 	foreach ( $_comments as $_comment ) {
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 4bff212b71..6676fe9e40 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-34728';
+$wp_version = '4.4-alpha-34729';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.