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

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.
 	 *