From 346e47b1764efedcd27b09ae371ec6150a95853a Mon Sep 17 00:00:00 2001
From: Jake Spurlock <whyisjake@git.wordpress.org>
Date: Tue, 8 Jun 2021 22:49:27 +0000
Subject: [PATCH] Permalinks: Limit pagination for posts with comments.

Additionally, redirect pages back to the source page if comments don't exist.

Props devrekli, carike, sumanm, mukesh27, chaion07, audrasjb, whyisjake, SergeyBiryukov.

Fixes #50233.


git-svn-id: https://develop.svn.wordpress.org/trunk@51118 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-includes/canonical.php                 | 12 +++++++++--
 .../phpunit/tests/link/wpGetCanonicalUrl.php  | 21 +++++++++++++++++++
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/src/wp-includes/canonical.php b/src/wp-includes/canonical.php
index 184fb756e8..0eba17d60d 100644
--- a/src/wp-includes/canonical.php
+++ b/src/wp-includes/canonical.php
@@ -27,6 +27,7 @@
  * or query in an attempt to figure the correct page to go to.
  *
  * @since 2.3.0
+ * @since 5.8.0 Checks comment page count to limit pagination.
  *
  * @global WP_Rewrite $wp_rewrite WordPress rewrite component.
  * @global bool       $is_IIS
@@ -504,8 +505,15 @@ function redirect_canonical( $requested_url = null, $do_redirect = true ) {
 				&& ( 'newest' === $default_comments_page && $cpage > 0
 					|| 'newest' !== $default_comments_page && $cpage > 1 )
 			) {
-				$addl_path  = ( ! empty( $addl_path ) ? trailingslashit( $addl_path ) : '' );
-				$addl_path .= user_trailingslashit( $wp_rewrite->comments_pagination_base . '-' . $cpage, 'commentpaged' );
+				// Checks comment page count to limit pagination.
+				$per_page = get_option( 'comments_per_page' );
+
+				// Get the total number of pages for comments.
+				$comments_total_pages = ceil( ( $wp_query->post->comment_count ) / $per_page );
+				if ( $cpage <= $comments_total_pages ) {
+					$addl_path  = ( ! empty( $addl_path ) ? trailingslashit( $addl_path ) : '' );
+					$addl_path .= user_trailingslashit( $wp_rewrite->comments_pagination_base . '-' . $cpage, 'commentpaged' );
+				}
 
 				$redirect['query'] = remove_query_arg( 'cpage', $redirect['query'] );
 			}
diff --git a/tests/phpunit/tests/link/wpGetCanonicalUrl.php b/tests/phpunit/tests/link/wpGetCanonicalUrl.php
index 5b7eddaada..a48f430b42 100644
--- a/tests/phpunit/tests/link/wpGetCanonicalUrl.php
+++ b/tests/phpunit/tests/link/wpGetCanonicalUrl.php
@@ -151,6 +151,27 @@ class Tests_Link_wpGetCanonicalUrl extends WP_UnitTestCase {
 		$this->assertSame( $this->canonical_url_filter(), $canonical_url );
 	}
 
+	/**
+	 * Limit pagination for comments.
+	 *
+	 *  @ticket 50233
+	 */
+	public function test_comments_limit_paged_with_plain_permalink_structure() {
+		$cpage = 5;
+
+		$link = add_query_arg(
+			array(
+				'cpage' => $cpage,
+				'foo'   => 'bar',
+			),
+			get_permalink( self::$post_id )
+		);
+
+		$this->go_to( $link );
+		$expected = get_permalink( self::$post_id ) . '#comments';
+		$this->assertSame( $expected, wp_get_canonical_url( self::$post_id ) );
+	}
+
 	/**
 	 * Filter callback for testing of filter usage.
 	 *