fix(categories): fix pager urls (#2913)

* fix(categories): fix pager urls

On a permalink structure like this /%category%/%postname%/ some fixes to
the pager was needed. Also guard against a post with the slug 'page' to
avoid confusion to routing.

* fix(categories): fix pager urls

Don't hardcode category base

* Don't hardcode category base and remove unneeded filter

* fix(categories): fix pager urls

* PR feedback adressed
* Use 'category' as default if base is empty

---------

Co-authored-by: Adam Boro <aborowski24@gmail.com>

includes/class-category-pager.php

@@ -0,0 +1,62 @@
+<?php
+/**
+ * Newspack category pager fix.
+ *
+ * @package Newspack
+ */
+
+namespace Newspack;
+
+defined( 'ABSPATH' ) || exit;
+
+/**
+ * Newspack category pager.
+ *
+ * This class adds tweaks to sites where the permalink structure is "/%category%/%postname%/".
+ *
+ * See https://core.trac.wordpress.org/ticket/8905 and https://core.trac.wordpress.org/ticket/21209
+ */
+final class Category_Pager {
+	/**
+	 * Initialize Hooks.
+	 */
+	public static function init() {
+		add_filter( 'paginate_links', [ __CLASS__, 'fix_category_pager' ] );
+	}
+
+	/**
+	 * Filter callback for paginate_links.
+	 *
+	 * Filter the pager urls on category pages.
+	 *
+	 * For a category with the slug "kitten" for instance, the url /kitten will show the content that
+	 * really should be on /category/kitten. On the /kitten page, WP will generate pager urls like "/kitten/page/2/"
+	 * – this fixes the pager urls to be "/category/kitten/page/2/".
+	 *
+	 * @param string $link The pager link to filter.
+	 *
+	 * @return mixed|string
+	 */
+	public static function fix_category_pager( $link ) {
+		if ( ! is_category() || ! str_starts_with( get_option( 'permalink_structure' ), '/%category%/' ) ) {
+			return $link;
+		}
+
+		$category_base = get_option( 'category_base' );
+		if ( empty( $category_base ) ) {
+			$category_base = 'category';
+		}
+
+		$path = wp_parse_url( $link, PHP_URL_PATH );
+		if ( str_starts_with( $path, '/' . $category_base ) ) {
+			// No fixing needed.
+			return $link;
+		}
+
+		$new_path = '/' . $category_base . $path;
+
+		return str_replace( $path, $new_path, $link );
+	}
+}
+
+Category_Pager::init();

includes/class-newspack.php

@@ -140,6 +140,7 @@ private function includes() {
 
 		include_once NEWSPACK_ABSPATH . 'includes/class-handoff-banner.php';
 		include_once NEWSPACK_ABSPATH . 'includes/class-donations.php';
+		include_once NEWSPACK_ABSPATH . 'includes/class-category-pager.php';
 		include_once NEWSPACK_ABSPATH . 'includes/class-salesforce.php';
 		include_once NEWSPACK_ABSPATH . 'includes/class-pwa.php';
 		include_once NEWSPACK_ABSPATH . 'includes/class-starter-content.php';